- Email: [email protected]
Sensitometric analyses of screen-film systems for mammography exams in Brazil
Radiation Physics and Chemistry 117 (2015) 64–69
Contents lists available at ScienceDirect
Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
Sensitometric analyses of screen-film systems for mammography exams in Brazil L.A.G. Magalhães a,n, G.G. Drexler a, C.E de Almeida a, L.L. Medeiros b, N.M.P.D. Ferreira b, J.J.S. Estrada b a Laboratório de Ciências Radiológicas (LCR), Universidade do Estado do Rio de Janeiro (UERJ), São Francisco Xavier, 524 Maracanã, sala 136, Pavilhão Lisboa da Cunha, Rio de Janeiro 20550-900, Brazil b Instituto Militar de Engenharia, Praça General Tibúrcio 90, Praia Vermelha, Rio de Janeiro 22290-270, Brazil
H I G H L I G H T S
Achievement quality control of mammographic films. Establishment of a methodology for verifying the quality control of mammographic films. Determination of sensitometric parameters of mammographic films utlizados in Brazil.
art ic l e i nf o
a b s t r a c t
Article history: Received 2 March 2015 Received in revised form 24 June 2015 Accepted 28 July 2015 Available online 29 July 2015
A determination of the sensitometric parameters of screen-film systems to evaluate their qualities was performed. The quality control of the automatic film processor was carried out to ensure a high level of efficiency. Based on ISO 9236-3, the following potentials were applied on the X-ray tubes: 25 kV, 28 kV, 30 kV and 35 kV. Four different mammography films from different manufacturers with and without screens were tested for curve shape, speed and average gradient. The results indicated that film 1 exhibited better contrast, film 3 demonstrated the highest energy dependence, and film 4 presented the largest base þ fog density. None of the four mammographic films tested achieved satisfactory results in all parameters analyzed. Improvements in the manufacturing process for these films must be completed to avoid losses in the image quality. & 2015 Elsevier Ltd. All rights reserved.
Keywords: Film mammography Quality control Processors Sensitometric
1. Introduction The image quality of a mammogram is the main goal services that use radiological films. To obtain an image useful for diagnosis, the radiological equipment must be controlled to ensure that its operating conditions are in ac Prod. Type: FTPcordance with the manufacturer’s recommendations. Therefore, quality assurance programs (QAP), which refer to the performance of X-ray equipment, processors and screen-film combinations, are important and should be efficient. The application of a QAP can reduce radiation exposure to the patient, decrease costs, and result in a significant improvement in service (Magalhães, 2001). Relevant factors, such as lowest dose and image quality, are dependent on other parameters, such as screenfilm speed, contrast and image processing. n
Corresponding author . E-mail address: [email protected] (L.A.G. Magalhães).
http://dx.doi.org/10.1016/j.radphyschem.2015.07.017 0969-806X/& 2015 Elsevier Ltd. All rights reserved.
The sensitometric parameters assessed in this study are as follows: characteristic curve, average gradient, speed and base þfog of the film-screen system used in mammography exams. The tests were conducted, in part, as recommended by the International Organization for Standardization (ISO 9236-3 1999). The verification of the conditions for the automatic film processing was also performed to ensure that no commitments in the evaluation of the sensitometric parameters occurred. Studies indicate that the percentage of films that are rejected in radiological services represent 13% of the films analyzed, due to the improper processing of these images (Magalhães et al., 2002).
2. Materials and methods The following equipment were used to carry out the work: X-ray tube (Philips, model PW 2185/00), ionization chamber (Radcal, 10 5–6 m model), electrometer (Keithley, 6517A model), aluminum plates (purity of 99.9% and variables thickness from
L.A.G. Magalhães et al. / Radiation Physics and Chemistry 117 (2015) 64–69
65
scale to compare the optical densities obtained. The optical densities ranged from 0.25 to 4.1. To obtain the kinetic energy released per unit mass (kerma) corresponding to each optical density, the ionization chamber was placed in the same location previously occupied by the films during the exposures (i.e., 100 cm distance between the film and the focal point). Next, irradiations were performed using the linear relationship between the kerma and exposure time, and only the set exposure was varied to modulate the intensity of the beam. From the optical densities and their respective kermas, the characteristic curves were obtained [log(kerma) DO]. Fig. 2 shows the experimental arrangement used for obtaining the kerma values. To calculate the average gradient and the sensitivity of the film tested, Eqs. (1) and (2) were used. Fig. 1. Experimental arrangement used by LCR to obtain the characteristic curves.
