Luis Benevides - Academia.edu (original) (raw)

Papers by Luis Benevides

Barry Pass1), Alexander Romanyukha2), Tania De1), Lyudmila Romanyukha2), Francois Trompier3), Isa... more Barry Pass1), Alexander Romanyukha2), Tania De1), Lyudmila Romanyukha2), Francois Trompier3), Isabelle Clairand3), Prabhakar Misra1), Luis Benevides2), David Schauer4) 1)Howard University, Washington, DC, 2)Uniformed Services University of the Health Sciences, Bethesda, MD, 3)French Institute for Radiological Protection and Nuclear Safety, Fontenay-aux-roses, 4)National Council on Radiation Protection, Washington, DC e-mail: bpass@howard.edu

Health physics, 2018

The U.S. Navy uses the Harshaw 8840/8841 dosimetric (DT-702/PD) system, which employs LiF:Mg,Cu,P... more The U.S. Navy uses the Harshaw 8840/8841 dosimetric (DT-702/PD) system, which employs LiF:Mg,Cu,P thermoluminescent dosimeters (TLDs), developed and produced by Thermo Fisher Scientific (TFS). The dosimeter consists of four LiF:Mg,Cu,P elements, mounted in Teflon® on an aluminum card and placed in a plastic holder. The holder contains a unique filter for each chip made of copper, acrylonitrile butadiene styrene (ABS), Mylar®, and tin. For accredited dosimetry labs, the ISO/IEC 17025:2005(E) requires an acceptance procedure for all new equipment. The Naval Dosimetry Center (NDC) has developed and tested a new non-destructive procedure, which enables the verification and the evaluation of embedded filters in the holders. Testing is based on attenuation measurements of low-energy radiation transmitted through each filter in a representative sample group of holders to verify that the correct filter type and thickness are present. The measured response ratios are then compared with the e...

Radiation Measurements

Abstract Thermo Fisher Scientific has introduced a new personnel dosimeter, model 8850. This new ... more Abstract Thermo Fisher Scientific has introduced a new personnel dosimeter, model 8850. This new dosimeter consists of a standard Thermo Scientific Harshaw TLD LiF: Mg,Cu,P card, with a new holder design. The reusable holder is small and lightweight, and contains filtration optimized for personnel dosimetry. This new dosimeter was type tested to IEC 62387:2012 along with the Thermo Scientific Harshaw Model 8800PLUS TLD Reader. Extensive testing of the radiological, environmental and mechanical performance of the system was performed according to the standard. The dosimeter is sensitive to a wide photon energy range from 16 keV and dose range from 0.01 mSv. It is also sensitive to beta from 85 Kr. Comprehensive angular and side effect tests for photon and beta were also completed. This paper presents the high-achieving type test results and uncertainty analysis of each test.

Radiation Protection Dosimetry, 2008

An extension of dosemeter issue period brings significant economic and logistic benefits. Therefo... more An extension of dosemeter issue period brings significant economic and logistic benefits. Therefore, it is desirable to have an extended period as long as possible without significant loss of the quality of dose measurements. There are many studies devoted to the investigation of fading or reduction of the dose accumulated in dosemeters with time. However, this is one of many critical factors that need's to be taken into account when extending the dosemeter issue period. Background radiation is also a critical factor that needs to be appropriately accounted. In this report, a new approach has been suggested for evaluating the effect of background radiation on the lower limit of detection (LLD) of occupational radiation dose. This approach is based on the data collected from control dosemeters that are routinely used for subtraction of background radiation from occupational dose measurements. The results show that for LiF:Mg,Cu,P thermoluminescence dosemeters, variations in background radiation have a higher impact on the LLD than dose fading and the absolute value of background radiation. Although there is no significant dose fading in LiF:Mg,Cu,P for a dosemeter issue period up to 1 y, variations in background radiation during this period of time can significantly increase photon LLDs (up to 700 microSv) for workers operating in an environment of variable radiation background.

