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British Journal of Radiology (2004) 77, 666-671
© 2004 British Institute of Radiology
doi: 10.1259/bjr/13566913
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Variation of the sensitometric characteristics of seven mammographic films with processing conditions

I A Tsalafoutas, PhD1, A D Dimakopoulou, MSc2, E D Koulentianos, MD, PhD3, A N Serefoglou, MD, PhD2 and E N Yakoumakis, PhD2

1 Medical Physics Unit and 3 Radiology Department "Konstantopoulio - Agia Olga" Hospital, 3–5 Agias Olgas, Nea Ionia, 142 33, Athens and 2 Medical Physics Department, Medical School, University of Athens, 75 Mikras Asias, 115 27, Athens, Greece

Correspondence: Dr E Yakoumakis, Department of Medical Physics, Medical School, University of Athens, 75 Mikras Asias, 115 27, Athens, Greece


   Abstract
Top
 Abstract
Introduction
 Materials and methods
 Results
 Discussion
 References
 
The effect of different processing conditions on the sensitometric characteristics of mammographic films was investigated and the implications of this effect on clinical practice are discussed. Three Agfa (MR5-II, HDR and HT), two Kodak (MinR-M, MinR-2000), one Fuji (AD-M) and one Konica (CM-H) single emulsion mammographic films were used. For each film type a 21-step sensitometric strip was developed in seven different processing conditions involving the use of four processors, five developing times and four chemistries. The different processing conditions produced a variable effect on the sensitometric characteristics of the mammographic films. While some films seemed relatively insensitive, others were greatly affected. Furthermore, not all the sensitometric parameters of a film were affected in the same way. For example, a change of processing conditions in some cases increased speed and decreased contrast but in some other cases increased both speed and contrast. Different mammographic films present different sensitometric characteristics that can be altered by processing conditions. Thus, in a mammographic facility any change in film processor/processing cycle or chemistry should be carefully investigated before mammograms of patients are acquired. Furthermore, the results of film comparisons under certain processing conditions should not be generalized to other processing conditions.


   Introduction
Top
 Abstract
 Introduction
Materials and methods
 Results
 Discussion
 References
 
Mammography is an examination with very high quality standard requirements [1]. The high radiosensitivity of the breast and the use of mammography for screening of asymptomatic women for breast cancer, have promoted research for better intensifying screens and films for mammography. As a result, numerous studies have been published investigating the characteristics of films or film–screen combinations manufactured for mammography.

It is well known that the sensitometric characteristics of a mammographic film are primarily determined by the film design. Manufacturers often introduce new films with special properties or revise older films in order to improve their clinical performance [2–4]. While it is the manufacturer's intention that a given film type will always have a predetermined sensitometric behaviour, differences from batch to batch have been reported [5].

However, film design is not the only parameter that determines its performance, since it is also known that the processing conditions can affect the film characteristics. The developing time, the developing chemicals and their temperature are some of the factors that have been reported to affect the sensitometric characteristics of the mammographic films [4, 6]. The processor design is also important, as depending on the developer tank capacity and the design of the film transporting system, the time that the film is immersed into the developer solution may vary among processors with the same nominal developing time.

Many different processing chemicals as well as processors are commercially available. Most new processors have an option of varying not only the developer temperature but also the processing cycle, thus changing the developing time. Chemical and processor manufacturers offer products dedicated for mammography. However, it is not uncommon for radiology departments to use the same processor for both radiological and mammographic film processing. Thus, a given type of mammographic film at different mammographic facilities will be processed under quite different processing conditions that may significantly alter the sensitometric characteristics provided by the manufacturers in the data product sheets.

In this study seven mammographic films were processed under different processing conditions and the effect of the different processors, developing times and chemicals used on the sensitometric characteristics of each film type was investigated.


   Materials and methods
Top
 Abstract
 Introduction
 Materials and methods
Results
 Discussion
 References
 
The seven single emulsion mammographic films used in this study were the MR5-II, HDR and HT (Agfa-Gevaert N.V., Mortsel, Belgium), MinR-M and MinR-2000 (Eastman Kodak Company, New York, NY), AD-M (Fuji Photo Film Co. Ltd, Tokyo, Japan) and CM-H (Konica Corporation, Tokyo, Japan). One box of each film type was used to avoid any differences that may exist among films from different batches [5].

A sensitometer (X-Rite 334; X-Rite, Grandville, MI) operated in the green spectrum was used to produce a 21-step sensitometric strip. One sensitometric strip from each film type was processed, immediately after exposure, under seven different processing conditions assigned with the codes A, B, C1, C2, D1, D2 and D3 as described in Table 1Go.


