Ria Mazumder | Widener University (original) (raw)

Papers by Ria Mazumder

Research paper thumbnail of POSTER PRESENTATION Open Access Diffusion

tensor imaging of formalin fixed infarcted porcine hearts

Research paper thumbnail of 6415 Cardiac Diffusion Tensor Imaging : Adaptive Anisotropic Gaussian Filtering to Reduce Acquisition Time

Cardiac Diffusion Tensor Imaging: Adaptive Anisotropic Gaussian Filtering to Reduce Acquisition T... more Cardiac Diffusion Tensor Imaging: Adaptive Anisotropic Gaussian Filtering to Reduce Acquisition Time Ria Mazumder, Bradley D. Clymer, Richard D. White, and Arunark Kolipaka Department of Electrical and Computer Engineering, The Ohio State University, Columbus, OH, United States, Department of Radiology, The Ohio State University, Columbus, OH, United States, Department of Internal Medicine-Division of Cardiology, The Ohio State University, Columbus, OH, United States

Research paper thumbnail of Potential of Diffusion Tensor Imaging as a Virtual Dissection Tool for Cardiac Muscle Bundles : A Pilot Study

Introduction: Diffusion-based tractography has the potential to delineate complex cardiac muscle ... more Introduction: Diffusion-based tractography has the potential to delineate complex cardiac muscle fiber architecture [1]. Although many cardiac diffusion tensor imaging (DTI) studies have been conducted, segmentation of cardiac muscle bundles has been rarely explored. The ultimate goal of such bundle-based segmentation would be to reveal the organization of the cardiac muscle fiber bundle architecture. As an initial step to achieve the goal, we performed a DTI study on a fixed porcine heart specimen. The study was carried out in two phases on the left ventricle (LV) of the fixed specimen. In the first phase, we explored the dependency of tractography on three fiber tracking constraints: fractional anisotropy (FA) threshold, maximum turning angle, and minimum fiber length. In the second phase, we performed segmentation of long muscle bundles (> 50 mm) using deterministic tractography and evaluated the feasibility of the muscle bundle segmentation in the given specimen. Materials an...

Research paper thumbnail of Estimation of Spatiotemporal Isotropic and Anisotropic Myocardial Stiffness using Magnetic Resonance Elastography: A Study in Heart Failure

.................................................................................................... more .............................................................................................................................. ii Dedication .......................................................................................................................... vi Acknowledgments............................................................................................................. vii Vita ...................................................................................................................................... x Publications ......................................................................................................................... x Fields of Study .................................................................................................................. xii Table of

Research paper thumbnail of Diffusion tensor imaging of formalin fixed infarcted porcine hearts

Journal of Cardiovascular Magnetic Resonance, 2013

Figure 1 Magnitude image of the infarcted porcine heart, showing the infarcted region near the apex.

Research paper thumbnail of In vivo quantification of aortic stiffness using MR elastography in hypertensive porcine model

Magnetic resonance in medicine, Jan 5, 2017

Aortic stiffness plays an important role in evaluating and predicting the progression of systemic... more Aortic stiffness plays an important role in evaluating and predicting the progression of systemic arterial hypertension (SAH). The aim of this study is to determine the stiffness of aortic wall using MR elastography (MRE) in a hypertensive porcine model and compare it against invasive aortic pressure measurements. Renal wrapping surgery was performed on eight pigs to induce SAH. Aortic MRE was performed at baseline and 2 months postsurgery using a retrospectively pulse-gated gradient-echo MRE sequence on a 1.5 tesla scanner. Mechanical waves of 70 Hz were introduced into the aorta. Invasive central aortic pressure measurements were obtained prior to each scan to calculate mean arterial pressure (MAP). MRE data were analyzed to obtain effective aortic stiffness. Spearman's rank correlation analysis was performed to assess the relationship between MAP and MRE-derived aortic stiffness. Significant increase in effective aortic stiffness was observed between baseline and 2 months pos...

