MRI Scanner Manufacturers & Implants... MROC... An Evolving Story

For many years, I have been a huge proponent of Philips' ScanWise product (even when it seemed that the company wasn't). It was the first -and for many years, only- tool that allowed users to constrain both Radio Frequency (RF) and Time-Varying Gradient (TVG) output to specific threshold values that the user typed-in, and provided some customized visualizations for an implant or device's specific spatial field gradient (SFG) limitations.

This was -in particular- tremendously helpful for RF, which is otherwise laborious to modify to hit the aggressive MR Conditional conditions set by some device manufacturers, such as 0.5 W/kg. And it was absolutely essential for meeting restrictive TVG conditions because most MR systems have no quantitative readout, much less control, for TVG.

ScanWise essentially let the operator type in the parameter for an MR Conditional implant or device, and the scanner would make all necessary modifications to a pulse sequence to make sure that the specified RF and TVG limits were not exceeded! In a world of rapidly growing implant & device complexity, ScanWise was (and is) a very welcome tool of simplicity for the users, providing an assurance that MR Conditional conditions are being met, even when a technologist may not have the time (or capability) to manually create a compliant set of pulse sequences.

In the years after ScanWise came out, I remained shocked by two things... One was the nonchalance with which Philips treated this product when I saw it as a godsend for sites struggling with scanning implants. I wanted them to shout it from the rooftops, and instead it seemed to me that they only whispered it to the customers who had already bought their systems. The second surprise was at how slowly (and often, poorly) the other OEMs replicated ScanWise functions for their systems.

In 2022 the IEC (International Electrotechnical Commission) released an updated version of the 60601-2-33 standard for MRI equipment safety (edition 4.0), which contained a new provision that defined a toolset for MR Equipment Output Control (MROC... pronounced "EM-rock"... don't ask me where the 'E' from equipment went... 🤷🏼) which established minimum function parameters which effectively said 'hey, ScanWise is the minimum way to do this.' At RSNA this past week I saw a few MRI manufacturers' new versions of MROC tools for implants, and I think others in the MRI world are now catching up to Philips... very quickly.

So I thought I'd share with you an ideal list of functions and features that an MROC tool, like ScanWise, should have. This list is a collection of ideas from Kellye Mantooth RT(R)(MR), MRSO(MRSC), MRSE(MRSC) and me. It is my hope that this list will push all the MRI manufacturers to improve the functionality and utility of their MROC tools. As far as I'm concerned, if an MRI safety 'arms race' begins among the OEMs, that might be the best of all possible outcomes!

MROC General Controls

There are a number of ways in which the mechanics of the implant or device data could be improved to acknowledge that we're scanning a patient, in whom there may be multiple different devices, each with multiple different exposure-based conditions or anatomical 'stations,' recognizing that the body part being imaged near isocenter of the MRI scanner may have enormous impact on what the implant is (or is not) being exposed to. All of the current products I've seen appear to have the capacity to manage conditions for only a single implant, and they all lack positional awareness or smart landmarking.

• It is increasingly common that patients have 2, 3, or more implants. MROC tools should have the capability to accept information and identifying details for multiple implants, and should have the capability of identifying the most stringent conditions from among the identified implants, and setting the exam controls accordingly.

• There are companies, like Medtronic, that have healthcare professional-accessible databases of the patients with Medtronic active cardiac devices (pacemakers and ICDs). What if instead of typing in all the details, manually, the scanner could simply download the implant specifics for that specific patient, with all the MR Conditional conditions, directly and use that data to inform the MROC tool's function?

• I'd also love if the MROC tools had the capability to let the radiographer show the MRI scanner where in the patient each implant or foreign body is. I'd love for the MRI radiographer to essentially be able to draw-in the position of a pacemaker, or DBS, onto a virtual anatomic model. That 'virtual implant' could then be identified and tagged with its conditions. [N.B., if you've ever used Dr. Emanuel Kanal's MagnetVision app, you have seen a higher-end version of what I'm imaging for these MROC tools.]

• It is also increasingly common that implants have multiple different sets of anatomic-station based conditions depending on what body part is being scanned. It's common for a single implant to have conditions for say head & neck, vs. thorax, arms, and pelvis, vs. legs. MROC tools should have the capability to have this information input, and the intelligence to know what body part is being scanned (in order to identify what set of conditions to apply to that specific exam).

