Design and operation of a nuclear medicine picture archiving and communication system

Design and Operation of a Nuclear Medicine Picture Archiving and Communication System Paul H. B r o w n and Gerbail T. Krishnamurthy C o n s t r u c t i o n of a n e w V e t e r a n s A d m i n i s t r a t i o n M e d ical Center p r o v i d e d a unique o p p o r t u n i t y t o design and i m p l e m e n t a s t a t e - o f - t h e - a r t nuclear medicine d e p a r t m e n t in a large teaching and research hospital. The n e w medical c e n t e r a l l o w e d the acquisition of all n e w g a m m a cameras and c o m p u t e r systems w i t h o u t any historical need to patch t o g e t h e r a system of old and n e w equipment. The picture archiving and communication system (PACS) w a s designed t o link five gamma cameras t o four image v i e w i n g areas, f o l l o w e d by digital archive on an optical disc. The g a m m a cameras" c o m p u t e r s and v i e w i n g areas" c o m p u t e r s are linked to a central n e t w o r k i n g c o m p u t e r in a manner t h a t provides nine i n d e p e n d e n t but digitally communicating image computers. Each nuclear medicine c o m p u t e r is capable of acquiring g a m m a camera data w h i l e possibly also p e r f o r m i n g up t o t h r e e o t h e r simultaneous tasks: analysis of image data, t r a n s f e r of image data f r o m node to node, and p a t i e n t database manipulation. The nine image c o m p u t e r s each appear to t h e user as a digital file cabinet, containing various folders, which in turn contain p a t i e n t studies. To t r a n s f e r a

p a t i e n t s t u d y from one location to another, t h e user simply queues a transfer request by selecting a file d r a w e r - f o l d e r combination for the source and destination locations. It takes only a f e w seconds to queue a t r a n s f e r request, and t h e t r a n s f e r is c o m p l e t e about a minute later w i t h o u t any f u r t h e r user intervention. A c o m p u t e r genie a w a k e n s during t h e early morning off-hours and p e r f o r m s housekeeping tasks, including m o v e m e n t of p a t i e n t studies (based on date of acquisition) from active v i e w i n g folders to inactive archive folders. All scheduling, w o r k l o a d data, p a t i e n t image reports, etc, are handled by a p a t i e n t t e x t u a l information database system. Patient r e p o r t s and scheduling information are t r a n s m i t t e d to t h e medical center's central c o m p u t e r w h e r e t h e y are made readily available t h r o u g h o u t t h e medical center. The PACS, in clinical use since t h e spring of 1988, is practical and w e l l - r e c e i v e d by technologists, nuclear medicine physicians, and m o r e i m p o r t a n t l y , our consumer, t h e referring physicians.

E S P I T E T H E F A C T that picture archiving and communication systems (PACS) have been available for several years, they have yet to become a truly practical tool in the daily operation of most radiology departments. A PACS in radiology raises many complex issues, including matrix size, number of images for each procedure, cost, and the difficulties involved in changing current methods of image interpretation to meet PACS requirements. Our first design goal for the PACS was to restrict it to nuclear medicine and to use a single computer vendor that could provide an interface to analog XYZ signals from a variety of newly purchased gamma cameras. Of course, the capabilities of the computer system for nuclear medicine acquisition and analysis software were an important consideration, 1 but this aspect of nuclear medicine computers is not the main thrust of this article, which will deal mainly with PACS considerations. We decided to purchase an off-the-shelf, turn-key PACS rather than attempt to design our own PACS without the aid of a nuclear medicine vendor. Our goal was to demonstrate the feasibility and clinical usefulness of a networked nuclear medicine computer system that we intended to use for all aspects of image

acquisition and display, ultimately leading to an all-digital nuclear medicine service. Since we were already in the position of purchasing all new computers for use with each of our gamma cameras, we hoped that the addition of a network would not be an undue financial burden. At the time of our purchasing decision (1984), no PACS was commercially available that met our needs, so we began a conceptual design of PACS with one of the nuclear medicine computer vendors. The vendor ( C E N T O R Network System, ADAC Laboratories, Milpitas, CA) considered our needs and goals, as well as those from other potential customers, to design and market the PACS that will be described here. In addition to the CENT O R image network software, the system uses standard ADAC nuclear medicine software. Viewpoint software from ADAC is used for the high-resolution PACS image interpretation sta-

D

Seminars in Nuclear Medicine, Vol XX, No 3 (July), 1990: pp 205-224

T h i s is a U S g o v e r n m e n t t i o n s o n i t s use,

work. There are no restric-

From the Veterans Administration Medical Center and Oregon Health Sciences University, Portland, OR. Address reprint requests to Paul H. Brown, PhD, VA Medical Center (I 15), PO Box 1034, Portland, OR 97207. This is a US government work. There are no restrictions on its use. 0001-2998/90/2003-0002500.00/0 205

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tions. The patient database computer system that handles scheduling, patient reports, etc, is a product known as Missouri Automated Radiology System (MARS), also from ADAC Laboratories. MARS is a standard radiology information system (RIS) that has been in use for several years at many other medical centers, mostly in radiology. We were the first site to adopt the MARS-R1S for use solely in nuclear medicine, which required some minor adjustments in the standard MARS software. The following were more specific design goals for the PACS system: 1. A dedicated nuclear medicine computer central processing unit (CPU), hereafter called a node, must be provided for each gamma camera and/or image viewing area. 2. Each CPU must be capable of acquiring gamma camera data while also using software windows to perform up to three other simultaneous tasks: analysis of image data, network CENTOR transfer of patient image studies, patient MARS database manipulation. 3. Image viewing areas should use a large format, high-resolution, user-friendly image display screen that offers high quality images in an environment of mouse-driven software that will be readily accepted by physician users. 4. The computer nodes should be independent, but able to communicate through a central host computer for image transfer. A hardware failure of one node (eg, one gamma camera room or one image viewing area) should not affect any other area. Image transfers should be effected by mouse-driven software involving only minimal keyboard interaction. Transfers should be queued by the user for source-destination node, and the transfer should complete without further user interaction. Image data acquisition may simultaneously be in progress during network requests and the user may return to any other software tasks (eg, image data analysis) once the transfer request is queued. A typical nuclear medicine study should transfer in 1 minute or less. 5. The CENTOR-PACS network depends on the central host computer for communication between nodes. In the event of failure

