Assessment of cerebral blood flow in neonates and infants: A phase-contrast MRI study.

Abnormal cerebral blood flow (CBF) is implicated in several neonatal and infant diseases. However, measurement of CBF in this population remains difficult and has not been used in routine clinical MRI. Arterial spin labeling (ASL) methods suffer from both low SNR and poor quantification when applied to very young children. Furthermore, rapid change in brain physiology in this age range makes it difficult to choose sequence parameters such as labeling pulse flip angle and post labeling delay. Phase-contrast (PC) MRI is another approach to measure flow. It provides fast and reliable global CBF assessment, and has great promises in pediatric applications. In this study, we aimed to apply PC-MRI technique for CBF quantification in neonates and infants up to 18 months of age. We first compared several implementations of time-of-flight (TOF) MR angiogram for the visualization of brain's feeding arteries, which provides anatomical information for the positioning of PC-MRI scans. We then measured flow velocity and CBF of the internal carotid artery (ICA) and vertebral artery (VA) in 21 subjects (age 34-114 gestational weeks, 3 females, 18 males), using six encoding velocities (Venc) in each vessel. In ICA, peak arterial flow velocity was 10.2 cm/s at birth and increased to 56.0 cm/s at 18 months old. These values were 4.5-36.3 cm/s, respectively, for VA. CBF after accounting for brain volume revealed a significant (p < 0.001) age-related increase from 13.1 to 84.7 ml/100  g/min within the first 18 months after birth. Based on the peak flow velocity, we provided age-specific recommendations for Venc selection in PC-MRI when one only has time for one scan. The present study used a multi-Venc scheme to determine flow velocities in major feeding arteries of infant brain and may lay a foundation for accurate measurement of whole-brain CBF in this population.