•
225
TECHNICAL NOTES
VOl. 115
Technical Notes
• Light Fog on Radiographic Films: How to Measure it Properly 1 Joel E. Gray, B.S., M.S.
A simple step wedge imaging technique is described for the proper evaluation of light fog iri radiographic darkrooms. Tests indicate that this technique Is a more sensitive indicator of light fog than the conventional techn ique utilizIng unexposed film. ~ is recommended that fog tests be carried out in radiographic darkrooms annually to maintain optimum radiographic image contrast. INDEX TERMS:
Darkroom. Films. proces sing. Radiography. image process-
ing
Radiology 115:225-227, April 1975
•
•
A Technical Note recently published in this Journal (1) indicates that OA safelight with 60-100-watt " bug" lights (at an illumination level of four lux, t.e.. lurnens/m'') could be utilized in conjunction with conventional radiographic films for an inexpensive daylight processing system. Results are shown for unexposed films only, although the author states that , " We tested exposed and unexposed film ... " The conclusion that the " results showed the film to be 'safe' for a period of two minutes," although possibly correct if other data are considered, cannot be drawn from the data presented in that technical note. The purpose of the present study is to point out the problems associated with measuring the amount of light fog which would be acceptable in radiographic darkrooms and to describe the proper techniques for such determinations. Fog on radiographic film caused by non-ionizing radiation may originate from two sources, safelights and "unsafe " lights. Even the best safelights when improperly used with higher wattage bulbs, or closer to the film than recommended by the manufacturer, or with aged and faded safelight filters will produce perceptible fog on radiographs during the usual darkroom handling of films. Under the category of "unsafe " lights are such sources of fog as indicator lights on equipment in the darkroom, light leaks around doors and processors , in faulty cassettes. through perforated (acoustical) ceiling tile, and light emitted from luminous dials of timers and various other sources. The proper method of testing for light fog on radiographic film is to expose a step wedge on the film under normal radiographic conditions and then expose half of this step wedge image to the safe light conditions of the darkroom. In performing these tests , it is recommended that the photographic material be taken directly from a new box of film and loaded into the cassette in a darkroom with all safelights and indicator lights jurneo off and all other sources of light, such as luminous dials, covered with opaque material. Three such films should be exposed, with half of each step wedge image then exposed to the normal darkroom safelight conditions (including indicator lights, luminous dials, etc .) for periods of one, two, and four minutes. The resultant step wedges may be evaluated visually or with a densitometer. For visual comparison, there should be virtually no detectable density difference on any step of the wedge between the two halves of the
Fig. 1. Two step wedges, one with and one without fog exposure, showing the effect of fog at the mid-densities but with no significant fogging at the lower densities.
wedge. For densitometric evaluation, the fogged half of the wedge should not show more , on any step of the wedge, than a 0.05 increase in density compared to the half which was not fogged. Any darkroom which can pass the four minute test is in excellent condition. If your darkroom passes the two-minute test , but not the four-minute test, it is in good condition and should not be the source of light fog as long as the film bins are light-tight. If your darkroom does not pass the one minute test, it is time to check it for " unsafe" light; install new safelight filters. if the filters are over a year old or have been used with higher wattage bulbs than recommended: assure that all safe lights are a minimum of three feet from film-handling surfaces ; and be sure that you are using the proper bulbs with the recommended safelight filters (normally a 15-watt bulb is used with a No. 68 filter at a minimum distance of three feet). To locate light leaks, a person should spend approximately ten minutes in the darkroom with all safelights and indicator lights extinguished. After such a period of adaptation , it is relatively easy for the eye to detect the location of light leaks which are not normally visible, but which will readily fog radiographic films. Figure 1 is an example of a step wedge fog test in which
226
TECHNICAL NOTES
t
190
2.]0
~
12e
>- 1.00
~0
70 [
0, 50
l
r
c. JO
0.10 [
1 ~ oqq
i ny T i rT1€'
(~, i nu t e s }
Fig. 2. Density as a functionof fog time for DuPontCronex 4 radiographic film underNo. 68 sa/elights at nine lux, approximately four to six times the recommended illumination level.