BROWN AND KRISHNAMURTHY

of this central host computer, a backup network should be capable of maintaining image transfers. Failure of the central host computer, or failure of any component of the network, should not affect image data acquisition. Therefore, images can always be acquired, analyzed, and viewed on the gamma camera node of origin. 6. Image archiving should proceed in a regular and automatic fashion to long-term optical disc media. A temporary short-term archive should allow rapid retrieval of current patients. Housekeeping functions, eg, deletion from short-term archive or viewing nodes of less current patient studies in favor of a more current patient, should be automatically performed by the PACS software. 7. The patient database (radiology information system IRIS]) should handle all administrative and textual functions beginning at scheduling and ending at transmission of the final patient report to the patient's ward physician. The RIS is connected to the medical center's central computer system (hospital information system [HIS]). Workload data (eg, how many patients from ward no. 3 had cardiac scans last month) and case retrieval data (eg, list all patients over 50 years old with ejection fraction less than 50% and with myocardial infarction) should be quickly available from the RIS. These were our goals 4 years ago. To what end we were successful in achieving these goals is discussed below. OPERATING SPECIFICATIONS

Hardware Location

The actual locations where the computer terminals are used (eg, gamma camera room, physician reading room) contain only the display screens, conserving space in these clinical areas. The computers themselves are located in a centralized computer room (Fig 1) that allows environmental control for such concerns as power distribution, heating and cooling, service accessibility, and security. Since the system runs 24hour days (archiving is automatic during the evening off-hours), our computer room is monitored for power levels, temperature and humidity, and smoke detectors via the medical center's central alarm system.

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Fig 1. The computer room houses seven of the nine nuclear medicine CPUs, the central host computer and archiving equipment, and the RIS patient data base computer. Equipment is centralized here for ease of service and control of power and environmental variables.

The hardware for the nuclear medicine computer acquisition and analysis nodes (ADAC 3300/33000), the PACS display nodes (Viewpoint), the PACS-CENTOR network, and the MARS patient database network are listed in Table 1. Figure 2 shows a schematic of the entire system. One of the nuclear medicine computer nodes is portable, allowing the computer to accompany the portable gamma camera for bedside acquisition. To aid the reader in understanding the operation of our PACS, the operation of

the CENTOR image network, the PACS display terminals, and the MARS patient database will be discussed separately. The total cost of the computer equipment was slightly over one million dollars.

Study Location Figure 3 shows how the PACS may be conceptualized by the user as simply a digital file cabinet, with one file drawer for each node. One node, or file drawer, represents each of the

Table 1. P A C S Hardware Specifications

No. of workstations CPU type (no.) Operating system Memory Disc Program Image Archive Tape Archive

Nuclear Medicine Acquisition and Analysis

Viewpoint I m a g e Display Stations

12 DEC LSIt 1 (9) RT- 11 1-2 megabytes

3 IBM PC AT (3) DOS 1 megabyte

40 megabytes 40 megabytes

474 megabytes

CENTOR-PACS Image Network

MARS Patient Database

14 DEC Microvax (1) VMS 16 megabytes

15 DEC 11-73 (1) MUMPS

73 megabytes 474 megabytes 2 gigabytes 295 megabytes

171 megabytes

46 megabytes

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Gamma Cameras Siemens Tomo

Image Acquire/Analyze, CENTOR Image Network, MARS Patient Database

Picker Tomo

Siemens Portable

Toshiba Dual Head

1

1

1

ADAC 33000, 80 Mb disk

ADAC 33000, 80 Mb

ADAC 33000.80 Mb

ADAC 3300.80 Mb

I

I

I

I

_

I

_

I

Resident Physician

Staff Physician x 2

ADAC Viewpoint

ADAC Viewpoint

_

/ Modemto '--CCU maging

I

Analysis x 6

Conference Room

ADAC 3300, 80 Mb

ADAC 3300.80 Mb

Viewing Stations, Images, Dictation, Case Retrieval

Viewpoint

Short-term Archive Long-term Archive Tape Archive

....

uVAX ADACCENTOR Image Database

,ta,;:/;~matoo

Fig 2. A schematic of the PACS showing paths of distribution from the gamma camera nodes, to physician viewing nodes, and then to archive locations. All workstations function via single keystroke software windows to access the computer for nuclear medicine acquisition and analysis, CENTOR image transfer, or MARS-RIS patient data base.

C E N T O R workstations, 14 of which are in gamma camera rooms and image viewing areas. Each file drawer may contain a series of userdefined folders, and the folders contain patient image studies. A user at any of the 14 C E N T O R nodes can request a transfer of a patient study to or from any other drawer-folder location. The names of the nodes, definitions of folders, residency times in viewing areas, etc, are defined by PACS management software that runs on the Microvax (Digital Equipment Corp, Maynard, MA) central host computer. The typical user of the PACS simply presses a single control key to leave the nuclear medicine menu window and enters instead the P A C S - C E N T O R window (Fig 4). The user then queues a transfer request by selecting a patient for transfer and specifying the destination node-folder combination. The patient may be selected, as shown in Fig 5, by searching on any combination of a large number of menudriven parameters including name, identification number, date, procedure, physician, and nodefolder source location. All parameters for the patient selection may be typed in at the keyboard, or if the user prefers, the menu will

display a list of locations, patients, etc, from which the user selects by using only directional arrow keys on the keypad. User friendliness is an important determinant of speed in any network system. The C E N T O R system is flexible and easily tailored via PACS management software to any particular configuration as the system changes over time. We have elected to keep the number of patient folders to the bare minimum so that each gamma camera node contains only one folder called "New Study."

Data Acquisition and Analysis The technologist acquires and processes the gamma camera data at one of the five gamma camera node locations shown at the top of Fig 2. When processing is complete, the technologist keys the workstations into the C E N T O R window (recall that acquisition and/or further processing of a different patient may simultaneously be in progress), selects a patient, and proceeds as shown in Fig 6 with the viewing and archiving process. The technologist performs three separate transfer queues: (1) patient raw data and processed data are queued for copy to the waste-

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A ~CameraRoom1 Drawer t

I B

I

PerUser Liver Cardiac NewStudies Folders

ResidentReading Drawer

I

Dr. Smith'sReading Drawer

B

[ - - ]

Fig 3. A pictorial representation of the PACS as a digital file cabinet. The digital file cabinet contains drawers (the computer workstations or nodes); the drawers contain folders that are named to typify the type of patient folders contained in each drawer. A user queues a request for transfer of a patient by choosing a source and destination drawer-folder combination.

