Present status and performance of PACS at Kyoto University Hospital

Computer Methods and Programs in Biomedicine, 36 (1991) 77-84 © 1991 Elsevier Science Publishers B,V. All rights reserved 0169-2607/91/$03.50

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COMMET 01217

Present status and performance of PACS at Kyoto University Hospital M a s a r u K o m o r i 1, Y o s h i h i s a N a k a n o 1, K o t a r o M i n a t o 1, I s h u K i m u r a 1, K a o r u O k a j i m a 1, T a k a s h i T a k a h a s h i 1, M i t u y u k i A b e 1, Junji K o n i s h i 1 a n d K a z u h i r o S a t o h 2 l Kyoto University Hospital, Sakyo, Kyoto, Japan and 2 Hitachi Medical Corporation, Kashiwa, Chiba, Japan

A pilot PACS project, named KIDS, has been running in Kyoto University Hospital. The purpose of the system is to establish a small PACS that includes all digital imaging modalities and to evaluate it. The project has been continued from the first phase (KIDS-l) to the second phase (KIDS-2). In the first phase, a small-scale PACS was developed. In the second phase, the expansion of coverage of modalities and completion of the image database was intended. At present, the database contains image data of 16264 patients amounting to 150 Gbytes. Simulation of the retrieval process to the database shows that 154.3 s per patient is required for retrieving his/her entire image data. This calculated value is close to the actual time. PACS; Image database; Retrieval simulation

1. Introduction The PACS project described here started in spring 1985. The project in cooperation with Hitachi Medical Corporation was authorized by the Ministry of Education. The system is named KIDS ( K y o t o University Hospital I m a g e Database System). The project was set up to study the feasibility of integrating all digital imaging modalities currently in use at the hospital. It serves as a pilot before constructing a hospital-wide PAC system. KIDS has been running for these years and has yielded some experience. In this paper, we describe the present status and statistics of KIDS.

Correspondence." M. Komori, KyotoUniversity Hospital, Sakyo,

Kyoto 606, Japan.

2. Background The first goal was to link a whole-body X-ray scanner (GE C T / T 8800) and an M R scanner (GE S I G N A ) to a digital network and to provide a central archiving system. Fig. 1 shows the system diagram of the first generation of KIDS (KIDS-l) [1]. Network based on 10 M b i t / s Token Ring optical fiber was used to link both nodes of modality and the image workstation through network interface units (NIU's). A standard interface IEEE-488 was adopted to connect each modality to the NIU. An IEEE-488 interface board was added on the mini-computer of the existing X-ray CT and MRI units, and a custom-made software was installed. For the central archive, a jukebox-style optical disk system called Optical Disk Library (ODL) was used. The O D L has thirty-two 12-inch optical

78 10 Mbps OpticalFiberTokenRing Workstation (3 CRT) Optical Disk [ Library 83 Gbytcs Fig. 1. The schematic diagram of KIDS-1 (1986-1988).

disks, each with a capacity of 2.6 Gbytes, and two disk drives. The earlier image workstation had three 20inch CRT monitors each with a resolution of 1024 x 1024 pixels. The workstation was equipped with a magnetic tape drive to acquire archived images. A laser film printer (2048 x 2048 pixels, 8 bits/pixel) was also connected to the workstation. Users of the workstation were radiologists. After trying to make primary diagnoses on the workstation, their impressions of the system were: (1) the image quality is good enough; (2) the response is slow for image handling; (3) the number of images simultaneously shown is insufficient; (4) the brightness of images is insufficient; (5) the operation is not easy enough. Therefore, they preferred the conventional film/ screen system. Although the system worked in a limited clinical environment, those problems showed the impropriety of the design of the system.

3. Design consideration After working with KIDS-I for 3 years, we concluded that the most important shortcoming of the system in getting the approval of radiologists was simply insufficient coverage of modalities. That is, all clinically required images should be available for display on the screens of a PACS workstation. The second generation of KIDS (KIDS-2) was designed to expand its coverage (Fig. 2). The new system has been in use since mid-summer 1988 [21.

Comparing with KIDS-l, the network system was replaced with a more powerful one, so that more modalities than before could be connected without slowing down the communication speed of the entire system. A 100 Mbps optical fiber is adopted as a backbone in the network. This backbone links two concentrator/exchangers called Local Control Stations (LCSs). Inside the high speed line, eight 10 Mbps communication links and 121 low-speed links are multiplexed. The network works like a distributed Private Branch Exchange (PBX). Neither baseline nor ring topology was adopted here, because this PBX-like topology largely prevents collisions that arise when the network nodes rushed to establish their links. HDLC protocol for the data link layer is adopted in the 10 Mbps line at each node. A second Optical Disk Library was added in order to keep all CT images online. Images are acquired online from the imaging modalities, magnetic tapes and the film scanner. Every acquired image is stored in the image database on the ODL. The image database is managed by a minicomputer (micro VAXII) using a relational database management system. The workstations are not yet located in any clinical department outside the radiology department. Instead of a workstation, a second film printer is used to distribute a hardcopy to those clinical departments which have requested the CT examination. There are three workstations, which have an almost identical architecture except for the number of CRT screens. The first one has six CRT screens to display more images simultaneously. The workstation is dedicated for reading CT ira-

79

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O p t i c a l Disk Library (83Gbytes*2)

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OFC:Optical F i b e r C a b l e ; G P I B : I E E E - 4 8 8 i n t e r f a c e ;

WS:Workstation

Fig. 2. The schematic diagram of KIDS-2 (1988).

