Proton MR spectroscopy in quantitative in vivo determination of fat content in human liver steatosis

Hepatic lipid profiling in chronic hepatitis C: an in vitro and in vivo proton magnetic resonance spectroscopy study

BACKGROUND & AIMS

Hepatic steatosis is an important factor in pathogenesis, progression and response to treatment in hepatitis C. We aimed to investigate differences in hepatic lipid composition in liver biopsies from patients with chronic hepatitis C using proton magnetic resonance spectroscopy ((1)H MRS) and to translate these findings to the in vivo clinical setting.

METHODS

Two cohorts of patients with histologically defined chronic hepatitis C were studied. High-resolution MR spectra were obtained from 47 liver biopsy samples. These data were used to derive biologically relevant prior knowledge for the assignment and interpretation of lower-resolution in vivo hepatic MRS data acquired at 1.5T from a second cohort of 59 patients. MRS data were obtained both in vitro and in vivo from a subset of 11 patients.

RESULTS

Multivariate factor analysis demonstrated characteristic MR spectral differences by fibrosis stage and genotype. Total lipid increased with fibrosis stage (r=0.43, p=0.003) and was higher in genotype 3 compared to genotype 1 (p=0.03), while lipid polyunsaturation decreased with increasing fibrosis stage (r=-0.55, p<0.0005) and, independently, with increasing steatosis. Non-invasive assessment using in vivo hepatic (1)H MRS corroborated in vitro findings, but the signal-to-noise ratio was insufficient for reliable assessment of lipid polyunsaturation in vivo.

CONCLUSIONS

Hepatic lipid composition was analysed using MRS in patients with chronic hepatitis C in vitro and in vivo, demonstrating significant differences in indices by disease severity. High-resolution data informed the analysis and interpretation of in vivo spectra, but further improvements in spectral quality in vivo are required.

Sonographic hepatic-renal ratio as indicator of hepatic steatosis: comparison with (1)H magnetic resonance spectroscopy

The aim of this study was to determine the diagnostic performance of ultrasound (US) in the quantitative assessment of steatosis by comparison with proton magnetic resonance spectroscopy ((1)H-MRS) as a reference standard. Three liver echo-intensity indices were derived: US hepatic mean gray level, hepatic-renal echo-intensity ratio (H/R), and hepatic-portal blood echo-intensity ratio. The (1)H-MRS degree of steatosis was determined as percentage fat by wet weight. Regression equations were used to estimate quantitatively hepatic fat content. The hepatic fat content by (1)H-MRS analysis ranged from 0.10% to 28.9% (median value, 4.8%). Ultrasound H/R was correlated with the degree of steatosis on (1)H-MRS (R(2)= 0.92; P < .0001), whereas no correlation with (1)H-MRS was found for hepatic mean gray level and hepatic-portal blood echo-intensity ratio. A receiver operating characteristic curve identified the H/R of 2.2 as the best cutoff point for the prediction of (1)H-MRS of at least 5%, yielding measures of sensitivity and specificity of 100% and 95%, respectively. In this pilot study, US H/R exhibits high sensitivity and specificity for detecting liver fatty changes. Our results indicate that quantitative evaluation of hepatic fat content can be performed using US H/R and could therefore be a valuable analytic tool in clinical investigation.

Nonalcoholic fatty liver disease in children living in the obeseogenic society

BACKGROUND

The problem of obesity in children has grown considerably in recent years in the United States as well as the rest of the world. This has resulted in a marked increase in the prevalence of nonalcoholic liver disease in the pediatric age group. Nonalcoholic fatty liver disease (NAFLD) is currently the most common hepatic disorder seen in pediatric hepatology practice.

DATA SOURCES

We have reviewed the most recent literature regarding the prevalence, pathogenesis as well as the most recent advances in the diagnostic and therapeutic modalities of NAFLD in children.

RESULTS

NAFLD affects a substantial portion of the population including children.

CONCLUSIONS

The rising incidence of NAFLD, nonalcoholic steatohepatitis (NASH) and cirrhosis emphasizes the need for effective treatment options. The lack of complete understanding of the pathogenesis of NAFLD still limits our ability to develop novel therapeutic modalities that can target the metabolic derangements implicated in the development of the disorder.

New imaging techniques for non-alcoholic steatohepatitis

No imaging modality has yet been proven to reliably differentiate simple hepatic steatosis from steatohepatitis. This review focuses on the predominant non-nuclear imaging modalities available to clinicians at the present time. The key feature of the techniques outlined in this review that demonstrate the most interesting results have one thing in common: imaging is not performed in a passive manner but is undertaken as a method to investigate functional differences between simple hepatic steatosis and steatohepatitis based upon the current working model for pathogenesis and progression. The purpose of this article is to review the strengths and weakness of current clinical and experimental imaging modalities for noninvasive detection of NAFLD, with an emphasis on NASH.

Imaging-based quantification of hepatic fat: methods and clinical applications

Fatty liver disease comprises a spectrum of conditions (simple hepatic steatosis, steatohepatitis with inflammatory changes, and end-stage liver disease with fibrosis and cirrhosis). Hepatic steatosis is often associated with diabetes and obesity and may be secondary to alcohol and drug use, toxins, viral infections, and metabolic diseases. Detection and quantification of liver fat have many clinical applications, and early recognition is crucial to institute appropriate management and prevent progression. Histopathologic analysis is the reference standard to detect and quantify fat in the liver, but results are vulnerable to sampling error. Moreover, it can cause morbidity and complications and cannot be repeated often enough to monitor treatment response. Imaging can be repeated regularly and allows assessment of the entire liver, thus avoiding sampling error. Selection of appropriate imaging methods demands understanding of their advantages and limitations and the suitable clinical setting. Ultrasonography is effective for detecting moderate or severe fatty infiltration but is limited by lack of interobserver reliability and intraobserver reproducibility. Computed tomography allows quantitative and qualitative evaluation and is generally highly accurate and reliable; however, the results may be confounded by hepatic parenchymal changes due to cirrhosis or depositional diseases. Magnetic resonance (MR) imaging with appropriate sequences (eg, chemical shift techniques) has similarly high sensitivity, and MR spectroscopy provides unique advantages for some applications. However, both are expensive and too complex to be used to monitor steatosis.

Contribution of individual organ mass loss to weight loss-associated decline in resting energy expenditure

BACKGROUND

Weight loss leads to reduced resting energy expenditure (REE) independent of fat-free mass (FFM) and fat mass (FM) loss, but the effect of changes in FFM composition is unclear.

OBJECTIVE

We hypothesized that a decrease in REE adjusted for FFM with weight loss would be partly explained by a disproportionate loss in the high metabolic activity component of FFM.

DESIGN

Forty-five overweight and obese women [body mass index (in kg/m(2)): 28.7-46.8] aged 22-46 y followed a low-calorie diet for 12.7 +/- 2.2 wk. Body composition was measured by magnetic resonance imaging, dual-energy X-ray absorptiometry, and a 4-compartment model. REE measured by indirect calorimetry (REEm) was compared with REE calculated from detailed body-composition analysis (REEc) by using specific organ metabolic rates (ie, organ REE/mass).

RESULTS

Weight loss was 9.5 +/- 3.4 kg (8.0 +/- 2.9 kg FM and 1.5 +/- 3.1 kg FFM). Decreases in REE (-8%), free triiodothyronine concentrations (-8%), muscle (-3%), heart (-5%), liver (-4%), and kidney mass (-6%) were observed (all P < 0.05). Relative loss in organ mass was significantly higher (P < 0.01) than was the change in low metabolically active FFM components (muscle, bone, and residual mass). After weight loss, REEm - REEc decreased from 0.24 +/- 0.58 to 0.01 +/- 0.44 MJ/d (P = 0.01) and correlated with the decrease in free triiodothyronine concentrations (r = 0.33, P < 0.05). Women with high adaptive thermogenesis (defined as REEm - REEc < -0.17 MJ/d) had less weight loss and conserved FFM, liver, and kidney mass.

CONCLUSIONS

After weight loss, almost 50% of the decrease in REEm was explained by losses in FFM and FM. The variability in REEm explained by body composition increased to 60% by also considering the weight of individual organs.

