High-Quality 3-Dimensional 1H Magnetic Resonance Spectroscopic Imaging of the Prostate Without Endorectal Receive Coil Using A Semi-LASER Sequence

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Abstract

Objectives

Inclusion of 3-dimensional 1H magnetic resonance spectroscopic imaging (3D-1H-MRSI) in routine multiparametric MRI of the prostate requires good quality spectra and easy interpretable metabolite maps of the whole organ obtained without endorectal coil in clinically feasible acquisition times. We evaluated if a semi-LASER pulse sequence with gradient offset independent adiabaticity refocusing pulses (GOIA-sLASER) for volume selection can meet these requirements.

Materials and Methods

Thirteen patients with suspicion of prostate cancer and 1 patient known to have prostate cancer were examined at 3 T with a multichannel body-receive coil. A 3D-1H-MRSI sequence with GOIA-sLASER volume selection (echo time, 88 milliseconds) was added to a routine clinical multiparametric MRI examination of these patients. Repetition times from 630 to 1000 milliseconds and effective voxel sizes of approximately 0.9 and 0.6 cm3 were tested. Spectral components were quantified by LCModel software for quality assessment and to construct choline and citrate maps.

Results

Three-dimensional MRSI of the prostate was successfully performed in all patients in measurement times of 5 to 10 minutes. Analysis of the multiparametric MRI examination or of biopsies did not reveal malignant tissue in the prostate of the 13 patients. In 1404 evaluated voxels acquired from 13 patients, the citrate resonance could be fitted with a high reliability (Cramér-Rao lower bound <30%), 100% for 7 × 7 × 7-mm3 voxels and 96 ± 7 in 6 × 6 × 6-mm3 voxels. The percentage of 7 × 7 × 7-mm3 voxels in which the choline signal was fitted with Cramér-Rao lower bound of less than 30% was approximately 50% at a TR of 630 milliseconds and increased to more than 80% for TRs of 800 milliseconds and above. In the patient with prostate cancer, choline was detectable throughout the prostate in spectra recorded at a TR of 700 milliseconds. The homogeneous B1- field over the prostate of the receive coil enabled the generation of whole organ metabolite maps, revealing choline and citrate variations between areas with normal prostate tissue, seminal vesicles, proliferative benign prostatic hyperplasia, and tumor.

Conclusions

The good signal-to-noise ratio and low chemical shift artifacts of GOIA-sLASER at an echo time of 88 milliseconds enable acquisition of high-quality 3D-1H-MRSI of the prostate without endorectal coil in less than 10 minutes. This facilitates reconstruction of easy interpretable, quantitative metabolite maps for routine clinical applications of prostate MRSI.

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