Teleradiology for the Emergency Room NOLAN J. KAGETSU“ AND RONALD C. ABLOW Department of Radiology St. Luke ’s-RooseveltHospital Center Columbia University College of Physicians and Surgeons 428 West 59th Street New York, New York 10019 Teleradiology is the point-to-point electronic transmission of diagnostic images. This subject has been recently reviewed.I Teleradiology systems have been evaluated in the laboratory.* Clinical evaluations include clinic-to-hospital and hospital-tohospital Many emergency room films are initially interpreted by nonradiologists. Review of these films at a later time is required by the Joint Commission on Accreditation of Hospitals, which states that “. , . a timely review of x-rays shall be conducted and the official interpretation shall be available to the private practitioner and the practitioner providing emergency care.”7 The American College of Radiology Policy Statement on Emergency Radiology states, “In those instances where patient mix and volume do not warrant full-time coverage by a radiologist, on-call services and delayed interpretations are a~ceptable.”~ Some clinicians have questioned the value of these delayed interpretations by radiologists. McLain and Kirkwood studied the influence of delayed interpretations of 294 cases from a rural emergency room and concluded that “. . . redundant interpretation of all routine films taken in the hospital emergency room added little (except perhaps cost) to the overall quality of care.”* Better training of clinicians in the interpretation of radiographs was suggested in order to improve patient care. In a previous study, 25 emergency room cases were transmitted from a television studio via satellite to several receiving stations.’ We studied 919 cases from our emergency room transmitted over standard phone lines using a commercially available digital teleradiology system.
METHODS Details of this study have been previously Over a four-month period, all films (919 examinations) generated from the emergency room of a 535-bed urban hospital between the hours of midnight and 8 A.M. were transmitted by radiology technologists to a resident radiologist covering the emergency room of a 780-bed hospital three miles away. Kodak XKl high-contrast, blue-sensitive film was used for radiographs. Films were placed on a transilluminator and optically zoomed so that the film image filled the monitor screen. The image was then digitized and transmitted. A commercially available teleradiology system (Dataspan, Orchard Park, NY) was used. Films as large as 14 x 17 in and as small an area as 5.1 x 7.3 cm (with maximum optical zooming) were digitized to a 512 x 512 x 8-bit image matrix. Data were compressed “e-mail: njk4 (n cunixf. cc. Columbia. edu 293
294
ANNALS NEW YORK ACADEMY OF SCIENCES
at a ratio of 2 5 1 before transmission by a 9600-baud modem over a standard phone line. Spatial resolution was measured using a line pair phantom in the transillumination mode with the optical zoom set for a 14 x 17- in film. The vertical and horizontal spatial resolution is about 0.6 LP/mm. The smallest area of a film that can be optically zoomed is 5.1 x 7.3 cm. The vertical and horizontal spatial resolution with this maximal optical zooming is about 4 LP/mm. Transmission time for images averaged three minutes. While transmission was in progress, whole images could not be reviewed and films could not be digitized at both the sending and receiving sites. If a group of images was being transmitted, transmission of the later images had to be delayed if immediate review of the earlier images was required. Images were viewed on an 11-inch monitor with its long axis oriented vertically. Contrast and brightness of the teleradiology image could be adjusted by the teleradiology reader. Additional image manipulation options included edge enhancement, reversal of gray scale, and special contrast manipulations (gamma correction and histogram equalization). The teleradiology image could be digitally zoomed by the resident to twice the original size. After digital zooming, a 256 x 256 image of one-quarter of the original film is displayed on the monitor. This is different from optical zooming of the original film where only a selected part of the original film is digitized by the technologist to a 512 x 512 image and transmitted to the resident. Left-right reversal and image rotation were not available. Nineteen different radiology residents with six months to three years of radiology training made preliminary interpretations of the teleradiology images. These reports were either phoned to an emergency room clerk or were made available on a Remote Telephone Access System (Sudbury Systems, Sudbury, MA). Teleradiology images were reviewed later the same morning by one of six attending radiologists at the 780-bed hospital. These final teleradiology interpretations were compared to the interpretation of the actual films made by one of six different attending radiologists at the 535-bed hospital.
