Brian Raterman

Measuring age-dependent myocardial stiffness across the cardiac cycle using MR elastography: A reproducibility study

To assess reproducibility in measuring left ventricular (LV) myocardial stiffness in volunteers throughout the cardiac cycle using MR elastography (MRE) and to determine its correlation with age.

Quantification of aortic stiffness using MR Elastography and its comparison to MRI-based pulse wave velocity

To determine the correlation in abdominal aortic stiffness obtained using magnetic resonance elastography (MRE) (μMRE) and MRI‐based pulse wave velocity (PWV) shear stiffness (μPWV) estimates in normal volunteers of varying age, and also to determine the correlation between μMRE and μPWV.

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.

Quantification of aortic stiffness using magnetic resonance elastography: Measurement reproducibility, pulse wave velocity comparison, changes over cardiac cycle, and relationship with age.

To assess MR elastography (MRE)‐derived aortic shear stiffness (μMRE) measurements for: 1) reproducibility, 2) comparison to pulse wave velocity, 3) changes over the cardiac cycle, and 4) relationship with age.

Quantification of breast stiffness using MR elastography at 3 Tesla with a soft sternal driver: A reproducibility study

Previous studies of breast MR elastography (MRE) evaluated the technique at magnetic field strengths of 1.5 Tesla (T) with the breast in contact with the driver. The aim of this study is to evaluate breast stiffness measurements and their reproducibility using a soft sternal driver at 3T and compare the results with qualitative measures of breast density.

MR Elastography–derived Stiffness: A Biomarker for Intervertebral Disc Degeneration

Purpose To determine the repeatability of magnetic resonance (MR) elastography-derived shear stiffness measurements of the intervertebral disc (IVD) taken throughout the day and their relationship with IVD degeneration and subject age. Materials and Methods In a cross-sectional study, in vivo lumbar MR elastography was performed once in the morning and once in the afternoon in 47 subjects without current low back pain (IVDs = 230; age range, 20-71 years) after obtaining written consent under approval of the institutional review board. The Pfirrmann degeneration grade and MR elastography-derived shear stiffness of the nucleus pulposus and annulus fibrosus regions of all lumbar IVDs were assessed by means of principal frequency analysis. One-way analysis of variance, paired t tests, concordance and Bland-Altman tests, and Pearson correlations were used to evaluate degeneration, diurnal changes, repeatability, and age effects, respectively. Results There were no significant differences between morning and afternoon shear stiffness across all levels and there was very good technical repeatability between the morning and afternoon imaging results for both nucleus pulposus (R = 0.92) and annulus fibrosus (R = 0.83) regions. There was a significant increase in both nucleus pulposus and annulus fibrosus MR elastography-derived shear stiffness with increasing Pfirrmann degeneration grade (nucleus pulposus grade 1, 12.5 kPa ± 1.3; grade 5, 16.5 kPa ± 2.1; annulus fibrosus grade 1, 90.4 kPa ± 9.3; grade 5, 120.1 kPa ± 15.4), and there were weak correlations between shear stiffness and age across all levels (R ≤ 0.32). Conclusion Our results demonstrate that MR elastography-derived shear stiffness measurements are highly repeatable, weakly correlate with age, and increase with advancing IVD degeneration. These results suggest that MR elastography-derived shear stiffness may provide an objective biomarker of the IVD degeneration process.

Quantification of myocardial stiffness using magnetic resonance elastography in right ventricular hypertrophy: initial feasibility in dogs

INTRODUCTION Myocardial stiffness is an important determinant of cardiac function and is currently invasively and indirectly assessed by catheter angiography. This study aims to demonstrate the feasibility of quantifying right ventricular (RV) stiffness noninvasively using cardiac magnetic resonance elastography (CMRE) in dogs with severe congenital pulmonary valve stenosis (PVS) causing RV hypertrophy, and compare it to remote myocardium in the left ventricle (LV). Additionally, correlations between stiffness and selected pathophysiologic indicators from transthoracic echocardiography (TTE) and cardiac magnetic resonance imaging were explored. METHODS In-vivo CMRE was performed on nine dogs presenting severe congenital PVS using a 1.5T MRI scanner. T1-MOLLI, T2-prepared-bSSFP, gated-cine GRE-MRE and LGE (PSIR) sequences were used to acquire a basal short-axis slice. RV and LV-free-wall (FW) stiffness measurements were compared against each other and also correlated to ventricular mass, RV and LV FW thickness, T1 and T2 relaxation times, and extracellular volume fraction (ECV). Peak transpulmonary pressure gradient and myocardial strain were also acquired on eight dogs by TTE and correlated to RV-FW systolic stiffness. Potential correlations were evaluated by Spearmans rho (rs). RESULTS RV-FW stiffness was found to be significantly higher than the LV-FW stiffness both during end-systole (ES) (p=0.002) and end-diastole (ED) (p=0.029). Significant correlations were observed between RV-FW ES and LV-FW ED stiffness versus ECV (rs=0.75; p-value=0.05). Non-significant moderate correlations were found between LV-FW ES (rs=0.54) and RV-FW ED (rs=0.61) stiffness versus ECV. Furthermore, non-significant correlations were found between RV or LV-FW stiffness and the remaining variables (rs<0.54; p-value>0.05). CONCLUSION This study demonstrates the feasibility of determining RV stiffness. The positive correlations between stiffness and ECV might indicate some interdependence between stiffness and myocardial extracellular matrix alterations. However, further studies are warranted to validate our initial observations.

Magnetic resonance elastography to estimate brain stiffness: Measurement reproducibility and its estimate in pseudotumor cerebri patients

This study determines the reproducibility of magnetic resonance elastography (MRE) derived brain stiffness in normal volunteers and compares it against pseudotumor patients before and after lumbar puncture (LP). MRE was performed on 10 normal volunteers for reproducibility and 14 pseudotumor patients before and after LP. During LP, opening and closing cerebrospinal fluid (CSF) pressures were recorded before and after removal of CSF and correlated to brain stiffness. Stiffness reproducibility was observed (r > 0.78; p < 0.008). Whole brain opening LP stiffness was significantly (p = 0.04) higher than normals, but no significant difference (p = 0.11) in closing LP measurements. No significant correlation was observed between opening and closing pressure and brain stiffness.

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