This activity may be available in multiple formats or from different sponsors. ARRT does not allow CE activities such as internet courses, home study programs or directed readings to be repeated for CE credit in the same or any subsequent biennium”

Objectives

Outline

Introduction

Section 6.1: What is PACS?

Section 6.2: Concepts of Image Capture

Section 6.3: Image Transfer

Section 6.4: Hospital Information Systems (HIS), RIS, and PACS

Section 6.5: Short-term Storage of PACS documents

Section 6.6: Long-term storage and data back-up

Section 6.7: The PACS Workstation

Section 6.8: The PACS Network

Section 6.9: Peripherals and output devices

Summary and References

Bottom

Objectives:

• Define the acronym PACS and state the basic functions of a PACS system.
• Given a diagram of a PACS network label the component parts and briefly state its function.
• Define what is meant by image capture and discuss the components of a digital system that perform image capture.
• Define what is meant by image transfer and list the PACS component that transfers images throughout the PACS network.
• Discuss the components of the image viewing system in a PACS network and give examples of primary, secondary and tertiary workstations.
• Define what is meant by short term storage; tell where in the PACS network short term storage functions.
• Discuss the legal obligation to store radiographic images and how this is done in a PACS network.
• Discuss the process of information data entry into PACS, and how information and images are retrieved from PACS system.
• Discuss the functions of a data bridge for entering paper information into PACS using ultrasound notes as an example.

Outline-Part I

1. What is PACS ?
1. Why do we need PACS?
2. The basic components of a PACS network
3. The PACS administration team


2. Concepts of image capture
1. Imaging modalities: Angiography, Computerized Axial Tomography (CT), Magnetic Resonance Imaging (MRI), Ultrasound (US), Mammography, Digital Radiography (DR), Computerized Radiography (CR), etc.
2. DICOM- the standard for medical imaging
3. DICOM service classes
4. Analog film entry into PACS-networking into the PACS server
5. The basics of converting an analog film to a digital image (digitizing)


3. Concepts of image transfer
1. What is image transfer and what component of PACS handles this function.
2. The network switchboard system


4. Hospital Information Systems (HIS), RIS, and PACS
1. The data bridge component of PACS
2. Radiology Information Systems (RIS)
3. Hospital Information Systems (HIS)
4. Health Level Seven (HL7)


5. Short-term storage of PACS documents
1. The purpose and function of short-term storage
2. The Network Attached Server (NAS)
3. Redundant Array of Independent Disks (RAID)
4. Back-up storage systems for network servers


6. Long-Term Storage and data back-up
1. Servers and image/data storage
2. Optical disk and optical disk jukebox
3. Digital linear tape storage.


7. The PACS Workstation
1. Types of workstations
2. Basic concepts of workstation use


8. The PACS Network
1. The structure of a PACS network
2. LAN structure and Ethernet
3. Network topology
4. Wide Area Network (WAN)
5. Transmission protocol for Ethernet and for internet
6. Bandwidth


9. Peripherals and output devices
1. Paper scanning documents into PACS
2. CD-ROM burner


10. Summary and Quiz

Introduction

The story of PACS (PACS-an acronym for picture archiving and communication system) is a very interesting one being that its history encompasses great successions of innovations in film processing and archiving. There was a time not so long ago that radiographers recorded images on glass plates and processed them in darkrooms by hand. Sometimes these plates broke making image reading, storage, and retrieval impossible. Shortly after the invention of polyester, medical imaging took on a completely new direction of change. Soon technologists were able to process flexible radiographic film, which was a remarkable improvement over the glass plate. Yet these films still had to be hand dipped in caustic darkroom chemicals, washed, rinsed, and dried before they could be handled and archived. Soon newer systems for loading and unloading cassettes called daylight systems came about and the technologist was able to process x-ray film without going into a darkroom. The next series of innovations would bring about automatic processors that could perform all of the steps from development to drying of the film in about 90 seconds or less. With daylight systems and automated processing, the medical imaging discipline was truly revolutionized. Soon every hospital and clinic in the U.S. had automatic film processors much like the ones in photolabs, in which x-ray films are processed and ready for viewing in a matter of a few minutes.

This picture of a traditional darkroom set up requires an automatic film processor, a constant water supply into it, and a drain for spent chemicals, silver recovery, and a lot of technologist waiting time to process multiple images. Although it was revolutionary over glass plates it is antiquated technology today.

Picture to the right shows an automatic processor from the darkroom side. Many institutions have already discontinued the use of automatic processors like the one pictured above and to the right. These processors requires a filtered water supply, processing chemicals, a well maintained drainage system, silver recovery system, vented darkroom, replenishment tanks, along with periodic cleaning, and a lot of quality control testing. All of these functions are eliminated by PACS and the darkroom space recovered for other use.

Today automatic film processing is still a common standard for medical imaging at many hospitals and clinics. These near antiquated film/screen imaging systems with all its chemical processing issues and film jacket storage concerns still persists. Today digital imaging and PACS hold the front position in medical imaging science. The implementation of digital imaging schemes and PACS has become ubiquitous throughout the radiology discipline to greater and lesser degrees of confidence. This is because the relationship of PACS to medical imaging is multitudinously more revolutionary than what the automatic processor and daylight systems were to glass plates. For the first time in radiology all subspecialties of radiology imaging (ultrasound, CT, MRI, GD, interventional, neuroradiology, orthopedic radiology, surgical radiography, bone densitometry, mobile radiography, fluoroscopy, and others) have come together to input into a giant electronic film jacket through PACS.

In traditional radiography an x-ray exposure stimulates fluorescent crystals in radiographic screens thereby exposing a radiographic film. Intensifying screens amplify the effect of exit radiation on the film, but without the image detail seen in direct exposure radiography. The image captured within the silver halide crystalline lattice is a latent or invisible image. The speed at which each image is ready for viewing in a film/screen imaging system is determined by the time it take for the invisible latent image to be reduced to a visible x-ray image in the film processing stage. The process of converting a latent image to a manifest image requires a chemical reduction of exposed silver halide to black metallic silver. Unexposed silver halide does not contain latent image centers and must be cleared from the film in order to make the manifest image clearly visible. Automatic film processing must include developing, rinsing, washing, and drying of the film to produce diagnostic quality images. The radiographic technique, film processing time, and view box illumination all play an important role in the final presentation of the film.

There are so many issues that surround darkroom systems like having the proper concentration and temperature of processing chemicals, and daily monitoring of chemicals to detect undesired changes. Contamination of developer solution is an example of a real problem which often causes repeat exposure to the patient due to improper processing and can causes film artifacts and films to jam in the roller system. Or perhaps we should talk about the cost of having a darkroom technician and the chemical hazards associated with a poorly vented darkroom. We could also talk about those plumbing problems that so often occur as a result of silver build-up in the drain, or having to haul several arms full of heavy cassettes to a functional darkroom because a main processor is down for repairs. The point here is that darkrooms are messy and pose electrical hazards especially when water and chemical leakage from processor reservoirs occur. What was once state of the art technology is now replaceable by PACS; not because of the problems of film/screen imaging, but because PACS is in itself a form of optimized digital imaging technology.

