MR high-resolution imaging of arterial intimal hyperplasia at 1.5 T

A novel method for simultaneous 3D B1 and T1 mapping: the method of slopes (MoS)

“…The NLLS algorithm further improves this B 1 map. However, the T 1 values derived from a simple ratio of slopes (initial estimates) are very sensitive to low SNR due to the non-linear relationship between the slope values and resulting T 1 , given by Equation [5] (Fig. 6b).…”

“…The accuracy of the proposed method depends on the accuracy of the straight line approximations. Figure 1 suggests that Equation [5] may be a good approximation for straight line fits over a range of flip angle values near 0˚and a null . Although high flip angle data must be sampled in a region near a null , this value is not known a priori and furthermore, a null is expected to vary spatially due to significant B 1 variations.…”

“…The proposed method, herein called MoS (Method of Slopes), aims to provide simultaneous B 1 and T 1 maps as follows: (i) the signal vs nominal flip angle curve is sampled at high flip angles and a straight line is fit to the data to extrapolate to the signal null point (when a = 180˚), yielding the B 1 map (ii) this straight line also yields the slope value: SI΄ null , (iii) a straight line is then approximated between the low flip angle data and the origin yielding an estimate for SI΄ 0, and (iv) the ratio of these slopes is used to calculate the T 1 map according to Equation [5] where T 1 = ÀTR/ln(E 1 ).…”

“…Spatial quantification of the longitudinal relaxation time, T 1 mapping, is of great interest for many clinical MR applications because T 1 is known to be an important marker of varying pathological conditions such as cancer , multiple sclerosis and arteriosclerosis . There is a high demand for efficient and accurate T 1 mapping methods that can be implemented at high spatial resolution, over large volumes of interest in a clinically reasonable time (scan time < 20 min).…”