0.1 mm to 2.0 mm, GoodFellow), intensifying screens (IBF R300MM), measuring tape, mammography films from different manufacturers, developer and fixer solutions (Kodak), stopwatch (accuracy of 70.1 s, MJ-1822-Moure Jar), digital thermometer (Digi-Sense Scanning Thermometer), pH meter (accuracy 0.1 pH, model PH-107), thiosulfate retention kit, Kodak Hypo clearing agent, densitometer (Densix, model 603, PTW), sensitometer (Sensix model 4071 PTW), automatic film processing instrument (Mamoray Classic, model 1754, AGFA). Four different mammography films (assigned numbers 1, 2, 3 and 4) from different manufacturers were tested and evaluated. The experimental setup to obtain the characteristic curves and the sensitometric parameters is illustrated in Fig. 1. The optical densities were obtained by positioning a fixed collimator and additional filter in relation to the focal point of the tube. Afterwards, the ionization chamber was set, as well the film or the film with cassette, at a fixed distance of 100 cm from the focal point. At that distance, scattering does not significantly influence the results because the ISO (ISO 9236-3, 1999) allows for a tolerance of up to 3 m to carry out the measurements. With the goal of limiting the exposed area of the mammography film was used a diaphragm of lead with a circular opening of 10 mm in diameter. For exposure without screen, the films were placed inside black plastic bag and sealed, to prevent light inside it. After the film was positioned, using a height-adjustable support. Between the film and the X-ray tube was placed lead plate that has been aligned with the window of the tube using a laser. In addition, two sheets, one of 1.8 mm thick Al and another of 0.03 mm thick Mo were fixed the on filter wheel. After the correct positioning and alignment were achieved, irradiation was carried out for the selected times. The films were exposed 14–23 times at 25 kV, 28 kV, 30 kV and 35 kV to obtain the characteristic curves; the results were plotted on a logarithmic
G¯ =
D2 − D1 log10K2 − log10K1
(1)
S=
K0 KS
(2)
where D1 and D2 are density values between 2.0 and 0.25, respectively. K1 and K2 are the corresponding values sobtained from the sensitometric kerma curve. K0 ¼10 3 Gy and K0 is the kerma with an optical density closest to 1.
3. Results Image processing can generate serious problems in important parameters such as gradient and sensitivity. Thus, the control of automatic processing was performed to monitor and analyze important processing features. Fig. 3 shows that the temperature of the developer remained within acceptable limits during the processing (i.e., with variation less than 0.3 °C), as recommended by its manufacturer (Magalhães et al., 2002). The pH of the developer and fixer solutions were within the recommended limits, as shown in Figs. 4 and 5, respectively. This result indicates that the chemical solutions were within the expiration date and prepared correctly. Figs. 6 and 7 show the variation in the processing time and the level of fog in the darkroom, respectively. The processing time remained below the threshold of 3% of the time determined by the processor’s manufacturer. The level of fog in the darkroom presented a variation in the optical density above 0.05 only for 4 min 35,0 34,8 34,6
Temperature (°C)
34,4 34,2 34,0 33,8 33,6 33,4 33,2 33,0 0
2
4
6
8
10
12
14
16
Measures Fig. 2. LCR experimental setup to obtain air kerma.
Fig. 3. Variation in the developer temperature of the processor.
18
66
L.A.G. Magalhães et al. / Radiation Physics and Chemistry 117 (2015) 64–69
6,0
5,5
Optical Density
pH
5,0
4,5
4,0
3,5
3,0 0
2
4
6
8
10
12
14
16
5,00 4,75 4,50 4,25 4,00 3,75 3,50 3,25 3,00 2,75 2,50 2,25 2,00 1,75 1,50 1,25 1,00 0,75 0,50 0,25 0,00
0 minutes 1 minutes 2 minutes 4 minutes
0
18
5
10
15
20
25
Step
Measures
Fig. 7. Darkroom fog curves for different exposure times.
Fig. 4. Variation in the fixer solution pH of the processor.
Table 1 Beam qualities for the determination of the sensitometric curve, with and without a screen (according to TRS 457).
12,0 11,8 11,6 11,4 11,2 11,0
pH
10,8 10,6 10,4
Beam qualities
X-ray tube voltage (kV)
Added filtration (mmMo þmmAl)
HVL (mmAl)
I II III IV
25 28 30 35
0.03 þ 1.8 0.03 þ 1.8 0.03 þ 1.8 0.03 þ 1.8
0.56 0.61 0.63 0.70
10,2 10,0 9,8 9,6 9,4 9,2 0
2
4
6
8
10
12
14
16
18
Measures Fig. 5. Variation in the developer solution pH of the processor.
130 128
Time (seconds)
126 124
Optical Density
9,0
4,50 4,25 4,00 3,75 3,50 3,25 3,00 2,75 2,50 2,25 2,00 1,75 1,50 1,25 1,00 0,75 0,50 0,25 0,00 0,01
Film 1 Film 2 Film 3 Film 4
0,1
1
Log kerma(mGy)
122
Fig. 8. The characteristic curves for the films from four different manufacturers using the same screen at beam quality I.