The two pictures illustrate two major problems of analog film processing in the darkroom, silver recovery and recurring plumbing issues. Pouring silver down the drain is a serious violation of Environmental Protection Agency policies (EPA) subject to large fines. Silver is a "characteristic hazardous material" even in low concentration in drinking water. Under federal law, silver cannot be freely dumped into the water drainage system.

Now take all the problems of the analog film/screen system and its associated darkroom to which we have all become accustomed, and realize that it is really ok for it to all come to an end. And all that frustration of going to the film file room and being unable to find a much needed x-ray file jacket... well, it too is all over. That’s right! No more searching for hours and then being unable to find a film jacket leaving it for someone else to search for the next day. The radiographer can at last exhale as we are no longer are expected to radiograph patients, process the films in a darkroom, provide the radiologist with quality images, move the entire film jacket with each new study, transport films between physicians, make copies of films for patient's to take to their physician, recover scattered radiographs from all over the hospital (caused by a single set of films, but too many viewers), put signed radiology reports into film jackets, file film jackets in short term storage if the patients are inpatients, file jackets in long term storage (usually in a dark corner of the basement next to the morgue), pull jackets for the next day... and that's assuming the films and jacket can be found... whoosh! Had enough of the analog film/screen mess? As we shall soon discover, digital imaging can eliminate all of these redundancies.

One of the most frustrating recurring concerns in analog film/screen systems is that x-ray file jackets absorb a significant amount of time in film processing, film viewing, archiving and retrieval of films, and storage space is costly.

PACS transmits digital images and reports over a high speed network utilizing centralizing electronic storage. Patient information and radiographic images can be retrieved from storage and viewed throughout a facility and online by many users simultaneously, in seconds.

Section 6.1: What is PACS?

In this section we will explore what is PACS and why do we need it, along with an introduction to the basic components of a PACS network, and the role of the PACS administrative team. PACS is an acronym for Picture Archiving and Communication System:

PACS is hardware and software that stores and manipulates digital information in the form of images and text data. It provides a contemporary radiology department with optimal storage of images and patient data files. It is also a digital centralized electronic storage system that provides easy access to images transmittable to any workstation on its network. An important key to understanding PACS is to realize that its software manages patient information data and radiographic images so that both can be viewed simultaneously. The advantages of PACS over analog film/screen imaging and processing are tremendous. Through PACS there is a whole new way in which radiographic images are displayed and archived. Reflect on the traditional scheme of imaging that requires the technologist to expose a plate, chemically process it, and transfer it with pertinent patient information such as the film jacket and reports from previous studies to the radiologist to be interpreted.

• PACS is more than just picture display and archiving, the way in which the image is captured for PACS is digitally and not analog film/screen processing.
• Because the image is an electronic data set, each can be stored into what is called memory in computer language. Memory is the key concept in archiving, which takes up less space than a counterpart x-ray film jacket.
• Through computer technology unlimited viewers can review and manipulate PACS images without degradation of the image, or permanent changes to the image data. Digital data can be communicated to any computer or workstation within its network.
• PACS software can interface with most computers commonly used in medicine to include the hospital information system (HIS) and radiology information systems (RIS). Patient information and radiology reports can be displayed with radiology images eliminating the need to store paper information as well.

These seven components of PACS are functional solutions to those problems that have plagued film/screen radiography for tens of years. Through PACS radiography has evolved into a high quality acquisition system that displays and archives. In the past these functions were handled in the post-processing component of radiographic imaging.

1. Because images are digitally captured the need for a radiographic darkroom and all of its chemical vapor hazards are eliminated; water drainage problems and silver recovery issues are also eliminated since images are electronically processed.
2. The storage of radiographic images, patient information, and radiographic reports into memory greatly diminishes the need for large film storage areas.
3. Through PACS radiographic images can be viewed from any workstation within its network.
1. Unlike analog films where the view box is the center of image review, a workstation is a dynamic electronic view box with enhanced capabilities. Any workstation in the network can be used and workstations can be distributed throughout a facility or to off location facilities.
2. The PACS workstation adds a new dimension, that of image manipulation: windowing (density and contrast), image rotation, and algorithm variation (bone window, soft tissue window), measurement, magnification, etc.
3. Retrieval of all digital exams in a patient's electronic file is also permitted with PACS, along with all associated radiographic reports and printing features.

With so many potential functions performed by a PACS system, especially with the type of upgrades found at a large multimodality facilities, the system must be monitored and responsibility for it functioning properly managed by a specialized team. All functions of the PACS system and network are managed by a PACS administrator. The PACS team sets up file server(s), registers users, and assigns passwords. They also maintain the network and correct information and transfer errors as they occur, such as the wrong patient name entered on a study. Special training beyond basic radiology technology education is required to be a PACS specialist. The PACS technologist is considered a specialized modality which is gaining in its own right to specialty recognition.

So why do we need PACS? Some benefits of PACS include reduction or elimination of lost films, reduced retakes due to poor image quality, significant reduction in storage space and film printing cost, greatly improved communications, productivity and efficiency between the radiology department and physicians greatly improves because images and reports are readily available to remote sites, clinics, and hospital wards immediately after acquisition.

Section 6.2: Concepts of Image Capture

One of the most basic functions of any PACS system is capturing images from all digital modalities. This function is managed by a server which is a computer hardware device driven by complex computer software programs. Of the many functions of the main network server, data acquisition is its most fundamental work. The server provides control of data acquisition into PACS and routing of digital information and radiographic images throughout the network system. Almost all imaging equipment used in the various radiology modalities are digital systems or can be purchased as a digital system that can be networked into a universal PACS network. Computerized radiography uses existing radiology equipment to make digital images so no new x-ray equipment is needed. An example of digital data acquisition is the CT scan. CT images are captured as data frames and displayed on the console monitor. Institutions that do not have a PACS network must print these images onto film for the radiologist to read. With PACS these images are routed through a server to a workstation for quick access and reading. Other modalities in which images are digitally captured include MRI, angiography (DSA), and most modern C-arms and stationary fluoroscopy units. As many institutions have found, it is quite easy to take the next step from stand alone digital imaging to PACS for communicating this information throughout a network of computers.

CT images are captured as digital images; however, if it is not routed to a PACS server they must be routed to a printer through a server. The net result of not having PACS is that the radiologist must still read these films from a viewbox which is a redundant use of digital data.

The PACS server is the workflow manager of the acquisition and processing portion of digital imaging. Here one of the most basic of PACS functions, image capture takes place. The server receives digital images from all sources such as: CT, MRI, Angiography, Surgery C-arm units, Ultrasound, Nuclear medicine, Mammography, digitizer, digital fluoroscopy, and a host of other imaging "centers." The server is the primary point of entry for digital images into PACS.

