- Email: [email protected]
analog hybrid system for filing of endoscopic images
Computer Methods and Programs in Biomedicine, 37 (1992) 291-298
291
© 1992 Elsevier Science Publishers B.V. All rights reserved 0169-2607/92/$05.00 COMMET 01283
Digital/analog hybrid system for filing of endoscopic images Masayuki A. Fujino, Masahiro Ikeda, Yasuyuki Y a m a m o t o , Atsuro Morozumi, Toshiya Nakamura, T s u t o m u Kawai and Hiroshi Suzuki First Department of Medicine, Yamanashi University School of Medicine, Tamaho, Nakakoma-gun, Yamanashi, Japan
A new system was developed for filing all the endoscopic images generated in our hospital. The system is composed of an on-line network for analog images supplied from the endoscopy stations and stored on 300 mm optical disks, on the one hand, and an off-line PACS for digital images recorded on a 130 mm magneto-optical disk (MOD) at each endoscopy station, on the other. For close examination of the images digital images are displayed from the MOD on a high-resolution computer graphic monitor, and for quick review of a large number of images, analog images are retrieved from the 300-mm optical disks. This system has been in clinical use at our university hospital for the past year and has proven useful for education of endoscopy, for the quality control of the endoscopy practice, and for the management of the patients. Filing of endoscopic image; Digital/analog hybrid system, Off-line PACS; On-line network of video processors; Full colour image
I. Introduction
An endoscopic image is in full colour, and carries a relatively large volume of information (750 kBytes: 500 × 500 × 8 bits, for each of red, green and blue components, in the field-sequential system). In oesophagogastroduodenoscopy a large number of images are recorded in Japan (40 images per case on average [1]). At our university hospital with 600 beds and with a centralized endoscopy unit having 5 endoscopy tables, 20-50 patients are endoscoped at each morning session, generating approximately 5000 endoscopic images every week. Laparoscopy is performed in the
Correspondence: Masayuki A. Fujino, First Department of Medicine, Yamanashi University School of Medicine, 1110 Shimokato, Tamaho, Nakakoma-gun, Yamanashi, 409-38 Japan. Phone: + 81-552-73-1111; Fax: + 81-552-73-6748.
operating theatre and fluoroscopy-requiring procedures such as ERCP (endoscopic retrograde cholangio-pancreatography) are done at the radiology unit. The number of endoscopic procedures performed at our hospital amounted to 5259 in 1989 [2] and is still increasing. Those images are required at the weekly conferences of the medical departments, at the preoperative conferences of the surgical departments held every morning, and they are needed also at the outpatient clinic, where they are shown to the patients for understanding of their disease. .The above description of our endoscopy practice illustrates the quantity of images to be stored and to be sent to different display stations. At the display stations, practically instant reproduction is required of all the images to be studied. In the field of radiology, following the pioneer work by Dwyer et al. [3], large-scale on-line systems for archiving digitized images and their
292
communication have been attempted, for which the term 'picture archiving and communication system' (PACS) was coined. But the cost of installing the PACS is enormous, and the capacity and speed of the local area networks (LAN) are still very limited [4] and, therefore, still insufficient for clinical use with the images of digestive endoscopy. 2. History of development of a filing system for endoscopic images The history of digestive endoscopy dates back to Bozzini, who attempted oesophagoscopy in 1795 [5]. The endoscopic images were documented first in the form of drawings by the artists.
Photography was introduced to endoscopy in the 1940s, markedly enhancing the accuracy of documentation, but this also had some innate problems: photographs were prone to injury and to image degradation such as fading of colours in the course of time. There was difficulty in the filing of films, particularly in retrieval of the desired endoscopic images; the films were often lost. The advent of electronic endoscopy in 1983 [6] made possible electronic filing of endoscopic images. The authors started the development of an endoscopic image filing system in 1987 with the cooperation of Olympus Optical Co., Japan; the Japanese Ministry of Education, Science and Culture funded this project in 1989. The system has
r ? , . ? . . . . . . - . . . . . . . . . . . . . . . . . . . . - . . . . . . . . . . . . ? ~
:i~ii: UPPER GI AND BRONCHOi!: ~i~,iiSUBSYSTEM:i~i~!iiiiiiiii!i!ii~i~iii!i:
:~: COLORECTAL:
',:??::SUBSYSTEM:', :~" SUBSYSTEM i: t... ~ . . . . . .
=t...........a
i:!ENDOSCOPICI M A G E ii FILING MAIN SYSTEM ::
DIGITALIMAGE ~ FILING DEVICE
I
IN!:o.J i
I
~.:i.s...uBsls!E.u]ii~:i::iii:ii
:~ii KNIX)SCOPIC ULTRASOUND ::!:
. : . : . : . . . . . . . . . .
VIDEO PRINTER ]
. . . . . . .
. . . . . . . . . . .