120 118 116 114 112 0
2
4
6
8
10
12
14
16
18
Measures Fig. 6. Variation in the film processing time.
exposures. This result ensured that the darkroom presented good operating conditions. An analysis of the factors related to processing indicated that these factors did not influence the results
obtained in the evaluation of the films. The values for air kerma ranged from 0.07 mGy to 58 mGy. Table 1 presents the beam qualities used to obtain the sensitometric curves, with and without a screen (Pires et al., 2010; ISO 9236-3, 1999). Figs. 8–15 show the characteristic curves of the four films for the beam qualities presented in Table 1, with and without a screen (Magalhães et al., 2013). The characteristic curve for film 3 presented differed from that of the other for all beam qualities evaluated. This result indicates that film 3 exhibits higher energy dependency, causing instability that can generate changes in the image contrast. With greater latitude (higher grayscale), film 3 render the visualization of small structures difficult, thus introducing bias to the diagnosis.
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67
4,00 3,75
4,25
3,50
4,00
3,25
3,75
3,00
3,25
2,75
Optical Density
3,00 2,75
Film 1 Film 2 Film 3 Film 4
2,50 2,25 2,00 1,75
Optical Density
3,50
2,50 2,25 2,00 1,75
Film 1 Film 2 Film 3
1,50 1,25
1,50
1,00
1,25
0,75
1,00
0,50
0,75
0,25
0,50
0,00 0,1
0,25 0,01
0,1
1
10
100
Log kerma(mGy)
1
Log kerma(mGy) Fig. 9. Characteristic curves for the films from four different manufacturers using the same screen at beam quality II.
Fig. 12. The characteristic curves for the films from three different manufacturers without a screen at beam quality I. 3,75 3,25 3,00 2,75 2,50
Film 1 Film 2 Film 3 Film 4
Optical Density
Optical Density
3,50
4,50 4,25 4,00 3,75 3,50 3,25 3,00 2,75 2,50 2,25 2,00 1,75 1,50 1,25 1,00 0,75 0,50 0,25
2,25 2,00
Film 1 Film 2 Film 3
1,75 1,50 1,25 1,00 0,75 0,50 0,25 0,00 0,1
1
10
100
Log kerma(mGy) 0,1
Fig. 13. The characteristic curves for the films from three different manufacturers without a screen at beam quality II.
1
Log kerma(mGy)
4,00
Fig. 10. The characteristic curves for the films from four different manufacturers using the same screen at beam quality III.
3,75 3,50 3,25 3,00 2,75
Optical Density
4,50 4,25 4,00 3,75 3,50
Optical Density
3,25 3,00
2,50 2,25 2,00
Film 1 Film 2 Film 3
1,75 1,50 1,25 1,00
2,75
Film 1 Film 2 Film 3 Film 4
2,50 2,25 2,00
0,75 0,50 0,25 0,00 0,1
1,75
1
10
100
Log kerma(mGy)
1,50 1,25
Fig. 14. The characteristic curves for the films from three different manufacturers without a screen at beam quality III.
1,00 0,75 0,50 0,1
1
Log kerma(mGy) Fig. 11. The characteristic curves for the films from four different manufacturers using the same screen at beam quality IV.
The characteristic curve of film 1 demonstrated a greater inclination to the axis of the densities (lower latitude) (i.e., higher contrast compared to the other films). This result characterizes film 1 as a material of better contrast that can provide a better
L.A.G. Magalhães et al. / Radiation Physics and Chemistry 117 (2015) 64–69
4,50 4,25 4,00 3,75 3,50 3,25 3,00 2,75 2,50 2,25 2,00 1,75 1,50 1,25 1,00 0,75 0,50 0,25 0,00
Film 1 Film 2 Film 3
1
10
100
Deviation of the Average Gradient
Optical Density
68
0,50 0,45 0,40 0,35 0,30 0,25 0,20 0,15 0,10 0,05 0,00 -0,05 -0,10 -0,15 -0,20 -0,25 -0,30 -0,35 -0,40 -0,45 -0,50
25kV 28kV 30kV 35kV
Film 1
Log kerma(mGy)
Optical Density
1,50 1,45 1,40 1,35 1,30 1,25 1,20 1,15 1,10 1,05 1,00 0,95 0,90 0,85 0,80 0,75 0,70 0,65
Film 1 Film 2 Film 4 Film 3
0,60
0,63
0,66
0,69
0,72
HVL (0,03 mmMo + 1,8 mm Al) Fig. 16. The energy dependency of the films from four manufactures for ISO qualities at an air kerma of 1 mGy.
