@article{hossain_gallippi_2022, title={Quantitative Estimation of Mechanical Anisotropy Using Acoustic Radiation Force (ARF)-Induced Peak Displacements (PD): In Silico and Experimental Demonstration}, volume={41}, ISSN={["1558-254X"]}, DOI={10.1109/TMI.2022.3141084}, abstractNote={Elastic degree of anisotropy (DoA) is a diagnostically relevant biomarker in muscle, kidney, breast, and other organs. Previously, elastic DoA was qualitatively assessed as the ratio of peak displacements (PD) achieved with the long-axis of a spatially asymmetric Acoustic Radiation Force Impulse (ARFI) excitation point spread function (PSF) aligned along versus across the axis of symmetry (AoS) in transversely isotropic materials. However, to better enable longitudinal and cross-sectional analyses, a quantitative measure of elastic DoA is desirable. In this study, qualitative ARFI PD ratios are converted to quantitative DoA, measured as the ratio of longitudinal over transverse shear elastic moduli, using a model empirically derived from Field II and finite element method (FEM) simulations. In silico, the median absolute percent error (MAPE) in ARFI-derived shear moduli ratio (SMR) was 1.75%, and predicted SMRs were robust to variations in transverse shear modulus, Young’s moduli ratio, speed of sound, attenuation, density, and ARFI excitation PSF dimension. Further, ARFI-derived SMRs distinguished two materials when the true SMRs of the compared materials differed by as little as 10%. Experimentally, ARFI-derived SMRs linearly correlated with the corresponding ratios measured by Shear Wave Elasticity Imaging (SWEI) in excised pig skeletal muscle ( $\text{R}^{{2}} ={0.91}$ , MAPE = 13%) and in pig kidney, in vivo ( $\text{R}^{{2}}= {0.99}$ , MAPE = 5.3%). These results demonstrate the feasibility of using the ARFI PD to quantify elastic DoA in biological tissues.}, number={6}, journal={IEEE TRANSACTIONS ON MEDICAL IMAGING}, author={Hossain, Md Murad and Gallippi, Caterina M.}, year={2022}, month={Jun}, pages={1468–1481} } @article{yokoyama_hossain_caughey_fisher_detweiler_chang_gallippi_2022, title={in vivo VisR Measurements of Viscoelasticity and Viscoelastic Anisotropy in Human Allografted Kidneys Differentiate Interstitial Fibrosis and Graft Rejection}, ISSN={["1948-5719"]}, DOI={10.1109/IUS54386.2022.9958358}, abstractNote={Assessment of renal transplant failure typically in-volves nonspecific biomarkers or invasive biopsies, presenting a clinical need for noninvasive imaging modalities that can identify pathologic changes in renal allografts. One approach is Viscoelastic Response (VisR) ultrasound, an acoustic radiation force (ARF)-based imaging method that qualitatively evaluates, relative to the applied ARF amplitude, tissue elasticity (RE) and viscosity (RV). We hypothesize that, by measuring the RE and RV degree of anisotropy (DoA) along versus across nephrons in the cortex and the regional ratio (RR) of RE and RV in the outer versus inner cortex, VisR can discriminate transplanted kidneys with fibrosis and rejection in humans in vivo. VisR imaging was performed in renal transplant patients from 3 to 36 months after transplantation at 3 mo. (quarterly) intervals, coincident with routine clinic visits. RE and RV-based DoA in outer and inner cortices were significantly different between patients with and without biopsy-confirmed interstitial fibrosis up to 4 quarters before the time of clinically indicated biopsies. VisR RE-based RR had similar performance but also differentiated rejected from fibrotic kidney. These results suggest that noninvasive VisR imaging is relevant to early detection of transplant kidney fibrosis and rejection, which could enable timely interventions that extend graft life.}, journal={2022 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IEEE IUS)}, author={Yokoyama, Keita A. and Hossain, Md. Murad and Caughey, Melissa C. and Fisher, Melrose W. and Detweiler, Randal K. and Chang, Emily H. and Gallippi, Caterina M.}, year={2022} } @article{wu_hossain_kim_gallippi_jiang_2021, title={A 1.5-D Array for Acoustic Radiation Force (ARF)-Induced Peak Displacement-Based Tissue Anisotropy Assessment With a Row-Column Excitation Method}, volume={68}, ISSN={["1525-8955"]}, url={https://doi.org/10.1109/TUFFC.2020.3030040}, DOI={10.1109/TUFFC.2020.3030040}, abstractNote={Many biological tissues, including muscle or kidney, are mechanically anisotropic, and the degree of anisotropy (DoA) in mechanical properties is diagnostically relevant. DoA can be assessed either using the ratio of shear wave velocities (SWVs) or acoustic radio forced impulse (ARFI)-induced peak displacements (PD) measured longitudinal over transverse orientations. Whether using SWV or PD as a basis, DoA expressed as the ratio of values requires 90° transducer rotation when a linear array is employed. This large rotation angle is prone to misalignment errors. One solution is the use of a fully sampled matrix array for electronic rotation of point spread function (PSF). However, the challenges of matrix array are its high fabrication cost and complicated fabrication procedures. The cheaper and simpler alternative of matrix array is the use of a row–column array. A

