Showing papers by "Enrico De Vita published in 2014"

Evaluation of segmented 3D acquisition schemes for whole-brain high-resolution arterial spin labeling at 3 T.

Abstract: Recent technical developments have significantly increased the SNR of arterial spin labeled (ASL) perfusion MRI. Despite this, typical ASL acquisitions still employ large voxel sizes. The purpose of this work was to implement and evaluate two ASL sequences optimized for whole-brain high-resolution perfusion imaging, combining pseudo-continuous ASL (pCASL), background suppression (BS) and 3D segmented readouts, with different in-plane k-space trajectories. Identical labeling and BS pulses were implemented for both sequences. Two segmented 3D readout schemes with different in-plane trajectories were compared: Cartesian (3D GRASE), and spiral (3D RARE Stack-Of-Spirals). High-resolution perfusion images (2×2×4 mm3) were acquired in fifteen young healthy volunteers with the two ASL sequences at 3T. The quality of the perfusion maps was evaluated in terms of SNR and gray-to-white matter contrast. Point-spread-function simulations were carried out to assess the impact of readout differences on the effective resolution. The combination of pCASL, in-plane segmented 3D readouts and BS provided high-SNR high-resolution ASL perfusion images of the whole brain. Although both sequences produced excellent image quality, the 3D RARE Stack-Of-Spirals readout yielded higher temporal and spatial SNR than 3D GRASE (Spatial SNR = 8.5 ± 2.8 and 3.7 ± 1.4; Temporal SNR = 27.4 ± 12.5 and 15.6 ± 7.6, respectively) and decreased through-plane blurring due to its inherent oversampling of the central k-space region, its reduced effective TE and shorter total readout time, at the expense of a slight increase in the effective in-plane voxel size.

Multi-modal Measurement of the Myelin-to-Axon Diameter g-ratio in Preterm-born Neonates and Adult Controls

Abstract: Infants born prematurely are at increased risk of adverse functional outcome. The measurement of white matter tissue composition and structure can help predict functional performance and this motivates the search for new multi-modal imaging biomarkers. In this work we develop a novel combined biomarker from diffusion MRI and multi-component T2 relaxation measurements in a group of infants born very preterm and scanned between 30 and 40 weeks equivalent gestational age. We also investigate this biomarker on a group of seven adult controls, using a multi-modal joint model-fitting strategy. The proposed emergent biomarker is tentatively related to axonal energetic efficiency (in terms of axonal membrane charge storage) and conduction velocity and is thus linked to the tissue electrical properties, giving it a good theoretical justification as a predictive measurement of functional outcome.

Single Voxel MR Spectroscopy in the Spinal Cord: Technical Challenges and Clinical Applications

Abstract: MR spectroscopy is an extremely valuable tool for assessing tissue biochemistry in vivo. Its use in the spinal cord presents several technical challenges due to geometrical, anatomical, and physiological constraints that have restricted its clinical application. With references to the limited literature available, issues relating to coil selection, patient immobilization, sequence choice, and placement of voxels of interest for single-voxel MRS studies in the spinal cord are discussed here. The importance of a reliable shimming routine is underlined, as well as cardiac gating. The selection of acquisition parameters is examined and postprocessing techniques are reviewed. Methods providing a quantitative estimation of metabolite concentrations are presented and potential pitfalls in interpretation discussed. Finally, suggestions are given to implement a robust protocol for single-voxel MRS in the cervical spinal cord.