Improving the clinical efficiency of T2(*) mapping of ligament integrity

Abstract

Current MR methods use T2(*) relaxation time as a surrogate measure of ligament strength. Currently, a multi-echo voxel-wise least squares fit is the gold standard to create T2(*) maps; however, the post-processing is time-intensive and serves as a stopgap for clinical use. The study objective was to determine if an alternative method could improve post-processing time without sacrificing fidelity of T2(*) values for eventual translational use in the clinic. Using a 6 echo FLASH sequence, three different methods were used to determine intact posterior cruciate ligament (PCL) median T2(*) Two of these methods utilized a voxel-wise method to establish T2(*) maps: (1) a current "gold standard" method using a voxel-wise 6 echo least-squares fit (6LS) and (2) a voxel-wise 2 echo point T2(*) determination (2MM). The third method used median ligament signal intensity and a single nonlinear least-squares fit (6LSROI) instead of a voxel-wise basis. The resulting median T2(*) values of the PCL and computational time were compared. The median T2(*) values were 42% higher using the 2MM compared to the 6LS method (p<0.0001). However, a strong correlation was found for the median T2(*) values between the 2MM and 6LS methods (R(2)=0.80). The median T2(*) values were not significantly different between the 6LS and 6LSROI methods (p=0.519). Using the 2MM (which provides a regional map) and the 6LSROI (which efficiently provides the median T2(*) value) methods in tandem would take only minutes of post-processing computational time compared to the 6LS method (~540 min), and hence would facilitate clinical application of T2(*) maps to predict ligament structural properties as a patient outcome measure.

Keywords: MRI; Posterior cruciate ligament; T(2)(⁎) relaxometry.