.erUser AwaitArchive TeaLh,~gC....

"~ tl

NewStudies

ConferenceRoom Drawer I

CENTORappears as a large user specified file drawer cabinet

B

Drawers contain folders

C

Folderscontain patients

I

l

Archive Drawer

B I

A

I

basket folder where they remain for 3 days in case reprocessing is needed; (2) patient data are edited to select only final results for physician viewing (eg, only tomographic slices) and are then queued for a copy to the Viewpoint physi-

3a,m,Genie ! Wastebasket LongTerm ShortTerm

Users move patients between drawers and folders

cian's viewing station; and (3) the selected viewing data are also queued for a move to the long-term archive drawer. Transfers require about 2 minutes of technologist time. Once the transfer requests are queued, no further human interven-

Fig 4. The main menu for CENTOR image transfer, To initiate a patient transfer, the user first searches for a patient and then moves, duplicates, or makes a copy of the patient study to another node-folder location. This menu also offers a choice to monitor node communications that show transfers in progress, a choice to display process conditions that show the states of various netw o r k hardware, or a choice to report recent activity, which is s log of all n e t w o r k requests and results.

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Fig 5. The CENTOR menu searches for a patient. This menu is called from the search option shown in Fig 4. The user may search for a patient based on any single choice or combination of name, date of acquisition, node-folder-label location, procedure name, identification number, etc. Searching is completed in a f e w seconds and the user then selects the desired patient from the list presented by the search. Then the user returns t o the main CENTOR menu and queues the transfer by selecting a destination nodefolder.

tion is needed to complete the transfers. The C E N T O R - P A C S software distinguishes between a copy of a patient study versus a move of a patient study. A copy is a transfer that makes a carbon copy of the patient study for viewing purposes only; the resultant copy is flagged such

that the network will never recognize the copy as a real patient study in the future, thereby allowing multiple viewing copies without resulting in future multiple archives of the same patient. The source study is unaffected by the copy function. On the other hand, the move function actually

GAMMA CAMERA ACQUISITON NODE

All raw and processed data

Fig 6. The archiving process involves several layers. The technologist completes the acquisition and analysis process and makes a duplicate of the patient study t o the w a s t e basket folder, a " s a f e t y " holding tank w i t h a 3-day residency. The user edits o u t the intermediate data that is not desired for physician viewing or archiving, and sends this edited data t o the physician viewing node (Viewpoint), and to a r c h i v e . Archive is automatic during off-hours w i t h the patient recorded on both the longt e r m optical disc and a shortt e r m archive disc that allows rapid retrieval of patient studies less than 21 days old.

I WASTEBASKET 3 day residency

copy

Edited viewing data

1 !

move

CENTRAL HOST

off-hours

copy

VIEWPOINT PHYSICIAN VIEWING 474 Mb disk 2 day residency

SHORT TERM ARCHIVE 474 Mb disk 21 day residency

2 Gbdisk

LONG TERM ARCHIVE

/\

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picks up the patient study and moves it to a different location. The system that we use, a copy to viewing node and a move to archive, accomplishes several tasks: the source node is cleaned of the patient data, requiring no further housekeeping and freeing gamma camera node disc space for the next patient; and the archive process is begun. We send to the physician viewing station and to the archive only those image studies that the physician will use for interpretation now or will view in the future from long-term archive retrieval. Nuclear medicine image processing often generates many intermediate studies that are not needed for physician interpretation, and these studies are not sent to the viewing station or the archive, thereby simplifying the operation o f physician viewing as well as economizing longterm archive storage capability. In addition, we make a duplicate of all the patient's raw and processed data, which are held in the wastebasket, a temporary storage tank, for 3 days. In the rare instance when reprocessing of a patient study is required, the need for reprocessing is discovered during physician viewing, and the study simply can be recovered from the wastebasket for reprocessing before the automatic 3-day deletion from the wastebasket. This 3-day limit can be changed if a longer or shorter time interval is warranted.

Archiving The archiving process is automatic at several levels after the user has queued the transfer to long-term archive. Actual transfers do not occur until midnight to avoid slowing down the network during the peak use daytime hours. At midnight the computer's archive genie wakes up and transfers the patient to the long-term archive on a 2-gigabyte optical disc cartridge. The patient study also is transferred to a 295-megabyte DEC-TK70 tape cartridge, providing archive backup in the event of destruction of an optical disc cartridge. Retrieval of a patient study from the optical disc in the future, say for comparison of an old study to a current study, requires several minutes because of the slowness of the optical disc system. It is therefore desirable to have a short-term archive on a faster disc that acts as a temporary storage for current patients, allowing more rapid retrieval of past studies from the short-term archive to the physician viewing

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node. The CENTOR genie also copies the patient study automatically to a 474-megabyte disc short-term archive, which acts as a write-through cache with a user-specified residency time (we use 21 days). A past study may then be recalled from short-term archive in about a minute for studies less than 21 days old or retrieved from long-term archive in about 5 minutes for studies over 21 days old. The entire patient directory always is maintained on-line in the central host computer, although the patient study itself is archived on a particular optical disc or tape cartridge. When searching for a past study of a patient in the archives, the CENTOR directory will show which optical disc cartridge contains the patient's previous study. The user must then remove the current optical disc cartridge and insert the desired optical disc cartridge so that the transfer from long-term archive to physician viewing may be achieved. Studies may similarly be recovered from the tape backup, which is to be used only in the event of' failure of an optical disc cartridge. This can be done by the secretary or file clerk performing a study much like pulling all the previous hard copies and presenting this with the current study.

