When we talk to people who are looking for an MRI for their hospital, clinic or practice, they always want more information about MRI coils—what they actually do, what types are available and which ones are right for the job. It’s actually one of the most important considerations when buying a new or pre-owned MRI. To that end, here’s a guide to everything you want (and need) to know about MRI channel coils.
What is a coil?A radiofrequency coil is a major part of the RF system in the magnetic frequency imaging hardware.
There are two kinds of coils: volume coils (phased array coils or matrix coils) and surface coils.
Volume coils are designed to provide a homogenous RF excitation across a large volume, although there are smaller ones constructed for imaging the head and other extremities. They partially or wholly surround a target volume. They take on a hollow 3D shape found in a head or knee coil.
Surface coils are the earliest version of independent receiver antennae that worked in conjunction with the MRI transmit body coil. They provide a very high RF sensitivity over a small region of interest and come in a variety of sizes. These coils lay against desired patient anatomy. A surface coil:
•Has basic resonating elements
• Is typically flat
• Can be slightly curved• Surface coils can be paired and then aligned to create an “array” of elements, each producing its own MRI signal received from the target anatomy.
• These are multi-element coils
• They are connected to a multi-receiver or x-channel MRI system
•Coils would be able to offer 4,6,8,16, 32 or even larger numbers of channels as required by customer and designed by OEM or a third party coil provider
What are “Phased Array” coils?
These are multi-element coils which are “configured to focus their sensitivity profiles using phase modulated sources or receiver templates.”
What are Matrix coils?
•This is actually a marketing term used to describe an array of elements.
•Placement is in overlapping rows and columns
• Each element generates its own MRI signal received from its nearby target volume
What does “Channel” mean?
• A channel refers to the receiver pathway of the MRI system. There are 4 channel systems and 8 channel systems. If you upgrade an MRI from 4 to an 8 channel this will provide for 8 signal paths and shorten acquisition time.
What is a coil element?
• A coil element is the basic signal-generating component of a coil or coil array
• When reviewing coils, be sure to ask how many elements are in the coil
• Most used and refurbished MRI systems offer 8 or 4 channel coils
4 Channel Facts and Benefits
• Many 4 channel coils can outperform 8 element coils in the same anatomy. This can only happen if the 8 element coil has an inferior design, compared to a better designed four channel coil
• A 4 element coil can operate on an 8 channel system by utilizing only 4 of the system channels.
8 Channel Facts and Benefits
• It can delivers better image quality
• It improves the speed of acquisition
• An 8 element coil will interface with an 8 channel system with a one-to-one correspondence between the two
Before You Buy
• If you are looking at an 8 channel or 4 channel make certain that your 8 element coil provides a better SNR than the old one before buying the coil.
Some blogs you may have missed:
- Top 4 Considerations Before Installing an MRI
- Before You Order That MRI: A Checklist
- MRI's - Top 5 Things to Consider Before Buying a MRI
- Your MRI and Cryogen Venting
- Free MRI Resources
Meet the author: Vikki Harmonay