Accelerated 3D T 2 mapping with dictionary‐based matching for prostate imaging

Purpose To develop a fast and accurate method for 3D T 2 mapping of prostate cancer using undersampled acquisition and dictionary‐based fitting. Methods 3D high‐resolution T 2 ‐weighted images (0.9 × 0.9 × 3 mm 3 ) were obtained with a multishot T 2 ‐prepared balanced steady‐state free precession (T 2 ‐prep‐bSSFP) acquisition sequence using a 3D variable density undersampled Cartesian trajectory. Each T 2 ‐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 T 2 ‐weighted images to retrieve quantitative T 2 values, which were then compared to gold‐standard spin echo acquisition values using monoexponential fitting. The proposed approach was validated in simulations and a T 1 /T 2 phantom, and feasibility was tested in 8 healthy subjects. Results The simulation analysis showed that the proposed T 2 mapping approach is robust to noise and typically observed T 1 variations. T 2 values obtained in the phantom with T 2 prep‐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). T 2 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 T 2 mapping of the whole prostate can be achieved in 3 minutes.