MULTI~~_ ADAPTER _
AUTOMATIC I PHOTODEVICEI
::~::LEC~URE THEATER SUI~YSTEM :~
35 mm CAMERA]
I.T C DECODERI
I
I FILM IMAGE INPUT DEVICE
ANALOGIMAGE FILINGDEVICE (CENTRAL CONTROL ROOM)
Fig. 1. Block diagram of the filing system. The system consists of endoscopy stations (1-6 in the figure) display stations (7 and 8) the main system for image filing (9), the computer system for data management (10) and the image processing system (11), the last three located in the central control room. The endoscopy stations in the operating theatre and radiology unit and display stations are off-line subsystems.
293 been used in daily clinical practice since March 1990 [2].
3. Developmental concepts The filing system was designed, based on the following concepts. 1. The images should be of the highest conceivable quality; no image degradation is allowed during communication and copying. 2. Safe and unified storage with easy access. 3. High-speed recording and display. 4. Research capability for image processing must be guaranteed. 5. Economy of cost and space. 6. The system must be flexible enough to allow introduction of future progresses in technology. The above concepts are mutually contradictory: Non-degradation of images calls for digital filing. High-speed recording and replaying suggests ana-
log filing. For easy and safe management of stored data, an on-line PACS is a natural solution, but it has still serious problems as mentioned earlier. A compromise had to be devised: the authors finally adopted the idea of a digital/analog hybrid system for filing of endoscopic images [7]. A detailed description of the system is presented here together with its clinical experience.
4. Digital/analog hybrid filing system (Fig. 1) 4.1. Handling of digital images 4.1.1. Endoscopy station The electronic endoscopes of field-sequential type (Olympus Optical Co.) are used. The endoscopic images captured by an electronic endoscope are sent through the video processor (CV200, Olympus) to the digital image filing device installed at each endoscopy station. The digital image filing device consists of an image compres-
Fig. 2. A scene of an endoscopy conference. There is an image compressor (top left of the display station), expanding the compressed images, and four MOD drive units (top right) above two CRT monitors and a personal computer. The high-resolution computer graphic monitor, at the right corner, is for display of multiple (up to 42) images, and the other (NTSC monitor) for enlarged display of an image selected from the multiple-imagedisplay.
294 sor (MD-702, Olympus), a personal computer (PC-9801RX, NEC) and a disk driving unit (RS9200EII, Ricoh) controlled by the personal computer. Rewritable, 130 ram, magneto optical disks ( M O D ) (MKR5A4, Mitsubishi Kasei) are used for digital image storage at each endoscopy station. An M O D records the images from many patients. The images generated during an endoscopic procedure are stored as a group. The data file format consists of the following: File management data, identification number of the patient, name of the patient, date of birth, sex, age, date of the procedure, comment data, number of images recorded, image data containing the sequentially recorded images tagged with their respective index number, and finally, system management data including identification number of the procedure. The M O D s with the digital images are carried, after completion of the endoscopic procedures, to the central control room for storage. The M O D ' s are carried to and replayed at the display stations (conference rooms and lecture theatre).
4.1.2. Display station A display unit is composed of the digital image filing device and C R T monitors for display; one of the monitors is a high-resolution (1280 x 1024 pixels) non-interlaced computer graphic monitor (GDM-1950, Sony), used for multi-image display of up to 42 pictures at a time, and the others are NTSC monitors (PVM-1442Q, Sony) for enlarged display of an image selected from the multiple image display. For a greater ease of image retrieval, four M O D drive units are installed, allowing up to four M O D s to be searched simultaneously. The image compressor also decompresses the compressed images. Fig. 2 shows an actual scene of endoscopy conference using a display station.
4.1.3. Image compression The algorithm for image compression is differential pulse code modulation (DPCM). Both reversible and irreversible compression modes are selectable at the time of recording. In the reversible mode the compression rate is 1/3,
Fig. 3. A view of the central control room. The equipment on the left desk is for the digital images and that on the right for the analog. A white box at the top right above the right desk is the multi-input adapter. A cable from the ceiling, seen right, supplies the analog signals from endoscopy stations. At the extreme left there is a video printer for hard copies, and an automatic photo device for transparencies.
295 whereas in the irreversible the rate is either 1 / 6 or 1/10.
The endoscopic ultrasonographs are also stored as analog images.
4.2. Flow of analog image 4.2.2. Endoscopy stations unconnected with central control room 4.2.1. Central control room The endoscopy stations are connected witk the central control room by cables. The images are sent as analog video signals to the multi-input adapter (MD-661, Olympus) in the central control room (Fig. 3). This adapter, consisting of large-capacity semiconductor memories, serves for traffic control of the images released independently from different (up to 8) endoscopes. The analog images are then forwarded to the analog image filing device (SDF-3D, Olympus), and recorded on a 300 mm optical disk (OD).
The endoscopic images generated at distant endoscopy stations not connected with the central control room, namely those in the radiology unit or operating theatre, are recorded first digitally on MOD; those MODs are carried after the procedures to the the central control room. The central control room also has a display unit with a digital image filing device, which is connected with the data management system and the analog file. Those images stored on MODs are reviewed on the central digital image display monitors and copied into the analog file as back
DIGITAL/ANALOG HYBRID FILING SYSTEM
ELECTRONIC ENDOSCOPE
VIDEO CONVERTER
_ voEo
PROCESSOR
I
H
I
FIBERSCOPE
ANALOGVOEOS'GNALIANALOG'OAGE] ~
FILING DEVICE
m / DIGITAL IMAGE FILING DEVICE
i
i
1
;I ":::~?' ^ - 'liiENDOSCOPY:i:ii!i;iii~ -'^" " -
" ................................
