1979, British Journal of Radiology, 52, 577-579
JULY 1979
Technical notes
A comparison of two hard-copy display systems for nuclear medicine images By C. P. Wells, M.Sc, B. L Diffey, Ph.D., F. M. Hall, D.M.R.T. and M. Johnson, H.N.C. Departments of Medical Physics and Nuclear Medicine, Kent and Canterbury Hospital, Canterbury CT1 3NG (Received May, 1978 and in revised form September, 1978)
We recently changed our method of hard-copy CRT) and imaged onto 20x25 cm X-ray film display of nuclear medicine images from a system (Kodak Xomat XL1) by means of a Picker folded based upon the use of Polaroid film to one employing optics camera incorporating a X2.5 magnification 20 X 25 cm X-ray film. Although our subjective im- enlarging lens (Corfield et al., 1978). An example of pression indicated an improvement in image quality, each display is shown in Fig. 1. we also sought some objective means of assessing The displays were then presented to a clinician, a whether there was an improvement in detectability scanning technician and two physicists, all exof lesions. perienced in nuclear medicine. Each participant was The requirements of a film for nuclear medicine imaging were discussed by Merrigan et al. (1977). A comparison of four different films was undertaken by Henry et al. (1973) who based their conclusions on clinical impressions and the reliability of each system. The present communication presents the results of assessing one hundred brain scans using a method described by Houston and Macleod (1977). It should be emphasized that the present work set out to compare two display systems and is not a direct comparison between Polaroid and X-ray film as a display medium. METHOD
Houston (1977) has produced from departmental records a series of one hundred normal brain scans, one view per normal patient, obtained with a Nuclear Chicago (Searle) Pho Gamma III camera with a high resolution collimator interfaced to a Varian 620/L-100 minicomputer. Fifty "tumours" were added mathematically at selected positions to scintigrams in this series, no more than one to a view. These scans were transferred to a disk on our DEC PDP8/E minicomputer via 8-track paper tape. The purpose of this investigation was simply to assess whether the change from a display system using Polaroid film as the hard copy to one employing X-ray film had produced a significant improvement in detectability. To this end, each scintigram was enhanced using an "unsharp masking" filter (Corfield, 1976) and displayed on both media as in routine practice. Each image was displayed in core as a 64x64 matrix array with eight grey-scale levels. Images on Polaroid film (type 107) were obtained using a Shackman camera coupled to a slave video monitor. The images were also displayed on a point-plot display (a short persistence Hewlett-Packard 1332A
FIG. 1. An image of one of the computer-processed brain scans used in the intercomparison of X-ray film and Polaroid film. X-ray above, Polaroid below.
577
VOL.
52, No. 619 Technical notes
informed that no more than one tumour was present in any view and that the probability of an abnormal was 0.5. The order of presentation of each set, i.e. Polaroid or X-ray film, was varied. Each participant was then asked to rate the views using the five-scale category suggested by Goodenough et al. (1974), and to indicate the Cartesian co-ordinate of the suspected lesion. Localization receiver operating characteristic (LROC) curves (Starr et al., 1975) were generated for each set of results together with a
Display
-
points score described by Houston and Macleod (1977). The positional discrepancy allowed was 2 cm or 2\ times the tumour radius, whichever was greater. RESULTS AND DISCUSSION
The LROC curves together with the points score for each participant using the two different display systems are shown in Fig. 2. Although the absolute score showed a large variation between observers in each of the two systems it is interesting to note that the ratio of scores between the two systems for each observer was approximately constant (in the range 1.46 to 1.82) irrespective of where the observer set his confidence thresholds. This suggests an increased performance using the new system although it is realized that this approach of evaluating the ratio is not strictly valid. Criticisms of the approach used here are worth mentioning so that the results obtained by LROC curve analysis should not be over-emphasized. The clinician who took part in the study found it difficult to make an assessment with only one view and with no clinical background. Also the large number of positives used in the study is certainly not representative of what we are used to. Furthermore the use of high-quality modern gamma cameras is tending to eliminate the need for static image processing by currently used data processing systems. Unprocessed analogue images cannot be appraised by the method although it is our belief that these images are better displayed on X-ray film rather than on Polaroid film. The results presented here are by no means exhaustive although it is feasible to use the same method of analysis with images other than brain scans. However it has increased our belief that changing our display format from a system using Polaroid film to one incorporating X-ray film has been worthwhile, not only because of reduced film cost but also because of an improved standard of image presentation.