25kV 28kV 30kV 35kV
0,7 0,6 0,5
Deviation of Sensitivity
0,4
Film 3
Film 4
Films
Fig. 15. The characteristic curves for the films from three different manufacturers without a screen at beam quality IV.
0,57
Film 2
0,3 0,2
Fig. 18. Plot of the medium gradient for the four films from different manufacturers using the beam quality recommended by the ISO.
for the average gradient, meaning that the useful diagnostic region is reduced. The energy dependency of the films from the four different manufacturers, shown in Fig. 16, was determined for an air kerma of 1 mGy to correlate the optical densities for this kerma with the half-value layers (HVLs) for each potential presented in Table 1. The HVLs for energetic dependence analysis were obtained based on a published paper (Pires et al., 2010). Film 1, as already noted for the sensitometric curve analysis, exhibits greater stability with changes in beam qualities. Thus, this film is more reliable for the development of diagnostics by presenting small variations in contrast and sensitivity. The HVL at 30 kV suggested that the film with the greatest energy dependence is film 3. Thus, this film demonstrated the highest level of instability and may, for example, introduce significant variations in the speed at each potential change, causing blurring and a consequent loss in the image resolution. The ISO (ISO 9236-3, 1999) recommends that the speeds (or sensitivities) should be inside the limit of 70.10, whereas the gradient (or radiographic contrast) of the film has a limit of 70.06. Most films exhibit speed and gradient deviations above the values recommended by the ISO, as shown in Figs. 17 and 18. The speed of only one film (film 1) remained within acceptable limits for all potentials applied. The other films demonstrated greater speed deviation at least two of the four potential applied. This feature indicates that most of the evaluated films exhibited greater sensitivity compared to film 1 and suggests that the films demonstrate unacceptable levels of instability.
0,1 0,0
4. Conclusions
-0,1 -0,2 -0,3 -0,4 -0,5 -0,6 -0,7 Film 1
Film 2
Film 3
Film 4
Films Fig. 17. Plot of the sensitivity for the four films from different manufactures using the beam quality of ISO 1 mGy.
image in mammography exams. The curve of Film 4 indicates that the base þfog density for all beam qualities is higher for this film. This observation indicates that this film also presents a problem
In this work, we evaluated the important sensitometric parameters of four mammography films from different manufacturers that are used in Brazil. The findings also demonstrated that the LCR automatic film processor did not interfere with the results obtained in the film evaluation. None of the four mammographic films tested achieved satisfactory results in all parameters analyzed. Film 1 presented the best results by exhibiting the greatest stability with potential changes (i.e., the emulsion of the film features minor variations in contrast and sensitivity). The calculation of the speed deviation indicated that film 1 was the only film that generated results within the acceptable limits for all potential applied, thus guaranteeing less image blurring. With respect to the calculation of the gradient deviation, all films presented results outside of the limits
L.A.G. Magalhães et al. / Radiation Physics and Chemistry 117 (2015) 64–69
recommended by the ISO (ISO 9236-3, 1999). From the comparison of the characteristic curves generated with and without a screen, the use of a screen was found to reduce the air kerma by as much as 50-fold. The presence of a screen also reduced the image quality. This difference can be appreciated by studying the characteristic curve shapes for the films exposed with a screen at different radiation qualities. The contrast parameter was highly degraded with increasing radiation qualities when a screen was used. Of the four mammography film analyzed, only one film provided satisfactory results. This finding indicates the need for more effective quality control during the manufacturing process of mammography films. In this way, a significant improvement in breast cancer diagnosis, due to early detection of possible changes in the breast tissue, could be achieved.
Acknowledgments The authors are grateful to CAPES (EN 12112) and FAPERJ (E-26/
69
110.651/2012) for the financial support provided and to all the individuals who directly or indirectly collaborated on this work.
References ISO (International Organization for Standardization), 1999. Photography-Sensitometry of Screen/Film Systems for Medical Radiography-Part 3: Determination of Sensitometric Curve Shape, Speed and Average Gradient for Mammography, 1st ed. ISO, Geneva (International Standard ISO 9236-3). Magalhães, L.A.G., 2001. Controle da qualidade de processadoras automáticas (Master’s dissertation). Universidade Federal do Rio de Janeiro, UFRJ, Rio de Janeiro, Brazil. Magalhães, L.A.G., Azevedo, A.C.P., Carvalho, A.C.P., 2002. A Importância do controle de qualidade de processadoras automáticas. Radiol. Bras. 35, 357–363. Magalhães, L.A.G., Drexler, G.G., de Almeida, C.E., 2013. Compatibility characteristics of five radiographic films utilized in Brazilian diagnostic radiology. Radiat. Protect. Dosim. vol 136 (2), 184–189. Pires, E.J., David, M.G., Peixoto, J.G., de ALMEIDA, C.E., 2010. Establishment of radiation qualities for mammography according to the IEC 61267 and TRS 457. Radiat. Protect. Dosim. 145 (1), 45–51.