Medical Imaging 2010: Physics of Medical Imaging, 2010

Pixel Signal to Noise Ratio (SNR) is a commonly used clinical metric for evaluating mammography. ... more Pixel Signal to Noise Ratio (SNR) is a commonly used clinical metric for evaluating mammography. However, we showed in this paper, the pixel SNR can produce misleading system detectability when image processing is utilized. We developed a simple, reliable and clinically applicable methodology to evaluate mammographic imaging systems using a task SNR that accounts for the imaging system performance in

Medical Physics, 2014

The purpose of this work is to evaluate the performance of the image acquisition chain of clinica... more The purpose of this work is to evaluate the performance of the image acquisition chain of clinical full field digital mammography (FFDM) systems by quantifying their image quality, and how well the desired information is captured by the images. The authors present a practical methodology to evaluate FFDM using the task specific system-model-based Fourier Hotelling observer (SMFHO) signal to noise ratio (SNR), which evaluates the signal and noise transfer characteristics of FFDM systems in the presence of a uniform polymethyl methacrylate phantom that models the attenuation of a 6 cm thick 20/80 breast (20% glandular/80% adipose). The authors model the system performance using the generalized modulation transfer function, which accounts for scatter blur and focal spot unsharpness, and the generalized noise power spectrum, both estimated with the phantom placed in the field of view. Using the system model, the authors were able to estimate system detectability for a series of simulated disk signals with various diameters and thicknesses, quantified by a SMFHO SNR map. Contrast-detail (CD) curves were generated from the SNR map and adjusted using an estimate of the human observer efficiency, without performing time-consuming human reader studies. Using the SMFHO method the authors compared two FFDM systems, the GE Senographe DS and Hologic Selenia FFDM systems, which use indirect and direct detectors, respectively. Even though the two FFDM systems have different resolutions, noise properties, detector technologies, and antiscatter grids, the authors found no significant difference between them in terms of detectability for a given signal detection task. The authors also compared the performance between the two image acquisition modes (fine view and standard) of the GE Senographe DS system, and concluded that there is no significant difference when evaluated by the SMFHO. The estimated human observer efficiency was 30 ± 5% when compared to the SMFHO. The results showed good agreement when compared to other model observers as well as previously published human observer data. This method generates CD curves from the SMFHO SNR that can be used as figures of merit for evaluating the image acquisition performance of clinical FFDM systems. It provides a way of creating an empirical model of the FFDM system that accounts for patient scatter, focal spot unsharpness, and detector blur. With the use of simulated signals, this method can predict system performance for a signal known exactly/background known exactly detection task with a limited number of images, therefore, it can be readily applied in a clinical environment.

Radiation Protection Dosimetry, 2011

The phototransferred thermoluminescence (PTTL) technique is applied to the Harshaw LiF:Mg,Cu,P ma... more The phototransferred thermoluminescence (PTTL) technique is applied to the Harshaw LiF:Mg,Cu,P material. It is demonstrated that using 254-nm UV light, dose levels as low as 0.2 mGy can be re-estimated. The PTTL efficiency was found to be ∼ 6 % in the dose range of 0.2 mGy-1 Gy, and it appears to be dose-independent. This implies that a simple calibration factor could be applied to the PTTL data for the re-estimation of dose levels. It was demonstrated that with a proper choice of the TL readout parameters, and the UV-light irradiation conditions, dose levels that are relevant to personal or environmental dosimetry can be re-estimated.

Radiation Protection Dosimetry, 2011

This study investigates several sources of uncertainty associated with the application of optical... more This study investigates several sources of uncertainty associated with the application of optically stimulated luminescence (OSL) to personal dosimetry. A commercial OSL system based on Al(2)O(3):C was used for this study. First, it is demonstrated that the concept of repeated evaluation (readout) of the same dosemeter, often referred to as 're-analysis', can introduce uncertainty in the re-estimated dose. This uncertainty is associated with the fact that the re-analysis process depletes some of the populated traps, resulting in a continuous decrease of the OSL signal with each repeated reading. Furthermore, the rate of depletion may be dose-dependent. Second, it is shown that the previously reported light-induced fading in this system is the result of light leaks through miniature openings in the dosemeter badge.

