Abhinav Jha - Academia.edu (original) (raw)

Papers by Abhinav Jha

Magnetic Resonance in Medicine, 2016

Design a statistically rigorous procedure to estimate a single apparent diffusion coefficient (AD... more Design a statistically rigorous procedure to estimate a single apparent diffusion coefficient (ADC) of lesion from the mean lesion signal intensity in diffusion MRI. A rigorous maximum-likelihood technique that incorporated the statistics of the mean lesion intensity and accounted for lesion heterogeneity was derived to estimate the ADC value. Performance evaluation included comparison with the conventionally used linear-regression and a statistically rigorous state-of-the-art ADC-map technique using realistic and clinically relevant simulation studies conducted with assistance of patient data for homogeneous and heterogeneous lesion models. The proposed technique outperformed the linear-regression and ADC-map approaches over a large spectrum of signal-to-noise ratio, ADC, lesion size, image-misalignment parameters, including at no image misalignment, and different amounts of lesion heterogeneity. The method was also superior at different sets of b values and in studies from specific patient-image-derived data. The technique took less than a second to execute. A rigorous, computationally fast, easy-to-implement, and convenient-to-use maximum-likelihood technique was proposed to estimate a single ADC value of the lesion. Results provide strong evidence in support of the method. Magn Reson Med, 2016. © 2016 Wiley Periodicals, Inc.

Medical Imaging 2015: Image Perception, Observer Performance, and Technology Assessment, 2015

Breast screening in the UK has been implemented for over 20 years and annually nearly two million... more Breast screening in the UK has been implemented for over 20 years and annually nearly two million women are now screened with an estimated 1,400 lives saved. Nationally, some 700 individuals interpret screening mammograms in almost 110 screening centres. Currently, ...

Physics in Medicine and Biology

In many studies, the estimation of the apparent diffusion coefficient (ADC) of lesions in viscera... more In many studies, the estimation of the apparent diffusion coefficient (ADC) of lesions in visceral organs in diffusion-weighted (DW) magnetic resonance images requires an accurate lesion-segmentation algorithm. To evaluate these lesion-segmentation algorithms, region-overlap measures are used currently. However, the end task from the DW images is accurate ADC estimation, and the region-overlap measures do not evaluate the segmentation algorithms on this task. Moreover, these measures rely on the existence of gold-standard segmentation of the lesion, which is typically unavailable. In this paper, we study the problem of task-based evaluation of segmentation algorithms in DW imaging in the absence of a gold standard. We first show that using manual segmentations instead of gold-standard segmentations for this task-based evaluation is unreliable. We then propose a method to compare the segmentation algorithms that does not require gold-standard or manual segmentation results. The no-gold-standard method estimates the bias and the variance of the error between the true ADC values and the ADC values estimated using the automated segmentation algorithm. The method can be used to rank the segmentation algorithms on the basis of both the ensemble mean square error and precision. We also propose consistency checks for this evaluation technique.

IEEE transactions on nuclear science, 2013

The response of a Silicon Photomultiplier (SiPM) to optical signals is affected by many factors i... more The response of a Silicon Photomultiplier (SiPM) to optical signals is affected by many factors including photon-detection efficiency, recovery time, gain, optical crosstalk, afterpulsing, dark count, and detector dead time. Many of these parameters vary with overvoltage and temperature. When used to detect scintillation light, there is a complicated non-linear relationship between the incident light and the response of the SiPM. In this paper, we propose a combined discrete-time discrete-event Monte Carlo (MC) model to simulate SiPM response to scintillation light pulses. Our MC model accounts for all relevant aspects of the SiPM response, some of which were not accounted for in the previous models. We also derive and validate analytic expressions for the single-photoelectron response of the SiPM and the voltage drop across the quenching resistance in the SiPM microcell. These analytic expressions consider the effect of all the circuit elements in the SiPM and accurately simulate t...

