Target-filter Combinations Research Articles

Target-filter combination effects on breast tissue characterization using mammographic X-rays: A Monte Carlo simulation study.

Characterization of normal and malignant breast tissues using X-ray scattering techniques has shown promising results and applications. To examine possibility of characterizing normal and malignant breast tissues using the scattered photon distribution of polyenergetic beams of 30 kV X-rays. A Monte Carlo simulation is upgraded so that it is capable of simulating input mammographic X-ray spectra from different target-filter combinations, tracing photon transport, and producing the distribution of scattered photons. The target-filter combinations include Mo-Mo, Mo-Al, Mo-Rh, Rh-Rh, Rh-Al, W-Rh, and W-Al. Analysis of obtained scattered photon distribution is carried out by comparing the ratio of count under the peak in the momentum transfer region from 0 to 1.55 nm-1, to that in the region from 1.6 to 9.1 nm-1 (covering the regions of scattering from fat and soft tissue, respectively) for breast samples with different percentages of normal tissue (0-100%). Mo-Mo target-filter combination shows a high linear dependence of the count under peak ratio on the percentage of normal tissue in breast samples (R2 = 0.9513). Despite slightly less linear than Mo-Mo, target-filter combinations other than Rh-Rh, W-Rh, and W-Al produce high linear responses (R2 > 0.9)CONCLUSION:Mo-Mo target-filter combination would probably be the most relevant in characterizing normal and malignant breast tissues from their scattered photon distribution.

Feasibility of determining mammography dose using LuSy dosimeter

Mammography is a radiological examination that utilises low-energy X-ray to detect breast cancer. The techniques include full-field digital mammography (FFDM) and digital breast tomosynthesis (DBT), which produce 2D and 3D breast images, respectively. Mean glandular dose (MGD) is used to describe the dose delivered by these techniques because it estimates the photon absorption by glandular tissues in the breast. This study aims to calibrate, characterise and determine the feasibility of measuring MGD using an in-house developed, real-time fibre-optic dosimeter called the LuSy dosimeter. LuSy was calibrated against a solid-state mammography dosimeter for three target-filter combinations of W/Rh, W/Ag and W/Al. Subsequently, characterisation towards mammography radiation was carried out. Finally, MGD was measured using LuSy and subsequently compared with the readings of a solid-state detector and those estimated by the mammography machine. The measured calibration coefficient was 342.10, 380.35 and 447.68 counts/mGy for W/Rh, W/Ag and W/Al target-filter combinations, respectively. For MGD, both LuSy and the mammography dosimeter measured a higher dose compared with the machine console. The mean deviation between LuSy and machine console was 14.72%. Meanwhile, the mean deviation between the mammography dosimeter and the machine console was 19.5%. In conclusion, the LuSy may be calibrated to measure low-energy X-ray, and its MGD reading is comparable with a solid-state dosimeter.

Characteristic evaluation of a simple hand-made semiconductor dosimeter for mammography

Daily quality control of mammography equipment is important for providing optimal images and determining appropriate doses. To popularise dosimeters, the Measurement Division, the Japanese Society of Radiological Technology hold a seminar on making simple dosimeters. At this seminar, a hand-made dosimeter for mammography (HD-M) can be made at low cost. However, HD-Ms employ semiconductors, and their energy responses are subject to significant variations. This investigation involved the determination of precautions when using HD-Ms, examining their energy response characteristics and measurable energy ranges. HD-M has four types of selectors for response correction. When the selector and the tube voltage were equal, the HD-M readings matched that of the ionisation chamber within 5%. However, in case of target filter combinations and measuring tube voltages that the selector does not support, the HD-M readings differed by up to 53% from the ionisation chamber values. HD-M may use different measurement circuits and semiconductor elements depending on the time of the seminar. In this study, it was clarified that the correction factor k, which is the average value of the ratio of the measured value of the ionisation chamber dosimeter to the measured value of HD-M, changes from 0.62 to 1.53 depending on irradiation conditions such as the combination of target filters and the tube voltage. It was demonstrated that HD-M functions sufficiently as a dosimeter for daily management by determining the correction factor using the method proposed in this study.

