Quantitative T₂ measurement of a single voxel with arbitrary shape using pinwheel excitation and CPMG acquisition

Objective: The aim of this study is to present a new approach for making quantitative single-voxel T₂ measurements from an arbitrarily shaped region of interest (ROI), where the advantage of the signal-to-noise ratio (SNR) per unit time of the single-voxel approach over conventional imaging approach can be achieved. Materials and methods: Two-dimensional (2D) spatially selective radiofrequency (RF) pulses are proposed in this work for T₂ measurements based on using interleaved spiral trajectories in excitation k-space (pinwheel excitation pulses), combined with a summed Carr-Purcell Meiboom-Gill (CPMG) echo acquisition. The technique is described and compared to standard multi-echo imaging methods, on a two-compartment water phantom and an excised brain tissue. Results: The studies show good agreement between imaging and our method. The measured improvement factors of SNR per unit time of our single-voxel approach over imaging approach are close to the predicted values. Conclusion: Measuring T₂ relaxation times from a selected ROI of arbitrary shape using a single-voxel rather than an imaging approach can increase the SNR per unit time, which is critical for dynamic T₂ or multi-component T₂ measurements.