Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Medical Biophysics

Supervisor

Ravi Menon

Abstract

Blood Oxygen Level Dependent (BOLD) functional Magnetic Resonance Imaging (fMRI) utilizes pulse sequences sensitive to changes in concentration of deoxyhemoglobin to indirectly measure neural activity. Sequences used for BOLD are sensitive to magnetic susceptibility differences that may cause signal voids. Our lab has designed an awake marmoset head coil that eliminates confounds associated with imaging an animal under anesthesia. This design requires a head chamber attached to an animal’s skull with a cement that may cause a susceptibility artifact. Motivation behind this project was to find an MRI compatible cement that remains secure to the skull with minimal artifacts. Four commercially available cements DuoLink Universal, BisFil, BisCem and CoreFlo DC were scanned with Spin-Echo (SE), Gradient-Echo (GE), and Gradient-Echo Echo Planar Imaging (GE-EPI) sequences on brain mimicking phantoms. Additionally, each cement was attached to bone and attempted to be removed. Only CoreFlo DC passed both criteria, being deemed MR compatible.

Summary for Lay Audience

Blood Oxygen Level Dependent (BOLD) functional Magnetic Resonance Imaging (fMRI) is an imaging technique that is sensitive to changes in concentration of deoxyhemoglobin. When neural activity occurs, there is a change in the amount of blood flow, and thus concentrations of deoxyhemoglobin, the oxygen free protein found in red blood cells. The ability to detect changes in deoxyhemoglobin concentration, allows us to measure the BOLD signal which is an indirect measure of neural activity. When neural activity occurs, the BOLD signal lags behind, proportional to the amount of neural activity occurring at one time.

BOLD fMRI is sensitive to magnetic susceptibility differences of substances. Magnetic susceptibility refers to the amount a substance is magnetized in an external magnetic field. While BOLD imaging is measuring the microscopic magnetic susceptibility differences, between oxy and deoxyhemoglobin, there are larger scale macroscopic susceptibility differences that may occur, such as between bone, air, and tissue. These macroscopic susceptibility differences can lead to portions of an image with signal loss, appearing blacked out.

In fMRI research, animal models are used to answer fundamental or experimental questions. Our lab has designed an awake marmoset head coil that minimizes motion and allows for imaging without anesthesia, as anesthesia can reduce the BOLD signal, among other confounds. This design requires a head chamber to fit in our head coil that is attached to an animal’s head via a cement. This cement, however, could produce a susceptibility artifact, leading to signal loss. The goal of this project was to find an MRI compatible cement that produces minimal artifacts and remains secure to the skull.

Four commercially available cements, DuoLink Universal, BisFil, BisCem, and CoreFlo DC were each attached to brain mimicking phantoms. Each cement was scanned to visualize if any artifacts were present. The four cements were then attached to bone and were attempted to be removed over a six-day period. Only CoreFlo DC produced minimal artifacts and remained secure to bone. In conclusion, CoreFlo DC was deemed MRI compatible and capable of being the cement used for head chamber placement, allowing for functional imaging.

Download

Share

COinS