Contents lists available at ScienceDirect
Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
Sensitometric analyses of screen-film systems for mammography exams in Brazil L.A.G. Magalhães a,n, G.G. Drexler a, C.E de Almeida a, L.L. Medeiros b, N.M.P.D. Ferreira b, J.J.S. Estrada b a Laboratório de Ciências Radiológicas (LCR), Universidade do Estado do Rio de Janeiro (UERJ), São Francisco Xavier, 524 Maracanã, sala 136, Pavilhão Lisboa da Cunha, Rio de Janeiro 20550-900, Brazil b Instituto Militar de Engenharia, Praça General Tibúrcio 90, Praia Vermelha, Rio de Janeiro 22290-270, Brazil
H I G H L I G H T S
Achievement quality control of mammographic films. Establishment of a methodology for verifying the quality control of mammographic films. Determination of sensitometric parameters of mammographic films utlizados in Brazil.
art ic l e i nf o
a b s t r a c t
Article history: Received 2 March 2015 Received in revised form 24 June 2015 Accepted 28 July 2015 Available online 29 July 2015
A determination of the sensitometric parameters of screen-film systems to evaluate their qualities was performed. The quality control of the automatic film processor was carried out to ensure a high level of efficiency. Based on ISO 9236-3, the following potentials were applied on the X-ray tubes: 25 kV, 28 kV, 30 kV and 35 kV. Four different mammography films from different manufacturers with and without screens were tested for curve shape, speed and average gradient. The results indicated that film 1 exhibited better contrast, film 3 demonstrated the highest energy dependence, and film 4 presented the largest base þ fog density. None of the four mammographic films tested achieved satisfactory results in all parameters analyzed. Improvements in the manufacturing process for these films must be completed to avoid losses in the image quality. & 2015 Elsevier Ltd. All rights reserved.
Keywords: Film mammography Quality control Processors Sensitometric
1. Introduction The image quality of a mammogram is the main goal services that use radiological films. To obtain an image useful for diagnosis, the radiological equipment must be controlled to ensure that its operating conditions are in ac Prod. Type: FTPcordance with the manufacturer’s recommendations. Therefore, quality assurance programs (QAP), which refer to the performance of X-ray equipment, processors and screen-film combinations, are important and should be efficient. The application of a QAP can reduce radiation exposure to the patient, decrease costs, and result in a significant improvement in service (Magalhães, 2001). Relevant factors, such as lowest dose and image quality, are dependent on other parameters, such as screenfilm speed, contrast and image processing. n
Corresponding author . E-mail address: [email protected] (L.A.G. Magalhães).
http://dx.doi.org/10.1016/j.radphyschem.2015.07.017 0969-806X/& 2015 Elsevier Ltd. All rights reserved.
The sensitometric parameters assessed in this study are as follows: characteristic curve, average gradient, speed and base þfog of the film-screen system used in mammography exams. The tests were conducted, in part, as recommended by the International Organization for Standardization (ISO 9236-3 1999). The verification of the conditions for the automatic film processing was also performed to ensure that no commitments in the evaluation of the sensitometric parameters occurred. Studies indicate that the percentage of films that are rejected in radiological services represent 13% of the films analyzed, due to the improper processing of these images (Magalhães et al., 2002).
2. Materials and methods The following equipment were used to carry out the work: X-ray tube (Philips, model PW 2185/00), ionization chamber (Radcal, 10 5–6 m model), electrometer (Keithley, 6517A model), aluminum plates (purity of 99.9% and variables thickness from
L.A.G. Magalhães et al. / Radiation Physics and Chemistry 117 (2015) 64–69
65
scale to compare the optical densities obtained. The optical densities ranged from 0.25 to 4.1. To obtain the kinetic energy released per unit mass (kerma) corresponding to each optical density, the ionization chamber was placed in the same location previously occupied by the films during the exposures (i.e., 100 cm distance between the film and the focal point). Next, irradiations were performed using the linear relationship between the kerma and exposure time, and only the set exposure was varied to modulate the intensity of the beam. From the optical densities and their respective kermas, the characteristic curves were obtained [log(kerma) DO]. Fig. 2 shows the experimental arrangement used for obtaining the kerma values. To calculate the average gradient and the sensitivity of the film tested, Eqs. (1) and (2) were used. Fig. 1. Experimental arrangement used by LCR to obtain the characteristic curves.