Comparação entre métodos de medição da camada semi-redutora em radiologia

The Half Value Layer (HVL) is a parameter used in Quality Control (QC), to evaluate the X-ray beam quality. The HVL can be measured through the X-ray primary beam attenuation measurement using knew thickness slabs of 99% purity aluminum (M1) or by adjusting the best curve (M2) or by multipurpose dosimeter (solid state detector) (M3). The M1 wears out the X-ray tube more and requires a long time of data acquisition and processing, however, it is the standard recommended method for the Radiological Safety Manual. The last one method (M3) is practical, and is not influenced by the abrupt change in the X-ray transmission spectrum, as it does not require the use of aluminum plates. The equipment used to measure radiation was the NOMEX dosemeter, Cobia Smart, UNFORS XI and Radcal Ionization Chamber. The sources were mobile and fixed X-rays and mammography equipment. The results showed that the biggest difference was 15.6% between M1 and M3 for mammography equipment with a filter\target W\Rh. For conventional X-rays, that the target-filter combination is W\Al, the biggest difference was 3.3% between M1 and M3. Thus, the results show that the HVL estimate can be performed by any of the three methods or equipment, as long as the target\filter combination is W/Al. For filter\target combination other than W/Al the percentage differences increase considerably and we do not recommend the use of M1 for this type of measurement.

Air-Kerma Standard for Mammography X-Ray in Japan: Progress and Prospects

In Japan, mammography was introduced in 2000 for the early detection of breast cancer. In quality control of mammography, dosimetry is one of the most important items. For accurate dosimetry, calibration of dosimeters is necessary because radiation quality (target-filter combination) of mammography x-ray is different from that of general radiography. Therefore, development of dosimetry standard based on radiation quality of mammography x-ray was required. AIST/NMIJ developed an air-kerma standard for mammography x-rays and started its dissemination in 2009. Since then, the air-kerma standard has been extended to various radiation qualities that have come to be used in digital mammography. In this paper, an overview of the air-kerma standard for mammography x-ray together with a future plan is briefly presented.

Characterization of the imaging settings in screening mammography using a tracking and reporting system: A multi-center and multi-vendor analysis

A tracking and reporting system was developed to monitor radiation dose in X-ray breast imaging. We used our tracking system to characterize and compare the mammographic practices of five breast imaging centers located in the United States and Brazil. Clinical data were acquired using eight mammography systems comprising three modalities: computed radiography (CR), full-field digital mammography (FFDM), and digital breast tomosynthesis (DBT). Our database consists of metadata extracted from 334,234 images. We analyzed distributions and correlations of compressed breast thickness (CBT), compression force, target-filter combinations, X-ray tube voltage, and average glandular dose (AGD). AGD reference curves were calculated based on AGD distributions as a function of CBT. These curves represent an AGD reference for a particular population and system. Differences in AGD and imaging settings were attributed to a combination of factors, such as improvements in technology, imaging protocol, and patient demographics. The tracking system allows the comparison of various imaging settings used in screening mammography, as well as the tracking of patient- and population-specific breast data collected from different populations.

Investigation of Exposure Factors for Various Breast Composition and Thicknesses in Digital Screening Mammography Related to Breast Dose

Objective: To investigate the effect of exposure factors used in digital screening mammography on image quality of different breast compositions. Material and Methods: A digital mammography unit, with tungsten (W) as target, rhodium (Rh) and silver (Ag) as filters, and amorphous selenium detectors, was used to image Computerized Imaging Reference Systems (CIRS) Model 12A phantoms of thickness 4, 5, and 6 cm. Images of each phantom were obtained using target-filter combinations of W/Rh and W/Ag, at 28, 30, and 32 kVp. Images were evaluated by 5 senior technologists with experience in mammography. Image scores were assigned, for each type of feature present in the phantom. Statistical analysis was performed using nonparametric tests to compare sets of image scores at p = 0.05. Results: A small but statistically significant improvement was detected in the visibility of microcalcifications (8.8 ± 0.2; p = 0.031) for the W/Rh combination but this did not show any differences in the visibility of masses or fibers. The entrance skin dose (ESD) and mean glandular dose (MGD) were lower for the W/Ag (ESD = 1.30–3.70; MGD = 0.44–0.93 mGy) combination compared to W/Rh (ESD = 1.66–5.40; MGD = 0.52–1.12 mGy). The Mann-Whitney test revealed that 30-kV exposure with the W/Rh combination showed a significantly better visibility of specks in the 30/70 phantom compared to other exposures. Conclusion: The use of an Rh filter showed a better image quality for all phantoms. 28 and 30 kVp with the W/Rh combination provided a slightly better image quality, and the MGD is less than 1.2 mGy.