Abnormal hepatic energy homeostasis in type 2 diabetes

Increased hepatocellular lipids relate to insulin resistance and are typical for individuals with type 2 diabetes mellitus (T2DM). Steatosis and T2DM have been further associated with impaired muscular adenosine triphosphate (ATP) turnover indicating reduced mitochondrial fitness. Thus, we tested the hypothesis that hepatic energy metabolism could be impaired even in metabolically well-controlled T2DM. We measured hepatic lipid volume fraction (HLVF) and absolute concentrations of gammaATP, inorganic phosphate (Pi), phosphomonoesters and phosphodiesters using noninvasive (1)H/ (31)P magnetic resonance spectroscopy in individuals with T2DM (58 +/- 6 years, 27 +/- 3 kg/m (2)), and age-matched and body mass index-matched (mCON; 61 +/- 4 years, 26 +/- 4 kg/m (2)) and young lean humans (yCON; 25 +/- 3 years, 22 +/- 2 kg/m (2), P < 0.005, P < 0.05 versus T2DM and mCON). Insulin-mediated whole-body glucose disposal (M) and endogenous glucose production (iEGP) were assessed during euglycemic-hyperinsulinemic clamps. Individuals with T2DM had 26% and 23% lower gammaATP (1.68 +/- 0.11; 2.26 +/- 0.20; 2.20 +/- 0.09 mmol/L; P < 0.05) than mCON and yCON individuals, respectively. Further, they had 28% and 31% lower Pi than did individuals from the mCON and yCON groups (0.96 +/- 0.06; 1.33 +/- 0.13; 1.41 +/- 0.07 mmol/L; P < 0.05). Phosphomonoesters, phosphodiesters, and liver aminotransferases did not differ between groups. HLVF was not different between those from the T2DM and mCON groups, but higher (P = 0.002) than in those from the yCON group. T2DM had 13-fold higher iEGP than mCON (P < 0.05). Even after adjustment for HLVF, hepatic ATP and Pi related negatively to hepatic insulin sensitivity (iEGP) (r =-0.665, P = 0.010, r =-0.680, P = 0.007) but not to whole-body insulin sensitivity.

CONCLUSION

These data suggest that impaired hepatic energy metabolism and insulin resistance could precede the development of steatosis in individuals with T2DM.

Reproducibility of 3.0 Tesla magnetic resonance spectroscopy for measuring hepatic fat content

PURPOSE

To investigate reproducibility of proton magnetic resonance spectroscopy ((1)H-MRS) to measure hepatic triglyceride content (HTGC).

MATERIALS AND METHODS

In 24 subjects, HTGC was evaluated using (1)H-MRS at 3.0 Tesla. We studied "between-weeks" reproducibility and reproducibility of (1)H-MRS in subjects with fatty liver. We also studied within liver variability and within day reproducibility. Reproducibility was assessed by coefficient of variation (CV), repeatability coefficient (RC), and intraclass correlation coefficient (ICC).

RESULTS

The CV of between weeks reproducibility was 9.5%, with a RC of 1.3% HTGC (ICC 0.998). The CV in fatty livers was 4.1%, with a RC of 1.3% HTGC (ICC 0.997). Within day CV was 4.5%, with a RC of 0.4% HTGC (ICC 0.999). CV for within liver variability was 14.5%.

CONCLUSION

Reproducibility of (1)H-MRS to measure HTGC for "between-weeks" measurements and in fatty livers is high, which is important for follow-up studies. Within liver variability displays a larger variation, meaning that liver fat is not equally distributed and during consecutive measurements the same voxel position should be used.

Prediction of non-alcoholic fatty liver disease and liver fat using metabolic and genetic factors

BACKGROUND & AIMS

Our aims were to develop a method to accurately predict non-alcoholic fatty liver disease (NAFLD) and liver fat content based on routinely available clinical and laboratory data and to test whether knowledge of the recently discovered genetic variant in the PNPLA3 gene (rs738409) increases accuracy of the prediction.

METHODS

Liver fat content was measured using proton magnetic resonance spectroscopy in 470 subjects, who were randomly divided into estimation (two thirds of the subjects, n = 313) and validation (one third of the subjects, n = 157) groups. Multivariate logistic and linear regression analyses were used to create an NAFLD liver fat score to diagnose NAFLD and liver fat equation to estimate liver fat percentage in each individual.

RESULTS

The presence of the metabolic syndrome and type 2 diabetes, fasting serum (fS) insulin, fS-aspartate aminotransferase (AST), and the AST/alanine aminotransferase ratio were independent predictors of NAFLD. The score had an area under the receiver operating characteristic curve of 0.87 in the estimation and 0.86 in the validation group. The optimal cut-off point of -0.640 predicted increased liver fat content with sensitivity of 86% and specificity of 71%. Addition of the genetic information to the score improved the accuracy of the prediction by only <1%. Using the same variables, we developed a liver fat equation from which liver fat percentage of each individual could be estimated.

CONCLUSIONS

The NAFLD liver fat score and liver fat equation provide simple and noninvasive tools to predict NAFLD and liver fat content.

Methods for assessing intrahepatic fat content and steatosis

PURPOSE OF REVIEW

Intrahepatic fat content is increasingly being recognized as an integral part of metabolic dysfunction. This article reviews available methods for the assessment of hepatic steatosis.

RECENT FINDINGS

Apart from liver biopsy, there are several noninvasive radiologic modalities for evaluating nonalcoholic fatty liver disease. Ultrasonography, computed tomography, and traditional MRI remain largely qualitative methods for detecting mild to severe degrees of steatosis rather than quantitative methods for measuring liver fat content, even though novel attempts to collect objective quantitative information have recently been developed. Still, their sensitivity at mild degrees of steatosis is poor. Undoubtedly, most methodological advances have occurred in the field of MRI and magnetic resonance spectroscopy, which currently enable the accurate quantification of intrahepatic fat even at normal or near normal levels. Xenon computed tomography was also recently shown to offer another objective tool for the quantitative assessment of steatosis, although more validation studies are required.

SUMMARY

Several modalities can be used for measuring intrahepatic fat and assessing steatosis; the choice will ultimately depend on the intended use and available resources.

Non-invasive assessment and quantification of liver steatosis by ultrasound, computed tomography and magnetic resonance

Hepatic steatosis is the most prevalent liver disorder in the developed world. It is closely associated with features of metabolic syndrome, especially insulin resistance and obesity. The two most common conditions associated with fatty liver are alcoholic liver disease (ALD) and non-alcoholic fatty liver disease (NAFLD). Liver biopsy is considered the gold standard for the assessment of liver fat, but there is a need for less invasive diagnostic techniques. New imaging modalities are emerging, which could provide more detailed information about hepatic tissue or even replace biopsy. In the present review, available imaging modalities (ultrasound, computed tomography, magnetic resonance imaging and proton magnetic resonance spectroscopy) are presented which are employed to detect or even quantify the fat content of the liver. The advantages and disadvantages of the above-mentioned imaging modalities are discussed. Although none of these techniques is able to differentiate between microvesicular and macrovesicular steatosis and to reveal all features visible using histology, the proposed diagnostic modalities offer a wide range of additional information such as anatomical and morphological information non-invasively. In particular, magnetic resonance imaging and proton magnetic resonance spectroscopy are able to quantify the hepatic fat content hence avoiding exposure to radiation. Except for proton magnetic resonance spectroscopy, all modalities offer additional information about regional fat distribution within the liver. MR elastography, which can estimate the amount of fibrosis, also appears promising in the differentiation between simple steatosis and steatohepatitis.

Magnetic resonance imaging and spectroscopy accurately estimate the severity of steatosis provided the stage of fibrosis is considered

BACKGROUND/AIMS

Currently the diagnosis and severity of hepatic steatosis can be established accurately only by liver biopsy. Previous small studies found that steatosis measured by magnetic resonance spectroscopy (MRS) and imaging (MRI) correlated with histological assessment of liver triglyceride content. However, the accuracy of MRS/MRI for grading the severity of steatosis has not been addressed. The aims of this study were (1) to determine whether MRS and MRI can discriminate grades of steatosis in a large cohort of consecutive patients with a wide spectrum of liver disease aetiology and severity (2) to evaluate the effect of hepatic fibrosis, inflammation and iron on quantitation of intrahepatocellular lipid (IHCL) by these techniques.

