Accelerated 3D T₂ mapping with dictionary-based matching for prostate imaging

To develop a fast and accurate method for 3D T₂ mapping of prostate cancer using undersampled acquisition and dictionary-based fitting.

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.

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 T₂ 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). 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.

3D quantitative T₂ mapping of the whole prostate can be achieved in 3 minutes.