DIGITAL IMAGE FILING DEVICE
]cENTRALililiiii!iiiiiiii
MAGNETO OPTICAL DISK
'- . . . . . . . . . . . . . . . .
-'
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
'
Fig. 4. Schematic illustration of digital/analog hybrid system. Analog image flow forms an on-line system connecting the central control room with the endoscopystations; digital image flow constitutes an off-line system, the information being carried in the form of MOD from the endoscopystations to the central control room and to the display stations. In the central control room both systems are connected by the computer system for data management.
296 up. The images are stored permanently both on the MOD and OD.
4.3. Summary of the hybrid filing system The filing system for digital images forms an off-line PACS, the communication being realised by transportation of the MODs. The retrieved digital images are excellent in quality and undergo no image degradation during copying. The system for analog image filing is an on-line system easy to manage and quick in retrieval, and serving as a back-up storage for the digital image file. The current filing system combines the merits of both digital and analog filing methods, hence a hybrid system (Fig. 4).
5. Clinical experience
We are currently managing three ODs and thirty-five MODs (October, 1991); the retrieval of a desired image is much easier, compared with the storage of films: You only need the I.D. number of the patient, date of the endoscopic procedure or other index items. The space occupied by the recorded disks is smaller than the conventional film storage. Analog images replayed on the ordinary TV monitor are of a sufficiently good quality. That the images are analog by no means interferes with making the diagnosis. The time required for replaying an image was less than 1 s, that is, replaying was practically instant; this was useful in viewing a large amount of images quickly: monthly review of endoscopic images, for instance. This quick review of endoscopic images provided a good opportunity for evaluating the technical aspects of the endoscopic procedures done by individual endoscopists, which information was helpful in improving their technical skills and was essential for quality assurance of our endoscopy practice. Analog images were displayed also for the patients. This display of the endoscopic images helped the patients understand their own ailment; it was a good means for obtaining their cooperation.
Digital filing enabled the endoscopists to study high-quality endoscopic images in detail, which was useful in studying the chronological changes in the follow-up case and in comparing the endoscopic images of related conditions. This was thought helpful for the advancement of diagnostics; a study on the earliest endoscopic appearance of neoplasia, for example, would certainly benefit from it. This was useful also for teaching in endoscopy. A problem with the display of digital images was the length of time it required; replaying a 1/10 compressed image took 5.2 s on average (range 4.9-5.6 s) including searching and displaying. Though multiple-image display on a high-resolution monitor markedly relieved the psychological tension of the viewers by giving the overview of all the images obtained in a case, this lag of 5 s was beyond the limit of endoscopists' patience. In the case of images of reversible compression (the compression ratio of 1/3), it required 10.3-11.2 s (the mean being 10.8 s) until display of an image. With the increase of stored images, the number of MODs has increased (35 in October 1991); it became a problem to locate a desired digital image from the many MODs. At the central control room this is easily done, since the images are centrally managed by a computer and the MOD storing the image is identified on the monitor screen; simply by inserting the identified MOD into the slot of the disk drive unit the image in question is displayed. When an image was searched at an independent display station distant from the central control room, like that at a conference room of the medical department, this 'became a serious and difficult problem. The images to be displayed there had to be located and the disks storing them had to be picked up beforehand. This complexity in the management of off-line images is certainly a shortcoming of the off-line filing system.
6. Discussion
By this hybrid filing system an efficient and safe storage of endoscopic images was realized. The digital filing ensured handling of high-quality
297
images without image degradation. By the use of simultaneous analog filing serving for back up storage, the safety of stored images has improved. The central data management has made the retrieval and utilization of endoscopic images easier. Combination of the quick replaying of analog images with high-resolution display and degradation-free copying of digital images has produced a clinically practicable, large-scale filing system of endoscopic images. In this system DPCM was used as the algorithm for compression of the digital images. The compression rate for reversible compression was approximately 1/3. Another compression algorithm, by colour subtraction based on the characteristics of R, G and B components of endoscopic images, is claimed to have attained a much greater compression rate (better than 1/10) in the reversible compression [8]. For irreversible compression of endoscopic images, discrete cosine transform (DCT) [9,10] and adaptive vector quantization (AVQ) [11] have been attempted. A study on image compression [12] suggested that the compression rate of 1/20 by DCT or by DPCM is within the range causing no interference with the diagnostic quality of the images. The problems with the system include the slowness of display of digital images and complexity in the management of off-line data. Slow display of digital images is probably the bottle neck for wider acceptance of digital image filing. To improve this shortcoming the authors have modified the display stations by moving the SCSI controller, which controls the MOD drive unit, from the personal computer to the image compressor; this modification resulted in a decrease of the time lag until display from 5 to 3 s in a 1/10 compressed image [13]. The complexity and difficulty in the management of off-line data leads to reassessment of the on-line filing system. Since the capacity and speed of the digital LAN is still too restricted for the quantity of endoscopic images to be conveyed among many stations, a possibility of an a n a l o g / digital hybrid LAN is being discussed, in which the ordinary images are sent via the analog LAN as index images and in which only those images
requiring careful analysis later are sent through the digital LAN [14]. The future of image filing lies without doubt in digital filing [15], but at the current level of digital image technology a hybrid system seems to be a practical solution.