Effect of exposure factors on image quality in screening mammography

IntroductionThe aim of this research was to study the effect of exposure factors on image quality for digital screening mammography units in Kuwait which use Tungsten (W) targets with Rhodium (Rh) and Silver (Ag) as filters. MethodsMammography Accreditation Phantom Model 015 was imaged using a Hologic Selenia Digital mammography unit with W targets and Rh and Ag filters. Four images, each at 26, 28, 30, and 32 kVp, were obtained using each target-filter combination (W/Rh and W/Ag). The images were evaluated by five senior technologists for the number of specks, fibers and masses visible on each image. Statistical analysis was carried out using non-parametric tests at p = 0.05 level. ResultsThere were significant changes in the visibility of fibers and specks between different kVp values with W/Rh (p < 0.001). However, with W/Ag combination, significant differences were observed in the fibers only (p < 0.001). Among the kVp values used, 28 kV emerged as the optimal value. Comparison of images obtained with the two filter materials, led to significant differences in the visibility of fibers and specks (p < 0.008). At 32 kVp, there were significant differences in the visibility of specks only (p < 0.008). ConclusionA W/Rh target-filter combination provides better image quality than that provided by W/Ag. In particular, 30 and 32 kVp X-ray beams produce higher quality images than the lower kV values.

Overview of the radiographers\u2019 practice in 65 healthcare centers using digital mammography systems in Portugal

PurposeTo assess current practices in digital mammography (DM) in Portuguese healthcare providers using digital systems. To investigate compliance with European standards regarding mean glandular dose and quality control practice and to identify optimisation needs.MethodsTwo questionnaires, targeted at breast radiographers and chief radiographers, were designed and applied in 65 imaging departments offering DM. Questions fielded were focused on the staff profile and technical/clinical practice.ResultsPrior to starting their activity in DM, 70% (82 out of 118) of the respondents received training in DM. The practice in 29 out of 59 providers was established by the manufacturers’ recommendations for image acquisition. Variations were observed between radiographers who belong to the same provider namely the selection of exposure parameters such as the target-filter combination and automatic mode. The use of the manual exposure mode was reported for imaging breast implants (44%) and surgical specimens (22%). The main causes of repeat examinations were skin folding (21%) and absence of pectoral muscle (PM) (20%).ConclusionsThe study revealed opportunities to optimise radiographers’ practice in DM regarding the selection of exposure parameters. A robust and consistent training programme in DM and established local protocols can help to reduce the variations observed and improve clinical practice.Main Messages• Radiographers adopted different practices selecting AEC modes and T/F combinations.• Radiographer practice is more consistent using DR than using CR systems.• The main causes for rejecting images were the visibility of skin folding and PM absence.• Radiographers were partly unaware of the dose indicator.• Radiographers’ training needs: QC, interventional procedures and breast dose optimisation.

O53. Dosimetric data for diagnostic digital mammography employing Fully Automated Self adjusting Tilt compression

Introduction Digital mammography aims to clinically detect breast pathology or cancer. This is important as breast cancer has one of the highest incident and mortality rates worldwide for women. The aim of this study was to evaluate several imaging and demographic parameters of the 2D imaging done at Universitas Academic Hospital and to compare the mean glandular dose (MGD) values obtained to recent studies published from other institutions worldwide. Materials and methods Data were collected for 200 patients who underwent mammographic imaging at Universitas Academic Hospital. The data were analysed for the patient age, MGD, mAs, kV, target filter combination, compression force and compressed thickness from the Digital Imaging and Communications in Medicine file. Results Imaging parameter results showed that the average MGD was 1.52 ± 0.71 mGy, the average compression force, 69 N, the average kV, 30, the average mAs, 138 and the average compressed thickness, 58 mm. The mean patient age was recorded as 55 years. Conclusion The MGD from Universitas Academic Hospital compared well with the average screening MGD values of other institutions worldwide (average 1.72 ± 0.36 mGy). Higher MGD values were expected for Universitas Academic Hospital as diagnostic mammography and not screening mammography is practiced at Universitas Academic Hospital. The mean compression force is considered low if compared to the recommendations from the European guidelines of a minimum of 110 N compression force. The performance of the Fully Automated Self adjusting Tilt compression mode could explain lower registered compression values found in this study.