System Structure The PACS network is structured as a logical star topology network, with all nodes connected to the central host via an Ethernet (Digital Equipment Corp, Maynard, MA) bus. 2"4 The central host (Table 1) is a Digital Equipment Corp (DEC) Microvax II computer, with a V M S (Digital Equipment Corp, Maynard, MA) operating system. VMS was chosen over UNIX (Digital Equipment Corp, Maynard, MA) as the central host because of the features of VMS with regard to system priorities, event scheduling, and file access control, which is an important issue where the nuclear medicine remote nodes are from varied hardware sources. The nuclear medicine nodes (Table 1) are DEC LSI- 1l's running RT-11 (Digital Equipment Corp, Maynard, MA) with gamma camera acquisition as the foreground job, image processing as the background job, and CENTOR as a system background job. The physician viewing station (Table 1) nodes are IBM (Boca Raton, FL) personal computerbased, with an MS-DOS (IBM, Boca Raton, FL) operating system. Also available, but not yet a

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part of our PACS, is a remote node consisting of a S U N (ADAC Laboratories, Milpitas, CA) microsystem computer running U N I X ( A T & T , New York, NY). Ethernet is a standard network protocol that uses a 10-megabits-per-second bandwidth on a l/2-inch coaxial cable. The Ethernet driver software communicates with the central host and remote node controllers at a maximum data rate of 85 Kbytes per second. Ethernet is a carrier-sense multiple-access with collision detection ( C S M A / C D ) network. The bus connecting all nodes has a 10-megabits-per-second carrier that allows nodes to transmit data when they sense a nonbusy bus. If two nodes transmit at the same time, resulting in a collision, the collision is detected and both nodes retry their transmission after waiting a different random time interval. Ethernet has several advantages for a nuclear medicine network: it is a reliable and welldebugged network system at moderate cost with many hardware vendors. Ethernet is best suited for relatively small matrix sizes on a network over modest distances, due to problems with collisions on the bus. 4 Ethernet may be configured over a coaxial cable up to 1,500 m, as in our case, or with fiberoptic cables for a several kilometer range, or with T1 telephone line for national range. Ethernet's disadvantage is a speed slower than several of the more recent network systems.

Study Transfer Rate Many conflicting claims and specifications can be given for a network's transfer rate, the rate at which bits can traverse an accessed data bus. What ultimately matters is not the specified transfer rate, but rather how long the network requires to transfer a typical patient image study. The patient study transfer rate is slower than the network transfer rate because of various overhead factors, traffic on the network, etc. For example, a patient study typically consists of a dozen or so files representing images, regions of interest, time activity curves, etc. When a patient study transfer request is queued on the CENT O R network, several events take place that may not be obvious to the user. These include (1) the network must evaluate whether or not the patient is in-use on the source node computer (if patient is in-use, then the patient cannot be transferred and the user who requested the transfer must be

BROWN AND KRISHNAMURTHY

notified of denial of transfer until after patient is no longer in-use); (2) the patient must be removed from the source node directory indicating that the transfer has begun; (3) all the patient's files must be transferred to the central host computer; (4) the correctness of the transferred data must be assessed, then the patient files must be transferred to the destination node; (5) the correctness of these transferred data must be assessed and the destination node directory must be updated to show the new patient; and (6) C E N T O R also keeps a log of all transfer requests that the user can view during or after the transfer. On our system we use a three-view gated heart study as the typical nuclear medicine study for a benchmark of patient transfer rates. Our gated heart studies, as sent to physician viewing and archive, comprise 15 files consisting of three image studies (each 64 Kbytes from 16 frames, 64 x 64 • 8), four graphics files (ventricular edges and ejection fraction curves), two textual report files (demographic data and ventricle volume data), and six small files for various header information. The total patient study thus consists of 258 Kbytes of data, and the time needed to complete the transfer of the patient from the source node to the central host computer is 28 seconds for an operational transfer rate of 74 Kbits per second. This observed patient transfer rate is slower by about a factor of 10 from the 10-megabits-per-second Ethernet transfer rate, in accordance with previous reports. 4 A total patient transfer (node-to-central host-tonode) requires another 28 seconds, for a total time of 56 seconds to transfer a typical patient study. This same transfer time of 56 seconds for our typical patient study is observed even when, during the transfer, both the source and destination nodes are simultaneously acquiring a dynamic study (30 seconds per frame) and displaying another patient's gated heart image study as a real-time display. Transfer rates (expressed as bits per second) would be faster for a patient study consisting of fewer larger files, and transfer rates would be slower for a patient study consisting of a larger number of smaller files.

Study Retrieval Retrieval of a typical gated heart patient study from the short-term archive to a viewing node (as would be the case to recover an archived patient

PICTURE ARCHIVING COMMUNICATION SYSTEM

study acquired within the past 21 days) requires only 28 seconds because it is only a central host-to-node transfer. Retrieval of this typical gated heart patient from the long-term archive requires 2.2 minutes if the patient is located on the currently inserted optical disc cartridge. If the patient is located on a different optical cartridge, then a few extra minutes are required to first insert the proper cartridge. We are currently generating archived data at the rate of 100 megabytes per month with a workload of about 200 patients per month. Therefore, we will fill an optical disc cartridge side (there are two sides, each 1 gigabytes) every 10 months, requiring insertion of a new cartridge or side to recover any old patient study thereafter. Multiple platter (jukebox) optical disc drives are available at considerable cost to solve this archive problem of changing disc cartridges. Difficulties with the archiving hardware remains a nemesis of PACS. s,6

Security Data security is an important issue for PACS. The PACS software and database are protected on the central host VMS operating system via login passwords that control data access. The correctness of patient image data transferred on the Ethernet network is assessed by the Ethernet hardware controllers for intactness of the data packets, leading to a retry of transmission if a damaged packet is received. The Ethernet file transfer software compares numbers of transmitted blocks and reports any errors. When a study is first moved, it is traveling from a nuclear medicine source node to the central host, and the original study on the source node is not deleted until after the study is verified as having transferred successfully to the central host. Once safely on the central host, a patient study can proceed to its destination node. As a safety feature to guard against data destruction during transfer from central host to destination node, a copy of the study is maintained automatically in a safety partition on the central host with a 2-day residency. These safety features are transparent to the user, resulting simply in a successful transfer. The C E N T O R message log immediately reports all successful transfers or any problems to the user. We have found the system to be very reliable; only five patient studies (out of

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about 3,600 patients to date) have disappeared into the PACS, never to reappear. These problems occurred over a year ago and we have experienced complete reliability of the network transfer system in the more recent past using software that has been well-debugged. The PACS network hardware and software has been found to be considerably more reliable than our typical experience with nuclear medicine acquisition or display nodes. The C E N T O R - P A C S network will not function in the event of a failure of the VAX central host computer because all PACS transfers involve the central host computer. In this case a backup network known as P A C N E T (ADAC Laboratories, Milpitas, CA) operates on all the RT-11 nuclear medicine nodes to allow transfer of images from node-to-node, although archiving or Viewpoint is not available. This meets our design goal of a backup network in the event of central host failure. PACS IMAGE VIEWING AND INTERPRETATION

