No one MRI exam is identical. Each scan adheres to the coil’s specific capabilities, which generates high-quality images of particular body parts. In short, no coil means no photos. An MRI transmits radio frequencies to the body. The coil is responsible for receiving the signal and sending it to a computer, generating the images. The coils pose no health risks or dangers to the body.
One Design for Every Body Part
Some coils are frames that fit over the body part in need of scanning. Others are less apparent—patients won’t even notice they’re there. Some are flexible, wrapping around the body, fastened with Velcro.
Brain scans require helmet-like coils that snap in place over your face. During an upright MRI, a technician will slide the coil down over your head, much like football gear. Openings allow patients to see out during the scan.
Types of MRI Coils
Whether you’re an MRI technologist or workaround an MRI machine, you’re likely to come across more coils than you can choose from. We’ve broken down the various types of coils and their purpose:
These coils create a secondary magnetic field to distort its primary field. Gradient coils allow spatial encoding of MRI signals. Some GCs include Figure 8, Maxwell, Golay, Helmholtz, Paired Saddle, and Shielded Gradient.
RF (Radio Frequency Coils)
RF coils are both transmitters and receivers. As a transmitter, they generate oscillations or rotations perpendicular to the Bo (static main magnetic field). As a receiver, they detect MR signals.
Unlike RF coils, the surface variety is receive-only. They boast excellent signal-to-noise ratios for tissues adjacent to the coil. The further from the tissue, the less sensitive it becomes. Most technicians use surface coils for spines, shoulders, joints, and smaller body parts.
These coils provide a homogenous RF excitation across a large volume of the skin, such as in whole-body imaging. Some volume coils are smaller, ideal for the head and other extremities. Typical designs include the Birdcage, Saddle, and TEM.
Shims provide auxiliary magnetic fields to adjust the homogeneity of their primary domain. Technicians use them before operating the magnet.
Array coils are a cross between the benefits of smaller and larger coils. They span Coupled, Isolated, and Phased types.
As its title suggests, extremity coils cover ankles, wrists, elbows, shoulders, and other smaller body parts.
Coils are a combination of physics and design and play various roles in the MRI sphere. You can better equip your clinic by knowing each type of coil and understanding its purpose within your specific machine.
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