7~ Conclusion A hybrid system was developed for filing of endoscopic images. The digital image filing system forms an off-line PACS, and for the analog image filing an on-line system is used. The clinical experience has shown the usefulness of the system, but some problems have become evident, which have led to some improvements; a possibility of on-line system with analog/digital hybrid LAN is being evaluated.
Acknowledgement This study was supported in part by a grant in 1990 from The Japanese Foundation for Research and Promotion of Endoscopy.
References [1] Y. Takasu and A. Kilamura, Practice of panendoscopy, Stomach and lntest. 19 (1984) 47-54. (in Japanese with English abstract) [2] M.A. Fujino, M. lkeda, Y. Yamamoto, A. Morozumi and H. Suzuki, Introduction of endoscopy units (endoscopy centres). A series: No. 45, Gastroenterol. Endosc. 32 (19901 2283-2284. (in Japanese) [3] S.J. Dwyer lIl, A.W. Templeton, N.L. Martin, K.R. Lee, E. Levine, S. Batnitzky, S.J. Rosenthal, D.F. Preston, H.1. Price, S. Faszold, W.H. Anderson and L.T. Cook, The cost of managing digital diagnostic images. Radiology 144 (19821 313 318. [4] K. Inamura, Whal are the current problems? For the advancement of PACS, Image Technol. Inf. Disp., Med. 211 (1988) 727-732. (in Japanese) [5] R. Schindler, History of gastroscopy, in Gastroscopy, 2nd Edn., pp. 1-13 (Hafner Publishing Co., New York NY, 19661. [6] M. Classen and J. Phillip, Electronic endoscopy of the gastrointestinal tract. Initial experience with a new type of endoscope that no fiberoptic bundle for imaging, Endoscopy 16 (1984) 16-19.
298 [7] M.A. Fujino, M. Ikeda, Y. Yamamoto, T. Kinose, H. Tachikawa, A. Morozumi, S. Sano, Y. Kojima, T. Nakamura, T. Kawai, A. Iijima, T. Sato, H. Otsuka, M. Otaka and H. Suzuki, Development of an integrated filing system for endoscopic images, Endoscopy 23 (1991) 11-15. [8] H. Ohta, H. Takashiri, Y. Goto, E. Masuko, S. Matsumoto, S. Sakamaki and Y. Niitsu, Development of compression by colour subtraction of R, G, B data in endoscopic images, Proc. 40th Congr. Jap. Gastroenterol. Endosc. Soc. (1990) 222. (in Japanese) [9] Y. Yamada, S. Suzuki, Y. Shiina and T. Miwa, Development of digital filing system for electronic endoscopic images with image compression by discrete cosine transform. 1st report, Gastroenterol. Endosc. 32 (1990) 21892197. (in Japanese with English abstract) [10] K. Kajiwara, Present and future of medical image transfer by personal computer, Image Technol. Inf. Disp. Ind. 22 (1990) 67-72, (in Japanese) [11] H. Morikubo, Data compression type digital filing system in various medical images, Image Technol. Inf. Disp. Med. 23 (1990) 423-428. (in Japanese) [12] T. Nakamura, M.A. Fujino, M. lkeda, Y. Yamamoto, T. Kinose, H. Tachikawa, A. Morozumi, Y. Kojima, T.
Kawai, T. Sato, H. Ohtsuka, M. Ohtaka, Y. Akahane and H. Suzuki, A study on image compression for filing of endoscopic images, Proc. 40th Congr. Jap. Gastroenterol. Endosc. Soc. (1990) 221. (in Japanese) [13] T. Kawai, M.A. Fujino, M. Ikeda, Y. Yamamoto, Y. Miyazaki, H. Tachikawa, A. Morozumi, T. Nakamura, Y. Kojima, T. Sato, H. Ohtsuka, M. Ohtaka, Y. Akahane and H. Suzuki, Development of display system of endoscopic images for case conference (2nd report), Proc. 40th Congr. Jap. Gastroenterol. Endoscopy Society (1990) 223. (in Japanese) [14] T, Kawai, M.A. Fujino, M. Ikeda, Y. Yamamoto, Y. Kojima, A, Morozumi, T. Nakamura, T. Sato, H. Ohtsuka. M. Ohtaka, Y. Miyazaki, Y. Akahane and H. Suzuki, Development of analog/digital hybrid system for filing of endoscopic images (2nd report). A consideration on a possibility of analog/digital hybrid LAN, Proc. 41st Congr. Jap. Gastroenterol. Endosc. Soc. (1991) 264. (in Japanese) [15] M. Classen, F. Wagner and W. Swobodnik, Electronic data base in gastroenterological endoscopy (Editorials), Endoscopy 23 (1991) 29-31.
