Quantification of 3D regional myocardial wall thickening from gated magnetic resonance images

Abstract

Purpose: To develop 3D quantitative measures of regional myocardial wall motion and thickening using cardiac magnetic resonance imaging (MRI) and to validate them by comparison to standard visual scoring assessment.

Materials and methods: In all, 53 consecutive subjects with short-axis slices and mid-ventricular 2-chamber/4-chamber views were analyzed. After correction for breath-hold-related misregistration, 3D myocardial boundaries were fitted to images and edited by an imaging cardiologist. Myocardial thickness was quantified at end-diastole and end-systole by computing the 3D distances using Laplace's equation. 3D thickening was represented using the standard 17-segment polar coordinates. 3D thickening was compared with 3D wall motion and with expert visual scores (6-point visual scoring of wall motion and wall thickening; 0 = normal; 5 = greatest abnormality) assigned by imaging cardiologists.

Results: Correlation between ejection fraction and thickening measurements was (r = 0.84; P < 0.001) compared to correlation between ejection fraction and motion measurements (r = 0.86; P < 0.001). Good negative correlation between summed visual scores and global wall thickening and motion measurements were also obtained (r(thick) = -0.79; r(motion) = -0.74). Additionally, overall good correlation between individual segmental visual scores with thickening/wall motion (r(thick) = -0.69; r(motion) = -0.65) was observed (P < 0.0001).

Conclusion: 3D quantitative regional thickening and wall motion measures obtained from MRI correlate strongly with expert clinical scoring.

Figure 1

(a) Short axis MRI scan with superimposed epicardial (outer) and endocardial (inner) boundaries. (b) 3D surface created generated from the contours and superimposed on the short axis slice.

Figure 2

Definition of thickness between surfaces S and S′. (a) Perpendicular projection from A to C, and B to A. (b) Minimum distance from A to B. (c) Thickness defined using Laplace’s equation (thickness lines) from A to B and C to D.

Figure 3

MRI scans and polar maps corresponding to a subject with summed visual score of 0. Short-axis MRI slices taken at ED at approximately the (a) basal-region, (b) mid-region, and (c) apical-region. The slices taken at ES corresponding to (d) basal, (e) mid and (f) apical-regions. The clinical scores on the 17-segment polar map (g), a grey-scale polar map of motion (h), and a thickening polar map (i) are also shown.

Figure 4

MRI scans and polar maps corresponding to a subject with summed visual score of 36. Short-axis MRI slices taken at ED, at approximately the (a) basal-region, (b) mid-region and (c) apical-region. The slices taken at ES corresponding to (d) basal, (e) mid and (f) apical-regions. The clinical scores on the 17 segment polar map (g), a grey-scale polar map of motion (h), and a thickening polar map (i) are also shown. The average thickening and wall motion of this subject was 25% and 6mm respectively.

Figure 5

Global and segmental analysis of wall thickening and motion. Global correlation of (a) average wall thickening and (b) average wall motion with EF. Segmental analysis of wall thickening (c) and motion (d) with visual clinical scores (all p<0.0001).

Figure 6

Summed visual clinical scores versus average quantitative (a) wall thickening and (b) motion in the 53 subjects studied.

Figure 7

Segmental average (±standard deviation) of (a) thickening in % and (b) motion in mm of normal subjects. (c) contains 90^th percentile of thickening in % for normal subjects. (d) contains 90^th percentile of motion in mm for normal subjects.