Multiparametric imaging of brain hemodynamics and function using gas-inhalation MRI

Abstract

Diagnosis and treatment monitoring of cerebrovascular diseases routinely require hemodynamic imaging of the brain. Current methods either only provide part of the desired information or require the injection of multiple exogenous agents. In this study, we developed a multiparametric imaging scheme for the imaging of brain hemodynamics and function using gas-inhalation MRI. The proposed technique uses a single MRI scan to provide simultaneous measurements of baseline venous cerebral blood volume (vCBV), cerebrovascular reactivity (CVR), bolus arrival time (BAT), and resting-state functional connectivity (fcMRI). This was achieved with a novel, concomitant O2 and CO2 gas inhalation paradigm, rapid MRI image acquisition with a 9.3 min BOLD sequence, and an advanced algorithm to extract multiple hemodynamic information from the same dataset. In healthy subjects, CVR and vCBV values were 0.23±0.03 %/mmHg and 0.0056±0.0006 %/mmHg, respectively, with a strong correlation (r=0.96 for CVR and r=0.91 for vCBV) with more conventional, separate acquisitions that take twice the scan time. In patients with Moyamoya syndrome, CVR in the stenosis-affected flow territories (typically anterior-cerebral-artery, ACA, and middle-cerebral-artery, MCA, territories) was significantly lower than that in posterior-cerebral-artery (PCA), which typically has minimal stenosis, flow territories (0.12±0.06 %/mmHg vs. 0.21±0.05 %/mmHg, p<0.001). BAT of the gas bolus was significantly longer (p=0.008) in ACA/MCA territories, compared to PCA, and the maps were consistent with the conventional contrast-enhanced CT perfusion method. FcMRI networks were robustly identified from the gas-inhalation MRI data after factoring out the influence of CO2 and O2 on the signal time course. The spatial correspondence between the gas-data-derived fcMRI maps and those using a separate, conventional fcMRI scan was excellent, showing a spatial correlation of 0.58±0.17 and 0.64±0.20 for default mode network and primary visual network, respectively. These findings suggest that advanced gas-inhalation MRI provides reliable measurements of multiple hemodynamic parameters within a clinically acceptable imaging time and is suitable for patient examinations.

Brain BOLD MRI O2and CO2stress testing: Implications for perioperative neurocognitive disorder following surgery

“…However, a carefully done study in rats anaesthetized with isofluane (a volatile agent) reports many of the same BOLD and CBF findings using similar imaging approaches, suggesting that the respiratory gas effects on cerebral perfusion translate to the anaesthetized state with volatile agents. 41 Recent work by Venkatraghavan et al 42 showing marked fluctuations in brain BOLD in 4 patients undergoing propofol anaesthesia with intracranial steal using a similar CO2 ramp protocol as in this study, indicating that the CO2 responsiveness we describe in the awake state persists under anaesthesia. Also well-known is the rapid response by the brain to alterations in ET CO2 to control intracranial volume during anaesthesia for neurosurgical procedures.…”

Cerebrovascular reactivity mapping without gas challenges

“…The gas inhalation scan utilized the concomitant CO 2 /O 2 modulation paradigm so that CVR and venous CBV maps were obtained simultaneously. Details of the concomitant CO 2 /O 2 modulation and data analysis were described previously (Liu et al, 2016). An ASL scan was performed to obtain CBF.…”

Effect sizes of BOLD CVR, resting-state signal fluctuations and time delay measures for the assessment of hemodynamic impairment in carotid occlusion patients

“…reaction time. As BOLD delay time assessment provides us with two important measures of cerebrovascular health, the technique has gained increasing attention ( Christen et al., 2015b ; Cogswell et al., 2017 ; Liu et al., 2017b ; Donahue et al., 2015 ; Champagne et al., 2017 ).…”

“…This is of importance when attributing BOLD signal amplitude fluctuations solely to neuronal activity or as a proxy for PaCO 2 -related changes in vascular dynamics. In this assessment, adopting previously-made assumptions, hyperoxia induced BOLD signal changes (HO-BOLD) were taken as a proxy for the vCBV ( Liu et al., 2017b ; Bulte et al., 2007 ).…”