Ria Mazumder

Rapid acquisition technique for MR elastography of the liver.

Magnetic resonance elastography (MRE) of the liver is a novel noninvasive clinical diagnostic tool to stage fibrosis based on measured stiffness. The purpose of this study is to design, evaluate and validate a rapid MRE acquisition technique for noninvasively quantitating liver stiffness which reduces by half the scan time, thereby decreasing image registration errors between four MRE phase offsets. In vivo liver MRE was performed on 16 healthy volunteers and 14 patients with biopsy-proven liver fibrosis using the standard clinical gradient recalled echo (GRE) MRE sequence (MREs) and a developed rapid GRE MRE sequence (MREr) to obtain the mean stiffness in an axial slice. The mean stiffness values obtained from the entire group using MREs and MREr were 2.72±0.85 kPa and 2.7±0.85 kPa, respectively, representing an insignificant difference. A linear correlation of R(2)=0.99 was determined between stiffness values obtained using MREs and MREr. Therefore, we can conclude that MREr can replace MREs, which reduces the scan time to half of that of the current standard acquisition (MREs), which will facilitate MRE imaging in patients with inability to hold their breath for long periods.

In vivo quantification of myocardial stiffness in hypertensive porcine hearts using MR elastography

To determine alteration in left ventricular (LV) myocardial stiffness (MS) with hypertension (HTN). Cardiac MR elastography (MRE) was used to estimate MS in HTN induced pigs and MRE‐derived MS measurements were compared against LV pressure, thickness and circumferential strain.

In vivo magnetic resonance elastography to estimate left ventricular stiffness in a myocardial infarction induced porcine model

To estimate change in left ventricular (LV) end‐systolic and end‐diastolic myocardial stiffness (MS) in pigs induced with myocardial infarction (MI) with disease progression using cardiac magnetic resonance elastography (MRE) and to compare it against ex vivo mechanical testing, LV circumferential strain, and magnetic resonance imaging (MRI) relaxometry parameters (T1, T2, and extracellular volume fraction [ECV]).

Determining Anisotropic Myocardial Stiffness from Magnetic Resonance Elastography: A Simulation Study

Although magnetic resonance elastography (MRE) has the potential to non-invasively measure myocardial stiffness, myocardium is known to be anisotropic and it is not clear whether all material parameters can be uniquely determined from MRE data. In this study, we examined the determinability of anisotropic stiffness parameters using finite element analysis (FEA) simulations of harmonic steady state wave behavior. Two models were examined: (i) a cylindrical and (ii) a canine left ventricular geometry with realistic fiber architecture. A parameter sweep was carried out, and the objective function, which summed the error between reference displacements and displacements simulated from MRE boundary data and material parameters, was plotted and determinability assessed from the Hessian. Then, given prescribed boundary displacements from the ground truth simulation with added Gaussian noise, an anisotropic material parameter optimization was run 30 times with different noise in order to investigate the effect of noise on determination of material parameters. Results show that transversely isotropic material parameters can be robustly determined using this method.

In-vivo waveguide cardiac magnetic resonance elastography

Background Myocardial stiffness (MS) is elevated in heart failure with preserved ejection fraction(HFPEF)[1]. In addition, stiffness elevation in HFPEF exhibits directional dependency [2]. Conventional determinants of MS such as pressurevolume relationship and mechanical testing are invasive and hence clinically inefficient. Therefore, there is a need to non-invasively estimate anisotropic MS to assist in diagnosis and prognosis of HFPEF. In this study we implement waveguide cardiac magnetic resonance elastography (CMRE)[3] to demonstrate the feasibility of estimating anisotropic MS non-invasively in an in-vivo porcine model.

In vivo quantification of aortic stiffness using MR elastography in hypertensive porcine model

Aortic stiffness plays an important role in evaluating and predicting the progression of systemic arterial hypertension (SAH). The aim of this study is to determine the stiffness of aortic wall using MR elastography (MRE) in a hypertensive porcine model and compare it against invasive aortic pressure measurements.