IEEE Nuclear Science Symposium conference record. Nuclear Science Symposium

We introduce and discuss photon-processing detectors and we compare them with photon-counting det... more We introduce and discuss photon-processing detectors and we compare them with photon-counting detectors. By estimating a relatively small number of attributes for each collected photon, photon-processing detectors may help understand and solve a fundamental theoretical problem of any imaging system based on photon-counting detectors, namely null functions. We argue that photon-processing detectors can improve task performance by estimating position, energy, and time of arrival for each collected photon. We consider a continuous-to-continuous linear operator to relate the object being imaged to the collected data, and discuss how this operator can be analyzed to derive properties of the imaging system. Finally, we derive an expression for the characteristic functional of an imaging system that produces list-mode data.

Physics in medicine and biology, Jan 9, 2015

Recent advances in technology are enabling a new class of nuclear imaging systems consisting of d... more Recent advances in technology are enabling a new class of nuclear imaging systems consisting of detectors that use real-time maximum-likelihood (ML) methods to estimate the interaction position, deposited energy, and other attributes of each photon-interaction event and store these attributes in a list format. This class of systems, which we refer to as photon-processing (PP) nuclear imaging systems, can be described by a fundamentally different mathematical imaging operator that allows processing of the continuous-valued photon attributes on a per-photon basis. Unlike conventional photon-counting (PC) systems that bin the data into images, PP systems do not have any binning-related information loss. Mathematically, while PC systems have an infinite-dimensional null space due to dimensionality considerations, PP systems do not necessarily suffer from this issue. Therefore, PP systems have the potential to provide improved performance in comparison to PC systems. To study these advan...

A maximum-likelihood-based scheme for estimating the Apparent Diffusion Coefficient (ADC) value i... more A maximum-likelihood-based scheme for estimating the Apparent Diffusion Coefficient (ADC) value in diffusion-weighted MRI is presented, using which data from multiple scans acquired at the same diffusion-gradient value can be used for accurate ADC computation.

Magnetic Resonance Imaging, 2015

To assess the value of semi-automated segmentation applied to diffusion MRI for predicting the th... more To assess the value of semi-automated segmentation applied to diffusion MRI for predicting the therapeutic response of liver metastasis. Conventional diffusion weighted magnetic resonance imaging (MRI) was performed using b-values of 0, 150, 300 and 450s/mm(2) at baseline and days 4, 11 and 39 following initiation of a new chemotherapy regimen in a pilot study with 18 women with 37 liver metastases from primary breast cancer. A semi-automated segmentation approach was used to identify liver metastases. Linear regression analysis was used to assess the relationship between baseline values of the apparent diffusion coefficient (ADC) and change in tumor size by day 39. A semi-automated segmentation scheme was critical for obtaining the most reliable ADC measurements. A statistically significant relationship between baseline ADC values and change in tumor size at day 39 was observed for minimally treated patients with metastatic liver lesions measuring 2-5cm in size (p=0.002), but not for heavily treated patients with the same tumor size range (p=0.29), or for tumors of smaller or larger sizes. ROC analysis identified a baseline threshold ADC value of 1.33μm(2)/ms as 75% sensitive and 83% specific for identifying non-responding metastases in minimally treated patients with 2-5cm liver lesions. Quantitative imaging can substantially benefit from a semi-automated segmentation scheme. Quantitative diffusion MRI results can be predictive of therapeutic outcome in selected patients with liver metastases, but not for all liver metastases, and therefore should be considered to be a restricted biomarker.

Medical Imaging 2015: Image Perception, Observer Performance, and Technology Assessment, 2015

Quantitative single-photon emission computed tomography (SPECT) imaging is emerging as an importa... more Quantitative single-photon emission computed tomography (SPECT) imaging is emerging as an important tool in clinical studies and biomedical research. There is thus a need for optimization and evaluation of systems and algorithms that are being developed for quantitative SPECT imaging. An appropriate objective method to evaluate these systems is by comparing their performance in the end task that is required in quantitative SPECT imaging, such as estimating the mean activity concentration in a volume of interest (VOI) in a patient image. This objective evaluation can be performed if the true value of the estimated parameter is known, i.e. we have a gold standard. However, very rarely is this gold standard known in human studies. Thus, no-gold-standard techniques to optimize and evaluate systems and algorithms in the absence of gold standard are required. In this work, we developed a no-gold-standard technique to objectively evaluate reconstruction methods used in quantitative SPECT when the parameter to be estimated is the mean activity concentration in a VOI. We studied the performance of the technique with realistic simulated image data generated from an object database consisting of five phantom anatomies with all possible combinations of five sets of organ uptakes, where each anatomy consisted of eight different organ VOIs. Results indicate that the method provided accurate ranking of the reconstruction methods. We also demonstrated the application of consistency checks to test the no-gold-standard output.

