High-resolution diffusion tensor mr imaging for the evaluation of myocardial anisotropy and fiber tracking at 3 T: effect of the numbers of diffusion-sensitizing gradient directions

Introduction

Diffusion tensor magnetic resonance imaging (DT-MRI) has provided a means for rapid and noninvasive evaluation of the cardiac geometry and three-dimensional fiber structure. However, most cardiac DT-MRI studies have used low diffusion resolution such as 6 directions in animal's fixed heart. To our knowledge, the effect of the numbers of diffusion-sensitizing gradient directions has not been studied for image quality of cardiac DT-MRI.

Purpose

To evaluate effect of numbers of diffusion-sensitizing gradient direction on image quality for the evaluation of myocardial anisotropy and fiber tracking by using ex vivo diffusion tensor MR imaging (DT-MRI).

Methods

DT-MRI using a SENSE-based echo-planar imaging technique was acquired by using a 3 T MR scanner from ten excised heart. With a b-value of 800 s/mm², the diffusion tensor images were obtained for 6, 15, 32 diffusion-sensitizing gradient directions at the midventricular level. For quantitative analysis, the numbers of tracked fibers, fractional anisotropy (FA), and the length of tracked fibers were measured. For qualitative analysis, two radiologists assessed the image quality of fiber tractography.

Results

By increasing the numbers of diffusion-sensitizing gradient directions from 6 to 15, and 32, FA and standard deviation were significantly reduced (P = 0.001), and the numbers of tracked fibers and the length of tracked fibers were significantly increased (P = 0.001). The image quality of fiber tractography was significantly increased as the increased numbers of diffusion-sensitizing gradient directions (P < 0.001). See Figure 1.

Figure 1

Conclusion

Image quality of ex vivo DT-MRI is significantly improved as the numbers of diffusion-sensitizing gradient directions increased.