A phantom for the testing and calibration of near infra-red spectrometers

This note describes a simple phantom which can be used to check the long term stability and accuracy of relative attenuation measurements made by near infra-red (NIR) spectrometers. The phantom has been calibrated, and the results of the calibration are shown to agree with theoretical predictions of the relative attenuation.     

Longitudinal study of cerebral blood flow SPECT in Parkinson's disease with dementia, and dementia with Lewy bodies

BACKGROUND: People with Parkinson's disease (PD) have an increased risk of developing dementia (PDD), which often has clinical features similar to dementia with Lewy bodies (DLB). Whilst perfusion studies have shown parieto-occipital hypoperfusion in DLB and PDD relative to controls, there have not been any longitudinal studies of perfusion changes in PDD and DLB. METHODS: In this study, we measured brain perfusion using Tc99m HMPAO SPECT over one year in 17 PDD, 18 DLB and 34 healthy subjects. We used SPM99 to compare perfusion changes in the two dementia groups against the control group. RESULTS: We did not see any reductions in perfusion in either of the dementia groups. However, in the DLB, but not PDD group, there was a significant increase in putamen perfusion relative to controls over the year. In both DLB and PDD groups, there was a correlation between striatal perfusion increase over the year, and worsening of parkinsonism. Perfusion changes were not secondary to changes in antiparkinsonian medication. CONCLUSION: The increase in striatal perfusion may be a compensatory change related to decreasing striatal dopaminergic input from the substantia nigra in PDD and DLB, consistent with the increased predominance of rigidity over tremor symptoms in these groups compared with non-demented PD.     

Longitudinal change in 99mTcHMPAO cerebral perfusion SPECT in Parkinson's disease over one year

BACKGROUND: Brain perfusion deficits have been reported previously in subjects with Parkinson's disease in comparison with healthy controls. OBJECTIVE: To carry out a longitudinal study of perfusion in patients with Parkinson's disease and controls to find areas showing a reduction in perfusion over one year. METHODS: Two HMPAO cerebral perfusion scans were acquired one year apart in 30 subjects with Parkinson's disease (mean (SD) age, 76 (5) years) and 34 healthy comparison subjects (76 (7) years). Scans were normalised to the mean intensity in the cerebellum. RESULTS: Using SPM99 within groups to investigate regions that showed a decrease in perfusion between scans, it was found that in Parkinson's disease subjects but not controls there was a significant cluster in the frontal lobe (Brodmann area 10) where perfusion decreased over the year. CONCLUSIONS: The progressive frontal perfusion deficits in Parkinson's disease are consistent with results from previous structural and neuropsychological studies suggesting frontal lobe involvement and executive dysfunction even in early Parkinson's disease.     

A volumetric study of MRI signal hyperintensities in late-life depression.

OBJECTIVE: An increase in white-matter lesions has been previously described in older subjects with depression. The authors investigated whether the regional location varied between depressed and normal subjects and determined the relationship of magnetic resonance (MR) signal hyperintensities to known clinical risk factors for vascular disease. METHODS: Authors used automated image-processing software to determine volumes of signal hyperintensities from MR brain scans of older people with depression (N=29; mean age: 76 years) and normal subjects of similar age (N=32). RESULTS: Overall, subjects with depression had a significantly greater frontal-lobe white-matter lesion volume than normal subjects (0.35% versus 0.22%). However, after excluding subjects with hypertension, diabetes, or ischemic heart disease (leaving 14 depressed and 15 normal subjects), we found even greater differences between groups, with a larger volume of MR signal hyperintensities in the frontal region of the depressed group, but no difference in the basal ganglia or parietal and occipital lobes. CONCLUSION: The results support the "vascular depression" hypothesis and suggest that those with depression but without traditional vascular risk factors may be much more susceptible to cerebrovascular disease than normal subjects. The mechanisms for this increased susceptibility remain to be determined.     

Magnetic resonance imaging: A biomarker for cognitive impairment in Parkinson's disease?

Dementia is a frequent and disabling complication of Parkinson's disease (PD). Clinicians and researchers lack a biomarker capable of tracking the structural and functional changes that underlie the evolution of cognitive dysfunction in PD. Magnetic resonance imaging (MRI) has been adopted as a biomarker in natural history and interventional studies of Alzheimer's disease (AD) and amnestic mild cognitive impairment (MCI), but its utility as a biomarker for PD and Parkinson's disease dementia (PDD) is unclear. In this review, the authors summarize the studies that have used MRI to investigate cognitive decline in PD, outline limitations of those studies, and suggest directions for future research. PD dementia is associated with extensive cortical atrophy, which may be quantified with structural MRI. More promisingly, patterns of atrophy may be present in those who have PD with MCI (PD‐MCI). Subcortical white matter tract degeneration is detectable early in the disease with diffusion tensor imaging and may precede changes observed on conventional structural MRI. Although less well studied, other MR techniques, such as functional MRI, MR perfusion imaging with arterial spin labeling, and MR spectroscopy, have demonstrated differences in activation and metabolism between PD and PDD. In this review, the ability to compare studies was limited by the heterogeneity of study populations, cognitive testing methods, and imaging protocols. Future work should adopt agreed scan protocols, should be adequately powered, and should use carefully phenotyped patients to fully maximize the contribution of MRI as a biomarker for PDD. © 2013 Movement Disorder Society     

Regional cerebral blood flow in Parkinson's disease with and without dementia

Tc99 HMPAO SPECT and T1 weighted 3D MRI scans were acquired in cognitively intact subjects with Parkinson's disease (PD) (n = 31), and in PD subjects with dementia (PDD) (n = 34), healthy controls (n = 37), those with Alzheimer's disease (AD) (n = 32), and those with dementia with Lewy bodies (DLB) (n = 15). We used SPM99 to look for regions which showed a reduction in perfusion on SPECT not related to associated structural brain changes assessed by a MRI scan. The precuneus and inferior lateral parietal regions showed a perfusion deficit in Parkinson's disease with dementia, similar to the pattern observed in DLB. In comparison, AD showed a perfusion deficit in the midline parietal region, in a more anterior and inferior location than in PDD, involving the posterior cingulate as well as the precuneus. The perfusion deficits in PDD are similar those in DLB, and in a location associated with visual processing, and may be associated with the visuospatial perception deficits which are present in persons with DLB and PDD.