The PACS server has many functions including image capture, image transfer, data control, routing, archiving, and data management. Servers perform these functions in accordance to DICOM standards; it is a complete DICOM language reader and data manager. DICOM is an acronym for Digital Imaging and Communications in Medicine. In the early 1970s the use of computer and digital technology entered the medical arena. These basic computer systems were used to acquire image data and process them to viewing monitors. Shortly after these computers entered the medical community the American College of Radiology (ACR) and the National Electrical Manufacturers Association (NEMA) formed a joint committee for the purpose of creating a standard method for the transmission of medical images and medical information. The standard formed was ACR-NEMA V2.0 which as now been replaced with the newest version of the standard called DICOM v3.0.

The DICOM Standards Committee is composed of many government agencies, manufacturing associations, and international committees. It sets standards nationally and internationally for biomedical, diagnostic, and therapeutic communication systems handling digital information. Its goals are to achieve compatibility with workflow effectiveness throughout all vendor communities' worldwide using compliance standards. DICOM specifies Information Objects that include images, whole studies, patients, reports and a host of other groupings of digital data. These enhancements of the DICOM standard allows for transfer of medical images and data across multi-vendor environments. Furthermore, DICOM standards are responsible for the expansion of PACS systems and interfacing with medical information technologies systems. Almost all medical systems producers and manufacturers subscribe to DICOM standards. Vendor membership to the DICOM committee include manufacturers such as General Electric Co., Siemens, Philips, Agfa Healthcare, Eastman Kodak, IDX Systems, Sony, and Toshiba to name a few.

DICOM is essentially a cooperative standard that exists between vendors. Connectivity exists between vendors because they cooperate across company product lines in all phases of development and testing. Every medical communication vendor in the world has incorporated DICOM standards into their products and tested them with member products for accurate functionality. Through the DICOM committee, compatibility and workflow efficiency is achieved for all medical imaging and information systems environments worldwide.

DICOM v3.0 also defines and specifies protocol operations of Service Classes. A service class is a subset of the DICOM protocol language that uniquely identifies Information Objects coming into the network as they are acted upon. A DICOM service class will specify how image data or information data is to be formatted and operations of the specific hardware. In this manner a PACS component only need to use that service class subset which pertains to the data it handles. Examples of DICOM service classes are: CR Image Storage Service Class and Basic Grayscale Print Management Service Class.

DICOM addresses all levels of digital data exchange and interchange in the form of application layers that guarantee any two implementations of a compatible set will effectively communicate and perform their designated functions. But one should bear in mind that just because two devices are DICOM compatible does not mean that their interface and data exchange is automatic. Usually there are some minor software upgrades that make the use of mixed vendor products a more compatible fit for institutional use. The five functional layers of PACS are: Transmission, query and retrieval, performance, workflow management, and consistency of data display and print. Because these functions are performed according to DICOM standards there is complete compatibility between different vendors of network devices. The PACS server utilizes the data collected in the manner in which it was intended by the primary device. PACS is not a base devise and does not generate any images from x-rays, magnetic energy, or ultrasound waves. It simply handles imaging data from those base devices that generate digital images. Its routing functions will transmit data to workstations, printer, or archive exactly as if it were the primary device. Likewise, it will retrieve data exactly as it was received because of the universality between DICOM subclass devices as written into the newest standards.

DICOM standards also consider that many institutions are heavily invested in analog film files. Analog film stores also need a port of entry into the PACS network. This need is satisfied by the use a device called a digitizer. A digitizer is a device that converts finished film/screen processed radiographs into digital images. Institutions that have converted to total digital imaging often receive radiographs from institutions that are not on a digital network. In order to maintain a record of these films and distribute them within their PACS network the images must be digitized. By digitizing analog films into PACS they can be viewed from any workstation and retrieved without visiting the film file room.

The digitizer pictured on the left is used to scan radiographs and record them in digital form (bytes, pixels, etc). They can be stored as an electronic file retrievable from PACS for viewing. The picture in the monitor shows the processed image. Patient information data can also be edited into PACS using software linked to the digitizer. A digitizer is connected in a PACS network to the main server. This allows for manipulating digitized images like any other PACS document to include: windowing, magnification, measurement, rotating, and the like.

Because the digitizer is directly linked to the PACS server images are available on network workstations instantaneously upon file completion. The PACS software will allow for data entry such as the patient's name, type of study, medical record number, date received, and other information normally added by radiology information system (RIS), or hospital information system (HIS) server. The technologists and film clerks should be trained in the proper orientation of films as they are loaded into the digitizer. Correct orientation of films will save time later if they do not have to be rotated or manipulated prior to being sent to PACS. Digitizers can also be purchased with compatibility to interface with existing RIS and HIS systems so that data entry selection is routed from institutional data systems. In such case patient information does not need to be entered line by line. Some institutions use multiple digitizers to load their filed films onto PACS and recover much needed storage space.

Section 6.3: Image Transfer

Once the server accepts DICOM image data into PACS it must be moved to remote parts of the network such as to workstations or to the WEB server. Image packets must also be linked to patient information data and sent to storage (memory) so that retrieval is possible. Other functions that may be pending on the images are printing, CD-ROM burning, presentation on a workstation, or distribution through a web browser. These functions and more are directed throughout the PACS system along local or wide area networks.

Data is transferred throughout the network to servers and from servers to other nodes as raw data. Consider the example below in which C-arm fluoroscopy is requested for an endoscopic retrograde cholangiopancreatogram (ERCP) in the operating room.

If the C-arm is a digital unit with a full Ethernet PACS connection, consultation between the surgeon and the radiologist can be handled through image transfer.

During the procedure the gastroenterologist questioned whether there was a residual stone in the common bile duct and requested a radiologist look at the images to help determine the presence or absence of choleliths.

The technologist was able to send the images from the C-arm to PACS by way of an Ethernet connection. A simple phone call to the radiologist and the images were viewed on a diagnostic workstation and a diagnosis given. Further images during the procedure were also sent for stat readings. The point here is that a whole new level of consultation is possible that would not be forthcoming without a PACS network. This is all possible because of a complex networking system in which images are transferred throughout the system managed by PACS servers. As you can imagine, there is a lot of data moved throughout the PACS network from CT, nuclear medicine, ultrasound, MRI, angiography, surgery, CR/ddR, DEXA, and many other sources. The network is a collection of interconnected computers, hardware and software that allows users to share data such as from the C-arm to the workstation, and from memory to workstations, and/print.

In a large institution with many imaging modalities transferring data over the network, there may be delays in images reaching the radiologist for viewing depending on the cable system's capacity to move data. To avoid delays most PACS networks use Ethernet, twisted pair cables, coaxial cables and fiber optic cables. The PACS administration team is able to track the flow of images and data through the network, and can spot and correct cable malfunctions, and numerous errors such as duplicate files that tax server memory as they occur.

These pictures show the inside of a PACS networking hardware room. The white arrow (below) shows the PACS server and how little space is required for it. The picture to the right shows the networking system that routes data between the components of the PACS system. The PACS administration team is responsible for all applications of the software and operations of the hardware that manages the PACS operational components. The main server receives data and information from all radiology modalities that are digital and DICOM compatible. It routes its data throughout the PACS network to include workstations, to storage, and to out of network devices like the CD-ROM burner and to printers.