A brief discussion of the physician viewing station (Viewpoint) seems in order because the ultimate purpose in the PACS is to interpret patient images on a digital display screen, leading to a filmless nuclear medicine department. There are, we feel, three determinants of the usefulness of a PACS: network speed, ie, time required to locate and move a patient; software speed and quality on the PACS image display; and image monitor quality on the PACS image display. To be useful, the PACS viewing screen must compete favorably with the speed and reliability found in hard copy on film. Our PACS display already contains the patient data (the technologist sent it), and it requires about 2 minutes of physician time at the PACS viewing node to select a patient and display it on the screen. This may sound fast to some readers and slow to others, but consider a department such as ours with up to 15 studies to be read by a staff physician while teaching three residents and you find an equivalent of 2 physician-man hours wasted each day waiting for the computer display to appear on the screen. Our system is feasible and technically operable; it is still slower -than desired at displaying the final product. The bottleneck of speed in our system is the Ethernet transfer rate from the central host 474-megabyte

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disc to the Viewpoint display (Fig 2). Considerably faster display on the Viewpoint could be achieved by displaying directly from a local high-speed disc attached to the Viewpoint. This is a future goal of our PACS. Larger PACS systems, as proposed for use in digital radiology, are currently capable of filling an eight-screen monitor in 3 seconds 7,s so the technology for high-speed display is available.

Viewpoint Our PACS-Viewpoin~ display screen is a 1024 • 1024 x 8 display (19-inch diagonal) based on an IBM personal computer (Table 1). Three of the PACS displays are located in our reading room (Fig 7) and in two staff.physicians' office. On them we can display, for example, an entire tomographic thallium study consisting of exercise-rest short-, horizontal-, and vertical-axis slices with a quantitative bulls-eye display (Figs 8 and 9), each 512 x 512 x 8. Figures 10 and 11 show our display format for gated cardiac studies. Figure 12 shows a mixed patient format for both a cardiac and kidney study in different colors. Figures 13 and 14 show bone scans at two different contrast windows. The software is all mouse-driven for user friendliness, offering multiple color tables, contrast enhancement, rapid cine display, instantaneous zoom in and out, or a digital magnifying glass. We have found the PACS display to be preferable to hard copy film in the case of most dynamic studies, such as

BROWN AND KRISHNAMURTHY

gated heart, hepatobiliary, renal, and most flow studies. For example, in the case of a multiple gated acquisition (MUGA) study, we can play the three-view cine and observe the ejection fraction curve to judge ventricular wall motion. The PACS display also is used heavily in interpreting tomographic studies where all the images from multiple planes can be gathered together on the screen. Static images also are available on the PACS display. We are currently working on adding whole-body bone scan capabilities to our system using a 512 x 5t2 • 16 matrix of simultaneous anterior and posterior views from a dual-headed gamma camera. This, we hope, will allow us to decrease the number of spot views taken after the whole-body scan by virtue of using the PACS display to contrast enhance or magnify particular areas of the whole-body scan. We have not as yet evaluated the suitability of an 8-bit display for interpretation of 16-bit bone data. The PACS display automatically converts 16-bit images to an 8-bit depth for display. The learning process for computer image display is a personal matter, varying from physician to physician according to preference regarding film versus computer display. The computer does not, in our experience, speed up the process of image interpretation. The ability to change the contrast to the desired level prompts the physicians to try many contrast levels and. color changes. All of this increases the time to interpret the image, hopefully towarda more accurate image interpre-

Fig 7. The PACS display (Viewpoint) screen in the physician reading room, showing a thallium 201 emissions computed tomography (ECT) study bulls-eye quantitative display with short-, horizontal-, and vertical-axis slices at exercise and rest. Not visible to the right is another workstation offering standard nuclear medicine analysis functions and manipulation of the patient database with MARS-RIS for viewing and electronic signature of patient reports.

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Fig 8. Close-up of the thallium 201 analysis display from the screen in Fig 7. The upper left is the bulls-eye quantitative data, proceeding to stress-redistribution slices for short-axis, horizontal long-axis, and vertical long-axis. Further display choices are mouse-selectable from the menu at the right.

tation. Image interpretation often requires more time on the computer, but the ability to digitally enhance the image leads to fewer spot films, fewer retakes, etc. For example, the number of second injections for a venogram can be reduced when the faintly visualized vein can be made prominent by contrast enhancement. Use of the computer display should enhance diagnostic accuracy, but computer use requires a commitment of time and effort from staff members to learn new techniques. We still take some film hard copies on all patients. Totally abandoning hard copy film at this time has not been feasible, and we consider some film necessary until we confirm the sensitivity and specificity of electronic image interpretation. There is also an issue of the availability of display terminals at all user sites, including remote sites. In an ideal PACS world the slowness of long-term archive retrieval is not a problem

because previous image studies are prefetched from the optical discs by a clerk who monitors each patient scheduled for a test that day. 93~ This clerk evaluates whether or not the patient has had any previous examinations on the PACS and if so, copies the previous studies to the physician viewing node. At the completion of the current study, the physician then has available on the screen both current and past studies. Evaluation of staffing necessary for a PACS is an important but often overlooked consideration in PACS design. 93~ PACS Role in Education

Another feature of our system that is helpful for educational purposes is the display-analysis node in our conference room where the patient images on the computer can be projected with a ceiling-mounted color video projector to a 72inch format on a screen at the front of the

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Fig 9. A few mouse clicks produce this blowup of t h e upper right quadrant from Fig 8, showing the exercise-redistribution short-axis slices proceeding from cardiac apex to base. The digital magnifying glass has been placed over the redistribution image in the lower left corner, This is a different color table than in Fig 8.

conference room (Fig 15). We have clinical case presentation conferences three times a week in this room for which the resident has prefetched the patient images to the conference room node. The resident then presents the patient data via the large format video display, allowing all participants in the room to easily participate in evaluation of the patient data. Images from sources other than our PACS (eg, x-ray films, cine angiography, video tape) also may be presented using the video projector. In one of the three weekly conferences, nuclear cardiology studies along with cardiac catheterization results are presented to cardiologists and cardiac surgeons to make therapeutic decisions based on myocardial viability as seen on the thallium 201 studies. PATIENT DATABASE/MARS

