Estimation of CBF Based on the Metabolic H217O Decay Rate in CMRO2 Measurement Using In Vivo 17O MR Approach

Xiao-Hong Zhu¹, Yi Zhang¹, Hannes Wiesner², Kamil Ugurbil¹, Wei Chen¹

In vivo ¹⁷O MRS imaging (MRSI) approach at high/ultrahigh field has been used to non-invasively mapping the cerebral metabolic rate of oxygen (CMRO₂) in small animals. However, imaging the cerebral blood flow (CBF) using the same ¹⁷O MR approach requires invasive procedures for introducing the NMR-visible H₂¹⁷O as exogenous tracer. In the present study, we demonstrate that the decay rate of the metabolic H₂¹⁷O water following a brief ¹⁷O₂ gas inhalation in the CMRO₂ measurement, although does not directly reflect the CBF value, is closely related to brain perfusion. A linear relationship between CBF and corresponding metabolic H₂¹⁷O decay rate has been determined experimentally from combined CBF and CMRO₂ measurements in rat brains under varied physiological conditions. The outcomes of the study indicate that in vivo ¹⁷O MRS/MRSI approach is a useful tool for noninvasively assessing not only CMRO₂ but also CBF simultaneously in the rat brain; and it provides new utilities for studying the cerebral oxygen metabolism and tissue perfusion associated with brain function and dysfunction.