METHODS

Ninety-four sequential patients who underwent percutaneous liver biopsy or liver resection had MRS and MRI (Dixon in phase/out of phase (Dixon IP/OP) and with/without fat saturation (+/-FS) images) to determine IHCL. Histology was used as the reference standard.

RESULTS

Close relationships were observed between the percentage of steatosis estimated by histology and MRS/MRI (r(s)=0.88 p<0.001 for all techniques). However, separate equations were required for the percentage of steatosis to avoid underestimation by imaging for patients with moderate or advanced fibrosis. All techniques had good diagnostic accuracy for mild steatosis (AUROC > or =0.87) as well as moderate/severe steatosis (AUROC > or =0.89). Hepatic inflammation and mild iron deposition (Perls' grade 1 and 2) did not interfere with estimation of steatosis by imaging.

CONCLUSIONS

MRS and MRI had good accuracy for grading the severity of steatosis in subjects with liver disease, provided that stage of fibrosis was considered.

Effect of PRESS and STEAM sequences on magnetic resonance spectroscopic liver fat quantification

PURPOSE

To compare PRESS and STEAM MR spectroscopy for assessment of liver fat in human subjects.

MATERIALS AND METHODS

Single-voxel (20 x 20 x 20 mm) PRESS and STEAM spectra were obtained at 1.5T in 49 human subjects with known or suspected fatty liver disease. PRESS and STEAM sequences were obtained with fixed TR (1500 msec) and different TE (five PRESS spectra between TE 30-70 msec, five STEAM spectra between TE 20-60 msec). Spectra were quantified and T2 and T2-corrected peak area were calculated by different techniques. The values were compared for PRESS and STEAM.

RESULTS

Water T2 values from PRESS and STEAM were not significantly different (P = 0.33). Fat peak T2s were 25%-50% shorter on PRESS than on STEAM (P < 0.02 for all comparisons) and there was no correlation between T2s of individual peaks. PRESS systematically overestimated the relative fat peak areas (by 7%-263%) compared to STEAM (P < 0.005 for all comparisons). The peak area given by PRESS was more dependent on the T2-correction technique than STEAM.

CONCLUSION

Measured liver fat depends on the MRS sequence used. Compared to STEAM, PRESS underestimates T2 values of fat, overestimates fat fraction, and provides a less consistent fat fraction estimate, probably due to J coupling effects.

Advanced MRI methods for assessment of chronic liver disease

OBJECTIVE

With recent advances in technology, advanced MRI methods such as diffusion-weighted and perfusion-weighted MRI, MR elastography, chemical shift-based fat-water separation, and MR spectroscopy can now be applied to liver imaging. We will review the respective roles of these techniques for assessment of chronic liver disease.

CONCLUSION

MRI plays an increasingly important role in assessment of patients with chronic liver disease because of the lack of ionizing radiation and the possibility of performing multiparametric imaging.

Reproducibility of hepatic triglyceride content assessment in normals using localized magnetic resonance spectroscopy

AIM

To investigate the reproducibility of measurements of hepatic triglyceride content (HTGC) in subjects with normal HTGC using localized (1)H-magnetic resonance spectroscopy ((1)H-MRS) and a clinical 1.5T scanner.

METHODS

The (1)H-MRS acquisition was performed with a common protocol using the whole-body coil and no respiratory triggering. An upper limit of normal HTGC of 5.56% was used. Duplicate measurements, including subject repositioning, were acquired from 23 subjects, 19 of whom had a normal HTGC.

RESULTS

The mean coefficient of variation (CV) from the duplicate measurements was 14.8% (20.5% before exclusion of a subject who was considered to be an outlier). Mean CVs of subgroups below and above the 1% HTGC limit were 19.8 and 7.0 respectively.

CONCLUSIONS

The mean CV calculated in subjects with HTGC in the normal range was found to be higher than CVs of wide range HTGC groups reported in the literature. It is concluded that the reproducibility of HTGC measurements using (1)H-MRS depends on the HTGC range. These findings are of importance in reproducibility studies and in estimations of required study group sizes.

Quantitative analysis of T2-correction in single-voxel magnetic resonance spectroscopy of hepatic lipid fraction

PURPOSE

To investigate the accuracy and reproducibility of hepatic lipid measurements using 1H magnetic resonance spectroscopy (MRS) with T2 relaxation correction, compared to measurements without correction.

MATERIALS AND METHODS

Experiments were conducted in phantoms of varying lipid and iron-induced susceptibility to simulate fatty liver with variable T2. Single-voxel 1H MRS was conducted with multiple TE values, and percent lipid content (lipid%) was determined at each TE to assess accuracy and TE dependency. Concurrently, T2 and equilibrium values of water and lipid were determined separately, and T2 effects on the lipid% were corrected. A similar procedure was conducted in 12 human subjects to determine susceptibility effects on water and lipid MRS signals and lipid%. Multiple measurements were used to test reproducibility.

RESULTS

The use of T2-correction was found to be more accurate than uncorrected lipid% in phantom samples (<10% error). Uncorrected lipid% error increased with increasing TE (>20% when TE>24 msec) and with increasing susceptibility effect. In humans, while measurement repeatability was high for both corrected and uncorrected MRS, uncorrected lipid% was sensitive to acquisition TE, with 83.6% of all measurements significantly different than T2-corrected measures (P<0.05).

CONCLUSION

Separate T2-correction of water and lipid 1H MRS signals provides more accurate and consistent measurements of lipid%, in comparison to uncorrected estimations.

Noninvasive quantitation of human liver steatosis using magnetic resonance and bioassay methods

The purpose was to evaluate the ability of three magnetic resonance (MR) techniques to detect liver steatosis and to determine which noninvasive technique (MR, bioassays) or combination of techniques is optimal for the quantification of hepatic fat using histopathology as a reference. Twenty patients with histopathologically proven steatosis and 24 control subjects underwent single-voxel proton MR spectroscopy (MRS; 3 voxels), dual-echo in phase/out of phase MR imaging (DEI) and diffusion-weighted MR imaging (DWI) examinations of the liver. Blood or urine bioassays were also performed for steatosis patients. Both MRS and DEI data allowed to detect steatosis with a high sensitivity (0.95 for MRS; 1 for DEI) and specificity (1 for MRS; 0.875 for DEI) but not DWI. Strong correlations were found between fat fraction (FF) measured by MRS, DEI and histopathology segmentation as well as with low density lipoprotein (LDL) and cholesterol concentrations. A Bland-Altman analysis showed a good agreement between the FF measured by MRS and DEI. Partial correlation analyses failed to improve the correlation with segmentation FF when MRS or DEI data were combined with bioassay results. Therefore, FF from MRS or DEI appear to be the best parameters to both detect steatosis and accurately quantify fat liver noninvasively.

Ethnic differences in hepatic steatosis: an insulin resistance paradox?

Nonalcoholic fatty liver disease is a burgeoning problem. We have previously shown that Hispanics were at greater risk for nonalcoholic fatty liver disease than were African-Americans despite a similar prevalence of risk factors between these groups. We have performed the largest, population-based study to date (n = 2170) utilizing proton magnetic resonance (MR) spectroscopy, dual-energy x-ray absorptiometry, and multislice abdominal MR imaging to determine the contribution of body fat distribution to the differing prevalence of hepatic steatosis in the three major U.S. ethnic groups (African-American, Hispanic, Caucasian). Despite controlling for age and total adiposity, African-Americans had less intraperitoneal (IP) fat and more lower extremity fat than their Hispanic and Caucasian counterparts. The differences in hepatic triglyceride content (HTGC) between these groups remained after controlling for total, abdominal subcutaneous, and lower extremity adiposity; however, controlling for IP fat nearly abolished the differences in HTGC, indicating a close association between IP and liver fat regardless of ethnicity. Despite the lower levels of IP and liver fat in African-Americans, their prevalence of insulin resistance was similar to Hispanics, who had the highest levels of IP and liver fat. Furthermore, insulin levels and homeostasis model assessment values were highest and serum triglyceride levels were lowest among African-Americans after controlling for IP fat.

