Regional assessment of LV wall in infarcted heart using tagged MRI and cardiac modelling

Abstract

A segmental two-parameter empirical deformable model is proposed for evaluating regional motion abnormality of the left ventricle. Short-axis tagged MRI scans were acquired from 10 healthy subjects and 10 postinfarct patients. Two motion parameters, contraction and rotation, were quantified for each cardiac segment by fitting the proposed model using a non-rigid registration algorithm. The accuracy in motion estimation was compared to a global model approach. Motion parameters extracted from patients were correlated to infarct transmurality assessed with delayed-contrast-enhanced MRI. The proposed segmental model allows markedly improved accuracy in regional motion analysis as compared to the global model for both subject groups (1.22-1.40 mm versus 2.31-2.55 mm error). By end-systole, all healthy segments experienced radial displacement by ~25-35% of the epicardial radius, whereas the 3 short-axis planes rotated differently (basal: 3.3°; mid: -1° and apical: -4.6°) to create a twisting motion. While systolic contraction showed clear correspondence to infarct transmurality, rotation was nonspecific to either infarct location or transmurality but could indicate the presence of functional abnormality. Regional contraction and rotation derived using this model could potentially aid in the assessment of severity of regional dysfunction of infarcted myocardium.

Assessment of infarct-specific cardiac motion dysfunction using modeling and multimodal magnetic resonance merging

“…c) shows a full thickness infarct within that myocardial region. When using the published model, the dyskinetic septal region showed erroneous tag matching and low coefficient value (Fig. d,e).…”

“…The ability to accurately assess the extent and severity of motion impairment as a result of different levels of structural damage caused by an infarct could significantly impact patient management towards improving short‐ and long‐term prognosis . In our previous work, the fixed‐sector segmental TPEDM was found to be inadequate in describing the wall motion of sectors containing a mixture of normal and infarcted myocardium. To accurately evaluate the contribution of an infarct on regional wall motion abnormality, we proposed the use of the infarct‐specific TPEDM.…”

“…For each predefined sector of LV, two interdependent regional motion parameters, α (contraction) and β (rotation), were tracked over the entire systolic cardiac phase by fitting of the segmental TPEDM model using nonrigid registration algorithm. Detailed formulation and implementation of the TPEDM was described in previous work …”

“…The search range for α was –8 to 25 mm, whereas that for β norm was –12‐12°. These ranges were selected empirically based on the observations of the minimum and maximum for both types of motion in our data, as well as the values reported in the literature …”

“…In addition, the fixed‐sector TPEDM has yet to account for dyskinetic motion, which involves stretching and out‐bulging of the infarcted region during systole, leading to a decrease in stroke volume (SV) . This paradoxical outward systolic motion is often associated with myocardial thinning due to muscle necrosis .…”