Research paper thumbnail of In vivo quantification of myocardial stiffness in hypertensive porcine hearts using MR elastography

Journal of magnetic resonance imaging : JMRI, Jan 26, 2016

To determine alteration in left ventricular (LV) myocardial stiffness (MS) with hypertension (HTN... more To determine alteration in left ventricular (LV) myocardial stiffness (MS) with hypertension (HTN). Cardiac MR elastography (MRE) was used to estimate MS in HTN induced pigs and MRE-derived MS measurements were compared against LV pressure, thickness and circumferential strain. Renal-wrapping surgery was performed to induce HTN in eight pigs. LV catheterization (to measure pressure) and cardiac MRI (1.5 Tesla; gradient echo-MRE and tagging) was performed pre-surgery at baseline (Bx), and post-surgery at month 1 (M1) and month 2 (M2). Images were analyzed to estimate LV-MS, thickness, and circumferential strain across the cardiac cycle. The associations between end-diastolic (ED) and end-systolic (ES) MS and (i) mean LV pressure; (ii) ED and ES thickness, respectively; and (iii) circumferential strain were evaluated using Spearman's correlation method. From Bx to M2, mean pressure, MRE-derived stiffness, and thickness increased while circumferential strain decreased significantly...

Research paper thumbnail of Quantification and comparison of 4D Flow MRI derived wall shear stress and MRE derived wall shear stiffness of abdominal aorta

Journal of Cardiovascular Magnetic Resonance, 2016

Illapani et al.: Quantification and comparison of 4D Flow MRI derived wall shear stress and MRE d... more Illapani et al.: Quantification and comparison of 4D Flow MRI derived wall shear stress and MRE derived wall shear stiffness of abdominal aorta.

Research paper thumbnail of Quantification of myocardial stiffness in heart failure with preserved ejection fraction porcine model using magnetic resonance elastography

Journal of Cardiovascular Magnetic Resonance, 2016

Research paper thumbnail of In vivo magnetic resonance elastography to estimate left ventricular stiffness in a myocardial infarction induced porcine model

Journal of magnetic resonance imaging : JMRI, Jan 17, 2016

To estimate change in left ventricular (LV) end-systolic and end-diastolic myocardial stiffness (... more To estimate change in left ventricular (LV) end-systolic and end-diastolic myocardial stiffness (MS) in pigs induced with myocardial infarction (MI) with disease progression using cardiac magnetic resonance elastography (MRE) and to compare it against ex vivo mechanical testing, LV circumferential strain, and magnetic resonance imaging (MRI) relaxometry parameters (T1 , T2 , and extracellular volume fraction [ECV]). MRI (1.5T) was performed on seven pigs, before surgery (Bx), and 10 (D10), and 21 (D21) days after creating MI. Cardiac MRE-derived MS was measured in infarcted region (MIR) and remote region (RR), and validated against mechanical testing-derived MS obtained postsacrifice on D21. Circumferential strain and MRI relaxometry parameters (T2 , T1 , and ECV) were also obtained. Multiparametric analysis was performed to determine correlation between cardiac MRE-derived MS and 1) strain, 2) relaxometry parameters, and 3) mechanical testing. Mean diastolic (D10: 5.09 ± 0.6 kPa; D...

Research paper thumbnail of Waveguide Magnetic Resonance Elastography in a Pressure-Varying Porcine Model

To determine anisotropic myocardial stiffness using waveguide cardiac magnetic resonance elastogr... more To determine anisotropic myocardial stiffness using waveguide cardiac magnetic resonance elastography (CMRE) in an ex-vivo porcine model with varying left ventricular pressure simulating heart failure with preserved ejection fraction and compare the results against isotropic myocardial stiffness. Methods Diffusion tensor imaging (DTI) and CMRE was implemented on three ex-vivo porcine hearts inflated with two different pressure values on a 3T MRI scanner to obtain fiber orientation and displacement information respectively. An orthotropic inversion was performed on the displacement data to estimate the anisotropic stiffness coefficients (compressional and shear) in the heart for both the inflation pressures and the results were compared against isotropic stiffness estimates. Paired student's t-test was performed to determine the significant difference in stiffness values between the two inflation pressures with the two different inversion techniques. Results Our results show that anisotropic stiffness estimates demonstrated a significant difference between the two inflation pressures both in the compressional (P-Value=0.0053) and shear (P-Value=0.0015) measurements. On the other hand, the isotopic stiffness measurements showed a minute slight increase in stiffness as a function of pressure with no significant difference (P-value=0.75). Conclusion From the results we can conclude that it is feasible to estimate anisotropic stiffness in the myocardium and anisotropic myocardial stiffness provides superior information as compared to isotropic myocardial stiffness.