Quantification and comparison of 4D Flow MRI derived wall shear stress and MRE derived wall shear stiffness of abdominal aorta

Background Aortic wall shear stiffness (AWS) and wall shear stress (WSS) are important indicators of pathological changes in the abdominal aorta. Previous studies have shown that AWS increases with diseases such as hypertension and atherosclerosis while WSS decreases with these diseases. Therefore, early detection of AWS and WSS could significantly impact timely treatment of these pathological conditions. Non-invasive estimation of AWS and WSS became feasible after the recent advent of phase contrast MRI based magnetic resonance elastography (MRE) and 4D flow MRI respectively. We hypothesize that investigating the relationship between AWS and WSS may provide additional information to assist in diagnosis of aortic diseases. Therefore, in this study, we use both MRE and 4D flow MRI to estimate and establish the correlation between AWS and WSS in normal human subjects.

Estimation of helical angle of the left ventricle using diffusion tensor imaging with minimum acquisition time

Background Myocardial fiber structure exhibits a helical geometry, characterized by the helical angle (HA). HA transitions smoothly from a negative helix in the epicardium to a positive helix in the endocardium. HA plays an important role in understanding the electrical and mechanical properties of the heart. Therefore, there exists a need to non-invasively quantify HA which can be determined using diffusion tensor imaging (DTI). The evaluation of HA measured from DTI depends on the accuracy of the diffusion tensors which in turn depend on the number of diffusion-encoding directions (DED) and the signal to noise ratio (SNR, which can be increased by increasing the total number of excitations (NEX)). However, increasing SNR and DED also increases the total acquisition time (TA). The aim of the study is to optimize the acquisition protocol (NEX and DED) to robustly estimate HA in the shortest possible TA.

Diffusion tensor imaging of formalin fixed infarcted porcine hearts: a comparison between 3T and 1.5T

BackgroundDiffusion Tensor Imaging (DTI) quantifies the amount ofanisotropic diffusion exhibited by biological tissues. Pro-cessing DTI images allow a 3D visualization of the fiberarchitecture by tracking the fiber trajectories within thetissue. Experimental evidence has shown that the myocar-dium undergoes remodeling as myocardial infarction pro-gresses over time[1]. The aim of this study is to investigateand compare the fiber architecture in an infarcted porcineheart using DTI at 1.5T and 3T, to analyze the effect ofhigh field magnets in imaging.MethodsEx-vivo DTI was performed on an infracted pig heart on1.5T (Avanto, Siemens Hea lthcare, Germany) and 3T(Tim Trio, Siemens Healthcare, Germany) MRI scan-ners. Infarcts were created in the apex region (Fig 1) byoccluding the left ante rior descending coronary artery.After 22 days, the hearts were dissected and formalinfixed for 6 months. A diffusion-weighted echo planarimaging sequence was used to acquire multi-slice shortaxis views covering the ventric les in the excised heart.Imaging parameters included: diffusion encoding direc-tions=256; TE=90ms; TR=7000(1.5T), 6600(3T) ms; slicethickness=2mm; matrix=128x128; FOV=256x256mm2;b-values=0,1000s/mm2; slices=37(1 .5T), 42(3T); isotro-pic resolution of 2x2x2mm. The images were masked tosegment the left ventricular myocardium (LVM).Explore DTI [2], was used to obtain a tensor map andtrack the fibers using a deterministic algorithm. For thisanalysis, fractional ani sotropy (FA) and the anglebetween the longest eigenvectors (V1) of the twosuccessive voxels were set to 0.2 and 45 degrees respec-tively. The lower limit of the length of the fibers wasvaried from 2mm to 30mm to see the correspondingchange in fiber tracts near the infracted region of theLVM obtained from both 1.5T and 3T scanners.ResultsFig 1 shows the magnitude image displaying the infarctwith thin myocardial wall. Fig 2 displays 3D visualizationof the fiber tracts in the LVM. In Fig 2 the upper rowand the lower row displays data from 3T and 1.5T scan-ners respectively. From left to right the lower limit of thefiber length was varied in the analysis to track the short

Diffusion tensor imaging of formalin fixed infarcted porcine hearts

Background Diffusion is the random motion exhibited by molecules as a result of thermal agitation. In biological tissues the random motion of water molecules is anisotropic since they are restricted by the tissue structure. The application of diffusion tensor imaging (DTI) makes it possible to quantify the amount of diffusion in tissues. Further processing allows a 3D visualization of the fiber architecture by tracking the fiber trajectories within a tissue. Experimental evidence has shown that fiber architecture in the myocardium changes with the onset of myocardial infarction [1]. Furthermore, the myocardium undergoes remodeling as the infarction progresses over time. The aim of this study is to evaluate the remodeling of the fiber architecture in an infarcted porcine heart. Methods