5 TECHNICAL EFFICACY: Stage 5 J. Magn. Reson. Imaging 2018;48:13-26.

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Purpose To develop a fast and accurate method for 3D T2 mapping of prostate cancer using undersampled acquisition and dictionary‐based fitting. Methods 3D high‐resolution T2‐weighted images (0.9 × 0.9 × 3 mm3) were obtained with a multishot T2‐prepared balanced steady‐state free precession (T2‐prep‐bSSFP) acquisition sequence using a 3D variable density undersampled Cartesian trajectory. Each T2‐weighted image was reconstructed using total variation regularized sensitivity encoding. A flexible simulation framework based on extended phase graphs generated a dictionary of magnetization signals, which was customized to the proposed sequence. The dictionary was matched to the acquired T2‐weighted images to retrieve quantitative T2 values, which were then compared to gold‐standard spin echo acquisition values using monoexponential fitting. The proposed approach was validated in simulations and a T1/T2 phantom, and feasibility was tested in 8 healthy subjects. Results The simulation analysis showed that the proposed T2 mapping approach is robust to noise and typically observed T1 variations. T2 values obtained in the phantom with T2prep‐bSSFP and the acquisition‐specific, dictionary‐based matching were highly correlated with the gold‐standard spin echo method (r = 0.99). Furthermore, no differences were observed with the accelerated acquisition compared to the fully sampled acquisition (r = 0.99). T2 values obtained in prostate peripheral zone, central gland, and muscle in healthy subjects (age, 26 ± 6 years) were 97 ± 14, 76 ± 7, and 36 ± 3 ms, respectively. Conclusion 3D quantitative T2 mapping of the whole prostate can be achieved in 3 minutes.

Purpose To achieve 3D T 2 w imaging of the prostate with 1‐mm isotropic resolution in less than 3 min. Methods We devised and implemented a 3D T 2 ‐prepared multishot balanced steady state free precession (T 2 prep‐bSSFP) acquisition sequence with a variable density undersampled trajectory combined with a total variation regularized iterative SENSE (TV‐SENSE) reconstruction. Prospectively undersampled images of the prostate (acceleration factor R = 3) were acquired in 11 healthy subjects in an institutional review board‐approved study. Image quality metrics (subjective signal‐to‐noise ratio, contrast, sharpness, and overall prostate image quality) were evaluated by 2 radiologists. Scores of the proposed accelerated sequence were compared using the Wilcoxon signed‐rank and Kruskal‐Wallis non‐parametric tests to prostate images acquired using a fully sampled 3D T 2 prep‐bSSFP acquisition, and with clinical standard 2D and 3D turbo spin echo (TSE) T 2 w acquisitions. A P ‐value < 0.05 was considered significant. Results The 3× accelerated 3D T 2 prep‐bSSFP images required a scan time (min:s) of 2:45, while the fully sampled 3D T 2 prep‐bSSFP and clinical standard 3D TSE images were acquired in 8:23 and 7:29, respectively. Image quality scores (contrast, sharpness, and overall prostate image quality) of the accelerated 3D T 2 prep‐bSSFP, fully sampled T 2 prep‐bSSFP, and clinical standard 3D TSE acquisitions along all 3 spatial dimensions were not significantly different ( P > 0.05). Conclusion 3D T 2 w images of the prostate with 1‐mm isotropic resolution can be acquired in less than 3 min, with image quality that is comparable to a clinical standard 3D TSE sequence but only takes a third of the acquisition time.

Quantification of regional cerebral metabolic rate of glucose (rCMRglu) via positron emission tomography (PET) imaging requires measuring the arterial input function (AIF) via invasive arterial blood sampling. In this study we describe a non-invasive approach, the non-invasive simultaneous estimation (nSIME), for the estimation of rCMRglu that considers a pharmacokinetic input function model and constraints derived from machine learning applied to a fusion of individual medical health records and dynamic [(18)F]-FDG-PET brain images data. The results obtained with our data indicate potential for future clinical application of nSIME, with correlation measures of 0.87 for rCMRglu compared to quantification with full arterial blood sampling.

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