RESULTS A total of 919 examinations were transmitted. No ultrasound or nuclear medicine studies were performed. Ten brain computerized tomography (CT) exams were performed. All other exams were plain films. The number of exams transmitted per night ranged from one to 21 with a mean of 7.2. Twenty-two plain film exams were lost to follow-up. The final film reading was normal in 455 (52.2%) exams. Discrepancies due to an inadequate video image were found in 14 of the 897 cases (1.6%) available for follow-up. For example, in one skull exam, the question of a zygoma fracture was only raised after a review of the original film with a bright light. In other cases, a triquetral fracture and a tuft fracture could only be confidently excluded after a review of the original films with a bright light. Fractures of ribs seven and eight were missed in one chest exam because of inadequate resolution. The fractures were seen well on an optically zoomed image. The diagnosis of rib fracture was made correctly in three out of all five cases of rib fracture in our series. (In one case, rib fractures were missed because of reader error.) There was an elbow exam where the question of a displaced anterior fat pad was raised only by the film reader using a bright light. In the other 23 elbow exams in this series, all five definite positive findings were seen by the teleradiology reader. These
KAGETSU & ABLOW EMERGENCY ROOM AND TELERADIOLOGY
295
included one olccranon fracture, one epicondyle fracture, two radial head fractures, and one joint effusion. A femoral neck fracture could not be excluded after review of the teleradiology images of an overpenetrated hip exam. This could only be done after review of the original film with bright light illumination. In the other 20 hip exams in this series, all eight eases of hip fracture were diagnosed correctly by the teleradiology reader. Limited contrast resolution of the teleradiology image was responsible for the inability to distinguish a lung nodule from a calcified granuloma. In another chest exam, engorged vessels and blurring of vessel borders of a patient with mild congestive heart failure were not seen well on the teleradiology image. Even with optical zooming, the subtle vessel blurring could not be appreciated. A subclavian catheter with its tip in the jugular vein was not seen by the teleradiology reader because of limited spatial resolution. Only in retrospect, after the history of central line placement was given, was the catheter seen. The catheter was best seen with edge enhancement. In another case, laminated gallstones were seen better with edge enhancement of the teleradiology image. Both limited spatial and contrast resolution make differentiation of abdominal calcifications, such as renal calculi, from artifacts more difficult. In one case, an optically zoomed image of the area in question improved the spatial resolution so that the differentiation could be made. In one abdominal exam, only one wall of a calcified abdominal aortic aneurysm was visible on the teleradiology image whereas both walls were clearly seen on the plain film. Both calcified walls were seen on a zoomed image. Both cases of pneumothorax in our series were missed. In the first case the pleural line was easily demonstrated on a redigitized image of the optically zoomed film. In the second case, the film was overexposed. The pleural line was best seen with a bright light. The pleural line could not be demonstrated on the digital image with maximal optical zooming, maximal transillumination intensity, and edge enhancement. DISCUSSION Analysis of the discrepancies resulting from an inadequate teleradiology image revealed problems with limited spatial resolution, limited contrast resolution, and poor images when the original radiographs were overexposed. In addition, transmission time was a problem. Limited spatial resolution makes the diagnosis of pneumothorax difficult. This problem has been previously described for film digital radiography'* and teleradiology.? The pleural line was visible in our first case on the optically zoomed image of the lung apex. If optically zoomed images of both apices are routinely transmitted in addition to the PA and lateral view, transmission time would increase to about 14 min 50 sec per chest exam. The use of secondary signs of pneumothorax, such as atelectasis of the lower lobe and absence of