Optimisation of T2 and M0 measurements of bi-exponential systems

Cramer-Rao theory and computer simulations were used to show that the errors involved in calculating the magnetization and relaxation parameters of a two-component system decrease with: (1) increasing SNR, (2) increasing number of echoes used in the fitting procedure, and (3) increasing ratio of the relaxation times of the two components, T22/T21. Images of bi-compartmental phantoms of known T2 values were acquired using an optimized imaging sequence, and an optimized fitting algorithm was used to calculate the T2 values of the two components by fitting the resulting images to a bi-exponential decay model. Accuracy better than 6% was achieved in the calculations of the T2 values of the two components, and region fitting provided better accuracy than pixel-by-pixel fitting. The procedures were used to calculate the T2 and M0 values of equine carpal bones with known degree of radiographic bone sclerosis. Although the T2 and M0 values of both water and fat components all decreased with the degree of radiographic bone sclerosis, the transverse relaxation of the water component, T2W, showed a greater decrease with advanced stages of bone sclerosis.