Hybrid PET/MRI imaging in healthy unsedated newborn infants with quantitative rCBF measurements using ¹⁵O-water PET

In this study, a new hybrid PET/MRI method for quantitative regional cerebral blood flow (rCBF) measurements in healthy newborn infants was assessed and the low values of rCBF in white matter previously obtained by arterial spin labeling (ASL) were tested. Four healthy full-term newborn subjects were scanned in a PET/MRI scanner during natural sleep after median intravenous injection of 14 MBq15O-water. Regional CBF was quantified using a one-tissue-compartment model employing an image-derived input function (IDIF) from the left ventricle. PET rCBF showed the highest values in the thalami, mesencephalon and brain stem and the lowest in cortex and unmyelinated white matter. The average global CBF was 17.8 ml/100 g/min. The average frontal and occipital unmyelinated white matter CBF was 10.3 ml/100 g/min and average thalamic CBF 31.3 ml/100 g/min. The average white matter/thalamic ratio CBF was 0.36, significantly higher than previous ASL data. The rCBF ASL measurements were all unsuccessful primarily owing to subject movement. In this study, we demonstrated for the first time, a minimally invasive PET/MRI method using low activity15O-water PET for quantitative rCBF assessment in unsedated healthy newborn infants and found a white/grey matter CBF ratio similar to that of the adult human brain.</jats:p

Comparison of prospective and retrospective motion correction in 3D-encoded neuroanatomical MRI

PURPOSE: To compare prospective motion correction (PMC) and retrospective motion correction (RMC) in Cartesian 3D-encoded MPRAGE scans and to investigate the effects of correction frequency and parallel imaging on the performance of RMC. METHODS: Head motion was estimated using a markerless tracking system and sent to a modified MPRAGE sequence which can continuously update the imaging FOV to perform PMC. The prospective correction was applied either before each echo-train (Before-ET) or at every sixth readout within the echo-train (Within-ET). RMC was achieved by adjusting k-space trajectories according to the measured motion during image reconstruction. The motion correction frequency was retrospectively decreased or increased through RMC or reverse RMC. Phantom and in vivo experiments were used to compare PMC and RMC, and to compare Within-ET and Before-ET correction frequency during continuous motion. The correction quality was quantitatively evaluated using the structural similarity index measure using a reference image without motion correction and without intentional motion. RESULTS: PMC resulted in superior image quality compared to RMC both visually and quantitatively. Increasing the correction frequency from Before-ET to Within-ET reduced motion artifacts in RMC. A hybrid PMC and RMC correction, i.e. retrospectively increasing the correction frequency of Before-ET PMC to Within-ET also reduced motion artifacts. Inferior performance of RMC compared to PMC was shown with GRAPPA calibration data without intentional motion, and without any GRAPPA acceleration. CONCLUSION: Reductions in local Nyquist violations with PMC resulted in superior image quality compared to RMC. Increasing the motion correction frequency to Within-ET reduced motion artifacts in both RMC and PMC