Prasanta Pal

Radial Basis Functions for Combining Shape and Speckle Tracking in 4D Echocardiography

Quantitative analysis of left ventricular deformation can provide valuable information about the extent of disease as well as the efficacy of treatment. In this work, we develop an adaptive multi-level compactly supported radial basis approach for deformation analysis in 3D+time echocardiography. Our method combines displacement information from shape tracking of myocardial boundaries (derived from B-mode data) with mid-wall displacements from radio-frequency-based ultrasound speckle tracking. We evaluate our methods on open-chest canines (N=8) and show that our combined approach is better correlated to magnetic resonance tagging-derived strains than either individual method. We also are able to identify regions of myocardial infarction (confirmed by postmortem analysis) using radial strain values obtained with our approach.

Multimodality Imaging Approach for Serial Assessment of Regional Changes in Lower Extremity Arteriogenesis and Tissue Perfusion in a Porcine Model of Peripheral Arterial Disease

Background—A standard quantitative imaging approach to evaluate peripheral arterial disease does not exist. Quantitative tools for evaluating arteriogenesis in vivo are not readily available, and the feasibility of monitoring serial regional changes in lower extremity perfusion has not been examined. Methods and Results—Serial changes in lower extremity arteriogenesis and muscle perfusion were evaluated after femoral artery occlusion in a porcine model using single photon emission tomography (SPECT)/CT imaging with postmortem validation of in vivo findings using gamma counting, postmortem imaging, and histological analysis. Hybrid 201Tl SPECT/CT imaging was performed in pigs (n=8) at baseline, immediately postocclusion, and at 1 and 4 weeks postocclusion. CT imaging was used to identify muscle regions of interest in the ischemic and nonischemic hindlimbs for quantification of regional changes in CT-defined arteriogenesis and quantification of 201Tl perfusion. Four weeks postocclusion, postmortem tissue 201Tl activity was measured by gamma counting, and immunohistochemistry was performed to assess capillary density. Relative 201Tl retention (ischemic/nonischemic) was reduced immediately postocclusion in distal and proximal muscles and remained lower in calf and gluteus muscles 4 weeks later. Analysis of CT angiography revealed collateralization at 4 weeks within proximal muscles (P<0.05). SPECT perfusion correlated with tissue gamma counting at 4 weeks (P=0.01). Increased capillary density was seen within the ischemic calf at 4 weeks (P=0.004). Conclusions—201Tl SPECT/CT imaging permits serial, regional quantification of arteriogenesis and resting tissue perfusion after limb ischemia. This approach may be effective for detection of disease and monitoring therapy in peripheral arterial disease.

Comparison of regional skeletal muscle tissue oxygenation in college athletes and sedentary control subjects using quantitative BOLD MR imaging

Blood oxygen level‐dependent (BOLD) magnetic resonance (MR) imaging permits noninvasive assessment of tissue oxygenation. We hypothesized that BOLD imaging would allow for regional evaluation of differences in skeletal muscle oxygenation between athletes and sedentary control subjects, and dynamic BOLD responses to ischemia (i.e., proximal cuff occlusion) and reactive hyperemia (i.e., rapid cuff deflation) would relate to lower extremity function, as assessed by jumping ability. College football athletes (linemen, defensive backs/wide receivers) were compared to sedentary healthy controls. BOLD signal of the gastrocnemius, soleus, anterior tibialis, and peroneus longus was assessed for peak hyperemic value (PHV), time to peak (TTP), minimum ischemic value (MIV), and time to recovery (TTR). Significantly higher PHVs were identified in athletes versus controls for the gastrocnemius (linemen, 15.8 ± 9.1%; defensive backs/wide receivers, 17.9 ± 5.1%; controls, 7.4 ± 3.5%), soleus (linemen, 25.9 ± 11.5%; backs/receivers, 22.0 ± 9.4%; controls, 12.9 ± 5.8%), and anterior tibialis (linemen, 12.8 ± 5.3%; backs/receivers, 12.6 ± 3.9%; controls, 7.7 ± 4.0%), whereas no differences in PHV were found for the peroneus longus (linemen, 14.1 ± 6.9%; backs/receivers, 11.7 ± 4.6%; controls, 9.0 ± 4.9%). In all subject groups, the gastrocnemius and soleus muscles exhibited the lowest MIVs during cuff occlusion. No differences in TTR were found between muscles for any subject group. PHV of the gastrocnemius muscle was significantly and positively related to maximal vertical (r = 0.56, P = 0.002) and broad jump (r = 0.47, P = 0.01). These results suggest that BOLD MR imaging is a useful noninvasive tool for evaluating differences in tissue oxygenation of specific muscles between active and sedentary individuals, and peak BOLD responses may relate to functional capacity.

4-D echocardiography assessment of local myocardial strain using 3-D speckle tracking combined with shape tracking

In 4-D echocardiography (4DE), displacement estimates obtained solely from multi-dimensional speckle tracking can exhibit large variances and peak hopping, making it challenging to accurately calculate myocardial strains. 3-D phase-sensitive speckle tracking can produce sensitive estimates along the axial direction, but typically provides poorer estimates in orthogonal directions and at tissue boundaries. Shape tracking provides complimentary information, as it effectively tracks myocardial boundaries and does not depend on beam orientation. We propose a method combining 3-D speckle tracking with 3-D shape tracking using a quality-based radial basis function approach. Echocardiographic data (3D+t) were acquired in an open chest canine model at six weeks following surgical coronary occlusion using a commercial 2-D phased array, on which 3-D phase-sensitive speckle tracking and 3-D shape tracking were performed. An adaptive, multi-level radial basis function method was used to combine information from the two tracking methods, utilizing confidence metrics to weight the contribution of each estimate to generate a dense 3-D displacement field throughout the myocardium. A multi-level approach was used to capture smaller scales of motion in regions of fine deformation variation and high tracking confidence. The 3-D combined approach produced displacement estimates with greatly reduced variance and peak hopping compared to 3-D speckle tracking alone. Lower radial strains were observed in the myocardial infarct region, corresponding to reduced local contractility. Strong correlations were observed for both radial and circumferential strains between the combined method and estimates from magnetic resonance (MR) tagging studies.

Flow vortex quantification in the left atrium

We have developed a novel high temporal resolution magnetic resonance (MR) imaging and image analysis method to quantify vorticity patterns in the left atrium (LA). Our data demonstrates the formation and evolution of atrial vortices during ventricular systole and ventricular diastasis period.