X ray film
40
• •a 30
o - I
Observer
Score 51
Y
20
D
o*
/V
— o
32
• ••
31
v - -•-v
27
o-
y 10
D- •
'7
10
20 False
30
40
Positives
40
30
20
ACKNOWLEDGMENT
We should like to thank Dr. A. S. Houston for making available the brain scans and for his critical evaluation of the manuscript. REFERENCES CORFIELD, J. R., 1976. Development of a fast image enhancement filter for routine use. Proc. 13. Internationale Jahrestagung der Gessellschaft fur Nuclearmedezin E.V., Copenhagen, 1975.
10
10
20
30
40
CORFIELD, J. R., COX, N. J. and DIFFEY, B. L., 1978. A film
False Positives FIG. 2.
display system for routine imaging in nuclear medicine (unpublished).
LROC curves for the two display systems constructed using the method described by Houston and Macleod
GOODENOUGH, D. J., ROSSMAN, K. and LUSTED, L. E., 1974.
(1977).
578
Radiographic applications of receiver operating characteristic (ROC) curves. Radiology, 110, 89-95.
JULY 1979
Technical notes HENRY, C. A., LARSEN, P., TIFFANY, M., BARNES M., YOUDATH C. LEWIS C. and Di PAOLA P. 1973. A
comparison of photographic methods for clinical nuclear medicine. Journal ofNuclear Medicine 14 All.
tative data processing techniques using mathematical tumours and receiver operating characteristic analysis. Proceedings of a Symposium on medical radionuclide imaging, Los Angeles 1976 (IAEA, Vienna).
An inter-
MERRIGAN, J. A., SANDERSON, G. K. and MAILLE, J. R. A.,
comparison of computer assisted data processing and display methods in radioisotope scintigraphy using mathematical tumours. Physics in Medicine and Biology 22, 1097-1114 HOUSTON, A. S., 1977. An intercomparison of three quanti-
STARR, S. J., METZ, C. E., LUSTED, L. B. and GOODENOUGH,
HOUSTON A. S. and MACLEOD M. A.
1977.
1977. Selection of film for imaging in nuclear medicine. Medical Radiography and Photography, 53, 22-30. D. J., 1975. Visual detection and localization of radiographic images. Radiology, 116, 533-538.
Book review A User's Guide to Diagnostic Ultrasound. By. I. M. Shirley,to the neck of the pancreas whereas in fact the junction is R. J. Blackwell, G. Cusick, D. J. Farman, and F. R. Vicary, invariably posterior to the neck of the pancreas. Presumably pp. xxi + 329, illus., 1978 (Pitman Medical, London), £12-00. this mistake does not account for the author's admitted ISBN 0-272-79419-8 difficulty in imaging this organ, since they do not appear to The material for this user's guide derives from the ultra- use this landmark to identify this part of the pancreas which sound course at University College Hospital, London, and is highly regrettable since this is a fundamental step used by aims to familiarize the newcomer to ultrasound with the all practising ultrasonologists. Perhaps their outmoded use essential physical principles and limitations of the technique. of compound scanning is to blame for their lack of success in It is an excellent example in the presentation of physics for a pancreatic imaging—single pass scans should be used to give non-mathematical reader. Not only the basic principles, but the kind of resolution necessary for clinically useful scanning complex, though relevant concepts such as the operation of in the abdomen. In the discussion of the use of ultrasound in the scan convertor and the effect of various signal compres- jaundice, the bald statement that "dilated intrahepatic ducts sion characteristics on ultrasonic images are explained are usually well seen" is really of no use whatsoever. The verbally in lucid fashion with excellent diagrammatic sup- good results obtainable have been achieved by close and port. It provides a good entree into the mysteries of ultra- systematic observation of established criteria for the diagsound physics and the workings of all types of scanners nosis of duct dilatation and these should have been discussed. currently on the market. As is clearly pointed out in the text, A disturbingly sweeping statement occurs in the section on such an understanding is most helpful in persuading the the kidney, that renal cysts are easily detected. It is well machine to give of its best for any given diagnostic problem known in fact that there is considerable difficulty in deciding and a knowledge of the physics has its practical application whether or not a small (less than 2 cm) lesion is a simple in aiding the operator to disentangle the genuine from cyst, because of spurious echoes appearing within small fluid areas. The crucial point made by B. B. Goldberg that spurious (artefactual) echo images. The book's title leads the reader to expect more than a all the criteria for a cyst must be fulfilled before one can be guide to the physical basis of diagnostic ultrasound, although sure tha tone is not dealing with a partly cystic tumour seems only about one-third of the text is devoted to clinical ultra- to have been missed. The discussion on the poorly reflective sound. This of course is disproportionate and inadequate; tumour illustrated (Fig. 13.7) clinches this: such a lesion the authors of these