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  		Table 1. Details of the different processing conditions used for the sensitometric evaluation of the seven mammographic films included in our study

 
For the sensitometric controls relating to the first three processors the existing chemicals were used, whereas for those made with the Mamoray MR processor (where chemicals from two different companies were tested) each test was performed with fresh chemicals. It should be noted that the Mamoray MR is a table processor specially designed for mammography with two consecutive developer tanks of small capacity (1.8 l each) with independent replenishment tanks (5 l each). The developing time in each developer tank is 21 s and with the presence of two consecutive developer tanks the developing time is doubled without decreasing the film transporting speed and thus increasing the total processing time.

The optical densities (ODs) of the processed sensitometric strips were measured with a calibrated optical densitometer (RMI 331; X-Rite, Grandville, MI). For each sensitometric strip the Hurter and Driffield (H&D) curve was plotted and the following sensitometric parameters were derived: OD of base plus fog (ODb+f), maximum OD (ODmax), average gradient (AG) and film speed. The AG is the slope of H&D curve for ODs from 0.25+ODb+f to 2.0+ODb+f, whereas the film speed was defined as the reciprocal of the relative light exposure required to obtain an OD equal to 1+ODb+f. Using this definition for film speed the higher the film speed value the less exposure is needed to obtain an OD of 1+ODb+f.

It should be noted that while light sensitometry is typically used for film processing quality control, it is also useful for the evaluation of the film performance [7]. The AG is used as an index of the film contrast and the film speed as an index of the dose to the breast. Thus, changes in the sensitometric parameters of a film may reflect corresponding changes in the image quality of the mammograms and in the dose to the breast. However, it should be stressed that in clinical practice, the image quality of a mammogram and the dose to the breast is also dependent on the screen with which the film is combined [2].


   Results
Top
 Abstract
 Introduction
 Materials and methods
 Results
Discussion
 References
 
In Figure 1Go the H&D curves are given separately for each film type to exhibit the influence of the processing conditions on the H&D curves. In Figure 2Go the dependence of the ODmax, average gradient and speed on the processing conditions is graphically illustrated. Finally, in Figure 3Go, the H&D curves of all films are given for comparison under the same processing conditions (B).



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  		Figure 1. The Hurter and Driffield (H&D) curves (optical density vs log relative exposure) under different processing conditions: (a) MR5-II (Agfa), (b) HT (Agfa), (c) HDR (Agfa), (d) MinR-M (Kodak), (e) MinR-2000 (Kodak), (f) AD-M (Fuji), (g) Konica (CM-H). The optical densities (ODs) of the 21 steps of the sensitometric strips correspond to log relative exposure values (LogE) that range from 0 to 3, in steps of 0.15 each. In these figures only the ODs for LogE=>ge;0.9 (steps 7 to 21) are presented in order to enhance the visibility of the differences in the linear part and the shoulder of the H&D curves.

 


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  		Figure 2. The variation of the sensitometric parameters with processing conditions: (a) maximum optical density (ODmax), (b) average gradient (AG), (c) film speed. (The details of processing conditions for each code are given in Table 1Go).

 


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  		Figure 3. The Hurter and Driffield (H&D) curves of all films under the processing assigned with the code B (the details of processing conditions are given in Table 1Go).

 
From Figures 1 and 2GoGo it can be clearly seen that the effect of the different processing conditions used on the H&D curves and the sensitometric parameters was variable and variations did not follow the same pattern for all the films. Changes in the H&D curves with processing conditions were more prominent for MR5-II, MinR-M, AD-M and CM-H, less prominent for HT and MinR-2000, whereas for HDR prominent differences were observed only when comparing the H&D curves with D1 and D2 to the rest of the processing conditions.

With the exception of ODb+f where the maximum variation did not exceed 0.03 OD, all the other sensitometric parameters were strongly affected by the processing conditions employed. The ODb+f measured ranged from 0.16 to 0.22 OD and except for HT (0.22 with C1 and 0.21 with C2) all the rest were ≤0.2 OD. Referring to the ODmax variations (Figure 2aGo), one can notice the abrupt increase of ODmax for HDR with D1 and D2. Furthermore, it is also striking that HT, CM-H and AD-M did not exhibit the intense decrease in ODmax with D3 observed in the rest of the films when compared with the ODmax with D1 and D2.

