Multipathway multi-echo (MPME) imaging: all main MR parameters mapped based on a single 3D scan

Quantitative parameter maps, as opposed to qualitative grayscale images, may represent the future of diagnostic MRI. A new quantitative MRI method is introduced here that requires a single 3D acquisition, allowing good spatial coverage to be achieved in relatively short scan times.

A multipathway multi-echo sequence was developed, and at least 3 pathways with 2 TEs were needed to generate T₁ , T₂ , T₂^* , B₁⁺ , and B₀ maps. The method required the central k-space region to be sampled twice, with the same sequence but with 2 very different nominal flip angle settings. Consequently, scan time was only slightly longer than that of a single scan. The multipathway multi-echo data were reconstructed into parameter maps, for phantom as well as brain acquisitions, in 5 healthy volunteers at 3 T. Spatial resolution, matrix size, and FOV were 1.2 × 1.0 × 1.2 mm³ , 160 × 192 × 160, and 19.2 × 19.2 × 19.2 cm³ (whole brain), acquired in 11.5 minutes with minimal acceleration. Validation was performed against T₁ , T₂ , and T₂^* maps calculated from gradient-echo and spin-echo data.

In Bland-Altman plots, bias and limits of agreement for T₁ and T₂ results in vivo and in phantom were -2.9/±125.5 ms (T₁ in vivo), -4.8/±20.8 ms (T₂ in vivo), -1.5/±18.1 ms (T₁ in phantom), and -5.3/±7.4 ms (T₂ in phantom), for regions of interest including given brain structures or phantom compartments. Due to relatively high noise levels, the current implementation of the approach may prove more useful for region of interest-based as opposed to pixel-based interpretation.

We proposed a novel approach to quantitatively map MR parameters based on a multipathway multi-echo acquisition.