Rh Filter Research Articles

CNR performance of semiconductor materials for X-ray imaging of breast calcifications

We present the results of a GAMOS/GEANT4 computer simulation of a standard X-ray mammography system, which consists of a Tungsten 28 kVp polychromatic X-ray source with a 50 μm Rh filter, a mammography phantom with Al2O3 spherical specks of different diameters, and a generic pixel detector (55 μm × 55 μm pixel size) with different types of semiconductor sensors. The number of photons simulated is calibrated to produce similar entrance surface dose (ESD) as the one used by a standard clinical mammography screening. Estimates of Contrast to Noise Ratio (CNR) as a function of ESD, sensor thickness and microcalcification diameter are presented for four different sensor materials: Silicon (Si), Cadmium Telluride (CdTe), Gallium Arsenide (GaAs) and Perovskite (MAPbI3). For the X-ray energy spectrum and pixel size considered, and an ESD dose of 4 mGy, our study shows that, with the exception of Si, these sensors, as thin as 200 μm, are able to resolve (with at least 3 standard deviations above background) Al2O3 spherical specks up to a minimum diameter of 180 μm, having statistically compatible CNR performance. The increase in substrate thickness has a substantial improvement in the CNR values provided by the Si sensor, while for the other cases the enhancement of CNR is marginal and consistent with statistical uncertainties with the thinnest case considered.

Application of isotherm models to combined filter systems for the prediction of iron and lead removal from automobile workshop stormwater runoff

Langmuir and Freundlich isotherm adsorption models were used to predict iron and lead removal from automobile workshop stormwater runoff. Combined low-cost filter systems consisting of granular activated carbon–rice husk (GAC–RH) and river gravel–granular activated carbon (GR–GAC) were used in this study. The effects of adsorbent dosage and contact time on the adsorption capacity of the adsorbents, as well as the removal efficiencies of the adsorbent systems, were also investigated. The results for the Langmuir model generally showed favourable adsorption processes., with all RL values < 1 (in the range 0.358–0.518). The Langmuir model gave better predictions for iron and lead removal, with high R2 values (in the range 0.842–0.969), while the root mean square error (RMSE) values ranged from 0.002 to 2.366. The Freundlich model parameters indicated chemisorption processes with all n values < 1 (in the range 0.1296–0.4675). R2 values were in the range of 0.634–0.916 while RMSE values ranged from 0.002 to 0.1765. Additionally, the removal efficiencies for iron and lead using GAC–RH filter system (54% and 48%, respectively) were found to be higher than those obtained using GR–GAC filter system (35% and 25%, respectively). The adsorption capacities of the adsorbents decreased with increased dosages of the adsorbent, with optimum adsorbent dosage of 0.5 g and equilibrium contact time of 80 min for the combined filter adsorbents. Further research towards modifying adsorbents for removal of oil and grease from polluted automobile workshop stormwater runoff are warranted.

Influence of the dosimeter calibration conditions on the mean glandular dose in mammography

Digital technology in mammography and breast tomosynthesis introduced the use of W and Rh target x-ray tubes with Al, Mo, Rh and Ag additional filters. In Brazil, due to the limited capability of metrology laboratories, x-ray dosimetry in mammography is done with different types of dosimeters that may not be calibrated for such specific clinical beams. The objective of this work was to study the influence of different calibration conditions on the determination of the mean glandular dose in dosimetry in mammography beams.

Image Quality and Radiation Dose for Fibrofatty Breast using Target/filter Combinations in Two Digital Mammography Systems.

Objectives:The aim of this study was to determine the optimum combinations of target and filter materials for various X-ray tube voltage settings, as well as their effects on image quality and radiation dose. This was done using different digital mammography (DM) imaging systems with a breast equivalent phantom.Material and Methods: Two DM units with a tungsten (W) target, silver (Ag), and rhodium (Rh) filters and dual molybdenum (Mo) and Rh targets/filters were used. A tissue-equivalent mammography phantom of 6 cm thickness equivalent to a fibrofatty breast was exposed 20 times to different target/filter material combinations (W/Rh, W/Ag, Rh/Rh, Mo/Rh, and Mo/Mo) and various kV settings (28–34 kV). The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated for each exposure.Results:The W/Ag combination resulted in the lowest entrance skin dose and mean glandular dose (MGD). The MGD for the W/Rh combination was 60% less than that of the W/Ag combination at 34 kV (P < 0.05). There was a direct relationship in the SNR with the Mo/Mo, Mo/Rh, and Rh/Rh combinations and an inverse relationship with the CNR in the 34 kV range. There were statistically significant differences between all five target/filter combinations, and the best SNR and CNR were observed for the W/Rh combination with a reduced radiation dose in the range of 28–30 kV (P < 0.05).Conclusion:For a breast thicknesses of 6 cm with a fibrofatty nature, the W/Rh combination delivers high performance in terms of image quality at a lower dose.

