1975, British Journal of Radiology, 48, 1038 Correspondence WILKINSON, I. M., BULL, J. W. D., DU BOULAY, G. H., MARSHALL, J., ROSS RUSSELL, R. W., and SYMON, L., 1969.
Regional blood flow in the normal cerebral hemisphere. Journal of Neurological Neurosurgerv and Psvchiatrv, 32, 367-378.
suggest that when purchasing scan-converter equipment two monitors should be obtained, one for viewing and one for photography, and also that the provision of a standard test pattern should be considered. Yours, etc., A. J. HALL. R. RAILTON.
THE EDITOR—SIR, RECORDING AND STORAGE OF ULTRASONIC GREY-SCALE IMAGES WITH A SCAN CONVERTER
Scan converters enable high-resolution grey-scale pictures to be obtained in ultrasonic examinations; the devices record in a non-integrating manner with only the peak value of an echo amplitude being recorded for any location, unlike storage oscilloscopes or short persistence oscilloscopes used with film. The ultrasound image information is converted to a 625-line television format, enabling standard monitors to be used for display and photographic recording; storage on video disc or videotape is also possible. The video disc allows the storage of a number of scans from a patient and thus assists in the selection of the most informative images for photography. Videotape has the same interactive possibilities but is not so convenient, as access to any image and comparison of selected images is more difficult. Consequently it appears that, even if either of these devices is used as an aid to the scanning process, the final recording medium is most likely to be negative or positive photographic film. This leads to consideration of the factors involved in obtaining the photographic record from a television monitor. The number of grey shades discernible in a picture depends on the observer and on the nature of the information ; for instance the perception of differing adjacent grey shades is enhanced if the boundary between them is clearly defined (Mach effect). No matter the criteria adopted for defining a grey shade, the number of shades is ultimately determined by the range of brightness from a black level to a white level, e.g. if a 2:1 variation is defined as one grey step and the range from black 7to white is 128:1, then seven shades can be perceived, as 2 = 128. Measurements on a standard television monitor, adjusted to give a visually pleasing picture, typically demonstrated a contrast range from peak white to background (black level) of 250:1. This figure was obtained using a universal photometer (Hagner SI) to measure the light intensities in the black and white areas of the screen. The test pattern was produced by inserting a step waveform into the scan converter signal path while sweeping the trace upwards in the time-position mode. As a static image is displayed it is now convenient to exploit the potential of a variety of films (both positive and negative) as the exposure conditions are readily adjustable. However, from the practical considerations of ease of development and patient identification, it is likely that for routine work at least, Polaroid* 107 will continue to be the film of choice. Consideration of the Polaroid characteristic curve (log exposure versus reflected density) reveals that a change in illumination (over the "straight line" portion of the film) of approximately 30 to 1 is sufficient to go from black to white—considerably less than the variation in brightness of the television monitor. Furthermore, the ratio of the intensities of reflected light from a Polaroid print is approximately 38:1 (2-5 per cent of a perfect reflector for black up to 95 per cent for white), and consequently there is no way in which the original brightness range can be reproduced. The monitor contrast can be adjusted to suit the 30:1 input capability of the Polaroid 107 film (most conveniently done using a grey-scale step wedge), but in this condition it is more difficult for the viewer to distinguish features so there is a temptation to increase the picture contrast. This conflict of operational settings leads us to *Trademark.
University of Glasgow, Ultrasonic Technology, Queen Mother's Hospital, Glasgow G3 8SH. West of Scotland Health Boards, Department of Clinical Physics and Bioengineering, 11 West Graham Street, Glasgow G4 9LF. THE EDITOR—SIR, ANGIOGRAPHIC FINDINGS OF A CHOLEDOCHAL CYST
In the case report on the angiographic findings of a choledochal cyst in an 18-year-old Chinese girl (Jacobs and Palubinskas, 1975) no mention is made that the patient also has recurrent pyogenic cholangitis. Dilated right and left hepatic ducts are illustrated though no explanation is advanced why this should be so. If it were due to obstruction by the cyst then all the intrahepatic ducts would be dilated. The operative cholangiogram shows that although the right and left hepatic ducts are dilated, the intrahepatic ducts are dilated proximally but taper rapidly towards the periphery. This feature is seen in recurrent pyogenic cholangitis (Fig. 1) and has been referred to as the arrow-head sign (Ho and Wesson, 1974).