vessels in the apex, would have been necessary to make the diagnosis in our second case. A repeat chest film with optimal technique possibly would have shown a pleural line on the teleradiology image. As suggested previou~ly,~ review of the original films at some later time is recommended because of the superior spatial and contrast resolution of film. Laser scanners can digitize images to a 2000 x 2500 matrix with a 12-bit dynamic range. This improved spatial and contrast resolution should improve the accuracy of interpretations. However, these scanners cost about $65,OOO-more than a complete system based on a video scanner. Furthermore, a 1600 x 1900 x 12-bit system was
296
ANNALS NEW YORK ACADEMY OF SCIENCES
recently shown to be less sensitive than film screen radiography in the detection of pneumothorax.I3 Murphey et a1.I4have shown that a 2048 x 2048 x 12-bit image is needed in order to detect nondisplaced fractures. Direct image capture is a method of obtaining the image directly from the device producing the image. In other words, it bypasses the step of producing a film and digitizing the film. For example, an image from a CT scan can be directly transmitted by the receiving site. This would eliminate a potential source of data loss. The disadvantage of this type of system is that because of lack of standard interfaces, different interfaces must be used for equipment from different vendors. Overpenetrated films that can only be read with a bright light should be repeated before teleradiology transmission. Use of wide-latitude film or a method to provide more transillumination intensity while the film is being digitized may result in better teleradiology images. Currently, transillumination intensity is limited because accidental exposure of the video camera to high-intensity light would permanently reduce the sensitivity of the camera. Another solution to the problem of overexposed films would make use of a laser film scanner. These digitizing devices have a wider dynamic range than video scanners. After acquisition, the image can be improved by modifying the window and level of the image. (This method has been described as a way of avoiding repeat exposures when the initial film is overe~posed.'~) Monitors have a limited range of contrast when compared to film.16The teleradiology reader can manipulate image contrast and brightness so that it is difficult to determine the absolute density of a lung opacity. Transmission of a gray scale (which is already present on many CT images) simultaneously with the radiograph would provide a reference standard on the teleradiology image. Transmission time was a problem. The inability to read an image while transmission was in progress combined with the transmission time of 2 min 50 sec per image delayed reporting. If an emergency CT scan was transmitted with 12 images, 37.5 minutes would elapse before interpretation could begin. These interpretation delays would be eliminated by microwave or fiberoptic transmission of images, which would reduce transmission time to about three seconds per image. However, these transmission systems are expensive. In addition, the ability to simultaneously receive and review images would reduce reporting delays.
CONCLUSIONS AND SUMMARY Many emergency rooms do not offer 24-hour on-site coverage by a radiologist. Teleradiology systems can enable a radiologist to offer services to a number of emergency rooms. A digital teleradiology system was evaluated in the emergency room. A total of 919 examinations were transmitted over standard telephone lines to a radiology resident at another hospital emergency room. The 512 X 512 images were reviewed by an attending radiologist and compared with another attending radiologist's interpretation of the original films. Cases with discrepant interpretations were analyzed. Inadequate teleradiology image quality was responsible for clinically significant discrepancies in 14 of 897 exams (1.6%). Review of the original films at some later time is recommended because of the superior spatial and contrast resolution of film. Radiologists must be aware of the limitations of teleradiology especially in the detection of pneumothoraces, abdominal calcifications, and nondisplaced fractures. Retransmission of optically zoomed images of areas of clinical and radiographic
KAGETSU & ABLOW EMERGENCY ROOM AND TELERADIOLOGY
297