In Figure 2bGo it can be seen that depending on the film type, the maximum AG was obtained with the processing conditions D1 (MR5-II, HT, MinR-M, AD-M), B (MinR-2000, CM-H) or D2 (HDR). Finally, from Figure 2cGo it can be appreciated that depending on film type the larger speed was obtained for MR5-II with C1, for HT with C1 and D2, for HDR with D1, for MinR-M with C1 and C2, for MinR-2000 with D1 and B and for AD-M and CM-H with D1. The smallest speed was obtained for most of the films with D3, except for MinR-2000 and CM-H where the speed with A was slightly smaller.

Commenting further on Figures 2b and 2cGo, it is important to stress that the results of film comparisons in terms of AG or speed are subject to processing conditions. For example, CM-H had larger AG than AD-M with B but with D1 the opposite was true while with D2 both films had almost the same AG. Similarly, MinR-M was much faster than HDR and CM-H with C1 or C2 but with D1 the situation was reversed. Furthermore, it should be noted that there was no specific pattern connecting the variation of AG and speed with the changes of processing conditions. In some cases an increase of AG was accompanied by a decrease in speed but in other cases an increase of both AG and speed was observed.

As far as the AG is concerned (Figure 2cGo), two points deserve further attention. First, D1 and D2 are the only processing conditions from those studied, where the AG obtained for MR5-II (an Agfa film that has been replaced in the market by HT and HDR), is satisfactory compared with the typical values of 3.0–4.0 quoted for the AG of modern films [1]. Second, the preparation of 5 l developer solution with the chemicals designated for preparation of 2.5 l solution (D3), did not degrade the AG as much as expected under this rather unusual case of developing conditions. In fact, with the exception of MR5-II, for the rest of the films the decrease in AG with D3 compared with D2 was insignificant (HT, MinR-M, MinR-2000) or small (HDR, AD-M, CM-H) and still the AG was larger than the AG obtained with those films with other processing conditions (e.g. the AG for CM-H was larger with D3 than with A). However, as can be seen in Figure 2cGo, even for this special processor, the reduced developer concentration did generally reduce the film speed but also the ODb+f.

Commenting on Figure 3Go, it can be seen that the H&D curves of the different films tested present considerable differences even under the same processing conditions. The specially designed H&D of the HDR should also be noted, where the short shoulder plateau is followed by a quasi-linear part at high ODs and the absence of the typical shoulder plateau for the MR5-II. From these curves, the higher speed of MinR-2000 (also observed with all the processing conditions tested) and the lower speed of AD-M (observed with all except D1 processing conditions as it can be seen Figure 2cGo) is clearly indicated.


   Discussion
Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
References
 
The films included in this study are only some of the films commercially available for mammography. Nevertheless they are adequate to exhibit the variety of the sensitometric characteristics that can be observed in mammographic films and their dependence on the processing conditions. Thus, it is important to note that since the adjustments of the automatic exposure control (AEC) system of a mammographic X-ray unit are dependent on the H&D curve shape, any change of film type or processing conditions may necessitate the re-adjustment of the AEC system.

This in turn implies that in a mammographic facility where a change of film type, processor, processing cycle or chemistry occurs, the AEC system should be thoroughly checked [1] to determine if a full re-adjustment of the AEC is required or a change in the baseline OD selection would be sufficient. Since such changes may not be brought to the attention of the medical physicist, the importance of the routine sensitometric control is evident. Besides, even without any change in the equipment used, changes in the H&D curve shape may occur for a number of reasons (from processor malfunctions to revisions of film or chemical properties) that can not be perceived without sensitometry.

In this study, it was observed that the sensitometric characteristics of some films are relatively insensitive to the processing conditions while for others the opposite is true. The stability of the sensitometric characteristics of a mammographic film is generally considered to be an advantage, as the behaviour of the film is predictable and manufacturers have often designed or even revised their film design to make it less dependent on processing conditions [2, 3]. On the other hand, the possibility of adjusting the characteristics of a film (mainly the contrast and speed) by deliberately altering the processing conditions is an interesting prospect, since it could be utilized in order to meet certain quality criteria or even accommodate the different preferences that may exist among radiologists. It should be mentioned, however, that in clinical practice a change of tube voltage setting, target/filter combination or cassette could be employed for the same purpose.