$3\times64$

elements 1.5-D array with a row–column excitation mode is proposed to assess DoA in mechanical properties using the PD ratio. Different numbers of elements in elevational and lateral directions were selected to have orthogonal ARFI excitation beams without rotating the transducer. A custom-designed flex circuit was used to fabricate the array with a simpler electrode connection than a fully sampled matrix array. The performance of the array was evaluated in Field II simulation and experiment. The output pressure was 0.57-MPa output under a 40-

${V}_{\text {pp}}$

excitation with a −6-dB point spread dimension of

$14\times4$

mm² in orthogonal directions. The PD was measured to be

$1.4~\mu \text{m}$

in an isotropic elastic phantom with Young’s modulus of 5.4 kPa. These results suggest that the array is capable of assessing DoA using PD ratio without physical rotation of the transducer. The array has the potential to reduce the misalignment errors for DoA assessment.}, number={4}, journal={IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Wu, Huaiyu and Hossain, Md Murad and Kim, Howuk and Gallippi, Caterina M. and Jiang, Xiaoning}, year={2021}, month={Apr}, pages={1278–1287} } @article{hossain_gallippi_2021, title={Electronic Point Spread Function Rotation Using a Three-Row Transducer for ARFI-Based Elastic Anisotropy Assessment: In Silico and Experimental Demonstration}, volume={68}, ISSN={["1525-8955"]}, DOI={10.1109/TUFFC.2020.3019002}, abstractNote={Degree of anisotropy (DoA) of mechanical properties has been assessed as the ratio of acoustic radiation force impulse (ARFI)-induced peak displacements (PDs) achieved using spatially asymmetric point spread functions (PSFs) that are rotated 90° to each other. Such PSF rotation has been achieved by manually rotating a linear array transducer, but manual rotation is cumbersome and prone to misalignment errors and higher variability in measurements. The purpose of this work is to evaluate the feasibility of electronic PSF rotation using a three-row transducer, which will reduce variability in DoA assessment. A Siemens 9L4, with $3\times192$ elements, was simulated in Field II to generate spatially asymmetric ARFI PSFs that were electronically rotated 63° from each other. Then, using the finite element method (FEM), PD due to the ARFI excitation PSFs in 42 elastic, incompressible, transversely isotropic (TI) materials with shear moduli ratios of 1.0–6.0 were modeled. Finally, the ratio of PDs achieved using the two rotated PSFs was evaluated to assess elastic DoA. DoA increased with increasing shear moduli ratios and distinguished materials with 17% or greater difference in shear moduli ratios (Wilcoxon, ${p} < 0.05$ ). Experimentally, the ratio of PDs achieved using ARFI PSF rotated 63° from each other distinguished the biceps femoris muscle from two pigs, which had median shear moduli ratios of 4.25 and 3.15 as assessed by shear wave elasticity imaging (SWEI). These results suggest that ARFI-based DoA assessment can be achieved without manual transducer rotation using a three-row transducer capable of electronically rotating PSFs by 63°. It is expected that electronic PSF rotation will facilitate data acquisitions and improve the reproducibility of elastic anisotropy assessments.}, number={3}, journal={IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL}, author={Hossain, Md Murad and Gallippi, Caterina M.}, year={2021}, month={Mar}, pages={632–646} } @article{hossain_gallippi_2020, title={Viscoelastic Response Ultrasound Derived Relative Elasticity and Relative Viscosity Reflect True Elasticity and Viscosity: In Silico and Experimental Demonstration}, volume={67}, ISSN={["1525-8955"]}, DOI={10.1109/TUFFC.2019.2962789}, abstractNote={Viscoelastic response (VisR) ultrasound characterizes the viscoelastic properties of tissue by fitting acoustic radiation force (ARF)-induced displacements in the region of ARF excitation to a 1-D mass-spring-damper (MSD) model. Elasticity and viscosity are calculated separately but relative to the applied ARF amplitude. We refer to these parameters as “relative elasticity (RE)” and “relative viscosity (RV).” We herein test the hypothesis that RE and RV linearly correlate to true elasticity and viscosity in tissue. VisR imaging was simulated in 144 homogeneous viscoelastic materials with varying elasticities and viscosities. Derived RE linearly correlated with material elasticity and varied by an average of 2.52% when the material viscosity changed from 0.1 to 1.3 Pa

