Abstract
Purpose of studyTo compare magnetic resonance elastography (MRE) with ventricular pressure changes in an animal model.MethodsThree pigs of different cardiac physiology (weight, 25 to 53 kg; heart rate, 61 to 93 bpm; left ventricular [LV] end-diastolic volume, 35 to 70 ml) were subjected to invasive LV pressure measurement by catheter and noninvasive cardiac MRE. Cardiac MRE was performed in a short-axis view of the heart and applying a 48.3-Hz shear-wave stimulus. Relative changes in LV-shear wave amplitudes during the cardiac cycle were analyzed. Correlation coefficients between wave amplitudes and LV pressure as well as between wave amplitudes and LV diameter were determined.ResultsA relationship between MRE and LV pressure was observed in all three animals (R2 ≥ 0.76). No correlation was observed between MRE and LV diameter (R2 ≤ 0.15). Instead, shear wave amplitudes decreased 102 ± 58 ms earlier than LV diameters at systole and amplitudes increased 175 ± 40 ms before LV dilatation at diastole. Amplitude ratios between diastole and systole ranged from 2.0 to 2.8, corresponding to LV pressure differences of 60 to 73 mmHg.ConclusionExternally induced shear waves provide information reflecting intraventricular pressure changes which, if substantiated in further experiments, has potential to make cardiac MRE a unique noninvasive imaging modality for measuring pressure-volume function of the heart.
Highlights
Today several cardiac imaging modalities are available that provide excellent information on cardiac morphology and tissue structure with high temporal resolution [14]
While this correlation confirmed the validity of the assumptions made for wave amplitude variation (WAV)-magnetic resonance elastography (MRE) [9] in principle, MRE was not correlated with left ventricular (LV) pressure because invasive examination of pressure-time function is precluded in healthy volunteers
It is clearly visible that U(t) alternates in synchrony with the pressure inside the left ventricle, confirming the validity of the correlation of LV pressure and MRE-WAV effect proposed in [10]
Summary
Today several cardiac imaging modalities are available that provide excellent information on cardiac morphology and tissue structure with high temporal resolution [14] As these modalities cannot measure forces, insight into myocardial physiology, initiation of contraction and relaxation, is limited. Cardiac magnetic resonance elastography (MRE) [8] was introduced as a noninvasive means for detecting relative changes in myocardial elasticity during the cardiac cycle [9-11]. This method employs low-frequency shear waves induced in the heart by an external harmonic vibrator and measures the wave amplitude variation (WAV). While this correlation confirmed the validity of the assumptions made for WAV-MRE [9] in principle, MRE was not correlated with LV pressure because invasive examination of pressure-time function is precluded in healthy volunteers
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