Development of a novel task-based functional magnetic resonance imaging phantom based on a bubble-compression...

Area of Science:

• Biomedical Engineering
• Neuroimaging
• Magnetic Resonance Imaging

Background:

• Previous functional magnetic resonance imaging (fMRI) phantoms had limitations including complex circuitry, single signal-change rates, and unrealistic T2* values.
• These limitations hindered accurate validation of task-based fMRI studies, particularly those using gradient-echo echo-planar imaging (GRE-EPI).

Purpose of the Study:

• To develop an innovative phantom for task-based fMRI (GRE-EPI) with bioequivalent T1 and T2* values to living human brain gray matter.
• To implement a novel method for controlling the rate of signal change within the phantom.

Main Methods:

• A gel phantom with brain-like T1 and T2* values was created, containing microscopic air bubbles within a container with multiple syringes.
• Signal change was controlled by altering water pressure, which modified bubble size and T2* values.
• The study investigated percent signal change, derived an equation for reproducibility, compared phantom samples, and assessed changes in relaxation time and bubble size over time.

Main Results:

• The gel phantom exhibited T1 and T2* values comparable to gray matter.
• Reproducible percent signal changes (0%-13.51%) were achieved, controlled by water pressure.
• An equation was derived to approximate arbitrary percent signal changes with high reproducibility (y = 0.000008x³ - 0.000771x² + 0.034222x - 0.026054).
• T2* values increased with pressure due to bubble size changes, mimicking in-vivo fMRI signal changes.
• The phantom remained stable for 60 days, though bubble size changed after 21 days.

Conclusions:

• A novel phantom for fMRI was successfully developed, capable of reproducing blood-oxygen-level-dependent (BOLD) like signal changes with bioequivalent T1 and T2* values.
• The phantom utilizes an innovative method to control percent signal change by compressing air, validating fMRI using GRE-EPI.
• This tool is expected to significantly advance task-based fMRI research by providing a more realistic simulation of human brain scanning.