Ask the Expert
ScanMed has become known for our depth of expertise. When we say we deliver experience, we mean it. Our highly accredited professionals bring a level of experience and knowledge to the table that is unsurpassed in our field. Contact us today to submit your question on MRI coils and technology and our experts will provide you with the insights and answers you are looking for.
Q: Are uneven fat/sat issues always a MRI coil issue or can the scanner be the cause?
A: Good question as this one comes up frequently. Fat Sat is dependent upon a very homogeneous magnetic field and as you probably know that field homogeneity commonly suffers near the bore wall. In fact, most scanners have different homogeneity specs to which they can be adjusted, the highest level reserved for spectroscopy. Often, the scanner is not adjusted to the highest homogeneity standard and this degrades the quality or effectiveness of Fat Sat as the coil and patient tissue move closer to the bore wall. Your FSE should be able to tell you how far from the bore wall the field is out of spec for such sequences as Fat Sat. Coils can also degrade Fat Sat if they are not adequately decoupled or detuned during the transmit pulse of the MRI sequence, or alternatively if their multiple receive elements are not designed to yield uniform sensitivity/brightness from a common imaging volume. So a poor design or a defective coil can degrade the Fat Sat effectiveness. If the coil worked before but it doesn’t work now, then likely it is the coil, but don’t hesitate to have the field homogeneity (shim) checked either.
Q: Is there a certain component or piece within a MRI coil that tends to break more often than others?
A: The most common failure mode that we see as trained coil designers and repair staff are manufacturing defects such as solder joints. These are often quite difficult to locate in complex coils or foam coated coils but we have created processes that locate them and validate the repairs. Mechanical failure of cables is common as are active components such as decoupling diodes, solid state switches and pre-amplifiers.
Q: How often should we/local field engineer test our coils to ensure they are working properly?
A: That really depends on your sites’ policies and accreditation criteria, but from a pure engineering stand-point, a monthly QA test with phantoms should be the minimum frequency. Many sites test their head coil every morning during start-up just to ensure that the system and main coil are within normal operating parameters.
Q: If we upgrade our MRI scanner, is it possible to upgrade our current coils?
A: Typically no and it technically isn’t allowed according to the FDA unless the company upgrading the coils is a registered and certified coil designer and manufacturer/remanufacturer that complies with the ISO13485 standards for coil design and manufacturing. If substantial changes are made, then FDA 510(k) filing is likely warranted. ScanMed is such a company and we can and do occasionally upgrade coils.
Q: Is an 8 channel coil better than a 4 channel coil since it is more channels?
A: I don’t mean to be glib or Bill Clinton, but we have to define “better”. If better means the image quality or the speed of acquisition is improved, then, yes, 8 channels are typically better than 4. Be careful with the use of the term channel as well. Channel refers to the receiver pathway of the MRI system. For example, a scanner is often upgraded from a 4 to an 8 channel system; hence, up to 8 signal paths can be acquired and processed simultaneously thereby shortening acquisition time and/or improving image quality – but not always! We refer to the element of a coil as being the basic signal generating component of a coil or coil array so an 8 element coil will interface with an 8 channel system with a one-to-one correspondence between the two and typically improve the performance of a similar sized or configured coil with only 4 elements – and yes, a 4 element coil can operate on an 8 channel system by utilizing only 4 of the system channels. Be careful on coil selections. Ask how many ELEMENTS are in the coil, not how-many-channel-scanner it can operate on. Finally, we have seen many a four channel or quadrature array coil that outperforms 8 element coils in the same anatomy due to the 8 element coil’s inferior design compared to a better designed quadrature coil. Proof is in the testing. Make certain that your 8 element coil provides a better SNR than the old one before accepting the purchase order!
Q: I hear a lot about surface coils, volume coils, phased array coils, and matrix coils. What is the difference between them? Sometimes I don’t feel so smart when these terms are tossed around.
A: Don’t feel too bad as the industry has evolved with many cooks in the kitchen or many designers and marketers creating their own lingo. I explained this in a doctoral record of study at Texas A&M University in 1990, so I’ll borrow from that record. Surface coils refers to those basic resonating elements that are typically flat or slightly curved to lay against desired patient anatomy. These are the earliest version of independent receiver antennae that worked in conjunction with the MRI transmit body coil. Later, these surface coils were paired, then bunched to create an “array” of elements, each producing its own MRI signal received from the target anatomy. These multi-element coils then connect to a multi-receiver or x-channel MRI system whereby x can be 4,6,8,16, 32 or even larger numbers of channels today. The term “phased array” is purely a marketing term for these multi-element coils – as opposed to the true antenna engineering definition of multiple antennae configured to focus their sensitivity profiles using phase modulated sources or receiver templates. Matrix coils are another marketing term coined by Siemens for arrays of elements arranged in overlapping rows and columns, each element generating its own MRI signal received from its nearby target volume. Volume coils are configurations of coil elements that partially or wholly surround a target volume; hence, they take on a hollow 3D shape of sorts such as a head or knee coil.
Q: We have a head coil that produces an artifact every once in a while. The artifact looks like lines running through the image. Am I doing something wrong?
A: It is likely that you are not doing something wrong unless you are leaving the door ajar while running the scan. Next suspect is the shielding of that door or other leak in the RF room followed by a potential intermittent RF energy source within the scan room or the coil (such as oscillatory preamplifiers). This is a tough one that can only be determined by testing and eliminating each and every suspect. The coil is the easiest of the list to determine whether it is intermittent and that isn’t truly an easy task as intermittent failures of any type take simulations, fixturing and often a fair amount of time and knowledge – something that the ScanMed team has. ScanMed also has PhD systems engineers and experienced MRI technologists that can help diagnose and find these problems.
Q: One of the coils on our Philips scanner gives an error that says “Unknown Coil”. Sometimes this goes away if I reposition the patient, or remove the connector and plug this back in. Is this something I can fix myself? I really need some help because our imaging center can’t afford the $62,000 for a replacement coil.
A: This is not a totally uncommon error code, and it is certainly a problem in your coil. As with any intermittent, such as discussed previously, it takes bench fixturing, excitation and measurements, and knowledge about the coil codes. Bad news is that few have this expertise and equipment. Good news is that ScanMed can repair this coil for a low price fixed fee and even do so in a guaranteed time-frame as short as same day service.
Q: We have an Hitachi Aperto scanner. I know these units are not sold in the U.S., but can you still repair these coils?
A: Yes, we have a catalog of data sets and technical information for all the Aperto coils and pretty much all manufacturer’s coils. Give us a call or email at email@example.com and we’ll get it handled for you and assist in the international shipping and customs clearance process.