Garry Liu

An experimental framework to validate 3D models of cardiac electrophysiology via optical imaging and MRI

Our aim is to develop a framework to validate 3-D computer models of cardiac electrophysiology using measurements of action potential obtained via optical imaging (based on voltage-sensitive fluorescence), and heart anatomy and fiber directions which are obtained from magnetic resonance imaging (MRI). In this paper we present preliminary results of this novel framework using a healthy porcine heart ex vivo model and the Aliev & Panfilov mathematical model. This experimental setup will facilitate the testing, validation and adjustment of computational models prior to their integration into clinical applications.

MRI characterization of peripheral arterial chronic total occlusions at 7 Tesla with microCT and histologic validation

Background Current treatment guidelines recommend surgical bypass for peripheral chronic total occlusions (CTOs)[1]. Percutaneous transluminal angioplasty (PTA), however, offers a less invasive approach with improved perioperative morbidity, shorter length of hospital stay, and lower cost[2]. Not all lesions are amenable to this technique and there is a significant primary failure rate[2]. Predicting lesion crossability is difficult because current imaging techniques offer limited information with which to characterize CTOs. The ability to distinguish between hard and soft biological substances that compose a CTO can aid procedural planning and facilitate intervention. This pilot study demonstrates the ability of high resolution MRI to characterize peripheral CTO components with microCT and histologic validation.

Improvement of LV functional performance in the chronic total coronary occlusion during the late stage is associated with the extensive collateral development

Methods In nine pigs a CTO was created by percutaneously inserting a fibrin plug (AngiosealΤΜ) into the mid-todistal left anterior descending artery (LAD). Animals were studied six (n=3) or twelve weeks (n=6) later prior to sacrifice. An x-ray angiogram confirmed the LAD CTO at those time points. Cardiac MR (CMR) studies were then conducted on a 1.5T (n=6) or on a 3.0T MRI system (n=3), which included SSFP short axis sections for wall motion and post-gadolinium LGE-MRIs for viability. After sacrifice, both right and left coronary systems were injected with Microfil. X-ray or MSCT angiography of the fixed heart was obtained. A longitudinal cardiac section including the CTO lesion, proximal/distal LAD and the borders of infarction was removed and prepared in gel, then imaged in a microCT system at 27 micron resolution. LV functional parameters including wall thickness at end-systole (WTES) and end-diastole (WTED) were measured in border zone, infarct and remote region. Systolic wall thickening (SWT) was calculated using as (WTES-WTED) x100/ WTED. CMR and micro-CT data were processed using commercial software. The extent of collaterals on micro-CT images was rated qualitatively using a score from 0 to 3, indicating that no, minimal, moderate, or extensive collaterals were observed. A Student’s t-test was used for the statistical significance of differences between measurements at 6 and 12 weeks.