291
© 1992 Elsevier Science Publishers B.V. All rights reserved 0169-2607/92/$05.00 COMMET 01283
Digital/analog hybrid system for filing of endoscopic images Masayuki A. Fujino, Masahiro Ikeda, Yasuyuki Y a m a m o t o , Atsuro Morozumi, Toshiya Nakamura, T s u t o m u Kawai and Hiroshi Suzuki First Department of Medicine, Yamanashi University School of Medicine, Tamaho, Nakakoma-gun, Yamanashi, Japan
A new system was developed for filing all the endoscopic images generated in our hospital. The system is composed of an on-line network for analog images supplied from the endoscopy stations and stored on 300 mm optical disks, on the one hand, and an off-line PACS for digital images recorded on a 130 mm magneto-optical disk (MOD) at each endoscopy station, on the other. For close examination of the images digital images are displayed from the MOD on a high-resolution computer graphic monitor, and for quick review of a large number of images, analog images are retrieved from the 300-mm optical disks. This system has been in clinical use at our university hospital for the past year and has proven useful for education of endoscopy, for the quality control of the endoscopy practice, and for the management of the patients. Filing of endoscopic image; Digital/analog hybrid system, Off-line PACS; On-line network of video processors; Full colour image
I. Introduction
An endoscopic image is in full colour, and carries a relatively large volume of information (750 kBytes: 500 × 500 × 8 bits, for each of red, green and blue components, in the field-sequential system). In oesophagogastroduodenoscopy a large number of images are recorded in Japan (40 images per case on average [1]). At our university hospital with 600 beds and with a centralized endoscopy unit having 5 endoscopy tables, 20-50 patients are endoscoped at each morning session, generating approximately 5000 endoscopic images every week. Laparoscopy is performed in the
Correspondence: Masayuki A. Fujino, First Department of Medicine, Yamanashi University School of Medicine, 1110 Shimokato, Tamaho, Nakakoma-gun, Yamanashi, 409-38 Japan. Phone: + 81-552-73-1111; Fax: + 81-552-73-6748.
operating theatre and fluoroscopy-requiring procedures such as ERCP (endoscopic retrograde cholangio-pancreatography) are done at the radiology unit. The number of endoscopic procedures performed at our hospital amounted to 5259 in 1989 [2] and is still increasing. Those images are required at the weekly conferences of the medical departments, at the preoperative conferences of the surgical departments held every morning, and they are needed also at the outpatient clinic, where they are shown to the patients for understanding of their disease. .The above description of our endoscopy practice illustrates the quantity of images to be stored and to be sent to different display stations. At the display stations, practically instant reproduction is required of all the images to be studied. In the field of radiology, following the pioneer work by Dwyer et al. [3], large-scale on-line systems for archiving digitized images and their
292
communication have been attempted, for which the term 'picture archiving and communication system' (PACS) was coined. But the cost of installing the PACS is enormous, and the capacity and speed of the local area networks (LAN) are still very limited [4] and, therefore, still insufficient for clinical use with the images of digestive endoscopy. 2. History of development of a filing system for endoscopic images The history of digestive endoscopy dates back to Bozzini, who attempted oesophagoscopy in 1795 [5]. The endoscopic images were documented first in the form of drawings by the artists.
Photography was introduced to endoscopy in the 1940s, markedly enhancing the accuracy of documentation, but this also had some innate problems: photographs were prone to injury and to image degradation such as fading of colours in the course of time. There was difficulty in the filing of films, particularly in retrieval of the desired endoscopic images; the films were often lost. The advent of electronic endoscopy in 1983 [6] made possible electronic filing of endoscopic images. The authors started the development of an endoscopic image filing system in 1987 with the cooperation of Olympus Optical Co., Japan; the Japanese Ministry of Education, Science and Culture funded this project in 1989. The system has
r ? , . ? . . . . . . - . . . . . . . . . . . . . . . . . . . . - . . . . . . . . . . . . ? ~
:i~ii: UPPER GI AND BRONCHOi!: ~i~,iiSUBSYSTEM:i~i~!iiiiiiiii!i!ii~i~iii!i:
:~: COLORECTAL:
',:??::SUBSYSTEM:', :~" SUBSYSTEM i: t... ~ . . . . . .
=t...........a
i:!ENDOSCOPICI M A G E ii FILING MAIN SYSTEM ::
DIGITALIMAGE ~ FILING DEVICE
I
IN!:o.J i
I
~.:i.s...uBsls!E.u]ii~:i::iii:ii
:~ii KNIX)SCOPIC ULTRASOUND ::!:
. : . : . : . . . . . . . . . .
VIDEO PRINTER ]
. . . . . . .
. . . . . . . . . . .
MULTI~~_ ADAPTER _
AUTOMATIC I PHOTODEVICEI
::~::LEC~URE THEATER SUI~YSTEM :~
35 mm CAMERA]
I.T C DECODERI
I
I FILM IMAGE INPUT DEVICE
ANALOGIMAGE FILINGDEVICE (CENTRAL CONTROL ROOM)
Fig. 1. Block diagram of the filing system. The system consists of endoscopy stations (1-6 in the figure) display stations (7 and 8) the main system for image filing (9), the computer system for data management (10) and the image processing system (11), the last three located in the central control room. The endoscopy stations in the operating theatre and radiology unit and display stations are off-line subsystems.