$\cdot $

s. Derived RV linearly correlated with material viscosity but varied by an average of 102.5% when material elasticity changed from 3.33 to 20 kPa. The effect of elasticity on RV measurement was compensated using the slope of the linear relationship between RV and natural frequency (

$\omega _{text{n}}$

). After compensation, RV

$^{\text {EC}}$

(elasticity compensated RV) linearly correlated with material viscosity and varied by less than 1.00% on average when the modeled shear elastic modulus changed from 3.3 to 20 kPa. In addition to elasticity compensation, variation in ARF amplitude over depth was compensated, yielding RE_DC and

${\text {RV}}_{\text {DC}}^{\text {EC}}$

. RE_DC and

${\text {RV}}_{\text {DC}}^{\text {EC}} $

successfully contrasted elastic and viscous inclusions, respectively, in three simulated phantoms. Experimentally, in the homogeneous oil-in-gelatin phantoms and excised livers, RE_DC linearly correlated with shear wave dispersion ultrasound vibrometry (SDUV) derived shear elastic modulus, and

${\text {RV}}_{\text {DC}}^{\text {EC}}$

linearly correlated with SDUV-derived shear viscosity. In excised livers containing viscoelastic oil-in-gelatin inclusions, the inclusions were successfully contrasted from the liver background by both RE_DC and

${\text {RV}}_{\text {DC}}^{\text {EC}}$

. These results suggest that RE and RV are relevant for qualitatively assessing the elastic and viscous properties of tissue.}, number={6}, journal={IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL}, author={Hossain, Md Murad and Gallippi, Caterina M.}, year={2020}, month={Jun}, pages={1102–1117} } @article{hossain_detwiler_chang_caughey_fisher_nichols_merricks_raymer_whitford_bellinger_et al._2019, title={Mechanical Anisotropy Assessment in Kidney Cortex Using ARFI Peak Displacement: Preclinical Validation and Pilot In Vivo Clinical Results in Kidney Allografts}, volume={66}, ISSN={["1525-8955"]}, DOI={10.1109/TUFFC.2018.2865203}, abstractNote={The kidney is an anisotropic organ, with higher elasticity along versus across nephrons. The degree of mechanical anisotropy in the kidney may be diagnostically relevant if properly exploited; however, if improperly controlled, anisotropy may confound stiffness measurements. The purpose of this study is to demonstrate the clinical feasibility of acoustic radiation force (ARF)-induced peak displacement (PD) measures for both exploiting and obviating mechanical anisotropy in the cortex of human kidney allografts, in vivo. Validation of the imaging methods is provided by preclinical studies in pig kidneys, in which ARF-induced PD values were significantly higher (

$p < 0.01$

, Wilcoxon) when the transducer executing asymmetric ARF was oriented across versus along the nephrons. The ratio of these PD values obtained with the transducer oriented across versus along the nephrons strongly linearly correlated (

$R^{2} = 0.95$

) to the ratio of shear moduli measured by shear wave elasticity imaging. On the contrary, when a symmetric ARF was implemented, no significant difference in PD was observed (

$p > 0.01$

). Similar results were demonstrated in vivo in the kidney allografts of 14 patients. The symmetric ARF produced PD measures with no significant difference (

$p > 0.01$

) between along versus across alignments, but the asymmetric ARF yielded PD ratios that remained constant over a six-month observation period post-transplantation, consistent with stable serum creatinine level and urine protein-to-creatinine ratio in the same patient population (