Section 6.4: Hospital Information Systems (HIS), RIS, and PACS

One of the most important benefits of a PACS system is the workstation! Image viewing on a workstation is available within seconds of being captured by the PACS server. Because the system recognizes patient information data from RIS and HIS hubs it is easy to bring up images using the patient's medical record number, or name and other connecting data such as their date of birth. Before we talk about how the workstation works within the PACS network we should discuss how the PACS server makes viewing images and information possible at the workstation.

Patient information such as the medical record number, name, date-of-birth, type of study, date of study and the like is entered into the PACS record through a data bridge. The data bridge is also a DICOM compatible device that adheres to DICOM subclass standards. Pre-selected information fields from the hospital information system (HIS) and radiology information system (RIS) servers are preset to populate PACS text data fields. This is coordinated with the generation of new images sent to the PACS server from a base device (CR, CT, MRI, etc). DICOM includes compatibility of HIS and RIS information systems networked to a PACS system. The DICOM standards are structured so that the PACS server will distribute images and information as if it were the primary base installed device that originated the data. DICOM also addresses interface standards between network peripheral devices based on "underlying" technologies such as HL7, V2, and 3, which allows information transfer in bulk using document paradigm.

The new DICOM standards version 3.0 of 1993 included the development and expansion of PACS to interface with medical information systems. This was an inclusive enterprise extending from the 1987 formation of Health Level Seven, Inc (HL7). HL7 is a non profit organization that in 1963 acquired ANSI accredited standing as a developing organization. This cooperative group of over 2,000 members representing over 500 corporations encompassing greater than 90% of the vendors of healthcare information system services.

Hospitals input and store patient data using what is known as a hospital information system (HIS). The hospital information system is a network of computers used to enter and store patient’s personal data, such as their full name, date of birth, social security number, insurance billing information, and the like. It contains highly personal and sensitive patient information and legal documents pertaining to the patient. These documents are specifically privacy protected by Federal legislation such as the Health Insurance Portability Act (HIPAA). The Radiology Information System (RIS) is a sub-network of HIS that uses certain data fields from HIS to compile the radiology exam and procedures requisition. HIS and RIS may use the same or different servers to interface with PACS through what is called a HIS/RIS gateway or PACS broker. The gateway uses Health Level Seven protocol since it is the most shared protocol for HIS/RIS records and supports DICOM standards for managing its synchronization into PACS. The functions of the HIS/RIS gateway includes managing, sorting, archiving, distributing, and translating patient text information into PACS and onto images.

The typical scenario is that the radiology department receives a computer generated request for an x-ray study that was place by a unit secretary. In order to enter the study all pre-selected fields would have been filled, such as the ordering physician, type of study, etc. Pertinent clinical data is taken from the clinical information system (CIS) and HIS patient file, and attached to the request to complete it. The accession number (A1015046) or exam number assigned to each study can be used for easy retrieval from PACS.

The radiology request (above) contains pertinent information as it was retrieved from the RIS/HIS gateway. Data fields are set-up according to the specific criteria of the hospital and billing services as well as the way the radiologist inputs. Because the data is populated from the RIS database the requisition and examination selected from the base device worklist matches. Entry errors are abolished since the technologist selects from a workflow list that edits patient information onto the digital images and into PACS for display at the workstation. The union between DICOM and HL7 is even stronger since the new April 2004 upgrades. Transcribed reports are also entered into PACS as HL7 documents so that they are displayed along with image documents.

The picture to the right demonstrates how the RIS/HIS gateway is used to add text patient information to each radiographic image as they are displayed and archived into PACS. Because this information comes from a universal RIS/HIS server that the technologist selected from a work list, patient information errors are minimized. And when patient information is entered incorrectly it can be changed throughout all of the patient's records image and text data files because of the interconnectivity of HIS & RIS to all patient files. This interconnectivity is the precursor to what will in the near future be a totally electronic patient enterprise file made up of Clinical information Systems (CIS), Hospital information system (HIS), and Radiology Information System (RIS), and emerging laboratory and surgical information systems.

Detailed patient information is not transferred to PACS, only those specific data fields needed to add information to radiographic images, reports, or identify files accessed by the RIS/HIS broker. PACS limited query of RIS/HIS information is in compliance with HIPAA standards for accessing patient information on a need-to-share basis. Detailed patient information enterprise files are currently being developed by researchers as a tool to easily access PACS documents, Hospital Information (HIS), and Clinical Information (CIS) files, and the like as a unit file, to enhance patient care strategies.

The picture to the right demonstrates how images can be displayed on the PACS workstation with the same image and study information as contained on the film. This is because of the cooperative nature of DICOM and HL7 data sharing. The simple workstation seen in the picture is used by technologist and file room clerks to verify images on PACS and to retro print images and reports.

Section 6.5: Short-term Storage of PACS documents

Just as film jacket files contain multiple exams that are stored for later retrieval so must digital images and reports be stored on electronic media called archiving, for later retrieval. Besides being electronic data, images stored at different times will be found in different locations in the computer system’s memory. Images stored on the PACS network by storage servers are said to be in short-term storage. Short term storage refers to those image documents available on the server that can be immediately viewed from any network workstation. This is usually accomplished by a specialized server such as a network attached server (NAS) which makes access to PACS images faster than it they are stored on a separate storage network. The recommended memory capacity of a NAS if used as a short-term storage device is usually several terabytes (2^40) which is expandable to petabytes (2^50). Regions hospital, Saint Paul, MN, a Level I trauma center is digital for all radiology modalities except mammography, uses a 5 terabyte NAS for short term storage of image documents. Storing digital data is only one of the many functions of the NAS; it must also retrieve errorless data files to network workstations, WEB servers, and to printers as well. To better understand these functions of the network attached server (NAS) let’s sample how it can be used to store and retrieve image documents.

We have already looked at one of the most important functions of the data bridge, transferring selected information from HIS and RIS into PACS so that the patient's electronic file is established. Since each patient has an exclusive medical records file number it can be used to retrieve electronic documents. Whenever a patient’s medical record number is accessed through a PACS workstation or is selected from a base unit such as the CT scanner worklist or CR worklist, the PACS workflow manager communicates specific instructions to the NAS to bring all folders forward in case they are needed for comparison, a feature called Prefetching. The network attached server will immediately access all of the patient's documents, retrieve and queried them from short and long term storage to the main server. The process of the workflow manager pulling all studies of a patient file to the main server when the patient medical record number is added to the worklist is called prefetching. Prefetching is analogous to the file clerk retrieving a patient's jacket for the radiologist in case prior studies are needed for comparison. When a workstation viewer opens the patient file, smooth seamless acquisition of all image studies are presented on the menu.