Research paper thumbnail of Diffusion Tensor Imaging of Healthy and Infarcted Porcine Hearts: Study on the Impact of Formalin Fixation

Journal of Medical Imaging and Radiation Sciences, 2016

Background-Due to complexities of in-vivo cardiac diffusion tensor imaging (DTI), ex-vivo formali... more Background-Due to complexities of in-vivo cardiac diffusion tensor imaging (DTI), ex-vivo formalin-fixed specimens are used to investigate cardiac remodeling in diseases, and reported results have shown conflicting trends. This study investigates the impact of formalin-fixation on diffusion properties and optimizes tracking parameters based on controls to understand remodeling in myocardial-infarction (MI). Methods-DTI was performed on 4 healthy (controls) and 4 MI induced formalin-fixed (PoMI) ex-vivo porcine hearts. Controls were scanned pre-fixation (PrCtrl) and re-scanned (PoCtrl) after formalin-fixation. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were estimated in all hearts. Tracking parameters (FA, tract termination angle (TTA), fiber-length) were optimized in controls and then used to investigate structural remodeling in PoMI hearts. Results-Fixation increased ADC and decreased FA. PoMI showed increased ADC but decreased FA in infarcted zone compared to remote zone. TTA showed sharp increase in slope from 5°-10°, which flattened after 25° in all groups. Mean fiber-length for different tracking length range showed that PoCtrl had shorter fibers compared to PrCtrl. Fibers around infarction were shorter in length and disarrayed compared to PoCtrl group.

Research paper thumbnail of Determining Anisotropic Myocardial Stiffness from Magnetic Resonance Elastography: A Simulation Study

Lecture Notes in Computer Science, 2015

Although magnetic resonance elastography (MRE) has the potential to non-invasively measure myocar... more Although magnetic resonance elastography (MRE) has the potential to non-invasively measure myocardial stiffness, myocardium is known to be anisotropic and it is not clear whether all material parameters can be uniquely determined from MRE data. In this study, we examined the determinability of anisotropic stiffness parameters using finite element analysis (FEA) simulations of harmonic steady state wave behavior. Two models were examined: (i) a cylindrical and (ii) a canine left ventricular geometry with realistic fiber architecture. A parameter sweep was carried out, and the objective function, which summed the error between reference displacements and displacements simulated from MRE boundary data and material parameters, was plotted and determinability assessed from the Hessian. Then, given prescribed boundary displacements from the ground truth simulation with added Gaussian noise, an anisotropic material parameter optimization was run 30 times with different noise in order to investigate the effect of noise on determination of material parameters. Results show that transversely isotropic material parameters can be robustly determined using this method.

Research paper thumbnail of In-vivo waveguide cardiac magnetic resonance elastography

Journal of Cardiovascular Magnetic Resonance, 2015

Research paper thumbnail of Rapid acquisition technique for MR elastography of the liver

Magnetic Resonance Imaging, 2014

Magnetic Resonance Elastography (MRE) of the liver is a novel noninvasive clinical diagnostic too... more Magnetic Resonance Elastography (MRE) of the liver is a novel noninvasive clinical diagnostic tool to stage fibrosis based on measured stiffness. The purpose of this study is to design, evaluate and validate a rapid MRE acquisition technique for noninvasively quantitating liver stiffness which reduces by half the scan time, thereby decreasing image registration errors between four MRE phase offsets. In vivo liver MRE was performed on 16 healthy volunteers and 14 patients with biopsy-proven liver fibrosis using the standard clinical Gradient Recalled Echo (GRE) MRE sequence (MREs) and a developed rapid GRE MRE sequence (MREr) to obtain the mean stiffness in an axial slice. The mean stiffness values obtained from the entire group using MREs and MREr were 2.72±0.85kPa and 2.7±0.85kPa, respectively, representing an insignificant difference. A linear correlation of R 2 =0.99 was determined between stiffness values obtained using MREs and MREr. Therefore, we can conclude that MREr can replace MREs, which reduces the scan time to half of that of the current standard acquisition (MREs), which will facilitate MRE imaging in patients with inability to hold their breath for long periods.

