Introduction of fast MR imaging in the assessment of hepatic steatosis

Relaxation effects in the quantification of fat using gradient echo imaging

“…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).…”

“…T2* Relaxation: include T2* terms for accuracy-Although neglecting T2* terms simplifies the model significantly, the effect on quantification can be important. For simplicity, assuming a common T2* for both fat and water and an echo time difference between IP and OP of ΔTE, the fat fraction estimated by Eq 4 can be calculated to be [7] This expression approaches F only as ΔTE/T2 * tends to zero. It is instructive to define a T2* amplification factor A 2 = F Dixon /F which for small ΔTE/T2* evaluates to [8] This equation shows that the accuracy of the 2-point technique is a function of ΔTE T2* but also of F .…”

“…Due to the shorter T1 of fat, the T1-weighted sequence tend to overestimate the fat fraction (7,15). A T1-weighting amplification factor A 1 may be defined, [9] where F (α = 90°)is the measured fat fraction at flip angle 90° and F is the true fat fraction (or T1-corrected fat fraction).…”

“…In addition to the effects of T2* relaxation, the fat fraction can be shown to be sensitive to differences in T1 relaxation (7), which introduces a dependence on imaging parameters such as repetition time (TR) and flip-angle (α). It is usually observed that the measured fat fraction increases with flip angle owing to the preferential suppression of longer T1 components.…”

In vivo magnetic resonance (MR) study of fatty liver: Importance of intracellular ultrastructural alteration for MR tissue parameters change

“…Although MR imaging (MRI) has higher sensitivity and specificity in tissue characterization than other imaging modalities, because of different relaxation times in normal and diseased tissues, in case of fatty liver, the MR diagnosis with conventional pulse sequences is not sensitive for detection of fatty deposition in the liver tissue (1,2). Chemical shift imaging works well in the assessment of the fatty amount in the liver by subtracting two sets of images, in-phase and out-phase images (3)(4)(5)(6)(7). MR spectroscopy, either by 1H or 13C techniques, successfully estimates fat content in the fatty liver (8 -14).…”