Proceedings of SPIE--the International Society for Optical Engineering, Jan 13, 2015

Recently a new class of imaging systems, referred to as photon-processing (PP) systems, are being... more Recently a new class of imaging systems, referred to as photon-processing (PP) systems, are being developed that uses real-time maximum-likelihood (ML) methods to estimate multiple attributes per detected photon and store these attributes in a list format. PP systems could have a number of potential advantages compared to systems that bin photons based on attributes such as energy, projection angle, and position, referred to as photon-counting (PC) systems. For example, PP systems do not suffer from binning-related information loss and provide the potential to extract information from attributes such as energy deposited by the detected photon. To quantify the effects of this advantage on task performance, objective evaluation studies are required. We performed this study in the context of quantitative 2-dimensional single-photon emission computed tomography (SPECT) imaging with the end task of estimating the mean activity concentration within a region of interest (ROI). We first the...

Proceedings / IEEE Southwest Symposium on Image Analysis and Interpretation. IEEE Southwest Symposium on Image Analysis and Interpretation, 2012

Accurate estimation of the apparent diffusion coefficient (ADC) of lesions in diffusion-weighted ... more Accurate estimation of the apparent diffusion coefficient (ADC) of lesions in diffusion-weighted magnetic resonance imaging (DWMRI) is important to predict and monitor anti-cancer therapy response. The task of ADC estimation of lesions is complicated due to noise in the image, different variances in signal strengths at different b values and other random phenomena. In organs that have visceral motion, due to motion across scans, estimating the ADC becomes even more complex. To get rid of inaccuracies due to motion, only a single ADC value of the lesion is estimated, conventionally using a linear-regression (LR) approach. The LR approach is based on an inaccurate noise model and also suffers from other deficiencies. In this paper, we propose an easy-to-implement and computationally-fast maximum-likelihood (ML) method to estimate the ADC value of heterogeneous lesions in visceral organs. The proposed method takes into account the Rician distribution of noise in DWMRI. In the process, ...

Medical Imaging 2013: Physics of Medical Imaging, 2013

Attenuation and scatter correction in single photon emission computed tomography (SPECT) imaging ... more Attenuation and scatter correction in single photon emission computed tomography (SPECT) imaging often requires a computed tomography (CT) scan to compute the attenuation map of the patient. This results in increased radiation dose for the patient, and also has other disadvantages such as increased costs and hardware complexity. Attenuation in SPECT is a direct consequence of Compton scattering, and therefore, if the scattered photon data can give information about the attenuation map, then the CT scan may not be required. In this paper, we investigate the possibility of joint reconstruction of the activity and attenuation map using listmode (LM) SPECT emission data, including the scattered-photon data. We propose a path-based formalism to process scattered-photon data. Following this, we derive analytic expressions to compute the Cramér-Rao bound (CRB) of the activity and attenuation map estimates, using which, we can explore the fundamental limit of information-retrieval capacity from LM SPECT emission data. We then suggest a maximum-likelihood (ML) scheme that uses the LM emission data to jointly reconstruct the activity and attenuation map. We also propose an expectation-maximization (EM) algorithm to compute the ML solution.

Biomedical optics express, 2013

With the emergence of diffuse optical tomography (DOT) as a non-invasive imaging modality, there ... more With the emergence of diffuse optical tomography (DOT) as a non-invasive imaging modality, there is a requirement to evaluate the performance of the developed DOT systems on clinically relevant tasks. One such important task is the detection of high-absorption signals in the tissue. To investigate signal detectability in DOT systems for system optimization, an appropriate approach is to use the Bayesian ideal observer, but this observer is computationally very intensive. It has been shown that the Fisher information can be used as a surrogate figure of merit (SFoM) that approximates the ideal observer performance. In this paper, we present a theoretical framework to use the Fisher information for investigating signal detectability in DOT systems. The usage of Fisher information requires evaluating the gradient of the photon distribution function with respect to the absorption coefficients. We derive the expressions to compute the gradient of the photon distribution function with res...

