Locus Coeruleus magnetic resonance imaging: a comparison between native-space and template-space approach.

Locus Coeruleus (LC) is the main noradrenergic nucleus of the brain, which is involved in many physiological functions including cognition; its impairment may be crucial in the neurobiology of a variety of brain diseases. Locus Coeruleus-Magnetic Resonance Imaging (LC-MRI) allows to identify in vivo LC in humans. Thus, a variety of research teams have been using LC-MRI to estimate LC integrity in normal aging and in patients affected by neurodegenerative disorders, where LC integrity my work as a biomarker. A number of variations between LC-MRI studies exist, concerning post-acquisition analysis and whether this had been performed within MRI native space or in ad hoc-built MRI template space. Moreover, the reproducibility and reliability of this tool is still to be explored. Therefore, in the present study, we analyzed a group of neurologically healthy, cognitively intact elderly subjects, using both a native space- and a template space-based LC-MRI analysis. We found a good inter-method agreement, particularly considering the LC Contrast Ratio. The template space-based approach provided a higher spatial resolution, lower operator-dependency, and allowed the analysis of LC topography. Our ad hoc-developed LC template showed LC morphological data that were in line with templates published very recently. Remarkably, present data significantly overlapped with a recently published LC "metaMask", that had been obtained by averaging the results of a variety of previous LC-MRI studies. Thus, such a template space-based approach may pave the way to a standardized LC-MRI analysis and to be used in future clinic-anatomical correlations.

Brain white matter involvement in hereditary spastic paraplegias: analysis with multiple diffusion tensor indices.

BACKGROUND AND PURPOSE: The hereditary spastic paraplegias are a group of genetically heterogeneous neurodegenerative disorders, characterized by progressive spasticity and weakness of the lower limbs. Although conventional brain MR imaging findings are normal in patients with pure hereditary spastic paraplegia, microstructural alteration in the cerebral WM can be revealed with DTI. Concomitant investigation of multiple intrinsic diffusivities may shed light on the neurobiologic substrate of the WM degeneration pattern in patients with pure hereditary spastic paraplegia across the whole brain. MATERIALS AND METHODS: Tract-based spatial statistics analysis was performed to compare fractional anisotropy and mean, axial, and radial diffusivities of the WM skeleton in a group of 12 patients with pure hereditary spastic paraplegia and 12 healthy volunteers. Data were analyzed counting age and sex as nuisance covariates. The threshold-free cluster-enhancement option was applied, and the family-wise error rate was controlled by using permutation tests for nonparametric statistics. RESULTS: In pure hereditary spastic paraplegia, group widespread fractional anisotropy decreases and radial diffusivity and mean diffusivity increases (P < .05, corrected) were found. No voxelwise difference was observed for the axial diffusivity map. Percentage of voxels within the WM skeleton that passed the significance threshold were 51%, 41.6%, and 11.9%, respectively, for radial diffusivity, fractional anisotropy, and mean diffusivity clusters. An anteroposterior pattern with preferential decrease of fractional anisotropy in the frontal circuitry was detected. CONCLUSIONS: In patients with pure hereditary spastic paraplegia, alterations in multiple DTI indices were found. Radial diffusivity seems more sensitive to hereditary spastic paraplegia-related WM pathology and, in line with the lack of axial diffusivity changes, might indicate a widespread loss of myelin integrity. A decrease of fractional anisotropy alone in the frontal circuitry may reflect subtle disruption of the frontal connections.

Diffusion tensor MRI and MR spectroscopy in long lasting upper motor neuron involvement in amyotrophic lateral sclerosis.

Upper motor neuron (UMN) dysfunction in Amyotrophic Lateral Sclerosis (ALS) is not easy to identify clinically: Diffusion Tensor Imaging (DTI) and single-voxel Magnetic Resonance Spectroscopy (H-MRS) can identify markers of UMN involvement. The aim of this study was to correlate brain DTI and MRS data with clinical parameters in ALS patients (PALS). We studied 32 PALS using Magnetic Resonance Imaging. The subjects were subdivided into definite/probable (D/P) and possible/suspected (P/S). DTI indices included Fractional Anisotropy (FA) and averaged Apparent Diffusion Coefficient (avADC). Anatomical areas were sampled by positioning regions of interest along corticospinal tracts, from the precentral cortex to the bulb. H-MRS voxels were localized bilaterally in precentral regions. D/P-PALS showed significantly lower FA values than healthy controls in almost all regions, whereas P/S-PALS FA values were significantly lower only in the left precentral gray matter (GM), right precentral white matter (WM), cerebral peduncles (CP), left hemipons, and left bulbar pyramid (BP). Significantly higher avADC values were observed in the D/P-PALS right precentral GM, precentral WM, right semioval center-posterior limb of the internal capsule (SC-PLIC), and left CP; and in the precentral WM, right SC-PLIC, left CP, and right hemipons of P/S-PALS. With increasing disability, only D/P-PALS showed significantly reduced FA values in the left precentral WM and hemipons, and increased avADC values in the precentral WM. Significantly lower N-acetylaspartate (NAA)/creatine-phosphocreatine complex (Cr) and higher choline (Cho)/Cr and myoinositol (mI)/Cr ratios were found in D/P-PALS, while only higher Cho/Cr and mI/Cr ratios were found in P/S-PALS. Our data highlight the usefulness of DTI and H-MRS in assessing UMN involvement. Given FA sensitivity and specificity, despite the small number of PALS, our findings support its use as a diagnostic marker in D/P-PALS.

In vivo thermoluminescence dosimetry for total body irradiation.

An improvement in the clinical results obtained using total body irradiation (TBI) with photon beams requires precise TBI treatment planning, reproducible irradiation, precise in vivo dosimetry, accurate documentation and careful evaluation. In vivo dosimetry using LiF Harshaw TLD-100 chips was used during the TBI treatments performed in our department. The results of in vivo thermoluminescence dosimetry (TLD) show that using TLD measurements and interactive adjustment of some treatment parameters based on these measurements, like monitor unit calculations, lung shielding thickness and patient positioning, it is possible to achieve high precision in absorbed dose delivery (less than 0.5%) as well as in homogeneity of irradiation (less than 6%).