FIG. 1. T tube cholangiogram in a 52-year-old Chinese female showing tapering of the intrahepatic ducts. The right and left hepatic ducts and the common bile duct are also dilated. (Courtesy of Charles C. Thomas and the Editor of the American Journal of Roentgenology.)
1038
1975, British Journal of Radiology, 48, 1039
DECEMBER 1975
Correspondence Recurrent pyogenic cholangitis is a disease with characteristic radiological manifestations (Wastie and Cunningham, 1973) occurring in South East Asia and in emigrants from these countries to North America and Europe. Yours, etc., M. L. WASTIE.
Department of Diagnostic Radiology, King's College Hospital, Denmark Hill, London SE5 9RS.
I would like to thank both you and Dr. Wastie for his very interesting and provocative letter. Yours, etc., R.JACOBS.
Department of Radiology, University of California, San Francisco 94110.
REFERENCES
REFERENCES
Ho, C. S., and WESSON, D. E., 1974. Recurrent pyogenic
cholangitis in Chinese immigrants. American Journal of Roentgenology, 122, 368-374.
Ho, C. S., and WESSON, D. E., 1974. Recurrent pyogenic
cholangitis in Chinese immigrants. American Journal of Roentgenology, 122, 368-374.
JACOBS, R. P., and PALUBINSKAS, A. J., 1975. Angiographic
findings of a choledochal cyst. British Journal of Radiology, 48, 51-52.
JACOBS, R. P., and PALUBINSKAS, A. J., 1975. Angiographic
findings of choledochal cyst. British Journal of Radiology, 48, 51-52.
WASTIE, M. L., and CUNNINGHAM, I. G. E., 1973. Roent-
genologic findings in recurrent pyogenic cholangitis.
WASTIE, M. L., and CUNNINGHAM, I. G. E., 1973. Roent-
genologic findings in recurrent pyogenic cholangitis.
American Journal of Roentgenology, 119, 71—77.
American Journal of Roentgenology, 119, 71—77'.
Editor's note—We are reprinting the following letter from Dr. G. M. Owen, which was originally published in BRITISH JOURNAL OF RADIOLOGY, July 1975, pages 610-611. UnforTHE EDITOR—SIR, ANGIOGRAPHIC FINDINGS OF A CHOLEDOCHAL CYST
Referring to the case report on the angiographic findings of a choledochal cyst, I appreciate the opportunity to reply to Dr. Wastie's letter and to investigate a disease entity (recurrent pyogenic cholangitis) with which I was unfamiliar. We feel that the patient we described (Jacobs and Palubinskas, 1975) did not have pyogenic cholangitis and that her radiographic findings are explicable by her choledochal cyst. Unlike patients with recurrent pyogenic cholangitis (Wastie and Cunningham, 1973), our patient had neither recurrent fevers nor chills. Bile which was withdrawn from her gall bladder and her choledochal cyst at the time of surgery exhibited no cells or bacteria by microscopic examination. Bile samples cultured for bacteria exhibited no growth. The choledochal cyst in our patient was drained of two litres of liquid green bile which did not contain concretions. No strictures, stones or sediment of any kind were seen in her biliary tree despite careful palpation and multiple cholangiograms at the time of surgery. The biliary tree of patients with recurrent pyogenic cholangitis is said to ". . . contain soft pigment stones, biliary mud or pus" (Wastie and Cunningham, 1973). Of the five patients described by Ho and Wesson (1974) four had fevers, five had biliary stones or sludge, four had organisms cultured from blood or bile. Our patient satisfied none of these criteria. Drs. Ho and Wesson (1974) noted the "arrow-head sign" in only one of their five patients. Though they state that recurrent pyogenic cholangitis has a "characteristic" radiologic appearance, Caroli's disease, sclerosing cholangitis and extrahepatic biliary obstruction are all included in their radiologic differential diagnosis. Can a radiologist definitively diagnose recurrent pyogenic cholangitis by evaluating only the calibre and shape of the bile ducts ? I know of no study in which the cholangiographic specificity of these observations has been critically investigated. We feel that: (1) tapering of peripheral intrahepatic ducts with dilated central ducts is a non-pathognomonic observation which may be seen with extrahepatic biliary obstruction; (2) our patient has a surgically proven choledochal cyst—an entity known to cause recurrent episodes of extrahepatic biliary obstruction; (3) the diagnosis of recurrent pyogenic cholangitis in our patient is clinically and bacteriologically untenable.
