T2 measurement in articular cartilage: Impact of the fitting method on accuracy and precision at low SNR

T₂ relaxation time is a promising MRI parameter for the detection of cartilage degeneration in osteoarthritis. However, the accuracy and precision of the measured T₂ may be substantially impaired by the low signal‐to‐noise ratio of images available from clinical examinations. The purpose of this work was to assess the accuracy and precision of the traditional fit methods (linear least‐squares regression and nonlinear fit to an exponential) and two new noise‐corrected fit methods: fit to a noise‐corrected exponential and fit of the noise‐corrected squared signal intensity to an exponential. Accuracy and precision have been analyzed in simulations, in phantom measurements, and in seven repetitive acquisitions of the patellar cartilage in six healthy volunteers. Traditional fit methods lead to a poor accuracy for low T₂, with overestimations of the exact T₂ up to 500%. The noise‐corrected fit methods demonstrate a very good accuracy for all T₂ values and signal‐to‐noise ratio. Even more, the fit to a noise‐corrected exponential results in precisions comparable to the best achievable precisions (Cramér‐Rao lower bound). For in vivo images, the traditional fit methods considerably overestimate T₂ near the bone‐cartilage interface. Therefore, using an adequate fit method may substantially improve the sensitivity of T₂ to detect pathology in cartilage and change in T₂ follow‐up examinations. Magn Reson Med, 2010. © 2009 Wiley‐Liss, Inc.