293 been used in daily clinical practice since March 1990 [2].
3. Developmental concepts The filing system was designed, based on the following concepts. 1. The images should be of the highest conceivable quality; no image degradation is allowed during communication and copying. 2. Safe and unified storage with easy access. 3. High-speed recording and display. 4. Research capability for image processing must be guaranteed. 5. Economy of cost and space. 6. The system must be flexible enough to allow introduction of future progresses in technology. The above concepts are mutually contradictory: Non-degradation of images calls for digital filing. High-speed recording and replaying suggests ana-
log filing. For easy and safe management of stored data, an on-line PACS is a natural solution, but it has still serious problems as mentioned earlier. A compromise had to be devised: the authors finally adopted the idea of a digital/analog hybrid system for filing of endoscopic images [7]. A detailed description of the system is presented here together with its clinical experience.
4. Digital/analog hybrid filing system (Fig. 1) 4.1. Handling of digital images 4.1.1. Endoscopy station The electronic endoscopes of field-sequential type (Olympus Optical Co.) are used. The endoscopic images captured by an electronic endoscope are sent through the video processor (CV200, Olympus) to the digital image filing device installed at each endoscopy station. The digital image filing device consists of an image compres-
Fig. 2. A scene of an endoscopy conference. There is an image compressor (top left of the display station), expanding the compressed images, and four MOD drive units (top right) above two CRT monitors and a personal computer. The high-resolution computer graphic monitor, at the right corner, is for display of multiple (up to 42) images, and the other (NTSC monitor) for enlarged display of an image selected from the multiple-imagedisplay.
294 sor (MD-702, Olympus), a personal computer (PC-9801RX, NEC) and a disk driving unit (RS9200EII, Ricoh) controlled by the personal computer. Rewritable, 130 ram, magneto optical disks ( M O D ) (MKR5A4, Mitsubishi Kasei) are used for digital image storage at each endoscopy station. An M O D records the images from many patients. The images generated during an endoscopic procedure are stored as a group. The data file format consists of the following: File management data, identification number of the patient, name of the patient, date of birth, sex, age, date of the procedure, comment data, number of images recorded, image data containing the sequentially recorded images tagged with their respective index number, and finally, system management data including identification number of the procedure. The M O D s with the digital images are carried, after completion of the endoscopic procedures, to the central control room for storage. The M O D ' s are carried to and replayed at the display stations (conference rooms and lecture theatre).
4.1.2. Display station A display unit is composed of the digital image filing device and C R T monitors for display; one of the monitors is a high-resolution (1280 x 1024 pixels) non-interlaced computer graphic monitor (GDM-1950, Sony), used for multi-image display of up to 42 pictures at a time, and the others are NTSC monitors (PVM-1442Q, Sony) for enlarged display of an image selected from the multiple image display. For a greater ease of image retrieval, four M O D drive units are installed, allowing up to four M O D s to be searched simultaneously. The image compressor also decompresses the compressed images. Fig. 2 shows an actual scene of endoscopy conference using a display station.
4.1.3. Image compression The algorithm for image compression is differential pulse code modulation (DPCM). Both reversible and irreversible compression modes are selectable at the time of recording. In the reversible mode the compression rate is 1/3,
Fig. 3. A view of the central control room. The equipment on the left desk is for the digital images and that on the right for the analog. A white box at the top right above the right desk is the multi-input adapter. A cable from the ceiling, seen right, supplies the analog signals from endoscopy stations. At the extreme left there is a video printer for hard copies, and an automatic photo device for transparencies.
295 whereas in the irreversible the rate is either 1 / 6 or 1/10.
The endoscopic ultrasonographs are also stored as analog images.
4.2. Flow of analog image 4.2.2. Endoscopy stations unconnected with central control room 4.2.1. Central control room The endoscopy stations are connected witk the central control room by cables. The images are sent as analog video signals to the multi-input adapter (MD-661, Olympus) in the central control room (Fig. 3). This adapter, consisting of large-capacity semiconductor memories, serves for traffic control of the images released independently from different (up to 8) endoscopes. The analog images are then forwarded to the analog image filing device (SDF-3D, Olympus), and recorded on a 300 mm optical disk (OD).
The endoscopic images generated at distant endoscopy stations not connected with the central control room, namely those in the radiology unit or operating theatre, are recorded first digitally on MOD; those MODs are carried after the procedures to the the central control room. The central control room also has a display unit with a digital image filing device, which is connected with the data management system and the analog file. Those images stored on MODs are reviewed on the central digital image display monitors and copied into the analog file as back
DIGITAL/ANALOG HYBRID FILING SYSTEM
ELECTRONIC ENDOSCOPE
VIDEO CONVERTER
_ voEo
PROCESSOR
I
H
I
FIBERSCOPE
ANALOGVOEOS'GNALIANALOG'OAGE] ~
FILING DEVICE
m / DIGITAL IMAGE FILING DEVICE
i
i
1
;I ":::~?' ^ - 'liiENDOSCOPY:i:ii!i;iii~ -'^" " -
" ................................
