Elasticity-based determination of isovolumetric phases in the human heart

Abstract

Background/MotivationTo directly determine isovolumetric cardiac time intervals by magnetic resonance elastography (MRE) using the magnitude of the complex signal for deducing morphological information combined with the phase of the complex signal for tension-relaxation measurements.MethodsThirty-five healthy volunteers and 11 patients with relaxation abnormalities were subjected to transthoracic wave stimulation using vibrations of approximately 25 Hz. A k-space-segmented, ECG-gated gradient-recalled echo steady-state sequence with a 500-Hz bipolar motion-encoding gradient was used for acquiring a series of 360 complex images of a short-axis view of the heart at a frame rate of less than 5.2 ms. Magnitude images were employed for measuring the cross-sectional area of the left ventricle, while phase images were used for analyzing the amplitudes of the externally induced waves. The delay between the decrease in amplitude and onset of ventricular contraction was determined in all subjects and assigned to the time of isovolumetric tension. Conversely, the delay between the increase in wave amplitude and ventricular dilatation was used for measuring the time of isovolumetric elasticity relaxation.ResultsWave amplitudes decreased during systole and increased during diastole. The variation in wave amplitude occurred ahead of morphological changes. In healthy volunteers the time of isovolumetric elasticity relaxation was 75 ± 31 ms, which is significantly shorter than the time of isovolumetric tension of 136 ± 36 ms (P < 0.01). In patients with relaxation abnormalities (mild diastolic dysfunction, n = 11) isovolumetric elasticity relaxation was significantly prolonged, with 133 ± 57 ms (P < 0.01), whereas isovolumetric tension time was in the range of healthy controls (161 ± 45 ms; P = 0.053).ConclusionThe complex MRE signal conveys complementary information on cardiac morphology and elasticity, which can be combined for directly measuring isovolumetric tension and elasticity relaxation in the human heart.

A Comparison of Acoustic Radiation Force-Derived Indices of Cardiac Function in the Langendorff Perfused Rabbit Heart

“…In 11 patients with diastolic dysfunction, the relaxation time constant was found to be 134 ms, significantly longer than in healthy subjects. Although the MR elastography based method of calculating the relaxation time constant was different from the method used in our study, these results demonstrate that elastography techniques can be used to measure the relaxation time constant for diastolic dysfunction assessment of the heart [27], [28]. …”

Viscoelastic Properties of Normal and Infarcted Myocardium Measured by a Multifrequency Shear Wave Method: Comparison with Pressure-Segment Length Method

“…Non-invasive measurements of myocardial elasticity (viscoelasticity) using transthoracic ultrasound and magnetic resonance imaging (Elgeti et al 2010; Muthupillai et al 1995; Rump et al 2007; Vappou 2012) are now under development and will facilitate clinical implementation. Recent results in seven healthy volunteers indicate that shear wave measurements in the heart using transthoracic ultrasound imaging are possible (Song et al 2013).…”

In vivo, high‐frequency three‐dimensional cardiac MR elastography: Feasibility in normal volunteers

“…As a result, to date, only a limited number of publications have reported on cardiac elastography in human subjects (7,10,14–17). Song et al (10), using ultrasound elastography, reported shear wave speeds in seven healthy human volunteers to be 1.5660.36m/s in end diastole.…”

“…Elgeti et al attempted cardiac MR elastography (MRE), but did not acquire 3D displacement fields nor did they attempt to quantitate myocardial stiffness. Instead they used a low driving frequency of 24.13 Hz to reduce the effects of shear wave attenuation and used shear wave amplitudes as a surrogate for myocardial stiffness (7,14). Kolipaka et al (17) compared 18 normal volunteers with two obstructive hypertrophic cardiomyopathy (HOCM) patients using a vibration frequency of 80 Hz and using 2D inversions on two single slices.…”