0.1 mm to 2.0 mm, GoodFellow), intensifying screens (IBF R300MM), measuring tape, mammography films from different manufacturers, developer and fixer solutions (Kodak), stopwatch (accuracy of 70.1 s, MJ-1822-Moure Jar), digital thermometer (Digi-Sense Scanning Thermometer), pH meter (accuracy 0.1 pH, model PH-107), thiosulfate retention kit, Kodak Hypo clearing agent, densitometer (Densix, model 603, PTW), sensitometer (Sensix model 4071 PTW), automatic film processing instrument (Mamoray Classic, model 1754, AGFA). Four different mammography films (assigned numbers 1, 2, 3 and 4) from different manufacturers were tested and evaluated. The experimental setup to obtain the characteristic curves and the sensitometric parameters is illustrated in Fig. 1. The optical densities were obtained by positioning a fixed collimator and additional filter in relation to the focal point of the tube. Afterwards, the ionization chamber was set, as well the film or the film with cassette, at a fixed distance of 100 cm from the focal point. At that distance, scattering does not significantly influence the results because the ISO (ISO 9236-3, 1999) allows for a tolerance of up to 3 m to carry out the measurements. With the goal of limiting the exposed area of the mammography film was used a diaphragm of lead with a circular opening of 10 mm in diameter. For exposure without screen, the films were placed inside black plastic bag and sealed, to prevent light inside it. After the film was positioned, using a height-adjustable support. Between the film and the X-ray tube was placed lead plate that has been aligned with the window of the tube using a laser. In addition, two sheets, one of 1.8 mm thick Al and another of 0.03 mm thick Mo were fixed the on filter wheel. After the correct positioning and alignment were achieved, irradiation was carried out for the selected times. The films were exposed 14–23 times at 25 kV, 28 kV, 30 kV and 35 kV to obtain the characteristic curves; the results were plotted on a logarithmic
G¯ =
D2 − D1 log10K2 − log10K1
(1)
S=
K0 KS
(2)
where D1 and D2 are density values between 2.0 and 0.25, respectively. K1 and K2 are the corresponding values sobtained from the sensitometric kerma curve. K0 ¼10 3 Gy and K0 is the kerma with an optical density closest to 1.
3. Results Image processing can generate serious problems in important parameters such as gradient and sensitivity. Thus, the control of automatic processing was performed to monitor and analyze important processing features. Fig. 3 shows that the temperature of the developer remained within acceptable limits during the processing (i.e., with variation less than 0.3 °C), as recommended by its manufacturer (Magalhães et al., 2002). The pH of the developer and fixer solutions were within the recommended limits, as shown in Figs. 4 and 5, respectively. This result indicates that the chemical solutions were within the expiration date and prepared correctly. Figs. 6 and 7 show the variation in the processing time and the level of fog in the darkroom, respectively. The processing time remained below the threshold of 3% of the time determined by the processor’s manufacturer. The level of fog in the darkroom presented a variation in the optical density above 0.05 only for 4 min 35,0 34,8 34,6
Temperature (°C)
34,4 34,2 34,0 33,8 33,6 33,4 33,2 33,0 0
2
4
6
8
10
12
14
16
Measures Fig. 2. LCR experimental setup to obtain air kerma.
Fig. 3. Variation in the developer temperature of the processor.
18
66
L.A.G. Magalhães et al. / Radiation Physics and Chemistry 117 (2015) 64–69
6,0
5,5
Optical Density
pH
5,0
4,5
4,0
3,5
3,0 0
2
4
6
8
10
12
14
16
5,00 4,75 4,50 4,25 4,00 3,75 3,50 3,25 3,00 2,75 2,50 2,25 2,00 1,75 1,50 1,25 1,00 0,75 0,50 0,25 0,00
0 minutes 1 minutes 2 minutes 4 minutes
0
18
5
10
15
20
25
Step
Measures
Fig. 7. Darkroom fog curves for different exposure times.
Fig. 4. Variation in the fixer solution pH of the processor.
Table 1 Beam qualities for the determination of the sensitometric curve, with and without a screen (according to TRS 457).
12,0 11,8 11,6 11,4 11,2 11,0
pH
10,8 10,6 10,4
Beam qualities
X-ray tube voltage (kV)
Added filtration (mmMo þmmAl)
HVL (mmAl)
I II III IV
25 28 30 35
0.03 þ 1.8 0.03 þ 1.8 0.03 þ 1.8 0.03 þ 1.8
0.56 0.61 0.63 0.70
10,2 10,0 9,8 9,6 9,4 9,2 0
2
4
6
8
10
12
14
16
18
Measures Fig. 5. Variation in the developer solution pH of the processor.
130 128
Time (seconds)
126 124
Optical Density
9,0
4,50 4,25 4,00 3,75 3,50 3,25 3,00 2,75 2,50 2,25 2,00 1,75 1,50 1,25 1,00 0,75 0,50 0,25 0,00 0,01
Film 1 Film 2 Film 3 Film 4
0,1
1
Log kerma(mGy)
122
Fig. 8. The characteristic curves for the films from four different manufacturers using the same screen at beam quality I.
