Gas enhanced magnetic resonance angiography of the cerebrum using carbon dioxide and oxygen - preliminary results

Purpose/introduction Standard imaging of the cerebral arteries is performed using intravenous contrast in CT angiography and x-ray angiography. Magnetic resonance angiography (MRA) of the cerebral arteries using intravenous contrast media does not perform well. Contrast in the venous bed and the meninges may obscure the signal from the arteries of interest. It is known that oxygen enhances the T1-weighted signal and that carbon dioxide increases the arterial blood flow. This paper presents preliminary results of gas enhanced MRA using combinations of atmospheric air, O2 and CO2. Subjects and Methods Two healthy volunteers were scanned during inhalation of three different gas mixtures: Gas I (air), Gas II (5% CO2, 21 % O2, 74 % N2), Gas III (5% CO2, 95% O2). For each gas mixture a time of flight (TOF) series on the cerebral arteries was performed. Following each TOF series an ECG-gated phase contrast sequence was performed to calculate volume flow in the common carotid arteries. MRA data was acquired with a 1.5 T Siemens VISION MR-system (SIEMENS Medical Systems, Germany) using a standard circularly polarized head coil. Reconstructed images of TOF series and volume flow measurements were compared. Results The TOF series showed an increase in MRA signal and vessel conspicuousness, when adding CO2 to air (gas I vs. gas II) and an additional increase was seen on MRA when adding O2 to CO2 (gas II vs. gas III). The increase in MRA signal was present on both volunteers. The volume flow increased as a response to the added CO2 (gas II). Free oxygen (gas III) enhanced the MRA blood signal but invoked a slight decrease in the volume flow. Discussion/conclusion Inhaling gas mixture during MRA examination containing CO2 and O2 increased the cerebral MRA signal. These preliminary results indicate that improved MRA of the cerebrum can be gained when inhaling 5 % CO2/ 95% O2 during examination bringing forth an alternative to CT and x-ray cerebral angiography. Furthermore, gas enhanced MRA could be an alternative to contrast enhanced MRA in other regions of interest than cerebrum.