European Journal of Nuclear Medicine

To assess the quantitative accuracy of current MR attenuation correction (AC) methods in neurological PET, in comparison to data derived using CT AC. This retrospective study included 25 patients who were referred for a neurological FDG PET examination and were imaged sequentially by PET/CT and simultaneous PET/MR. Differences between activity concentrations derived using Dixon and ultrashort echo time (UTE) MR-based AC and those derived from CT AC were compared using volume of interest and voxel-based approaches. The same comparisons were also made using PET data represented as SUV ratios (SUVr) using grey matter cerebellum as the reference region. Extensive and statistically significant regional underestimations of activity concentrations were found with both Dixon AC (P < 0.001) and UTE AC (P < 0.001) in all brain regions when compared to CT AC. The greatest differences were found in the cortical grey matter (Dixon AC 21.3 %, UTE AC 15.7 %) and cerebellum (Dixon AC 19.8 %, UTE AC 17.3 %). The underestimation using UTE AC was significantly less than with Dixon AC (P < 0.001) in most regions. Voxel-based comparisons showed that all cortical grey matter and cerebellum uptake was underestimated with Dixon AC compared to CT AC. Using UTE AC the extent and significance of these differences were reduced. Inaccuracies in cerebellar activity concentrations led to a mixture of predominantly cortical underestimation and subcortical overestimation in SUVr PET data for both MR AC methodologies. MR-based AC results in significant underestimation of activity concentrations throughout the brain, which makes the use of SUVr data difficult. These effects limit the quantitative accuracy of neurological PET/MR.

Bone scans and X-rays from 23 subjects with symptomatic Paget's disease were evaluated. One-hundred and twenty-seven sites of Pagetoid involvement were found, of which 120 (94.5%) were recognised on the bone scan as compared to 94 (74%) on X-ray. The anatomical distribution and relationship of lesions on scan and X-ray to the patient's symptoms are also discussed. It is concluded that the bone scan is more sensitive than radiology in detecting Paget's disease and only rarely will a lesion that is seen on X-ray not be visualised by scanning.

MRI using manganese as a trans-synaptic axonal tracing agent can unveil dynamics of axonal transport in living subjects. We use this technology to test the hypotheses if impaired axonal transport is a significant pathophysiological process in aging and early Alzheimer’s disease (AD) and in part accounting for “selective vulnerability” of projection neurons in AD. To allow quantitative assessment of axonal transport in vivo, we developed voxel-based statistical mapping technology as well as a tracer kinetic modeling method based on mass transport for manganese-enhanced MRI to estimate axonal transport rates in aging rats and AD transgenic mice. These techniques demonstrated manganese-enhanced signal changes in axonal projections of the olfactory tract and decreased axonal transport rates in rodent models of aging and AD. Altered axonal transport may be a critical pathophysiological process in aging and AD. Manganese-enhanced MRI provides exciting opportunities for the investigations of altered axonal transport in AD and related disorders.