Proton NMR imaging of cerebral blood flow using H₂¹⁷O

Abstract

Cerebral blood flow was quantitatively mapped by monitoring the cerebral washout of H2(17)O using rapid, single-shot proton NMR imaging. H2(17)O acts as a freely diffusible contrast agent for proton imaging via its scalar-coupled term, enhancing T2 relaxation. Measured values for CBF ranged from 29 to 106 ml/min/100 g over a range of arterial pCO2 between 23 and 81 Torr.

In vivo17O NMR approaches for brain study at high field

“…In vivo 17 O approaches can be potentially applied to measuring and imaging two important physiological parameters, namely CMRO 2 and CBF. 6,8,14,16,[37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54] The 17 O NMR approaches for in vivo determinations of CMRO 2 and CBF involve the measurement of (i) the amount of 17 O-labeled water metabolically generated from the inhaled 17 O 2 gas through the oxidative pathway, and (ii) the washout rate of the 17 O-labeled water tracer introduced by a bolus injection, respectively. In terms of methodology, there is a close similarity between the in vivo 17 O approaches and PET approaches, especially for CBF measurements.…”

“…The early studies for developing indirect 17 O approaches focused on the use of the T 2 -weighted spinecho MRI to observe the proton signal reduction after the introduction of 17 O-labeled water. 14,39,[67][68][69][70] The T 2 -weighted 1 H signal changes observed in these studies can be linked to cerebral blood perfusion at different physiological conditions in normal and ischemic brain. 68 The time courses of the signal changes were successfully applied to quantify and image CBF in a wide range of CBF values induced by hypercapnia and hypocapnia in animals.…”

“…68 The time courses of the signal changes were successfully applied to quantify and image CBF in a wide range of CBF values induced by hypercapnia and hypocapnia in animals. 39,70 The subsequent studies applied the indirect 17 O approaches for imaging the metabolic H 2 17 O water generated from 17 O-labeled oxygen gas, which was introduced either by inhalation 40 or through artificial blood. 71 The proton signal changes detected in these studies should relate to the cerebral oxidative metabolism and could be potentially linked to CMRO 2 .…”

17O relaxation time and NMR sensitivity of cerebral water and their field dependence

“…Most of these studies were based on indirect measurements that exploited, using different strategies, the effect of 17 O on the transverse spin relaxation time (T 2 ) of water protons (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11). The proton T 2 for the H 2 17 O molecule is known to be shorter than that of protons in H 2 16 O due to the 1 H- 17 O scalar coupling (12).…”

“…The proton T 2 for the H 2 17 O molecule is known to be shorter than that of protons in H 2 16 O due to the 1 H- 17 O scalar coupling (12). For example, Kwong et al (5) utilized this property as a direct MRI contrast mechanism in T 2 -weighted 1 H images, and monitored changes in image intensity in response to 17 O to measure cerebral blood flow (CBF). A subsequently introduced approach utilized 17 O decoupling to increase the effective water proton T 2 , and monitored difference spectra or images acquired with and without 17 O decoupling as a measure of H 2 17 O content (6 -8,10,11).…”