T2 quantification from only proton density and T2-weighted MRI by modelling actual refocusing angles

Proton density and transverse relaxation (T2)-weighted fast spin echo images are frequently acquired. T2 quantification is commonly performed by applying an exponential fit to these two images, despite recent evidence that an exponential fit is insufficient to correctly quantify T2 in the presence of imperfect RF refocusing due to standard 2D slice selection or use of reduced refocusing angles. Here we examine the feasibility of accurate two echo fitting using standard proton density and T2-weighted images by utilizing Bloch equation simulations and prior knowledge of refocusing angles. This method is demonstrated in simulation, phantom, and human brain experiments, in comparison to the exponential approach, and to a 32 echo multiple-echo spin echo approach. Comparison to single spin echo is also performed in phantom experiments. The two echo method, which compensates for indirect and stimulated echoes, enables accurate quantitative T2 over a wide range of flip angle and T2 values using standard MRI methods, provided there is adequate SNR and flip angle knowledge. Observed T2 decay is non-exponential due to contamination by indirect and stimulated echoes. Fitting true spin response allows for accurate T2 quantification using only PD and T2-weighted FSE images. [Display omitted] •Two point T2 fitting with proton density and T2-weighting was studied.•Slice profiles and refocusing flip angles can make T2 decay non-exponential.•Bloch simulations modelled signal decay, using known flip angles.•This modelling approach enabled accurate T2 quantification.