CONCLUSION

IP fat is linked to HTGC, irrespective of ethnicity. The differing prevalence of hepatic steatosis between these groups was associated with similar differences in visceral adiposity. The metabolic response to obesity and insulin resistance differs in African-Americans when compared to either Hispanics or Caucasians: African-Americans appear to be more resistant to both the accretion of triglyceride in the abdominal visceral compartment (adipose tissue and liver) and hypertriglyceridemia associated with insulin resistance.

Nonalcoholic fatty liver disease: diagnostic and fat-grading accuracy of low-flip-angle multiecho gradient-recalled-echo MR imaging at 1.5 T

PURPOSE

To assess the accuracy of four fat quantification methods at low-flip-angle multiecho gradient-recalled-echo (GRE) magnetic resonance (MR) imaging in nonalcoholic fatty liver disease (NAFLD) by using MR spectroscopy as the reference standard.

MATERIALS AND METHODS

In this institutional review board-approved, HIPAA-compliant prospective study, 110 subjects (29 with biopsy-confirmed NAFLD, 50 overweight and at risk for NAFLD, and 31 healthy volunteers) (mean age, 32.6 years +/- 15.6 [standard deviation]; range, 8-66 years) gave informed consent and underwent MR spectroscopy and GRE MR imaging of the liver. Spectroscopy involved a long repetition time (to suppress T1 effects) and multiple echo times (to estimate T2 effects); the reference fat fraction (FF) was calculated from T2-corrected fat and water spectral peak areas. Imaging involved a low flip angle (to suppress T1 effects) and multiple echo times (to estimate T2* effects); imaging FF was calculated by using four analysis methods of progressive complexity: dual echo, triple echo, multiecho, and multiinterference. All methods except dual echo corrected for T2* effects. The multiinterference method corrected for multiple spectral interference effects of fat. For each method, the accuracy for diagnosis of fatty liver, as defined with a spectroscopic threshold, was assessed by estimating sensitivity and specificity; fat-grading accuracy was assessed by comparing imaging and spectroscopic FF values by using linear regression.

RESULTS

Dual-echo, triple-echo, multiecho, and multiinterference methods had a sensitivity of 0.817, 0.967, 0.950, and 0.983 and a specificity of 1.000, 0.880, 1.000, and 0.880, respectively. On the basis of regression slope and intercept, the multiinterference (slope, 0.98; intercept, 0.91%) method had high fat-grading accuracy without statistically significant error (P > .05). Dual-echo (slope, 0.98; intercept, -2.90%), triple-echo (slope, 0.94; intercept, 1.42%), and multiecho (slope, 0.85; intercept, -0.15%) methods had statistically significant error (P < .05).

CONCLUSION

Relaxation- and interference-corrected fat quantification at low-flip-angle multiecho GRE MR imaging provides high diagnostic and fat-grading accuracy in NAFLD.

Characterization of adrenal pheochromocytoma using respiratory-triggered proton MR spectroscopy: initial experience

OBJECTIVE

The aim of our study was to evaluate the feasibility of respiratory-triggered proton single-voxel MR spectroscopy for the diagnosis of adrenal pheochromocytoma and to determine whether certain spectral resonances detected on single-voxel MR spectroscopy are specific for adrenal pheochromocytomas compared with adrenal adenomas.

CONCLUSION

Adrenal pheochromocytomas have a unique MR spectral signature, showing 6.8 ppm resonance that is not seen in adenomas. This unique spectral signature may be attributed to the presence of catecholamines and catecholamine metabolites that are abundant in pheochromocytomas.

Quantification of absolute fat mass using an adipose tissue reference signal model

PURPOSE

To develop a method for quantifying absolute fat mass, and to demonstrate its feasibility in phantoms and in ex vivo swine specimens at 3 Tesla.

MATERIALS AND METHODS

Chemical-shift-based fat-water decomposition was used to first reconstruct fat-only images. Our proposed model used a reference signal from fat in pure adipose tissue to calibrate and normalize the fat signal intensities from the fat-only images. Fat mass was subsequently computed on a voxel-by-voxel basis and summed across each sample. Feasibility of the model was tested in six ex vivo swine samples containing varying mixtures of fat (adipose) and lean tissues. The samples were imaged using 1.5-mm isotropic voxels and a single-channel birdcage head coil at 3 Tesla. Lipid assay was independently performed to determine fat mass, and served as the comparison standard.

RESULTS

Absolute fat mass values (in grams) derived by our proposed model were in excellent agreement with lipid assay results, with a 5% to 7% difference (r > 0.99; P < 0.001).

CONCLUSION

Preliminary results in ex vivo swine samples demonstrated the feasibility of computing absolute fat mass as a quantitative endpoint using chemical-shift fat-water MRI with a signal model based on reference fat from pure adipose tissue.

Noninvasive assessment of hepatic steatosis

Hepatic steatosis, the accumulation of lipids within hepatocytes, is a common condition. The prevalence of its most frequent manifestation, nonalcoholic fatty liver disease (NAFLD), has been estimated to be as high as 35% in some populations. Currently, liver biopsy is the gold standard for the diagnosis and assessment of severity of hepatic steatosis, staging of fibrosis, and is the only modality able to differentiate bland steatosis from steatohepatitis. However, its invasiveness, significant side effect profile, and susceptibility to sampling error ultimately make it a suboptimal tool. Accordingly, focus has been placed on noninvasive radiologic techniques for hepatic fat detection and quantification. The rationale, performance characteristics, and limitations of traditional noninvasive measures, including ultrasound, computed tomography, and magnetic resonance (MR) spectroscopy and imaging, are reviewed. A novel MR method, the spectrally modeled relaxation-invariant technique, overcomes the inherent weaknesses of conventional MR to diagnose and quantify hepatic steatosis over its entire range of severity. Noninvasive radiologic techniques, particularly MR, can be applied broadly, including in the diagnosis of NAFLD in asymptomatic patients with elevated serum aminotransferase levels, longitudinal monitoring of disease progression or response to treatment, population-based epidemiologic or observational studies, and drug discovery.

Magnetic resonance imaging and spectroscopy for monitoring liver steatosis

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 in-phase/out-of-phase (IP/OP) and plus/minus fat saturation (+/-FS) 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) = 0.928, P < 0.0001) and MRI (IP/OP r(s) = 0.942, P < 0.0001; FS r(s) = 0.935, P < 0.0001). Following weight reduction, four of five patients with >5% weight loss had a decrease in IHCL of >or=50%.

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.

Quantification of liver fat content: comparison of triple-echo chemical shift gradient-echo imaging and in vivo proton MR spectroscopy

PURPOSE

To validate a triple-echo gradient-echo sequence for measuring the fat content of the liver, by using hydrogen 1((1)H) magnetic resonance (MR) spectroscopy as the reference standard.

MATERIALS AND METHODS

This prospective study was approved by the appropriate ethics committee, and written informed consent was obtained from all patients. In 37 patients with type 2 diabetes (31 men, six women; mean age, 56 years), 3.0-T single-voxel point-resolved (1)H MR spectroscopy of the liver (Couinaud segment VII) was performed to calculate the liver fat fraction from the water (4.7 ppm) and methylene (1.3 ppm) peaks, corrected for T1 and T2 decay. Liver fat fraction was also computed from triple-echo (consecutive in-phase, opposed-phase, and in-phase echo times) breath-hold spoiled gradient-echo sequence (flip angle, 20 degrees), by estimating T2* and relative signal intensity loss between in- and opposed-phase values, corrected for T2* decay. Pearson correlation coefficient, Bland-Altman 95% limit of agreement, and Lin concordance coefficient were calculated.

RESULTS

Mean fat fractions calculated from the triple-echo sequence and (1)H MR spectroscopy were 10% (range, 0.7%-35.6%) and 9.7% (range, 0.2%-34.1%), respectively. Mean T2* time was 14.7 msec (range, 5.4-25.4 msec). Pearson correlation coefficient was 0.989 (P < .0001) and Lin concordance coefficient was 0.988 (P < .0001). With the Bland-Altman method, all data points were within the limits of agreement.