Our MARS patient database system (Table l) is a standard RIS that we modified slightly to allow for entry of data particular to nuclear

medicine (eg, radiopharmaceutical, dose, etc). The RIS runs off a separate CPU, unfortunately not connected to our CENTOR-PACS. Use of the MARS begins at installation time with definition of MARS dictionaries that define users of the system, image procedure names, image procedure duration data, types of studies that can be performed in each gamma camera room, etc. Users of the MARS system are assigned a security password and a job title (eg, transcriber, technologist, resident, staff physician) that controls which software menus will be offered to which user. We have chosen to assign procedure names and duration according to Current Procedure Terminology (CPT) codes that are a standard nomenclature for defining nuclear medicine procedures. 11 Gamma camera rooms can be tied to various working hours and types of procedures. Adequate design and definition of these MARS dictionaries is crucial to the success of the RIS, suggesting that a team of physician, technologist,

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Fig 10. The PACS display format for a gated cardiac study, showing the 16-frame study in the anterior, left anterior oblique, and left lateral view. The right lower quadrant shows quantitative results including the ejection fraction and cardiac edges at end-diastole and end-systole in the three views. A click of the mouse will put this study into cine mode with further instantaneous mouse control over zoom, color table, and brightness window.

secretary, and computer manager should be involved in system dictionary design. The RIS vendor needs to provide on-site and off-site training in the design and use of the system.

Interface to Hospital Information System Patient demographics are acquired by a scheduling secretary or technologist, using any of our 15 RIS workstations (a software window at the nuclear medicine nodes). O u r RIS is interfaced to the Veterans Administration Medical Center HIS central computer system and the central computer transmits patient demographics (name, social security number, ward, etc) to our RIS as soon as the patient is admitted or scheduled for any test. We use a written physician consult order form to request an imaging procedure, and the nuclear medicine scheduling person then enters a few characters of identification into the RIS and chooses the patient from the list sup-

plied by the HIS central computer. Outpatients, whose first stop in the medical center may be in nuclear medicine, may need to be entered entirely from our RIS and then these demographics are transmitted to the HIS central computer. The scheduling person selects the desired image procedure, which we have categorized by organ system and CPT 11 code, from a menu list. The RIS, or the scheduling person, will then select a room and time for the study. The test scheduling is then completed and transmitted to the HIS computer where it is readily accessible on any workstation throughout the medical center. Various other items also are automatically generated on a printer, including patient film jacket labels, transportation requests, and an appointment letter. Room schedules can be viewed in graphic form by room and date on any of the RIS workstations. When the patient arrives in the nuclear medicine department, the technologist uses the RIS to note the start and end of the test,

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Fig 11. Another gated cardiac study showing the power of t h e 1024 • 1024 • screen to hold several studies. This is a 1 6 - f r a m e gated cardiac study, w i t h each 1/18of t h e screen r e p r e s e n t i n g 1/18of the cardiac cycle for t h r e e v i e w s at rest (the three larger images w i t h i n each 1/18), as w e l l as for three different exercise levels in t h e left a n t e r i o r oblique v i e w . The display is really most effective when the mouse is clicked for cine display w i t h a few more clicks to zoom t h e images so t h a t w h a t is n o w 1/16of the screen w i l l fill the screen in cine mode.

confirm that the imaging test was completed, and enter extra views, etc. The technologist also confirms the radiopharmaceutical and dose administered.

Diagnostic Reporting The resident-staff physicians use the CENT O R / P A C S or film to interpret the images and dictate a patient diagnostic report on an audio tape for transcription by a secretary. A few physicians with faster typing skills can dictate directly on the MARS terminal and bypass the need for secretarial assistance for generation of reports. The secretary uses the RIS word processor to type this report into the RIS for the image procedure just completed. The physicians then use their RIS workstations to edit the patient report as necessary and provide an electronic signature for a completed report. The physician

concurrently has the ability to look at the patient image data on the nuclear medicine or Viewpoint node in his or her office. The diagnostic report is printed (Fig 16), placed in the patient chart, and the report is sent to the HIS central computer where it is readily accessible to hospital personnel with sufficient security clearance. The RIS uses the concept of mnemonic reports, or predefined dictation protocols, which provide simplified and standardized transcribed entry formats. A standard mnemonic report can be defined for any desired test, eg, a report form for a normal total body bone scan, or a report form such as shown in Fig 16 with a predefined data table for quantitative results.

Workload and Billing The RIS also is used to generate our workload and billing data as required by various groups

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Fig 12. A technetium 99m-DTPA kidney study at the top that is from a different patient than the cardiac study at the bottom (as in Fig 11 ), shown in two different color tables. Multiple patients can be loaded to the screen in a format similar to loading a lightbox for film viewing. Again, the mouse can be used for instantaneous cine, zoom, color table, or contrast adjustment.

that need monthly, quarterly, and/or yearly productivity reports. 11 Productivity or workload reports may be created for almost any combination, eg, workload by CPT code or type of study, by patient ward, by gamma camera room, etc. We have found that these types of data assume an ever increasing importance in our medical center setting. The RIS also is capable of billing functions that are not generally applicable in the VA Medical Center environment. The RIS provides a mechanism for case retrieval and teaching case database. For example, using case retrieval, it is possible to obtain a list of all patients who had a certain type of test, or all patients from a particular referring physician, etc. It is possible to search the database on almost any of the parameters associated with a patient's study, or to search for a certain text string in the body or impression of the diagnostic report.

Patients may be flagged for entry in teaching case files, facilitating resident education. The MARS-RIS has automated many of the normal scheduling and reporting functions in our nuclear medicine service. It has markedly improved access by ward physicians to the patient diagnostic report files. The nuclear medicine report is available on the ward the moment the nuclear medicine physician electronically signs the report. Therefore, the ward physician does not have to wait 12 to 24 hours for the report to arrive via internal mail. This cuts down on the enormous number of housestaff telephone calls requesting results of tests. The secretary simply informs the telephone caller that the report is available on the ward through the HIS terminal. The RIS offers a high degree of reliability through a mirrored disc operation, daily journaling to tape, and monthly backup of the entire

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Fig 13. A display of multiple bone spots with the digital magnifying glass shown over the right knee. The mouse can be used to position the magnifying glass or to instantaneously zoom any single frame to fill the screen. The zoomed images can be panned across the screen, Here the window is from 0% to 100%, (0 to 255 counts).

system. After about 15 months, a patient diagnostic report on the RIS is trimmed to contain just a few lines of impression and archived to magnetic tape. FUTURE CONCERNS

A feature of PACS that has proven very useful is a modem link to the vendor for on-line debugging of software or hardware problems. The P A C S - C E N T O R modem support is maintained on workdays 8 AM to 6 PM and the M A R S - R I S modem support is available at all times. Once one begins reliance on a computerized image processing and patient reporting system, any interruption of the computer brings the entire department to its knees, requiring immediate action from the site manager and the vendor. The modem provides a rapid link for testing and communication through a computer mail system.

