An algorithm for correcting the distortions that occur in diffusion-weighted echo-planar images due to the strong diffusion-sensitizing gradients is presented. The dominant distortions may be considered to be only changes of scale coupled with a shear and linear translation in the phase-encoding direction. It is then possible to correct for them by using an algorithm in which each line of the image in the phase-encoding direction is considered in turn, with only one parameter (the scale) to be found by searching.

No abstract

Purpose:To test the feasibility of pediatric perfusion imaging using a pulsed arterial spin labeling (ASL) technique at 1.5 T.Materials and Methods: ASL perfusion imaging was carried out on seven neurologically normal children and five healthy adults. The signal-to-noise ratio (SNR) of the perfusion images along with T1, M 0 , arterial transit time, and the temporal fluctuation of the ASL image series were measured and compared between the two age groups. In addition, ASL perfusion magnetic resonance (MR) was performed on three children with neurologic disorder. Results:In the cohort of neurologically normal children, a 70% increase in the SNR of the ASL perfusion images and a 30% increase in the absolute cerebral blood flow compared to the adult data were observed. The measures of ASL SNR, T1, and M 0 were found to decrease linearly with age. Transit time and temporal fluctuation of the ASL perfusion image series were not significantly different between the two age groups. The feasibility of ASL in the diagnosis of pediatric neurologic disease was also illustrated. Conclusion:ASL is a promising tool for pediatric perfusion imaging given the unique and reciprocal benefits in terms of safety and image quality .

No abstract