@article{yokoyama_nichols_gallippi_2022, title={Quantitative Estimation of Shear Elastic Heterogeneity and Anisotropy in Excised Canine Kidneys using Double Profile Intersection (DoPIo) Ultrasound}, ISSN={["1948-5719"]}, DOI={10.1109/IUS54386.2022.9957981}, abstractNote={Quantitative elastography methods based on dis-placement measurements coaxial to ARFI excitations are ad-vantageous over shear wave-based approaches in heterogeneous and anisotropic tissues, such as kidney, that confound or limit shear wave propagation. Double-Profile Intersection (DoPIo) elastography quantifies shear elasticity by tracking ARF -induced displacements using two different focal configurations, identifying the time at which the profiles intersect, and then estimating modulus from times intersect via FEM-derived models. We demonstrate herein quantitative estimates of shear modulus, elastic regional ratios (RR) between anatomical features, and elastic degree of anisotropy (DoA) using DoPIo ultrasound in dog kidneys. Three ex vivo canine kidney with no known pathologies were imaged, shear elastic modulus was estimated in the renal cortex, medulla, and crest, and DoA and RR were measured in each region and compared against ARFI peak displacements (PD). DoPIo distinguished differences in elasticity between the cortex (median and MAD $\boldsymbol{9.3\pm 3.1\ \mathbf{kPa}}$) and inner parenchymal structures $(\boldsymbol{4.8 \pm 0.9}\ \mathbf{kPa};\ \boldsymbol{p\leq 0.0077})$, and DoPIo-based DoA indicated higher shear elasticity along nephrons versus across them in the renal crest in a consistent manner as PD. Thus, DoPIo may be relevant to on-axis measurement of shear elasticity, elastic RR, and elastic DoA in heterogeneous and anisotropic kidneys.}, journal={2022 IEEE INTERNATIONAL ULTRASONICS SYMPOSIUM (IEEE IUS)}, author={Yokoyama, Keita A. and Nichols, Timothy C. and Gallippi, Caterina M.}, year={2022} }
 @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{yokoyama_anand_gallippi_2021, title={Assessing the Impact of ARF Excitation Beam Width and Tracking Beam Concurrency on DoPIo Imaging Performance in a Calibrated Phantom}, ISSN={["1948-5719"]}, DOI={10.1109/IUS52206.2021.9593658}, abstractNote={Double-profile intersection (DoPIo) ultrasound combines two displacement profiles capturing identical tissue motion following an acoustic radiation force (ARF) push to estimate shear elastic modulus via an empirically derived model. However, the displacement-tracking scheme may be impacted by differences in focal configurations for both the push and track beams. A wider push beam imparts a more uniform displacement gradient than narrow ARF pushes for on-axis tracking beams, while the simultaneous formation of two displacement profiles from a single, wide transmit pulse enables the tracking of identical scatterer distributions at the cost of diminished differences between the two displacement profiles. In silico experiments suggested that DoPIo acquisitions performed using a wide ARF push beam and simultaneous tracking provided the most accurate and precise elasticity estimates. While all four combinations of parameters enabled the differentiation of a soft inclusion within a stiff background in vitro, elasticity estimates on a commercially calibrated phantom were consistently overestimated.}, journal={INTERNATIONAL ULTRASONICS SYMPOSIUM (IEEE IUS 2021)}, author={Yokoyama, Keita A. and Anand, Keerthi S. and Gallippi, Caterina M.}, year={2021} }