A
coil is a large inductor with a considerable dimension and a defined
wavelength, commonly used in configurations for
MR imaging. The
frequency of the
radio frequency coil is defined by the Larmor relationship.
The
MRI image quality depends on the
signal to noise ratio (SNR) of the acquired signal from the patient. Several
MR imaging coils are necessary to handle the diversity of applications. Large
coils have a large
measurement field, but low
signal intensity and vice versa (see also
coil diameter). The closer the
coil to the object, the stronger the signal - the smaller the volume, the higher the
SNR.
SNR is very important in obtaining clear images of the human body. The shape of the
coil depends on the image
sampling. The best available
homogeneity can be reached by choice of the appropriate
coil type and correct
coil positioning.
Orientation is critical to the sensitivity of the RF
coil and therefore the
coil should be perpendicular to the static
magnetic field.
RF
coils can be differentiated by there function into three general categories:
The RF signal is in the range of 10 to 100 MHz. During a typical set of clinical image measurements, the entire
frequency spectrum of interest is of the order 10 kHz, which is an extremely narrow band, considering that the center
frequency is about 100 MHz. This allows the use of single-frequency matching techniques for
coils because their inherent
bandwidth always exceeds the image
bandwidth. The
multi turn solenoid,
bird cage coil,
single turn solenoid, and
saddle coil are typically operated as the
transmitter and
receiver of RF
energy. The surface and phased array
coils are typically operated as a receive only
coil.
See also the related poll result: '
3rd party coils are better than the original manufacturer coils'
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] and 162 definitions [
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