Improved sensitivity of proton MR to oxygen‐17 as a contrast agent using fast imaging: Detection in brain

Abstract

The potential utility of H2(17)O as a contrast agent has been demonstrated in biological solutions and isolated tissues but its use has been impaired by the need to run heavily T2-weighted spin-echo images. By choosing an appropriate steady-state free precession experiment sensitive to T1/T2, we have improved the available contrast-to-noise per unit time by more than a factor of 5. This allows easy measurement of the proton effects for concentrations as low as 0.4% H2(17)O in less than 1 min. Injection into small animals produces a marked reduction in the overall image intensity. Consecutive imaging at the rate of one every 52 s has been used to follow the rate of change in brain image intensity immediately after injection.

In vivo17O NMR approaches for brain study at high field

“…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.…”

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

“…The potential use of MR techniques to monitor metabolic H 2 17 O as a tracer of oxygen consumption rate or tissue blood flow has previously been proposed and examined in several works. 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).…”

“…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). 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).…”

“…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). All of these indirect detection techniques suffer from the difficulty of quantitatively correlating the 1 H signal with the H 2 17 O concentration.…”

“…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). All of these indirect detection techniques suffer from the difficulty of quantitatively correlating the 1 H signal with the H 2 17 O concentration. The relaxation rates of both H 2…”