Academic journal article Alcohol Health & Research World

Magnetization Transfer and Off-Resonance Saturation

Academic journal article Alcohol Health & Research World

Magnetization Transfer and Off-Resonance Saturation

Article excerpt

Magnetization transfer (MT) is a phenomenon that allows researchers to obtain indirect evidence for portions, or pools, of a compound (e.g., alcohol) that otherwise would not be observable using magnetic resonance spectroscopy (MRS). Researchers have hypothesized that alcohol exists in the brain in two pools: a "free" pool, in which alcohol molecules are not bound to any tissues, and a "bound" pool, in which alcohol molecules are bound to cell membranes. To obtain evidence that some alcohol may be invisible to MRS, investigators must somehow alter the MRS signals from visible pools. As shown in part (a) of the figure, the bound pool emits a broad, shallow signal that is essentially invisible on MRS. This broad signal is thought to have the same central frequency as the signal produced by the free-alcohol pool, which appears as a tall triplet peak at the center of the bound pool's broad signal. Researchers can use the interactions that occur between the two alcohol pools to establish the existence of the invisible pool. One such interaction is a rapid exchange of alcohol molecules between the pools.

An MRS experiment has been designed that cancels the broad signal of the bound pool and indirectly affects the signal from the free pool. The experiment uses a technique called off-resonance saturation, in which the magnetic resonance machine applies energy to the tissue at a certain frequency different from that of the free pool (i. …

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