Imaging the fatty liver

Diffuse and focal liver fat: advanced imaging techniques and diagnostic insights

The fatty liver disease represents a complex, multifaceted challenge, requiring a multidisciplinary approach for effective management and research. This article uses conventional and advanced imaging techniques to explore the etiology, imaging patterns, and quantification methods of hepatic steatosis. Particular emphasis is placed on the challenges and advancements in the imaging diagnostics of fatty liver disease. Techniques such as ultrasound, CT, MRI, and elastography are indispensable for providing deep insights into the liver's fat content. These modalities not only distinguish between diffuse and focal steatosis but also help identify accompanying conditions, such as inflammation and fibrosis, which are critical for accurate diagnosis and management.

Imaging of the chemotherapy-induced hepatic damage: Yellow liver, blue liver, and pseudocirrhosis

The liver is the major drug-metabolizing and drug-detoxifying organ. Many drugs can cause liver damage through various mechanisms; however, the liver response to injury includes a relatively narrow spectrum of alterations that, regardless of the cause, are represented by phlogosis, oxidative stress and necrosis. The combination of these alterations mainly results in three radiological findings: vascular alterations, structural changes and metabolic function reduction. Chemotherapy has changed in recent decades in terms of the drugs, protocols and duration, allowing patients a longer life expectancy. As a consequence, we are currently observing an increase in chemotherapy-associated liver injury patterns once considered unusual. Recognizing this form of damage in an early stage is crucial for reconsidering the therapy regimen and thus avoiding severe complications. In this frontier article, we analyze the role of imaging in detecting some of these pathological patterns, such as pseudocirrhosis, “yellow liver” due to chemotherapy-associated steatosis-steatohepatitis, and “blue liver”, including sinusoidal obstruction syndrome, veno-occlusive disease and peliosis.

MR Imaging of Diffuse Liver Disease

The liver performs many vital functions for the human body. It stores essential vitamins and minerals, such as iron and vitamins A, D, K, and B₁₂. It synthesizes proteins, such as blood clotting factors, albumin, and glycogen, as well as cholesterol, carbohydrates, and triglycerides. Additionally, it acts as a detoxifier, metabolizing and helping to clear alcohol, drugs, and ammonia. Typical MR imaging protocols for liver imaging include T2-weighted, chemical shift imaging, and precontrast and postcontrast T1-weighted sequences. This article discussed MR imaging of diffuse liver diseases and their typical imaging findings.

Liver Imaging Reporting and Data System Comprehensive Guide: MR Imaging Edition

The Liver Imaging Reporting and Data System (LI-RADS) is a comprehensive system for standardizing the lexicon, technique, interpretation, reporting, and data collection of liver imaging. Developed specifically for assessment of liver observations in patients at risk for hepatocellular carcinoma (HCC), LI-RADS classifies hepatic observations on the basis of the probability of their being HCC, from LR-1 (definitely benign) to LR-5 (definitely HCC). This article discusses the technical requirements, major features, and ancillary features of and a systematic approach for using the LI-RADS diagnostic algorithm, with special emphasis on MR imaging.

Imaging Features of Non-Alcoholic Fatty Liver Disease in Children and Adolescents

Non-invasive diagnosis and quantification of liver steatosis is important to overcome limits of liver biopsy, in order to follow up patients during their therapy and to establish a reference standard that can be used in clinical trials and longitudinal studies. Imaging offers several methods in this setting: ultrasound, which is the cheapest technique and easy to perform; magnetic resonance spectroscopy (MRS), which reflects the real content of triglycerides in a specific volume; and proton density fat fraction (PDFF) magnetic resonance, which is a simple method that reflects the distribution of the fat in the whole liver. Other techniques include ultrasound elastography (EUS) and magnetic resonance elastrography (MRE), which can evaluate the progression of non-alcoholic fatty liver disease (NAFLD) into non-alcoholic steato-hepatitis (NASH) and cirrhosis, by quantifying liver fibrosis.

Focal fat deposition in the liver: diagnostic challenges on imaging

While focal fat deposition in the liver mostly occurs in typical locations related to non-portal venous supply, unusual patterns of focal fat deposition, including multi-nodular, mass-like, and perivascular patterns, mimic malignancies and cause diagnostic challenges. Patients with unusual focal fat deposition often have potential underlying etiologies such as diabetes, alcohol abuse, metabolic disease, or various medications/chemotherapy. Some cases can be explained by non-portal venous supply or ischemia. Chemical-shift MRI or contrast-enhanced ultrasound (CEUS) is useful for non-invasive diagnosis of focal fat deposition. We illustrate a series of US, CT, and MR imaging features of focal fatty deposition in the liver mimicking other conditions and seek possible causes. Understanding of imaging patterns of focal fat deposition and its potential causes can help a non-invasive diagnosis by performing confirmatory imaging tests and prevent unnecessary invasive procedures.

Imaging patterns of fatty liver in pediatric patients

Fatty liver can present as focal, diffuse, heterogeneous, and multinodular forms. Being familiar with various patterns of steatosis can enable correct diagnosis. In patients with equivocal findings on ultrasonography, magnetic resonance imaging can be used as a problem solving tool. New techniques are promising for diagnosis and follow-up. We review imaging patterns of steatosis and new quantitative methods such as proton density fat fraction and magnetic resonance elastography for diagnosis of nonalcoholic fatty liver disease in children.

Fatty liver in acute pancreatitis: characteristics in magnetic resonance imaging

OBJECTIVE

The objective of this research was to study the characteristics of fatty liver (FL) in acute pancreatitis (AP) in 2-dimensional in-phase (IP)/out-of-phase (OP) magnetic resonance imaging (MRI).

