No abstract

Treatment-refractory fever during the first 10 days after subarachnoid hemorrhage (SAH) is predicted by poor clinical grade and intraventricular hemorrhage, and is associated with increased mortality and more functional disability and cognitive impairment among survivors. Clinical trials are needed to evaluate the impact of prophylactic fever control on outcome after SAH.

Neuromelanin-sensitive MRI can consistently delineate SNpc and LC.

We characterize the contrast behavior of substantia nigra (SN) in both magnetization transfer (MT) imaging, which is believed to be sensitive to neuromelanin (NM), and susceptibility weighted imaging (SWI). Images were acquired with a MT prepared dual echo gradient echo sequence. The first echo was taken as the MT contrast image and the second was used to generate the SWI image. SN volumes were segmented from these two types of images using a thresholding method. The spatial and signal characteristics of the extracted SWI and MT volumes were compared. Both images showed the presence of SN but the volumes of the SN identified in the two are spatially incongruent. The MT volume was more caudal than the SWI volume and with only a 12% overlap between the two volumes. Considering the SN volumes in each hemisphere separately, the average distances between the centers of mass of the volumes from the two types images are 5.1±1.1 mm and 4.1±1.2 mm, respectively. The frequency offsets (homodyne filtered phase/echo time) for the volumes derived from MT (NM) images and SWI images are 0.09±0.32 radians/s and -1.12±0.57 radians/s (p<0.0001), respectively. The MT contrasts for the two volumes are 0.16±0.02 and 0.10±0.03 (p<0.001), respectively. Our results indicate that the two contrasts are sensitive to different portions of the SN, with MT seeing the more caudal portion of the SN than SWI, likely due to variations of NM and iron content in the SN. Despite the small overlap, these regions are complementary. Our results provide a new understanding of the contrast behavior of the SN in the two imaging approaches commonly used to image it and indicate that using both may yield a more comprehensive visualization of the SN.

Objective To analyze diffusion tensor imaging (DTI) data in the substantia nigra (SN) using a more consistent region of interest defined by neuromelanin-sensitive MRI in order to assess Parkinson's disease (PD) related changes in diffusion characteristics in the SN. Methods T1-weighted and DTI data were obtained in a cohort of 37 subjects (20 control subjects and 17 subjects with PD). The subjects in the PD group were clinically diagnosed PD patients with an average Unified Parkinsonian Disease Rating Scale (UPDRS)-III score of 23.2±9.3. DTI data were analyzed using SN ROIs defined by neuromelanin-sensitive MRI and, for comparison, with ROIs defined on T2-weighted images (b=0 images). Results Compared to control subjects, significantly lower fractional anisotropy was observed in PD in the neuromelanin SN ROI but not in the ROI derived from the T2-weighted image. This decrease was largest in the rostral and lateral portions of the neuromelanin volume, which were found to have more hypointensity in the T2-weighted image and, presumably, higher iron content in the PD group. In addition, a larger decrease in fractional anisotropy was seen in the SN region of interest on the side contralateral to the side exhibiting more severe symptoms. These results indicate that the use of neuromelanin sensitive MRI to define the ROI in the SN for analyzing DTI data leads to more significant results, enhancing the robustness of DTI study and DTI based biomarkers of PD.

T2*-weighted hypointense signal in the SNpc defined by neuromelanin-sensitive MRI is significantly increased in PD. It is most likely a measure sensitive to PD-related iron deposition and may serve as a robust biomarker of PD. © 2016 International Parkinson and Movement Disorder Society.

Objective To use a novel region of interest to measure neuromelanin-sensitive MRI contrast changes in the lateral-ventral tier of substantia nigra pars compacta in Parkinson’s disease (PD). Background Histopathological studies of PD have demonstrated both massive loss of melanized dopamine neurons and iron accumulation in the substantia nigra pars compacta. Neurodegeneration is most profound in the lateral-ventral tier of this structure. We have previously shown in both healthy controls and individuals with PD that neuromelanin-sensitive MRI and iron-sensitive MRI contrast regions in substantia nigra overlap. This overlap region is located in the lateral-ventral tier. Experimental Design Exploiting this area of contrast overlap for region of interest selection, we developed a semi-automated image processing approach to characterize the lateral-ventral tier in MRI data. Here we apply this approach to measure magnetization transfer contrast, which corresponds to local neuromelanin density, in both the lateral-ventral tier and the entire pars compacta in 22 PD patients and 19 controls. Results Significant contrast reductions were seen in PD in both the entire pars compacta (p = 0.009) and in its lateral-ventral tier (p = 0.0002); in PD contrast was significantly lower in the lateral-ventral tier than in the entire pars compacta (p = 0.0008). Conclusion These findings are the first in vivo evidence of the selective vulnerability of this nigral subregion in PD, and this approach may be developed for high impact biomarker applications.

A B S T R AC TBackground: Previous studies investigating nigral iron accumulation used T 2 or T 2 *-weighted contrasts to define the regions of interest (ROIs) in the substantia nigra with mixed results. Because these contrasts are not sensitive to neuromelanin, ROIs may have inadvertently missed the SNpc. An approach sensitive to neuromelanin should yield consistent results. We examine iron deposition in ROIs derived from neuromelaninsensitive and T 2 *-weighted contrasts, respectively. Methods: T 1 -weighted and multiecho gradient echo imaging data were obtained in 2 cohorts. Multiecho gradient echo imaging data were analyzed using neuromelaninsensitive SNpc ROIs as well as T 2 *-weighted SNr ROIs. Results: When compared with controls, significantly larger R 2 * values were seen in the SNpc of PD patients in both cohorts. Mean R 2 * values in the SNr of PD patients showed no consistency, with 1 cohort showing a small, statistically significant increase, whereas the other cohort exhibited no statistical difference. Conclusion: Mean R 2 * in the SNpc defined by neuromelanin-sensitive MRI is significantly increased in PD.