Optimized RF excitation for anatomical brain imaging of the occipital lobe using the 3D MDEFT sequence and a surface transmit coil

Wellcome Department of Imaging Neuroscience, Institute of Neurology, London, UK.
Magnetic Resonance in Medicine (Impact Factor: 3.57). 05/2005; 53(5):1212-6. DOI: 10.1002/mrm.20421
Source: PubMed


An RF excitation scheme is presented for anatomical imaging of occipital brain areas at 3T using the 3D modified driven equilibrium Fourier transform (MDEFT) sequence and a transmit-receive surface coil. Surface coils operated in the transmit mode usually display a high B(1) inhomogeneity. This causes variations of the flip angle and impairs fat saturation, resulting in blurring, signal losses, and artifacts due to high scalp intensities. A composite binomial pulse with one spectral component for water selective excitation and one spatial component for B(1) inhomogeneity compensation is presented. It is shown experimentally that the pulse prevents image blurring and reduces the scalp signal considerably. The total pulse duration of only 2.4 ms is compatible with the relatively short repetition times (TRs) required for MDEFT imaging. The method is particularly useful for certain applications in neuroimaging that require technical equipment that is too large for standard coils or should not be exposed to RF fields.

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    • "Data were acquired at the Berlin NeuroImaging Center (Germany) on a 1.5-T MR scanner equipped with a circular-polarized head coil (Siemens Sonata, Erlangen, Germany) with an T2*-weighted single-shot gradient echo planar imaging sequence: 35 slices (interleaved), 3 mm isotropic resolution, 64 × 64 matrix, FOV = 192 mm, TE = 40 ms, TR = 2.00 s, flip angle = 90°, 1640 AC-PC oriented images for each run. Before functional runs, 176 anatomical T1-weighted slices were acquired (spatial resolution 1 mm × 1 mm × 1 mm, TR = 12.24 ms, TE = 3.56 ms, flip angle = 23°, 256 × 224 matrix; Deichmann, 2005). A vacuum head cushion was used to immobilize the participants’ heads and necks in order to reduce movement artifacts. "
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    • "Stimuli were generated using Presentation (Neurobehavioral Systems) and were projected by means of a mirror system attached to the head coil. Anatomical high-resolution T1-weighted scans (spatial resolution 1 × 1 × 1 mm, TR = 12.24 ms, TE= 3.56 ms, flip angle= 23°, 256 × 224 matrix) (Deichmann, 2005) were acquired during the training session of the MID task. "
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