DIGITAL IMAGE FILING DEVICE
]cENTRALililiiii!iiiiiiii
MAGNETO OPTICAL DISK
'- . . . . . . . . . . . . . . . .
-'
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
'
Fig. 4. Schematic illustration of digital/analog hybrid system. Analog image flow forms an on-line system connecting the central control room with the endoscopystations; digital image flow constitutes an off-line system, the information being carried in the form of MOD from the endoscopystations to the central control room and to the display stations. In the central control room both systems are connected by the computer system for data management.
296 up. The images are stored permanently both on the MOD and OD.
4.3. Summary of the hybrid filing system The filing system for digital images forms an off-line PACS, the communication being realised by transportation of the MODs. The retrieved digital images are excellent in quality and undergo no image degradation during copying. The system for analog image filing is an on-line system easy to manage and quick in retrieval, and serving as a back-up storage for the digital image file. The current filing system combines the merits of both digital and analog filing methods, hence a hybrid system (Fig. 4).
5. Clinical experience
We are currently managing three ODs and thirty-five MODs (October, 1991); the retrieval of a desired image is much easier, compared with the storage of films: You only need the I.D. number of the patient, date of the endoscopic procedure or other index items. The space occupied by the recorded disks is smaller than the conventional film storage. Analog images replayed on the ordinary TV monitor are of a sufficiently good quality. That the images are analog by no means interferes with making the diagnosis. The time required for replaying an image was less than 1 s, that is, replaying was practically instant; this was useful in viewing a large amount of images quickly: monthly review of endoscopic images, for instance. This quick review of endoscopic images provided a good opportunity for evaluating the technical aspects of the endoscopic procedures done by individual endoscopists, which information was helpful in improving their technical skills and was essential for quality assurance of our endoscopy practice. Analog images were displayed also for the patients. This display of the endoscopic images helped the patients understand their own ailment; it was a good means for obtaining their cooperation.
Digital filing enabled the endoscopists to study high-quality endoscopic images in detail, which was useful in studying the chronological changes in the follow-up case and in comparing the endoscopic images of related conditions. This was thought helpful for the advancement of diagnostics; a study on the earliest endoscopic appearance of neoplasia, for example, would certainly benefit from it. This was useful also for teaching in endoscopy. A problem with the display of digital images was the length of time it required; replaying a 1/10 compressed image took 5.2 s on average (range 4.9-5.6 s) including searching and displaying. Though multiple-image display on a high-resolution monitor markedly relieved the psychological tension of the viewers by giving the overview of all the images obtained in a case, this lag of 5 s was beyond the limit of endoscopists' patience. In the case of images of reversible compression (the compression ratio of 1/3), it required 10.3-11.2 s (the mean being 10.8 s) until display of an image. With the increase of stored images, the number of MODs has increased (35 in October 1991); it became a problem to locate a desired digital image from the many MODs. At the central control room this is easily done, since the images are centrally managed by a computer and the MOD storing the image is identified on the monitor screen; simply by inserting the identified MOD into the slot of the disk drive unit the image in question is displayed. When an image was searched at an independent display station distant from the central control room, like that at a conference room of the medical department, this 'became a serious and difficult problem. The images to be displayed there had to be located and the disks storing them had to be picked up beforehand. This complexity in the management of off-line images is certainly a shortcoming of the off-line filing system.
6. Discussion
By this hybrid filing system an efficient and safe storage of endoscopic images was realized. The digital filing ensured handling of high-quality
297
images without image degradation. By the use of simultaneous analog filing serving for back up storage, the safety of stored images has improved. The central data management has made the retrieval and utilization of endoscopic images easier. Combination of the quick replaying of analog images with high-resolution display and degradation-free copying of digital images has produced a clinically practicable, large-scale filing system of endoscopic images. In this system DPCM was used as the algorithm for compression of the digital images. The compression rate for reversible compression was approximately 1/3. Another compression algorithm, by colour subtraction based on the characteristics of R, G and B components of endoscopic images, is claimed to have attained a much greater compression rate (better than 1/10) in the reversible compression [8]. For irreversible compression of endoscopic images, discrete cosine transform (DCT) [9,10] and adaptive vector quantization (AVQ) [11] have been attempted. A study on image compression [12] suggested that the compression rate of 1/20 by DCT or by DPCM is within the range causing no interference with the diagnostic quality of the images. The problems with the system include the slowness of display of digital images and complexity in the management of off-line data. Slow display of digital images is probably the bottle neck for wider acceptance of digital image filing. To improve this shortcoming the authors have modified the display stations by moving the SCSI controller, which controls the MOD drive unit, from the personal computer to the image compressor; this modification resulted in a decrease of the time lag until display from 5 to 3 s in a 1/10 compressed image [13]. The complexity and difficulty in the management of off-line data leads to reassessment of the on-line filing system. Since the capacity and speed of the digital LAN is still too restricted for the quantity of endoscopic images to be conveyed among many stations, a possibility of an a n a l o g / digital hybrid LAN is being discussed, in which the ordinary images are sent via the analog LAN as index images and in which only those images
requiring careful analysis later are sent through the digital LAN [14]. The future of image filing lies without doubt in digital filing [15], but at the current level of digital image technology a hybrid system seems to be a practical solution.
