Magnetic Resonance Imaging Based Cerebral Blood Flow Changes in Asymptomatic Human Immunodeficiency Virus Infected Subjects

Background: Human Immunodeficiency Virus (HIV) infected individuals are at high risk for ischemic stroke. Magnetic resonance imaging (MRI) method of measurement of cerebral blood flow (CBF) and oxygen extraction fraction (OEF) may help assess the stroke risk in asymptomatic HIV subjects. Objectives: To evaluate MR measured CBF and OEF in treatment naïve asymptomatic HIV+ subjects and HIV- controls. Methods: Treatment naïve asymptomatic HIV+ subjects and age-gender-race matched HIV- controls were assessed for CBF using a pulsed arterial spin labeling (PASL) approach and Oxygen Extraction Fraction (OEF) using MRI T2*-weighted echo-planar imaging (EPI) sequences. All images were acquired using a Siemens 3T MR scanner (Treo, Siemens Medical Systems Inc). Quantitative CBF and OEF measurements were made in the whole-brain, gray matter and white matter and compared between the groups using unpaired t-test. Results: A total of 65 subjects of who, 35 treatment naïve HIV+ subjects (Mean age ± SD=30±7,89% male, 31% white, 49% black and 20% others) and 30 age-gender-race matched HIV- controls (Mean age± SD= 31±8,93% male, 37% white, 53% black and 10% others) consented to the protocol. HIV+ subjects compared to HIV- controls had significantly higher whole brain CBF (58.0 ± 13.8 ml/100g/min vs. 51.3 ± 9.0 ml/100g/min; p=0.03) and gray matter CBF (72.9 ± 16.2 ml/100g/min vs. 63.9 ± 9.9 ml/100g/min; p=0.01). However, values for whole brain OEF (0.4 ± 0.04) and gray matter OEF (0.4 ± 0.05) were similar for both groups. White matter CBF in HIV+ subjects (41.5 ± 13.1 ml/100g/min) compared to HIV- controls (37.2 ± 9.2 ml/100g/min) was not significantly higher (p=0.16) while white matter OEF (0.4 ± 0.04 HIV+ subjects vs. 0.4 ± 0.03 HIV-controls) showed no changes. Conclusions: The observed increase of whole brain CBF in treatment naïve HIV + subjects compared to HIV- matched controls, without corresponding changes in the OEF appears to be driven by a pronounced significant change in the gray matter compared with the white matter. These changes in CBF without corresponding changes in OEF suggest increase in metabolic activity, and may explain the higher stroke risk in asymptomatic HIV subjects.