Let's consider the retrieval of a file for a patient who is to undergo a follow-up chest x-ray to monitor the progression of treatment for pneumonia. As soon as the physician’s order is entered into the radiology information system (evidenced by a requisition being printed) the workflow server is primed. When the technologist selects a patient study from a base unit workflow list, the NAS server prefetches all files with that medical record number for potential viewing. Then stored files bearing the medical record number are sent to PACS, the workflow manager function provides accesses to all image documents for that patient (CT, MRI, US, CR, etc) through the NAS server. Likewise a new image document is archived in short term storage on the NAS so that it too can be quickly retrieved for diagnostic reading. The point here is that the workflow software in PACS will bring forward all images in a patient's file whether new data is added or not whenever a medical record number is accessed. This is much like going to the film file room and asking for filed radiographs of a patient's ankle. The file room clerk will pull the entire patient film jacket and retrieve the ankle films. If prior films of the patient’s ankle are then requested, the films can be immediately pulled from the jacket for viewing. The PACS workflow manager anticipates that studies in the "electronic file" may be needed for comparison or that reviewing of previous reports may be desired, and therefore makes them readily available as a prefetched function.

Anticipating the need for image files is an important function of the workflow manager because images from different modalities are acquired at different times and may be stored in different memory locations on the network server or be located in long-term storage. By anticipating file use image documents are retrieved as a group to be easily accessed from the NAS; if they are not used they are not permanently moved or resaved onto the NAS. But if a new study is added, the entire sets of files are saved as a group. This keep images updated so they are not discarded for a minimum of 5-7 years following inactivity.

Another function of the short term storage server is to back-up imaging documents in case of a system failure. The NAS provides data protection through what is called a redundant array of independent disks (RAID) formatting. Within the NAS server are several hard drives with multiple disks (at least 2 or more) that are designed for reliability of data storage and optimal retrieval performance. One type of array in which identical copies of data are written on two different disks drives within a server is called disk mirroring. Mirroring provides data back-up so should a system failure occur on any one disk its identical disk will respond so that the workstation user experiences no loss. Disk mirroring is also called a RAID Level 1 format. Drives in a mirror array must be added in pairs because they also function as a back-up data retrieval system. There are several types of storage arrays that back-up data from complete loss. They are discussed in part II-Advanced Concepts – PACS.

Section 6.6: Long-term storage and data back-up

The main server or the network attached server can handle most of the data storage capacity for a large institution; however, there are medical legal requirements for long-term storage of medical information that must also be considered. Some states require medical information to be stored for up to 5-7 years and for pediatric patients until after their 22nd birthday. These regulations include medical images and radiology reports. Almost all of us can remember purging hundreds of outdated x-ray files to make room on shelves for current year files. Moving these files and reorganizing file room space takes time and a lot of muscle. The PACS system must carry out similar functions of data storage that include long-term storage of records. These records can easily be retrieved from PACS just as a film jacket can be retrieved from a remote location if needed or purged if outdated.

A storage function not easily accomplished with analog films is the recording of back-up files in case of a disaster that destroys the main systems. A back-up disaster image file for analog film is primarily accomplished using a microfilm scanner or a minifier system. These may require some darkroom processing and a lot of time to produce and store duplicate images. PACS is able to provide disaster file using optical disk technology and/or digital linear tape technology.

Imaging data can be stored indefinitely on the NAS server if enough memory is provided. Most institutions save data on network servers, optical disk within an optical disk jukebox (ODJ), and on digital linear tape (DLT), or in a DLT jukebox, or combinations of all of the methods mentioned. An optical disk jukebox is a long-term storage hardware device which encompasses optical disk drives, optical disk storage slots, and associated robotic arms and software for fetching data disk(s).

Pictures above shows an Optical disc jukebox (white arrow) used to store images for long-term storage. The pictures with the blue arrows are of an optical disc with a 2.3 gigabyte capacity and OD burner commonly used to back-up CT images

Because the data stored in an ODJ must be fetched from its location by a robotic arm to the driver to be read, the time required to process images from an optical disk jukebox to the main server can be upwards to 30x retrieval time of a network attached server. This is why the workflow manager uses software protocols to pre-fetch image files when a medical record number with prior studies is sent to the workflow list. The workflow manager server will bring forward all data records from short and long term stores such as the NAS and optical disk jukebox, but never from digital linear tape stores.

Data back-up in case of a disaster that could destroy the NAS or Storage Area Network (SAN) servers is handled by digital linear tapes (DLT). The DLT recorder stores all images in PACS on 1/2 inch magnetic tape. These tapes can be combined into a jukebox, but are most often stored at a remote location since the tapes are not accessed by PACS for routine use. The information they contain must be loaded into PACS should a disaster occur; therefore, testing should be done whenever hospital wide disaster drills are held. DLT offers the cheapest method of backing up medical imaging files, and requires the least space for storing disaster recovery files.

The two pictures to the left are of a digital linear tape system used to make disaster tapes of all images recorded onto PACS. This is provided in addition to other storage servers for image viewing. The tape shown looks like an old cassette type and is less than 5 inches long. These tapes are stored at a remote location away from the institution.

Both short-term and long-term data can be stored on a separate sub-network of dedicated storage devices called a Storage Area Network (SAN). The speed of data transferred over a network is dependent on type of line over which data is transmitted such as a fiber optic line, and the network architecture. Most digital images are several megabytes in size each; in order for a SAN to handle data from so many inputs it is important that it uses fiber optic lines and Fibre Channel architecture to move duplex data at transfer rates of near 100 megabytes per second. At this speed a separate network for image storage is reasonable; otherwise a network attached server is much faster at retrieval.

Section 6.7: The PACS Workstation

The workstation is a special type of computer display system that uses high resolution monitor(s) for display and manipulation of radiographic images. Workstations have from one to four high resolution monitors depending on their use and are classified accordingly as either a primary, secondary, or tertiary workstation. A primary workstation (a.k.a. Diagnostic workstation) is the type used by the radiologist. It is equipped with strong array of tools to manipulate images acquired from all imaging modalities. A secondary workstation (a.k.a. clinical workstation) is used for clinical review and is generally found on patient wards, emergency room viewing stations, and clinics. A clinical workstation is usually a two monitor set-up with almost the full array of software tools as a diagnostic workstation. The tertiary workstation is a single-monitor computer designed for use at a remote site through a wide area network (WAN). Examples of tertiary image review sites are physician offices, Web distribution access users, and teleradiography sites such as the radiologist's residence. It is important to understand that a PACS workstation is not the same as a home computer system and monitor. A PACS workstation requires a high resolution monitor and computer software system designed specifically for image viewing.

A PACS network is designed so that any workstation in its network may be accessed by an authorized user; however, in order to log in the operator must have permission via a password provided by the PACS administrator. Passwords are not ubiquitously assigned but are user specific so that compliance with the Health Insurance Portability and Accountability Act (HIPAA) of 1996 can be expected of each user. It is important that each user log-off after each use so that patient information and privacy is maintained.

Above. Secondary and Tertiary workstations are available for viewing images and reports; however, they have fewer image manipulation capabilities than does the primary diagnostic workstation the radiologist requires for multimodality image manipulations.