Validation of kVp measurement using the HVL approach for standard beam qualities for mammography

In mammography imaging, the most common target material used in mammography machines are Molybdenum (Mo) target with Mo filters. In the publication of International Electrotechnical Commission (IEC) 61267, the establishment of mammography beam qualities assembly are given in 3 fixed parameters namely the target material which is Mo, the Mo filter thickness and the tube voltage. While, Mo target with rhodium (Rh) filters combination standard beam qualities were established by the Physikalish-Technische Bundesanstalt (PTB) primary standard Laboratory. The objective of this study is to measure the kVp and HVL ranging from 23-31 kV. Later compare the displayed kilovoltage peak (kVp) on the control panel with the kVp measured using a non-invasive kVp meter and validating them with the HVL measurement. From the results, the kVp dialed and kVp measured shows significant difference by 2-4 kV. The HVL measured for the kVp before and after corrected also shows similar pattern, where the HVL after kVp is correct is almost identical to the standard beam qualities with the difference of 1%. This verifies that the kVp measurement using a non-invasive kVp meter can be validated with just a simple measurement of its HVL for mammography standard beam qualities.

Simulation Study of a Monochromatic X-ray Beam with K-edge Filter for Low Dose Mammography

X-ray mammography can be used to acquire images useful for early breast cancer detection in medical applications. There have been a number of approaches to diagnostic low-dose mammography. The purpose of this study was to design a concept for use of monochromatic X-ray beams by using K-edge filters for low dose mammography. The SRS-78 X-ray simulation code and Monte Carlo simulation GATE code were used to model the X-ray tube, target material, filter material, breast phantom, and detector. To achieve a monochromatic X-ray beam, molybdenum (Mo) and rhodium (Rh) were used as filter materials in various thicknesses. The direct conversion detector (FDXD 1417, Drtech, Seongnam, Korea) composed of thin-film transistor (TFT)-amorphous selenium (a-Se) was modelled through Monte Carlo simulation. According to the CVR and EER results, the filter thickness for optimal mammographic imaging is set to 6 and 3 HVL for Mo and Rh, respectively. SNR values with the Rh filter improved by 1.01, 6.28, 5.60, 5.60, 5.60, 5.60 % over the range from 0.1 to 0.6 μGy compared to analogous SNR values without filter. The present work demonstrates that monochromatic X-ray beams can be generated for low dose mammography. According to the results, Rh filter could be useful for enhancing calcification while absorbed dose is reduced.

A study for the optimization of tube voltage and filter in digital mammography

Objective To investigate the image quality and average glandular dose from different breast compression thickness, and to provide recommendations for filtration material and tube voltage in digital mammography. Methods The CDMAM phantom of 2 to 7 cm thickness were exposed by manual exposure modes(proper mAs, 21 to 39 kVp range) using Mo/Mo and Mo/Rh anode/filer combinations at full-field digital mammography. The image quality figure (IQF), contrast to noise ratio (CNR), figure of merit (FOM) and the average glandular dose (AGD) were obtained from images. The optimum filtration and kVp for each breast thickness were found from the calculated FOMs. And the paired sample rank sum test was used to analyze the difference of AGD, CNR, IQF and FOM for Mo and Rh filters. Results For both Mo and Rh as used filter, under the compression of 2 to 7 cm thickness and the fixed mAs, with the increasing of tube voltage, AGD, CNR and IQF will gradually increase as following: AGD had the significant increasing while CNR and IQF gradually increasing to balance. Under different compression thickness, the AGD for Mo and Rh were statistically different (P 0.05).When the compression thickness was 4 cm, CNR for Mo and Rh were with no statistical significance (P 0.05) under the thickness of 5 cm and 7 cm; the IQF for Mo and Rh with no statistical significance (P>0.05). The FOM in each thickness for Mo and Rh filtration had statistical significance (P FOMMo. For different compression thickness, the suitable matching of tube voltage and filter material were Rh filtration, 2 cm and 27 kVp, 3 cm and 29 kVp, 4 cm and 29 kVp, 5 cm and 30 kVp, 6 cm and 31 kVp, 7 cm and 32 kVp. Conclusion Considering both image quality and radiation dose, Rh filtration is the optimum selection material and there is a corresponding optimal energy response in all kinds of thickness. Key words: Mammography; Image quality; Radiation dosage

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.

