Australas Radio1 1992; 36: 234-237

An Evaluation of the Effect of Processing Conditions on Mammographic Film Contrast, Fog Levels and Speed DONALD McLEAN, M.Appl.Sc. The University of Sydney, Faculty of Health Sciences School of Medical Radiation Technology, Lidcombe NSW 2141 Australia.

ABSTRACT While it is well established that extended development times an d temperatures will increase mammographic film contrast and speed (l), little work has been done to date in extending this work to encompass all common screen-film types and to study the effect of processing chemistry variations on contrast speed results. This paper reports on four locally available mammographic films which, after exposure in conditions that closely simulate clinical conditions, have been developed with four different development chemicals as a function of development temperature and time. Three development times were used (23, 32 and 42 seconds) in combination with f o u r development temperatures (32,34, 36 and 38 degrees). The results support the previousl y published result of increased speed and contrast with extending development time and temperature. It was further found that, for some film types, the film contrast varied significantly over film density when developed with extended processing. Other film types, however, maintained high contrasts over large film density ranges. In some cases the increased contrast was accompanied by elevated film fog levels. T h e development of mam mo g rap h ic

Key words: mammography, processing film-screen, quality control Address for correspondence: Donald McLean The University of Sydney Faculty of Health Sciences School of Medical Radiation Technology Lidcombe NSW 2141 Australia

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films in non recommended chemistries p ro d u c e d v a r y in g results, mostly detrimental, which d emo n s tr a te d t h a t selection of development chemistry as well as optimal development times and temperatures, is critical for good film performance. INTRODUCTION Screen-film mammography is recognised as the modality of choice for the early detection of breast cancer in women (2). Cancer detection rates, both overseas and locally (3, 4), have demonstrated the effectiveness of mammographic screening programmes with effective quality assurance programmmes (5). Clinical experience has demonstrated the diagnostic advantage attainable through the use of extended processing (6) with scientific experimentation quantifying the sensitometric advantages thereby gained (1). While this early work introduced the principle of extended processing to mammography, the advent of many mammographic films with differing emulsion characteristics using different development chemistries implies that the specific application of processing conditions to the clinical environment requires further consideration. This paper reports on a recent set of experiments which compared the response of four mammographic films when processed with a variety of development temperatures and times for four development chemistries. MATERIALS AND METHOD The films used were selected and provided by the agents of four mammographic film manufacturers in Australia (Table 1). The films were exposed under conditions best simulating clinical conditions (7) with the use of intensification screens also selected and supplied by the film agents (Table 1). The films were handled in a safely lit darkroom and sliced in half, allowing two different films to be exposed simultaneously in a film cassette. A sensitometric step wedge was produced on the film by use of a calibrated delrin step wedge described previously (8). The X-ray unit used

was a GEC unit with a Dynamax MMX-HD X-ray tube. Exposures were made at 28 kVp with the beam quality being monitored by a RMI 232 kVp meter. The tube output was recorded by an mdh 2025 dosimeter with a 20x5-6M ionization chamber calibrated at the Australian Radiation Laboratories. TABLE 1 Film - Screen Combinations Investigated - Du Pont Microvision with Min-R Screens - Kodak SO-177 with Min-R Screens - Fuji MI-MA with Fuji Marnmo Fine Screens - Agfa MR3-I1 with MR Detail Screens

The films were processed though a Du Pont T5A processor, which had the facility to select three development times (23, 32 and 42 seconds). Film samples were developed at the temperatures of 32, 34, 36 and 38 degrees for each development time. The developer and fixer chemistries were automatically replenished according to the film area developed. Four experimental runs were made, one for each of the development chemistries as supplied by the manufacturer (Table 2). Du Pont XMF fixer was used for all films except for the run using Kodak developer, where Kodak fixer was used on request. On conclusion of an experimental run, the chemistry was neutralised with Ilford neutraliser and the discarded after 20 minutes of agitation. This was followed by two water rinses of the development tank ensuring the processor was thoroughly clean for future use. TABLE 2 Processor Chemistries Used - Du Pont HSD - Kodak Rp Xomat -Fuji RD3 - Agfa G138c

Submitted for publication on: 17th September, 1991 Accepted for publication on: 21st January, 1992

Australasian Radiology, Vol. 36, No. 3, August, 1992

AN EVALUATION OF THE EFFECT OF PROCESSING CONDITIONS ON MAMMOGRAPHIC FILM CONTRAST SYSTEM 3 AT 36 DEGREES V S . DEV. TIME Characteristic Curve Gamma Curve

SYSTEM 1 AT 36 DEGRKES VS. DEV. TIME Characteristic C u r v e Gamma Curve I

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SYSTEM 2 AT 36 DEGREES VS. DEV. TIME Characteristic Curve Gamma Curve