CONCLUSION

A breath-hold triple-echo gradient-echo sequence with a low flip angle and correction for T2* decay is accurate for quantifying fat in segment VII of the liver. Given its excellent correlation and concordance with (1)H MR spectroscopy, this triple-echo sequence could replace (1)H MR spectroscopy in longitudinal studies.

New diagnostic and treatment approaches in non-alcoholic fatty liver disease (NAFLD)

Non-alcoholic fatty liver disease or NAFLD is a chronic liver condition characterized by hepatic steatosis and associated with insulin resistance and type 2 diabetes mellitus (T2DM). In many patients fat accumulation leads to steatohepatitis (NASH) with chronic necrosis, inflammation, and fibrosis, and eventually to the development of cirrhosis. Obese and T2DM patients are at the greatest risk for NASH and progressive disease. New diagnostic techniques, such as magnetic resonance imaging and spectroscopy (MRS), have enhanced our way to non-invasively quantify liver fat and suggest that the epidemic of NAFLD is much larger than previously believed. However, the diagnosis of NAFLD for clinicians remains difficult due to a number of factors: limited awareness, non-specific symptoms, few laboratory findings, and the need for a liver biopsy to confirm the diagnosis. Traditional treatment approaches have centered on weight loss, but data are limited on its long-term efficacy, and the overall compliance is poor. Recently, pioglitazone has been shown to be safe and effective in patients with NASH and may radically change our approach to the disease. Still, many aspects remain poorly understood. Taken together, wider use of new diagnostic methods and treatment approaches appears to signal the dawn of a new era in the management of NAFLD.

Genetic variation in PNPLA3 confers susceptibility to nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a burgeoning health problem of unknown etiology that varies in prevalence among ancestry groups. To identify genetic variants contributing to differences in hepatic fat content, we carried out a genome-wide association scan of nonsynonymous sequence variations (n = 9,229) in a population comprising Hispanic, African American and European American individuals. An allele in PNPLA3 (rs738409[G], encoding I148M) was strongly associated with increased hepatic fat levels (P = 5.9 x 10(-10)) and with hepatic inflammation (P = 3.7 x 10(-4)). The allele was most common in Hispanics, the group most susceptible to NAFLD; hepatic fat content was more than twofold higher in PNPLA3 rs738409[G] homozygotes than in noncarriers. Resequencing revealed another allele of PNPLA3 (rs6006460[T], encoding S453I) that was associated with lower hepatic fat content in African Americans, the group at lowest risk of NAFLD. Thus, variation in PNPLA3 contributes to ancestry-related and inter-individual differences in hepatic fat content and susceptibility to NAFLD.

Nonalcoholic fatty liver disease: rapid evaluation of liver fat content with in-phase and out-of-phase MR imaging

PURPOSE

To evaluate in-phase and out-of-phase magnetic resonance (MR) imaging in the estimation of liver fat content (LFC) in patients with nonalcoholic fatty liver disease (NAFLD), with hydrogen ((1)H) MR spectroscopy as the reference standard.

MATERIALS AND METHODS

Written informed consent was obtained from all subjects, and the local ethics committee approved this prospective study protocol. A total of 33 patients with type 2 diabetes mellitus who were at high risk for NAFLD (23 men, 10 women; overall mean age, 62.8 years +/- 8.3 [standard deviation]; age range, 48-77 years) underwent 1.5-T MR imaging with (1)H MR spectroscopy and in-phase and out-of-phase imaging of the liver. Three fat indexes were calculated from the signal intensity (SI) measured on the images. Two radiologists independently graded SI changes between in-phase and out-of-phase images by means of visual inspection. The Pearson correlation coefficient was used to study the relationship between the obtained parameters of SI change and LFC measured with (1)H MR spectroscopy.

RESULTS

Fat indexes calculated from in-phase and out-of-phase images correlated linearly with LFC measured with (1)H MR spectroscopy (P < .001, r = 0.94-0.96) and were superior (P = .004) to visual estimates (P < .001, r = 0.88). The simple difference in SI between in-phase and out-of-phase images was used to calculate the fat index. An intercept of the regression line with the x-axis was observed at 5.1%, discriminating between normal and elevated LFC with high sensitivity (95%) and specificity (98%).

CONCLUSION

In-phase and out-of-phase imaging can be used to rapidly estimate the LFC in patients with NAFLD. The cutoff value of 5.1% enables objective rapid and reliable discrimination of normal LFC from elevated LFC.

Respiratory motion-corrected proton magnetic resonance spectroscopy of the liver

PURPOSE

To develop a post-processing, respiratory-motion correction algorithm for magnetic resonance spectroscopy (MRS) of the liver and to determine the incidence and impact of respiratory motion in liver MRS.

MATERIALS AND METHODS

One hundred thirty-two subjects (27 healthy, 31 with nonalcoholic fatty liver disease and 74 HIV-infected with or without hepatitis C) were scanned with free breathing MRS at 1.5 T. Two spectral time series were acquired on an 8-ml single voxel using TR/TE=2500 ms/30 ms and (1) water suppression, 128 acquisitions, and (2) no water suppression, 8 acquisitions. Individual spectra were phased and frequency aligned to correct for intrahepatic motion. Next, water peaks more than 50% different from the median water peak area were identified and removed, and remaining spectra averaged to correct for presumed extrahepatic motion. Total CH(2)+CH(3) lipids to unsuppressed water ratios were compared before and after corrections.

RESULTS

Intrahepatic-motion correction increased the signal to noise ratio (S/N) in all cases (median=11-fold). Presumed extrahepatic motion was present in 41% (54/132) of the subjects. Its correction altered the lipids/water magnitude (magnitude change: median=2.6%, maximum=290%, and was >5% in 25% of these subjects). The incidence and effect of respiratory motion on lipids/water magnitude were similar among the three groups.

CONCLUSION

Respiratory-motion correction of free breathing liver MRS greatly increased the S/N and, in a significant number of subjects, changed the lipids/water ratios, relevant for monitoring subjects.

Comparison of combined aerobic and high-force eccentric resistance exercise with aerobic exercise only for people with type 2 diabetes mellitus

BACKGROUND AND PURPOSE

The purpose of this study was to compare the outcomes between a diabetes exercise training program using combined aerobic and high-force eccentric resistance exercise and a program of aerobic exercise only.

SUBJECTS AND METHODS

Fifteen participants with type 2 diabetes mellitus (T2DM) participated in a 16-week supervised exercise training program: 7 (mean age=50.7 years, SD=6.9) in a combined aerobic and eccentric resistance exercise program (AE/RE group) and 8 (mean age=58.5 years, SD=6.2) in a program of aerobic exercise only (AE group). Outcome measures included thigh lean tissue and intramuscular fat (IMF), glycosylated hemoglobin, body mass index (BMI), and 6-minute walk distance.

RESULTS

Both groups experienced decreases in mean glycosylated hemoglobin after training (AE/RE group: -0.59% [95% confidence interval (CI)=-1.5 to 0.28]; AE group: -0.31% [95% CI=-0.60 to -0.03]), with no significant between-group differences. There was an interaction between group and time with respect to change in thigh lean tissue cross-sectional area, with the AE/RE group gaining more lean tissue (AE/RE group: 15.1 cm(2) [95% CI=7.6 to 22.5]; AE group: -5.6 cm(2) [95% CI=-10.4 to 0.76]). Both groups experienced decreases in mean thigh IMF cross-sectional area (AE/RE group: -1.2 cm(2) [95% CI=-2.6 to 0.26]; AE group: -2.2 cm(2) [95% CI=-3.5 to -0.84]) and increases in 6-minute walk distance (AE/RE group: 45.5 m [95% CI=7.5 to 83.6]; AE group: 29.9 m [95% CI=-7.7 to 67.5]) after training, with no between-group differences. There was an interaction between group and time with respect to change in BMI, with the AE/RE group experiencing a greater decrease in BMI.

DISCUSSION AND CONCLUSION

Significant improvements in long-term glycemic control, thigh composition, and physical performance were demonstrated in both groups after participating in a 16-week exercise program.