3·00
2.50
2.00
~ 1.50
1.00
D.50
0.00 '--_ _--'-_ _---'-- _ _- - . i 0.00
0.50
1.00
1.50
'--_
2.00
Log Re 1a t i ve Expos u r e
Fig. 3. Characteristic curve of DuPont Cronex 4 film with no fog exposure and a 1.5 minute fog exposure indicating the decrease in contrast and increase in density for the fogged film. (Foggingconditions were the same as in Fig. 2.)
two step wedges were exposed, one being fogged and the other receiving no fog. It is apparent in the mid-densities that there is a considerable difference in the darkness of the corresponding steps. However, close examination of the low densities shows no visual difference in the darkness of the corresponding steps. In this case, the darkroom would have been declared "safe" if only the base-plus-fog and/or lowdensity levels were checked, but on examination of the middensities, it is obvious that the film is being fogged. Why is it necessary to use such a test? Photographic materials have a threshold level which causes the phenomenon shown in Figure 1. It takes approximately three visible light photons to make a grain of silver halide developable. The first few photons absorbed by the grain may have no effect on
April 1975
film darkening, while additional photons cause a rapid buildup in density. Consequently, subjecting an unexposed sheet of radiographic film to a low level of light may not cause any darkening of the film, but the addition of this same exposure to an area of radiographic film which has been, or will be exposed, will cause considerable darkening of the film. Figure 2 shows this effect graphically. Step wedges were exposed on DuPont Cronex 4 film and then half of each wedge image was exposed with a suitable safelight filter (No. 68) and a 15-watt bulb at a distance of one foot (at an illumination level of nine lux, approximately four to six times brighter than the recommended illumination levets)." This situation would appear safe for up to four minutes of fogging time if we base our decision on fogged samples of unexposed film. If we base our decision on the density of approximately 1.00, we find that in just slightly over 30 seconds we have added 0.05 in density to the step wedge exposure, while it takes about 45 seconds to add this density at a level of 0.52, and one minute to add this density at 2.70. This result is typical and indicates that the mid-densities (from approximately 0.50 to 2.00) are most sensitive to light fogging. Such an increase in mid-densities, while the lower and higher densities are not effected significantly, results in a decrease in contrast. The resultant fogged radiograph will have a somewhat lower contrast which will most likely be compensated for by the use of a slightly lower kVp, with a subsequent increased dose to the patient. The visual result will appear similar to scattered radiation on the radiograph. Since various types of film will not be fogged by the same amount, the contrast may vary inconsistently. In addition, fog will cause the radiograph to appear darker. If we compare the characteristic curves of two films (Fig. 3), one of which has been fogged for 1.5 minutes and one of which has received no fog exposure, the decrease in slope will be apparent. A shift of the curve to the left indicates that we will also see increased densities for the same radiographic exposure. In fact, in this particular case, the fog exposure is the equivalent of a 26 % increase in mAs for the mid-densities. Consequently, if your films are receiving even this relatively small amount of fog exposure, you may expect erratic results in terms of contrast and overall exposure. If you find that your darkroom is producing fogged films, it may be necessary to reduce the illumination levels. This usually causes considerable difficulty in film handling for the technologist. In order to compensate for the reduced illumination levels, all walls and surfaces in the darkroom may be painted white, and the black counter tops typically used in radiographic darkrooms may be replaced by white or stainless steel tops. If your darkroom is illuminated with the proper safelight filters, recommended wattage bulbs, and at the distances specified by the manufacturer, all surfaces may be white without causing fogging on radiographic films. Darkrooms with white surfaces, which have been properly illuminated according to the manufacturer's instructions, and have no sources of stray "unsafe" light, are visually similar to darkrooms in which dark surfaces are used with approximately eight times the recommended safelight levels. The radiographic effect with the recommended safe lights and white surfaces is the same as for the recommended safelight levels and dark surfaces.
227
TECHNICAL NOTES
Vol. 115
Technical Notes
SUMMARY
REFERENCE
A simple step wedge technique is described for the proper evaluation of light fog levels in radiographic darkrooms. A comparison of this technique to that normally utilized, using unexposed radiographic film, indicates that the step wedge technique is a more sensitive detector of the presence of contrast-lowering fog. The reduced radiographic contrast may be compensated for by decreasing the kVp, but this increases the dose to the patient. Consequently, light fog levels in radiographic darkrooms should be evaluated at least once a year to assure optimum radiographic contrast while helping to minimize patient exposure.
