Rofo 2008; 180 - A18
DOI: 10.1055/s-2008-1052579

Ultra high spectral and spatial resolution of proton MR spectroscopic imaging of the prostate at 7T

DWJ Klomp 1, AK Bitz 2, A Heerschap 1, TWJ Scheenen 1
  • 1Radboud University Nijmegen, Medical Centre, Radiology, the Netherlands
  • 2Erwin L. Hahn Institute for Magnetic Resonance Imaging, Essen, Germany

Purpose: Proton MR spectroscopic imaging (MRSI) of the prostate has been proven to help in the detection of prostate cancer. At 1.5T however, the sensitivity of this method is often insufficient to detect small cancer foci, and moreover, the low spectral resolution causes overlap of signals from choline, creatine and polyamines, hampering accurate assessments. By moving to 7T with its potentially increased spectral and spatial resolution, MRSI of the prostate is expected to improve the sensitivity in tumour detection and localization.

Materials and methods: To work around some of the challenges of MRSI of the prostate at 7T, we constructed an endorectal coil to be positioned close to the prostate via the rectum. Use of a small RF coil for transmit and receive in combination with adiabatic RF pulses allowed high bandwidth excitation and refocusing pulses to be obtained at relatively low RF power.

Theoretical RF power deposition was validated with an optical thermometer positioned at the hottest RF spot (Fig.4). A 3D MRSI semi-LASER sequence with combined water and lipid suppression was used with an optimized timing for full absorptive citrate signal shapes (Fig 3), and tested in a phantom.

Results: We present the first results ever of MRSI of the prostate at 7T in vivo (Fig.1,2).

Conclusion: We demonstrate that excellent spectra could be obtained in a healthy volunteer at a nominal spatial resolution of only (3mm)3, showing well-separated signals for choline, polyamines, creatine and citrate.

Fig 1. MRSI of the prostate at 7T (nominal voxel size=(3mm)3, Tacq=8.5min. TR=2s, TE=56ms).

Fig 2. MR spectrum from MRSI at 7T of the prostate at high SNR (voxel size=(4mm)3, Tacq=15min. TR=2s, TE=56ms).

Fig 3. RF pulse sequence with optimized timing for prostate MRSI at 7T (semi LASER with MEGA water and lipid supp.)

Fig 4. Proofs for remaining within SAR guidelines; left: MR thermometry to locate RF hot-spot (in gel-phantom); right: fiber-optic temp. measurements in vivo at RF hot-spot (1W)

We present the first results ever of MRSI of the prostate at 7T in vivo (Fig.1,2). We demonstrate that excellent spectra could be obtained in a healthy volunteer at a nominal spatial resolution of only (3mm)3, showing well-separated signals for choline, polyamines, creatine and citrate.