Both the PACS and the RIS provide a detailed network of error logging and messages to the users and site manager concerning system operation. There are many possible reasons for a failure to complete a queued patient study transfer, including the patient study in use on the source node, destination node is powered off, two users queued the same study to go two different places, etc. In a teaching-research environment, we constantly have many new users, often with little computer expertise, who often send patient studies to other than their correct destination. The PACS must provide a readily available log of all activities, and it should recover spontaneously from problems once the offending node is corrected, eg, a transfer should remain queued if a destination node is powered off and the transfer should complete by itself once the problem with the destination node is corrected. Archiving, which takes place after-hours, also generates a

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Fig 14. Same as Fig 13, but n o w the mouse was used to adjust contrast instantly for a rib w i n d o w , 0% to 20%. The ability to quickly change contrast or color table is v e r y helpful in bone scans.

log and mails messages to the site manager for perusal the next day. Hopefully, the mail is a series of positive messages stating "archive operated properly," "all transfer requests honored promptly," etc. When problems occur the message changes, eg, "disk full on destination device in g a m m a camera room A for transfer of patient

Fig 15. The nuclear medicine conference room showing a 25-inch color video monitor in the upper left w i t h t h e 72-inch color video projector display at center. This display is used for clinical case presentations at our conferences and classes. Besides nuclear medicine PACS images, w e can also display cable television, cine angiography films, x-ray (radiographic, ultrasound, CT, MRI) films, or videotapes via this equipment.

Jones, John." The PACS manager can then take appropriate steps to correct the problem and/or train personnel in how to avoid future problems. Problems Related to Nonstandardization Our system is similar to others devised for use in nuclear medicine 12 and simpler than a PACS

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MEDICINE MEDICAL PORTLAND.

NUCLEAR VA

SERVICE CENTER OR

NAME: . . . . . SSN#: AGE/SEX: 6_1_1L~ . . . . . . . WARD:OPT AGENT I : 99M~TC__RBC _(IN VIVO)DOSE: 2 6 . 0 M C I INSTRUMENT: BASI_CAM VIEWS: LLAT,LAO STUDY CODE: H ~ . ~ . ~ ANT

TEST DATE: 17-Au9-89 REF. MD: LEIKAM~BECKY ROUTE: I_V TIME TO IMMED. IMAGE:

STUDY : REST I NG MUGA HISTORY: 60 year old male, S/P heart t r a n s p l a n t Feb'89 f o r ischemic cardiomyopathy. VENTRICULAR FUNCTION ICARDIACINDEX WORK PULSE ITOTALI % ILV IEDVI IESVI I SVI LOAD / M I N IBEATSIACCEPTIEF% IML/SM IML/SM ~ML/SM I(L/MIN/SM) REST

88

I 962 I

100 I 50% I

48

I

23

25

I

.

.

.

.

.

.

2.2

t

NORMAL~60-10016-12KI95-100149-65150-90 110-40 I ' I I I I I . . . . I

:

32-s8

I 2.S:4.5 1

FINDINGS: There appears to be mild hypokinesis of the posterobasal myocardium, which is not observed on the l a s t MUGA study of 28Mar'89. The e j e c t i o n f r a c t i o n of 50% has decreased from the value of 59% measured 5 months ago. L e f t v e n t r i c u l a r volume indices are e s s e n t i a l l y unchanged, and his cardiac index remains 2.2L/min/msq. Septal f i x a t i o n with s y s t o l i c thickening is noted, a commonly observed phenomenon post-pericardiotomy. IMPRESSION

:

1. MILD POSTEROBASAL HYPOKINESIS, NOT PREVIOUSLY OBSERVED. 2. DETERIORATING EJECTION FRACTION OVER PAST 5 MONTHS.

RICHARD M. BROWN,MD Resident Signature

MING-JEN CHIANG, MD Date Staff Signature

Date

Fig 16. A typical patient diagnostic report produced by the MARS-RIS. The information on the top lines is entered into the MARS by the technologist at the time the test is performed. The information starting with the w o r d " h i s t o r y " is typed into the MARS by a transcriptionist (or physician) from a dictated physician report. The transcriptionist can choose predefined report protocols, such as the data table shown here, and then fill in the numeric values. The typed report is reviewed and edited by the physician at the MARS workstation in the physician's office. Then the physician provides an electronic signature that initiates transmittal of the report to the medical center's central computer and then to all the terminals on the wards.

that would suffice in a radiology environment of digital radiography.4'8'13 Users interested in designing their own system might enjoy reading the top-down simulation articles that summarize the needs of a PACS network. 9'I~We feel that most of our design goals have been met as our system matured over the past 18 months. Remaining goals include merging the image PACS with the RIS data. We feel that the PACS image display also should offer display and editing of the diagnostic report. Images should be viewed concurrently, on the same system, with the diagnostic report. Our current system requires that we choose the patient for review on two different systems: the PACS and the RIS. We recently completed several site visits to evaluate the de-

sign for a larger PACS for use as medical centerwide image network, and we found little progress from the PACS vendors in terms of integrating RIS functions into the PACS. Another formidable problem with attempting to link all areas of the hospital (eg, nuclear medicine, radiology, computed tomography (CT), ultrasound, magnetic resonance imaging (MRI), digital angiography) into one medical center-wide PACS is the lack of standardized American College of Radiology-National Electrical Manufacturers Association (ACR-NEMA) digital communication between vendors. 14 Our CENTOR-PACS has side-stepped this issue by providing a separate computer node to interface to each gamma camera's XYZ analog output.

