Abstract
BackgroundAgar has been commonly used as one of the materials to fabricate magnetic resonance imaging phantoms in the past few decades. In this study, eleven agar gel phantoms with different iron (III) oxide (Fe2O3) masses were prepared. This study was aimed to evaluate the signal-to-noise ratio (SNR) uniformity and stability of agar gel phantoms with and without the addition of Fe2O3 at two different time points (TPs). Fe2O3 powder was used as a relaxation modifier to manipulate and produce various SNR, T1 and T2 values. These phantoms were scanned using turbo spin echo pulse sequence to produce T1- and T2-measurement images. The SNR was then computed by plotting 1, 3 and 25 regions of interest on the images using ImageJ software. The T1 and T2 relaxation equations were then fitted to the experimental results of SNR versus TR and SNR versus TE curves for the determination of saturation (SNRo), T1 and T2 values.ResultsThe results demonstrated that the agar gel phantoms were able to maintain SNR uniformity but not SNR stability after 4 weeks of phantom preparation. The change in the water content and microstructure of the phantoms have no significant effect on T2 relaxation but on T1 relaxation. The T1 and T2 of the agar gel phantoms were minimally affected although there was a systemic increase in the content of the Fe2O3 powder.ConclusionsIt can be concluded that the agar gel phantoms exhibited the characteristics of SNR uniformity, but they showed instability of SNR at TP2. The Fe2O3 in powder form is not an effective relaxation modifier to reduce the T1 and T2 when it is introduced into the agar gel phantoms. Dissolved nanosized particles should be the focus of future studies.
Highlights
Agar has been commonly used as one of the materials to fabricate magnetic resonance imaging phantoms in the past few decades
The T2 curves for all agar gel phantoms exhibit an exponentially decreasing trend as Echo time (TE) is increased while Repetition time (TR) is fixed at 2000 ms, while for distilled water phantom, the trend is different from the phantoms but consistent among all Region of interest (ROI) and at both Time point (TP)
It can be summarized that all agar gel phantoms show similar trend of T1 and T2 relaxations for all ROIs and at both TP1 and TP2 as indicated by the overlapping of the T1 and T2 curves
Summary
Agar has been commonly used as one of the materials to fabricate magnetic resonance imaging phantoms in the past few decades. Fe2O3 powder was used as a relaxation modifier to manipulate and produce various SNR, T1 and T2 values These phantoms were scanned using turbo spin echo pulse sequence to produce T1- and T2-measurement images. MRI phantom has developed a new role in the standardization protocol of quantitative MRI (qMRI) biomarkers. Repeatability and reproducibility of qMRI biomarkers, the use of phantom is crucial. Basic imaging parameters, such as SNR and relaxation times, should be acquired from the MRI phantom and established as part of the quality assurance program for qMRI [8]. It is crucial to obtain the practical T1 and T2 for agar to investigate its suitability as a phantom material [3]
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