Impacto da pureza dos filtros de alumínio no valor de Camada Semi-Redutora em radiologia convencional e mamografia

Half Value Layer (HVL) test is an important technical information in conventional radiology once it is the only test which allows us to quantify beam quality in a complete way. This work promotes a preliminary analysis of the impact of aluminum alloy composition in the determination of HVL value taking into account a realistic geometry. Deterministic calculations and Monte Carlo Method were applied in order to make the proposed analysis. Six aluminum alloys (99% pure) commercialized and pure aluminum were used as comparative basis for both methods. Experimental data were collected in conventional radiology, using tungsten target and aluminum filter for two peak tensions (66 kVp, 81 kVp), and in mammography, using three target filter combinations( molybdenum-molybdenum, molybdenum-rhodium, tungsten-rhodium) for three peak tensions (25 kVp, 30 kVp and 35 kVp). Spectra used in the deterministic calculations were taken from Report No 78 of Institute of Physics and Engineering in Medicine, 1997. Results show that Mammography is more sensitive than conventional X-ray equipment to impurities in aluminum alloys (up to 34.65% variation for W-Rh combination with 30 kVp).

Avaliação da qualidade da imagem e da Dose Glandular Média em Mamografia Digital.

The most important reference for breast cancer diagnosis is still the mammography. Mammographic technology has evolved in such a way that we have digital systems nowadays. Thus, image generation quality control must evolve as well. In this work, we have evaluated digital image quality and entrance skin dose (ESD) for different breast thicknesses simulated by PMMA plates (one, two, three and four centimeters) for different target filter combinations, suggesting a protocol optimization to the mammographic automatic system.We have used CDMAM 3.4 phantom (a contrast detail phantom) and its software in order to analyze digital images from a Siemens Mammomat Inspiration mammographic equipment. It has been used three combinations of target-filter: Molybdenum Molybdenum, Molybdenum Rhodium, Tungsten Rhodium. Different peak tensions were tested to each configuration: 24 kVp, 26 kVp, 28 kVp and 30 kVp. Altogether 52 different configurations were tested. In order to measure ESD, we used Radcal’s 10x5–6M ionization chamber.Results show that automatic configuration does not offer an optimized process. Tungsten Rhodium was the best option for all breast thicknesses, once it offered the best relation between image quality and mean glandular dose. This result differs from literature which states that the Molybdenum Molybdenum combination is the best option for thin breasts.

Task-based strategy for optimized contrast enhanced breast imaging: Analysis of six imaging techniques for mammography and tomosynthesis

The use of contrast agents in breast imaging has the capability of enhancing nodule detectability and providing physiological information. Accordingly, there has been a growing trend toward using iodine as a contrast medium in digital mammography (DM) and digital breast tomosynthesis (DBT). Widespread use raises concerns about the best way to use iodine in DM and DBT, and thus a comparison is necessary to evaluate typical iodine-enhanced imaging methods. This study used a task-based observer model to determine the optimal imaging approach by analyzing six imaging paradigms in terms of their ability to resolve iodine at a given dose: unsubtracted mammography and tomosynthesis, temporal subtraction mammography and tomosynthesis, and dual energy subtraction mammography and tomosynthesis. Imaging performance was characterized using a detectability index d', derived from the system task transfer function (TTF), an imaging task, iodine signal difference, and the noise power spectrum (NPS). The task modeled a 10 mm diameter lesion containing iodine concentrations between 2.1 mg/cc and 8.6 mg/cc. TTF was obtained using an edge phantom, and the NPS was measured over several exposure levels, energies, and target-filter combinations. Using a structured CIRS phantom, d' was generated as a function of dose and iodine concentration. For all iodine concentrations and dose, temporal subtraction techniques for mammography and tomosynthesis yielded the highest d', while dual energy techniques for both modalities demonstrated the next best performance. Unsubtracted imaging resulted in the lowest d' values for both modalities, with unsubtracted mammography performing the worst out of all six paradigms. At any dose, temporal subtraction imaging provides the greatest detectability, with temporally subtracted DBT performing the highest. The authors attribute the successful performance to excellent cancellation of inplane structures and improved signal difference in the lesion.

