“Continuous Arterial Spin Labeling“ (CASL) at 3 Tesla MRI for the assessment of increasing nCPAP – Pressure effect on cerebral perfusion

Purpose: Nasal Continuous Positive Airway Pressure (nCPAP) therapy is the treatment of choice for all kinds of obstructive sleep apnoea syndrome (OSAS). The direct effect on cerebral blood flow (CBF) of this therapy was previously studied by invasive methods like DSC MRI (Dynamic Susceptibility Contrast MRT) or using radioactive tracers (99 mTc-HMPAO SPECT), and noninvasive by transcranial Doppler. These methods are limited in quantification and repeatability, and may limit the possibilities of an interindividuel comparison respectively.

High field MRI, especially at 3 Tesla provides to possibility to measure noninvasive the CBF as an indicator of perfusion by Arterial Spin Labeling (ASL). This technique this uses blood water as an endogenous contrast agent for the measurement of CBF and is easily to be quantified (in ml/min/100g of Tissue) and has a proven repeatability.

The goal for this study was to evaluate quantitatively the effect of increasing nCPAP-Pressures on the cerebral perfusion using the “Continuous Arterial Spin Labeling“ (CASL) technique at 3 Tesla MRI.

Methods: Intra-individual study on 5 male volunteers (Mean age 27). All examination were conducted at a 3 Tesla MRI (3.0T Intera, Philips Medical Systems, NL) using a ssh-EPI CASL sequence (TR/TE 4500/37, 13–15 sections, 40 dynamics). The 3 measurements with increasing nCPAP-Pressures (0, 8, 15 mbar) were performed. During the examination the heart rate, blood pressure, respiratory frequency, expiratory CO2 and SaO2 were monitored. From the acquired datasets quantitative CBF-maps were calculated. Regional CBF was measured in the cortex, white mater and the basal ganglia. The mean quantitative values were statistically tested using a paired Student-t Test and a Wilcoxon Test.

Results: An increase of the nCPAP-Pressure from 0 to 8 mbar did not show a significant reduction of the CBF in the Cortex (0 mbar: 36.2ml/min/100g±? 8.4/8 mbar: 36.4ml/min/100g±11.6). A significant reduction of the CBF was found when increasing the nCPAP-Pressure from 8 to 15 mbar (8 mbar: 36.4ml/min/100g±11.6/15 mbar: 31.9ml/min/100g±13.2). Increasing nCPAP-Pressure revealed a significant decrease of CBF in the basal ganglia between 0 to 8 mbar and between 8 to 15 mbar (0 mbar: 34.9ml/min/100g±7.9/8 mbar 31.9±6.2/15 mbar 29.9±6.3). There was no significant change of White Matter CBF with increasing nCPAP-Pressure (0 mbar: 8.4ml/min/100g±6.7/8 mbar: 8.1±3.7/15 mbar: 6.9±4.2).

Conclusion: nCPAP-Pressure up to 8 mbar do not have significant effects on cortical CBF and cause minor CBF decrease in the basal ganglia. However, a nCPAP-Pressure of 15 mbar significantly lowers the CBF in the Cortex by approx. 13%. Even high nCPAP-Pressure does not influence the CBF in the White Matter.