Karen Chin

Vortex Formation Time Index in Patients With Hypertrophic Cardiomyopathy

Vortex ring formation in early diastole helps with left ventricular (LV) filling without an increase in left atrial (LA) pressure. Vortex formation time (VFT) is a dimensionless parameter derived from LV geometry and indexes of LV systolic and diastolic performance [(1)][1]. The optimal range was

Magnetic resonance based control of a robotic manipulator for interventions in the beating heart

As a part of an ongoing project, in this paper we introduce the first version of a system which has a novel methodology for Cine (as in cinema) MRI based control of a cardiac robot for beating heart surgeries. The system uses the preoperative planning approach that we developed earlier, and integrates it to the intraoperative algorithms for controlling a robot and tracking some specific landmarks of a highly dynamical surgical field. In particular, our late studies presented herein aim to demonstrate the feasibility of integrating appropriate computational tools to achieve the volumetric image guidance for minimally invasive surgeries in the beating heart. We conceive of the system as practicable for in vitro experiments upon the completion of the first physical prototype, which may pave the way for expansion of the approach for other complex surgeries as well.

Association of Left Ventricular Diastolic Dysfunction with Subclinical Coronary Atherosclerotic Disease Burden Using Coronary Artery Calcium Scoring.

AIM Diastolic dysfunction is a common problem in patients with obesity, hypertension, diabetes, or coronary artery disease. The purpose of this study was to evaluate the association of left ventricular diastolic dysfunction with an abnormal coronary artery calcium score (CAC score). METHODS This study considered a cohort of patients ≥ 18 years of age with normal ejection fraction who were admitted to the hospital with chest pain. All patients underwent regadenoson myocardial perfusion stress imaging and had no evidence of ischemia or infarction. Patients then underwent cardiac CT for measurement of CAC score. Patients were excluded if they had prior history of coronary artery disease, ECG findings diagnostic of an acute coronary syndrome, an elevated troponin level, or hemodynamic instability. RESULTS A total of 114 patients were included and 52 (45.6%) patients had echocardiographic evidence of diastolic dysfunction. Patients with diastolic dysfunction were more likely to have an abnormal calcium score (79.6% vs 20%; OR 15.10, 95% CI 5.70 to 43.85; p ＜ 0.001). In multivariable analysis, the presence of diastolic dysfunction on echocardiogram was significantly associated with an abnormal calcium score (OR 13.82, 95% CI 5.57 to 37.37; p ＜ 0.001) after adjusting for Framingham Risk Score or clinical risk factors (age, gender, diabetes mellitus, dyslipidemia, and obesity; OR 19.06,95% CI 4.66 to 107.97; p ＜ 0.001). CONCLUSIONS Our study demonstrates that left ventricular diastolic dysfunction is associated with an abnormal CAC score even after adjusting for Framingham Risk Score or clinical risk factors. Patients without known coronary artery disease that present with chest pain and have normal perfusion imaging with evidence of abnormal diastolic function on echocardiogram may warrant more thorough evaluation for coronary atherosclerotic disease with CAC score assessment.

An in vitro validation of cardiac magnetic resonance 4D flow measurements with bioprosthetic mitral valve flow volumes quantification

Background Four dimensional flow MRI is a new methodology for evaluating the morphology of the heart using phase contrast cardiac magnetic resonance imaging not only in the usual three dimensions (x, y and z), but also across time. The full breadth of this new form of imaging has yet to be fully established. In order to evaluate this modality and its accuracy, we decided to use 4D flow MRI to quantify diastolic flow volumes across a bioprosthetic valve (BPV) in a controlled and reproducible in vitro system. Methods Three different sizes of BMV’s (27, 29, and 31 mm) were consecutively mounted in an MRI compatible flow loop where the flow conditions could be controlled using software that programmed a pump to generate pulsatile, physiologic ventricular ejection and filling simulations. The generated pulses were generated using each valve and mimicked diastolic flow volumes of about 70, 90 and 110 ml/beat at a rate of 70 bpm. An in-series ultrasonic flow transducer (UFT) was used to measure flow (L/min) by which diastolic flow volumes were determined. The acquisition of 3D cine (4D flow) phase contrast velocity data was acquired in a 1.5 Tesla MRI scanner (Avanto, Siemens Medical Solutions, Inc., Erlangen, Germany). The typical imaging parameters were: repetition time 45-48 ms, echo time 2.75 ms, flip angle 15°, slice thickness 1.5 mm, field of view 350 × 260 mm2, voxel size 1.5 × 1 × 1.25 mm3. The flow measurements were determined at 3 locations within the valve in post-imaging examination including at the valve base, leaflet tips, and midway between the base and the tips. Results