concern as well as repeat radiographs of overpenetrated films are suggested to improve teleradiology performance. Further evaluations are needed to determine the effect of these systems on patient outcomes. REFERENCES S., S. J. ROSENTHAL, E. L. SIEGEL,L. H. WETZEL,M. D. MURPHEY, G. G. 1. BATNITZKY, Cox, J. H. MCMILLIN, A. W. TEMPLETON & S. J. DWYER.1990. Teleradiology: An assessment. Radiology 177: 11-17. F. L. SKINNER & J. CERVA.1981. 2. GAYLER,B. W.. J. N. GITLIN,W. RAPPAPORT, Teleradiology: An evaluation of a microcomputer-based system. Radiology 140: 355360. G. CLAUDE, ef a/. 1981. Teleradiology in northern Quebec. 3. PAGE,G., A. GREGOIRE, Radiology 140: 361-366. 1983. Teleradiology: J. N. GITLIN& M. B. HARRINGTON. 4. CURTIS,D. J., B. W. GAYLER, Results of a field trial. Radiology 149 415418. L. S. 1985.Teleradiology: Part of a comprehensive telehealth system. Radio]. Clin. 5. CAREY, North Am. 23: 357-362. J. N. 1986. Teleradiology. Radiol. Clin. North Am. 2 4 55-68. 6. GITLIN. 7. American College of Radiology Policy Statement on Emergency Radiology, amended 9/11/85. 1985. The quality of emergency room radiograph x. MCLAIN,P. L. & C. R. KIRKWOOD. interpretations. J. Fam. Pract. 2 0 443-448. Y. JAMES,J. J., W. GRABOWSKI & A. D. MANGELDORFF. 1982. The transmission and interpretation of emergency department radiographs. Ann. Emerg. Med. 11: 404-408. 10. KAGETSU, N. J., D. R. P. ZULAUF& R. C. ABLOW.1987. Clinical trial of digital teleradiology in the practice of emergency room radiology. Radiology 165 551-554. & R. C. ABLOW.1989. Teleradiology for the emergency I I. KAGETSU,N. J., D. R. P. ZULAUF room. Appl. Radio]. 6 33-35. 12. GOODMAN, L. R., W. D. FOLEY,C. R. WILSON,A. A. RIMM& T. L. LAWSON. 1986. Digital and conventional chest images: Observer performance with film digital radiography system. Radiology 158: 27-33. 13. ELAM,E. A,, K. REHM,B. J. HILLMAN, K. MALONEY, L. L. FAJARW& K. MCNEILL.1992. Efficacy of digital radiography for the detection of pneumothorax: Comparison with conventional chest radiography. AJR 158: 509-514. L. T. COOK,N. L. MARTIN& S. J. DWYER.1990. M. D., J. M. BRAMBLE, 14. MURPHEY, Nondisplaced fractures: Spatial resolution requirements for detection with digital skeletal imaging. Radiology 174 865-870. D. J. & F. G. SOMMER.1984. Film salvage using digital processing. AJR 15. SARTORIS, 142: 1225-1226. 16. KUNDEL, H. L. 1986. Visual perception and image display terminals. Radio]. Clin. North Am. 2 4 69-78.
METHODS Details of this study have been previously Over a four-month period, all films (919 examinations) generated from the emergency room of a 535-bed urban hospital between the hours of midnight and 8 A.M. were transmitted by radiology technologists to a resident radiologist covering the emergency room of a 780-bed hospital three miles away. Kodak XKl high-contrast, blue-sensitive film was used for radiographs. Films were placed on a transilluminator and optically zoomed so that the film image filled the monitor screen. The image was then digitized and transmitted. A commercially available teleradiology system (Dataspan, Orchard Park, NY) was used. Films as large as 14 x 17 in and as small an area as 5.1 x 7.3 cm (with maximum optical zooming) were digitized to a 512 x 512 x 8-bit image matrix. Data were compressed “e-mail: njk4 (n cunixf. cc. Columbia. edu 293
294
ANNALS NEW YORK ACADEMY OF SCIENCES
at a ratio of 2 5 1 before transmission by a 9600-baud modem over a standard phone line. Spatial resolution was measured using a line pair phantom in the transillumination mode with the optical zoom set for a 14 x 17- in film. The vertical and horizontal spatial resolution is about 0.6 LP/mm. The smallest area of a film that can be optically zoomed is 5.1 x 7.3 cm. The vertical and horizontal spatial resolution with this maximal optical zooming is about 4 LP/mm. Transmission time for images averaged three minutes. While transmission was in progress, whole images could not be reviewed and films could not be digitized at both the sending and receiving sites. If a group of images was being transmitted, transmission of the later images had to be delayed if immediate review of the earlier images was required. Images were viewed on an 11-inch monitor with its long axis oriented vertically. Contrast and brightness of the teleradiology image could be adjusted by the teleradiology reader. Additional image manipulation options included edge