MRI endoscopy using intrinsically localized probes

Abstract

Magnetic resonance imaging (MRI) is traditionally performed with fixed externally applied gradient magnetic fields and is hence intrinsically locked to the laboratory frame of reference (FoR). Here a method for high-resolution MRI that employs active, catheter-based, tiny internal probes that utilize the spatial properties of the probe itself for localization is proposed and demonstrated at 3 T. Because these properties are intrinsic to the probe, they move with it, transforming MRI from the laboratory FoR to the FoR of the device itself, analogous to an endoscope. The "MRI endoscope" can utilize loop coils and loopless antennas with modified sensitivity, in combination with adiabatic excitation by the device itself, to restrict the MRI sensitivity to a disk-shaped plane a few mm thick. Excitation with the MRI endoscope limits the eddy currents induced in the sample to an excited volume whose size is orders of magnitude below that excited by a conventional body MRI coil. Heat testing shows maximum local temperature increases of <1 degrees C during MRI, within regulatory guidelines. The method is demonstrated in a kiwifruit, in intact porcine and rabbit aortas, and in an atherosclerotic human iliac artery specimen, with in-plane resolution as small as 80 microm and 1.5-5 mm slice thickness.

Implanted, inductively-coupled, radiofrequency coils fabricated on flexible polymeric material: Application to in vivo rat brain MRI at 7T

“…Dedicated microtechnological fabrication processes can also be used to improve the RF field pattern and provide better flexibility and mechanical properties [22][23][24][25][26][27][28]. Alternatively, catheter-based coils can be loopless, consisting of a dipole antenna at the tip of a coaxial cable [29][30][31][32][33]. This principle provides further coil diameter reduction, increased flexibility and improved field pattern near the coil conductor.…”

Radiofrequency Ablation, MR Thermometry, and High-Spatial-Resolution MR Parametric Imaging with a Single, Minimally Invasive Device

“…Furthermore, it requires fast high-resolution imaging to locate the applicator, to demarcate the target tissue and to monitor the energy delivery, as well to monitor the tissue’s response at a sufficiently high spatial resolution in order to minimize potential collateral damage. The recent introduction of intravascular MRI (IVMRI) probes at magnetic field strengths of 3T and higher affords 80–300 μm transluminal resolution at speeds of up to several frames-per-second (5–8). Until now, the use of these probes was primarily limited to imaging.…”

SNR in MI Catheter Receivers for MRI

“…NTERNAL magnetic resonance imaging (MRI) using small coils has been demonstrated [1][2][3], but clinical acceptance is relatively slow. There are difficulties associated with delivery into the patient, MR compatibility of endoscopic tools and the non-uniform sensitivity of the coils.…”