Now let's begin our journey to understand what advantages there are to a PACS system and particularly the workstation for viewing over traditional view box and radiographic film imaging. The workstation contains computer software that allows for a complex array of image manipulation tools. Its software applications provide optimized viewing functions such as study filters, measurement capability, data reconstruction (CT and MR images), 3D, windowing, magnification, loading studies for review, and transferring studies over the PACS network, filming, CD-ROM burning, and a host of other functions.

Workstation software support almost all radiology modalities: computed tomography (CT), computed radiography (CR), digital X-ray (DX), magnetic resonance (MR), nuclear medicine (NM), radiographic fluoroscopy (RF), secondary capture (SC) e.g., digitized film (SC-DF), ultrasound (US), digital C-arm imagers, and x-ray angiography (XA). Connectivity to the PACS network is assured because DICOM vendors adhere to connectivity standards for all subclasses of the DICOM protocol and HL7 languages.

The diagnostic workstation used by a radiologist is very different from secondary or tertiary workstations. Radiologists need different tools to manipulate images for diagnosing than does a physician who browses the patient's exam as a follow-up to understanding the radiology report or to look at the images prior to a radiology report. Now let's consider some of the functions of the software at the diagnostic workstation. Keep in mind that one of the important functions of PACS is to optimize film viewing relative to x-ray film, and to provide easy access to patient files.

The main network attached server and workflow manager server will bring all exams to the worklist. The worklist can be accessed from the study selection dialog box by entering the patient's I.D. or medical record number. The PACS workstation is a "windows" driven software package that is responsive to mouse click protocol. It comes with a pull-down menu that is relatively easy to follow. Some computer skills are required to maximize its functions; however, no experience is necessary since training is usually provided or a workbook that explains in details its many functions. Workstation functions are too numerous to mention here; however, we will look at some functions that will help the reader understand just how flexible PACS viewing is over conventional x-ray film viewing. Special functions of the workstation such as 3D reconstruction, retro-reconstruction of images in coronal and sagittal planes, voice recognition, etc. will not be covered since workstation functions training is usually provided by the manufacturer after purchase. Our purpose is to emphasize the flexibility of PACS viewing over traditional rolodex film box viewing. Let's look at features such as the dialog box, menu toolbar, personal filter, study/review toolbar, thumbnail navigation, and file merge.

An important advantage of image viewing from a workstation is that the radiologist only needs the radiology request to access the patient's file. This keeps the radiologist reading area simple and less cluttered. To access a file the patient's identification number is entered into the appropriate field. This is easily done using a keyboard or more commonly by a barcode reader. The barcode reader is preferred since the study I.D. can be used to assure that each study request is match with its exam so no study is left unread. What these fields do for the radiologist is allow access to patient files quickly to see images and to retrieve prior studies for comparison. Having four monitors is very convenient to image study display and can be worked independently or as four electronic view boxes. The radiologist reading volumes of studies can select to display a list of all "not read" studies. Using the unread feature the radiologist can monitor exam volume even before the request arrives in case there is a call by a consulting physician prior to receiving the request or to check for unread studies at the end of the day.

The diagnostic workstation allows for personalized filtering so that if the reader is specialized and only reads nuclear medicine studies, or ultrasound, etc., they can customize their work study list. The radiologist can select special filters such as CT (computerized tomography); CR (computed radiography, or US (ultrasound), etc so that they can read all of the films from a specific modality rather than search the worklist in general. Filters can be selected at anytime from the diagnostic workstation. Prior studies and reports can be displayed along with current studies.

Like other Microsoft Windows^tm applications, the user is able to access options within applications from a toolbar menu or by right clicking the mouse. There are study toolbars and windows toolbar functions. Study toolbar allows for rotation of images, next image in series, display options such as 1 image per monitor, or 2x2 images per monitor, 3x3 images per monitor, 4x4 images per monitor, and so forth. Algorithm options such as lung filter, abdomen filter, bone window, high resolution, windowing (density or contrast), measurement, and more is also permitted.

You're probably wondering why we are discussing the workstation when the technologist does not routinely use a diagnostic workstation. The reason is that it is important for the technologist working with digital images and computed radiology images to know that windowing and leveling options are provided on the workstation so that they do not get into the habit of gross density and contrast adjustments of raw data prior to sending it to PACS. When the manufacturer of computerized radiography equipment recommends an optimal density range for their equipment (Fuji will be different from Kodak will be different from Agfa, etc.) it is also an optimal range for workstation viewing. Unfortunately with computed radiography imaging technologist are taught that it is impossible to overexpose an image so when it happens the technologist is reluctant to repeat the view. To compensate for the poor images quality seen on the reader monitor the technologist may change its density and contrast prior to sending it to PACS. The data is then permanently lost and the image data the technologist used to manipulate the image is not available to the radiologist providing the diagnostic reading. Instead of drastically manipulating a poor image the technologist should provide an image within the specified windowing range recommended by the equipment manufacturer. Manipulating image data from a CR monitor prior to sending it to PACS causes it to be permanently changed. Then when the radiologist manipulates the data from the workstation it is not from the total raw data but from that data sent to PACS following the technologists' manipulations. If the image was poor on the remote operator panel, then it is even further degraded by manipulations at the workstation. It is better to send the poor images and let the radiologist perform their own windowing and leveling of the quality rather than the technologist manipulating it to their liking and removing raw data then sending it to PACS (see part III on radiographic technique for digital imaging with CR if this is not fully understood).

The radiologist is able to navigate through patient exams including prior studies and their associated reports using the thumbnail guide. Thumbnails are the small picture elements seen above the image displayed on the monitor above. The viewer is able to quickly select a study by clicking on the thumbnail, then using drag and drop windows technology move the study to the monitor. Thumbnails of all studies appear along with the study date for easy reference. This is a lot easier than searching through a conventional film jacket full of out of order studies. After dictating, the radiologist can mark the study as read and close the folder. The workstation is designed to enhance images for diagnostic purposes. The technologist should understand how it works because they too will be called upon for technical questions countless times. A technologist working alone at night in a smaller institution may be confronted with workstation questions from nighthawk physicians. Many situations may require the technologist to have a working knowledge of its use. Simple questions such as "how do I magnify images, or how do I switch from a positive image to a negative image" may seem trivial, but they are routinely asked of the technologist. Issues such as how to reboot the workstation in case of system failure and the like should be known to the technologist as well as to the PACS administration team.

Thumbnails (blue arrow) are a very useful option for quickly navigating through studies. By click and drag windows technology the viewer is able to move the entire study to the monitor. Display options on the monitor (e.g. 2x2,) make it possible to display images or studies side by side for easy comparison. In our example a PET image and CT are displayed side by side. Becoming handy with workstation features takes a little practice but anyone can become proficient rather quickly.