sections could not be expected to give a should never be diagnosed as a cyst since it does not show comprehensive coverage in so short a space but their degree increased through transmission of sound. of success is uneven. Obstetrics is divided into elementary A sensible section on toxicity, or rather apparent lack of and advanced sections. Each is highly practical and the toxicity of diagnostic ultrasound follows, and then there is a description on how to measure fetal maturity by a BPD is rather less useful discussion on recording systems, spending especially well written. More complex diagnoses are dis- too much time on focusing problems, too little on exposure cussed and illustrated, although it is sad to see the safe and none at all on video recording systems. The calibration procedure of amniocentesis done under ultrasound control of B scanners is duly emphasized and a chapter gives a rendered less safe by the suggestion that it can be carried out bird's-eye view of the newer types of scanning systems in the obstetrics ward according to ultrasonic directions. The available including cine-sonar (real-time) scanners. degree of uterine rotation with posture and bladder filling As a straightforward account of the physics and instrucan be surprising! The section on ultrasound in gynaecology, mentation of diagnostic ultrasound, this book can be warmly though brief, is accurate but the findings in the upper recommended as in a class of its own and should be read by abdomen are treated so superficially as to be a real barrier to all would-be ultrasound diagnosticians. The clinical seca learner. For example, in the description of pancreatic tions, especially that dealing with the abdomen, cannot be scanning the crucial relationships of the neck of this organ to recommended but there are several recent textbooks that the superior mesenteric vessels contains an important error: give adequate coverage of this area. it is stated that the junction of the superior mesenteric vein DAVID O. COSGROVE. and the splenic vein to form the portal vein occurs anterior
579
JULY 1979
Technical notes
A comparison of two hard-copy display systems for nuclear medicine images By C. P. Wells, M.Sc, B. L Diffey, Ph.D., F. M. Hall, D.M.R.T. and M. Johnson, H.N.C. Departments of Medical Physics and Nuclear Medicine, Kent and Canterbury Hospital, Canterbury CT1 3NG (Received May, 1978 and in revised form September, 1978)
We recently changed our method of hard-copy CRT) and imaged onto 20x25 cm X-ray film display of nuclear medicine images from a system (Kodak Xomat XL1) by means of a Picker folded based upon the use of Polaroid film to one employing optics camera incorporating a X2.5 magnification 20 X 25 cm X-ray film. Although our subjective im- enlarging lens (Corfield et al., 1978). An example of pression indicated an improvement in image quality, each display is shown in Fig. 1. we also sought some objective means of assessing The displays were then presented to a clinician, a whether there was an improvement in detectability scanning technician and two physicists, all exof lesions. perienced in nuclear medicine. Each participant was The requirements of a film for nuclear medicine imaging were discussed by Merrigan et al. (1977). A comparison of four different films was undertaken by Henry et al. (1973) who based their conclusions on clinical impressions and the reliability of each system. The present communication presents the results of assessing one hundred brain scans using a method described by Houston and Macleod (1977). It should be emphasized that the present work set out to compare two display systems and is not a direct comparison between Polaroid and X-ray film as a display medium. METHOD
Houston (1977) has produced from departmental records a series of one hundred normal brain scans, one view per normal patient, obtained with a Nuclear Chicago (Searle) Pho Gamma III camera with a high resolution collimator interfaced to a Varian 620/L-100 minicomputer. Fifty "tumours" were added mathematically at selected positions to scintigrams in this series, no more than one to a view. These scans were transferred to a disk on our DEC PDP8/E minicomputer via 8-track paper tape. The purpose of this investigation was simply to assess whether the change from a display system using Polaroid film as the hard copy to one employing X-ray film had produced a significant improvement in detectability. To this end, each scintigram was enhanced using an "unsharp masking" filter (Corfield, 1976) and displayed on both media as in routine practice. Each image was displayed in core as a 64x64 matrix array with eight grey-scale levels. Images on Polaroid film (type 107) were obtained using a Shackman camera coupled to a slave video monitor. The images were also displayed on a point-plot display (a short persistence Hewlett-Packard 1332A
FIG. 1. An image of one of the computer-processed brain scans used in the intercomparison of X-ray film and Polaroid film. X-ray above, Polaroid below.
