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At the time the article was created J. Ray Ballinger had no recorded disclosures.View J. Ray Ballinger's current disclosures
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Radiofrequency coils (RF coils) are the "antennae" of the MRI system, broadcasting the RF signal to the patient and/or receiving the return signal. RF coils can be receive-only, in which case the body coil is used as a transmitter; or transmit and receive (transceiver).
Surface coils are the simplest design of coil. They are simply a loop of wire, either circular or rectangular, that is placed over the region of interest (figure 1). The depth of the image of a surface coil is generally limited to about one radius. Surface coils are commonly used for spines, shoulders, temporomandibular joints, and other relatively small body parts.
The Helmholtz pair coils consist of two circular coils parallel to each other (figure 3). They are used as z gradient coils in MRI scanners. They are also used occasionally as RF coils for pelvis imaging and cervical spine imaging.
The birdcage coil provides the best RF homogeneity of all the RF coils. It has the appearance of a birdcage (figure 4); hence, its name. This coil is commonly used as a transceiver coil for imaging of the head. This type of coil is also used occasionally for imaging of the extremities, such as the knees.
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