Biomedical Optics and 3-D Imaging, 2010

Page 1. Solutions to the Radiative Transport Equation for Non-uniform Media Abhinav K. Jha, Matth... more Page 1. Solutions to the Radiative Transport Equation for Non-uniform Media Abhinav K. Jha, Matthew A. Kupinski, Dongyel Kang, Eric Clarkson College of Optical Sciences, University of Arizona, 1630 E University Blvd Tucson ...

Biomedical Optics and 3-D Imaging, 2010

Diffuse optical imaging (DOI) researchers need metrics for quantifying signal detectability to as... more Diffuse optical imaging (DOI) researchers need metrics for quantifying signal detectability to assess different hardware configurations. Using Monte Carlo and statistical model observers, we estimated DOI signal detectability to compare source, signal, and detector parameters.

Penetrating Radiation Systems and Applications XIV, 2013

2011 IEEE Nuclear Science Symposium Conference Record, 2011

The response of a Silicon Photomultiplier (SiPM) to optical signals is affected by many factors i... more The response of a Silicon Photomultiplier (SiPM) to optical signals is affected by many factors including optical cross talk, afterpulsing, dark current, detector dead time, recovery time and gain. Many of these parameters vary with over-voltage. When used to detect scintillation light, it is difficult to relate the response of the SiPM with the incident light and the relationship can be highly nonlinear. In this paper, we propose a Monte Carlo (MC) model for simulating the response of the SiPM to scintillation induced light pulses, which can be used to relate the optical signal with the SiPM response. Developing further on the previous works in this field, the model simulates the various aspects of SiPM response, including photon detection efficiency, recovery time, gain variation and dead time while accounting for the temporal and statistical distribution of the incident light, optical cross-talk, afterpulsing and dark current. It also considers the variation of the different SiPM parameters with varying over-voltage. We have also derived analytic expressions for the single photon response and the voltage drop across the quenching resistance, that help in accurate simulation of the SiPM response. The model compares well with the measurements on a SiPM based scintillation detector. It is also in agreement with the expected mathematical response when the input is an instantaneous light pulse.

Magnetic Resonance in Medicine, 2016

Design a statistically rigorous procedure to estimate a single apparent diffusion coefficient (AD... more Design a statistically rigorous procedure to estimate a single apparent diffusion coefficient (ADC) of lesion from the mean lesion signal intensity in diffusion MRI. A rigorous maximum-likelihood technique that incorporated the statistics of the mean lesion intensity and accounted for lesion heterogeneity was derived to estimate the ADC value. Performance evaluation included comparison with the conventionally used linear-regression and a statistically rigorous state-of-the-art ADC-map technique using realistic and clinically relevant simulation studies conducted with assistance of patient data for homogeneous and heterogeneous lesion models. The proposed technique outperformed the linear-regression and ADC-map approaches over a large spectrum of signal-to-noise ratio, ADC, lesion size, image-misalignment parameters, including at no image misalignment, and different amounts of lesion heterogeneity. The method was also superior at different sets of b values and in studies from specific patient-image-derived data. The technique took less than a second to execute. A rigorous, computationally fast, easy-to-implement, and convenient-to-use maximum-likelihood technique was proposed to estimate a single ADC value of the lesion. Results provide strong evidence in support of the method. Magn Reson Med, 2016. © 2016 Wiley Periodicals, Inc.

Medical Imaging 2015: Image Perception, Observer Performance, and Technology Assessment, 2015

Breast screening in the UK has been implemented for over 20 years and annually nearly two million... more Breast screening in the UK has been implemented for over 20 years and annually nearly two million women are now screened with an estimated 1,400 lives saved. Nationally, some 700 individuals interpret screening mammograms in almost 110 screening centres. Currently, ...

