No abstract

We evaluated brain tissue compartments in 72 healthy volunteers between the ages of 18 and 81 years with quantitative MRI. The intracranial fraction of white matter was significantly lower in the age categories above 59 years. The CSF fraction increased significantly with age, consistent with previous reports. The intracranial percentage of gray matter decreased somewhat with age, but there was no significant difference between the youngest subjects and the subjects above 59. A covariance adjustment for the volume of hyperintensities did not alter the foregoing results. The intracranial percentage of white matter volume was strongly correlated with the percentage volume of CSF. The finding of a highly significant decrease with age in white matter, in the absence of a substantial decrease in gray matter, is consistent with recent neuropathologic reports in humans and nonhuman primates.

The goal of the present study was to examine the volume of selective brain regions in a group of mildly impaired AD patients. Five regions were selected for analysis, all of which have been reported to show substantial change in the majority of AD patients at some time in the course of disease. Three of the volumetric measures were significantly different between AD patients and controls: the hippocampus, the temporal horn of the lateral ventricles and the temporal lobe. Two of the measures did not significantly differentiate AD patients and controls: the amygdala and the basal forebrain. A discriminant function analysis demonstrated that a linear combination of the volumes of the hippocampus and the temporal horn of the lateral ventricles differentiated 100% of the patients and controls from one another. These results have implications for both the early diagnosis and treatment of AD.

Magnetic resonance (MR) image-based computerized segmentation was used to measure various intracranial compartments in 49 normal volunteers ranging in age from 24 to 80 years to determine age-related changes in brain, ventricular, and extraventricular cerebrospinal fluid (CSF) volumes. The total intracranial volume (sum of brain, ventricular, and extraventricular CSF) averaged 1469 +/- 102 cm3 in men and 1289 +/- 111 cm3 in women. The difference was attributable primarily to brain volume, which accounted for 88.6% of the respective intracranial volumes in both sexes, but was significantly larger in men (1302 +/- 112 cm3) than in women (1143 +/- 105 cm3). In both, the cranial CSF volume averaged 11.4%. Total intracranial volume did not change with age, although the normalized brain volume of both men and women began to decrease after the age of 40 years. This decrease was best reflected by expansion of the extraventricular CSF volume which, after the age of 50 years, was more marked in men than in women. The volume of the cranial CSF, as determined by MR image-based computerized segmentation, is considerably larger than traditionally accepted and resides mostly extraventricularly. Expansion of CSF volume with age provides a good index of brain shrinkage although evolving changes and growth of the head with age tend to confound the results.

The purpose of this study was to determine the relation between vessel wall shear stress and the rate of atherosclerosis progression. Quantitative angiography was used to calculate the change in coronary arterial diameter over 3.0 years in patients enrolled in the Harvard Atherosclerosis Reversibility Project pilot study (n=20 arterial segments). Vessel wall shear stress was calculated by means of a validated finite-difference model of the Navler-Stokes' equation that assumes a coronary flow rate of 8 ml/sec The correlation between vessel wall shear stress and the change in arterial diameter at multiple points (mean, 70) along the length of the artery was then calculated for each of the 20 segments with a focal stenosis. In 15 of the 20 arterial segments there was a significant correlation (p<0.05) between low shear stress and an increased rate of atherosclerosis progression. A Fisher's z transformation was then used to combine the correlation coefficients from all 20 segments. Low shear stress was significantly correlated (z=0.37 ± 0.00074, p< 0.0001) with an increased rate of atherosclerosis progression. This serial quantitative evaluation of human coronary arteries is consistent with previous data that have suggested that low shear stress promotes atherosclerosis progression. Variations in local vessel wall shear stress may explain the previously reported near-independent rate of atherosclerosis progression in multiple lesions within the same patient despite exposure to the same circulating lipoprotein values and systemic hemodynamics. 7 However, we have previously reported that despite being exposed to the same concentrations of serum lipoproteins and systemic hemodynamics, coronary arterial obstructions within the same patient progress at near-independent rates.8 Similarly, right coronary artery lesions seem to progress at a more rapid rate than those of the left anterior descending coronary artery, 9 -10 and coronary segments proximal to the insertion of a saphenous vein graft progress at a more rapid rate than those distal to graft insertion.11 These recent findings support the hypothe- Received September 30, 1991; revision accepted November 23, 1992. sis that in addition to systemic risk factors, local mechanical forces may also play a role in determining the rate of atherosclerosis progression. The role of mechanical forces in human coronary atherosclerosis progression has been previously investigated by the use of casts of vascular structures such as the aorta or carotid circulations.12 -32 The purpose of this study was to determine by means of quantitative angiography if shear stress at multiple points along the length of the human coronary artery could be related to the rate of atherosclerosis progression over time in vivo. Methods Patient SelectionThe Harvard Atherosclerosis Reversibility Project (HARP) pilot study was undertaken to assess the rate of change in coronary artery diameter in patients treated by means of either diet or medication over 3.0 years to develop quantitative angiographic t...