1. Gaynor LL, Irwin GAL: Is the darkroom necessary? Radiology 112:221-222,Jul1974
Abdominal Aorta Catheterization via the Left Axillary Art ery 1 James H. Glenn, M.D. A simple technique is described for catheterization of the abdominal aorta via the left axillary artery. A commercially available pigtail catheter is used to direct the guide wire toward the descending aorta, and the contrast material may be injected through this catheter. This method works well, even in elderly patients with elongated, tortuous aortas. Index terms: Aorta. Arteries, axillary. Catheters and catheterization Radiology 115:227-228, April 1975
1 From the Radiological Research Laboratories (J. E. G., Edward Christie Stevens Fellow in Radiological Sciences), Medical Sciences Bldg., University of Toronto, Toronto M5S 1AB, Canada. Accepted for publication in October 1974. 2 Due to differences in the spectral sensitivities between most light meters and radiographic films, the measurement of illumination levels is not a sufficient test. The best method of checking for safe levels of darkroom illumination is the step wedge method using the type of radiographic film utilized in that specificdarkroom. vb
The relatively small number of cases is due to the fact that we prefer the femoral approach to the abdominal aorta. The left axillary arterial approach is generally reserved for patients with absent or extremely weak femoral pulses. Sometimes the left axillary arterial approach was used following an unsuccessful attempt at catheterization via the femoral artery route. Most of the patients on whom the left axillary arterial approach was used had severe arteriosclerotic disease. Of these 24 patients, 18 had peripheral ischemia, and aortofemoral arteriography was performed; five had a known or suspected abdominal aortic aneurysm, and abdominal aortography was performed; and one had upper gastrointestinal bleeding, and abdominal aortography and selective celiac arteriography were performed. TECHNIQUE
Several techniques have been used in the past to pass a catheter via the left axillary artery route into the descending thoracic aorta and abdominal aorta. These have included the use of a double catheter (2, 6), a multiple-curve guide wire (4), and a deflector catheter (3). More recently, a report from our institution described a custom-made pigtail catheter which was used to direct the guide wire into the descending aorta (1), but which had to be exchanged for a straight catheter through which the injection into the abdominal aorta was made. In that report, the present author's method of using a standard pigtail catheter was briefly mentioned as being suitable for young or middle-aged patients with only moderate elongation of the aorta. This technique utilizes a standard, commercially available pigtail catheter and avoids the need to exchange catheters. It is described now in detail and, for the first time, case material is presented. It is proposed that this technique may be the method of choice for catheterizing the abdominal aorta via the left axillary route, even in elderly patients. CASE MATERIAL Twenty-four patients were examined by this method, either by the author or by radiology residents under his direct supervision. This technique, rapidly learned by radiology residents, was used regardless of the patients' ages which ranged from 48 to 86 years with a median of 63. Of these 24 patients, only 8 were below age sixty, 9 were in their seventh decade of life, 5 in their eighth, and 2 in their ninth.
This technique utilizes a 100-cm, 7.3 French pigtail catheter 2 (Fig. 1, A) which is wiped before use with a gauze sponge soaked in heparinized saline. To lessen stiffness, the ring of the pigtail is straightened three or four times while being wiped with the sponge. The left axillary artery is punctured with an arterial needle, and a wide-curved guide wire is passed through the left axillary and left subclavian arteries and into the aortic arch. The wide curve of the guide wire is helpful in redirecting the guide wire if an undesired vessel is entered on the way to the aortic arch. A 100-cm pigtail catheter is passed over the guide wire, and the ring of the catheter is placed just within the aortic arch, adjacent to the origin of the left subclavian artery. Further advancement into the aortic arch is avoided at this time because of the possibility the catheter will go in the direction of the ascending aorta. The guide wire is removed and a small amount of contrast material is injected by hand to determine that the catheter is in the proper position. The patient is then rotated about 20 0 toward the right posterior oblique position so as to "open up" the aortic arch to facilitate early passage of the guide wire and catheter in the correct direction. The pigtail catheter is rotated so that its loop is pointed in the direction of the descending aorta. (The torque control of this type of catheter facilitates this rotation.) The guide wire is then reinserted and advanced beyond the tip of the catheter. The wire initially extends toward the ascending aorta (Fig. 1, B). At this point, those unfamiliar with this technique may ro-
225
TECHNICAL NOTES
VOl. 115
Technical Notes
• Light Fog on Radiographic Films: How to Measure it Properly 1 Joel E. Gray, B.S., M.S.