80 ages and it is located adjacent to the CT rooms. The digital images from the two CT scanners are sent directly to this workstation. One sends automatically just after a scan is completed. The other one transfers stored data after several examinations have been done. The second workstation is located in the 'database room' where the O D L s are installed. The second workstation has three C R T screens and is directly connected with a DSA unit. The third one also has three C R T screens and is located in the lecture room. For educational use, an image displayed on its screen can be transferred to a video projector and video monitors located as shown in Fig. 3. Each workstation has an image memory plane of 2 Mbytes to display an image in 1024 by 1024 pixels. Each pixel has 12-bit image data and is displayed in 8-bit depth. Basic functions such as lookup table manipulation, zooming and so on, required for reading radiological images, are implemented. Fig. 4 shows a typical display. Icons are displayed on the top and bottom on the monitor. A user can select any manipulation by clicking these icons with a mouse button. In order

tO accelerate image data handling, a bank of 64 Mbyte R A M is used for temporary storage between the image memory and disk storage. Only a single task could be run in the workstation of KIDS-1. The software has been improved to run two tasks in some limited combination such as communication and a hardcopy printout. Data acquisition from one CT scanner and one M R scanner is continuously operated. Data from other modalities are transferred on demand. Whenever an image of analog films from the conventional f i l m / s c r e e n units and films of CT image from other hospitals are required, the film scanner is used. Image data which have been archived on magtape before the system started are converted to optical disk format using a magtape station and stored in the image database. On the DSA, the data are so numerous that the manipulation of them on the workstation and transfer to the O D L requires a lot of time. Therefore, improvement of its speed is required. On the other hand, radiologists and technicians are trying to pick up the key images from the acquired images to reduce the number of frames

Fig. 3. The workstation with video projector in the lecture room.

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to be stored. However, the trial has not been successful yet because of the slowness of the workstation. Because only one CR has been installed in the hospital, most of the radiological procedures are done by the conventional film/screen system. Radiologists and physicians tend to prefer the conventional system except for special purposes such as breast cancer diagnosis.

4. Performance of KIDS -2

The Optical Disk Library (ODL) used for the image database module has thirty-two 2.6 Gbyte

disks and two drives to hold image data of 83.2 Gbytes. As described above, this image database is managed by a relational database system (RDB) in micro VAXII. Keys of the RDB are patient IDs, dates of examinations, type of modalities and volume name of disks. Although any combination of these keys can be used for database retrieval, only a query by the patient's ID is usually utilized. The ODL stores not only image data transferred from modalities since 1987, but also image data archived on magtape such as whole-body CT, Head CT, MR and CR images. The statistics of data stored till February 1990 are listed in Table l.

Fig. 4. Typical workstation display.

82 TABLE 1 Statistics of stored image data in the database

N u m b e r of patients N u m b e r of examinations N u m b e r of images A m o u n t of data (GB) N u m b e r of images per patient A m o u n t of data per patient (MB) N u m b e r of images per exam. A m o u n t of data per exam (MB) Stored i m a g e s / a c t u a l images

Body CT

Head CT

MR

CR

DSA

7 303 17787 260 754 53.4 36 7.3 15 3.0 98%

5 064 11 189 123 045 25.2 24 5.0 11 2.3 25%

6660 8764 491360 64.4 74 9.7 56 7.3 100%

169 191 576 3.2 3 19 3 5.6 < 1%

16 17 2050 2.9 181 91 171 86 41%

For an example of the annual statistics, the number of whole-body and head CT and MR examinations in 1989 were 5394 and 2170, respectively. And the corresponding annual amounts of data were 8.9 Gbytes and 8.8 Gbytes, respectively. To store them, 7 optical disks were required. The extreme examples found in the database are as follows. The maximum number of examinations per patient: 78 The maximum number of images per patient: 1008 The maximum amount of data per patient (MB): 60O The maximum number of optical disks where the patient's data are stored: 24

Including all modalities in the database, the average amount of image data per patient is 9.3 Mbytes. Optical disks in the ODL are grouped by modalities, and the images of an individual examination are written on the same optical disk. The information in the RDB gives the whereabouts of images among optical disks. The average number of disks per patient is 1.6.

