Oral Abstract Session
SCMR 22nd Annual Scientific Sessions
Jordi Martorell, PhD
Head of the Vascular Engineering and Applied Medicine Group
Department of Chemical Engineering and Material Sciences, IQS School of Engineering, Universitat Ramon Llull, Barcelona, Spain
Myocardial stiffness (MS) is widely acknowledged in playing an important role in abnormal left ventricular relaxation and the ever increasingly recognised diagnosis of diastolic heart failure or heart failure with preserved ejection fraction (HfpEF), however it is difficult to measure in-vivo. The recognised gold standard method of measuring MS is during cardiac catheterisation, which is invasive and carries associated risk of complications. Tissue stiffness values, via shear wave analysis, evaluated by magnetic resonance elastography (MRE) have been clinically validated and are in common clinical practise within other areas of MR imaging. Transferring MRE to cardiac MRI could provide an non-invasive solution to the assessment of MS but has thus far been challenging due to cardiac intrinsic motion and complex 3D geometry.
Transient magnetic resonance elastography imaging (tMRE) was performed using a Philips Achieva 3T MR system. The flexural component of a shear wave generated by aortic valve closure was visualised by a 2D pencil beam navigator positioned transverse to the left ventricular septum at two separate locations; basal and apical. At each location, 60 consecutive R-R intervals were acquired divided into 4 breath-holds averaging 15 seconds, maintaining a temporal resolution of 0.33ms. A resulting 1D phase magnitude image is generated once post-processed (see Image 1) and the shear wave visualised as a change in phase, which can be seen as a change in contrast in the phase image (see Image 2). Shear wave speed was calculated using a time-of-flight approach by determining the time difference between waves and distance between the basal and apical navigators. Conversion of measured shear wave speed (c) to estimated myocardial stiffness (shear modulus µ) assumed a lossless material with density equal to water (ρ), i.e. µ=ρc2.
Nine healthy volunteers and two patients with pathology associated with diastolic dysfunction were scanned implementing the tMRE technique. We observed increased myocardial stiffness values in the patient group compared to healthy volunteers as exhibited in Image 3 (flexural shear wave speed 4.43 ± 1.16 m/s in volunteers and 11.18 ± 1.10 m/s in patients; stiffness 20.8 ± 9.5 kPa and 122.4 ± 20.15 kPa respectively).
We have developed a non-invasive and patient friendly tMRE technique to quantify myocardial stiffness. Increased left ventricular shear wave speeds indicate increased myocardial stiffness.