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 x 0.9 x 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.