SUBJECTS

in the AE/RE group demonstrated additional improvements in thigh lean tissue and BMI. Improvements in thigh lean tissue may be important in this population as a means to increase resting metabolic rate, protein reserve, exercise tolerance, and functional mobility.

Genetic variation in PNPLA3 confers susceptibility to nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a burgeoning health problem of unknown etiology that varies in prevalence among ancestry groups. To identify genetic variants contributing to differences in hepatic fat content, we carried out a genome-wide association scan of nonsynonymous sequence variations (n = 9,229) in a population comprising Hispanic, African American and European American individuals. An allele in PNPLA3 (rs738409[G], encoding I148M) was strongly associated with increased hepatic fat levels (P = 5.9 x 10(-10)) and with hepatic inflammation (P = 3.7 x 10(-4)). The allele was most common in Hispanics, the group most susceptible to NAFLD; hepatic fat content was more than twofold higher in PNPLA3 rs738409[G] homozygotes than in noncarriers. Resequencing revealed another allele of PNPLA3 (rs6006460[T], encoding S453I) that was associated with lower hepatic fat content in African Americans, the group at lowest risk of NAFLD. Thus, variation in PNPLA3 contributes to ancestry-related and inter-individual differences in hepatic fat content and susceptibility to NAFLD.

Biomedical imaging in the safety evaluation of new drugs

Toxicology accounts for approximately one-third of attrition in new drug development and is a major concern in the pharmaceutical industry. This paper reviews the role of biomedical imaging in the safety evaluation of new candidate drugs. Ex vivo high-resolution three-dimensional imaging of specimens can provide a quick overview of the specimens. Volumetric measurements of tissue structures and lesions can be made with higher precision and reproducibility than histology approaches. As opposed to histology, in vivo animal imaging permits longitudinal studies of the same animals over an extended period of time, with individual animals serving as their own control. Therefore, the number of animals required for a study can be significantly reduced and the intra-subject variability is minimized. Repeated in vivo imaging allows monitoring of the occurrence and progression, or regression, of various structural and functional abnormalities. Compared with other biological assays, imaging can provide anatomically specific information about tissue abnormality. Imaging offers the opportunity to carry forward the same methodology in animal experiments into human studies and has an important role in clinical trials when other safety biomarkers for early toxicities are not available.

Non-invasive means of measuring hepatic fat content

Hepatic steatosis affects 20% to 30% of the general adult population in the western world. Currently, the technique of choice for determining hepatic fat deposition and the stage of fibrosis is liver biopsy. However, it is an invasive procedure and its use is limited, particularly in children. It may also be subject to sampling error. Non-invasive techniques such as ultrasound, Computerized tomography (CT), magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopy (¹H MRS) can detect hepatic steatosis, but currently cannot distinguish between simple steatosis and steatohepatitis, or stage the degree of fibrosis accurately. Ultrasound is widely used to detect hepatic steatosis, but its sensitivity is reduced in the morbidly obese and also in those with small amounts of fatty infiltration. It has been used to grade hepatic fat content, but this is subjective. CT can detect hepatic steatosis, but exposes subjects to ionizing radiation, thus limiting its use in longitudinal studies and in children. Recently, magnetic resonance (MR) techniques using chemical shift imaging have provided a quantitative assessment of the degree of hepatic fatty infiltration, which correlates well with liver biopsy results in the same patients. Similarly, in vivo¹H MRS is a fast, safe, non-invasive method for the quantification of intrahepatocellular lipid (IHCL) levels. Both techniques will be useful tools in future longitudinal clinical studies, either in examining the natural history of conditions causing hepatic steatosis (e.g. non-alcoholic fatty liver disease), or in testing new treatments for these conditions.

Quantitative proton magnetic resonance spectroscopy of the normal liver and malignant hepatic lesions at 3.0 Tesla

This comparative study of tumour patients and volunteers aimed at differentiating liver parenchyma from neoplastic lesions by using localised (1)H MRS at 3.0 T as an adjunct to MRI. In total 186 single-voxel proton spectra of the liver were acquired at 3.0 T using the body transmit receive coil. Consecutive stacks of breath-hold spectra were acquired in the PRESS technique at a short echo time of 35 ms and a repetition time of 2,000 ms. Processing of the spectra included spectral alignment with the software package SAGE and quantitative processing with LCModel. The resulting metabolite concentrations were presented in arbitrary units relative to the internal water. In general, the spectra showed four main groups of resonances originating from the methyl protons (0.8-1.1 ppm) and methylene protons of the lipids (1.1-1.5 ppm; 2.0-2.2 ppm) as well as the methyl protons of choline-containing compounds (CCC) at 3.2 ppm. Overall, the CCC and lipid values in malignant liver tumours showed no significant differences to liver parenchyma. On average, total lipid measurements in normal liver parenchyma increased with age, while those of the CCC did not show pertinent changes. Significant differences between the contents of CCC in malignant liver tumours and normal liver parenchyma were not observed, because in patients and volunteers normal liver tissue showed a large variability in the content of CCC.

Nonalcoholic fatty liver disease

OBJECTIVE

The inflammatory subtype of nonalcoholic fatty liver disease, nonalcoholic steatohepatitis, is becoming one of the most important causes of chronic liver disease. In this article, we discuss the epidemiology, pathogenesis, and clinical and radiologic diagnosis of the subtypes of nonalcoholic fatty liver disease.

CONCLUSION

We discuss the current and evolving imaging tests in the evaluation of hepatic fatty content, inflammation, and fibrosis.

Hepatic fat content is a determinant of postprandial triglyceride levels in type 2 diabetes mellitus patients with normal fasting triglyceride

Postprandial hypertriglyceridemia is common in type 2 diabetes mellitus (T2D). Significant numbers of T2D patients who have normal fasting triglyceride (TG) have postprandial hypertriglyceridemia. The role of regional adipose tissue and adiponectin on postprandial TG responses in this group of T2D patients is unclear. This study aimed to examine the contribution of regional adipose tissue and adiponectin to the variation of postprandial TG responses in T2D patients who have normal fasting TG levels. Thirty-one Thai T2D patients who had fasting TG<1.7 mmol/L were studied. All were treated with diet control or sulphonylurea and/or metformin. None was treated with lipid-lowering agents. Mixed-meal test was performed after overnight fast. Plasma glucose, insulin, and TG were measured before and 1, 2, 3, and 4 hours after the test. Adiponectin was measured in fasting state. Visceral as well as superficial and deep subcutaneous abdominal adipose tissues were determined by magnetic resonance imaging, and hepatic fat content (HFC) was determined by magnetic resonance spectroscopy. Univariate and multivariate regression analyses of postprandial TG and regional adipose tissue and metabolic parameters were performed. The TG levels before and 1, 2, 3, and 4 hours after the mixed meal were 1.32+/-0.40 (SD), 1.40+/-0.41, 1.59+/-0.40, 1.77+/-0.57, and 1.80+/-0.66 mmol/L, respectively (P<.0001). The area under the curve (AUC) of postprandial TG was positively and significantly correlated with fasting TG (r=0.84, P<.0001) and log.HFC (r=0.456, P=.033) and was inclined to be correlated with log.deep subcutaneous adipose tissue (r=0.38, P=.05) and sex (r=0.326, P=.073). The AUC of postprandial TG was not correlated with age, body mass index, waist circumference, log.superficial subcutaneous adipose tissue, log.visceral adipose tissue, hemoglobin A1c, fasting glucose, AUC.glucose, log.fasting insulin, log.AUC.insulin, log.homeostasis model assessment%B, log.homeostasis model assessment of insulin resistance, and adiponectin. Only fasting TG (beta=.815, P<.0001) and log.HFC (beta=.249, P=.035) predicted AUC of postprandial TG in regression model (adjusted R2=0.84, P<.0001). In conclusion, in T2D patients with normal fasting TG, the increase of postprandial TG levels is directly determined by fasting TG level and the amount of hepatic fat.

Fast-food-based hyper-alimentation can induce rapid and profound elevation of serum alanine aminotransferase in healthy subjects

OBJECTIVE

To study the effect of fast-food-based hyper-alimentation on liver enzymes and hepatic triglyceride content (HTGC).

