MRI- Radiofrequency Coils | Volume, surface, phased-array Coil

MRI- Radiofrequency colis, volume, surface, phased array
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Radiofrequency Coils

A loop of wire of the coil. Radiofrequency (RF) coils are used to transmit RF pulses into the patient and to receive the signals from the patient.RF coils are transmitters, receivers, or both (transceivers). Energy is transmitted in the form of short intense bursts of radio frequencies known as radiofrequency pulses. These RF pulses cause phase coherence and flip some of the protons from a low energy state to a high energy state. An RF pulse that causes the net magnetization vector to flip away from the longitudinal axis by 90 degrees is called a 90 degree RF pulse. Rotating transverse magnetization (TM) induces a current in the receiver coil, which forms the MR signal. Based on design RF coils can be divided into volume coil, surface coil, and phased-array coil.

Volume Coil

A volume coil typically surrounds either the whole body or a specific region. It provides a homogeneous B1 field (RF field perpendicular to main field B0) in the imaging volume circumscribed by the coil. However, the SNR of the images obtained with volume coil is usually less than that obtained with surface or phased-array coil. Body and head coils are examples of volume coils. The main coil of the magnet, also called the body coil, is a volume coil. It is located in the magnet bore as the innermost ring.

Surface Coil

A surface coil placed on the surface of a region of interest to acquire images with very high SNR.High SNR is obtained at the cost of limited volume coverage and decreasing B1 homogeneity with distance from the coil. Surface coils are operated in receive-only mode and RF transmission is performed separately, typically by a volume coil surface coils can be either flexible (can be wrapped around the region of interest) or rigid in design.

Phased-array (PA) Coil

A phased array coil consists of two or more geometrically aligned surface coils used in conjunction. This coil combines the advantages of a surface coil(highSNR) and a volume coil(large FOV). The advantages of high SNR and resolution obtained from a PA coil may be traded off for reduced scan time by decreasing the number of signal averages. Depending on the number of surface coil elements PA coils are called 4,6,8 or 32 channel PA coils. The increasing number of elements allows faster dynamic scans with the consequent reduction of motion artifacts. Computers and Accessories Computer systems control every application. They perform functions of data collection and manipulation, image, viewing, storage, retrieval, and documentation

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