MO-FG-CAMPUS-IeP1-01: Alternative K-Edge Filters for Low-Energy Image Acquisition in Contrast Enhanced Spectral Mammography

Purpose: In Contrast Enhanced Spectral Mammography (CESM), Rh filter is often used during low-energy image acquisition. The potential for using Ag, In and Sn filters, which exhibit K-edge closer to, and just below that of Iodine, instead of the Rh filter, was investigated for the low-energy image acquisition. Methods: Analytical computations of the half-value thickness (HVT) and the photon fluence per mAs (photons/mm2/mAs) for 50µm Rh were compared with other potential K-edge filters (Ag, In and Sn), all with K-absorption edge below that of Iodine. Two strategies were investigated: fixed kVp and filter thickness (50µm for all filters) resulting in HVT variation, and fixed kVp and HVT resulting in variation in Ag, In and Sn thickness. Monte Carlo simulations (GEANT4) were conducted to determine if the scatter-to-primary ratio (SPR) and the point spread function of scatter (scatter PSF) differed between Rh and other K-edge filters. Results: Ag, In and Sn filters (50µm thick) increased photon fluence/mAs by 1.3–1.4, 1.8–2, and 1.7–2 at 28-32 kVp compared to 50µm Rh, which could decrease exposure time. Additionally, the fraction of spectra closer to and just below Iodine's K-edge increased with these filters, which could improve post-subtraction image contrast. For HVT matched to 50µm Rh filtered spectra, the thickness range for Ag, In, and Sn were (41,44)µm, (49,55)µm and (45,53)µm, and increased photon fluence/mAs by 1.5–1.7, 1.6–2, and 1.6–2.2, respectively. Monte Carlo simulations showed that neither the SPR nor the scatter PSF of Ag, In and Sn differed from Rh, indicating no additional detriment due to x-ray scatter. Conclusion: The use of Ag, In and Sn filters for low-energy image acquisition in CESM is potentially feasible and could decrease exposure time and may improve post-subtraction image contrast. Effect of these filters on radiation dose, contrast, noise and associated metrics are being investigated. Funding Support: Supported in part by NIH R01CA195512. The contents are solely the responsibility of the authors and do not reflect the official views of the NIH or NCI.

Low dose high energy x-ray in-line phase sensitive imaging prototype: Investigation of optimal geometric conditions and design parameters.

The objective of this study was to investigate the optimization of a high energy in-line phase sensitive x-ray imaging prototype under different geometric and operating conditions for mammography application. A phase retrieval algorithm based on phase attenuation duality (PAD) was applied to the phase contrast images acquired by the prototype. Imaging performance was investigated at four magnification values of 1.67, 2, 2.5 and 3 using an acrylic edge, an American College of Radiology (ACR) mammography phantom and contrast detail (CD) phantom with tube potentials of 100, 120 and 140 kVp. The ACR and CD images were acquired at the same mean glandular dose (MGD) of 1.29 mGy with a computed radiography (CR) detector of 43.75 μm pixel pitch at a fixed source to image distance (SID) of 170 cm. The x-ray tube focal spot size was kept constant as 7 μm while a 2.5 mm thick aluminum (Al) filter was used for beam hardening. The performance of phase contrast and phase retrieved images were compared with computer simulations based on the relative phase contrast factor (RPF) at high x-ray energies. The imaging results showed that the x-ray tube operated at 100 kVp under the magnification of 2.5 exhibits superior imaging performance which is in accordance to the computer simulations. As compared to the phase contrast images, the phase retrieved images of the ACR and CD phantoms demonstrated improved imaging contrast and target discrimination. We compared the CD phantom images acquired in conventional contact mode with and without the anti-scatter grid using the same prototype at 1.295 mGy and 2.59 mGy using 40 kVp, a 25 μm rhodium (Rh) filter. At the same radiation dose, the phase sensitive images provided improved detection capabilities for both the large and small discs, while compared to the double dose image acquired in conventional mode, the observer study also indicated that the phase sensitive images provided improved detection capabilities for the large discs. This study therefore validates the potential of using high energy phase contrast x-ray imaging to improve lesion detection and reduce radiation dose for clinical applications such as mammography.

