An interventional MRI guidewire combining profile and tip conspicuity for catheterization at 0.55T

Abstract

Purpose:We describe a clinical grade, "active", monopole antenna-based metallic guidewire that has a continuous shaft-to-tip image profile, a pre-shaped tip-curve, standard 0.89 mm (0.035 ′′ ) outer diameter, and a detachable connector for catheter exchange during cardiovascular catheterization at 0.55T. Methods: Electromagnetic simulations were performed to characterize the magnetic field around the antenna whip for continuous tip visibility. The active guidewire was manufactured using medical grade materials in an ISO Class 7 cleanroom. RF-induced heating of the active guidewire prototype was tested in one gel phantom per ASTM 2182-19a, alone and in tandem with clinical metal-braided catheters. Real-time MRI visibility was tested in one gel phantom and in-vivo in two swine. Mechanical performance was compared with commercial equivalents. Results:The active guidewire provided continuous "profile" shaft and tip visibility in-vitro and in-vivo, analogous to guidewire shaft-and-tip profiles under X-ray. The MRI signal signature matched simulation results. Maximum unscaled RF-induced temperature rise was 5.2 • C and 6.5 • C (3.47 W/kg local background specific absorption rate), alone and in tandem with a steel-braided catheter, respectively. Mechanical characteristics matched commercial comparator guidewires. Conclusion:The active guidewire was clearly visible via real-time MRI at 0.55T and exhibits a favorable geometric sensitivity profile depicting the guidewire continuously from shaft-to-tip including a unique curved-tip signature. RF-induced heating is clinically acceptable. This design allows safe device navigation through luminal structures and heart chambers. The detachable connector allows delivery and exchange of cardiovascular catheters while maintaining guidewire position. This enhanced guidewire design affords the expected performance of X-ray guidewires during human MRI catheterization.

Cardiac MRI at Low Field Strengths

“…Design constraints related to RF-induced heating are eased at 0.55 T, allowing for increased flexibility in device configuration. A safe-by-design active guidewire with continuous shaft-to-tip profile that is mechanically comparable to off-the-shelf devices has been demonstrated for 0.55 T. 111 Additionally, a new technique of thin-film printed circuitry which can fabricate RF antenna components direction onto metallic surfaces with conductive ink has been demonstrated for needle devices at 0.55 T. 112 Most recently, interventional studies on a commercial 0.55 T system has demonstrated promising real-time imaging results despite the reduced gradient performance. Armstrong et al demonstrated cardiac catheterization, angioplasty, and stenting on the commercial 0.55 T (Fig.…”

“…Design constraints related to RF‐induced heating are eased at 0.55 T, allowing for increased flexibility in device configuration. A safe‐by‐design active guidewire with continuous shaft‐to‐tip profile that is mechanically comparable to off‐the‐shelf devices has been demonstrated for 0.55 T 111 . Additionally, a new technique of thin‐film printed circuitry which can fabricate RF antenna components direction onto metallic surfaces with conductive ink has been demonstrated for needle devices at 0.55 T 112 …”

Interventional cardiovascular magnetic resonance: state-of-the-art

“…Conspicuity is provided by the inclusion of iron oxide powder markers. An active guidewire, in commercial development in collaboration with NHLBI ( TRACR , Transmural Systems, Andover, Massachusetts), uses a modified loopless antennae to ensure conspicuity of the guidewire along its length [ 44 ] (see section on device visualization below).…”

Interventional device tracking under MRI via alternating current controlled inhomogeneities

“…Several types of device markers have been proposed to enhance the MRI visibility of interventional medical devices: passive, 21–24 active, 25–28 and semi‐active (resonant) markers 29,30 . Another approach generates local field disruption using tiny inductors, wherein a direct current (DC) is applied to the conductive wire wound around the device 31 .…”