Patterns of age-related shrinkage in cerebellum and brainstem observed in vivo using three-dimensional MRI volumetry.

This study investigates the time course and regional differences in age-related volume loss in cerebellum and brainstem. Three-dimensional (3D) magnetic resonance imaging (MRI) volumetry was used to measure the volumes of 11 regions in the cerebellum and three regions in the brainstem in 48 healthy volunteers (age 19.8-73.1 years). Landmark-adjusted lattices were used to divide the cerebellum into three radial (lobules I-V = lingula/lobulus/culmen, lobules VI-VII = declive/folium/tuber, lobules VIII-X = pyramis/uvula/nodulus) and three transverse subdivisions (vermis, medial, lateral hemisphere). The radial sectors extended laterally throughout the vermis and the medial hemisphere. The brainstem was divided into midbrain, metencephalon (pons and tegmentum pontis) and medulla. Total cerebellar volume marginally declined with age using a linear regression model. An exponential model better described the age dependency of total cerebellar volume. The curve predicted that the volume remained stable until age 50 years and declined thereafter. Volume loss in the cerebellar vermis was striking. Shrinkage in the medial hemisphere was markedly less and only the inferior sector showed a trendwise negative association with age. The lateral hemisphere was not affected by age. No age effects were found for total brainstem volume, metencephalon and medulla. Only the mid-brain showed a trend for age-related shrinkage. The mediolateral gradient of decreasing age effects is similar to the histological pattern of alcoholic cerebellar atrophy (although our subjects were non-alcoholics according to DSM-IIIR criteria and laboratory data) suggesting that a common factor is involved in both processes. In search for a cause of the regional vulnerability, vascular, functional, structural and molecular/genetic factors may be considered.

Autosomal dominant cerebellar ataxia type I. MRI-based volumetry of posterior fossa structures and basal ganglia in spinocerebellar ataxia types 1, 2 and 3.

Twenty-six patients suffering from autosomal dominant cerebellar ataxia type I were subjected to a genotype-phenotype correlation analysis using molecular genetic assignment to the genetic loci for spinocerebellar ataxia type 1, 2 or 3 (SCA1, SCA2, SCA3) and MRI-based volumetry of posterior fossa structures and basal ganglia nuclei. There was significant atrophy of the cerebellum and brainstem in all three SCA mutations compared with a group of 31 age- and sex-matched controls. Comparison between the SCA groups showed that cerebellar and brainstem atrophy was more severe in SCA2 than in SCA1 and SCA3. Putaminal and caudate volume was reduced only in SCA3, but not in SCA1 and SCA2. A set of three morphological criteria was defined that enabled us to assign all SCA2 and SCA3 patients correctly to the underlying genotype. In contrast, these criteria did not distinguish SCA1 from SCA2 and SCA3. Regression analysis failed to reveal a significant association between CAG repeat length and the volumes of the respective brain structures in any of the SCA mutant types. The present data provide in vivo evidence that SCA2 and SCA3 lead to distinct patterns of brain atrophy, while the atrophy changes in SCA1 overlap with both SCA2 and SCA3.

A new semiautomated, three-dimensional technique allowing precise quantification of total and regional cerebellar volume using MRI.

A new method was developed to measure total and regional cerebellar volumes using MRI. Previously, the volumes of the cerebellum and its substructure had been studied planimetrically. The new method uses three-dimensional semiautomated volumetry with focus on reliability and performance. The method consists of a manual presegmentation using landmark-adjusted planes followed by region-growing segmentation and calculation of volume. The cerebellum is partitioned into 11 regions defined by planes, which are adjusted for internal cerebellar landmarks (three radial regions inside the vermis that extend into the medial hemisphere (one-fourth of the transverse diameter of the hemisphere); one region in the lateral hemisphere (remaining three-fourths)). Forty-six healthy volunteers were examined and the effects of age, gender, and symmetry were estimated. Shrinkage in the vermis (especially anterior superior compartment) was marked. Age effects diminished laterally and were not observed in the lateral hemisphere. Age effects on the total cerebellar volume were marginal. Effects of gender and symmetry were nonsignificant. Technique and results are discussed and related to methods and findings of others.

Reliability and exactness of MRI-based volumetry: a phantom study.

This study investigated the influence of slice thickness, section orientation, contrast, shape, and sequence type on the exactness of MRI-based volumetry. Ni-doped agarose gel phantoms (4 to 46 ml) were scanned with a T1-weighted three-dimensional Fourier transform (FT) fast low-angle shot (FLASH) and a multiecho two-dimensional FT-Turbo spin-echo (SE) sequence. After segmentation with a three-dimensional region-growing algorithm, the geometric volume was measured considering the partial volume effect. The variability coefficient (Pearson) was .7%. The volumetric error increased with slice thickness, depending on the size and form of the object. Cross sections resulted in smaller error than longitudinal sections (finger-shaped phantoms, nonisotropic image data). Three-dimensional FT imaging. Results of slice thickness and section orientation experiments can be explained by the partial volume effect Higher errors in two-dimensional FT imaging were caused by object movements between two interleaved acquisitions. The study shows a considerable influence of the imaging parameters on the exactness, which depends on size and form of the structure of interest.

Chronic occupational exposure to organic solvents. XV. Glycol ether exposure during the manufacture of brakehoses.

Twenty-two persons (20 men and 2 women) were examined for their external and internal exposure to the glycol ether 1-methoxypropan-2-ol (PGME) during the production, leak testing and mounting of brakehoses. For the measurement of external exposure, personal air monitoring was the method of choice. Average concentrations of PGME of 82.2 mg/m3 (22.3 ppm), 68.6 mg/m3 (18.6 ppm) and 11.3 mg/m3 (3.1 ppm) were found in the air of the brakehose production, leak test and mounting areas, respectively. For the estimation of internal exposure to PGME, this glycol ether was measured in both urine and blood. The biological samples were taken post-shift. The highest internal exposure levels were found in the brakehose production section and in the leak test area. The average post-shift concentrations for PGME in workers in the brakehose production section were 4.6 mg/l in urine and 13.5 mg/l in blood; the corresponding figures for workers in the leak test area were 4.2 mg/l in urine and 11.0 mg/l in blood. In blood and urine samples of workers engaged in the mounting area, PGME levels were below the detection limits. The elimination kinetics of PGME were also studied in three highly exposed persons, and mean excretion half-lives of PGME of approximately 4.4 h were found. On the basis of our results we made a rough calculation of a future biological tolerance value: we would except that concentrations of 38-109 mg per litre of blood and 10-31 mg per litre of urine would correspond to the German MAK value for PGME (375 mg/m3).