120 118 116 114 112 0
2
4
6
8
10
12
14
16
18
Measures Fig. 6. Variation in the film processing time.
exposures. This result ensured that the darkroom presented good operating conditions. An analysis of the factors related to processing indicated that these factors did not influence the results
obtained in the evaluation of the films. The values for air kerma ranged from 0.07 mGy to 58 mGy. Table 1 presents the beam qualities used to obtain the sensitometric curves, with and without a screen (Pires et al., 2010; ISO 9236-3, 1999). Figs. 8–15 show the characteristic curves of the four films for the beam qualities presented in Table 1, with and without a screen (Magalhães et al., 2013). The characteristic curve for film 3 presented differed from that of the other for all beam qualities evaluated. This result indicates that film 3 exhibits higher energy dependency, causing instability that can generate changes in the image contrast. With greater latitude (higher grayscale), film 3 render the visualization of small structures difficult, thus introducing bias to the diagnosis.
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67
4,00 3,75
4,25
3,50
4,00
3,25
3,75
3,00
3,25
2,75
Optical Density
3,00 2,75
Film 1 Film 2 Film 3 Film 4
2,50 2,25 2,00 1,75
Optical Density
3,50
2,50 2,25 2,00 1,75
Film 1 Film 2 Film 3
1,50 1,25
1,50
1,00
1,25
0,75
1,00
0,50
0,75
0,25
0,50
0,00 0,1
0,25 0,01
0,1
1
10
100
Log kerma(mGy)
1
Log kerma(mGy) Fig. 9. Characteristic curves for the films from four different manufacturers using the same screen at beam quality II.
Fig. 12. The characteristic curves for the films from three different manufacturers without a screen at beam quality I. 3,75 3,25 3,00 2,75 2,50
Film 1 Film 2 Film 3 Film 4
Optical Density
Optical Density
3,50
4,50 4,25 4,00 3,75 3,50 3,25 3,00 2,75 2,50 2,25 2,00 1,75 1,50 1,25 1,00 0,75 0,50 0,25
2,25 2,00
Film 1 Film 2 Film 3
1,75 1,50 1,25 1,00 0,75 0,50 0,25 0,00 0,1
1
10
100
Log kerma(mGy) 0,1
Fig. 13. The characteristic curves for the films from three different manufacturers without a screen at beam quality II.
1
Log kerma(mGy)
4,00
Fig. 10. The characteristic curves for the films from four different manufacturers using the same screen at beam quality III.
3,75 3,50 3,25 3,00 2,75
Optical Density
4,50 4,25 4,00 3,75 3,50
Optical Density
3,25 3,00
2,50 2,25 2,00
Film 1 Film 2 Film 3
1,75 1,50 1,25 1,00
2,75
Film 1 Film 2 Film 3 Film 4
2,50 2,25 2,00
0,75 0,50 0,25 0,00 0,1
1,75
1
10
100
Log kerma(mGy)
1,50 1,25
Fig. 14. The characteristic curves for the films from three different manufacturers without a screen at beam quality III.
1,00 0,75 0,50 0,1
1
Log kerma(mGy) Fig. 11. The characteristic curves for the films from four different manufacturers using the same screen at beam quality IV.
The characteristic curve of film 1 demonstrated a greater inclination to the axis of the densities (lower latitude) (i.e., higher contrast compared to the other films). This result characterizes film 1 as a material of better contrast that can provide a better
L.A.G. Magalhães et al. / Radiation Physics and Chemistry 117 (2015) 64–69
4,50 4,25 4,00 3,75 3,50 3,25 3,00 2,75 2,50 2,25 2,00 1,75 1,50 1,25 1,00 0,75 0,50 0,25 0,00
Film 1 Film 2 Film 3
1
10
100
Deviation of the Average Gradient
Optical Density
68
0,50 0,45 0,40 0,35 0,30 0,25 0,20 0,15 0,10 0,05 0,00 -0,05 -0,10 -0,15 -0,20 -0,25 -0,30 -0,35 -0,40 -0,45 -0,50
25kV 28kV 30kV 35kV
Film 1
Log kerma(mGy)
Optical Density
1,50 1,45 1,40 1,35 1,30 1,25 1,20 1,15 1,10 1,05 1,00 0,95 0,90 0,85 0,80 0,75 0,70 0,65
Film 1 Film 2 Film 4 Film 3
0,60
0,63
0,66
0,69
0,72
HVL (0,03 mmMo + 1,8 mm Al) Fig. 16. The energy dependency of the films from four manufactures for ISO qualities at an air kerma of 1 mGy.
25kV 28kV 30kV 35kV
0,7 0,6 0,5
Deviation of Sensitivity
0,4
Film 3
Film 4
Films
Fig. 15. The characteristic curves for the films from three different manufacturers without a screen at beam quality IV.