Radiation Protection Dosimetry, 2011

The effects of UV-induced bleaching of deep traps on Harshaw thermoluminescent (TL) LiF:Mg,Cu,P a... more The effects of UV-induced bleaching of deep traps on Harshaw thermoluminescent (TL) LiF:Mg,Cu,P and LiF:Mg,Ti materials were investigated. During a normal heating cycle, LiF:Mg,Cu,P is limited to a maximum temperature of 240 °C. LiF:Mg,Ti can be read to higher temperatures; however, encapsulation in polytetrafluoroethylene limits the maximum readout temperature to 300 °C. Generally, for both materials, these respective temperatures are sufficient for emptying traps corresponding to the main dosemetric peaks. However, when the dosemeters are subjected to a high dose level, such as 1 Gy (much higher than individual monitoring dose levels), higher temperature traps are filled that cannot be emptied without exceeding the above-mentioned maximum temperatures. These high temperature traps tend to be unstable during normal readout and can significantly increase the residual TL signal. The purpose of this study was to investigate the applicability of a UV-induced bleaching technique for emptying higher temperature traps following high-dose applications. In addition, in the case of LiF:Mg,Cu,P, where the maximum readout temperature is significantly lower, we investigated the possibility of reducing the residual signal using the application of repeated readout cycles. The optical bleaching approach was found to be effective in the case of LiF:Mg,Ti; however, for LiF:Mg,Cu,P, no reduction in the residual signal was observed. For this latter material, the application of repeatable readout cycles is very effective and residual signals equivalent to dose levels as low as 0.01 mGy were observed following an initial dose of 5 Gy. To the best of our knowledge, this work is the first attempt to apply an 'optical annealing' technique to the Harshaw thermoluminescent dosemeter (TLD) materials.

Radiation Measurements, 2014

Radiation Measurements, 2011

... MANUSCRIPT EFFECT OF TLD-700H (LIF:Mg,Cu,P) SENSITIVITY LOSS AT MULTIPLE READ-IRRADIATION CYC... more ... MANUSCRIPT EFFECT OF TLD-700H (LIF:Mg,Cu,P) SENSITIVITY LOSS AT MULTIPLE READ-IRRADIATION CYCLES ON TLD READER CALIBRATION SHANNON P. VOSS, ARTURSUCHETA, ALEX ROMANYUKHA ... Kim, J., Lee, J., Pradhan, A., Kim, B., Kim, S. 2010. ...

Radiation Measurements, 2011

Ideally, dosimeters should measure the dose without their dosimetric properties being affected by... more Ideally, dosimeters should measure the dose without their dosimetric properties being affected by the radiation type being measured. Industry-wide occupational radiation workers that can be potentially exposed to neutron radiation fields are routinely monitored by thermoluminescent (TLD) dosimeters. The neutron dose measured by these devices is obtained from the interaction products of thermal (slow) neutrons and 6Li. The number of

Cone Beam Breast CT imaging (CBBCT) is a promising tool for diagnosis of breast tumors and calcif... more Cone Beam Breast CT imaging (CBBCT) is a promising tool for diagnosis of breast tumors and calcifications. However, as the sizes of calcifications in early stages are very small, it is not easy to distinguish them from background tissues because of the relatively high noise level. Therefore, it is necessary to enhance the visualization of calcifications for accurate detection. In this work, the Papoulis-Gerchberg (PG) method was introduced and modified to improve calcification characterization. PG method is an iterative algorithm of signal extrapolation and has been demonstrated to be very effective in image restoration like super-resolution (SR) and inpainting. The projection images were zoomed by bicubic interpolation method, then the modified PG method were applied to improve the image quality. The reconstruction from processed projection images showed that this approach can effectively improve the image quality by improving the Modulation Transfer Function (MTF) with a limited increase in noise level. As a result, the detectability of calcifications was improved in CBBCT images.

