Hepatic fat fraction (HFF) was measured in 28 lean/obese humans by single-voxel proton spectroscopy (MRS), a two-point Dixon (2PD), and a three-point iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) method (3PI). For the lean, obese, and total subject groups, the range of HFF measured by MRS was 0.3-3.5% (1.1 ؎ 1.4%), 0.3-41.5% (11.7 ؎ 12.1), and 0.3-41.5% (10.1 ؎ 11.6%), respectively. For the same groups, the HFF measured by 2PD was ؊6.3-2.2% (؊2.0 ؎ 3.7%), ؊2.4 -42.9% (12.9 ؎ 13.8%), and ؊6.3-42.9% (10.5 ؎ 13.7%), respectively, and for 3PI they were 7.9 -12.8% (10.1 ؎ 2.0%), 11.1-49.3% (22.0 ؎ 12.2%), and 7.9 -49.3% (20.0 ؎ 11.8%), respectively. The HFF measured by MRS was highly correlated with those measured by 2PD (r ؍ 0.954, P < 0.001) and 3PI (r ؍ 0.973, P < 0.001). With the MRS data as a reference, the percentages of correct differentiation between normal and fatty liver with the MRI methods ranged from 68 -93% for 2PD and 64 -89% for 3PI. Our study demonstrates that the apparent HFF measured by the MRI methods can significantly vary depending on the choice of water-fat separation methods and sequences. Such variability may limit the clinical application of the MRI methods, particularly when a diagnosis of early fatty liver needs to be performed. Therefore, protocol-specific establishment of cutoffs for liver fat content may be necessary. Magnetic resonance techniques provide for a noninvasive means of estimating fat content in vivo. It is widely accepted that single-voxel proton magnetic resonance spectroscopy (MRS) allows for MR fat quantification in the liver with superior sensitivity and dynamic range over that of MRI. However, MRS is prone to liver inhomogeneity, although this can be compensated for by using data acquisition from multiple voxels but with the disadvantage of an increased scan time.To fully profit from the larger spatial coverage with MRI, a variety of fat quantification methods have been proposed. Among the MRI methods to date, chemical shiftbased multipoint water-fat separation methods (to be referred to as multipoint water-fat separation) have been most widely used, which may be represented by the twopoint Dixon method (1), the 3,4-point Dixon method with phase correction (2,3), and the iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) method (4,5). Among these multipoint water-fat separation methods, the original two-point Dixon (2PD) method in conjunction with a spoiled gradient echo sequence (SPGR) and the magnitude-based postdata processing (6) is often used in clinical applications due to its simplicity (7-14). Despite its well-recognized limited dynamic range when fat content is larger than water content in a pixel (15,16), high correlations between the 2PD and MRS or histology have been reported in many studies (8,13,14,16).The outcome of MRS (e.g., signal-to-noise ratio (SNR)) in fat quantification largely depends on sequence parameters such as the number of signal averages ...
Fatty liver is increasingly common in obese adolescents. We determined its association with glucose dysregulation in 118 (37M/81F) obese adolescents of similar age and percent total fat. Fast-magnetic resonance imaging (MRI) and simple MRI were used to quantify hepatic fat content and abdominal fat distribution. All subjects had a standard oral glucose tolerance test. Insulin sensitivity was estimated by the Matsuda Index and homeostasis model assessment of insulin resistance. Baseline total and high molecular weight (HMW)-adiponectin and interleukin (IL)-6 levels were measured. The cohort was stratified according to tertiles of hepatic fat content. Whereas age and %fat were comparable across tertiles, ethnicity differed in that fewer Blacks and more Whites and Hispanics were in the moderate and high category of hepatic fat fraction (HFF). Visceral and the visceral-to-subcutaneous fat ratio increased and insulin sensitivity decreased across tertiles. Two-hour plasma glucose rose with increasing hepatic steatosis (P < 0.008). 73.7% of the subjects in the high HFF had the metabolic syndrome compared to 19.5% and 30.6%, respectively, in the low and moderate categories. Both total and HMWadiponectin decreased, and IL-6 increased with increasing hepatic steatosis. Conclusion: In obese adolescents, independent of total fat, increasing severity of fatty liver is associated with glucose dysregulation, metabolic syndrome, and with a proinflammatory milieu. (HEPATOLOGY 2009;49: 1896-1903 E ctopic fat deposition in insulin-sensitive tissues such as liver and muscle strongly correlates with insulin resistance. 1 Previously, we reported that increased intramyocellular fat in obese adolescents was associated with impaired glucose intolerance and insulin resistance. 2 Furthermore, moderate elevation in alanine aminotransferase (ALT) levels, a poor surrogate of fatty liver, was found to be associated with high-normal glucose levels, 3 whereas abnormal ALT levels were reported in youngsters with type 2 diabetes (T2DM), 4 raising the question of a potential role of fatty liver in the onset of T2DM in obese youth. Fatty liver in obese adolescents is becoming increasingly common. [5][6][7] Nevertheless, its role in the dysregulation of glucose metabolism is unclear. We hypothesize that, independent of overall obesity, the severity of hepatic steatosis will strongly affect the presence of prediabetes and diabetes in obese adolescents. Furthermore, we determined if the balance between antiinflammatory markers such as total and high molecular weight (HMW) adiponectin and proinflammatory markers like interleukin-6 (IL-6) would vary as a function of the degree of hepatic steatosis. Using fast-magnetic resonance imaging (MRI) we quantified intrahepatic fat content in a large multiethnic group of obese adolescents matched for age and overall adiposity. Subjects and MethodsThe Cohort. In all, 118 obese adolescents, 13 to 16 years old with a body mass index (BMI)-z score ranging
For ultrasensitive magnetic resonance imaging (MRI), magnetic nanoparticles with extremely high r2 relaxivity are strongly desired. Magnetosome-like nanoparticles were prepared by coating polyethylene glycol-phospholipid (PEG-phospholipid) onto ferrimagnetic iron oxide nanocubes (FIONs). FIONs exhibited a very high relaxivity (r2) of 324 mM −1 s −1 , allowing efficient labeling of various kinds of cells. The magnetic resonance (MR) imaging of single cells labeled with FIONs is demonstrated not only in vitro but also in vivo. Pancreatic islet grafts and their rejection could be imaged using FIONs on a 1.5 T clinical MRI scanner. The strong contrast effect of FIONs enabled MR imaging of transplanted islets in small rodents as well as in large animals. Therefore, we expect that MR imaging of pancreatic islet grafts using FIONs has the potentials for clinical applications. Furthermore, FIONs will enable highly sensitive noninvasive assessment after cell transplantation.cell tracking | contrast agent | molecular imaging | diabetes | islet transplantation
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