577
VOL.
52, No. 619 Technical notes
informed that no more than one tumour was present in any view and that the probability of an abnormal was 0.5. The order of presentation of each set, i.e. Polaroid or X-ray film, was varied. Each participant was then asked to rate the views using the five-scale category suggested by Goodenough et al. (1974), and to indicate the Cartesian co-ordinate of the suspected lesion. Localization receiver operating characteristic (LROC) curves (Starr et al., 1975) were generated for each set of results together with a
Display
-
points score described by Houston and Macleod (1977). The positional discrepancy allowed was 2 cm or 2\ times the tumour radius, whichever was greater. RESULTS AND DISCUSSION
The LROC curves together with the points score for each participant using the two different display systems are shown in Fig. 2. Although the absolute score showed a large variation between observers in each of the two systems it is interesting to note that the ratio of scores between the two systems for each observer was approximately constant (in the range 1.46 to 1.82) irrespective of where the observer set his confidence thresholds. This suggests an increased performance using the new system although it is realized that this approach of evaluating the ratio is not strictly valid. Criticisms of the approach used here are worth mentioning so that the results obtained by LROC curve analysis should not be over-emphasized. The clinician who took part in the study found it difficult to make an assessment with only one view and with no clinical background. Also the large number of positives used in the study is certainly not representative of what we are used to. Furthermore the use of high-quality modern gamma cameras is tending to eliminate the need for static image processing by currently used data processing systems. Unprocessed analogue images cannot be appraised by the method although it is our belief that these images are better displayed on X-ray film rather than on Polaroid film. The results presented here are by no means exhaustive although it is feasible to use the same method of analysis with images other than brain scans. However it has increased our belief that changing our display format from a system using Polaroid film to one incorporating X-ray film has been worthwhile, not only because of reduced film cost but also because of an improved standard of image presentation.
X ray film
40
• •a 30
o - I
Observer
Score 51
Y
20
D
o*
/V
— o
32
• ••
31
v - -•-v
27
o-
y 10
D- •
'7
10
20 False
30
40
Positives
40
30
20
ACKNOWLEDGMENT
We should like to thank Dr. A. S. Houston for making available the brain scans and for his critical evaluation of the manuscript. REFERENCES CORFIELD, J. R., 1976. Development of a fast image enhancement filter for routine use. Proc. 13. Internationale Jahrestagung der Gessellschaft fur Nuclearmedezin E.V., Copenhagen, 1975.
10
10
20
30
40
CORFIELD, J. R., COX, N. J. and DIFFEY, B. L., 1978. A film
False Positives FIG. 2.
display system for routine imaging in nuclear medicine (unpublished).
LROC curves for the two display systems constructed using the method described by Houston and Macleod
GOODENOUGH, D. J., ROSSMAN, K. and LUSTED, L. E., 1974.
(1977).
578
Radiographic applications of receiver operating characteristic (ROC) curves. Radiology, 110, 89-95.
JULY 1979
Technical notes HENRY, C. A., LARSEN, P., TIFFANY, M., BARNES M., YOUDATH C. LEWIS C. and Di PAOLA P. 1973. A
comparison of photographic methods for clinical nuclear medicine. Journal ofNuclear Medicine 14 All.
tative data processing techniques using mathematical tumours and receiver operating characteristic analysis. Proceedings of a Symposium on medical radionuclide imaging, Los Angeles 1976 (IAEA, Vienna).
An inter-
MERRIGAN, J. A., SANDERSON, G. K. and MAILLE, J. R. A.,
comparison of computer assisted data processing and display methods in radioisotope scintigraphy using mathematical tumours. Physics in Medicine and Biology 22, 1097-1114 HOUSTON, A. S., 1977. An intercomparison of three quanti-
STARR, S. J., METZ, C. E., LUSTED, L. B. and GOODENOUGH,
HOUSTON A. S. and MACLEOD M. A.
1977.