Research paper thumbnail of Estimation of helical angle of the left ventricle using diffusion tensor imaging with minimum acquisition time

Journal of Cardiovascular Magnetic Resonance, 2014

Research paper thumbnail of MR Elastography as a Method to Determine the Mechanical Properties of Fresh and Formalin Fixed Porcine Hearts

Purpose: Formalin fixed cardiac muscles are an integral part of ex-vivo cardiac research [1]. For... more Purpose: Formalin fixed cardiac muscles are an integral part of ex-vivo cardiac research [1]. Formalin fixation alters the mechanical properties of the heart muscle, by changing its stiffness value. The standard quantitative measurement of stiffness is done by performing mechanical testing on myocardial strips. Magnetic resonance elastography (MRE) is a novel phasecontrast technique used to determine the spatial stiffness maps of soft tissues non-invasively. The purpose of this study is to determine the variation in stiffness of the left ventricular (LV) myocardium before (fresh) and after formalin fixation.

Research paper thumbnail of Adaptive anisotropic gaussian filtering to reduce acquisition time in cardiac diffusion tensor imaging

The International Journal of Cardiovascular Imaging, Feb 2, 2016

Diffusion tensor imaging (DTI) is used to quantify myocardial fiber orientation based on helical ... more Diffusion tensor imaging (DTI) is used to quantify myocardial fiber orientation based on helical angles (HA). Accurate HA measurements require multiple excitations (NEX) and/or several diffusion encoding directions (DED). However, increasing NEX and/or DED increases acquisition time (TA). Therefore, in this study, we propose to reduce TA by implementing a 3D adaptive anisotropic Gaussian filter (AAGF) on the DTI data acquired from ex-vivo healthy and infarcted porcine hearts. DTI was performed on ex-vivo hearts [9-healthy, 3-myocardial infarction (MI)] with several combinations of DED and NEX. AAGF, mean (AVF) and median filters (MF) were applied on the primary eigenvectors of the diffusion tensor prior to HA estimation. The performance of AAGF was compared against AVF and MF. Root mean square error (RMSE), concordance correlation-coefficients and Bland-Altman's technique was used to determine optimal combination of DED and NEX that generated the best HA maps in the least possible TA. Lastly, the effect of implementing AAGF on the infarcted porcine hearts was also investigated. RMSE in HA estimation for AAGF was lower compared to AVF or MF. Post-filtering (AAGF) fewer DED and NEX were required to achieve HA maps with similar integrity as those obtained from higher NEX and/or DED. Pathological alterations caused in HA orientation in the MI model were preserved post-filtering (AAGF). Our results demonstrate that AAGF reduces TA without affecting the integrity of the myocardial microstructure.

Research paper thumbnail of POSTER PRESENTATION Open Access Diffusion

tensor imaging of formalin fixed infarcted porcine hearts

Research paper thumbnail of 6415 Cardiac Diffusion Tensor Imaging : Adaptive Anisotropic Gaussian Filtering to Reduce Acquisition Time

Cardiac Diffusion Tensor Imaging: Adaptive Anisotropic Gaussian Filtering to Reduce Acquisition T... more Cardiac Diffusion Tensor Imaging: Adaptive Anisotropic Gaussian Filtering to Reduce Acquisition Time Ria Mazumder, Bradley D. Clymer, Richard D. White, and Arunark Kolipaka Department of Electrical and Computer Engineering, The Ohio State University, Columbus, OH, United States, Department of Radiology, The Ohio State University, Columbus, OH, United States, Department of Internal Medicine-Division of Cardiology, The Ohio State University, Columbus, OH, United States

Research paper thumbnail of Potential of Diffusion Tensor Imaging as a Virtual Dissection Tool for Cardiac Muscle Bundles : A Pilot Study

Introduction: Diffusion-based tractography has the potential to delineate complex cardiac muscle ... more Introduction: Diffusion-based tractography has the potential to delineate complex cardiac muscle fiber architecture [1]. Although many cardiac diffusion tensor imaging (DTI) studies have been conducted, segmentation of cardiac muscle bundles has been rarely explored. The ultimate goal of such bundle-based segmentation would be to reveal the organization of the cardiac muscle fiber bundle architecture. As an initial step to achieve the goal, we performed a DTI study on a fixed porcine heart specimen. The study was carried out in two phases on the left ventricle (LV) of the fixed specimen. In the first phase, we explored the dependency of tractography on three fiber tracking constraints: fractional anisotropy (FA) threshold, maximum turning angle, and minimum fiber length. In the second phase, we performed segmentation of long muscle bundles (> 50 mm) using deterministic tractography and evaluated the feasibility of the muscle bundle segmentation in the given specimen. Materials an...

