Super-resolution reconstruction of T2-weighted thick-slice neonatal brain MRI scans.

BACKGROUND AND PURPOSE: Super-resolutionreconstruction (SRR) can be used to reconstruct 3-dimensional (3D) high-resolution (HR) volume from several 2-dimensional (2D) low-resolution (LR) stacks of MRI slices. The purpose is to compare lengthy 2D T2-weighted HR image acquisition of neonatal subjects with 3D SRR from several LR stacks in terms of image quality for clinical and morphometric assessments. METHODS: LR brain images were acquired from neonatal subjects to reconstruct isotropic 3D HR volumes by using SRR algorithm. Quality assessments were done by an experienced pediatric radiologist using scoring criteria adapted to newborn anatomical landmarks. The Wilcoxon signed-rank test was used to compare scoring results between HR and SRR images. For quantitative assessments, morphology-based segmentation was performed on both HR and SRR images and Dice coefficients between the results were computed. Additionally, simple linear regression was performed to compare the tissue volumes. RESULTS: No statistical difference was found between HR and SRR structural scores using Wilcoxon signed-rank test (p = .63, Z = .48). Regarding segmentation results, R2 values for the volumes of gray matter, white matter, cerebrospinal fluid, basal ganglia, cerebellum, and total brain volume including brain stem ranged between .95 and .99. Dice coefficients between the segmented regions from HR and SRR ranged between .83 ± .04 and .96 ± .01. CONCLUSION: Qualitative and quantitative assessments showed that 3D SRR of several LR images produces images that are of comparable quality to standard 2D HR image acquisition for healthy neonatal imaging without loss of anatomical details with similar edge definition allowing the detection of fine anatomical structures and permitting comparable morphometric measurement.

Micron-sized PFOB liquid core droplets stabilized with tailored-made perfluorinated surfactants as a new class of endovascular sono-sensitizers for focused ultrasound thermotherapy.

The purpose of this study was to develop micron-sized droplet emulsions able to increase the heat deposition of high intensity focused ultrasound (HIFU), aiming to accelerate the tumour ablation in highly perfused organs with reduced side effects. The investigated droplets consisted of a perfluorooctyl bromide (PFOB) core coated with a biocompatible fluorinated surfactant called F-TAC. The novelty of this work relies on the use, for this application, of a high boiling point perfluorocarbon core (142 °C), combined with an in-house fluorinated surfactant to formulate the emulsion, yielding quasi-reversible strong interactions between the HIFU beam and the droplets. In order to fine-tune the emulsion size, surfactants with different hydrophobic/hydrophilic ratios were screened. Different concentrations of PFOB droplets were homogeneously embedded in two different MRI compatible materials, exhibiting either ultrasound (US) absorbing or non-absorbing properties. For the US absorbing TMM, the speed of sound at each droplet concentration was also assessed. These TMM were sonicated by 1 MHz HIFU with acoustical power of 94 W at two different duty cycles. The temperature elevation was monitored accurately by MRI proton shift resonance frequency in near real-time. The presence of sono-sensitive droplets induced a significant increase of the HIFU thermal effect that persisted under repeated sonication of the same locus. Optimal enhancement was observed at the lowest concentration tested (0.1%) with an additional temperature rise at the focal point of approximately 4 °C per applied kJ of acoustic energy corresponding to one order of magnitude augmentation of the thermal dose. Furthermore, no deformation of the heating pattern pre- or post-focal was observed.