enhancement, reversal of gray scale, and special contrast manipulations (gamma correction and histogram equalization). The teleradiology image could be digitally zoomed by the resident to twice the original size. After digital zooming, a 256 x 256 image of one-quarter of the original film is displayed on the monitor. This is different from optical zooming of the original film where only a selected part of the original film is digitized by the technologist to a 512 x 512 image and transmitted to the resident. Left-right reversal and image rotation were not available. Nineteen different radiology residents with six months to three years of radiology training made preliminary interpretations of the teleradiology images. These reports were either phoned to an emergency room clerk or were made available on a Remote Telephone Access System (Sudbury Systems, Sudbury, MA). Teleradiology images were reviewed later the same morning by one of six attending radiologists at the 780-bed hospital. These final teleradiology interpretations were compared to the interpretation of the actual films made by one of six different attending radiologists at the 535-bed hospital.
RESULTS A total of 919 examinations were transmitted. No ultrasound or nuclear medicine studies were performed. Ten brain computerized tomography (CT) exams were performed. All other exams were plain films. The number of exams transmitted per night ranged from one to 21 with a mean of 7.2. Twenty-two plain film exams were lost to follow-up. The final film reading was normal in 455 (52.2%) exams. Discrepancies due to an inadequate video image were found in 14 of the 897 cases (1.6%) available for follow-up. For example, in one skull exam, the question of a zygoma fracture was only raised after a review of the original film with a bright light. In other cases, a triquetral fracture and a tuft fracture could only be confidently excluded after a review of the original films with a bright light. Fractures of ribs seven and eight were missed in one chest exam because of inadequate resolution. The fractures were seen well on an optically zoomed image. The diagnosis of rib fracture was made correctly in three out of all five cases of rib fracture in our series. (In one case, rib fractures were missed because of reader error.) There was an elbow exam where the question of a displaced anterior fat pad was raised only by the film reader using a bright light. In the other 23 elbow exams in this series, all five definite positive findings were seen by the teleradiology reader. These
KAGETSU & ABLOW EMERGENCY ROOM AND TELERADIOLOGY
295
included one olccranon fracture, one epicondyle fracture, two radial head fractures, and one joint effusion. A femoral neck fracture could not be excluded after review of the teleradiology images of an overpenetrated hip exam. This could only be done after review of the original film with bright light illumination. In the other 20 hip exams in this series, all eight eases of hip fracture were diagnosed correctly by the teleradiology reader. Limited contrast resolution of the teleradiology image was responsible for the inability to distinguish a lung nodule from a calcified granuloma. In another chest exam, engorged vessels and blurring of vessel borders of a patient with mild congestive heart failure were not seen well on the teleradiology image. Even with optical zooming, the subtle vessel blurring could not be appreciated. A subclavian catheter with its tip in the jugular vein was not seen by the teleradiology reader because of limited spatial resolution. Only in retrospect, after the history of central line placement was given, was the catheter seen. The catheter was best seen with edge enhancement. In another case, laminated gallstones were seen better with edge enhancement of the teleradiology image. Both limited spatial and contrast resolution make differentiation of abdominal calcifications, such as renal calculi, from artifacts more difficult. In one case, an optically zoomed image of the area in question improved the spatial resolution so that the differentiation could be made. In one abdominal exam, only one wall of a calcified abdominal aortic aneurysm was visible on the teleradiology image whereas both walls were clearly seen on the plain film. Both calcified walls were seen on a zoomed image. Both cases of pneumothorax in our series were missed. In the first