$p> 0.01$

). The results of this pilot in vivo clinical study suggest the feasibility of 1) implementing symmetrical ARF to obviate mechanical anisotropy in the kidney cortex when anisotropy is a confounding factor and 2) implementing asymmetric ARF to exploit mechanical anisotropy when mechanical anisotropy is a potentially relevant biomarker.}, number={3}, journal={IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL}, author={Hossain, Md Murad and Detwiler, Randal K. and Chang, Emily H. and Caughey, Melissa C. and Fisher, Melrose W. and Nichols, Timothy C. and Merricks, Elizabeth P. and Raymer, Robin A. and Whitford, Margaret and Bellinger, Dwight A. and et al.}, year={2019}, month={Mar}, pages={551–562} } @article{selzo_moore_hossain_palmeri_gallippi_2019, title={On the Quantitative Potential of Viscoelastic Response (VisR) Ultrasound Using the One-Dimensional Mass-Spring-Damper Model (vol 63, pg 1276, 2016)}, volume={66}, ISSN={["1525-8955"]}, DOI={10.1109/TUFFC.2018.2883811}, abstractNote={In the original publication of this paper [1], equation (3) contained sign errors for the amplitude of the third and fourth Heaviside functions. The corrected equation is shown in the following: [Formula: see text].}, number={1}, journal={IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL}, author={Selzo, Mallory R. and Moore, Christopher J. and Hossain, Md Murad and Palmeri, Mark L. and Gallippi, Caterina M.}, year={2019}, month={Jan}, pages={251–251} } @article{hossain_gallippi_2019, title={On the feasibility of quantifying mechanical anisotropy in transversely isotropic elastic materials using acoustic radiation force (ARF)-induced displacements}, volume={10955}, ISSN={["1996-756X"]}, DOI={10.1117/12.2511765}, abstractNote={Many soft tissues, including skeletal muscle and kidney, can be modeled astransversely isotropic (TI) materials defined by an axis of symmetry (AoS) perpendicular to a plane of isotropy. In such materials, mechanical properties differ along versus across the AoS. The degree of mechanical anisotropy in TI materials was previously assessed as the ratio of peak displacement (PD) achieved when the long axis of an asymmetric acoustic radiation force (ARF) excitation point spread function (PSF) was aligned along versus across the material’s AoS, but the measurement was qualitative. The objectives of this work were: (i) to derive an empirical model describing the relationship between the PD ratio and shear moduli ratio; (ii) to investigate the impact of ARF excitation PSF aberration due to speed of sound (c), attenuation (α), and dimension of ARF excitation PSF on the empirical model; and (iii) to estimate mechanical anisotropy in excised pig biceps femoris muscles and in vivo pig kidney using the empirical model. The empirical model was derived by simulating ARF Impulse (ARFI) imaging of ‘train’ TI materials (shear moduli ratios varying from 1.0 to 10 in steps of 0.75) and validated on ‘test’ materials (shear moduli ratios varying from 1.25 to 8.75 in steps of 0.75) using finite element method (FEM) models. Siemens VF73 transducer parameter with lateral F/1.5 was simulated for ARFI imaging. The speed of sound and attenuation was set to1540 ms-1 and 0.5 dB/cm/MHZ, respectively for train materials and was set to1540 or 1620 ms-1 and 0.5 or 1.0 dB/cm/MHZ, respectively for test materials. To find the impact of ARF excitation PSF dimension, a matrix array was simulated and the lateral and elevational F/# was set to 2.0 and 3.4, respectively for train materials and was set to 2.0 or 3.0 and 3.4 or 5.1, respectively for test materials. Ultrasound tracking of FEM displacements was performed in Field II with an SNR of 30 dB. The average absolute percent error in predicting shear moduli ratio of all ‘test’ materials was 1.6%. The empirical model was not impacted by the deviation from expected attenuation, sound speed, and ARF excitation PSF dimension. Shear moduli ratios derived using the empirical model matched those derived from shear wave elasticity imaging (SWEI) in pig muscle (model: 4.44 ± 0.47 and SWEI: 4.38 ± 0.27), renal medulla (model: 1.31 ± 0.07 and SWEI: 1.32 ± 0.04) and renal cortex (model: 2.0 ± 0.19 and SWEI: 1.99 ± 0.06). These results suggest the feasibility of using the PD empirical model to quantify mechanical anisotropy in biological tissues.}, journal={MEDICAL IMAGING 2019: ULTRASONIC IMAGING AND TOMOGRAPHY}, author={Hossain, Md Murad and Gallippi, Caterina M.