Research paper thumbnail of Estimation of Spatiotemporal Isotropic and Anisotropic Myocardial Stiffness using Magnetic Resonance Elastography: A Study in Heart Failure

.................................................................................................... more .............................................................................................................................. ii Dedication .......................................................................................................................... vi Acknowledgments............................................................................................................. vii Vita ...................................................................................................................................... x Publications ......................................................................................................................... x Fields of Study .................................................................................................................. xii Table of

Research paper thumbnail of Diffusion tensor imaging of formalin fixed infarcted porcine hearts

Journal of Cardiovascular Magnetic Resonance, 2013

Figure 1 Magnitude image of the infarcted porcine heart, showing the infarcted region near the apex.

Research paper thumbnail of In vivo quantification of aortic stiffness using MR elastography in hypertensive porcine model

Magnetic resonance in medicine, Jan 5, 2017

Aortic stiffness plays an important role in evaluating and predicting the progression of systemic... more Aortic stiffness plays an important role in evaluating and predicting the progression of systemic arterial hypertension (SAH). The aim of this study is to determine the stiffness of aortic wall using MR elastography (MRE) in a hypertensive porcine model and compare it against invasive aortic pressure measurements. Renal wrapping surgery was performed on eight pigs to induce SAH. Aortic MRE was performed at baseline and 2 months postsurgery using a retrospectively pulse-gated gradient-echo MRE sequence on a 1.5 tesla scanner. Mechanical waves of 70 Hz were introduced into the aorta. Invasive central aortic pressure measurements were obtained prior to each scan to calculate mean arterial pressure (MAP). MRE data were analyzed to obtain effective aortic stiffness. Spearman's rank correlation analysis was performed to assess the relationship between MAP and MRE-derived aortic stiffness. Significant increase in effective aortic stiffness was observed between baseline and 2 months pos...

Research paper thumbnail of In vivo quantification of myocardial stiffness in hypertensive porcine hearts using MR elastography

Journal of magnetic resonance imaging : JMRI, Jan 26, 2016

To determine alteration in left ventricular (LV) myocardial stiffness (MS) with hypertension (HTN... more To determine alteration in left ventricular (LV) myocardial stiffness (MS) with hypertension (HTN). Cardiac MR elastography (MRE) was used to estimate MS in HTN induced pigs and MRE-derived MS measurements were compared against LV pressure, thickness and circumferential strain. Renal-wrapping surgery was performed to induce HTN in eight pigs. LV catheterization (to measure pressure) and cardiac MRI (1.5 Tesla; gradient echo-MRE and tagging) was performed pre-surgery at baseline (Bx), and post-surgery at month 1 (M1) and month 2 (M2). Images were analyzed to estimate LV-MS, thickness, and circumferential strain across the cardiac cycle. The associations between end-diastolic (ED) and end-systolic (ES) MS and (i) mean LV pressure; (ii) ED and ES thickness, respectively; and (iii) circumferential strain were evaluated using Spearman's correlation method. From Bx to M2, mean pressure, MRE-derived stiffness, and thickness increased while circumferential strain decreased significantly...

Research paper thumbnail of Quantification and comparison of 4D Flow MRI derived wall shear stress and MRE derived wall shear stiffness of abdominal aorta

Journal of Cardiovascular Magnetic Resonance, 2016

Illapani et al.: Quantification and comparison of 4D Flow MRI derived wall shear stress and MRE d... more Illapani et al.: Quantification and comparison of 4D Flow MRI derived wall shear stress and MRE derived wall shear stiffness of abdominal aorta.

Research paper thumbnail of Quantification of myocardial stiffness in heart failure with preserved ejection fraction porcine model using magnetic resonance elastography

Journal of Cardiovascular Magnetic Resonance, 2016

Research paper thumbnail of In vivo magnetic resonance elastography to estimate left ventricular stiffness in a myocardial infarction induced porcine model

Journal of magnetic resonance imaging : JMRI, Jan 17, 2016

To estimate change in left ventricular (LV) end-systolic and end-diastolic myocardial stiffness (... more To estimate change in left ventricular (LV) end-systolic and end-diastolic myocardial stiffness (MS) in pigs induced with myocardial infarction (MI) with disease progression using cardiac magnetic resonance elastography (MRE) and to compare it against ex vivo mechanical testing, LV circumferential strain, and magnetic resonance imaging (MRI) relaxometry parameters (T1 , T2 , and extracellular volume fraction [ECV]). MRI (1.5T) was performed on seven pigs, before surgery (Bx), and 10 (D10), and 21 (D21) days after creating MI. Cardiac MRE-derived MS was measured in infarcted region (MIR) and remote region (RR), and validated against mechanical testing-derived MS obtained postsacrifice on D21. Circumferential strain and MRI relaxometry parameters (T2 , T1 , and ECV) were also obtained. Multiparametric analysis was performed to determine correlation between cardiac MRE-derived MS and 1) strain, 2) relaxometry parameters, and 3) mechanical testing. Mean diastolic (D10: 5.09 ± 0.6 kPa; D...

