Results showed that IVIM could be performed in free breathing, with a weighted-averaging procedure, a simultaneous diffusion gradient scheme and only four optimized b-values (0, 10, 80, and 800) reducing scan duration by a factor of nine compared with a nonoptimized protocol. Preliminary results have shown that parameters such as DSlow and DFast based on optimized IVIM protocol can be relevant biomarkers to distinguish between nonadvanced and advanced fibrosis.
Purpose: To combine parallel imaging with 3D single-shot acquisition (echo volumar imaging, EVI) in order to acquire high temporal resolution volumar functional MRI (fMRI) data.
Materials and Methods:An improved EVI sequence was associated with parallel acquisition and field of view reduction in order to acquire a large brain volume in 200 msec. Temporal stability and functional sensitivity were increased through optimization of all imaging parameters and Tikhonov regularization of parallel reconstruction. Two human volunteers were scanned with parallel EVI in a 1.5T whole-body MR system, while submitted to a slow eventrelated auditory paradigm.Results: Thanks to parallel acquisition, the EVI volumes display a low level of geometric distortions and signal losses. After removal of low-frequency drifts and physiological artifacts, activations were detected in the temporal lobes of both volunteers and voxelwise hemodynamic response functions (HRF) could be computed. On these HRF different habituation behaviors in response to sentence repetition could be identified.
Conclusion:This work demonstrates the feasibility of high temporal resolution 3D fMRI with parallel EVI. Combined with advanced estimation tools, this acquisition method should prove useful to measure neural activity timing differences or study the nonlinearities and nonstationarities of the BOLD response. UNTIL NOW, functional MRI (fMRI) data were mostly acquired using echo planar imaging (EPI), allowing the acquisition of multislice brain volumes with a spatial resolution of about 3 mm and a temporal resolution of 1-2 seconds. EPI is thus well suited to the detection of cerebral activations and the mapping of activated areas. Nevertheless, with the development of event-related fMRI (1) and the growing interest in the temporal features of the hemodynamic response function (HRF) (2,3), higher scanning rates are called for by neuroscientists.High temporal resolution fMRI is feasible with echo volumar imaging (EVI), a 3D extension of EPI, in which a 3D Fourier space is encoded in a single-shot acquisition. Some applications of EVI have been reported, especially in fMRI (4 -6). As compared with EPI, EVI presents several advantages for fMRI. First, EVI acquisition offers very short TR, on the order of 200 msec. Second, 3D single-shot acquisition makes slicetiming correction unnecessary and reduces the risk of intravolume motion of the subject. Finally, true 3D acquisition is known to reduce vascular inflow effects (7) that often confuse the interpretation of fMRI results (8).Nevertheless, EVI has seldom been used in fMRI, due to its heavy demand on gradient hardware. Actually, because of hardware limitations the echo train duration (ETD) is high in EVI and the voxel bandwidth along the direction of partition (third encoding direction) is very low. Thus, if high spatial resolution and wide brain coverage are required in an EVI acquisition, susceptibility-induced distortions and signal losses due to T2* relaxation dramatically alter image quality. To overcome ...
SUMMARY:We performed non-contrast-enhanced 3D fast spin-echo T1 imaging with variable flip angles (CUBE T1) at 3T in 11 patients with CAD. CUBE T1 allowed easy diagnosis of CAD, owing to its comprehensive neck coverage, high spatial resolution enabling multiplanar reformations, fat saturation, and BB effect, the latter also allowing lumen patency to be studied. This sequence may replace 2D axial T1WI for the diagnosis of CAD.ABBREVIATIONS: BB ϭ black-blood; CAD ϭ cervical artery dissection; IQR ϭ interquartile range
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