WE-G-103-09: The Impact of Mammography Physics Instrumentation On Entrance Air Kerma and Mean Glandular Dose

Purpose: Recent mammography equipment evaluations for new installations showed discrepancies in measurements of parameters related to MGD with different physics instrumentation. The purpose of this study is to evaluate the reasons for these discrepancies for two major vendors of mammography equipment. Methods: This study tested GE Essential and Hologic Dimensions units (6 target-filter combinations) with 4 instruments from 3 vendors using techniques specified by ACR and in agreement with manufacturers recommendations. Relative MGDs were calculated from measured entrance air kerma (EAK), kVp and HVL for each target-filter combination at fixed mAs for each instrument. The effect of each parameter on MGD was evaluated independently. Particular attention was paid to the relevant kVps (28–30) and target-filter combinations required for mammography phantom MGD calculations by interpolation from published dose tables. Results: EAK was found to be nearly independent of field size and varied nearly linearly with kVp for all instruments. In the range of kVps for phantom MGD measurements, a measured error as large as 1 kV had very small (0.5–1.5%) impact on decreasing MGD, whereas +5% error in HVL reduced MGD by 4%. Errors in instrument response for kVp and HVL of these magnitudes were seen and reported separately. For the 6 target-filter combinations and all instruments, the variability in calculated MDG ranged from −5.8% to +5.3%. Analysis of each relevant parameter independently for two instruments showed occasional fortuitous compensations between errors in HVL and EAK that reduced the total error in MGD from 10% to 5%. Conclusion: Discrepancies in measured EAK are likely to be attributed to the fact that NIST beams for mammography calibrations are limited to Mo/Mo. Errors reported here Result from measurements made with extreme care in a well-defined setup. Larger errors in a typical clinical setting could reasonably be expected.

Alternative Exposure Parameters and Post Process Noise Reduction Expect Considerable Dose Reduction in Single Mammography Views—Initial Experience on Mastectomy Specimens

Objective: To experimentally indicate a lower limit of dose in mammographic imaging yielding adequate image quality for complementary diagnostic views, by evaluation of image series with different exposure parameters and additional image processing on mastectomy specimens with diverse pathology. Methods: Image series were obtained on seven specimens with different target-filter combinations at different exposure values. Three experienced radiologists assessed the lowest acceptable dose level per specimen using a relative grading technique. With the standard image as reference, fibroglandular tissue and pathological structures, including microcalcifications, were evaluated. Subsequently, a series of pixel binning processes was tested and subjectively assessed on the selected images. Results: The lowest dose level at which image quality was acceptable, and achieved with a W/Ag target-filter combination at 32 kV and 4 mAs. These images can be acquired with 10.4% to 22.4% of the average glandular dose in standard images. Post process pixel binning added to the interpretability of such low dose images. Conclusion: This specimen study suggests that dose level of mammography images might be reduced substantially by general application of a W/Ag spectrum, particularly when combined with post process noise reduction. Future studies should focus on the feasibility of this technique in clinical mammography.

MO-A-218-01: CT Protocol Review - Practical Tips for Imaging Physicists.

In the 1980's and 90's, when every mammography department had a wet film processor and a sundial to keep the schedule, medical physicists performing mammography surveys were primarily focused on measuring machine performance and image quality. As our professional experience matured, medical physicists began to learn that they were uniquely qualified to help to recommend technique factors that would balance dose and image quality. Technique charts using different kVp, target-filter combinations and AEC modes gradually became common and patients benefitted from our input. With the revolutionary change in CT Scanner technology and utilization, medical physicists have begun to contribute their expertise to developing and improving CT protocols. This presentation will present practical challenges and offer some directions for the practicing medical physicist who desires to participate in this critical and emerging aspect of imaging physics practice: CT Protocol Review.

SU-E-I-60: Validation of An Optically Stimulated Luminescent (OSL) Dosimeter for Use in Output Exposure Control Verification of Mammography Imaging Systems.