Research paper thumbnail of Waveguide Magnetic Resonance Elastography in a Pressure-Varying Porcine Model

To determine anisotropic myocardial stiffness using waveguide cardiac magnetic resonance elastogr... more To determine anisotropic myocardial stiffness using waveguide cardiac magnetic resonance elastography (CMRE) in an ex-vivo porcine model with varying left ventricular pressure simulating heart failure with preserved ejection fraction and compare the results against isotropic myocardial stiffness. Methods Diffusion tensor imaging (DTI) and CMRE was implemented on three ex-vivo porcine hearts inflated with two different pressure values on a 3T MRI scanner to obtain fiber orientation and displacement information respectively. An orthotropic inversion was performed on the displacement data to estimate the anisotropic stiffness coefficients (compressional and shear) in the heart for both the inflation pressures and the results were compared against isotropic stiffness estimates. Paired student's t-test was performed to determine the significant difference in stiffness values between the two inflation pressures with the two different inversion techniques. Results Our results show that anisotropic stiffness estimates demonstrated a significant difference between the two inflation pressures both in the compressional (P-Value=0.0053) and shear (P-Value=0.0015) measurements. On the other hand, the isotopic stiffness measurements showed a minute slight increase in stiffness as a function of pressure with no significant difference (P-value=0.75). Conclusion From the results we can conclude that it is feasible to estimate anisotropic stiffness in the myocardium and anisotropic myocardial stiffness provides superior information as compared to isotropic myocardial stiffness.

Research paper thumbnail of Diffusion Tensor Imaging of Healthy and Infarcted Porcine Hearts: Study on the Impact of Formalin Fixation

Journal of Medical Imaging and Radiation Sciences, 2016

Background-Due to complexities of in-vivo cardiac diffusion tensor imaging (DTI), ex-vivo formali... more Background-Due to complexities of in-vivo cardiac diffusion tensor imaging (DTI), ex-vivo formalin-fixed specimens are used to investigate cardiac remodeling in diseases, and reported results have shown conflicting trends. This study investigates the impact of formalin-fixation on diffusion properties and optimizes tracking parameters based on controls to understand remodeling in myocardial-infarction (MI). Methods-DTI was performed on 4 healthy (controls) and 4 MI induced formalin-fixed (PoMI) ex-vivo porcine hearts. Controls were scanned pre-fixation (PrCtrl) and re-scanned (PoCtrl) after formalin-fixation. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were estimated in all hearts. Tracking parameters (FA, tract termination angle (TTA), fiber-length) were optimized in controls and then used to investigate structural remodeling in PoMI hearts. Results-Fixation increased ADC and decreased FA. PoMI showed increased ADC but decreased FA in infarcted zone compared to remote zone. TTA showed sharp increase in slope from 5°-10°, which flattened after 25° in all groups. Mean fiber-length for different tracking length range showed that PoCtrl had shorter fibers compared to PrCtrl. Fibers around infarction were shorter in length and disarrayed compared to PoCtrl group.

Research paper thumbnail of Determining Anisotropic Myocardial Stiffness from Magnetic Resonance Elastography: A Simulation Study

Lecture Notes in Computer Science, 2015

Although magnetic resonance elastography (MRE) has the potential to non-invasively measure myocar... more Although magnetic resonance elastography (MRE) has the potential to non-invasively measure myocardial stiffness, myocardium is known to be anisotropic and it is not clear whether all material parameters can be uniquely determined from MRE data. In this study, we examined the determinability of anisotropic stiffness parameters using finite element analysis (FEA) simulations of harmonic steady state wave behavior. Two models were examined: (i) a cylindrical and (ii) a canine left ventricular geometry with realistic fiber architecture. A parameter sweep was carried out, and the objective function, which summed the error between reference displacements and displacements simulated from MRE boundary data and material parameters, was plotted and determinability assessed from the Hessian. Then, given prescribed boundary displacements from the ground truth simulation with added Gaussian noise, an anisotropic material parameter optimization was run 30 times with different noise in order to investigate the effect of noise on determination of material parameters. Results show that transversely isotropic material parameters can be robustly determined using this method.