0,57
Film 2
0,3 0,2
Fig. 18. Plot of the medium gradient for the four films from different manufacturers using the beam quality recommended by the ISO.
for the average gradient, meaning that the useful diagnostic region is reduced. The energy dependency of the films from the four different manufacturers, shown in Fig. 16, was determined for an air kerma of 1 mGy to correlate the optical densities for this kerma with the half-value layers (HVLs) for each potential presented in Table 1. The HVLs for energetic dependence analysis were obtained based on a published paper (Pires et al., 2010). Film 1, as already noted for the sensitometric curve analysis, exhibits greater stability with changes in beam qualities. Thus, this film is more reliable for the development of diagnostics by presenting small variations in contrast and sensitivity. The HVL at 30 kV suggested that the film with the greatest energy dependence is film 3. Thus, this film demonstrated the highest level of instability and may, for example, introduce significant variations in the speed at each potential change, causing blurring and a consequent loss in the image resolution. The ISO (ISO 9236-3, 1999) recommends that the speeds (or sensitivities) should be inside the limit of 70.10, whereas the gradient (or radiographic contrast) of the film has a limit of 70.06. Most films exhibit speed and gradient deviations above the values recommended by the ISO, as shown in Figs. 17 and 18. The speed of only one film (film 1) remained within acceptable limits for all potentials applied. The other films demonstrated greater speed deviation at least two of the four potential applied. This feature indicates that most of the evaluated films exhibited greater sensitivity compared to film 1 and suggests that the films demonstrate unacceptable levels of instability.
0,1 0,0
4. Conclusions
-0,1 -0,2 -0,3 -0,4 -0,5 -0,6 -0,7 Film 1
Film 2
Film 3
Film 4
Films Fig. 17. Plot of the sensitivity for the four films from different manufactures using the beam quality of ISO 1 mGy.
image in mammography exams. The curve of Film 4 indicates that the base þfog density for all beam qualities is higher for this film. This observation indicates that this film also presents a problem
In this work, we evaluated the important sensitometric parameters of four mammography films from different manufacturers that are used in Brazil. The findings also demonstrated that the LCR automatic film processor did not interfere with the results obtained in the film evaluation. None of the four mammographic films tested achieved satisfactory results in all parameters analyzed. Film 1 presented the best results by exhibiting the greatest stability with potential changes (i.e., the emulsion of the film features minor variations in contrast and sensitivity). The calculation of the speed deviation indicated that film 1 was the only film that generated results within the acceptable limits for all potential applied, thus guaranteeing less image blurring. With respect to the calculation of the gradient deviation, all films presented results outside of the limits
L.A.G. Magalhães et al. / Radiation Physics and Chemistry 117 (2015) 64–69
recommended by the ISO (ISO 9236-3, 1999). From the comparison of the characteristic curves generated with and without a screen, the use of a screen was found to reduce the air kerma by as much as 50-fold. The presence of a screen also reduced the image quality. This difference can be appreciated by studying the characteristic curve shapes for the films exposed with a screen at different radiation qualities. The contrast parameter was highly degraded with increasing radiation qualities when a screen was used. Of the four mammography film analyzed, only one film provided satisfactory results. This finding indicates the need for more effective quality control during the manufacturing process of mammography films. In this way, a significant improvement in breast cancer diagnosis, due to early detection of possible changes in the breast tissue, could be achieved.
Acknowledgments The authors are grateful to CAPES (EN 12112) and FAPERJ (E-26/
69
110.651/2012) for the financial support provided and to all the individuals who directly or indirectly collaborated on this work.
References ISO (International Organization for Standardization), 1999. Photography-Sensitometry of Screen/Film Systems for Medical Radiography-Part 3: Determination of Sensitometric Curve Shape, Speed and Average Gradient for Mammography, 1st ed. ISO, Geneva (International Standard ISO 9236-3). Magalhães, L.A.G., 2001. Controle da qualidade de processadoras automáticas (Master’s dissertation). Universidade Federal do Rio de Janeiro, UFRJ, Rio de Janeiro, Brazil. Magalhães, L.A.G., Azevedo, A.C.P., Carvalho, A.C.P., 2002. A Importância do controle de qualidade de processadoras automáticas. Radiol. Bras. 35, 357–363. Magalhães, L.A.G., Drexler, G.G., de Almeida, C.E., 2013. Compatibility characteristics of five radiographic films utilized in Brazilian diagnostic radiology. Radiat. Protect. Dosim. vol 136 (2), 184–189. Pires, E.J., David, M.G., Peixoto, J.G., de ALMEIDA, C.E., 2010. Establishment of radiation qualities for mammography according to the IEC 61267 and TRS 457. Radiat. Protect. Dosim. 145 (1), 45–51.