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The processed film step wedge patterns were read on a Macbeth TD902 densitometer and entered into a computer programme which calculated sensitometric parameters, reported elsewhere (8), and displayed the characteristic and gamma curves for the films under the conditions tested. RESULTS Figure 1 shows the effect of extended development time for the four films when processed in their own development chemistries at 36 degrees. For all screen-film systems it is seen that extended development time increases the speed of the system. The effects on contrast are of more interest. Screen-film system 1 shows the greatest improvement in contrast with longer development times. For 42 seconds development the contrast is maximal and remains high for a large density range on the film. System 2, conversely, shows little change in contrast as development time increases, with the film having reached full contrast after 32 seconds. System 3 displays a contrast density (gamma) curve which was characteristic of this film in all processing conditions. A high contrast peak is attained at an optical density of approximately one, particularly with extended processing. Australasian Radiology, Vol. 36, No. 3 , August, I992

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FIGURES 1A and 1B - Characteristic curves and gamma curves for each screen-film system developed in its own chemistry as a function of development time. The screen-film systems are (a) system 1, (b) system 2, (c) system 3 and (d) system 4.

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SYSTEM 4 AT 36 DEGREES VS. DEV. TIME Characteristic Curve Gamma Curve

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FIGURES 1C AND 1D.

This high contrast subsequently diminishes for film densities of two or higher where a twenty five percent drop off in contrast is experienced. Extended processing with system 4 results in large speed gains, with only small gains in film contrast. The effect of development temperature change on the screen-film systems is seen in Figure 2. At 32 degrees, low film speed and contrast indicates a lower limit for development temperatures. All films had maximal speed at 38 degress, but at this temperature elevated base plus fog levels were expenenced. This was a particular problem for system 3 which also had elevated fog levels at the lower temperature of 36 degrees. System 1, (Figure 2A), had significantly enhanced contrast at 36 degrees, while at 38 degrees the contrast becomes peaked with a reduction in contrast at higher densities. System 2 showed a slight increase in contrast with temperature up to 36 degrees, with 38 degrees giving a significant contrast increase. System 3 displays its characteristic gamma curve with very high and peaked contrast at 38 degrees. System 4 differs from the other systems as it attains peak contrast at 36 degrees with the contrast actually decreasing for 38 degrees. This screen-film system also had the least evidence of ele-

vated fog levels at high development temperatures. The high base plus fog levels, seen particularly at 38 degrees, were compared with mammographic film from system 1 exposed to excessive darkroom safe light irradiation. Figure 3 shows that in this case increased fog levels were accompanied by depressed contrast levels throughout the film density range. This commonly experienced result for film fogging should not be confused with the film fog received from extended processing where, as already seen, the film fog is associated with increased contrast levels. While the results of extending processing largely follow expected patterns when the film is developed in its designated chemistry, the effect of development in different or foreign chemistry, is dependent on the particular case examined as seen in Figure 4. Screen-film system 1, when developed in its own chemistry, is seen to have high contrast over a large density range, while the other ‘foreign’ films do not attain their full contrast potentials. This effect is even more pronounced with chemistry 2, where screen-film system 2 shows high contrast over a large density range. A similar effect was seen for system 4. 235

DONALD McLEAN SYSTEM 1 AT 42 S E C . DEV. TIME VS. TEMPERATURE Characteristic Curve G a m m a Curve

SYSTEM 3 AT 42 S E C . DEV. TIME VS. TEMPERATURE Characteristic Curve G a m m a Curve

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SYSTEM 2 AT 42 S E C . DEV. TIME VS. T E M P E R A T U R E Characteristic Curve G a m m a Curve

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SYSTEM 4 AT 42 S E C . DEV. TIME VS. TEMPERATURE G a m m a Curve Characteristic Curve 4,

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FIGURE 3 - Characteristic curves and gamma curves for film I developed in its own chemistry as a function of darkroom safelight illumination time.

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maximum contrast after 32 seconds. System 3 characteristically displays a higher contrast magnitude over a short density range with extended development, which would be expected to have clinical implications for the higher density regions of the

Screen-fi1m s y s t e m s * when processed in their recommended development chemistries, show increased system speed as times Or temperatures were increased. The effect of development time on contrast, however, varied with the type Of system used. System 1 showed the greatest increase in contrast magnitude and range with extended development time, while system 2 appears to have attained

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FIGURES 2C and D.

mammogram.

SYSTEM 1 AT 35 DEGREES 23 SEC. VS. FOG TIMES Gamma Curve Characteristic Curve

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FIGURES 2A and B - Characteristic curves and gamma curves for each screen-film system developed in its own chemistry as a function of development temperature. The screen-film systems are (a) system 1, (b) system 2.(c) system 3 and (d) system 4.

Systems 3 and 4 however show poor contrast in this developer. Developer chemistries 3 and 4 allowed high contrasts for all film types, with screenfilm system 1 displaying superior contrast compared with other systems in developer 3, while in developer 4 screen-film system 3 exhibited a very high contrast. Once again system displayed the characteristic contrast density curve seen earlier, demonstrating that this effect was a product of the film emulsion rather than the development chemistry.