Research paper thumbnail of In-vivo waveguide cardiac magnetic resonance elastography

Journal of Cardiovascular Magnetic Resonance, 2015

Research paper thumbnail of Rapid acquisition technique for MR elastography of the liver

Magnetic Resonance Imaging, 2014

Magnetic Resonance Elastography (MRE) of the liver is a novel noninvasive clinical diagnostic too... more Magnetic Resonance Elastography (MRE) of the liver is a novel noninvasive clinical diagnostic tool to stage fibrosis based on measured stiffness. The purpose of this study is to design, evaluate and validate a rapid MRE acquisition technique for noninvasively quantitating liver stiffness which reduces by half the scan time, thereby decreasing image registration errors between four MRE phase offsets. In vivo liver MRE was performed on 16 healthy volunteers and 14 patients with biopsy-proven liver fibrosis using the standard clinical Gradient Recalled Echo (GRE) MRE sequence (MREs) and a developed rapid GRE MRE sequence (MREr) to obtain the mean stiffness in an axial slice. The mean stiffness values obtained from the entire group using MREs and MREr were 2.72±0.85kPa and 2.7±0.85kPa, respectively, representing an insignificant difference. A linear correlation of R 2 =0.99 was determined between stiffness values obtained using MREs and MREr. Therefore, we can conclude that MREr can replace MREs, which reduces the scan time to half of that of the current standard acquisition (MREs), which will facilitate MRE imaging in patients with inability to hold their breath for long periods.

Research paper thumbnail of Estimation of helical angle of the left ventricle using diffusion tensor imaging with minimum acquisition time

Journal of Cardiovascular Magnetic Resonance, 2014

Research paper thumbnail of MR Elastography as a Method to Determine the Mechanical Properties of Fresh and Formalin Fixed Porcine Hearts

Purpose: Formalin fixed cardiac muscles are an integral part of ex-vivo cardiac research [1]. For... more Purpose: Formalin fixed cardiac muscles are an integral part of ex-vivo cardiac research [1]. Formalin fixation alters the mechanical properties of the heart muscle, by changing its stiffness value. The standard quantitative measurement of stiffness is done by performing mechanical testing on myocardial strips. Magnetic resonance elastography (MRE) is a novel phasecontrast technique used to determine the spatial stiffness maps of soft tissues non-invasively. The purpose of this study is to determine the variation in stiffness of the left ventricular (LV) myocardium before (fresh) and after formalin fixation.

Research paper thumbnail of Adaptive anisotropic gaussian filtering to reduce acquisition time in cardiac diffusion tensor imaging

The International Journal of Cardiovascular Imaging, Feb 2, 2016

Diffusion tensor imaging (DTI) is used to quantify myocardial fiber orientation based on helical ... more Diffusion tensor imaging (DTI) is used to quantify myocardial fiber orientation based on helical angles (HA). Accurate HA measurements require multiple excitations (NEX) and/or several diffusion encoding directions (DED). However, increasing NEX and/or DED increases acquisition time (TA). Therefore, in this study, we propose to reduce TA by implementing a 3D adaptive anisotropic Gaussian filter (AAGF) on the DTI data acquired from ex-vivo healthy and infarcted porcine hearts. DTI was performed on ex-vivo hearts [9-healthy, 3-myocardial infarction (MI)] with several combinations of DED and NEX. AAGF, mean (AVF) and median filters (MF) were applied on the primary eigenvectors of the diffusion tensor prior to HA estimation. The performance of AAGF was compared against AVF and MF. Root mean square error (RMSE), concordance correlation-coefficients and Bland-Altman's technique was used to determine optimal combination of DED and NEX that generated the best HA maps in the least possible TA. Lastly, the effect of implementing AAGF on the infarcted porcine hearts was also investigated. RMSE in HA estimation for AAGF was lower compared to AVF or MF. Post-filtering (AAGF) fewer DED and NEX were required to achieve HA maps with similar integrity as those obtained from higher NEX and/or DED. Pathological alterations caused in HA orientation in the MI model were preserved post-filtering (AAGF). Our results demonstrate that AAGF reduces TA without affecting the integrity of the myocardial microstructure.