MRI Information for IsoMed Pump Models: IsoMed: All models beginning with 8472 Reference: SynchroMed IsoMed Information for Prescribers Manual
Introduction IsoMed pump performance has not been established in >1.5 Tesla (T) magnetic resonance scanners. Patients should not have magnetic resonance imaging (MRI) using >1.5 T scanners.
Exposure of IsoMed pumps to MRI fields of 1.5 T has demonstrated no impact on pump performance and a limited effect on the quality of the diagnostic information. Testing on the IsoMed pump has established the following with regard to MRI safety and diagnostic issues:
Tissue heating adjacent to implant during MRI scans Specific absorption rate (SAR) — Presence of the pump can potentially cause a twofold increase of the local temperature rise in tissues near the pump. During a 20-minute pulse sequence in a 1.5 T GE Signa scanner with a whole-body average SAR of 1 W/kg, a temperature rise of 1 degrees C in a static phantom was observed near the pump implanted in the “abdomen” of the phantom. The temperature rise in a static phantom represents a worst case for physiological temperature rise and the 20- minute scan time is representative of a typical imaging session. Implanting the pump in other locations may result in higher temperature rises in tissues near the pump.
In the unlikely event that the patient experiences uncomfortable warmth near the pump, the MRI scan should be stopped and the scan parameters adjusted to reduce the SAR to comfortable levels.
Peripheral Nerve Stimulation during MRI scans Time-varying gradient magnetic fields — Presence of the pump may potentially cause a two-fold increase of the induced electric field in tissues near the pump. With the pump implanted in the abdomen, using pulse sequences that have dB/dt up to 20 T/ s, the measured induced electric field near the pump is below the threshold necessary to cause stimulation.
In the unlikely event that the patient reports stimulation during the scan,the proper procedure is the same as for patients without implants—stop the MRI scan and adjust the scan parameters to reduce the potential for nerve stimulation.
Static magnetic field For magnetic fields up to 1.5 T, the magnetic force and torque on the pump will be less than the force and torque due to gravity. In the unlikely event that the patient reports a slight tugging sensation at the pump implant site, an elastic garment or wrap may be used to prevent the pump from moving and reduce the sensation the patient may experience.
Image distortion The IsoMed pump will cause image dropout on MRI images in the region surrounding the pump. The extent of image artifact depends on the pulse sequence chosen with gradient echo sequences generally causing the most image dropout. Spin echo sequences will cause image dropout in a region approximately 50% larger than the pump itself, about 12 cm across, but with little image distortion or artifact beyond that region
Minimizing Image Distortion — MRI image artifact may be minimized by careful choice of pulse sequence parameters and location of the angle and location of the imaging plane. However, the reduction in image distortion obtained by adjustment of pulse sequence parameters will usually be at a cost in signal-to-noise ratio. These general principles should be followed:
– Use imaging sequences with stronger gradients for both slice and read encoding directions. Employ higher bandwidth for both radio-frequency pulse and data sampling. – Choose an orientation for read-out axis that minimizes the appearance of in-plane distortion. – Use spin echo or gradient echo MR imaging sequences with a relatively high data sampling bandwidth. – Use shorter echo time for gradient echo technique, whenever possible. – Be aware that the actual imaging slice shape can be curved in space due to the presence of the field disturbance of the pump (as stated above). – Identify the location of the implant in the patient, and when possible, orient all imaging slices away from the implanted pump.
MR healthcare professionals are advised to contact the respective manufacturer in order to obtain the latest safety information to ensure patient safety relative to the use of an MR procedure.