Abstract

Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) is a safe non-invasive tool to study the physiological mechanisms of the human brain. MRS has the capability to provide the information regarding neurochemicals in brains of patients with neuropsychiatric disorders. Therefore, to produce measurable and interpretable information in MRI and MRS, a quality control (QC) program is required.

Magnetic field homogeneity (MFH) is an important factor for QC when the volume sizes and neurochemical levels are quantified. Poor main (B₀) MFH leads to artifacts, signal losses and broadened line widths. The American College of Radiology's (ACR) MRI QC manual mandates annual checks of MFH, suggesting tests using spectral line widths (FWHM) and phase-difference (Δϕ) maps. A new method, dubbed the bandwidth-difference (ΔBW) method, is proposed along with a prototype phantom for determining MFH. The ΔBW method is compared with standard methods and has also been tested in different model MRI systems from various manufacturers.

Direct comparisons of the data obtained using the ΔBW method demonstrated good agreement with data obtained using the linewidth method and the frequency map data provided by one MRI system manufacturer. As a result, the ΔBW method produces measurements of MFH at various Diameter Sphere Volume (DSV) values that can be obtained from a single set of phantom images. The conclusion of the study is that the accuracy of ΔBW B₀ homogeneity measurements of MFH is comparable to the other methods tested while the ease of measurement in practical clinical setting is considerably improved.