Proton MR spectroscopic imaging ( 1 H-MRSI) of the human prostate, which has an interesting clinical potential, may be improved by increasing the magnetic field strength from 1.5T to 3T. Both theoretical and practical considerations are necessary to optimize the pulse timing for spectroscopic imaging of the human prostate at 3T. For in vivo detection of the strongly coupled spin system of citrate, not only should the spectral shape of the signal be easy to identify, but the timing used should produce MR signals at reasonably short echo times (TEs). In this study the spectral shape of the methylene protons of citrate was simulated with density matrix calculations and checked with phantom measurements. Different calculated optimal spectral shapes were measured in patients with prostate cancer with a 2D spectroscopic imaging sequence. T 1 and T 2 relaxation times were calculated for citrate and choline, the two major metabolites of interest in the prostate. We conclude that the optimum timing for in vivo point-resolved spectroscopy (PRESS) imaging at 3T is an interpulse timing sequence of 90°-25 ms -180°-37. Key words: citrate; choline; relaxation times; AB spin system; density matrix; computer simulations Whole-body scanners with a magnetic field strength of 3T are becoming more and more available to the scientific and clinical communities. With the construction of appropriate radiofrequency (RF) coils for different parts of the body, it becomes possible for researchers and clinicians to make full use of the increased sensitivity of a field strength of 3T compared to 1.5T. We have been using an endorectal coil for 3T to explore the possibilities of proton ( 1 H) MRI and MR spectroscopic imaging (MRSI) of the prostate at this field strength (1). In the continuing search for a noninvasive imaging technique that can reliably differentiate prostate cancer from benign prostatic hyperplasia and healthy tissue, 1 H-MRSI has been shown to have great potential (2-4). In fact, prostate cancer tissue is characterized by reduced levels of citrate and increased levels of choline (5,6), which are both detectable in vivo with 1 H-MRSI.The spin-spin coupling constant J and the chemical shift difference ␦ of the four methylene protons of citrate are of the same order of magnitude at 1.5 and at 3T, which means that the corresponding 1 H-spectral shape of these protons at these field strengths is an AB-type multiplet. The exact shape of this multiplet, centered at 2.60 ppm, depends not only on J and ␦, but also on the type and timing of the RF pulses of the MR pulse sequence used. An optimal shape of the citrate AB spin system at echo time (TE) in a pointresolved spectroscopy (PRESS) (7) pulse sequence (90 x -1 -180 y -2 -180 z -( 2 -1 ) echo) was previously reported for 1.5T (8): with 1 ϭ 11 ms and 2 ϭ 60 ms (TE ϭ 2 ϫ 2 ϭ 120 ms), the outer lines of the multiplet almost completely disappear, whereas the inner lines of the multiplet have maximum absorptive intensity in the in-phase spectrum.In addition to the spectral shape of citra...

2 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2018;48:359-368.

The aim of the study was to determine the quantitative T2 values in prostate tissue and evaluate them for detection and grading of prostate cancer. Materials and Methods: After approval from the local ethics committee, morphological T2-weighted (T2w) images, apparent diffusion coefficient (ADC) maps from diffusion-weighted images, quantitative T2 maps, and calculated T2w images from 75 men (median age, 66.3 years; median PSA, 8.2 ng/mL) were acquired at 3 T magnetic resonance imaging (MRI). Data were retrospectively evaluated for their distinction between prostate pathologies.Eight hundred fifty-seven areas of normal gland (n = 378), prostate cancer (54x Gleason score 6, 98x Gleason score 7, 25x Gleason score 8), benign prostatic hyperplasia (BPH) nodes (n = 150), prostatitis (n = 119), and precancerous lesions (n = 33) were determined on calculated and morphological T2w images. Histological criterion standards were whole gland sections (16 patients), MRI-guided in-bore biopsies (32 patients), MRI/transrectal ultrasound-fusion biopsies (15 patients), and systematic 12-core transrectal ultrasound-guided biopsies (12 patients). Significance was assumed to be P < 0.05. Results:The quantitative T2 values vary significantly between prostate cancer and normal gland tissue (area under the curve [AUC], 0.871), cancer and BPH nodes (AUC = 0.827), and Gleason score 6 and 7 or higher (AUC, 0.742). The quantitative T2 values decrease with increasing Gleason scores and correlate significantly with the ADC values (r = 0.806).The detection accuracy of prostate cancer on calculated (AUC = 0.682) and morphological T2w images (AUC = 0.658) is not significantly different. Conclusions: Quantitative T2 values seem to be suitable for distinguishing between prostate cancer and normal gland tissue or BPH nodes. Similar to the ADC values, they offer an indication of the aggressiveness of the prostate cancer.

A total of 70% of voxels in noncancer tissue and 90% of voxels in cancer tissue passed the quality check of the automatically fitted spectra. The median CC/C was significantly different between any noncancer and cancer tissue (P < 0.0001), but not between the different contributing centers. CC/C increased with cancer focus size (P =0.0008) and certainty of voxel mapping to histopathologic cancer site (P 0.0001). The area under the receiver operating characteristic curve for discriminating voxels of cancer tissue from noncancer tissue was 0.88 (confidence interval: 0.84-0.92) in the PZ and 0.76 (confidence interval: 0.71- 0.81) in the CG.