A simple step wedge imaging technique is described for the proper evaluation of light fog iri radiographic darkrooms. Tests indicate that this technique Is a more sensitive indicator of light fog than the conventional techn ique utilizIng unexposed film. ~ is recommended that fog tests be carried out in radiographic darkrooms annually to maintain optimum radiographic image contrast. INDEX TERMS:
Darkroom. Films. proces sing. Radiography. image process-
ing
Radiology 115:225-227, April 1975
•
•
A Technical Note recently published in this Journal (1) indicates that OA safelight with 60-100-watt " bug" lights (at an illumination level of four lux, t.e.. lurnens/m'') could be utilized in conjunction with conventional radiographic films for an inexpensive daylight processing system. Results are shown for unexposed films only, although the author states that , " We tested exposed and unexposed film ... " The conclusion that the " results showed the film to be 'safe' for a period of two minutes," although possibly correct if other data are considered, cannot be drawn from the data presented in that technical note. The purpose of the present study is to point out the problems associated with measuring the amount of light fog which would be acceptable in radiographic darkrooms and to describe the proper techniques for such determinations. Fog on radiographic film caused by non-ionizing radiation may originate from two sources, safelights and "unsafe " lights. Even the best safelights when improperly used with higher wattage bulbs, or closer to the film than recommended by the manufacturer, or with aged and faded safelight filters will produce perceptible fog on radiographs during the usual darkroom handling of films. Under the category of "unsafe " lights are such sources of fog as indicator lights on equipment in the darkroom, light leaks around doors and processors , in faulty cassettes. through perforated (acoustical) ceiling tile, and light emitted from luminous dials of timers and various other sources. The proper method of testing for light fog on radiographic film is to expose a step wedge on the film under normal radiographic conditions and then expose half of this step wedge image to the safe light conditions of the darkroom. In performing these tests , it is recommended that the photographic material be taken directly from a new box of film and loaded into the cassette in a darkroom with all safelights and indicator lights jurneo off and all other sources of light, such as luminous dials, covered with opaque material. Three such films should be exposed, with half of each step wedge image then exposed to the normal darkroom safelight conditions (including indicator lights, luminous dials, etc .) for periods of one, two, and four minutes. The resultant step wedges may be evaluated visually or with a densitometer. For visual comparison, there should be virtually no detectable density difference on any step of the wedge between the two halves of the
Fig. 1. Two step wedges, one with and one without fog exposure, showing the effect of fog at the mid-densities but with no significant fogging at the lower densities.
wedge. For densitometric evaluation, the fogged half of the wedge should not show more , on any step of the wedge, than a 0.05 increase in density compared to the half which was not fogged. Any darkroom which can pass the four minute test is in excellent condition. If your darkroom passes the two-minute test , but not the four-minute test, it is in good condition and should not be the source of light fog as long as the film bins are light-tight. If your darkroom does not pass the one minute test, it is time to check it for " unsafe" light; install new safelight filters. if the filters are over a year old or have been used with higher wattage bulbs than recommended: assure that all safe lights are a minimum of three feet from film-handling surfaces ; and be sure that you are using the proper bulbs with the recommended safelight filters (normally a 15-watt bulb is used with a No. 68 filter at a minimum distance of three feet). To locate light leaks, a person should spend approximately ten minutes in the darkroom with all safelights and indicator lights extinguished. After such a period of adaptation , it is relatively easy for the eye to detect the location of light leaks which are not normally visible, but which will readily fog radiographic films. Figure 1 is an example of a step wedge fog test in which
226
TECHNICAL NOTES
t
190
2.]0
~
12e
>- 1.00
~0
70 [
0, 50
l
r
c. JO
0.10 [
1 ~ oqq
i ny T i rT1€'
(~, i nu t e s }
Fig. 2. Density as a functionof fog time for DuPontCronex 4 radiographic film underNo. 68 sa/elights at nine lux, approximately four to six times the recommended illumination level.