Physics in Medicine and Biology

In many studies, the estimation of the apparent diffusion coefficient (ADC) of lesions in viscera... more In many studies, the estimation of the apparent diffusion coefficient (ADC) of lesions in visceral organs in diffusion-weighted (DW) magnetic resonance images requires an accurate lesion-segmentation algorithm. To evaluate these lesion-segmentation algorithms, region-overlap measures are used currently. However, the end task from the DW images is accurate ADC estimation, and the region-overlap measures do not evaluate the segmentation algorithms on this task. Moreover, these measures rely on the existence of gold-standard segmentation of the lesion, which is typically unavailable. In this paper, we study the problem of task-based evaluation of segmentation algorithms in DW imaging in the absence of a gold standard. We first show that using manual segmentations instead of gold-standard segmentations for this task-based evaluation is unreliable. We then propose a method to compare the segmentation algorithms that does not require gold-standard or manual segmentation results. The no-gold-standard method estimates the bias and the variance of the error between the true ADC values and the ADC values estimated using the automated segmentation algorithm. The method can be used to rank the segmentation algorithms on the basis of both the ensemble mean square error and precision. We also propose consistency checks for this evaluation technique.

IEEE transactions on nuclear science, 2013

The response of a Silicon Photomultiplier (SiPM) to optical signals is affected by many factors i... more The response of a Silicon Photomultiplier (SiPM) to optical signals is affected by many factors including photon-detection efficiency, recovery time, gain, optical crosstalk, afterpulsing, dark count, and detector dead time. Many of these parameters vary with overvoltage and temperature. When used to detect scintillation light, there is a complicated non-linear relationship between the incident light and the response of the SiPM. In this paper, we propose a combined discrete-time discrete-event Monte Carlo (MC) model to simulate SiPM response to scintillation light pulses. Our MC model accounts for all relevant aspects of the SiPM response, some of which were not accounted for in the previous models. We also derive and validate analytic expressions for the single-photoelectron response of the SiPM and the voltage drop across the quenching resistance in the SiPM microcell. These analytic expressions consider the effect of all the circuit elements in the SiPM and accurately simulate t...

IEEE Nuclear Science Symposium conference record. Nuclear Science Symposium

We introduce and discuss photon-processing detectors and we compare them with photon-counting det... more We introduce and discuss photon-processing detectors and we compare them with photon-counting detectors. By estimating a relatively small number of attributes for each collected photon, photon-processing detectors may help understand and solve a fundamental theoretical problem of any imaging system based on photon-counting detectors, namely null functions. We argue that photon-processing detectors can improve task performance by estimating position, energy, and time of arrival for each collected photon. We consider a continuous-to-continuous linear operator to relate the object being imaged to the collected data, and discuss how this operator can be analyzed to derive properties of the imaging system. Finally, we derive an expression for the characteristic functional of an imaging system that produces list-mode data.

Physics in medicine and biology, Jan 9, 2015

Recent advances in technology are enabling a new class of nuclear imaging systems consisting of d... more Recent advances in technology are enabling a new class of nuclear imaging systems consisting of detectors that use real-time maximum-likelihood (ML) methods to estimate the interaction position, deposited energy, and other attributes of each photon-interaction event and store these attributes in a list format. This class of systems, which we refer to as photon-processing (PP) nuclear imaging systems, can be described by a fundamentally different mathematical imaging operator that allows processing of the continuous-valued photon attributes on a per-photon basis. Unlike conventional photon-counting (PC) systems that bin the data into images, PP systems do not have any binning-related information loss. Mathematically, while PC systems have an infinite-dimensional null space due to dimensionality considerations, PP systems do not necessarily suffer from this issue. Therefore, PP systems have the potential to provide improved performance in comparison to PC systems. To study these advan...

A maximum-likelihood-based scheme for estimating the Apparent Diffusion Coefficient (ADC) value i... more A maximum-likelihood-based scheme for estimating the Apparent Diffusion Coefficient (ADC) value in diffusion-weighted MRI is presented, using which data from multiple scans acquired at the same diffusion-gradient value can be used for accurate ADC computation.

