Fast‐spin‐echo imaging of inner fields‐of‐view with 2D‐selective RF excitations

Purpose:

To demonstrate the feasibility of two‐dimensional selective radio frequency (2DRF) excitations for fast‐spin‐echo imaging of inner fields‐of‐view (FOVs) in order to shorten acquisitions times, decrease RF energy deposition, and reduce image blurring.

Materials and Methods:

Fast‐spin‐echo images (in‐plane resolution 1.0 × 1.0 mm² or 0.5 × 1.0 mm²) of inner FOVs (40 mm, 16 mm oversampling) were obtained in phantoms and healthy volunteers on a 3 T whole‐body MR system using blipped‐planar 2DRF excitations.

Results:

Positioning the unwanted side excitations in the blind spot between the image section and the slice stack to measure yields minimum 2DRF pulse durations (about 6 msec) that are compatible with typical echo spacings of fast‐spin‐echo acquisitions. For the inner FOVs, the number of echoes and refocusing RF pulses is considerably reduced which compared to a full FOV (182 mm) reduces the RF energy deposition by about a factor of three and shortens the acquisition time, e.g., from 39 seconds to 12 seconds for a turbo factor of 15 or from 900 msec to 280 msec for a single‐shot acquisition, respectively. Furthermore, image blurring occurring for high turbo factors as in single‐shot acquisitions is considerably reduced yielding effectively higher in‐plane resolutions.

Conclusion:

Inner‐FOV acquisitions using 2DRF excitations may help to shorten acquisitions times, ameliorate image blurring, and reduce specific absorption rate (SAR) limitations of fast‐spin‐echo (FSE) imaging, in particular at higher static magnetic fields. J. Magn. Reson. Imaging 2010;31:1530–1537. © 2010 Wiley‐Liss, Inc.