DENSE: displacement encoding with stimulated echoes in cardiac functional MRI

Abstract

Displacement encoding with stimulated echoes (DENSE) was developed for high-resolution myocardial displacement mapping. Pixel phase is modulated by myocardial displacement and data spatial resolution is limited only by pixel size. 2D displacement vector maps were generated for the systolic action in canines with 0.94 x 1.9 mm nominal in-plane resolution and 2.3 mm/pi displacement encoding. A radial strain of 0.208 was measured across the free left ventricular wall over 105 ms during systole. DENSE displacement maps require small first-order gradient moments for encoding. DENSE magnitude images exhibit black-blood contrast which allows for better myocardial definition and reduced motion-related artifacts.

FIG. 1

DENSE pulse sequence. Spin phase wrapping occurs through the application of gradient pulses G₁, G₃, and G₅. The corresponding gradient pulses G₂, G₄, and G₆ totally unwrap the phase for static tissue. Spins that have moved during the TM period will retain phase as described in the text.

FIG. 2

Phase error introduced by poor hardware performance. Since static phantom DENSE data were acquired at isocenter; this residual phase is caused by eddy currents and by the poor high-frequency response of the gradient system rather than Maxwell terms.

FIG. 3

Magnitude short-axis DENSE image. Black-blood contrast is inherent to data acquisition with stimulated echoes at long TM periods.

FIG. 4

(a) Short axis displacement vector map over 105 ms. The marked area of the LV is shown in more detail in (b). (b) Detail from the left ventricular wall. The radial strain along the solid line was 0.208 over the 105-ms encoding period.

FIG. 5

The radial displacement gradient as measured along the solid line in Fig. 4b from endocardium (2.6 mm) to epicardium (10.6 mm).

FIG. 6

Through-plane motion DENSE data. Maximum scale corresponds to 4-mm displacement normal to the slice plane.

FIG. 7

Fast-STEAM magnitude image from the human heart at 1.5 T (phased array cardiac coil, voxel size of 2.5 × 2.5 × 7.0 mm, TM 105 ms, TE 4.5 ms, receiver bandwidth 62.5 kHz, acquisition matrix 128 × 96, flip angle 30°, six soft pulses, acquisition time 8 s).