Medical Imaging 2010: Physics of Medical Imaging, 2010

Pixel Signal to Noise Ratio (SNR) is a commonly used clinical metric for evaluating mammography. ... more Pixel Signal to Noise Ratio (SNR) is a commonly used clinical metric for evaluating mammography. However, we showed in this paper, the pixel SNR can produce misleading system detectability when image processing is utilized. We developed a simple, reliable and clinically applicable methodology to evaluate mammographic imaging systems using a task SNR that accounts for the imaging system performance in

Medical Physics, 2014

The purpose of this work is to evaluate the performance of the image acquisition chain of clinica... more The purpose of this work is to evaluate the performance of the image acquisition chain of clinical full field digital mammography (FFDM) systems by quantifying their image quality, and how well the desired information is captured by the images. The authors present a practical methodology to evaluate FFDM using the task specific system-model-based Fourier Hotelling observer (SMFHO) signal to noise ratio (SNR), which evaluates the signal and noise transfer characteristics of FFDM systems in the presence of a uniform polymethyl methacrylate phantom that models the attenuation of a 6 cm thick 20/80 breast (20% glandular/80% adipose). The authors model the system performance using the generalized modulation transfer function, which accounts for scatter blur and focal spot unsharpness, and the generalized noise power spectrum, both estimated with the phantom placed in the field of view. Using the system model, the authors were able to estimate system detectability for a series of simulated disk signals with various diameters and thicknesses, quantified by a SMFHO SNR map. Contrast-detail (CD) curves were generated from the SNR map and adjusted using an estimate of the human observer efficiency, without performing time-consuming human reader studies. Using the SMFHO method the authors compared two FFDM systems, the GE Senographe DS and Hologic Selenia FFDM systems, which use indirect and direct detectors, respectively. Even though the two FFDM systems have different resolutions, noise properties, detector technologies, and antiscatter grids, the authors found no significant difference between them in terms of detectability for a given signal detection task. The authors also compared the performance between the two image acquisition modes (fine view and standard) of the GE Senographe DS system, and concluded that there is no significant difference when evaluated by the SMFHO. The estimated human observer efficiency was 30 ± 5% when compared to the SMFHO. The results showed good agreement when compared to other model observers as well as previously published human observer data. This method generates CD curves from the SMFHO SNR that can be used as figures of merit for evaluating the image acquisition performance of clinical FFDM systems. It provides a way of creating an empirical model of the FFDM system that accounts for patient scatter, focal spot unsharpness, and detector blur. With the use of simulated signals, this method can predict system performance for a signal known exactly/background known exactly detection task with a limited number of images, therefore, it can be readily applied in a clinical environment.

The objective of this study was show that a clinical dosimetry protocol that utilizes a dosimetri... more The objective of this study was show that a clinical dosimetry protocol that utilizes a dosimetric breast phantom series based on population anthropometric measurements can reliably predict the average glandular dose (AGD) imparted to the patient during a routine screening mammogram. In the study, AGD was calculated using entrance skin exposure and dose conversion factors based on fibroglandular content, compressed breast thickness, mammography unit parameters and modifying parameters for homogeneous phantom (phantom factor), compressed breast lateral dimensions (volume factor) and anatomical features (anatomical factor). The protocol proposes the use of a fiber-optic coupled (FOCD) or Metal Oxide Semiconductor Field Effect Transistor (MOSFET) dosimeter to measure the entrance skin exposure at the time of the mammogram without interfering with diagnostic information of the mammogram. The study showed that FOCD had sensitivity with less than 7% energy dependence, linear in all tube current-time product stations, and was reproducible within 2%. FOCD was superior to MOSFET dosimeter in sensitivity, reusability, and reproducibility. The patient fibroglandular content was evaluated using a calibrated modified breast tissue equivalent homogeneous phantom series (BRTES-MOD) designed from anthropomorphic measurements of a screening mammography population and whose elemental composition was referenced to International Commission on Radiation Units and Measurements Report 44 tissues. The patient fibroglandular content, compressed breast thickness along with unit parameters and spectrum half-value layer were used to derive the currently used dose conversion factor (DgN). The study showed that the use of a homogeneous phantom, patient compressed breast lateral dimensions and patient anatomical features can affect AGD by as much as 12%, 3% and 1%, respectively. The protocol was found to be superior to existing methodologies. In addition, the study population anthropometric measurements enabled the development of analytical equations to calculate the whole breast area, estimate for the skin layer thickness and optimal location for automatic exposure control ionization chamber. The clinical dosimetry protocol developed in this study can reliably predict the AGD imparted to an individual patient during a routine screening mammogram.

