High Temporal Resolution MRI Quantification of Global Cerebral Metabolic Rate of Oxygen Consumption in Response to Apneic Challenge

Abstract

We present a technique for quantifying global cerebral metabolic rate of oxygen consumption (CMRO2) in absolute physiologic units at 3-second temporal resolution and apply the technique to quantify the dynamic CMRO2 response to volitional apnea. Temporal resolution of 3 seconds was achieved via a combination of view sharing and superior sagittal sinus-based estimation of total cerebral blood flow (tCBF) rather than tCBF measurement in the neck arteries. These modifications were first validated in three healthy adults and demonstrated to produce minimal errors in image-derived blood flow and venous oxygen saturation (SvO2) values. The technique was then applied in 10 healthy adults during an apnea paradigm of three repeated 30-second breath-holds. Subject-averaged baseline tCBF, arteriovenous oxygen difference (AVO2D), and CMRO2 were 48.6 ± 7.0 mL/100 g per minute, 29.4 ± 3.4 %HbO2, and 125.1 ± 11.4 μmol/100 g per minute, respectively. Subject-averaged maximum changes in tCBF and AVO2D were 43.5 ± 9.4% and -32.1 ± 5.7%, respectively, resulting in a small (6.0 ± 3.5%) but statistically significant (P=0.00044, two-tailed t-test) increase in average end-apneic CMRO2. This method could be used to investigate neurometabolic-hemodynamic relationships in normal physiology, to better define the biophysical origins of the BOLD signal, and to quantify neurometabolic responsiveness in diseases of altered neurovascular reactivity.

Cerebral Oxygen Metabolism in Neonates with Congenital Heart Disease Quantified by MRI and Optics

“…17 Total CBF was quantified by PC MRI, 8 a standard technique for measuring blood flow velocity in the SSS, from which CBF was calculated by multiplying average velocity in the vessel by the cross-sectional area. As the SSS is known to drain 45% of the total brain blood volume, 18,19 it is Figure 1. (A) Sketch of an anesthetized and intubated patient entering the scanner with magnetic resonance imaging (MRI) compatible optical probe secured to the forehead.…”

“…Blood flow in the SSS, which drains only the cortical mantle, was used to determine total CBF, based on recent work showing that the SSS accounts for 45% of total CBF as pointed out earlier. 19 Finally, the MRI measurements require transport and are not amenable to bedside monitoring; however, once in-magnet, the pulse sequences employed permit rapid quantification of cerebral hemodynamics (o5 minutes including localizer scans) and can be conveniently added to standard clinical protocols without additional time penalties.…”

Rapid T2- and susceptometry-based CMRO2 quantification with interleaved TRUST (iTRUST)

“…By adding flow encoding to the same dual-echo GRE used for Y v quantification, SSS blood flow (SSSBF) and Y v can be quantified from data acquired in the same TR period. SSSBF can then be retrospectively up-scaled to tCBF based on a single measurement of the SSSBF:tCBF ratio at baseline (Rodgers et al, 2013a). …”

“…CMRO 2 changes significantly over the course of neonatal development (Liu et al, 2014a) and aging (Peng et al, 2014), and is altered in many of the most common neurologic diseases, including mild cognitive impairment (Liu et al, 2014b) and Alzheimer's disease (Ishii et al, 1996), Parkinson's disease (Borghammer et al, 2010), and multiple sclerosis (Ge et al, 2012). However, CMRO 2 is relatively stable across healthy subjects at baseline (Xu et al, 2009; Jain et al, 2010), and in response to physiologic challenges such as hypercapnia (Chen and Pike, 2010; Xu et al, 2011; Jain et al, 2011), hypoxia (Xu et al, 2012a), and apnea (Rodgers et al, 2013a). Thus, CMRO 2 is an important quantity for understanding brain function in health and disease.…”

“…This hybrid sequence was originally implemented via a two-slice interleaved approach with CMRO 2 quantification temporal resolution of 25 seconds (Jain et al, 2010). Recently, addition of view-sharing and SSS-based estimation of tCBF improved OxFlow temporal resolution to three seconds, allowing study of the regulation of CMRO 2 in response to dynamic physiologic paradigms such as breath-hold apnea (Rodgers et al, 2013a). Compared to OxFlow, TRUST has inherently lower temporal resolution, compounded by the need for a separate PC-MRI measurement to quantify CMRO 2 .…”