DESIGN

Prospective interventional study with parallel control group.

SETTING

University Hospital of Linköping, Sweden.

PARTICIPANTS

12 healthy men and six healthy women with a mean (SD) age of 26 (6.6) years and a matched control group.

INTERVENTION

Subjects in the intervention group aimed for a body weight increase of 5-15% by eating at least two fast-food-based meals a day with the goal to double the regular caloric intake in combination with adoption of a sedentary lifestyle for 4 weeks.

MAIN OUTCOME MEASURES

Weekly changes of serum aminotransferases and HTGC measured by proton nuclear magnetic resonance spectroscopy at baseline and after the intervention.

RESULTS

Subjects in the intervention group increased from 67.6 (9.1) kg to 74.0 (11) kg in weight (p<0.001). Serum ALT increased from 22.1 (11.4) U/l at study start to an individual mean maximum level of 97 (103) U/l (range 19.4-447 U/l). Eleven of the 18 subjects persistently showed ALT above reference limits (women >19 U/l, men >30 U/l) during the intervention. Sugar (mono- and disaccharides) intake during week 3 correlated with the maximal ALT/baseline ALT ratio (r = 0.62, p = 0.006). HTGC increased from 1.1 (1.9)% to 2.8 (4.8)%, although this was not related to the increase in ALT levels. ALT levels were unchanged in controls.

CONCLUSION

Hyper-alimentation per se can induce profound ALT elevations in less than 4 weeks. Our study clearly shows that in the evaluation of subjects with elevated ALT the medical history should include not only questions about alcohol intake but also explore whether recent excessive food intake has occurred.

Liver fat content and T2*: simultaneous measurement by using breath-hold multiecho MR imaging at 3.0 T--feasibility

Research ethics committee approval was obtained for this study, and written informed consent was obtained from all participants. The purpose was to prospectively evaluate the feasibility of breath-hold multiecho in- and out-of-phase magnetic resonance (MR) imaging for simultaneous lipid quantification and T2* measurement. A spoiled gradient-echo sequence with seven echo times alternately in phase and out of phase was used at 3.0 T. Imaging was performed in a lipid phantom, in five healthy volunteers (all men; mean age, 37 years), and in five obese individuals with hyperlipidemia or diabetes (four men, one woman; mean age, 53 years). A biexponential curve-fitting model was used to derive the relative signal contributions from fat and water, and these results were compared with results of liver proton MR spectroscopy, the reference standard. There was a significant correlation between multiecho and spectroscopic measurements of hepatic lipid concentration (r(2) = 0.99, P < .001). In vivo, the T2* of water was consistently longer than that of fat and reliably enabled the signal components to be correctly assigned. In the lipid phantom, the multiecho method could be used to determine the fat-to-water ratio and the T2* values of fat and water throughout the entire range of fat concentrations. Multiecho imaging shows promise as a method of simultaneous fat and T2* quantification.

Assessment of in vivo 1H magnetic resonance spectroscopy in the liver: a review

With increased availability of magnetic resonance (MR) systems at ultra-high field strength for clinical studies, other organs besides the brain have received renewed consideration for MR spectroscopy (MRS). Because signal-to-noise ratio and chemical shift increase proportional to the static magnetic field, a concomitant increase in signal intensity and spectral resolution of metabolite resonances can be exploited. Improved resolution of adjacent metabolite peaks would not only provide for more accuracy of metabolite identification but also metabolite quantification. While the superiority of high-field imaging and spectroscopy has already been demonstrated clearly in the brain, this article reviewed issues around 1H MRS of the liver. These include optimization strategies such as coil technology, minimizing of motion artefacts using breath-holding and postprocessing of the spectra. Moreover, we reviewed the pertinent experience hitherto reported in the literature on potential clinical issues where liver MRS may be useful. These included determination and characterization of liver fat content, liver tumours and focal lesions. While these applications have been used experimentally, liver MRS does not yet have a clearly defined role in the clinical management of any disease state. Accordingly, it remains primarily a research modality to date.

Increased mediastinal fat and impaired left ventricular energy metabolism in young men with newly found fatty liver

Fatty liver is characterized by metabolic abnormalities at the liver, but also at skeletal muscle and adipose tissue sites. It is hypothesized that the heart may be suffering metabolic alterations, and this study was undertaken to ascertain whether individuals with fatty liver have left ventricular (LV) alterations of energy metabolism, structure, and function and abnormal amounts of epicardial fat as a specific marker of visceral fat accumulation. To this end we studied young, nondiabetic men matched for anthropometric features with (n = 21) or without (n = 21) fatty liver by means of (1) cardiac magnetic resonance imaging (MRI); (2) cardiac (31)P-MR spectroscopy (MRS); and (3) hepatic (1)H-MRS to assess quantitatively the intrahepatic fat (IHF) content. Insulin sensitivity was determined by the updated HOMA-2 computer model. Individuals with fatty liver showed reduced insulin sensitivity, increased serum free fatty acid (FFA), and E-selectin, abnormal adipokine concentrations, and higher blood pressure. LV morphology and systolic and diastolic functions were not different; however, in the scanned intrathoracic region, the intrapericardial (7.8 +/- 3.1 versus 5.9 +/- 2.5 cm(2); P < 0.05) and extrapericardial (11.7 +/- 6.1 versus 7.8 +/- 3.2 cm(2); P < 0.03) fat was increased in men with fatty liver compared with those without fatty liver. The phosphocreatine (PCr)/adenosine triphosphate (ATP) ratio, a recognized in vivo marker of myocardial energy metabolism, was reduced in men with fatty liver in comparison with normals (1.85 +/- 0.35 versus 2.11 +/- 0.31; P < 0.016). In conclusion, in newly found individuals with fatty liver, fat was accumulated in the epicardial area and despite normal LV morphological features and systolic and diastolic functions, they had abnormal LV energy metabolism.

Fatty Liver

Although the epidemic of obesity has been accompanied by an increase in the prevalence of the metabolic syndrome, not all obese develop the syndrome and even lean individuals can be insulin resistant. Both lean and obese insulin resistant individuals have an excess of fat in the liver which is not attributable to alcohol or other known causes of liver disease, a condition defined as nonalcoholic fatty liver disease (NAFLD) by gastroenterologists. The fatty liver is insulin resistant. Liver fat is highly significantly and linearly correlated with all components of the metabolic syndrome independent of obesity. Overproduction of glucose, VLDL, CRP, and coagulation factors by the fatty liver could contribute to the excess risk of cardiovascular disease associated with the metabolic syndrome and NAFLD. Both of the latter conditions also increase the risk of type 2 diabetes and advanced liver disease. The reason why some deposit fat in the liver whereas others do not is poorly understood. Individuals with a fatty liver are more likely to have excess intraabdominal fat and inflammatory changes in adipose tissue. Intervention studies have shown that liver fat can be decreased by weight loss, PPARγ agonists, and insulin therapy.

Pancreatic fat content and beta-cell function in men with and without type 2 diabetes

OBJECTIVE

Insulin resistance, associated with increased lipolysis, results in a high exposure of nonadipose tissue to lipids. Experimental data indicate that fatty infiltration of pancreatic islets may also contribute to beta-cell dysfunction, but whether this occurs in humans in vivo is unknown.

RESEARCH DESIGN AND METHODS

Using proton magnetic resonance spectroscopy and oral glucose tolerance tests, we studied the association of pancreatic lipid accumulation in vivo and various aspects of beta-cell function in 12 insulin-naive type 2 diabetic and 24 age- and BMI-matched nondiabetic men.

RESULTS

Patients versus control subjects had higher A1C, fasting plasma glucose, and insulin and triglyceride levels and lower HDL cholesterol, but similar waist circumference. Median (interquartile range) pancreatic fat content in patients and control subjects was 20.4% (13.4-43.6) and 9.7% (7.0-20.2), respectively (P = 0.032). Pancreatic fat correlated negatively with beta-cell function parameters, including the insulinogenic index adjusted for insulin resistance, early glucose-stimulated insulin secretion, beta-cell glucose sensitivity, and rate sensitivity (all P < 0.05), but not potentiation. However, these associations were significantly affected by the diabetic state, such that a significant association of pancreatic fat with beta-cell dysfunction was only present in the nondiabetic group (all P < 0.01), suggesting that once diabetes occurs, factors additional to pancreatic fat account for further beta-cell function decline. In control subjects, the association of pancreatic fat and beta-cell function remained significant after correction for BMI, fasting plasma glucose, and triglycerides (P = 0.006).