Barry Pass1), Alexander Romanyukha2), Tania De1), Lyudmila Romanyukha2), Francois Trompier3), Isa... more Barry Pass1), Alexander Romanyukha2), Tania De1), Lyudmila Romanyukha2), Francois Trompier3), Isabelle Clairand3), Prabhakar Misra1), Luis Benevides2), David Schauer4) 1)Howard University, Washington, DC, 2)Uniformed Services University of the Health Sciences, Bethesda, MD, 3)French Institute for Radiological Protection and Nuclear Safety, Fontenay-aux-roses, 4)National Council on Radiation Protection, Washington, DC e-mail: bpass@howard.edu

Health physics, 2018

The U.S. Navy uses the Harshaw 8840/8841 dosimetric (DT-702/PD) system, which employs LiF:Mg,Cu,P... more The U.S. Navy uses the Harshaw 8840/8841 dosimetric (DT-702/PD) system, which employs LiF:Mg,Cu,P thermoluminescent dosimeters (TLDs), developed and produced by Thermo Fisher Scientific (TFS). The dosimeter consists of four LiF:Mg,Cu,P elements, mounted in Teflon® on an aluminum card and placed in a plastic holder. The holder contains a unique filter for each chip made of copper, acrylonitrile butadiene styrene (ABS), Mylar®, and tin. For accredited dosimetry labs, the ISO/IEC 17025:2005(E) requires an acceptance procedure for all new equipment. The Naval Dosimetry Center (NDC) has developed and tested a new non-destructive procedure, which enables the verification and the evaluation of embedded filters in the holders. Testing is based on attenuation measurements of low-energy radiation transmitted through each filter in a representative sample group of holders to verify that the correct filter type and thickness are present. The measured response ratios are then compared with the e...

Radiation Measurements

Abstract Thermo Fisher Scientific has introduced a new personnel dosimeter, model 8850. This new ... more Abstract Thermo Fisher Scientific has introduced a new personnel dosimeter, model 8850. This new dosimeter consists of a standard Thermo Scientific Harshaw TLD LiF: Mg,Cu,P card, with a new holder design. The reusable holder is small and lightweight, and contains filtration optimized for personnel dosimetry. This new dosimeter was type tested to IEC 62387:2012 along with the Thermo Scientific Harshaw Model 8800PLUS TLD Reader. Extensive testing of the radiological, environmental and mechanical performance of the system was performed according to the standard. The dosimeter is sensitive to a wide photon energy range from 16 keV and dose range from 0.01 mSv. It is also sensitive to beta from 85 Kr. Comprehensive angular and side effect tests for photon and beta were also completed. This paper presents the high-achieving type test results and uncertainty analysis of each test.

Radiation Protection Dosimetry, 2008

An extension of dosemeter issue period brings significant economic and logistic benefits. Therefo... more An extension of dosemeter issue period brings significant economic and logistic benefits. Therefore, it is desirable to have an extended period as long as possible without significant loss of the quality of dose measurements. There are many studies devoted to the investigation of fading or reduction of the dose accumulated in dosemeters with time. However, this is one of many critical factors that need's to be taken into account when extending the dosemeter issue period. Background radiation is also a critical factor that needs to be appropriately accounted. In this report, a new approach has been suggested for evaluating the effect of background radiation on the lower limit of detection (LLD) of occupational radiation dose. This approach is based on the data collected from control dosemeters that are routinely used for subtraction of background radiation from occupational dose measurements. The results show that for LiF:Mg,Cu,P thermoluminescence dosemeters, variations in background radiation have a higher impact on the LLD than dose fading and the absolute value of background radiation. Although there is no significant dose fading in LiF:Mg,Cu,P for a dosemeter issue period up to 1 y, variations in background radiation during this period of time can significantly increase photon LLDs (up to 700 microSv) for workers operating in an environment of variable radiation background.

