Stimulated echo induced misestimates on diffusion tensor indices and its remedy

Abstract

Purpose: To report possible erroneous estimates of diffusion parameters in the twice-refocused spin-echo (TRSE) technique, proposed to eliminate eddy-current-induced geometric distortions in diffusion-weighted echo-planar imaging, when stimulated echo signals are inappropriately included.Materials and Methods: Eleven subjects were included for imaging experiments on two 1.5 Tesla systems using the TRSE sequence. Three versions, two with unbalanced crusher gradients inserted to dephase the stimulated echo from the b ¼ 0 images and one with balanced crusher gradients, were implemented. The apparent diffusion coefficients (ADC) and fractional anisotropy (FA) were derived and compared.Results: The ADCs obtained with unbalanced crusher gradients were closer to values reported in the literature. Stimulated echo led to ADC over-estimations by 34.2%, 50.4%, 54.0%, 51.5%, 24.0%, and 41.9% in the genu of corpus callosum, splenium of corpus callosum, bilateral corona radiata, internal capsule, mediofrontal gyrus, and the cuneus, respectively (P < 0.01), with concomitant reduction in FA in highly anisotropic regions. Over-estimations of diffusion coefficients were found to be roughly equal along all directions.Conclusion: Formation of stimulated echo in the TRSE technique can lead to erroneous estimations of the diffusion parameters, even if no prominent morphological artifacts are seen.

Gradient- and spin-echo (GRASE) MR imaging: a long-existing technology that may find wide applications in modern era

“…Smart reordering of the phase encoding steps allows a separation of phase error and T2 modulation in the k-space (10), hence permitting appropriate manipulation and filtering of the k-space data differently along the two phase-encoding directions to minimize artifacts (30). T2related blurring can be further reduced using variable flip angle for the refocusing pulses (31) in a way to incorporate stimulated echo signals into the echo train (32). Along with the multiple gradient-echoes that effectively increase acquisition efficiency, 3D imaging at reduced scan time with stability approaching that of FSE becomes a possibility at high field strengths.…”

Direct measurement of the signal intensity of diffusion-weighted magnetic resonance imaging for preoperative grading and treatment guidance for brain gliomas

“…Therefore, evaluating the DWI characteristics of gliomas in a larger patient cohort is a clinically demanding task. Considering possible variations of the technical factors, such as the b value for diffusion weighting 11 or eddy-current-related geometric distortions/corrections that might affect the quantification of ADC, 12,13 DWI which is less sensitive to scan settings would be preferential over ADC. In a recent study by El Kady et al, ADC values measured on a routine picture archiving and communicating system (PACS) workstation proved to be as accurate as the values obtained using a dedicated specialized workstation.…”