tunately at the last stage of correcting proofs of the original version we were over enthusiastic and edited out the very anomalies which were the original stimulus to Dr. Owen's letter. We apologise to the author for being, on this occasion, too consistent in dealing with s's and z's. THE EDITOR—SIR, TERMINOLOGY IN RADIATION PROTECTION
It is widely known that there is a high probability that the Euratom Treaty will shortly affect radiological protection (otherwise known as health physics or radiation safety) in hospitals, research establishments and medical schools throughout the United Kingdom. It is hoped that the various organizations concerned, which include the British Institute of Radiology, will take advantage of the opportunity and adopt a more uniform terminology in place of the variations used at present in the two "Codes of Practice", one issued by the Department of Health and Social Security and the other by the Department of Employment, and also the Universities Handbook (Committee of Vice-Chancellors and Principals). Although the three publications advocate very similar administrative structures, most of the possible combinations of relevant words are used (Table I). Notwithstanding the connotations of the 1920s, to most readers of your Journal, "radiology" is the work undertaken in diagnostic X-ray departments and does not refer to saturation analysis, radiotherapy and the safe disposal of radioactive waste. The word "radiation" includes these topics and many others. It is more difficult to choose between "safety" and "protection": although the links of the latter with unsavoury illegal practices may be an argument for using the former. The exact difference between an officer and an adviser are not at all obvious especially when the titles seem interchangeable ; the Department of Health and Social Security has a Radiological Protection Adviser and a Supervisory Medical Officer but the Department of Employment has a Safety Officer and a Medical Adviser. The types of radiation to be included are of course another matter of debate. The BRITISH JOURNAL OF RADIOLOGY publishes papers on ultra-
sonic radiation. Recently the N.R.P.B. undertook some responsibilities regarding safety from microwaves and lasers. In one report {Nature, 1974) there was an implication that the "R" in N.R.P.B. now stood for "radiation" although this may have been a printing error. In one ICRP report (ICRP, 1964) radionuclides are separated according to their toxicity into "groups". For a similar purpose the Department of Employment uses
1039
Regional blood flow in the normal cerebral hemisphere. Journal of Neurological Neurosurgerv and Psvchiatrv, 32, 367-378.
suggest that when purchasing scan-converter equipment two monitors should be obtained, one for viewing and one for photography, and also that the provision of a standard test pattern should be considered. Yours, etc., A. J. HALL. R. RAILTON.
THE EDITOR—SIR, RECORDING AND STORAGE OF ULTRASONIC GREY-SCALE IMAGES WITH A SCAN CONVERTER
Scan converters enable high-resolution grey-scale pictures to be obtained in ultrasonic examinations; the devices record in a non-integrating manner with only the peak value of an echo amplitude being recorded for any location, unlike storage oscilloscopes or short persistence oscilloscopes used with film. The ultrasound image information is converted to a 625-line television format, enabling standard monitors to be used for display and photographic recording; storage on video disc or videotape is also possible. The video disc allows the storage of a number of scans from a patient and thus assists in the selection of the most informative images for photography. Videotape has the same interactive possibilities but is not so convenient, as access to any image and comparison of selected images is more difficult. Consequently it appears that, even if either of these devices is used as an aid to the scanning process, the final recording medium is most likely to be negative or positive photographic film. This leads to consideration of the factors involved in obtaining the photographic record from a television monitor. The number of grey shades discernible in a picture depends on the observer and on the nature of the information ; for instance the perception of differing adjacent grey shades is enhanced if the boundary between them is clearly defined (Mach effect). No matter the criteria adopted for defining a grey shade, the number of shades is ultimately determined by the range of brightness from a black level to a white level, e.g. if a 2:1 variation is defined as one grey step and the range from black 7to white is 128:1, then seven shades can be perceived, as 2 = 128. Measurements on a standard television monitor, adjusted to give a visually pleasing picture, typically demonstrated a contrast range from peak white to background (black level) of 250:1. This figure was obtained using a universal photometer (Hagner SI) to measure the light intensities in the black and white areas of the screen. The test pattern was produced by inserting a step waveform into the scan converter signal path while sweeping the trace upwards in the time-position mode. As a static image is displayed it is now convenient to exploit the potential of a variety of films (both positive and negative) as the exposure conditions are readily adjustable. However, from the practical considerations of ease of development and patient identification, it is likely that for routine work at least, Polaroid* 107 will continue to be the film of choice. Consideration of the Polaroid characteristic curve (log exposure versus reflected density) reveals that a change in illumination (over the "straight line" portion of the film) of approximately 30 to 1 is sufficient to go from black to white—considerably less than the variation in brightness of the television monitor. Furthermore, the ratio of the intensities of reflected light from a Polaroid print is approximately 38:1 (2-5 per cent of a perfect reflector for black up to 95 per cent for white), and consequently there is no way in which the original brightness range can be reproduced. The monitor contrast can be adjusted to suit the 30:1 input capability of the Polaroid 107 film (most conveniently done using a grey-scale step wedge), but in this condition it is more difficult for the viewer to distinguish features so there is a temptation to increase the picture contrast. This conflict of operational settings leads us to *Trademark.