To develop and validate an Optically Stimulated Luminescent (OSL) dosimeter for exposure control verification of x-ray projection mammography imaging systems. The active detection element of the dosimeter is a strip of OSL material 3.0 mm wide, 0.13 mm thick and 30.0 mm long with an overlying aluminum step wedge with thicknesses of 0, 0.2, 0.4 and 0.6 mm Al, encapsulated in a light-tight plastic enclosure with outer dimensions of 10.0 mm wide, 5.4 mm thick, and 54.0 mm long. The dosimeter is used in conjunction with a breast phantom for the purpose of estimating the half-value layer (HVL), entrance surface exposure (ESE), and average glandular dose (AGD) in conventional projection mammography. ESE and HVL were computed based on analysis of exposure profiles obtained from exposed strip dosimeters. The AGD was estimated by multiplying the ESE by the appropriate exposure to dose conversion factor for the thickness and % glandular tissue fraction represented by the phantom and target-filter combination employed. The accuracy and reproducibility of the ESE, HVL and AGD estimates obtained using the dosimeter positioned on the surface of the ACR phantom at the chest wall edge, was evaluated using mammography systems utilizing different imaging receptor technology, i.e. screen-film (SF), computed radiography (CR) and direct radiography (DR) and compared against results obtained using a calibrated ion chamber fitted with a mammography probe. ESE, AGD and HVL results obtained using the OSL mammography QA dosimeter agreed with results obtained using an ion chamber to within 5-10%, depending on the target-filter combination used. Repeat readings were highly consistent with a coefficient of variation = 5%. The OSL mammography QA dosimeter has been shown to effectively estimate ESE, HVL and AGD, demonstrating its usefulness for secondary monitoring of output exposure of mammography imaging systems.

Estudo comparativo de dosimetria computacional entre modelos homogêneos e um modelo voxel em mamografia: uma discussão de aplicações em testes de constância e cálculo de dose glandular em pacientes

OBJETIVO: Comparar dados de dosimetria e fluência de fótons entre diferentes modelos de mama, discutindo as aplicações em testes de constância e estudos dosimétricos aplicados à mamografia. MATERIAIS E MÉTODOS: Foram simulados diferentes modelos homogêneos e um modelo antropomórfico de mama tipo voxel, sendo contabilizadas: a dose total absorvida no modelo, a dose absorvida pelo tecido glandular/material equivalente, e a dose absorvida e a fluência de fótons em diferentes profundidades dos modelos. Uma câmara de ionização simulada coletou o kerma de entrada na pele. As combinações alvo-filtro estudadas foram Mo-30Mo e Mo-25Rh, para diferentes potenciais aceleradores de 26 kVp até 34 kVp. RESULTADOS: A dose glandular normalizada, comparada ao modelo voxel, resultou em diferenças entre -15% até -21% para RMI, -10% para PhantomMama e 10% para os modelos Barts e Keithley. A variação dos valores da camada semirredutora entre modelos foi geralmente inferior a 10% para todos os volumes sensíveis. CONCLUSÃO: Para avaliar a dose glandular normalizada e a dose glandular, em mamas médias, recomenda-se o modelo de Dance. Os modelos homogêneos devem ser utilizados para realizar testes de constância em dosimetria, mas eles não são indicados para estimar a dosimetria em pacientes reais

Monte Carlo Simulation of Average Glandular Dose and an Investigation of Influencing Factors

This study aims to determine the average absorbed dose of radiation in glandular tissue during mammography and to investigate factors that influence the average glandular dose, particularly the local distribution of glandular tissue within the breast and breast skin thickness. An EGSnrc Monte Carlo code and associated codes were employed in the simulation. The breast voxel models used consist of a homogeneous and heterogeneous mixture of adipose and glandular tissues embedded in a skin layer. The percent depth dose and normalized average glandular dose coefficients for spectra of Mo-Mo target-filter combination were calculated. The results showed good agreement with the experimental results (percent depth dose) and literature values (normalized average glandular dose coefficients) when the breast model is homogeneous. Additional investigation of a heterogeneous breast phantom indicates that the local distribution of glandular tissue within the breast, as well as breast skin thickness, could affect the average glandular dose considerably more than that of a typical homogeneous breast model. This problem may be a concern in most practical situations of breast dosimetry when assessing the radiation risk to patients.

Evaluation of subject contrast and normalized average glandular dose by semi-analytical models

In this work, two semi-analytical models are described to evaluate the subject contrast of nodules and the normalized average glandular dose in mammography. Both models were used to study the influence of some parameters, such as breast characteristics (thickness and composition) and incident spectra (kVp and target-filter combination) on the subject contrast of a nodule and on the normalized average glandular dose. From the subject contrast results, detection limits of nodules were also determined. Our results are in good agreement with those reported by other authors, who had used Monte Carlo simulation, showing the robustness of our semi-analytical method.