Magnetic resonance (MR) examinations of the brain are routinely performed with circularly polarized (CP) head coils. These volume coils are closely shaped around the head of the patient. At best, CP coils provide a signal-to-noise ratio (SNR) gain of √2 compared with non-CP coils. In superconducting systems, they usually have a ‘bird-cage’ configuration. In MR systems where the direction of the B 0 field is oriented perpendicular to the long axis of the body, e.g., open-design resistive or permanent magnet systems, solenoid head coils are used. By diagonally crossing two solenoid wire loops, a CP head coil can be created. Surface coils are rarely used for brain imaging, and are usually reserved for ‘special’ applications: high-resolution imaging of the orbits, or the temporo-mandibular joints (double-doughnut surface coil). A promising new development is the use of phased-array coils to perform high-resolution imagine of the cerebral cortex.
KeywordsMultiple Sclerosis Arachnoid Cyst Primary Central Nervous System Lymphoma Spin Echo Cavernous Malformation
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