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 × 1.9 mm nominal in-plane resolution and 2.3 mm/π 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.
An interleaved gradient-echo echo-planar imaging (IGEPI) sequence was modified for and applied to dynamic contrast-enhanced imaging of the heart. Using IGEPI, images with 3.0 x 3.9 mm nominal in-plane resolution are acquired in 100 ms, enabling eight slices per heartbeat for a heart rate of 60 beats/min. The acquisition speed and use of saturation prepulses allows acquisition of short- and long-axis images during the same contrast bolus. IGEPI maintains the acquisition characteristics required for performing a quantitative first-pass perfusion analysis as well as providing improved coverage compared with conventional fast gradient echo.
A multi-echo imaging sequence suitable for high-resolution and accurate in vivo transverse relaxation time (T2) mapping has been implemented. The sequence was tested on phantoms and was used to measure T2 values in vivo in the rat brain, muscle, and fat at 7 T. Brain T2 maps are shown and regional variations in brain T2 are reported (41.8 ms in cortex, 47.9 ms in hippocampus). Results are compared to literature values obtained at lower field in vivo as well as high-field T2 measurements on excised rat tissues. The reported T2 values are generally smaller compared to lower-field-strength literature values. A discussion of the possible causes of these field effects on T2 is included (dipolar interaction, fast chemical exchange, and diffusion in susceptibility gradients).
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