3·00
2.50
2.00
~ 1.50
1.00
D.50
0.00 '--_ _--'-_ _---'-- _ _- - . i 0.00
0.50
1.00
1.50
'--_
2.00
Log Re 1a t i ve Expos u r e
Fig. 3. Characteristic curve of DuPont Cronex 4 film with no fog exposure and a 1.5 minute fog exposure indicating the decrease in contrast and increase in density for the fogged film. (Foggingconditions were the same as in Fig. 2.)
two step wedges were exposed, one being fogged and the other receiving no fog. It is apparent in the mid-densities that there is a considerable difference in the darkness of the corresponding steps. However, close examination of the low densities shows no visual difference in the darkness of the corresponding steps. In this case, the darkroom would have been declared "safe" if only the base-plus-fog and/or lowdensity levels were checked, but on examination of the middensities, it is obvious that the film is being fogged. Why is it necessary to use such a test? Photographic materials have a threshold level which causes the phenomenon shown in Figure 1. It takes approximately three visible light photons to make a grain of silver halide developable. The first few photons absorbed by the grain may have no effect on
April 1975
film darkening, while additional photons cause a rapid buildup in density. Consequently, subjecting an unexposed sheet of radiographic film to a low level of light may not cause any darkening of the film, but the addition of this same exposure to an area of radiographic film which has been, or will be exposed, will cause considerable darkening of the film. Figure 2 shows this effect graphically. Step wedges were exposed on DuPont Cronex 4 film and then half of each wedge image was exposed with a suitable safelight filter (No. 68) and a 15-watt bulb at a distance of one foot (at an illumination level of nine lux, approximately four to six times brighter than the recommended illumination levets)." This situation would appear safe for up to four minutes of fogging time if we base our decision on fogged samples of unexposed film. If we base our decision on the density of approximately 1.00, we find that in just slightly over 30 seconds we have added 0.05 in density to the step wedge exposure, while it takes about 45 seconds to add this density at a level of 0.52, and one minute to add this density at 2.70. This result is typical and indicates that the mid-densities (from approximately 0.50 to 2.00) are most sensitive to light fogging. Such an increase in mid-densities, while the lower and higher densities are not effected significantly, results in a decrease in contrast. The resultant fogged radiograph will have a somewhat lower contrast which will most likely be compensated for by the use of a slightly lower kVp, with a subsequent increased dose to the patient. The visual result will appear similar to scattered radiation on the radiograph. Since various types of film will not be fogged by the same amount, the contrast may vary inconsistently. In addition, fog will cause the radiograph to appear darker. If we compare the characteristic curves of two films (Fig. 3), one of which has been fogged for 1.5 minutes and one of which has received no fog exposure, the decrease in slope will be apparent. A shift of the curve to the left indicates that we will also see increased densities for the same radiographic exposure. In fact, in this particular case, the fog exposure is the equivalent of a 26 % increase in mAs for the mid-densities. Consequently, if your films are receiving even this relatively small amount of fog exposure, you may expect erratic results in terms of contrast and overall exposure. If you find that your darkroom is producing fogged films, it may be necessary to reduce the illumination levels. This usually causes considerable difficulty in film handling for the technologist. In order to compensate for the reduced illumination levels, all walls and surfaces in the darkroom may be painted white, and the black counter tops typically used in radiographic darkrooms may be replaced by white or stainless steel tops. If your darkroom is illuminated with the proper safelight filters, recommended wattage bulbs, and at the distances specified by the manufacturer, all surfaces may be white without causing fogging on radiographic films. Darkrooms with white surfaces, which have been properly illuminated according to the manufacturer's instructions, and have no sources of stray "unsafe" light, are visually similar to darkrooms in which dark surfaces are used with approximately eight times the recommended safelight levels. The radiographic effect with the recommended safe lights and white surfaces is the same as for the recommended safelight levels and dark surfaces.
227
TECHNICAL NOTES
Vol. 115
Technical Notes
SUMMARY
REFERENCE
A simple step wedge technique is described for the proper evaluation of light fog levels in radiographic darkrooms. A comparison of this technique to that normally utilized, using unexposed radiographic film, indicates that the step wedge technique is a more sensitive detector of the presence of contrast-lowering fog. The reduced radiographic contrast may be compensated for by decreasing the kVp, but this increases the dose to the patient. Consequently, light fog levels in radiographic darkrooms should be evaluated at least once a year to assure optimum radiographic contrast while helping to minimize patient exposure.
