Effect of age on cerebral blood flow: measurement with ungated two-dimensional phase-contrast MR angiography in 250 adults.

PURPOSE: To determine the normal values and effects of age and sex on total cerebral blood flow (CBF) as measured with ungated two-dimensional phase-contrast magnetic resonance (MR) angiography. MATERIALS AND METHODS: Volume flow rates in the basilar artery and both internal carotid arteries were measured on two-dimensional phase-contrast MR angiograms obtained in 250 subjects (age range, 19-88 years; mean age, 50 years) undergoing MR imaging because of indications other than cerebrovascular disease. Volume flow rates for the three arteries were summed to obtain the total CBF, and the values were analyzed in terms of age and sex. RESULTS: Mean total CBF was 616 mL/min +/- 143. There was a significant yearly decrease with age in total CBF of 4.8 mL/min (P < .001). Mean total CBF ranged from 748 mL/min +/- 121 to 474 mL/min +/- 105 in subjects aged 19-29 and 80-89 years, respectively. No sex differences were found. Mean relative contributions of the right and left internal carotid arteries and the basilar artery to total CBF were 41%, 40%, and 19%, respectively, with no substantial change due to age. CONCLUSION: Ungated two-dimensional phase-contrast MR angiography is a useful, noninvasive technique for assessing total CBF. By using this technique, a significant decrease in total CBF with age was demonstrated.

Circle of Willis: morphologic variation on three-dimensional time-of-flight MR angiograms.

PURPOSE: To establish normal reference values for the presence of the anatomic variants of the circle of Willis and average diameters for its component vessels by using three-dimensional time-of-flight magnetic resonance (MR) angiography and to determine whether age- or sex-related differences exist in the circle's anatomy. MATERIALS AND METHODS: One hundred fifty volunteers were grouped according to age: those aged 20-25 years (n = 50) and those aged 60-88 years (n = 100). All subjects underwent three-dimensional time-of-flight MR angiography of the arterial circle at 1.5 T. The anatomic variants of the anterior and posterior parts of the circle were determined separately, the completeness of the entire circle was assessed, and the diameters of all component vessels were measured. RESULTS: On MR angiograms, 111 (74%) subjects demonstrated a complete anterior part of the circle, 78 (52%) demonstrated a complete posterior part of the circle, and 63 (42%) demonstrated an entirely complete circle of Willis (complete anterior and posterior parts of the circle combined). The presence of an entirely complete circle of Willis was slightly higher in younger persons and in women. Most vessel diameters were smaller in women, except for the diameter of the posterior communicating artery. Statistically significant differences were found in vessel diameters between the younger and the older age groups. CONCLUSION: The authors determined normal reference values for morphologic variants and diameter measurements of the circle of Willis specific to three dimensional time-of-flight MR angiography.