case the pleural line was easily demonstrated on a redigitized image of the optically zoomed film. In the second case, the film was overexposed. The pleural line was best seen with a bright light. The pleural line could not be demonstrated on the digital image with maximal optical zooming, maximal transillumination intensity, and edge enhancement. DISCUSSION Analysis of the discrepancies resulting from an inadequate teleradiology image revealed problems with limited spatial resolution, limited contrast resolution, and poor images when the original radiographs were overexposed. In addition, transmission time was a problem. Limited spatial resolution makes the diagnosis of pneumothorax difficult. This problem has been previously described for film digital radiography'* and teleradiology.? The pleural line was visible in our first case on the optically zoomed image of the lung apex. If optically zoomed images of both apices are routinely transmitted in addition to the PA and lateral view, transmission time would increase to about 14 min 50 sec per chest exam. The use of secondary signs of pneumothorax, such as atelectasis of the lower lobe and absence of vessels in the apex, would have been necessary to make the diagnosis in our second case. A repeat chest film with optimal technique possibly would have shown a pleural line on the teleradiology image. As suggested previou~ly,~ review of the original films at some later time is recommended because of the superior spatial and contrast resolution of film. Laser scanners can digitize images to a 2000 x 2500 matrix with a 12-bit dynamic range. This improved spatial and contrast resolution should improve the accuracy of interpretations. However, these scanners cost about $65,OOO-more than a complete system based on a video scanner. Furthermore, a 1600 x 1900 x 12-bit system was
296
ANNALS NEW YORK ACADEMY OF SCIENCES
recently shown to be less sensitive than film screen radiography in the detection of pneumothorax.I3 Murphey et a1.I4have shown that a 2048 x 2048 x 12-bit image is needed in order to detect nondisplaced fractures. Direct image capture is a method of obtaining the image directly from the device producing the image. In other words, it bypasses the step of producing a film and digitizing the film. For example, an image from a CT scan can be directly transmitted by the receiving site. This would eliminate a potential source of data loss. The disadvantage of this type of system is that because of lack of standard interfaces, different interfaces must be used for equipment from different vendors. Overpenetrated films that can only be read with a bright light should be repeated before teleradiology transmission. Use of wide-latitude film or a method to provide more transillumination intensity while the film is being digitized may result in better teleradiology images. Currently, transillumination intensity is limited because accidental exposure of the video camera to high-intensity light would permanently reduce the sensitivity of the camera. Another solution to the problem of overexposed films would make use of a laser film scanner. These digitizing devices have a wider dynamic range than video scanners. After acquisition, the image can be improved by modifying the window and level of the image. (This method has been described as a way of avoiding repeat exposures when the initial film is overe~posed.'~) Monitors have a limited range of contrast when compared to film.16The teleradiology reader can manipulate image contrast and brightness so that it is difficult to determine the absolute density of a lung opacity. Transmission of a gray scale (which is already present on many CT images) simultaneously with the radiograph would provide a reference standard on the teleradiology image. Transmission time was a problem. The inability to read an image while transmission was in progress combined with the transmission time of 2 min 50 sec per image delayed reporting. If an emergency CT scan was transmitted with 12 images, 37.5 minutes would elapse before interpretation could begin. These interpretation delays would be eliminated by microwave or fiberoptic transmission of images, which would reduce transmission time to about three seconds per image. However, these transmission systems are expensive. In addition, the ability to simultaneously receive and review images would reduce reporting delays.
