Hardware, IPGs, and MRI Conditionality

Evidence status. Device specifications and MRI labeling change frequently. This page teaches a verification workflow, not scan clearance. Use the current manufacturer MRI manual and institutional radiology policy for the exact implanted configuration.

1.Leads, contacts, and directionality

Conventional ring contacts create a circumferential field. Segmented directional leads can steer current away from an adverse-effect boundary and may widen the therapeutic window, but add programming complexity and orientation uncertainty. Contact spacing, length, number, and connector standards affect targeting, replacements, and compatibility.

Lead location remains primary. Directionality can shape an imperfect field; it cannot reliably rescue a lead outside the useful network.

2.IPG choices

Nonrechargeable generators reduce charging burden but require replacement when depleted. Rechargeable generators can reduce replacement frequency and may suit high-energy settings, young patients, or dystonia, but require dexterity, cognition, adherence, and reliable caregiver support. Constant-current and voltage-controlled systems respond differently to impedance, though clinical programming principles overlap.

Choose with the patient's lifetime pathway in mind: expected energy, body habitus, sleep position, work, travel, cognition, future MRI needs, remote programming, and likely revision strategy.

3.Failure and infection

Interrogate impedance and battery status; inspect incisions and connector sites; image the full hardware path when fracture or migration is suspected. Abrupt symptom return suggests depletion, therapy-off state, fracture, connector failure, migration, or reset. Gradual loss can reflect disease change, tolerance, target mismatch, or rising energy demand.

4.Identify the exact system

Obtain the implant card, operative notes, model numbers, lead and extension laterality, adapters, implant location, and history of revision. Determine whether any lead is abandoned, capped, fractured, partially explanted, or connected to another manufacturer's component. If records conflict, reconcile them with imaging and manufacturer technical support.

Current examples illustrate why model-level detail matters. Selected Medtronic Percept systems with eligible leads have 1.5 T and 3 T full-body pathways. Abbott Infinity systems have a specified 1.5 T pathway, restricted to cylindrical-bore horizontal-field magnets, with MRI mode on and stimulation off. Boston Scientific Vercise systems have 1.5 T pathways whose radiofrequency ceilings differ by generator, by adapter, and by whether the patient has a full system or leads only; the staged patient with leads implanted and no generator is covered by a separate condition set. NeuroPace RNS-320 has an eligible 1.5 T pathway, but on terms that invert the usual deep brain stimulation reflex: labeling requires a full-body quadrature radiofrequency transmit coil and explicitly prohibits a head or extremity transmit coil, MRI mode must be turned on before the scan, and separate head and torso B1+rms ceilings apply that have to be read off the current guidelines document. The older RNS-300M is MR Unsafe, without exception. Confirm any newer generator, including recently approved rechargeable models, against its own current manual rather than against its predecessor's. These statements are not transferable across configurations.

5.Translate labeling into a scan protocol

6.Why MRI can harm

Radiofrequency energy can heat conductive leads, especially near electrode tips. Gradient fields can induce voltage or stimulation; static fields can exert force or torque; device electronics can malfunction; image artifact can obscure anatomy. Broken, abandoned, capped, or adapted components may change eligibility, but the rule is device-specific. Many DBS configurations exclude abandoned or damaged leads; conversely, the RNS MRI manual explicitly includes specified unattached, capped, cut, or broken NeuroPace leads under its conditions, and some DBS manuals define eligible lead-only systems. Verify the exact configuration in the applicable manual. If it falls outside labeling, do not extrapolate from an intact-system pathway; involve the implanting team and radiology MR safety service in a documented risk assessment and consider alternative imaging.

7.Build a hardware passport

Give the patient a concise record with indication, manufacturer, all model numbers, implant dates, laterality, battery type, last settings, MRI status, and emergency contacts. Store the same data in a searchable chart field. Update it after every revision.

Before elective replacement, review future imaging, target performance, lead integrity, adapter needs, recharge suitability, sensing/adaptive options, and the consequences of switching ecosystems. Generator exchange is an opportunity to remove ambiguity, not create it.

8.Perioperative and emergency care

Therapeutic diathermy (shortwave, microwave, or therapeutic ultrasound) is contraindicated in DBS labeling, whether the system is on or off and including leads without a generator, because lead heating has caused serious brain injury and death. Plan electrocautery, external defibrillation, radiation therapy, dental and surgical procedures, infection evaluation, and device shutoff according to manufacturer guidance. Many blanket rules are outdated or device-specific; route decisions through a documented neuromodulation pathway.

An MRI or perioperative checklist should identify who confirms eligibility, who programs the device, what happens if the patient cannot communicate, and who restores therapy. Safety is a handoff design problem as much as a physics problem.