Medical Imaging 2010: Physics of Medical Imaging, 2010

Pixel Signal to Noise Ratio (SNR) is a commonly used clinical metric for evaluating mammography. ... more Pixel Signal to Noise Ratio (SNR) is a commonly used clinical metric for evaluating mammography. However, we showed in this paper, the pixel SNR can produce misleading system detectability when image processing is utilized. We developed a simple, reliable and clinically applicable methodology to evaluate mammographic imaging systems using a task SNR that accounts for the imaging system performance in

Medical Physics, 2014

The purpose of this work is to evaluate the performance of the image acquisition chain of clinica... more The purpose of this work is to evaluate the performance of the image acquisition chain of clinical full field digital mammography (FFDM) systems by quantifying their image quality, and how well the desired information is captured by the images. The authors present a practical methodology to evaluate FFDM using the task specific system-model-based Fourier Hotelling observer (SMFHO) signal to noise ratio (SNR), which evaluates the signal and noise transfer characteristics of FFDM systems in the presence of a uniform polymethyl methacrylate phantom that models the attenuation of a 6 cm thick 20/80 breast (20% glandular/80% adipose). The authors model the system performance using the generalized modulation transfer function, which accounts for scatter blur and focal spot unsharpness, and the generalized noise power spectrum, both estimated with the phantom placed in the field of view. Using the system model, the authors were able to estimate system detectability for a series of simulated disk signals with various diameters and thicknesses, quantified by a SMFHO SNR map. Contrast-detail (CD) curves were generated from the SNR map and adjusted using an estimate of the human observer efficiency, without performing time-consuming human reader studies. Using the SMFHO method the authors compared two FFDM systems, the GE Senographe DS and Hologic Selenia FFDM systems, which use indirect and direct detectors, respectively. Even though the two FFDM systems have different resolutions, noise properties, detector technologies, and antiscatter grids, the authors found no significant difference between them in terms of detectability for a given signal detection task. The authors also compared the performance between the two image acquisition modes (fine view and standard) of the GE Senographe DS system, and concluded that there is no significant difference when evaluated by the SMFHO. The estimated human observer efficiency was 30 ± 5% when compared to the SMFHO. The results showed good agreement when compared to other model observers as well as previously published human observer data. This method generates CD curves from the SMFHO SNR that can be used as figures of merit for evaluating the image acquisition performance of clinical FFDM systems. It provides a way of creating an empirical model of the FFDM system that accounts for patient scatter, focal spot unsharpness, and detector blur. With the use of simulated signals, this method can predict system performance for a signal known exactly/background known exactly detection task with a limited number of images, therefore, it can be readily applied in a clinical environment.

Radiation Protection Dosimetry, 2011

The phototransferred thermoluminescence (PTTL) technique is applied to the Harshaw LiF:Mg,Cu,P ma... more The phototransferred thermoluminescence (PTTL) technique is applied to the Harshaw LiF:Mg,Cu,P material. It is demonstrated that using 254-nm UV light, dose levels as low as 0.2 mGy can be re-estimated. The PTTL efficiency was found to be ∼ 6 % in the dose range of 0.2 mGy-1 Gy, and it appears to be dose-independent. This implies that a simple calibration factor could be applied to the PTTL data for the re-estimation of dose levels. It was demonstrated that with a proper choice of the TL readout parameters, and the UV-light irradiation conditions, dose levels that are relevant to personal or environmental dosimetry can be re-estimated.

Radiation Protection Dosimetry, 2011

This study investigates several sources of uncertainty associated with the application of optical... more This study investigates several sources of uncertainty associated with the application of optically stimulated luminescence (OSL) to personal dosimetry. A commercial OSL system based on Al(2)O(3):C was used for this study. First, it is demonstrated that the concept of repeated evaluation (readout) of the same dosemeter, often referred to as 're-analysis', can introduce uncertainty in the re-estimated dose. This uncertainty is associated with the fact that the re-analysis process depletes some of the populated traps, resulting in a continuous decrease of the OSL signal with each repeated reading. Furthermore, the rate of depletion may be dose-dependent. Second, it is shown that the previously reported light-induced fading in this system is the result of light leaks through miniature openings in the dosemeter badge.