CONCLUSIONS AND SUMMARY Many emergency rooms do not offer 24-hour on-site coverage by a radiologist. Teleradiology systems can enable a radiologist to offer services to a number of emergency rooms. A digital teleradiology system was evaluated in the emergency room. A total of 919 examinations were transmitted over standard telephone lines to a radiology resident at another hospital emergency room. The 512 X 512 images were reviewed by an attending radiologist and compared with another attending radiologist's interpretation of the original films. Cases with discrepant interpretations were analyzed. Inadequate teleradiology image quality was responsible for clinically significant discrepancies in 14 of 897 exams (1.6%). Review of the original films at some later time is recommended because of the superior spatial and contrast resolution of film. Radiologists must be aware of the limitations of teleradiology especially in the detection of pneumothoraces, abdominal calcifications, and nondisplaced fractures. Retransmission of optically zoomed images of areas of clinical and radiographic
KAGETSU & ABLOW EMERGENCY ROOM AND TELERADIOLOGY
297
concern as well as repeat radiographs of overpenetrated films are suggested to improve teleradiology performance. Further evaluations are needed to determine the effect of these systems on patient outcomes. REFERENCES S., S. J. ROSENTHAL, E. L. SIEGEL,L. H. WETZEL,M. D. MURPHEY, G. G. 1. BATNITZKY, Cox, J. H. MCMILLIN, A. W. TEMPLETON & S. J. DWYER.1990. Teleradiology: An assessment. Radiology 177: 11-17. F. L. SKINNER & J. CERVA.1981. 2. GAYLER,B. W.. J. N. GITLIN,W. RAPPAPORT, Teleradiology: An evaluation of a microcomputer-based system. Radiology 140: 355360. G. CLAUDE, ef a/. 1981. Teleradiology in northern Quebec. 3. PAGE,G., A. GREGOIRE, Radiology 140: 361-366. 1983. Teleradiology: J. N. GITLIN& M. B. HARRINGTON. 4. CURTIS,D. J., B. W. GAYLER, Results of a field trial. Radiology 149 415418. L. S. 1985.Teleradiology: Part of a comprehensive telehealth system. Radio]. Clin. 5. CAREY, North Am. 23: 357-362. J. N. 1986. Teleradiology. Radiol. Clin. North Am. 2 4 55-68. 6. GITLIN. 7. American College of Radiology Policy Statement on Emergency Radiology, amended 9/11/85. 1985. The quality of emergency room radiograph x. MCLAIN,P. L. & C. R. KIRKWOOD. interpretations. J. Fam. Pract. 2 0 443-448. Y. JAMES,J. J., W. GRABOWSKI & A. D. MANGELDORFF. 1982. The transmission and interpretation of emergency department radiographs. Ann. Emerg. Med. 11: 404-408. 10. KAGETSU, N. J., D. R. P. ZULAUF& R. C. ABLOW.1987. Clinical trial of digital teleradiology in the practice of emergency room radiology. Radiology 165 551-554. & R. C. ABLOW.1989. Teleradiology for the emergency I I. KAGETSU,N. J., D. R. P. ZULAUF room. Appl. Radio]. 6 33-35. 12. GOODMAN, L. R., W. D. FOLEY,C. R. WILSON,A. A. RIMM& T. L. LAWSON. 1986. Digital and conventional chest images: Observer performance with film digital radiography system. Radiology 158: 27-33. 13. ELAM,E. A,, K. REHM,B. J. HILLMAN, K. MALONEY, L. L. FAJARW& K. MCNEILL.1992. Efficacy of digital radiography for the detection of pneumothorax: Comparison with conventional chest radiography. AJR 158: 509-514. L. T. COOK,N. L. MARTIN& S. J. DWYER.1990. M. D., J. M. BRAMBLE, 14. MURPHEY, Nondisplaced fractures: Spatial resolution requirements for detection with digital skeletal imaging. Radiology 174 865-870. D. J. & F. G. SOMMER.1984. Film salvage using digital processing. AJR 15. SARTORIS, 142: 1225-1226. 16. KUNDEL, H. L. 1986. Visual perception and image display terminals. Radio]. Clin. North Am. 2 4 69-78.