University of Glasgow, Ultrasonic Technology, Queen Mother's Hospital, Glasgow G3 8SH. West of Scotland Health Boards, Department of Clinical Physics and Bioengineering, 11 West Graham Street, Glasgow G4 9LF. THE EDITOR—SIR, ANGIOGRAPHIC FINDINGS OF A CHOLEDOCHAL CYST
In the case report on the angiographic findings of a choledochal cyst in an 18-year-old Chinese girl (Jacobs and Palubinskas, 1975) no mention is made that the patient also has recurrent pyogenic cholangitis. Dilated right and left hepatic ducts are illustrated though no explanation is advanced why this should be so. If it were due to obstruction by the cyst then all the intrahepatic ducts would be dilated. The operative cholangiogram shows that although the right and left hepatic ducts are dilated, the intrahepatic ducts are dilated proximally but taper rapidly towards the periphery. This feature is seen in recurrent pyogenic cholangitis (Fig. 1) and has been referred to as the arrow-head sign (Ho and Wesson, 1974).
FIG. 1. T tube cholangiogram in a 52-year-old Chinese female showing tapering of the intrahepatic ducts. The right and left hepatic ducts and the common bile duct are also dilated. (Courtesy of Charles C. Thomas and the Editor of the American Journal of Roentgenology.)
1038
1975, British Journal of Radiology, 48, 1039
DECEMBER 1975
Correspondence Recurrent pyogenic cholangitis is a disease with characteristic radiological manifestations (Wastie and Cunningham, 1973) occurring in South East Asia and in emigrants from these countries to North America and Europe. Yours, etc., M. L. WASTIE.
Department of Diagnostic Radiology, King's College Hospital, Denmark Hill, London SE5 9RS.
I would like to thank both you and Dr. Wastie for his very interesting and provocative letter. Yours, etc., R.JACOBS.
Department of Radiology, University of California, San Francisco 94110.
REFERENCES
REFERENCES
Ho, C. S., and WESSON, D. E., 1974. Recurrent pyogenic
cholangitis in Chinese immigrants. American Journal of Roentgenology, 122, 368-374.
Ho, C. S., and WESSON, D. E., 1974. Recurrent pyogenic
cholangitis in Chinese immigrants. American Journal of Roentgenology, 122, 368-374.
JACOBS, R. P., and PALUBINSKAS, A. J., 1975. Angiographic
findings of a choledochal cyst. British Journal of Radiology, 48, 51-52.
JACOBS, R. P., and PALUBINSKAS, A. J., 1975. Angiographic
findings of choledochal cyst. British Journal of Radiology, 48, 51-52.
WASTIE, M. L., and CUNNINGHAM, I. G. E., 1973. Roent-
genologic findings in recurrent pyogenic cholangitis.
WASTIE, M. L., and CUNNINGHAM, I. G. E., 1973. Roent-
genologic findings in recurrent pyogenic cholangitis.
American Journal of Roentgenology, 119, 71—77.
American Journal of Roentgenology, 119, 71—77'.