Radiation Protection Dosimetry, 2011

The effects of UV-induced bleaching of deep traps on Harshaw thermoluminescent (TL) LiF:Mg,Cu,P a... more The effects of UV-induced bleaching of deep traps on Harshaw thermoluminescent (TL) LiF:Mg,Cu,P and LiF:Mg,Ti materials were investigated. During a normal heating cycle, LiF:Mg,Cu,P is limited to a maximum temperature of 240 °C. LiF:Mg,Ti can be read to higher temperatures; however, encapsulation in polytetrafluoroethylene limits the maximum readout temperature to 300 °C. Generally, for both materials, these respective temperatures are sufficient for emptying traps corresponding to the main dosemetric peaks. However, when the dosemeters are subjected to a high dose level, such as 1 Gy (much higher than individual monitoring dose levels), higher temperature traps are filled that cannot be emptied without exceeding the above-mentioned maximum temperatures. These high temperature traps tend to be unstable during normal readout and can significantly increase the residual TL signal. The purpose of this study was to investigate the applicability of a UV-induced bleaching technique for emptying higher temperature traps following high-dose applications. In addition, in the case of LiF:Mg,Cu,P, where the maximum readout temperature is significantly lower, we investigated the possibility of reducing the residual signal using the application of repeated readout cycles. The optical bleaching approach was found to be effective in the case of LiF:Mg,Ti; however, for LiF:Mg,Cu,P, no reduction in the residual signal was observed. For this latter material, the application of repeatable readout cycles is very effective and residual signals equivalent to dose levels as low as 0.01 mGy were observed following an initial dose of 5 Gy. To the best of our knowledge, this work is the first attempt to apply an 'optical annealing' technique to the Harshaw thermoluminescent dosemeter (TLD) materials.

Radiation Measurements, 2014

Radiation Measurements, 2011

... MANUSCRIPT EFFECT OF TLD-700H (LIF:Mg,Cu,P) SENSITIVITY LOSS AT MULTIPLE READ-IRRADIATION CYC... more ... MANUSCRIPT EFFECT OF TLD-700H (LIF:Mg,Cu,P) SENSITIVITY LOSS AT MULTIPLE READ-IRRADIATION CYCLES ON TLD READER CALIBRATION SHANNON P. VOSS, ARTURSUCHETA, ALEX ROMANYUKHA ... Kim, J., Lee, J., Pradhan, A., Kim, B., Kim, S. 2010. ...

Radiation Measurements, 2011

Ideally, dosimeters should measure the dose without their dosimetric properties being affected by... more Ideally, dosimeters should measure the dose without their dosimetric properties being affected by the radiation type being measured. Industry-wide occupational radiation workers that can be potentially exposed to neutron radiation fields are routinely monitored by thermoluminescent (TLD) dosimeters. The neutron dose measured by these devices is obtained from the interaction products of thermal (slow) neutrons and 6Li. The number of

Cone Beam Breast CT imaging (CBBCT) is a promising tool for diagnosis of breast tumors and calcif... more Cone Beam Breast CT imaging (CBBCT) is a promising tool for diagnosis of breast tumors and calcifications. However, as the sizes of calcifications in early stages are very small, it is not easy to distinguish them from background tissues because of the relatively high noise level. Therefore, it is necessary to enhance the visualization of calcifications for accurate detection. In this work, the Papoulis-Gerchberg (PG) method was introduced and modified to improve calcification characterization. PG method is an iterative algorithm of signal extrapolation and has been demonstrated to be very effective in image restoration like super-resolution (SR) and inpainting. The projection images were zoomed by bicubic interpolation method, then the modified PG method were applied to improve the image quality. The reconstruction from processed projection images showed that this approach can effectively improve the image quality by improving the Modulation Transfer Function (MTF) with a limited increase in noise level. As a result, the detectability of calcifications was improved in CBBCT images.