Magnetic Resonance Imaging, 2015

To assess the value of semi-automated segmentation applied to diffusion MRI for predicting the th... more To assess the value of semi-automated segmentation applied to diffusion MRI for predicting the therapeutic response of liver metastasis. Conventional diffusion weighted magnetic resonance imaging (MRI) was performed using b-values of 0, 150, 300 and 450s/mm(2) at baseline and days 4, 11 and 39 following initiation of a new chemotherapy regimen in a pilot study with 18 women with 37 liver metastases from primary breast cancer. A semi-automated segmentation approach was used to identify liver metastases. Linear regression analysis was used to assess the relationship between baseline values of the apparent diffusion coefficient (ADC) and change in tumor size by day 39. A semi-automated segmentation scheme was critical for obtaining the most reliable ADC measurements. A statistically significant relationship between baseline ADC values and change in tumor size at day 39 was observed for minimally treated patients with metastatic liver lesions measuring 2-5cm in size (p=0.002), but not for heavily treated patients with the same tumor size range (p=0.29), or for tumors of smaller or larger sizes. ROC analysis identified a baseline threshold ADC value of 1.33μm(2)/ms as 75% sensitive and 83% specific for identifying non-responding metastases in minimally treated patients with 2-5cm liver lesions. Quantitative imaging can substantially benefit from a semi-automated segmentation scheme. Quantitative diffusion MRI results can be predictive of therapeutic outcome in selected patients with liver metastases, but not for all liver metastases, and therefore should be considered to be a restricted biomarker.

Medical Imaging 2015: Image Perception, Observer Performance, and Technology Assessment, 2015

Quantitative single-photon emission computed tomography (SPECT) imaging is emerging as an importa... more Quantitative single-photon emission computed tomography (SPECT) imaging is emerging as an important tool in clinical studies and biomedical research. There is thus a need for optimization and evaluation of systems and algorithms that are being developed for quantitative SPECT imaging. An appropriate objective method to evaluate these systems is by comparing their performance in the end task that is required in quantitative SPECT imaging, such as estimating the mean activity concentration in a volume of interest (VOI) in a patient image. This objective evaluation can be performed if the true value of the estimated parameter is known, i.e. we have a gold standard. However, very rarely is this gold standard known in human studies. Thus, no-gold-standard techniques to optimize and evaluate systems and algorithms in the absence of gold standard are required. In this work, we developed a no-gold-standard technique to objectively evaluate reconstruction methods used in quantitative SPECT when the parameter to be estimated is the mean activity concentration in a VOI. We studied the performance of the technique with realistic simulated image data generated from an object database consisting of five phantom anatomies with all possible combinations of five sets of organ uptakes, where each anatomy consisted of eight different organ VOIs. Results indicate that the method provided accurate ranking of the reconstruction methods. We also demonstrated the application of consistency checks to test the no-gold-standard output.

Proceedings of SPIE--the International Society for Optical Engineering, Jan 13, 2015

Recently a new class of imaging systems, referred to as photon-processing (PP) systems, are being... more Recently a new class of imaging systems, referred to as photon-processing (PP) systems, are being developed that uses real-time maximum-likelihood (ML) methods to estimate multiple attributes per detected photon and store these attributes in a list format. PP systems could have a number of potential advantages compared to systems that bin photons based on attributes such as energy, projection angle, and position, referred to as photon-counting (PC) systems. For example, PP systems do not suffer from binning-related information loss and provide the potential to extract information from attributes such as energy deposited by the detected photon. To quantify the effects of this advantage on task performance, objective evaluation studies are required. We performed this study in the context of quantitative 2-dimensional single-photon emission computed tomography (SPECT) imaging with the end task of estimating the mean activity concentration within a region of interest (ROI). We first the...

Proceedings / IEEE Southwest Symposium on Image Analysis and Interpretation. IEEE Southwest Symposium on Image Analysis and Interpretation, 2012

Accurate estimation of the apparent diffusion coefficient (ADC) of lesions in diffusion-weighted ... more Accurate estimation of the apparent diffusion coefficient (ADC) of lesions in diffusion-weighted magnetic resonance imaging (DWMRI) is important to predict and monitor anti-cancer therapy response. The task of ADC estimation of lesions is complicated due to noise in the image, different variances in signal strengths at different b values and other random phenomena. In organs that have visceral motion, due to motion across scans, estimating the ADC becomes even more complex. To get rid of inaccuracies due to motion, only a single ADC value of the lesion is estimated, conventionally using a linear-regression (LR) approach. The LR approach is based on an inaccurate noise model and also suffers from other deficiencies. In this paper, we propose an easy-to-implement and computationally-fast maximum-likelihood (ML) method to estimate the ADC value of heterogeneous lesions in visceral organs. The proposed method takes into account the Rician distribution of noise in DWMRI. In the process, ...