CONCLUSIONS

These findings indicate that pancreatic lipid content may contribute to beta-cell dysfunction and possibly to the subsequent development of type 2 diabetes in susceptible humans.

Evaluation and management of obesity-related nonalcoholic fatty liver disease

The clinicopathologic spectrum of nonalcoholic fatty liver disease (NAFLD) ranges from simple steatosis to nonalcoholic steatohepatitis (NASH). Simple steatosis has a relatively benign clinical course, but NASH can progress to cirrhosis and hepatocellular carcinoma. NAFLD occurs in the absence of significant alcohol use and is considered to be the hepatic manifestation of metabolic syndrome. NAFLD affects approximately 30% of the US population and the incidence seems to be rising as the obesity epidemic continues. At present, the most accurate modality for the diagnosis of NASH is liver biopsy; however, many patients do not have a liver biopsy, and in the absence of more-accurate imaging technologies and serum markers, the diagnosis is frequently one of exclusion. As yet there is no convincingly effective treatment for NAFLD--a multimodal treatment plan that targets obesity, insulin resistance, hyperlipidemia and hypertension might be the best option for these patients.

Postprandial lipemia associates with liver fat content

CONTEXT/OBJECTIVE

Postprandial lipemia and low adiponectin represent novel risk factors for vascular disease. This study aimed to determine whether liver fat content and adiponectin are predictors of postprandial triglyceride (TG)-rich lipoproteins (TRL).

PATIENTS/INTERVENTIONS

Twenty-nine men were allocated into subgroups with either low (< or =5%) or high (>5%) liver fat measured with magnetic resonance proton spectroscopy. Subjects underwent an oral fat tolerance test with measurements of postprandial TG, cholesterol, apolipoprotein B-48 (apoB-48), and apoB-100 in TRL fractions, a euglycemic hyperinsulinemic clamp, and determination of abdominal fat volumes by magnetic resonance imaging.

RESULTS

Subjects with high liver fat displayed increased response of postprandial lipids in plasma, chylomicron, and very-low-density lipoprotein 1 (VLDL1) (Svedberg flotation rate 60-400) fractions. Liver fat correlated positively with postprandial responses (area under the curve) of TG (r = 0.597; P = 0.001), cholesterol (r = 0.546; P = 0.002), apoB-48 (r = 0.556; P = 0.002), and apoB-100 (r = 0.42; P = 0.023) in the VLDL1 fraction. Respective incremental areas under the curve correlated significantly with liver fat. Fasting adiponectin levels were inversely correlated with both postprandial lipids and liver fat content. Liver fat remained the only independent correlate in a multiple linear regression analysis for chylomicron and VLDL1 responses.

CONCLUSIONS

Liver fat content is a close correlate of postprandial lipids predicting the responses of TRL in chylomicrons and VLDL1 better than measures of glucose metabolism or body adiposity. Low adiponectin concentration is closely linked to high liver fat content and impaired TRL metabolism. High liver fat content associated with postprandial lipemia represents potential risk factors for cardiovascular disease.

The expression of NAD(P)H:quinone oxidoreductase 1 is high in human adipose tissue, reduced by weight loss, and correlates with adiposity, insulin sensitivity, and markers of liver dysfunction

CONTEXT

We have previously identified nicotinamide adenine dinucleotide phosphate:quinone oxidoreductase 1 (NQO1), an enzyme involved in the protection against oxidative stress, as a gene predominantly expressed in human adipocytes. Studies in mice deficient in NQO1 activity suggest that NQO1 may also play an important role in metabolism.

OBJECTIVE

The aim of this study was to explore the expression and regulation of NQO1 in human adipose tissue (AT) and isolated adipocytes.

PATIENTS AND RESULTS

The high expression of NQO1 in adipocytes was verified in human adipocytes and AT by real-time PCR. DNA microarray analysis showed that NQO1 was expressed at higher levels in large compared with small adipocytes, isolated from the same fat biopsy. Furthermore, NQO1 mRNA levels were positively correlated with adipocyte size (n = 7; P < 0.002). During an 18-wk diet regime (n = 24; mean weight loss 27 kg), the NQO1 expression in human sc AT was down-regulated (P < 0.0001), and mRNA levels correlated with body mass index (P = 0.0005), sc, and total abdominal AT areas, as determined by computerized tomography (P < 0.0001, both) and metabolic parameters. NQO1 mRNA levels were also positively correlated with aspartate aminotransferase (P = 0.0028) and alanine aminotransferase (P = 0.0219), markers known to be associated with severity of hepatic steatosis.

CONCLUSIONS

NQO1 is highly expressed in human AT, particularly in large adipocytes. AT NQO1 expression is reduced during diet-induced weight loss, and the expression levels positively correlate with adiposity, glucose tolerance, and markers of liver dysfunction. Together, these findings indicate a role for NQO1 in the metabolic complications of human obesity.

Diagnosis of hepatic steatosis and fibrosis by transient elastography in asymptomatic healthy individuals: a prospective study of living related potential liver donors

BACKGROUND

This prospective study aimed to assess the ability of transient elastography to identify histologic parameters, including steatosis, in asymptomatic healthy individuals such as potential liver donors, and to compare these findings with results in liver disease patients.

METHODS

Forty-seven patients with abnormal liver function and/or hepatitis symptoms and 80 living related potential liver donors were consecutively enrolled, and liver biopsy and a Fibroscan test were performed in each subject. Histologic parameters were evaluated according to METAVIR scale by a single pathologist.

RESULTS

In liver disease patients, stiffness was significantly correlated with fibrosis stage (Spearman correlation coefficient, 0.700; P < 0.001), and the optimal stiffness cutoff values for F >or= 2, F >or= 3, and F = 4 were 7.35, 8.85, and 15.1 kPa respectively. In potential liver donors, however, stiffness was not correlated with fibrosis (0.023; P = 0.851). In the latter group, the area under the receiver-operating characteristics curve was 0.70 (95% confidence interval, 0.58-0.81), and the optimal stiffness cutoff value was 4.00 for F >or= 2, which was lower than that in liver disease patients. Steatosis was not correlated with stiffness (0.088; P = 0.463) in potential liver donors.

CONCLUSIONS

Transient elastography has limited value for detecting steatosis in asymptomatic healthy individuals, and the cutoff value for fibrosis should be reevaluated in these subjects.

Effect of insulin-metformin combination on hepatic steatosis in patients with type 2 diabetes

OBJECTIVE

Hepatic steatosis occurs in up to 78% of patients with type 2 diabetes. Studies evaluating the effect of metformin on hepatic steatosis are conflicting. Insulin is believed to be detrimental due to its lipogenic effect. Since insulin-metformin combination is commonly used for the treatment of diabetes, it is important to assess the effect of this combined therapy on hepatic steatosis. We evaluated the change in hepatic steatosis following the initiation of insulin and metformin in patients with type 2 diabetes.

METHODS

Newly diagnosed treatment-naïve patients with type 2 diabetes had their hepatic triglyceride (TG) content measured by magnetic resonance spectroscopy at baseline and after 3 months of treatment with BiAsp 30 insulin, in combination with metformin. Insulin was administered twice daily and titrated to achieve normal capillary blood glucose levels. Metformin was titrated during the first month from 500 mg daily to 1000 mg bid.

RESULTS

The average hepatic TG content in 19 enrolled subjects was 11.83+/-7.61% (range, 0.93-23.16%) and correlated with body mass index (r=.567). Three months of treatment reduced hepatic steatosis by 45%, with 75% of the study subjects achieving a normal level. The change in hepatic TG content was partially explained by changes in HbA1c (P=.006) and cholesterol (P=.003) levels.

CONCLUSIONS

The combined treatment with insulin and metformin significantly reduced hepatic steatosis in patients with newly diagnosed type 2 diabetes.