5. Database access simulation The retrieval time of all the images per patient can be simulated using the database. Assume a situation where a radiologist is going to read

TABLE 2 The sequence of the image database retrieval from the workstation No.

Procedures

Line used

1 2 3 4 5 6 7 8 9 10 11 12

The The The The The The The The The The The The

Lh L L L L L H c H L L H L

WS sends out the patient's ID to the R D B for a request for h i s / h e r image list a R D B returns the image list to the WS WS sends out a request for image data to R D B R D B returns the acknowledgment WS waits for image data R B D passes the transfer request and its address to the O D L O D L establishes a link with the WS O D L sends out image data to the WS O D L returns the completion message of transfer to the R D B WS returns the completion message of reception to the R D B O D L cuts the link with the WS R D B sends out the completion message of communication to the WS

a The image list m e a n s a set of attributes on a series of examinations of the patient; b L m e a n s the low-speed RS-232C line; c H m e a n s the high-speed (10 M b i t / s ) optical fiber cable.

83 TABLE 3 Parameters related to the retrieval process Parameter

Contents

Measured value

/rdb twr

time for retrieving a record from the RDB communication time between WS and RDB communication time between RDB and ODL time for establishment of link between ODL and WS time for mounting an off-drive disk on the drive time for opening (spinning up) a disk disk-to-disk transfer rate (from OD to WS's disk) time for cutting the link and dismount of the disk

0.6 s/retrieval 1.1 s/call 1.1 s/call 4.6 s (constant) 7.0 s/disk 6.0 s/disk 0.083 Mbyte/s 7.0 s (constant)

tro /lin

tmou todo rimg tclo

images just scanned, and therefore has to retrieve all previous image data of the patient from the image database. According with the request operation from the Workstation (WS), the system works in the sequence as shown in Table 2. The experimentally measured values shown in Table 3 are related to the retrieval process described above. When a patient has had nex studies and image data of d Mbytes are stored among noa disks, the total time for retrieval of all image tre t is

though it will largely reduce d / r i m g , the overhead time during the c o m p r e s s i o n / d e c o m p r e s s i o n process must be avoided. Therefore, a high-speed hardware for c o m p r e s s i o n / d e c o m p r e s s i o n which hopefully compresses into 1 / 3 to 1 / 1 0 within 1 s per lk by lk image for instance, is needed. In the near future, we plan to implement such a compression mechanism into the system.

tre t = (twr + tra b + tro)nex + tli n + (tmo u + toOo)rtod

For the CTs and MR, the daily operation is established and the database has been developed. However, other modalities were difficult to operate with the system. The reason for the difficulty seems to be insufficient performance of the system and the improper m a n a g e m e n t of usage of digital modalities with conventional ones. The retrieval time was simulated based on the actually archived database of images. The calculated time, 154.3 s, is close to the actual time when the system is not busy. However, for the more practical condition, a more detailed analysis is required including a queuing process of retrieval requests. The retrieval time is fast enough compared with a manually archived film library. One of the benefits is that a user can retrieve images at night without the librarian. The most important improvement of KIDS-2 over KIDS-1 is t h a t most CT and M R images can be retrieved and displayed. However, images of other modalities are at present hard to acquire automatically.

+ d/rimg + tclo(nod -- 1) = 2.8nex + 20.0nod + 12.0d - 2.4

(1)

The time tre t w a s calculated for every patient in the database by counting nex, nod and d. The average value was 154.3 s. The practical retrieval time for a patient who had two examinations is around the calculated value. However, when the system is busy, the time becomes three or more times longer. This happens, for instance, when another modality invokes an updating request during the retrieval. The average values of nex , nod and d are 2.14 examinations, 1.63 disks and 9.3 Mbytes, respectively. The result shows a considerable overhead. The analysis shows that the disk-to-disk transfer time (d/rimg) is dominant in this situation. For reduction of reading time of disk, an image compression technology is one of the natural solutions. However, we have not yet adopted it. Al-

6. Conclusion

84 On the workstation, the speed of image handling is faster due to the R A M bank. But its man-machine interface is not yet good enough to radiologists. Further improvement in speed and handling is needed for the modalities other than CT and MR. It also becomes clear that a multitasking environment is necessary for the PACS workstation. The system still has many problems when used for primary diagnosis. However, the well-developed image database is useful. Radiologists who do not use the system for the primary diagnosis

feel it helpful in consultation, research and case conferences.

References [1] M. Komori, K. Minato, Y. Nakano et al., Pilot PACS with on-line communicationbetween an image workstation and CT scanners in a clinical environment, SPIE Med. lmag. 767 (1987) 744-751. [2] K. Minato, M. Komori, Y. Nakano et al., PACS Development at KyotoUniversity Hospital, SPIE Med. Imag. 1093 (1989) 20-23.