• There's also FDA guidance to implant and device manufacturers about not needing to worry about heating or vibration, or neuroelectric stimulation effects if an implant is wholly outside the bore. If the MRI scanner knew where in the patient an implant was (because Medtronic, or the tech, told it so), the rough height of the patient (already required for SAR calculations), and knew what body part was at center (which the scanner needs to know for the scan), then the scanner should be able to tell the user that RF or TVG restrictions aren't going to provide any safety benefit when the implant is entirely outside of the volumes of those depositions. As it stands today, none of these MROC tools are 'positionally aware,' meaning that inputting a set of restrictive conditions for an intercranial pressure (ICP) monitor for an ankle scan on the patient will result in a severely throttled (for RF and / or TVG) ankle exam, even though the ICP monitor will be well outside the bore, and not subject to meaningful RF or TVG energies. Restricting the ankle exam's RF or TVG based on conditions for the ICP monitor only increases exam time and / or decreases image quality without any associated patient safety benefit.

• And if we're inputting all this patient-specific device information, what happens to it after the scan? Does it stay attached to the patient identifier, or does the next MR tech have to do this all over again? Not a big deal if it's an automated task, but a big pain in the butt if it all has to be done manually.

MROC RF Controls

Governing the transmitted RF energies associated with MR scans is perhaps the single most consequential, and most frequently used feature of ScanWise and the new cohort of MROC tools.

• The existing tools that I'm aware of can control RF for both W/kg for SAR values, and µT for B1+rms. Some let you specify RF 'Normal Mode' in the MROC tool, as well (which I think is a good idea, because often that's specified in the MR Conditional conditions). What I don't think any of them can currently do is let you specify "and" or "or" or "preferred" operators for SAR or B1+rms, to let the machine either choose the most conservative or most permissive version of the two-condition labels. Some require the user to only pick one or the other, others let you input both values (but I'm not sure which one governs when they -invariably- will describe different practical limits for any given MR study).

• An MROC tool should also let the user indicate whether time of completion or image quality is of greater importance for a particular study. If a patient with a disabled ("MR Mode") neuro stimulator must have a study modified by the MROC tool to get below 0.5 W/kg, the user should help direct whether speed is the greater concern (because of the patient's difficulty tolerating a long exam), or if image quality is. A lower-SAR sequence that lasts 10 minutes for a patient who can only hold still for 3 minutes isn't helping anyone.

• An MROC tool should let the user select either quadrature / circularly polarized (CP) or RF shimmed options in the tool. The drive mode is a very frequently occurring MR Conditional condition.

• MR Conditions for many more contemporary devices also include restrictions on any or all of the following time elements: Maximum continuous acquisition (i.e., RF exposure), Minimum intervening pause (i.e., cool-down period), and Maximum total cumulative acquisition time. An MROC tool should minimally inform the user about changes to a protocol that would be necessary to comply with total cumulative acquisition time, and prompt the user to start the indicated timed cool-down period when the next pulse sequence would push the continuous (or cumulative, up to that point) scan time in excess of what the label indicates.

MROC Time-Varying Gradient Controls

• An MROC tool should allow users to define limits on either / both dB/dt (T/s) and slew rate (T/m/s), as well as TVG 'Normal Mode.'

MROC Magnetic Field Controls

This is a bit of a misnomer, because unlike RF and TVG, MR systems can't manipulate the field strength or spatial field gradient (SFG) for any study. What they do do, however, is provide spatial information for specific SFG tolerances, and the recommendation, below, is based on that functionality.

• MROC tools should provide a scaled grid superimposed on their diagrams to help MR radiographers better understand the distances from bore walls and face of the gantry of a specific device's conditional threshold. Grids or reference distances should be provided from the bore wall, and not from a central Z-axis, because that's not a physical location that an MR tech can reference when placing a patient.

I also believe that risk vs. benefit is ultimately the domain of the supervising physician, and there ought to be the opportunity to override any limit imposed on conventional MR system operation by one of these MROC tools.

At this point, while Philips Imaging's ScanWise has been the unequivocal market-leader for many years, the products I saw from Siemens Healthineers and United Imaging - North America were certainly competitive. I didn't get to see if the GE HealthCare product (which I found quite under-whelming last year) has had a meaningful upgrade, and I've not seen whether Canon Inc. or FUJIFILM Holdings America Corporation even have MROC-type product offerings at this point.

If you have seen demos or -even better- have used one of these implant condition-limiting tools from any of the manufacturers, I'd love to hear your thoughts!

If you would prefer to listen to an AI "podcasted" version of this article, click this link: https://notebooklm.google.com/notebook/935283bb-5bcd-4889-90a8-9e290a34636d/audio