An Electrocorticography Grid with Conductive Nanoparticles in a Polymer Thick Film on an Organic Substrate Improves CT and MR Imaging

Abstract

Purpose To develop an electrocorticography (ECoG) grid by using deposition of conductive nanoparticles in a polymer thick film on an organic substrate (PTFOS) that induces minimal, if any, artifacts on computed tomographic (CT) and magnetic resonance (MR) images and is safe in terms of tissue reactivity and MR heating. Materials and Methods All procedures were approved by the Animal Care and Use Committee and complied with the Public Health Services Guide for the Care and Use of Animals. Electrical functioning of PTFOS for cortical recording and stimulation was tested in two mice. PTFOS disks were implanted in two mice; after 30 days, the tissues surrounding the implants were harvested, and tissue injury was studied by using immunostaining. Five neurosurgeons rated mechanical properties of PTFOS compared with conventional grids by using a three-level Likert scale. Temperature increases during 30 minutes of 3-T MR imaging were measured in a head phantom with no grid, a conventional grid, and a PTFOS grid. Two neuroradiologists rated artifacts on CT and MR images of a cadaveric head specimen with no grid, a conventional grid, and a PTFOS grid by using a four-level Likert scale, and the mean ratings were compared between grids. Results Oscillatory local field potentials were captured with cortical recordings. Cortical stimulations in motor cortex elicited muscle contractions. PTFOS implants caused no adverse tissue reaction. Mechanical properties were rated superior to conventional grids (χ(2) test, P < .05). The temperature increase during MR imaging for the three cases of no grid, PTFOS grid, and conventional grid was 3.84°C, 4.05°C, and 10.13°C, respectively. PTFOS induced no appreciable artifacts on CT and MR images, and PTFOS image quality was rated significantly higher than that with conventional grids (two-tailed t test, P < .05). Conclusion PTFOS grids may be an attractive alternative to conventional ECoG grids with regard to mechanical properties, 3-T MR heating profile, and CT and MR imaging artifacts. (©) RSNA, 2016 Online supplemental material is available for this article.

Figure 1:

A, Cross-sectional diagram of the prototype PTFOS grid with the electrode and trace layer (gray layer) sandwiched between two insulating dielectric layers (white layers); all three layers were deposited on gelatin film (blue layer). The relative thickness of the gelatin film is much thicker than what is shown in the schematic. B, Photograph of a PTFOS demonstrates the flexibility of the construct when it is hydrated with saline solution.

Figure 2:

Comparison of PTFOS and conventional grids at CT and MR imaging. Photographs show that the human cadaveric specimen was used for imaging, A, with no grid, B, with a standard grid, and, C, with a PTFOS grid. Axial CT images were acquired of the head specimen, D, with no grid, E, with a standard grid, and, F, with a PTFOS grid. G–I, Axial FLAIR images of the specimen were obtained with a 3-T imaging unit: The electrodes of the standard grid produced regions of signal intensity loss (arrowheads on H) that were not seen with PTFOS (I). J–L, Axial FLASH images of the specimen were obtained with a 7-T imaging unit: The standard grid resulted in a sharp peak and a slowly varying intensity distortion (arrow on K), as well as areas of signal intensity loss (arrowheads on K); these artifacts were not seen with PTFOS (L).

Figure 2:

Comparison of PTFOS and conventional grids at CT and MR imaging. Photographs show that the human cadaveric specimen was used for imaging, A, with no grid, B, with a standard grid, and, C, with a PTFOS grid. Axial CT images were acquired of the head specimen, D, with no grid, E, with a standard grid, and, F, with a PTFOS grid. G–I, Axial FLAIR images of the specimen were obtained with a 3-T imaging unit: The electrodes of the standard grid produced regions of signal intensity loss (arrowheads on H) that were not seen with PTFOS (I). J–L, Axial FLASH images of the specimen were obtained with a 7-T imaging unit: The standard grid resulted in a sharp peak and a slowly varying intensity distortion (arrow on K), as well as areas of signal intensity loss (arrowheads on K); these artifacts were not seen with PTFOS (L).