Editor's note—We are reprinting the following letter from Dr. G. M. Owen, which was originally published in BRITISH JOURNAL OF RADIOLOGY, July 1975, pages 610-611. UnforTHE EDITOR—SIR, ANGIOGRAPHIC FINDINGS OF A CHOLEDOCHAL CYST
Referring to the case report on the angiographic findings of a choledochal cyst, I appreciate the opportunity to reply to Dr. Wastie's letter and to investigate a disease entity (recurrent pyogenic cholangitis) with which I was unfamiliar. We feel that the patient we described (Jacobs and Palubinskas, 1975) did not have pyogenic cholangitis and that her radiographic findings are explicable by her choledochal cyst. Unlike patients with recurrent pyogenic cholangitis (Wastie and Cunningham, 1973), our patient had neither recurrent fevers nor chills. Bile which was withdrawn from her gall bladder and her choledochal cyst at the time of surgery exhibited no cells or bacteria by microscopic examination. Bile samples cultured for bacteria exhibited no growth. The choledochal cyst in our patient was drained of two litres of liquid green bile which did not contain concretions. No strictures, stones or sediment of any kind were seen in her biliary tree despite careful palpation and multiple cholangiograms at the time of surgery. The biliary tree of patients with recurrent pyogenic cholangitis is said to ". . . contain soft pigment stones, biliary mud or pus" (Wastie and Cunningham, 1973). Of the five patients described by Ho and Wesson (1974) four had fevers, five had biliary stones or sludge, four had organisms cultured from blood or bile. Our patient satisfied none of these criteria. Drs. Ho and Wesson (1974) noted the "arrow-head sign" in only one of their five patients. Though they state that recurrent pyogenic cholangitis has a "characteristic" radiologic appearance, Caroli's disease, sclerosing cholangitis and extrahepatic biliary obstruction are all included in their radiologic differential diagnosis. Can a radiologist definitively diagnose recurrent pyogenic cholangitis by evaluating only the calibre and shape of the bile ducts ? I know of no study in which the cholangiographic specificity of these observations has been critically investigated. We feel that: (1) tapering of peripheral intrahepatic ducts with dilated central ducts is a non-pathognomonic observation which may be seen with extrahepatic biliary obstruction; (2) our patient has a surgically proven choledochal cyst—an entity known to cause recurrent episodes of extrahepatic biliary obstruction; (3) the diagnosis of recurrent pyogenic cholangitis in our patient is clinically and bacteriologically untenable.
tunately at the last stage of correcting proofs of the original version we were over enthusiastic and edited out the very anomalies which were the original stimulus to Dr. Owen's letter. We apologise to the author for being, on this occasion, too consistent in dealing with s's and z's. THE EDITOR—SIR, TERMINOLOGY IN RADIATION PROTECTION
It is widely known that there is a high probability that the Euratom Treaty will shortly affect radiological protection (otherwise known as health physics or radiation safety) in hospitals, research establishments and medical schools throughout the United Kingdom. It is hoped that the various organizations concerned, which include the British Institute of Radiology, will take advantage of the opportunity and adopt a more uniform terminology in place of the variations used at present in the two "Codes of Practice", one issued by the Department of Health and Social Security and the other by the Department of Employment, and also the Universities Handbook (Committee of Vice-Chancellors and Principals). Although the three publications advocate very similar administrative structures, most of the possible combinations of relevant words are used (Table I). Notwithstanding the connotations of the 1920s, to most readers of your Journal, "radiology" is the work undertaken in diagnostic X-ray departments and does not refer to saturation analysis, radiotherapy and the safe disposal of radioactive waste. The word "radiation" includes these topics and many others. It is more difficult to choose between "safety" and "protection": although the links of the latter with unsavoury illegal practices may be an argument for using the former. The exact difference between an officer and an adviser are not at all obvious especially when the titles seem interchangeable ; the Department of Health and Social Security has a Radiological Protection Adviser and a Supervisory Medical Officer but the Department of Employment has a Safety Officer and a Medical Adviser. The types of radiation to be included are of course another matter of debate. The BRITISH JOURNAL OF RADIOLOGY publishes papers on ultra-
sonic radiation. Recently the N.R.P.B. undertook some responsibilities regarding safety from microwaves and lasers. In one report {Nature, 1974) there was an implication that the "R" in N.R.P.B. now stood for "radiation" although this may have been a printing error. In one ICRP report (ICRP, 1964) radionuclides are separated according to their toxicity into "groups". For a similar purpose the Department of Employment uses
1039
