Vectors through a cross-sectional image (VCI): A visualization method for four-dimensional motion analysis for cardiac computed tomography

Abstract

Background: Cardiac computed tomography (CT) has the potential for fully four-dimensional (4D for 3D plus time) motion analysis of the heart. We aimed at developing a method for assessment and presentation of the 4D motion for multi-phase, contrast-enhanced cardiac CT data sets and demonstrating its clinical applicability.

Methods: Four patients with normal cardiac function, old myocardial infarction (OMI), takotsubo cardiomyopathy, and hypertrophic cardiomyopathy (HCM) underwent contrast-enhanced cardiac CT for one heartbeat using a 320-row CT scanner with no tube current modulation. CT images for 10 cardiac phases (with a 10%-increment of the R-R interval) were reconstructed with the isotropic effective resolution of (0.5 mm)³ An image-based motion-estimation (iME) algorithm, developed previously, has been used to estimate a time series of 3D cardiac motion, from the end-systole to the other nine phases. The iME uses down-sampled images with a resolution of (1.0 mm)³ deforms the end-systole images non-rigidly to match images at other phases. Once the agreement is maximized, iME outputs a 3D motion vector defined for each voxel for each phase, that smoothly changes over voxels and phases. The proposed visualization method, which is called "vectors through a cross-sectional image (VCI)," presents 3D vectors from the end-diastole to the end-systole as arrows with an end-diastole CT slice. We performed visual assessment of the VCI with calculated the mean vector lengths to evaluate regional left ventricular (LV) contraction.

Results: The VCI images showed the magnitude and direction of systolic 3D vectors, including the through-plane motion, and successfully visualized the relations of LV wall segments and abnormal regional wall motion. Decreased regional motion and asymmetric motion due to hypokinetic infarct segment, takotsubo cardiomyopathy, and hyper trophic cardiomyopathy was clearly observed. It was easy to appreciate the relation of the abnormal regional wall motion to the affected LV wall segments. The mean vector lengths of the affected segments with pathologies were clearly smaller than the other unaffected segments (1.2-1.7 mm versus 2.5-4.7 mm).

Conclusions: VCI images could capture the magnitude and direction of through-plane motion and show the relations of LV wall segments and abnormal wall motion.

Keywords: Cardiac computed tomography; Cardiac wall motion; Cardiomyopathy; Image-based motion estimation; Myocardial infarction.

Fig. 1

A 61-year-old male with no coronary artery disease and normal cardiac function on echocardiography. Motion vectors (pink arrows) are shown every eight pixels in each direction. The vector length indicates the length of pixel movement from end-diastole to end-systole. The units of the labels were pixels, and 1 pixel was 0.39 mm in the x and y axes; the unit of the label was millimeters in the z-axis. The relatively symmetric LV contraction is demonstrated by the VCI image. The mean vector lengths were 4.5 mm at the septal wall, 3.7 mm at the inferior wall, 3.4 mm at the lateral wall, and 3.1 mm at the anterior wall.

Fig. 2

A 65-year-old male with an old myocardial infarction involving the left circumflex artery. The perfusion defect in the apical lateral wall was severe, as shown on nuclear myocardial perfusion imaging (A, arrow). Cardiac CT at end-diastole (0% phase of the R-R interval) revealed myocardial fat deposition after LV myocardial infarction in the apical lateral wall (B, arrow). The VCI image shows that the wall motion of the apical lateral wall was hypokinetic (C, asterisk). The mean vector lengths were 2.5 mm at the septal wall, 4.7 at the inferior wall, 1.2 mm at the lateral wall (infarcted segment), and 3.9 mm at the anterior wall.

Fig. 3

A-79-year-old female with takotsubo cardiomyopathy and hypokinesis of the apex on echocardiography. A: A horizontal long-axis image at the end-diastole (0% phase of the R-R interval). There was no obstructive coronary artery disease. B, C: The VCI images show LV systolic dysfunction with hypokinesis of the apex. We detected weak wall motion in the opposite direction in the apex compared with normal wall motion in the mid-ventricle (C, arrowhead). The mean vector lengths were 1.3 mm at the apex and 4.3 mm at the base.

Fig. 3

A-79-year-old female with takotsubo cardiomyopathy and hypokinesis of the apex on echocardiography. A: A horizontal long-axis image at the end-diastole (0% phase of the R-R interval). There was no obstructive coronary artery disease. B, C: The VCI images show LV systolic dysfunction with hypokinesis of the apex. We detected weak wall motion in the opposite direction in the apex compared with normal wall motion in the mid-ventricle (C, arrowhead). The mean vector lengths were 1.3 mm at the apex and 4.3 mm at the base.

Fig. 4

A 54-year-old male with hypertrophic cardiomyopathy. A: LV asymmetric septal hypertrophy (asterisk). B: The VCI image shows asymmetric LV wall motion. The mean vector lengths were 1.4 mm at the septal wall, 3.3 mm at the inferior wall, 3.4 mm at the lateral wall, and 1.7 mm at the anterior wall.