Correlation study of effect of additional filter on radiation dose and image quality in digital mammography

Objective To explore the effect of different additional filters on radiation dose and image quality in digital mammography.Methods Hologic company's Selenia digital mammography machine and the post-processing workstations and 5 M high resolution medical monitor were used in this study.Mammography phantoms with the thickness from 1.6 cm to 8.6 cm were used to simulate human breast tissue.The same exposure conditions,pressure,compression thickness,the anode were employed with the additional filters of Mo and Rh under the automatic and manual exposure mode.The image kV,mAs,pressure,filter,average glandular dose (AGD),entrance surface dose (ESD),signal-to-noise ratio (SNR),contrast-to-noise ratio (CNR) and image score according to ACR criteria were recorded for the two additional filters.Paired sample t test was performed to compare the indices of Mo and Rh groups by using SPSS 17.0.Results AGD and ESD of Rh and Mo group were both higher with the increase of the thickness of all the phantoms.AGD,ESD and their increased value of Rh filter(1.484 ± 1.041,7.969 ± 7.633,0.423 ± 0.190 and 3.057 ± 2.139) were lower than those of Mo filter(1.915 ± 1.301,12.516 ± 11.632,0.539 ±0.246 and 4.731 ± 3.294),in all the phantoms with different thickness (t values were 4.614,3.209,3.396 and 3.605,P ＜0.05).SNR,CNR,and image score of Rh and Mo group both decreased with the increase of the thickness of all the phantoms.There were no statistical difference (P ＞ 0.05).Conclusions Compared with Mo filter,Rh filter could reduce the radiation dose,and this advantage is more obvious in the thicker phantom when the same image quality is required. Key words: Mammography; Radiation dosage; Comparative study

SU-E-I-04: A Mammography Phantom to Measure Mean Glandular Dose and Image Quality

Purpose: To evaluate mean glandular dose (MGD) and image quality in a selection of mammography systems using a novel phantom based on thermoluminescent dosemeters and the ACR wax insert. Methods: The phantom consists of two acrylic, 19 cm diameter, 4.5 cm thick, semicircular modules, used in sequence. The image quality module contains the ACR insert and is used to obtain a quality control image under automatic exposure conditions. The dosimetric module carries 15 TLD-100 chips, some under Al foils, to determine air kerma and half-value-layer. TL readings take place at our laboratory under controlled conditions. Calibration was performed using an ionization chamber and a Senographe 2000D unit for a variety of beam qualities, from 24 to 40 kV, Mo and Rh anodes and filters. Phantom MGD values agree, on the average, within 3% with ionization chamber data, and their precision is better than 10% (k=1). Results: MGD and image quality have been evaluated in a selection of mammography units currently used in Mexican health services. The sample includes analogic (screen/film), flexible digital (CR), and full-field digital image receptors. The highest MDG are associated to the CR technology. The most common image quality failure is due to artifacts (dust, intensifying screen scratches, and processor marks for film/screen, laser reader defects for CR). Conclusion: The developed phantom permits the MGD measurement without the need of a calibrated ionization chamber at the mammography site and can be used by a technician without the presence of a medical physicist. The results indicate the urgent need to establish quality control programs for mammography.

In-vivo dosimetry in 3D conformal radiotherapy of breast and head and neck cancer

In-vivo dosimetry in 3D conformal radiotherapy of breast and head and neck cancer

SU‐C‐116‐02: Volumetric Dose Deposition in the Breast Using Real‐Time Dosimetry

Purpose: To empirically determine the angular dose distribution to a breast in a digital breast tomosythesis and mammography system using real‐time dosimetry technology. Methods: Three breast phantoms, constructed from polyethylene to simulate adipose tissue, were fabricated based on ninety cranio‐caudal mammography patients. The smallest (3.2 cm), average (5.1 cm), and largest (7.0 cm) breast thickness matched the measured breast shape using 13 mm polyethylene sheets. Technique factors, which matched the automatic settings in both tomo and mammo were used. Phantoms were designed to be modular allowing a dose probe to be placed in various heights and depths. A total of 390 signal trains, comprised of 15‐individual pulses (one for each angle) in tomo‐mode and a single pulse for mammo, were collected using a real‐time air ionization chamber (AccuGold, Radcal, Monrovia, CA). The signal train was integrated to generate a dose value at each location. This data was then used to generate a dynamic model of cumulative dose deposition as a function of x‐ray tube angle in tomo and mammo modes. Additionally, the effective linear attenuation coefficient for each energy was calculated. Using a look up table for the linear attenuation of polyethylene, the effective energy was calculated. Results: The dose deposition decreases from the compression paddle to the detector. Cumulative dose from tomo scan was comparable to that of mammo; differences in cumulative dose increased with phantom size. The effective energy for tomo at 28, 31 and 35 kVp with Al filter was calculated to be 19.7, 21.7 and 25 kV respectively. For mammo at 26, 29 (Rh filter) and 30 kV (Ag filter) was found to be19.1, 20.4 and 23.7 respectively. Conclusion: The volumetric dose deposition in Hologics dBT system shows angular dependence as a function of angle in tomo mode. NIH Grants