New films are in general of high contrast and as it was seen, with the exception of MR5-II, for the rest of the films an AG from 2.95 to 4.36 was obtained for the various processing conditions used. In the European quality control protocol [1], the implications of using high contrast films are briefly mentioned and a detailed analysis is given by Meeson et al [8]. They concluded that high contrast films (like the AD-M and MinR-2000 included in their work), generally improve the image quality of mammograms especially for fatty breasts. However, in certain occasions, dense breasts were better visualized with films of lower contrast, as dense glandular tissues were underexposed with high contrast films. Now, taking the example of the AD-M film, it was seen that the AG of 4.28 and 4.2 at D1 and D2, respectively, was reduced to 3.75 at D3 and at 3.42 at A, but at the cost of film speed. This decrease in contrast may be useful for moderating the problems reported by Meeson et al [8], while the increase in dose of about 10–15% required may improve the image quality as a result of the reduced quantum mottle and the increase of signal to noise ratio [4, 6, 9]. Besides, the decrease in contrast may also be accompanied by an increase in speed, as for MinR-M, where the AG decreases from 3.77 with D1 to 3.40 with C1, with a simultaneous increase of about 30% in speed.

Apart from the implications that high contrast films may have in clinical practice, a reduction in the AG may be required for some technical reasons. In some mammographic units the proper adjustment of the AEC system may be impossible with very high contrast films and for this reason a limit is sometimes given in the technical manuals for the maximum AG that the AEC system can accommodate.

It should be noted that the relatively small effect of the larger developer dilution in AG observed when comparing D3 with D2 cannot be generalized to processors with a single developer tank and shorter developing times. However, when processors like Mamoray MR are used in conjunction with very high contrast films, using a larger dilution in one or both of the developer tanks could be a method for reducing the AG or the ODb+f, if needed.

Finally, an important remark should be made concerning the comparative evaluation of films in terms of image quality and dose to the breast. A film exhibiting a larger AG or film speed than another under certain processing conditions may exhibit lower AG or speed when processing conditions are altered. Thus, the results of comparisons of films or film–screen combinations should not be generalized to other processing conditions, as they may be misleading.


   Acknowledgments
 
The authors would like to thank Mr Vassilios Ferentinos (Kodak Near East Inc.), Mr Konstantinos Markatis (Agfa-Gevaert A.E.B.E) and Mr Leonidas Konstantinidis (distributor of Fuji film), for providing free samples of MinR-2000, HDR and AD-M, respectively. Also, Mrs Christina Kapsalaki from Lekatsa Diagnostic Centers and Mrs Afroula Flioni-Vyza from Agios Savvas Hospital, for giving access to their radiology departments to perform the sensitometric controls. The authors would finally like to thank Mr Jean-Marc Schneider (field service engineer of GE Medical Systems Hellas), for providing technical information on the operation and adjustments of the AEC systems in mammographic units.

Received for publication October 3, 2003. Revision received January 5, 2004. Accepted for publication March 30, 2004.


   References
Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 

  1. van Woudenberg S, Thijssen M, Young K. European protocol for the quality control of the physical and technical aspects of mammography screening. In: Perry N, Broeders M, de Wolf C, Kirkpatrick A, Törnberg S, editors. European guidelines for quality assurance in mammography screening (3rd Edn). Office for Official Publications of the European Communities, Luxembourg, 2001.
  2. Kimme-Smith C, Bassett LW, Gold RH, Zheutlin J, Gornbeign JA. New mammography screen/film combinations: imaging characteristics and radiation dose. AJR Am J Roentgenol 1990;154:713–9.[Abstract/Free Full Text]
  3. Tabar L, Haus AG. Processing of mammographic films: technical and clinical considerations. Radiology 1989;173:65–9.[Abstract/Free Full Text]
  4. Kimme-Smith C, Rothschild PA, Bassett LW, Gold RH, Moler C. Mammographic film-processor temperature, development time and chemistry: effect on dose, contrast and noise. AJR Am J Roentgenol 1989;152:35–40.[Abstract/Free Full Text]
  5. Kimme-Smith C, Bassett LW, Gold RH, Chow S. Increased radiation dose at mammography due to prolonged exposure, delayed processing, and increased film darkening. Radiology 1991;178:387–91.[Abstract/Free Full Text]
  6. Brink C, de Villiers JFK, Lötter MG, van Zyl M. The influence of film processing temperature and time on mammographic image quality. Br J Radiol 1993;66:685–90.[Abstract/Free Full Text]
  7. West MS, Spelic DC. Using light sensitometry to evaluate mammography film performance. Med Phys 2000;27:854–60.[CrossRef][Medline]
  8. Meeson S, Young KC, Rust A, Wallis MG, Cooke J, Ramsdale ML. Implications of using high contrast mammography X-ray film-screen combinations. Br J Radiol 2001;74:825–35.[Abstract/Free Full Text]
  9. Robson KJ, Kotre CJ, Faulkner K. The use of a contrast-detail object in the optimization of optical density in mammography. Br J Radiol 1995;68:277–82.[Abstract/Free Full Text]



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