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PACS Capacity Another problem for us is the limited capacity of our single-platter optical disc archive. No matter how many patients can be stored on a single optical disc cartridge, the cartridge will eventually fill, and it must then be replaced, meaning that any past patient from that time onward is no longer available for retrieval without a cumbersome, personnel-intensive change of laser disc cartridge. Our concurrent short-term archive has solved the problem to some extent, providing ready access to any patient study less than 21 days old. Of course, the number of days of patient data that can be stored on short-term archive will be dictated by the volume of patient studies done at any particular hospital. A largecapacity, high-speed, multicartridge optical disc archive is obviously one high-priced solution, and many vendors are working on optical tape archives for future use. 5'6'8 Regardless of which storage media is used, it is desirable to have as many patient studies as possible stored on any particular storage medium. This speaks for the need for image data compression, 4'a5'16 which our system does not yet offer. Compression can be done error-free via run length encoding or Huffman entropy encoding with about a threefold increase in the number of patients stored in the archive. Irreversible compression destroys the raw data and is available with much higher compression ratios (up to 30:1) using software and hardware that are still under development. 4'15'16 Some authors have suggested that PACS can be phased in, starting with the transfer of image studies from the site of origin to a physician viewing area, without any archiving being required/7 We believe that archiving is fundamental to a successful PACS, with a sideby-side comparison of old and new image studies, and this will necessitate development of data compression techniques for image archives.

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editorial level in major journals, where PACS was referred to as "Danger Ahead" in one editorial, 19with a following editorial that labeled PACS as "Opportunity Ahead. ''2~ We have successfully implemented a nuclear medicine PACS and found it to be an extremely useful addition that has improved our clinical efficacy in a modern medical center. The secret of PACS's success lies in the willingness to change the mode of operation. Our success in PACS implementation at the VA Medical Center is primarily due to a readiness to change from old established methods to newly conceived, but untested methods of operation. This called for the cooperation of the entire staff, including secretaries, technologists, physicists, radiopharmacists, residents, and staff physicians. In the beginning, it was very stressful, and the nuclear medicine staff morale was found to be at the lowest level in the medical center. The stress was imposed by the demands of learning many new skills and operations simultaneously, including the operation of all new gamma cameras, computers, software, etc. However, the staff's determination to succeed prevailed over these adversities, and everyone contributed solutions to the many new challenges presented by PACS. There was no thought given to a return to the old system, which might have temporarily alleviated the stress but, in the long run, would not have led to progress. The future, we believe, lies with larger PACS to tie together all imaging modalities. The nuclear medicine single-photon emission computed tomography image of the brain should be interpreted concurrently with the magnetic resonance imaging (MRI) or computed tomography (CT) brain study, all on the same viewing workstation. We hope that this brief description of our PACS will aid the reader in deciding which way to go in a PACS, hopefully to avoid the conundrum between Alice (who did not know which way to go) and the Cheshire cat (who said you could go wherever you like if you do not have a goal in mind).

The Secret for PACS Success The PACS literature offers much in the way of philosophical meanderings concerning predictions about the future of PACS, which has been referred to as the "Cheshire cat" of medical imaging, 18from Lewis Carroll's Alice in Wonderland. One can see the grin, but the rest of the cat may be hard to see. Controversy exists at the

Consumer Satisfaction The final verdict on the success of PACS lies in consumer (referring physicians) satisfaction. At this moment, most of the nuclear cardiology studies are displayed in a user-friendly format. The cardiologist may walk into nuclear medicine, call for a patient study, and view the three-axis

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image sequences at stress a n d rest with polar plot images displayed on the screen. T h e physician can m a g n i f y the i m a g e a n d adjust the contrast and color, all by the push of a button. This has been a useful tool to teach the housestaff. The cardiology staff a n d the housestaff find the P A C S helpful and practical. O u r consulting physicians

would like to see similar changes to digital i m a g i n g in other modalities, including diagnostic x-rays, ultrasound, CT, M R I , a n d cardiac catheterization studies. This wish for future expansion is prompted primarily by our successful operation of P A C S in n u c l e a r medicine. W e hope to expand P A C S to meet further clinical demands.

REFERENCES

1. Graham MM, Links JM, LewellenTK, et al: Considerations in the purchase of a nuclear medicine computer system. J Nucl Med 29:717-724, 1988 2. Metcalfe RM, Boggs DR: Ethernet: Distributed packet switching for local computer networks. Commun Assoc Comput Machine 19:395-404, 1976 3. Rorabaugh B: Data Communications and Local Area Networking Handbook. Blue Ridge Summit, PA, Tab Books, 1985, pp 163-172 4. Huang HK, Mankovich N J, Taira RK, et al: Picture archivingand communicationsystemsfor radiologicalimages: State of the art. CRC Crit Rev Diagn Imaging 28:383-427, 1988 5. Stockburger WT: An evaluation of the financial impacts of optical disk storage for digital radiography. Radiol Man 9(4):35-39, 1987 6. Taaffe J: Digital image archive: Using statisticalcaching techniques. Appl Radiol 17(i):39-43, 1988 7. Cox GG, Templeton AW, Dwyer SJ: Digital image management: Networking, display, and archiving. Med Instrum 20:206-219, 1986 8. Templeton AW, Cox GG, Dwyer SJ: Digital image management network: Current status. Radiology 169:193199, 1988 9. Didden HW, deValk JPJ, Bakker AR: Top-downdesign of a picture archiving and communications system (PACS) by means of simulation. Comput Methods Programs Biomed 26:85-96, 1988

10. Stut WJJ, deValk JPJ, Didden HW, et al: First experiences with the modelingand simulation package MIRACLES applied to a picture archiving and communication system (PACS) in a clinical environment. Comput Methods Programs Biomed 28:63-70, 1989 11. Allen M, Preston DF, RobinsonRG, et al: Standardizing productivity measurements for nuclear medicine. J Nucl Med Tech 17:145-148, 1989 12. Siegal ME, Lee KH: DACS for nuclear medicine. Admin Radiol 7(6):50-54, 1988 13. Mun SK, Benson HR, Florii S, et al: The comprehensive image network at Georgetown. Admin Radiol 8(5): 37-39, 1989 14. Maquire GQ, Nog ME: PACS compatibility in search of a universal language for digital image exchange. Admin Radiol 8(7):46-51, 1989 15. Cannavo, MJ: Compressed data transmit faster without degrading image quality. Diagn Imaging i0(8):85-89, 184, 1988 16. Bramble JM, Huang HK, Murphy MD: Image data compression. Invest Radiol 23:707-712, 1988 17. Cannavo MJ: Low risk strategy for PACS calls for modular phase-in. Diagn Imaging 10(7):135-145, 1988 18. Vanden Brink J: The Cheshire cat of medical imaging. Admin Radiol 8(5):32-35, 1989 19. Fischer HW: Danger ahead? Radiology 169:267, 1988 20. Arenson RL: Opportunity ahead. Radiology 169:267268, 1988