}, year={2019} } @article{hossain_moore_gallippi_2017, title={Acoustic Radiation Force Impulse-Induced Peak Displacements Reflect Degree of Anisotropy in Transversely Isotropic Elastic Materials}, volume={64}, ISSN={["1525-8955"]}, DOI={10.1109/tuffc.2017.2690223}, abstractNote={In transversely isotropic (TI) materials, mechanical properties (Young’s modulus, shear modulus, and Poisson’s ratio) are different along versus across the axis of symmetry (AoS). In this paper, the feasibility of interrogating such directional mechanical property differences using acoustic radiation force impulse (ARFI) imaging is investigated. We herein test the hypotheses that: 1) ARFI-induced peak displacements (PDs) vary with TI material orientations when an asymmetrical ARFI excitation point spread function (PSF) is used, but not when a symmetrical ARFI PSF is employed and 2) the ratio of PDs induced with the long axis of an asymmetrical ARFI PSF oriented along versus across the material’s AoS is related to the degree of anisotropy of the material. These hypotheses were tested in silico using finite-element method (FEM) models and Field II. ARFI excitations had F/1.5, 3, 4, or 5 focal configurations, with the F/1.5 and F/5 cases having the most asymmetrical and symmetrical PSFs at the focal depth, respectively. These excitations were implemented for ARFI imaging in 52 different simulated TI materials with varying degrees of anisotropy, and the ratio of ARFI-induced PDs was calculated. The change in the ratio of PDs with respect to the anisotropy of the materials was highest for the F/1.5, indicating that PD was most strongly impacted by the material orientation when the ARFI excitation was the most asymmetrical. On the contrary, the ratio of PDs did not depend on the anisotropy of the material for the F/5 ARFI excitation, suggesting that PD did not depend on material orientation when the ARFI excitation was symmetrical. Finally, the ratio of PDs achieved using asymmetrical ARFI PSF reflected the degree of anisotropy in TI materials. These results support that symmetrical ARFI focal configurations are desirable when the orientation of the ARFI excitation to the AoS is not specifically known and measurement standardization is important, such as for longitudinal or cross-sectional studies of anisotropic organs. However, asymmetrical focal configurations are useful for exploiting anisotropy, which may be diagnostically relevant. Feasibility for future experimental implementation is demonstrated by simulating ultrasonic displacement tracking and by varying the ARF duration.}, number={6}, journal={IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL}, author={Hossain, Md Murad and Moore, Christopher J. and Gallippi, Caterina M.}, year={2017}, month={Jun}, pages={989–1001} } @article{selzo_moore_hossain_palmeri_gallippi_2016, title={On the Quantitative Potential of Viscoelastic Response (VisR) Ultrasound Using the One-Dimensional Mass-Spring-Damper Model}, volume={63}, ISSN={["1525-8955"]}, DOI={10.1109/tuffc.2016.2539323}, abstractNote={Viscoelastic response (VisR) ultrasound is an acoustic radiation force (ARF)-based imaging method that fits induced displacements to a one-dimensional (1-D) mass-spring-damper (MSD) model to estimate the ratio of viscous to elastic moduli, τ, in viscoelastic materials. Error in VisR τ estimation arises from inertia and acoustic displacement underestimation. These error sources are herein evaluated using finite-element method (FEM) simulations, error correction methods are developed, and corrected VisR τ estimates are compared with true simulated τ values to assess VisR's relevance to quantifying viscoelasticity. With regard to inertia, adding a mass term in series with the Voigt model, to achieve the MSD model, accounts for inertia due to tissue mass when ideal point force excitations are used. However, when volumetric ARF excitations are applied, the induced complex system inertia is not described by the single-degree-of-freedom MSD model, causing VisR to overestimate τ. Regarding acoustic displacement underestimation, associated deformation of ARF-induced displacement profiles further distorts VisR τ estimates. However, median error in VisR τ is reduced to approximately -10% using empirically derived error correction functions applied to simulated viscoelastic materials with viscous and elastic properties representative of tissue. The feasibility of corrected VisR imaging is then demonstrated in vivo in the rectus femoris muscle of an adult with no known neuromuscular disorders. These results suggest VisR's potential relevance to quantifying viscoelastic properties clinically.}, number={9}, journal={IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL}, author={Selzo, Mallory R. and Moore, Christopher J. and Hossain, Md. Murad and Palmeri, Mark L. and Gallippi, Caterina M.}, year={2016}, month={Sep}, pages={1276–1287} }