Medical Imaging 2013: Physics of Medical Imaging, 2013

Attenuation and scatter correction in single photon emission computed tomography (SPECT) imaging ... more Attenuation and scatter correction in single photon emission computed tomography (SPECT) imaging often requires a computed tomography (CT) scan to compute the attenuation map of the patient. This results in increased radiation dose for the patient, and also has other disadvantages such as increased costs and hardware complexity. Attenuation in SPECT is a direct consequence of Compton scattering, and therefore, if the scattered photon data can give information about the attenuation map, then the CT scan may not be required. In this paper, we investigate the possibility of joint reconstruction of the activity and attenuation map using listmode (LM) SPECT emission data, including the scattered-photon data. We propose a path-based formalism to process scattered-photon data. Following this, we derive analytic expressions to compute the Cramér-Rao bound (CRB) of the activity and attenuation map estimates, using which, we can explore the fundamental limit of information-retrieval capacity from LM SPECT emission data. We then suggest a maximum-likelihood (ML) scheme that uses the LM emission data to jointly reconstruct the activity and attenuation map. We also propose an expectation-maximization (EM) algorithm to compute the ML solution.

Biomedical optics express, 2013

With the emergence of diffuse optical tomography (DOT) as a non-invasive imaging modality, there ... more With the emergence of diffuse optical tomography (DOT) as a non-invasive imaging modality, there is a requirement to evaluate the performance of the developed DOT systems on clinically relevant tasks. One such important task is the detection of high-absorption signals in the tissue. To investigate signal detectability in DOT systems for system optimization, an appropriate approach is to use the Bayesian ideal observer, but this observer is computationally very intensive. It has been shown that the Fisher information can be used as a surrogate figure of merit (SFoM) that approximates the ideal observer performance. In this paper, we present a theoretical framework to use the Fisher information for investigating signal detectability in DOT systems. The usage of Fisher information requires evaluating the gradient of the photon distribution function with respect to the absorption coefficients. We derive the expressions to compute the gradient of the photon distribution function with res...

Biomedical Optics and 3-D Imaging, 2010

Page 1. Solutions to the Radiative Transport Equation for Non-uniform Media Abhinav K. Jha, Matth... more Page 1. Solutions to the Radiative Transport Equation for Non-uniform Media Abhinav K. Jha, Matthew A. Kupinski, Dongyel Kang, Eric Clarkson College of Optical Sciences, University of Arizona, 1630 E University Blvd Tucson ...

Biomedical Optics and 3-D Imaging, 2010

Diffuse optical imaging (DOI) researchers need metrics for quantifying signal detectability to as... more Diffuse optical imaging (DOI) researchers need metrics for quantifying signal detectability to assess different hardware configurations. Using Monte Carlo and statistical model observers, we estimated DOI signal detectability to compare source, signal, and detector parameters.

Penetrating Radiation Systems and Applications XIV, 2013

2011 IEEE Nuclear Science Symposium Conference Record, 2011

The response of a Silicon Photomultiplier (SiPM) to optical signals is affected by many factors i... more The response of a Silicon Photomultiplier (SiPM) to optical signals is affected by many factors including optical cross talk, afterpulsing, dark current, detector dead time, recovery time and gain. Many of these parameters vary with over-voltage. When used to detect scintillation light, it is difficult to relate the response of the SiPM with the incident light and the relationship can be highly nonlinear. In this paper, we propose a Monte Carlo (MC) model for simulating the response of the SiPM to scintillation induced light pulses, which can be used to relate the optical signal with the SiPM response. Developing further on the previous works in this field, the model simulates the various aspects of SiPM response, including photon detection efficiency, recovery time, gain variation and dead time while accounting for the temporal and statistical distribution of the incident light, optical cross-talk, afterpulsing and dark current. It also considers the variation of the different SiPM parameters with varying over-voltage. We have also derived analytic expressions for the single photon response and the voltage drop across the quenching resistance, that help in accurate simulation of the SiPM response. The model compares well with the measurements on a SiPM based scintillation detector. It is also in agreement with the expected mathematical response when the input is an instantaneous light pulse.