Hepatic Fat Fraction: MR Imaging for Quantitative Measurement and Display—Early Experience

177

142

Purpose:To compare noninvasive MRI and magnetic resonance spectroscopy (MRS) methods with liver biopsy to quantify liver fat content. Materials and Methods:Quantification of liver fat was compared by liver biopsy, proton MRS, and MRI using inphase/out-of-phase (IP/OP) and plus/minus fat saturation (ϮFS) techniques. The reproducibility of each MR measure was also determined. An additional group of overweight patients with steatosis underwent hepatic MRI and MRS before and after a six-month weight-loss program. Results:A close correlation was demonstrated between histological assessment of steatosis and measurement of intrahepatocellular lipid (IHCL) by MRS (r s ϭ 0.928, P Ͻ 0.0001) and MRI (IP/OP r s ϭ 0.942, P Ͻ 0.0001; FS r s ϭ 0.935, P Ͻ 0.0001). Following weight reduction, four of five patients with Ͼ5% weight loss had a decrease in IHCL of Ն50%. Conclusion:These findings suggest that standard MRI protocols provide a rapid, safe, and quantitative assessment of hepatic steatosis. This is important because MRS is not available on all clinical MRI systems. This will enable noninvasive monitoring of the effects of interventions such as weight loss or pharmacotherapy in patients with fatty liver diseases.

Section: Discussionmentioning

confidence: 99%

Magnetic resonance imaging and spectroscopy for monitoring liver steatosis

Cowin

Jonsson

Bauer

et al. 2008

177

142

“…S 1 >S 2 ), then the ambiguity may be resolved on this basis, which is a valid approach for either complex or amplitude data. All of these approaches have been used in previous studies (2,7,15). For example, the relatively short T1 of fat compared to most other tissues means the fat fraction increases with flip angle when fat is a minority but decreases when fat is a majority (15).…”

Section: Model Simplificationsmentioning

confidence: 99%

“…All of these approaches have been used in previous studies (2,7,15). For example, the relatively short T1 of fat compared to most other tissues means the fat fraction increases with flip angle when fat is a minority but decreases when fat is a majority (15). Likewise the fat component has been reported to have a short T2* relative to liver tissue (16).…”

Section: Model Simplificationsmentioning

confidence: 99%

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Relaxation effects in the quantification of fat using gradient echo imaging

Bydder

Yokoo

Hamilton

et al. 2008

370

579

Quantification of fat has been investigated using images acquired from multiple gradient echos. The evolution of the signal with echo time and flip angle was measured in phantoms of known fat and water composition and in 21 research subjects with fatty liver. Data were compared to different models of the signal equation, in which each model makes different assumptions about the T1 and/ or T2* relaxation effects. A range of T1, T2*, fat fraction and number of echos was investigated to cover situations of relevance to clinical imaging. Results indicate that quantification is most accurate at low flip angles (to minimize T1 effects) with a small number of echos (to minimize spectral broadening effects). At short echo times the spectral broadening effects manifest as a short apparent T2 for the fat component.

“…Options for a protocol of this sort include inphase and out-of-phase (IP/OP) GRE imaging (29), two-point or three-point Dixon techniques (30), or variations such as General Electric's IDEAL, which makes use of asymmetric echo times to resolve dominant fraction ambiguities (31,32).…”

Section: Protocol Developmentmentioning

confidence: 99%

Quantitative MR in multi‐center clinical trials

Ashton¹

2010

MRI has a wide variety of applications in the clinical trials process. MR has shown particular utility in the early phases of clinical development, when trial sponsors are interested in demonstrating proof of concept and must make decisions about allocation of resources to a particular compound based on the results from a small number of experimental subjects. This utility is largely due to the many different imaging endpoints that can be measured using MR, ranging from structural (tumor burden, hippocampal volume) to functional (blood flow, vascular permeability) to molecular (hepatic fat fraction, glycosaminoglycan content). The unique flexibility of these systems has proven to be both a blessing and a curse to those attempting to deploy MR in multi-center clinical trials, however, as differences among scanner manufacturers and models in pulse sequence implementation, hardware capabilities, and even terminology make it increasingly difficult to ensure that results obtained at one center are comparable to those at another. These problems are compounded by the differences between the procedures used in clinical trials and those used in routine clinical practice, which make trial-specific training for site technologists and radiologists a necessity in many cases. This article will briefly review the benefits of including quantitative MR imaging in clinical trials, then explore in detail the challenges presented by the need to develop and deploy a detailed MR protocol that is both effective and implementable across many different MR systems and software versions.