BACKGROUND AND PURPOSE:Arterial spin-labeling (ASL) with image acquisition at multiple delay times can be exploited in perfusion MR imaging to visualize and quantify the temporal dynamics of arterial blood inflow. In this study, we investigated the consequences of an internal carotid artery (ICA) occlusion and collateral blood flow on regional timing parameters.

BACKGROUND AND PURPOSE: Although the added diagnostic value of arterial spin-labeling is shown in various cerebral pathologies, its use in clinical practice is limited. To encourage clinical adoption of ASL, we investigated the reproducibility of CBF measurements and the effects of variations in acquisition parameters compared to the recommended ASL implementation.

BACKGROUND AND PURPOSE: Experienced freedivers can endure prolonged breath-holds despite severe hypoxemia and are therefore ideal subjects to study apnea-induced cerebrovascular reactivity. This multiparametric study investigated CBF, the spatial coefficient of variation as a correlate of arterial transit time and brain metabolism, dynamics during prolonged apnea. MATERIALS AND METHODS: Fifteen male freedivers (age range, 20-64 years; cumulative previous prolonged breath-holds Ͼ2 minutes and 30 seconds: 4-79,200) underwent repetitive 3T pseudocontinuous arterial spin-labeling and 31 P-/ 1 H-MR spectroscopy before, during, and after a 5-minute breath-hold (split into early and late phases) and gave temporally matching venous blood gas samples. Correlation of temporal and regional cerebrovascular reactivity to blood gases and cumulative previous breath-holds of Ͼ2 minutes and 30 seconds in a lifetime was assessed. RESULTS: The spatial coefficient of variation of CBF (by arterial spin-labeling) decreased during the early breath-hold phase (Ϫ30.0%, P ϭ .002), whereas CBF remained almost stable during this phase and increased in the late phase (ϩ51.8%, P ϭ .001). CBF differed between the anterior and the posterior circulation during all phases (eg, during late breath-hold: MCA, 57.3 Ϯ 14.2 versus posterior cerebral artery, 42.7 Ϯ 10.8 mL/100 g/min; P ϭ .001). There was an association between breath-hold experience and lower CBF (1000 previous breath-holds reduced WM CBF by 0.6 mL/100 g/min; 95% CI, 0.15-1.1 mL/100 g/min; P ϭ .01). While breath-hold caused peripheral lactate rise (ϩ18.5%) and hypoxemia (oxygen saturation, Ϫ24.0%), cerebral lactate and adenosine diphosphate remained within physiologic ranges despite early signs of oxidative stress [Ϫ6.4% phosphocreatine / (adenosine triphosphate ϩ adenosine diphosphate); P ϭ .02]. CONCLUSIONS: This study revealed that the cerebral energy metabolism of trained freedivers withstands severe hypoxic hypercarbia in prolonged breath-hold due to a complex cerebrovascular hemodynamic response. ABBREVIATIONS: ATP ϭ adenosine triphosphate; ASL ϭ arterial spin-labeling; ASL-sCoV ϭ spatial coefficient of variation of CBF (by ASL); ATT ϭ arterial transit time; CVR ϭ cerebrovascular reactivity; HR ϭ heart rate; P i ϭ inorganic phosphates; PCr ϭ phosphocreatine; pO 2 ϭ partial pressure of oxygen; SpO 2 ϭ oxygen saturation