Crossed Cerebellar Diaschisis in Alzheimer's Disease.

BACKGROUND: We describe the phenomenon of crossed cerebellar diaschisis (CCD) in four subjects diagnosed with Alzheimer's disease (AD) according to the National Institute on Aging - Alzheimer Association (NIA-AA) criteria, in combination with 18F-FDG PET and 11C-PiB PET imaging. METHODS: 18F-FDG PET showed a pattern of cerebral metabolism with relative decrease most prominent in the frontal-parietal cortex of the left hemisphere and crossed hypometabolism of the right cerebellum. 11C-PiB PET showed symmetrical amyloid accumulation, but a lower relative tracer delivery (a surrogate of relative cerebral blood flow) in the left hemisphere. CCD is the phenomenon of unilateral cerebellar hypometabolism as a remote effect of supratentorial dysfunction of the brain in the contralateral hemisphere. The mechanism implies the involvement of the cortico-ponto-cerebellar fibers. The pathophysiology is thought to have a functional or reversible basis but can also reflect in secondary morphologic change. CCD is a well-recognized phenomenon, since the development of new imaging techniques, although scarcely described in neurodegenerative dementias. RESULTS: To our knowledge this is the first report describing CCD in AD subjects with documentation of both 18F-FDG PET and 11C-PiB PET imaging. CCD in our subjects was explained on a functional basis due to neurodegenerative pathology in the left hemisphere. There was no structural lesion and the symmetric amyloid accumulation did not correspond with the unilateral metabolic impairment. CONCLUSION: This suggests that CCD might be caused by non-amyloid neurodegeneration. The pathophysiological mechanism, clinical relevance and therapeutic implications of CCD and the role of the cerebellum in AD need further investigation.

A way to reduce the radius of rotation in brain SPET with a single-head system.

To optimize spatial resolution in single photon emission tomography (SPET), it is essential to minimize the radius of rotation. In brain studies, different methods have been used to avoid shoulder interference when the radius of rotation is minimized: rectangular fields of view, modifications to the shielding around circular detectors and fan or cone beam collimators. However, few single-head systems can adopt these developments, particularly older cameras. A non-standard image acquisition method to reduce the radius of rotation in brain SPET with a single-head gamma camera is presented. The method applies a defined transformation to the original acquired images, maintaining the whole of the brain inside the field of view without shoulder interference and meeting the condition: pixel size < or = FWHM/3. With this method, it is possible to reduce the radius of rotation to 16 cm and to obtain a transaxial spatial resolution of 15.98 mm, which is 3.5 mm less than with the standard method used in our laboratory. This procedure was implemented for a Siemens Gammasonics ZLC 3700 gamma camera and has been validated in single-slice brain phantom studies. The method has the advantage of not requiring any complex or costly hardware.