7~ Conclusion A hybrid system was developed for filing of endoscopic images. The digital image filing system forms an off-line PACS, and for the analog image filing an on-line system is used. The clinical experience has shown the usefulness of the system, but some problems have become evident, which have led to some improvements; a possibility of on-line system with analog/digital hybrid LAN is being evaluated.
Acknowledgement This study was supported in part by a grant in 1990 from The Japanese Foundation for Research and Promotion of Endoscopy.
References [1] Y. Takasu and A. Kilamura, Practice of panendoscopy, Stomach and lntest. 19 (1984) 47-54. (in Japanese with English abstract) [2] M.A. Fujino, M. lkeda, Y. Yamamoto, A. Morozumi and H. Suzuki, Introduction of endoscopy units (endoscopy centres). A series: No. 45, Gastroenterol. Endosc. 32 (19901 2283-2284. (in Japanese) [3] S.J. Dwyer lIl, A.W. Templeton, N.L. Martin, K.R. Lee, E. Levine, S. Batnitzky, S.J. Rosenthal, D.F. Preston, H.1. Price, S. Faszold, W.H. Anderson and L.T. Cook, The cost of managing digital diagnostic images. Radiology 144 (19821 313 318. [4] K. Inamura, Whal are the current problems? For the advancement of PACS, Image Technol. Inf. Disp., Med. 211 (1988) 727-732. (in Japanese) [5] R. Schindler, History of gastroscopy, in Gastroscopy, 2nd Edn., pp. 1-13 (Hafner Publishing Co., New York NY, 19661. [6] M. Classen and J. Phillip, Electronic endoscopy of the gastrointestinal tract. Initial experience with a new type of endoscope that no fiberoptic bundle for imaging, Endoscopy 16 (1984) 16-19.
298 [7] M.A. Fujino, M. Ikeda, Y. Yamamoto, T. Kinose, H. Tachikawa, A. Morozumi, S. Sano, Y. Kojima, T. Nakamura, T. Kawai, A. Iijima, T. Sato, H. Otsuka, M. Otaka and H. Suzuki, Development of an integrated filing system for endoscopic images, Endoscopy 23 (1991) 11-15. [8] H. Ohta, H. Takashiri, Y. Goto, E. Masuko, S. Matsumoto, S. Sakamaki and Y. Niitsu, Development of compression by colour subtraction of R, G, B data in endoscopic images, Proc. 40th Congr. Jap. Gastroenterol. Endosc. Soc. (1990) 222. (in Japanese) [9] Y. Yamada, S. Suzuki, Y. Shiina and T. Miwa, Development of digital filing system for electronic endoscopic images with image compression by discrete cosine transform. 1st report, Gastroenterol. Endosc. 32 (1990) 21892197. (in Japanese with English abstract) [10] K. Kajiwara, Present and future of medical image transfer by personal computer, Image Technol. Inf. Disp. Ind. 22 (1990) 67-72, (in Japanese) [11] H. Morikubo, Data compression type digital filing system in various medical images, Image Technol. Inf. Disp. Med. 23 (1990) 423-428. (in Japanese) [12] T. Nakamura, M.A. Fujino, M. lkeda, Y. Yamamoto, T. Kinose, H. Tachikawa, A. Morozumi, Y. Kojima, T.
Kawai, T. Sato, H. Ohtsuka, M. Ohtaka, Y. Akahane and H. Suzuki, A study on image compression for filing of endoscopic images, Proc. 40th Congr. Jap. Gastroenterol. Endosc. Soc. (1990) 221. (in Japanese) [13] T. Kawai, M.A. Fujino, M. Ikeda, Y. Yamamoto, Y. Miyazaki, H. Tachikawa, A. Morozumi, T. Nakamura, Y. Kojima, T. Sato, H. Ohtsuka, M. Ohtaka, Y. Akahane and H. Suzuki, Development of display system of endoscopic images for case conference (2nd report), Proc. 40th Congr. Jap. Gastroenterol. Endoscopy Society (1990) 223. (in Japanese) [14] T, Kawai, M.A. Fujino, M. Ikeda, Y. Yamamoto, Y. Kojima, A, Morozumi, T. Nakamura, T. Sato, H. Ohtsuka. M. Ohtaka, Y. Miyazaki, Y. Akahane and H. Suzuki, Development of analog/digital hybrid system for filing of endoscopic images (2nd report). A consideration on a possibility of analog/digital hybrid LAN, Proc. 41st Congr. Jap. Gastroenterol. Endosc. Soc. (1991) 264. (in Japanese) [15] M. Classen, F. Wagner and W. Swobodnik, Electronic data base in gastroenterological endoscopy (Editorials), Endoscopy 23 (1991) 29-31.