Calculation of Absorbed Glandular Dose using a FORTRAN Program Based on Monte Carlo X-ray Spectra in Mammography

Introduction: Average glandular dose calculation in mammography with Mo-Rh target-filter and dose calculation for different situations is accurate and fast. Material and Methods: In this research, first of all, x-ray spectra of a Mo target bombarded by a 28 keV electron beam with and without a Rh filter were calculated using the MCNP code. Then, we used the Sobol-Wu parameters to write a FORTRAN code to calculate average glandular dose. Results: Average glandular dose variation was calculated against the voltage of the mammographic x-ray tube for d = 5 cm, HVL= 0.35 mm Al, and different value of g. Also, the results related to average glandular absorbed dose variation per unit roentgen radiation against the glandular fraction of breast tissue for kV = 28 and HVL = 0.400 mmAl and different values of d are presented. Finally, average glandular dose against d for g = 60% and three values of kV (23, 27, 35 kV) with corresponding HVLs have been calculated. Discussion and Conclusion: The absorbed dose computational program is accurate, complete, fast and user friendly. This program can be used for optimization of exposure dose in mammography. Also, the results of this research are in good agreement with the computational results of others.

SU‐GG‐I‐130: An Evaluation of Image Quality and Dose for a Hologic Selenia Digital Mammography System with a Tungsten Anode X‐Ray Tube

Purpose: Image quality and breast dose for an amorphous selenium detector digital mammography system with a tungsten (W) anode x‐ray tube and rhodium (Rh) and silver (Ag) filters were compared to an equivalent model system with a molybdenum (Mo) anode x‐ray tube and Mo and Rh filters. Method and Materials: Signal difference to noise ratio (SDNR) and mean glandular dose (MGD) were measured for 4, 6 and 8‐cm thick breast equivalent material slabs and an aluminum contrast object. Values were compared over a range of kVp and mAs selections for Mo/Mo, Mo/Rh, W/Rh and W/Ag anode/filter combinations. The kVp selection that resulted in the highest SDNR for each thickness and anode/filter combination was determined. SDNR at the optimum kVp for each anode/filter was then compared. The automatic exposure control (AEC) selections for the W and Mo system were also compared with regards to SDNR and MGD. Results: W/Rh was found to produce the highest SDNR over a wide MGD range, followed by W/Ag, Mo/Rh and Mo/Mo. The W anode system provided a 30–35% improvement in SDNR for the same breast dose as compared to the Mo anode system. When the SDNR of the W anode and M anode systems are matched, the W anode system resulted in a 40–50% reduction in MGD. Using the W anode system default AEC for selection of exposure parameters, a 7–25% improvement in SDNR and a 10–30% reduction in MGD was achieved, as compared to the Mo anode system. Conclusion: The W anode system provides superior image quality for the same breast dose. The default AEC for this system provides a compromise between image quality improvement and decreased dose as compared to the Mo anode system.

Monte Carlo simulation of DNA damage induction by x-rays and selected radioisotopes

To better assess the potential biological consequences of diagnostic x-rays and selected γ-emitting radioisotopes used in brachytherapy, we used the PENELOPE Monte Carlo radiation transport code to estimate the spectrum of initial electrons produced by photons in single cells and in an irradiation geometry similar to those used in cell culture experiments. We then combined estimates of the initial spectrum of electrons from PENELOPE with DNA damage yields for monoenergetic electrons from the fast Monte Carlo damage simulation (MCDS). The predicted absolute yields (Gbp−1 Gy−1) and RBE values for single-strand break (SSB) and double-strand break (DSB) induction by 220 kVp x-rays are within 1% of the results from detailed track-structure simulations (Friedland et al 1999 Radiat. Environ. Biophys. 38 39). The measured RBE for DSB induction reported by Kühne et al (2005 Radiat. Res. 164 669) for γ-rays from 60Co and for 29 kVp x-rays with a 50 µm Rh (mammography) filter are in excellent agreement (1.15 versus 1.16). DSB yields predicted by the MCDS also agree to within 7% with the absolute DSB yields reported by de Lara et al (2001 Radiat. Res. 155 440) and Botchway et al (1997 Radiat. Res. 148 317) for the irradiation of V79 cells by low energy (<2 keV) characteristic x-rays. The predicted RBE for DSB induction by γ-rays from bare 169Yb and 131Cs to 60Co are 1.06 and 1.14, respectively. Tabulated RBE values for the single-cell and monolayer cell culture geometries differ by at most 15%. The proposed methodology is computationally efficient and may also be useful for the prediction of damage yields for mixtures of other types of charged particles, such as those found in proton therapy, space applications or internal dosimetry.

