SU‐G‐IeP1‐06: Estimating Relative Tissue Density From Quantitative MR Images: A Novel Perspective for MRI‐Only Heterogeneity Corrected Dose Calculation

Abstract

Purpose:To explore the feasibility of extracting the relative density from quantitative MRI measurements as well as estimate a correlation between the extracted measures and CT Hounsfield units.Methods:MRI has the ability to separate water and fat signals, producing two separate images for each component. By performing appropriate corrections on the separated images, quantitative measurement of water and fat mass density can be estimated. This work aims to test this hypothesis on 1.5T.Peanut oil was used as fat‐representative, while agar as water‐representative. Gadolinium Chloride III and Sodium Chloride were added to the agar solution to adjust the relaxation times and the medium conductivity, respectively. Peanut oil was added to the agar solution with different percentages: 0%, 3%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100%. The phantom was scanned on 1.5T GE Optima 450W with the body coil using a multigradient echo sequences. Water/fat separation were performed while correcting for main field (B0) inhomogeneity and T2* relaxation time. B1+ inhomogeneities were ignored. The phantom was subsequently scanned on a Philips Brilliance CT Big Bore. MR‐corrected fat signal from all vials were normalized to 100% fat signal. CT Hounsfield values were then compared to those obtained from the normalized MR‐corrected fat values as well as to the phantom for validation.Results:Good agreement were found between CT HU and the MR‐extracted fat values (R2 = 0.98). CT HU also showed excellent agreement with the prepared fat fractions (R2=0.99). Vials with 70%, 80%, and 90% fat percentages showed inhomogeneous distributions, however their results were included for completion.Conclusion:Quantitative MRI water/fat imaging can be potentially used to extract the relative tissue density. Further in‐vivo validation are required.