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Higher development temperatures also increase system contrast. However the application of these temperatures seems limited due to elevated fog levels seen with all systems with the exception of system 4.At 38 degrees film noise was visually apparent which may further re i t r i 6t- c 1in i c a 1 a p p 1i c a t i on and requires further investigation. System 3 showed pronounced fogging effects, even at 36 degrees, but this screenfilm system did perform with high contrast and speed at 34 degrees and may, after the required sensitometric testing, be advantageously used at this temperature. The results of the above experiments clearly shows that the correct selection of development chemistry is critical for optimal-contrast and speed results. Chemistries 3 and 4 appeared to allow all films to attain a high contrast result at extended processing. Chemistries 1 and 2 had a very adverse effect On non recommended films. It is of interest that in chemistry

Australasian Radiology. Vol. 36, N o . 3. August. I992

AN EVALUATION OF THE EFFECT OF PROCESSING CONDITIONS ON MAMMOGRAPHIC FILM CONTRAST CHEMISTRY 1 AT 36 D E G R E E S 42 S E C . VS. FILM T Y P E Characteristic Curve G a m m a Curve

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FIGURES 4A and B - Characteristic curves and gamma curves for all screen-film systems developed in each of the development chemistries. The development time was 4 2 seconds at 3 6 degrees in all cases. The developer chemistries used were (a) developer chemistry 1, (b) developer chemistry 2, (c) developer chemistry 3 and (d) developer chemistry 4.

3, film 1 performs well, while in chemistry 4 film 3 performs well.

CONCLUSION All mammographic screen-film systems tested increased in speed with extended processing times. The effect of extended processing on film contrast, although generally increasing contrast, varied according to the type of film used, with some film types being more critically dependent on development time. No films performed optimally at 38 degrees, but most films appeared to operate best at higher temperatures. The use of an appropriate development chemistry was found to be critical, with non recommended chemistries proving satisfactory in only a limited number of cases. While the above results highlighted differences between screen-film systems with regard to their contrast and speed due to extended processing, it should be appreciated that film emulsions and deveIopment chemicals are being revised continually and that

Australasian Radiology, Vol. 36, No. 3,August, 1992

Optical Density

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CHEMISTRY 4 AT 36 DEGREES 42 SEC. VS. FILM T Y P E Characteristic Curve G a m m a Curve

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CHEMISTRY 2 AT 36 DEGREES 42 SEC. VS. FILM T Y P E Characteristic Curve G a m m a Curve

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CHEMISTRY 3 AT 36 DEGREES 42 S E C . VS. FILM T Y P E Characteristic Curve G a m m a Curve 4 1

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FIGURES 4C and D.

films of the same name may behave quite differently depending on their time of manufacture. For this reason it is recommended that once the important decision of film and developer selection has been made, time be set aside for a sensitometric evaluation of the processing system in order to identify the processing time and temperature which gives optimal contrast and speed for the mammographic process. ACKNOWLEDGEMENT I would like to acknowledge the help provided by Mr Peter Carmody and Mr Ken Jackson of Du Pont Australia in providing the use of their processing facilities, film and chemistry and to Mr Ken Walters who assisted in the preparation of development chemistries, experimental method and densitometric readings. I would also like to thank Mr Roy Anelzark and Mr David Crosby from Agfa Gavaert, Mr John Dean from Kodak and Mr John Petit from Fuji who provided encouragement and supplied film and chemicals for this project.

REFERENCES 1. Tabar L and Haus AG. Processing of mammographic films: technical and clinical considerations. Radiology 1989; 173: 65-69. 2. AIH. Screening mammography technology. Health Care Technology Series No 3. 1990; Aust. Insitute of Health. 3. Tabar L and Dean PB. The control of breast cancer through mammographic screening. What is the evidence? Radio1 Clinics of North Am 1987; Vol25(5): 993-1005. 4. Rickard MT,Lee W, Read JW et al. Breast cancer diagnosis by screening marnmography: early results of the Central Sydney Area Health Service Breast X-ray Programme. Med J Aust 1991; Vol 154(2): 126-131. 5. ACPSEM Position Paper. A quality assurance programme for mass screening in mammography. Aust Phys & Eng Sc in Med 1989; 12(4): 252-259. 6. Tabar L, and Dean PB. Basic principles of mammographic diagnosis. Diag h a g Clin Med 1985; 54: 146-157. 7. Haus AG and Dickerson RE. Problem associated with simulated light sensitometry for low-crossover medical x-ray films. Med Phys 1990; 17(4): 691-695. 8. McLean D. Sensitometric evaluation of some mammographic film-screen combinations. Aust Phys & Eng Sc in Med 1991; 14(3): 157-162.

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An evaluation of the effect of processing conditions on mammographic film contrast, fog levels and speed.

While it is well established that extended development times and temperatures will increase mammographic film contrast and speed (1), little work has ...
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