Receive-Only RF Coils are a type of coil that’s used in MRI (Magnetic Resonance Imaging) systems.
A Receive-Only RF coil is crucial for capturing radio frequency signals emitted by hydrogen nuclei (protons) in a patient’s body when they are excited by a primary magnetic field and RF energy pulses. Receive-Only RF coils are only capable of the reception function when are placed close to a patient’s body. RF Transmission coils are of the birdcage or TEM variety.
The most simple form of Receive-Only RF coils consist of a single loop design. After RF-stimulation, changes in magnetic flux are generated by the precessions of net nuclear magnetization within the subject. This includes a small current within the coil, which is in accordance with Faraday’s Law. Faraday’s Law of Induction is a law of electromagnetism that predicts how a magnetic field will interact with an electric circuit to produce emf (electromotive force.)
The tiny received MR signal is measured in microvolts. It’s then amplified, digitized and processed to extract the frequency, phase and amplitude information. This allows construction of the MR image.
There are quite a few loop coil configurations. The majority of the simpler single coils are linearly polarized, as are those arrayed in a plane. They receive the components of an MR signal in a single direction only. However, there are planar coils that are of more complex design, as are simple loop coils in 3D arrays. These are circularly polarized and capable of quadrature detection, which offers an improvement in signal-to-noise by a factor of √2 (≈ 1.41) compared to that of linearly polarized coils.
Whether yours has an LP or CP coil type, both the coil size and the distance from the object imaged are critical determinants of coil sensitivity and the signal-to-noise ration.
Typically, the penetration depth for reception from a simple loop RF surface coil is only 50-75% of the diameter of the coil. As a result of this underlying physics, currently most MR signal detection uses large arrays of small loop coils on or close to the patient.
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