1977. Selection of film for imaging in nuclear medicine. Medical Radiography and Photography, 53, 22-30. D. J., 1975. Visual detection and localization of radiographic images. Radiology, 116, 533-538.
Book review A User's Guide to Diagnostic Ultrasound. By. I. M. Shirley,to the neck of the pancreas whereas in fact the junction is R. J. Blackwell, G. Cusick, D. J. Farman, and F. R. Vicary, invariably posterior to the neck of the pancreas. Presumably pp. xxi + 329, illus., 1978 (Pitman Medical, London), £12-00. this mistake does not account for the author's admitted ISBN 0-272-79419-8 difficulty in imaging this organ, since they do not appear to The material for this user's guide derives from the ultra- use this landmark to identify this part of the pancreas which sound course at University College Hospital, London, and is highly regrettable since this is a fundamental step used by aims to familiarize the newcomer to ultrasound with the all practising ultrasonologists. Perhaps their outmoded use essential physical principles and limitations of the technique. of compound scanning is to blame for their lack of success in It is an excellent example in the presentation of physics for a pancreatic imaging—single pass scans should be used to give non-mathematical reader. Not only the basic principles, but the kind of resolution necessary for clinically useful scanning complex, though relevant concepts such as the operation of in the abdomen. In the discussion of the use of ultrasound in the scan convertor and the effect of various signal compres- jaundice, the bald statement that "dilated intrahepatic ducts sion characteristics on ultrasonic images are explained are usually well seen" is really of no use whatsoever. The verbally in lucid fashion with excellent diagrammatic sup- good results obtainable have been achieved by close and port. It provides a good entree into the mysteries of ultra- systematic observation of established criteria for the diagsound physics and the workings of all types of scanners nosis of duct dilatation and these should have been discussed. currently on the market. As is clearly pointed out in the text, A disturbingly sweeping statement occurs in the section on such an understanding is most helpful in persuading the the kidney, that renal cysts are easily detected. It is well machine to give of its best for any given diagnostic problem known in fact that there is considerable difficulty in deciding and a knowledge of the physics has its practical application whether or not a small (less than 2 cm) lesion is a simple in aiding the operator to disentangle the genuine from cyst, because of spurious echoes appearing within small fluid areas. The crucial point made by B. B. Goldberg that spurious (artefactual) echo images. The book's title leads the reader to expect more than a all the criteria for a cyst must be fulfilled before one can be guide to the physical basis of diagnostic ultrasound, although sure tha tone is not dealing with a partly cystic tumour seems only about one-third of the text is devoted to clinical ultra- to have been missed. The discussion on the poorly reflective sound. This of course is disproportionate and inadequate; tumour illustrated (Fig. 13.7) clinches this: such a lesion the authors of these sections could not be expected to give a should never be diagnosed as a cyst since it does not show comprehensive coverage in so short a space but their degree increased through transmission of sound. of success is uneven. Obstetrics is divided into elementary A sensible section on toxicity, or rather apparent lack of and advanced sections. Each is highly practical and the toxicity of diagnostic ultrasound follows, and then there is a description on how to measure fetal maturity by a BPD is rather less useful discussion on recording systems, spending especially well written. More complex diagnoses are dis- too much time on focusing problems, too little on exposure cussed and illustrated, although it is sad to see the safe and none at all on video recording systems. The calibration procedure of amniocentesis done under ultrasound control of B scanners is duly emphasized and a chapter gives a rendered less safe by the suggestion that it can be carried out bird's-eye view of the newer types of scanning systems in the obstetrics ward according to ultrasonic directions. The available including cine-sonar (real-time) scanners. degree of uterine rotation with posture and bladder filling As a straightforward account of the physics and instrucan be surprising! The section on ultrasound in gynaecology, mentation of diagnostic ultrasound, this book can be warmly though brief, is accurate but the findings in the upper recommended as in a class of its own and should be read by abdomen are treated so superficially as to be a real barrier to all would-be ultrasound diagnosticians. The clinical seca learner. For example, in the description of pancreatic tions, especially that dealing with the abdomen, cannot be scanning the crucial relationships of the neck of this organ to recommended but there are several recent textbooks that the superior mesenteric vessels contains an important error: give adequate coverage of this area. it is stated that the junction of the superior mesenteric vein DAVID O. COSGROVE. and the splenic vein to form the portal vein occurs anterior
579