Medical Imaging 2010: Physics of Medical Imaging, 2010

Pixel Signal to Noise Ratio (SNR) is a commonly used clinical metric for evaluating mammography. ... more Pixel Signal to Noise Ratio (SNR) is a commonly used clinical metric for evaluating mammography. However, we showed in this paper, the pixel SNR can produce misleading system detectability when image processing is utilized. We developed a simple, reliable and clinically applicable methodology to evaluate mammographic imaging systems using a task SNR that accounts for the imaging system performance in

Medical Physics, 2014

The purpose of this work is to evaluate the performance of the image acquisition chain of clinica... more The purpose of this work is to evaluate the performance of the image acquisition chain of clinical full field digital mammography (FFDM) systems by quantifying their image quality, and how well the desired information is captured by the images. The authors present a practical methodology to evaluate FFDM using the task specific system-model-based Fourier Hotelling observer (SMFHO) signal to noise ratio (SNR), which evaluates the signal and noise transfer characteristics of FFDM systems in the presence of a uniform polymethyl methacrylate phantom that models the attenuation of a 6 cm thick 20/80 breast (20% glandular/80% adipose). The authors model the system performance using the generalized modulation transfer function, which accounts for scatter blur and focal spot unsharpness, and the generalized noise power spectrum, both estimated with the phantom placed in the field of view. Using the system model, the authors were able to estimate system detectability for a series of simulated disk signals with various diameters and thicknesses, quantified by a SMFHO SNR map. Contrast-detail (CD) curves were generated from the SNR map and adjusted using an estimate of the human observer efficiency, without performing time-consuming human reader studies. Using the SMFHO method the authors compared two FFDM systems, the GE Senographe DS and Hologic Selenia FFDM systems, which use indirect and direct detectors, respectively. Even though the two FFDM systems have different resolutions, noise properties, detector technologies, and antiscatter grids, the authors found no significant difference between them in terms of detectability for a given signal detection task. The authors also compared the performance between the two image acquisition modes (fine view and standard) of the GE Senographe DS system, and concluded that there is no significant difference when evaluated by the SMFHO. The estimated human observer efficiency was 30 ± 5% when compared to the SMFHO. The results showed good agreement when compared to other model observers as well as previously published human observer data. This method generates CD curves from the SMFHO SNR that can be used as figures of merit for evaluating the image acquisition performance of clinical FFDM systems. It provides a way of creating an empirical model of the FFDM system that accounts for patient scatter, focal spot unsharpness, and detector blur. With the use of simulated signals, this method can predict system performance for a signal known exactly/background known exactly detection task with a limited number of images, therefore, it can be readily applied in a clinical environment.

The objective of this study was show that a clinical dosimetry protocol that utilizes a dosimetri... more The objective of this study was show that a clinical dosimetry protocol that utilizes a dosimetric breast phantom series based on population anthropometric measurements can reliably predict the average glandular dose (AGD) imparted to the patient during a routine screening mammogram. In the study, AGD was calculated using entrance skin exposure and dose conversion factors based on fibroglandular content, compressed breast thickness, mammography unit parameters and modifying parameters for homogeneous phantom (phantom factor), compressed breast lateral dimensions (volume factor) and anatomical features (anatomical factor). The protocol proposes the use of a fiber-optic coupled (FOCD) or Metal Oxide Semiconductor Field Effect Transistor (MOSFET) dosimeter to measure the entrance skin exposure at the time of the mammogram without interfering with diagnostic information of the mammogram. The study showed that FOCD had sensitivity with less than 7% energy dependence, linear in all tube current-time product stations, and was reproducible within 2%. FOCD was superior to MOSFET dosimeter in sensitivity, reusability, and reproducibility. The patient fibroglandular content was evaluated using a calibrated modified breast tissue equivalent homogeneous phantom series (BRTES-MOD) designed from anthropomorphic measurements of a screening mammography population and whose elemental composition was referenced to International Commission on Radiation Units and Measurements Report 44 tissues. The patient fibroglandular content, compressed breast thickness along with unit parameters and spectrum half-value layer were used to derive the currently used dose conversion factor (DgN). The study showed that the use of a homogeneous phantom, patient compressed breast lateral dimensions and patient anatomical features can affect AGD by as much as 12%, 3% and 1%, respectively. The protocol was found to be superior to existing methodologies. In addition, the study population anthropometric measurements enabled the development of analytical equations to calculate the whole breast area, estimate for the skin layer thickness and optimal location for automatic exposure control ionization chamber. The clinical dosimetry protocol developed in this study can reliably predict the AGD imparted to an individual patient during a routine screening mammogram.