Abstract
We evaluated dual-echo Dixon in-phase and out-of-phase (IP-OP), chemical shift imaging (CSI), and (1)H MRS (hydrogen MR spectroscopy) in estimating fat content (FC) in phantoms and in livers of mice. Phantoms were made according to the volume percentage of fat ranging from 0% to 100%. The three MR methods were performed to measure FC in phantoms and in livers of obese leptin-deficient (ob/ob), human BSCL2/seipin gene knockout (SKO), and wild-type (WT) mice. The results were compared with known FC in phantoms and to a reference standard from mice by histological semiautomatic vacuole segmentation (HIS-S) procedure and liver lipid (LL) chemical analysis. In phantoms, CSI underestimated FC from 50% to 100%, to a lesser extent than IP-OP. In vivo, liver FC in ob/ob and SKO mice measured by the three MR methods were all significantly higher than that in WT mice. Liver FC measured by IP-OP were significantly lower than that measured by CSI and MRS, with no significant difference between CSI and MRS. CSI and MRS showed a linear correlation with LL analysis and with each other. IP-OP underestimated FC, whereas CSI and MRS were more accurate for quantifying FC in both phantoms and liver. CSI and MRS have the potential to replace HIS-S and LL analysis in longitudinal studies.
Highlights
We evaluated dual-echo Dixon in-phase and outof-phase (IP-OP), chemical shift imaging (CSI), and 1H hydrogen MR (MR) spectroscopy (MRS) in estimating fat content (FC) in phantoms and in livers of mice
When the actual FC was less than 50%, fat concentration was calculated using the formula: FCIP-OP = 100 × [(SIIP - SIOP)/ (2 × SIIP)], but when the actual FC was greater than 50%, fat concentration was calculated using WIP-OP = 100 × [(SIIP Ϫ SIOP) / (2 × SIIP)], FCIP-OP = 1 Ϫ WIP-OP
With the visual analysis of 1H MRS fatwater peak size to guide for fat and water dominance on IP-OP images, the corrected IP-OP underestimated fat concentration when FC ranged from 10% to 60%: 4.5 ± 0%, 9.2 ± 2.0%, 16.0 ± 1.0%, 26.2 ± 0.1%, 31.9 ± 1.0%, and 56.1 ± 0.2%, respectively
Summary
We evaluated dual-echo Dixon in-phase and outof-phase (IP-OP), chemical shift imaging (CSI), and 1H MRS (hydrogen MR spectroscopy) in estimating fat content (FC) in phantoms and in livers of mice. The three MR methods were performed to measure FC in phantoms and in livers of obese leptindeficient (ob/ob), human BSCL2/seipin gene knockout (SKO), and wild-type (WT) mice. The results were compared with known FC in phantoms and to a reference standard from mice by histological semiautomatic vacuole segmentation (HIS-S) procedure and liver lipid (LL) chemical analysis. IP-OP underestimated FC, whereas CSI and MRS were more accurate for quantifying FC in both phantoms and liver. Quantification of liver fat in mice: comparing dual-echo Dixon imaging, chemical shift imaging, and 1H-MR spectroscopy. Hydrogen magnetic resonance (1H MR) imaging offers several noninvasive methods to obtain separate fat and water images for liver FC quantification. The authors presented two imaging sequences: one was conventional spin echo imaging with water and fat signals in-phase, and the second had the readout gradient slightly
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