Monte Carlo Simulation of X-ray Source Characteristics Using MCPETS and MCNPX Codes for Mammography

Monte Carlo simulation of X-ray emission from thick anodes irradiated by a monochromatic electron beam is described. To verify the code, we simulated the spectra of molybdenum and tungsten targets and compared the results to the reference data and to the results obtained with the MCNPX code. Then, the spectra of an X-ray tube with a tungsten anode supplemented with various filters were simulated with the developed code. The goal was to find the optimal values of the tube voltage and the filter thickness in order to increase the relative number of outgoing photons within the energy interval of 18 ‐ 25 keV. Our simulation shows that in the case of hundreds of µm thick filters, the total number of photons for a Ag filter is approximately twice that for a Rh filter. Having ascertained these characteristics, one can choose an appropriate filter for special case of X-ray systems.

Experimental investigation on the choice of the tungsten/rhodium anode/filter combination for an amorphous selenium-based digital mammography system

The signal difference-to-noise ratio (SDNR) between aluminium sheets and a homogeneous background was measured for various radiation qualities and breast thicknesses to determine the optimal radiation quality when using a Novation DR mammography system. Breast simulating phantoms, with a thickness from 2 cm to 7 cm, and aluminium sheet, with a thickness of 0.2 mm, were used. Three different combinations of anode/filter material and a wide range of tube voltages were employed for each phantom thickness. Each radiation quality was studied using three different dose levels. The tungsten (W) anode and rhodium (Rh) filter combination achieved the specified SDNR at the lowest mean glandular dose for all the phantom thicknesses and X-ray tube voltages. The difference between the doses for different anode/filter combinations increased with the phantom thickness. For a 5-cm phantom, with a peak tube voltage of 27 kV and a SDNR of 5, the mean glandular dose associated with the use of W/Rh was reduced by 49% when compared to the molybdenum/molybdenum (Mo/Mo) anode/filter combination and by 33% when compared to Mo/Rh. Based on these measurements, the use of the W/Rh anode/filter can be recommended. It remains important, however, to select the appropriate dose level.

Comportamento da dose glandular versus contraste do objeto em mamografia: determinação de formalismo semi-empírico para diferentes combinações alvo-filtro

OBJETIVO: Verificar o efeito da mudança no contraste do objeto, tempo de exposição e dose de radiação quando diferentes espessuras de filtração de molibdênio (Mo) e ródio (Rh) são empregadas em mamógrafos. MATERIAIS E MÉTODOS: Realizaram-se medidas da exposição na entrada da pele com uma câmara de ionização para diferentes espessuras para os filtros de Mo e Rh. Para determinar a dose glandular média foi utilizado simulador de BR12 (50% tecido adiposo e 50% tecido glandular) de diferentes espessuras (4 cm e 8 cm). Energias na faixa de 24 kVp a 34 kVp foram empregadas e filmes Kodak MinR 2000 foram utilizados. RESULTADOS: Os resultados evidenciaram dados de contraste do objeto, dose glandular e tempo de exposição para diferentes espessuras de filtros adicionais e diferentes tensões. Esses dados indicaram aumento nos valores de contraste do objeto e tempo de exposição, com o aumento da espessura dos filtros. A dose glandular apresentou comportamento com diferentes tendências para cada caso analisado. Equações foram definidas para possibilitar a estimativa do contraste do objeto, dose glandular e tempo de exposição para os casos estudados. CONCLUSÃO: Os resultados possibilitaram a estimativa de equações que auxiliam na verificação do comportamento do contraste do objeto e da dose glandular para simuladores com espessura de 4 cm e 8 cm e para os filtros de Rh e Mo. Dessa forma, torna-se possível estimar a figura de mérito (razão entre o contraste do objeto e a dose glandular), podendo auxiliar na análise da relação risco-benefício dos casos estudados.