Left ventricular function in patients with hypertrophic cardiomyopathy and its relation to myocardial fibrosis and exercise tolerance

We sought to determine the relation between myocardial extracellular volume (ECV), left ventricular (LV) diastolic function, and exercise tolerance in patients with hypertrophic cardiomyopathy (HCM). Forty five HCM patients with an ejection fraction >50% and no previous septal reduction therapy underwent imaging by CMR and transthoracic echocardiography. CMR was used to quantify LV volumes, mass, EF, LA volumes, scar burden, pre and post contrast T1 relaxation times and ECV. Echocardiography was used to measure outflow tract gradients, mitral inflow and annular velocities, circumferential strain, systolic, early and late diastolic strain rates. Exercise duration and peak oxygen consumption were noted. HCM patients had increased native T1 relaxation time and ECV vs. controls [ECV controls: 24.7 (23.2–26.4) vs. HCM: 26.8 (24.6–31.3)%, P = 0.014]. Both parameters were significantly associated with LV diastolic dysfunction, circumferential strain, diastolic strain rate and peak oxygen consumption (r = −0.73, P < 0.001). Compared to controls, HCM patients have significantly longer native T1 relaxation time and higher ECV. These structural changes lead to worse LV global and segmental diastolic function and in turn reduced exercise tolerance.

Manipulator-driven selection of semi-active MR-visible markers

A method for the identification of semi‐active fiducial magnetic resonance (MR) markers is presented based on selectively optically tuning and detuning them.

3D Reconstruction of Tubular Structures from Three Orthogonal MRI Projections

This study presents a novel method for 3D imaging of tubular structures, such as blood vessels and catheters. With this method, the 3D object is reconstructed from three mutually exclusive orthogonal projections of the same volume. This triplanar projection imaging (TPI) was evaluated on a phantom filled with T1-shortening, Gd-based contrast agent embedded into a matrix. The projected structures were segmented out on each one of the projections and a backprojection algorithm was used to generate a rendering of the tubular structure in 3D. The accuracy of the method was investigated by comparing the centerline of the 3D tubular structure generated from TPI with the centerline extracted from a multislice set of images of the same volume. The two tubular structures were well matched in 3D. With further optimization and reduction of acquisition time, this method can be used for 3D fast imaging of interventional tools or blood vessels with applications in interventional MRI.

Bioprosthetic Mitral Valve Effective Orifice Area Using 4D Flow Cardiac Magnetic Resonance Derived Time Velocity Integral. An In-Vitro Comparison with Doppler Echocardiography

\Background 4D Flow Cardiac Magnetic Resonance (CMR) is a novel imaging modality to assess bioprosthetic mitral valve (BMV) function. We describe a new, 4D Flow derived velocity time integral (TVI) based method to assess effective orifice area (EOA) for BMVs. Methods In our MRI-compatible circulatory loop 4 stented porcine BMVs (27, 29, 31, 33mm) underwent CMR with a 1.5T Siemens scanner. The valves were evaluated at forward stroke volumes of 70, 90 and 110ml at a beat rate of 70bpm. We plotted instantaneous peak velocities and calculated TVI for each scenario. 4D CMR-EOA was

Bioprosthetic mitral valve effective orifice area by phase-contrast CMR. An in vitro comparison with Doppler echocardiography

Background Introduction: Current guidelines for the functional evaluation of bioprosthetic heart valves recommend the effective orifice area (EOA) as the product of the transvalvular stroke volume divided by Doppler derived diastolic time velocity integral (TVI). Phase contrast CMR may offer an alternative imaging modality to assess bioprosthetic valve EOA when Doppler methods are technically limited or unreliable. Methods Our circulatory loop includes a mock ventricle and a heart valve imaging chamber that has been fabricated using MRI-compatible components. In this study 3 different sized stented porcine mitral valve bioprostheses were evaluated (27 mm, 29 mm, 31 mm) replicating three different hemodynamic conditions with forward stroke volume of 70 ml, 90 ml and 110 ml respectively at a beat rate of 70 bpm. Imaging was performed with a

DEVELOPMENT OF A MULTI-MODALITY IMAGING MODEL OF DYNAMIC MITRAL VALVE DYSFUNCTION

A robust, controlled in vitro model of mitral valve regurgitation (MR) would facilitate the exploration of MR repair techniques and provide a reference test environment for the validation of new imaging applications – including 3D Doppler and phase contrast CMR. Design software, 3D printing