The last topic of our discussion on workstation options is the file merge function. This is very useful because the radiologist is able to compare studies of different patients side by side for teaching purposes, or can merge files that are similar to create an electronic teaching file. While viewing a study the radiologist may wish to tag images to be reviewed with the ordering physician during a consultation. These features and many more allow for easy access to information without having to go through an entire image file. In addition, integrated modules enables viewing patient reports previously stored in the Radiology Information System (RIS) through a RIS broker or Data Bridge. Both reports and images can be printed from a PACS workstation, or on to a CD-ROM for teaching files, lectures, and patient consults. More detailed information on a specific workstation is available from the manufacturer(s).

Section 6.8: The PACS Network

From image capture, to short term storage, to viewing on the workstation, we can see that PACS is a sophisticated network of dynamic digital data transfers. Networking components of PACS consists of computer hardware and software that communicate information along cables so that the various nodes can share data and peripheral devices. The PACS network is a system of interconnected, individually controlled computers (called nodes), and together with the hardware and software used to connect their operating functions forms the network. Even the cables connecting the network are special data control lines that allow computers to input data into PACS and transmit to remote client nodes; duplex pathways allow simultaneous retrieval of image studies and reports. Most of the functions of manipulating image data and their associated reports are performed by servers and data bridges that communicate through shared protocols. The PACS network protocol (DICOM) allows users to share data and peripherals devices. Most PACS systems use multiple servers distributed within the network; this architecture is termed a decentralized or distributed network. But in order for the network to communicate effectively and efficiently there must be organization within the environment of data transfer. Organization of data trafficking is the central focus of networking through PACS.

PACS is a server-client node system in which one or more computers act as servers to store data and programs that are accessed by client computers on the system. Servers by function are designed to be faster than other computers on the network, like an orchestrated organized system of pacemakers. Servers such as the workflow server, archive server, and workgroup servers may be distributed within the PACS network to increase transmission speed of the system. These servers have full duplex bidirectional functions as well as fast input/output speed for transmission on the network. A workflow server is an expandable computer with versatile storage options. An archive server performs data back-up and PACS synchronization with HIS/CIS/RIS systems, and fetches prior studies anticipating the need to review stored files. A workgroup server communicates between long-term storage devices, the archive server, and short-term storage devices to deliver seamless documents to clinical workstations. How all of this is orchestrated is a function of networking layout schemes, cabling systems, and transmission protocols.

The simplest form of a PACS network is that physical network whereby a group of computers are connected on a single transmission cable system for the purpose of sharing resources, an arrangement called a local area network or LAN. A LAN usually covers a small community such as a hospital building and may include adjacent clinics. The types of cable line used in a typical LAN delimit the distance over which computers may communicate. Take the case of a computer such as the C-arm used to acquire dynamic surgical images; it may be connected to PACS as part of a LAN network using Ethernet. Let's explore how a simple PACS LAN is organized using the Ethernet model and then explore how it can be modified to transmit data over a wider network such as the Internet.

Ethernet is a communication cabling system developed in 1973 by Bob Metcalfe while working on a method to connect a Xerox printer to a computer. His connection methods solved the most common problems faced in connecting computers and peripherals today. Present day Ethernet is the most common type of connection to PACS. Basic Ethernet networking relies on a single cable network to which additional devices may be attached without requiring modification to those devices already on the network. In order for Ethernet connectivity to work for all devices on the network, they must speak the same language, which is called a protocol. All devices on the Ethernet network used in PACS have the protocol DICOM. In addition to communicating in DICOM, each device on the network must have its unique broadcast address. Data frames or images must contain the address of the sending computer and the address of the intended recipient device. All data frames sent over the Ethernet network must contain the sending device's address and receivers address coded for that data. It is like mailing a letter in which there is a sender’s address and a recipient address or the envelope will not be delivered.

All nodes on the network receive transmitted data; however, only the intended addressed recipient whose address matches the data frame will "open" the frame, process, and perform its intended function. Because so much information is sent over a LAN, the Ethernet protocol uses what is called CSMA/CD which is an acronym for carrier-sense multiple access collision detection protocol. What this means in layperson terms is that every device on the network "listens" to hear if other devices are sending, if so it will wait until there is silence, then it will send its message. In this way incoming information is received by the intended device as a priority over data sending.

The GE-OEC C-arm pictured above communicates digital images to PACS. The C-arm has a designated address for communicating data frames through its Ethernet connection. The same in principle applies to all components on the PACS network (e.g. PACS server, printers, CD-ROM burner, MRI machines, CT scanner, DEXA, ultrasound, nuclear medicine cameras, CR, etc).

The shape of the network in terms of how the various nodes are connected is referred to as the network's topology. There are four main types of topologies used to connect a LAN used for PACS: Bus, Ring, Star, and Tree designs. The most common and efficient topology for PACS networking is the Bus architecture. The bus topology uses a central cable such as Ethernet to which the various nodes are connected. The ring design is a closed loop and is difficult to install and is very expensive to maintain. The star is easy to install but is an inefficient way to transfer data. The tree topology is a combination bus and star designs.

Besides the topology of a network its bandwidth must accommodate the traffic it will handle. Bandwidth is the amount of data transmitted in a fixed amount of time. When we consider a wide area network connected PACS system, such as a web browser, the media must also be considered. By media we mean the cables connecting components of the system. The most common types of media are the twisted pair, coaxial, and fiber optic cables. Most people have heard of these types of cables in relation to their television, phone lines, or entertainment systems. The Web distribution component of PACS is a remote access for referring physicians to consult with radiologist about their patients. For Web distribution a Web server and a strong firewall is required to protect the PACS system. Intranet view is preferred over Internet viewing of PACS documents and data because firewall protection sufficient for HIPAA regulations is difficult to design.

The Web distribution server interfaces with the PACS server and archiving server to translate PACS data into a form that can be viewed over the Internet. The internet requires Transmission Control Protocol/Internet Protocol (TCP/IP) between nodes on the Internet network to ensure data packages are delivered in the order they are sent since different transmission routes are possible. Because the PACS server accesses HIS and RIS servers the Web server must be properly configured and managed through a firewall to protect the hospital's computers and the information they contain. A remote workstation must have the proper software installed and access codes issued to users in order to access images and to print images and data.

Section 6.9: Peripherals and output devices

In addition to viewing there are several peripherals that can input into PACS and output devices such as printers and CD-ROM burners for image recording. One such input is the paper scanner that can be used to enter paper notes and reports into PACS. This is usually the case with ultrasound notes, bone densitometry notes, spine notes, and clinical history like contrast media screening, or treatment for contrast media reactions. Regardless of the peripheral that is added to the PACS network, it must use a DICOM service class language which is a subclass protocol recognized by PACS. Consider the set-up below:

A simple paper scanner is interfaced with the PACS system so that once the desired file is located, related papers can be scanned into the file. This is the case for almost all ultrasound studies in which the sonographer makes notes that are important to the scan. The set-up in this picture places the paper scanner in a universal location so that technologist can add notes, incident report, contrast screening sheet, MRI screen forms, etc. to patient studies. The point here is that devices can be added to the PACS network so long as they meet DICOM protocol. The PACS manufacturer or administrator should be contacted if such a set-up addition is desired to an existing PACS network.