1. Gaynor LL, Irwin GAL: Is the darkroom necessary? Radiology 112:221-222,Jul1974
Abdominal Aorta Catheterization via the Left Axillary Art ery 1 James H. Glenn, M.D. A simple technique is described for catheterization of the abdominal aorta via the left axillary artery. A commercially available pigtail catheter is used to direct the guide wire toward the descending aorta, and the contrast material may be injected through this catheter. This method works well, even in elderly patients with elongated, tortuous aortas. Index terms: Aorta. Arteries, axillary. Catheters and catheterization Radiology 115:227-228, April 1975
1 From the Radiological Research Laboratories (J. E. G., Edward Christie Stevens Fellow in Radiological Sciences), Medical Sciences Bldg., University of Toronto, Toronto M5S 1AB, Canada. Accepted for publication in October 1974. 2 Due to differences in the spectral sensitivities between most light meters and radiographic films, the measurement of illumination levels is not a sufficient test. The best method of checking for safe levels of darkroom illumination is the step wedge method using the type of radiographic film utilized in that specificdarkroom. vb
The relatively small number of cases is due to the fact that we prefer the femoral approach to the abdominal aorta. The left axillary arterial approach is generally reserved for patients with absent or extremely weak femoral pulses. Sometimes the left axillary arterial approach was used following an unsuccessful attempt at catheterization via the femoral artery route. Most of the patients on whom the left axillary arterial approach was used had severe arteriosclerotic disease. Of these 24 patients, 18 had peripheral ischemia, and aortofemoral arteriography was performed; five had a known or suspected abdominal aortic aneurysm, and abdominal aortography was performed; and one had upper gastrointestinal bleeding, and abdominal aortography and selective celiac arteriography were performed. TECHNIQUE
Several techniques have been used in the past to pass a catheter via the left axillary artery route into the descending thoracic aorta and abdominal aorta. These have included the use of a double catheter (2, 6), a multiple-curve guide wire (4), and a deflector catheter (3). More recently, a report from our institution described a custom-made pigtail catheter which was used to direct the guide wire into the descending aorta (1), but which had to be exchanged for a straight catheter through which the injection into the abdominal aorta was made. In that report, the present author's method of using a standard pigtail catheter was briefly mentioned as being suitable for young or middle-aged patients with only moderate elongation of the aorta. This technique utilizes a standard, commercially available pigtail catheter and avoids the need to exchange catheters. It is described now in detail and, for the first time, case material is presented. It is proposed that this technique may be the method of choice for catheterizing the abdominal aorta via the left axillary route, even in elderly patients. CASE MATERIAL Twenty-four patients were examined by this method, either by the author or by radiology residents under his direct supervision. This technique, rapidly learned by radiology residents, was used regardless of the patients' ages which ranged from 48 to 86 years with a median of 63. Of these 24 patients, only 8 were below age sixty, 9 were in their seventh decade of life, 5 in their eighth, and 2 in their ninth.
This technique utilizes a 100-cm, 7.3 French pigtail catheter 2 (Fig. 1, A) which is wiped before use with a gauze sponge soaked in heparinized saline. To lessen stiffness, the ring of the pigtail is straightened three or four times while being wiped with the sponge. The left axillary artery is punctured with an arterial needle, and a wide-curved guide wire is passed through the left axillary and left subclavian arteries and into the aortic arch. The wide curve of the guide wire is helpful in redirecting the guide wire if an undesired vessel is entered on the way to the aortic arch. A 100-cm pigtail catheter is passed over the guide wire, and the ring of the catheter is placed just within the aortic arch, adjacent to the origin of the left subclavian artery. Further advancement into the aortic arch is avoided at this time because of the possibility the catheter will go in the direction of the ascending aorta. The guide wire is removed and a small amount of contrast material is injected by hand to determine that the catheter is in the proper position. The patient is then rotated about 20 0 toward the right posterior oblique position so as to "open up" the aortic arch to facilitate early passage of the guide wire and catheter in the correct direction. The pigtail catheter is rotated so that its loop is pointed in the direction of the descending aorta. (The torque control of this type of catheter facilitates this rotation.) The guide wire is then reinserted and advanced beyond the tip of the catheter. The wire initially extends toward the ascending aorta (Fig. 1, B). At this point, those unfamiliar with this technique may ro-
