Proton magnetization transfer of metabolites in human brain

Abstract

Off-resonance or pulsed on-resonance saturation pulses were used together with localized proton magnetic resonance spectroscopy in three brain regions of 20 healthy individuals. Statistically significant signal attenuations were observed for creatinecontaining metabolites in posterior-parietal brain (12%), basal ganglia (18%), and cerebellum (15%). N-acetyl-and cholinecontaining metabolites were not significantly attenuated upon application of saturation pulses in either brain region. The findings are interpreted to reflect possible magnetization transfer between pools of creatine-containing metabolites with different molecular mobility. Magn Reson Med 42:417-420, 1999.1999 Wiley-Liss, Inc.Key words: magnetization transfer; magnetic resonance spectroscopy; dipolar coupling; human brain; creatine Magnetization transfer (MT) techniques have been used in high-resolution NMR to investigate molecular structure and chemical reaction equilibria based on cross-relaxation and chemical exchange. After they were described by Wolff and Balaban in 1989 (1), these methods also found a place in in vivo MRI. The unique way of obtaining MT contrast has led to a range of new applications in the evaluation of pathologies such as multiple sclerosis, metastatic disease, and human immunodeficiency virus infection (e.g., ref.2). This unique contrast is created by saturating a motionally restricted pool of water bound to macromolecules (proteins or membranes) and observing the decreased magnetization of the bulk mobile water that is not associated with macromolecules. Although the exact mechanisms underlying these effects are still a matter of discussion, it is thought that both chemical exchange and through-space dipolar interactions are responsible for this MT effect on tissue water. Both off-resonance and on-resonance saturation methods are commonly used for selective saturation of the motionally restricted water pool that is not directly observable by standard in vivo MR methods.Recently, MT effects have also been reported for 1 H magnetic resonance spectroscopy (MRS)-detectable metabolites in brain (3)(4)(5)(6)(7)(8)(9)(10). MT experiments at high field strengths showed signal reductions of lactate in rat glioma tissue (7) and of creatine/phosphocreatine in rat brain (3-5) and in rat and mouse skeletal muscle (8,9). In addition, we reported signal intensity decreases of alcohol in the human brain at 1.5 T (10) and in rat brain (6) and rat brain membrane suspensions upon off-resonance saturation at high fields (11). These latter experiments gave evidence of the postulated existence of more than one pool of alcohol in brain, and they add to our understanding of mechanisms of alcohol-induced tolerance in heavy drinkers (12). An MR-invisible pool of brain alcohol and alcohol MT effects may also provide partial explanations for the commonly reported low MRS-visibility of alcohol in the brain upon using certain water suppression and localization methods. Detailed studies of MT effects in tissue not only provide a view of mechanisms gove...

Ethanol in Human Brain by Magnetic Resonance Spectroscopy: Correlation With Blood and Breath Levels, Relaxation, and Magnetization Transfer

“…Both methods, including MT pulse power, have been described in detail previously (Meyerhoff et al, 1999a). The power of the MT pulses was as high as possible and was a tradeoff between optimal saturation of short T 2 -components and specific absorption rate limitations given by the application of the entire pulse sequence.…”

Magnetization transfer in MRI: a review

“…Only very recently has MT from metabolites been demonstrated. [41][42][43] MT-MRS is discussed further in the article by D. Leibfritz and W. Dreher in this issue. 44 It is still possible that this effect will have significant application in understanding tissue metabolism in the future.…”

Magnetization transfer MRS

“…The magnetization transfer effect on Cr/PCr was subsequently confirmed in various studies in rat brain [17][18][19]44 and skeletal muscle, [45][46][47][48][49] and in human brain. [50][51][52] Various mechanisms may account for the observed MT effect:…”