Know how MRI conditional labeling impacts Image Experience with SNM

Know how MRI conditional labeling impacts Image Experience with SNM

The ability to have a full body MRI with an SNM device only became available in November 2019 with Axonics followed by Medtronic in August 2020. MRIs are a common imaging modality with 1 in 9 U.S. adults obtaining an MRI yearly and over 40% of patients needing an MRI over a 15-year period (Lifetime of rechargeable SNM devices).1,2 Conditional labeling varies amongst SNM brands with parameters defined to minimize risk associated with the device such as overheating, implant damage, unintended stimulation, uncomfortable vibration and reduced image quality.

The table below shows a comparison of MRI conditions between Axonics and Medtronic to protect the prepared patient and ensure device integrity which determines maximum duration of scan times and wait time in between images.  The SAR Limit & B1+rms Limit determines the maximum exposure amount to the RF field while the Scan Time Limit caps the duration of continuous exposure to the RF field. The Wait Time allocates the minutes needed prior to another scan being performed after a 30-minute scan has been completed. Before an MRI image is performed the devices are put into MRI readiness mode by the MRI technician with the Axonics SmartMRI remote ( or Eligibility Checked using the Medtronic Programmer& Remote (Accomplished by MDT representative, SNM implantor or patient). The higher the Scanner Strength (3T) the lower the limits usually become but approximately 80% of MRI machines utilize the lesser strength (1.5T). 1

These differences in parameters affect the MRI experience and image quality. For example, the above table shows the projected approximate time to complete a 1.5T Breast Scan with Axonics (32 Minutes) versus Medtronic (143 Minutes) based on evaluation by an experienced MRI technologist from Overland, Kansas. A longer time could create a logistical nightmare especially if a patient requires conscious sedation.  In summary, the broader MRI scan conditions of Axonics potentially delivers a more simplified process for patients allowing MRI technicians to achieve the best image quality with faster overall scan times.

[1] IMV Benchmark Report MR 2018

[2] Ashish Gulve, MRI conditionality across spinal cord stimulation devices: the myths & science. NeuroNews, 17th August 2017

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