Perhaps the most common output device is the laser printer. Many institutions that are "filmless" have come to recognize this term as meaning they do not print films for their record, but they do incur an expense to print films for patients having consultations at other institutions. Unfortunately we may never see PACS cooperation between medical institutions which is one of the many capabilities of PACS, therefore medical institutions still transfer images mainly through printed films. Laser printers are configured for digital imaging which means that from 1 to 30 images can be printed on a 14 x 17 film. Most printers have only one size film so it is important to know what the receiving physician prefers in filming. For example, a PA and Lateral chest images can be printed together on a single film; however, the orthopedic surgeon would prefer the AP and Lateral of the femur and knee to be printed at actual size so measurements can be made prior to the surgery.

Another nice addition to the PACS system is a CD-ROM burner. As we all know printing images on x-ray film is expensive; however, putting them on a CD-ROM is extremely cost efficient. It has been estimated that the cost to reduce 100 14 x 17 films to one CD-ROM disk is less than one U.S. dollar. Institutions using digital imaging already have their data in a format that can easily be burned on to a compact disc. This is perhaps one of the most cost effective additions to any radiology department that is digital. Most of these CD-ROM burners designed for radiographic images will come with software that creates a self-start disc, full PACS manipulation tools, and lock-out software so it cannot play on a home computer unless it has the appropriate software to open it. Physicians wishing to have a CD-ROM instead of films will need to have the software installed on their viewing computer prior to receiving imaging CD’s.

The image to the left is of a commercial EMED CD-ROM burner that has been installed in the "film file" room. The computer is used to locate files from a worklist and execute disc copying. This burner also contains a CD-printer which will label the disc with the patient's name and list all studies burned on the disc. CE-ROMS can be printed from any computer such as the reception desk clerk's computer or tech area computer.

• In conventional radiography the image captured in the emulsion of x-ray film is called a latent image.
• The process of converting an invisible latent image to a visible manifest image requires chemical reduction of silver halide crystals.
• PACS is an acronym for Picture Archiving and Communicating System.
• Images that are captured into PACS must be digital or digitized.
• Seven components of a PACS: image capture, image transfer, image viewing, short term storage of data, long term storage of data, retrieval, networking, and peripherals.
• Monitoring and maintaining the various function of PACS is the responsibility of the PACS administration team. Log-on codes and maintaining HIPAA standards during PACS use is the responsibility of the PACS administrator.
• Benefits of PACS include: decrease lost films, decrease retakes, decrease room storage space, decrease film cost, increase productivity, increase efficiency, and better communications between radiology and our clients.
• The main PACS server is a hardware device whose function includes data acquisition into PACS from all digital imaging sources.
• Some functions of PACS servers include: data control, routing, archiving, and managing workflow.
• DICOM is an acronym for Digital Imaging and Communication in Medicine; it is the standard for digital medical imaging worldwide.
• DICOM is a cooperative standard between medical imaging vendors, associated information vendors, American College of Radiology, and the National Manufacturers Association.
• The current DICOM standard is DICOM v3.0, which defines protocol operations of subclasses of DICOM as well.
• The scope of DICOM includes digital data exchange and interconnectivity of electronic devices used in medicine, but does not specify the architecture of a system or control functionality of a device.
• DICOM addresses 5 layers of functionality: Data transmission, query and retrieval, performance, workflow management, and quality and consistency of image appearance across all medical imaging devices.
• A digitizer is a device that converts analog film into digital bits of information.
• Information such as the patient’s name, medical record number, type of study, etc. is entered into PACS documents from hospital information system (HIS) and radiology information system (RIS) servers.
• The protocol for hospital and radiology information systems is called Health Level Seven (HL7).
• The RIS/HIS gateways are responsible for managing, sorting, archiving, distributing, and translating patient text information into PACS-DICOM.
• A network attached server (NAS) functions as an in network server that routs and stores imaging data making it quickly available to network workstations.
• The process of the workflow server pulling all prior examination in an “electronic” file is called pre-fetching. Pre-fetching is the equivalent function of pulling a patient jacket so the viewer of a study has access to all prior exams for comparison.
• Short term storage servers such as a NAS may use several hard drives with multiple disks. They are designed for data storage and optimal retrieval performance.
• Mirroring is a type of memory back-up system in which data is stored on two different identical disks in case of system failure; each is a back-up to the other.
• A popular type of long term storage system is the optical disk jukebox (ODJ) that uses optical disk, optical disk drives, and robotic arms to retrieve data into PACS.
• Digital linear tape (DLT) jukebox is a type of disaster recovery back-up memory system that uses digital linear tape to store images.
• A separate storage network (SAN) is a separate storage network that uses fiber optic line and fiber channel architecture to move data quickly at speeds of near 100 megabytes per second.
• Not all workstations are created equal. A diagnostic workstation has 4 high resolution monitors and operates with a sophisticated array of image manipulation tools. A clinical workstation has 2 high resolution monitors and has strong but limited software image manipulation capabilities. Tertiary workstation offer single monitor PACS viewing and image manipulation tools.
• In compliance with the Health Insurance Portability and Accountability Act of 1996, all users of a PACS workstation must have their own unique log-on/off code, and each user is responsible for logging off after each use.
• The PACS workstation software supports viewing images from all radiology modalities including: nuclear medicine, ultrasound, MRI, CT, DX, XA, SC, and others.
• The operator of a workstation communicates to the workflow manager server to bring exams to the monitor using a dialog box in which patient information is entered.
• Workstations operate on Windows^tm software so that most functions are controlled with a mouse accessed pull-down menus, and filters.
• Thumbnails are small picture elements that appear on the menu for easy location of image studies. They respond to the drag and click windows protocol.
• PACS is a server-client node system in which one or more computers act as servers to store data and programs and are accessible by client computers on the system.
• Most PACS systems are local area networks (LAN) which is a physical network of computers interconnected on a single transmission cable system for the purpose of sharing resources.
• Ethernet is a type of LAN developed by Bob Metcalfe in 1973 while working on a way to connect Xerox copiers to a computer. It solved almost all communication paradigms between devices.
• In order for Ethernet connectivity to work for all devices on a network they must all use the same language called a protocol.
• Ethernet uses a additional protocol called carrier-sense multiple access collision detection (CSMA/CD); devices on the server are bound to rules that govern Ethernet use:
• Each device must have an Ethernet address
• Data frames are sent with sender and recipient’s address.
• All devices must listen before sending and if data is being transmitted the device must wait until the network is clear.
• The shape of a network in terms of how the various nodes are connected is called the network’s topology. Ethernet and PACS use BUS topology.
• Bandwidth is the amount of data transmitted in a fixed amount of time. The media is the cabling connections between components of PACS.
• For wide area networking (WAN) of PACS a web distribution server is required. This is because internet uses a Transmission Control Protocol/Internet Protocol (TCP/IP) between nodes to ensure data packages are delivered in the order transmitted over different routes.

References

Copyright

2006 Nicholas Joseph Jr.