Magnetization transfer in MR imaging

✍ Scribed by Giles E. Santyr; Robert V. Mulkern

• Publisher: John Wiley and Sons
• Year: 1995
• Tongue: English
• Weight: 403 KB
• Volume: 5
• Category: Article
• ISSN: 1053-1807
• DOI: 10.1002/jmri.1880050121

✦ Synopsis

THE MANY DIFFERENT local environments of hydrogen nuclei within tissue give rise to complicated magnetic relaxation behavior while ensuring the rich and diverse contrast seen in magnetic resonance (MR) imaging. From an operational point of view, it has proved convenient to classify the multiple environments into two basic types: a solid-like environment and a liquid-like environment. Protons in the solid-like environmentmostly associated with macromolecules-do not experience sufficiently fast rotational or translational motions to average out mutual magnetic dipole-dipole interactions. As a consequence, the MR spectrum from the solid-like pool is represented by a broad distribution of Larmor frequencies (several kilohertz). Such spins dephase quickly, with T2 values generally less than 1 msec (1). In contrast, hydrogen nuclei in the liquid-like environment-mostly associated with small mobile molecules such as water-experience rapid rotational and translational motions that serve to substantially average out mutual magnetic dipoledipole interactions. Thus, the MR spectrum of these protons is represented by a relatively narrow distribution of Larmor frequencies (several hertz), with consequently long T2 values.

In conventional MR imaging, the liquid-like pool produces the bulk of observable MR signal. However, magnetization transfer between the solid-like pool and the liquid-like pool has a con-Index tumm: Contrast enhancement -Magnetization transfer contrast -SMRl Reports