Cerebral blood flow by using pulsed arterial spin-labeling in elderly subjects with white matter hyperintensities

BACKGROUND AND PURPOSE: On MR imaging, white matter hyperintensities (WMH) on T2-weighted images are generally considered as a surrogate marker of ischemic small vessel disease in elderly subjects. Pulsed arterial spin-labeling (PASL) is a noninvasive MR perfusion-weighted technique. We hypothesized that elderly subjects with diffuse confluent WMH should have lower cerebral blood flow (CBF) measurements than subjects with punctiform or beginning confluent WMH.MATERIALS AND METHODS: MR images of 21 subjects (13 women; mean age, 76 years; SD, 5), stratified for the degree of WMH, from a single center within the multinational Leukoaraiosis and Disability (LADIS) study, were investigated. CBF images were obtained by means of quantitative imaging of perfusion by using a single-subtraction second version, with thin-section TI periodic saturation PASL. Values of cortical gray matter, subcortical (including white matter and deep gray matter), and global CBF were calculated. CBF measurements of subjects with diffuse confluent WMH (n = 7) were compared with those of subjects with punctiform or beginning confluent WMH (n = 14).RESULTS: Subjects with diffuse confluent WMH were found to have approximately 20% lower mean global CBF (43.5 mL/100 mL/min; SD, 6.3) than subjects with punctiform or beginning confluent WMH (57.9 mL/100 mL/min; SD, 8.6; P < .01), as well as approximately 20% lower mean subcortical (P < .01) and cortical gray matter CBF (P < .05).CONCLUSION: PASL revealed a significant reduction of CBF measurements in elderly subjects with diffuse confluent WMH.

On MR imaging, white matter hyperintensities (WMH) on T2-weighted images, fluid-attenuated inversion recovery (FLAIR) images, and proton density–weighted images are generally considered as a surrogate marker of ischemic small vessel disease in elderly subjects,¹ but their significance is still under debate.Arterial spin-labeling (ASL) is a functional MR imaging technique that represents an alternative to both nuclear medicine and dynamic susceptibility contrast echo-planar MR imaging (EPI) for the evaluation of cerebral perfusion. By using water as a diffusible tracer, ASL does not require either ionizing radiation or an exogenous contrast bolus injection. Water proton spins in the arterial blood can be inverted (magnetically labeled) before entering the capillary level, after applying an appropriate series of radio-frequency pulses. When these labeled water protons enter the capillary level, they alter the magnetization of the tissue in a way that can be measured quantitatively.² Pulsed ASL (PASL) techniques generally label a large blood volume in a thick slab just below the planes of image acquisition, by inverting the magnetization of water protons with adiabatic hyperbolic secant radio-frequency pulses.³Because WMH most probably represent ischemic small vessel disease,^1,4 we hypothesized that subjects with diffuse confluent WMH should have lower cerebral blood flow (CBF) measurements than subjects with punctiform or beginning confluent WMH. In fact, single-photon emission CT, positron-emission tomography, and dynamic susceptibility contrast perfusion-weighted MR imaging studies have shown that diffuse confluent WMH are associated with reduced cerebral perfusion,^5–7 but most of them did not yield quantification of CBF. To our knowledge, no previous study has shown a relation between different grades of WMH and CBF measurements by means of ASL. Therefore, our purpose was to compare CBF measurements of subjects with diffuse confluent WMH with those of subjects with punctiform or beginning confluent WMH by using PASL.