METHODS

Fifty patients with AP (23 men, 27 women; mean age, 44 [SD, 12] years [range, 16-73 years]) were included in this retrospective study. Patients' informed consent was waived. All of them performed abdominal MRI within 72 hours of symptom onset and MRI follow-up. The severity of the AP was graded according to the magnetic resonance severity index (MRSI). The MRSI cutoff was 7.0 points between the mild and the severe AP. Fatty liver in MRI was determined by the hepatic signal intensity difference between OP and IP images. Correlations between the severity of FL and MRSI or serum triglyceride levels were analyzed.

RESULTS

Of the 50 patients with AP, FL was found in 66% of patients' MRIs. A close correlation can be seen between the difference of liver signal intensities on IP/OP images and the MRSI (r = 0.83, P < 0.001). Close correlations were found between FL appearance on MRI and serum triglyceride levels in both mild (r = 0.93, P < 0.001) and severe AP (r = 0.95, P < 0.001). During follow-up MRI, the appearance of FL decreased following the decrease in MRSI scores and serum triglyceride levels in both mild and severe AP.

CONCLUSIONS

Fatty liver in AP is frequently observed in MRI. The appearance of FL in MRI may decrease after subsidence of AP.

Noninvasive quantification of hepatic fat content using three-echo dixon magnetic resonance imaging with correction for T2* relaxation effects

OBJECTIVE

To investigate three-echo T2*-corrected Dixon magnetic resonance imaging (MRI) for noninvasively estimating hepatic fat content (HFC) compared with biopsy.

MATERIALS AND METHODS

One hundred patients (50 men, 50 women; mean age, 57.7±14.2 years) underwent clinically indicated liver core biopsy (102 valid tissue samples) and liver MRI 24 to 72 hours later. MRI was performed at 1.5T (Magnetom Avanto, Siemens Healthcare, Erlangen, Germany) using Dixon imaging with T2* correction (work in progress, WIP-432.rev.1, Siemens Healthcare). An ultrafast breath-hold three-echo 3D-gradient echo sequence with TR/TE1/TE2/TE3 of 11/2.4/4.8/9.6 milliseconds, and online calculation of T2*-corrected water images (signal intensities of water [SIW]), fat images (SIF), and fat content map (SIFAT=10×SIF/(SIW+SIF)) was used. SIs of the calculated fat content map (SIFAT) were verified using the histologically quantified HFC (HFC(path)). Spearman correlation for HFC(path) and SIFAT was calculated. Stage of fibrosis, hepatic iron content, and patterns of liver fat (macrovesicular, microvesicular, mixed) and their influence on predicting HFC by MRI were determined.

RESULTS

Correlation between SIFAT and HFC(path) was rspearman=0.89. Agreement between HFC predicted by MRI and HFC(path) calculated by nonlinear saturation-growth regression was rspearman=0.89. Kruskal-Wallis analysis revealed no significant difference for SIFAT across fibrosis grades (P=0.90) and liver iron content (P=0.76). Regarding the cellular architecture of liver fat, the microvesicular pattern showed lower mean ranks in SI than macrovesicular and mixed patterns (P=0.01).

CONCLUSION

T2*-corrected Dixon MRI is a noninvasive tool for estimating HFC, showing excellent correlation with liver biopsy without being limited by liver iron content and fibrosis/cirrhosis.

Detection of a fatty liver after binge drinking: correlation of MR-spectroscopy, DECT, biochemistry and histology in a rat model

RATIONALE AND OBJECTIVES

The purpose of this study was to evaluate the possibility of detecting a fatty liver after binge drinking in an animal model using (1)H magnetic resonance spectroscopy ((1)H-MRS), dual-energy computed tomography (DECT), biochemistry, and the gold standard of histology.

MATERIALS AND METHODS

In 20 inbred female Lewis rats, an alcoholic fatty liver was induced; 20 rats served as controls. To simulate binge drinking, each rat was given a dose of 9.3 g/kg body weight 50% ethanol twice, with 24 hours between applications. Forty-eight hours after the first injection, DECT and (1)H-MRS were performed. Fat content as well as triglycerides were also determined histologically and biochemically, respectively. To assess specific liver enzymes, blood was drawn from the orbital venous plexus.

RESULTS

In all 20 animals in the experimental group, fatty livers were detected using (1)H-MRS, DECT, and biochemical and histologic analysis. The spectroscopic fat/water ratio and the biochemical determination were highly correlated (r = 0.892, P < .05). A significant correlation was found between (1)H-MRS and histologic analysis (r = 0.941, P < .001). Also, a positive linear correlation was found between the dual-energy computed tomographic density of ΔHU and the biochemical (r = 0.751, P < .05) and histologic (r = 0.786, P < .001) analyses.

CONCLUSIONS

Quantification of hepatic fat content on (1)H-MRS showed high correlation with histologic and biochemical steatosis determination. In comparison to DECT, it is more suitable to reflect the severity of acute fatty liver.

Correlation of hepatic vein Doppler waveform and hepatic artery resistance index with the severity of nonalcoholic fatty liver disease

PURPOSE

The study was conducted to evaluate the effect of various degrees of fatty infiltration in patients with nonalcoholic fatty liver disease on hepatic artery resistance index and hepatic vein waveform patterns.

METHODS

After identification and grading of fatty infiltration, 60 patients and 20 normal healthy subjects were examined using color and spectral Doppler sonography. The level of fatty liver infiltration was ascertained and graded by biopsy in patients and excluded by MRI in controls. The patients were allocated to four study groups consecutively, until the required number was reached, according to infiltration level as follows: normal (group A), mild (group B), moderate (group C), and severe (group D). The hepatic vein waveforms were classified into the three following groups: triphasic, biphasic, and monophasic waveform. The hepatic artery resistance index was calculated as the mean of three different measurements.

RESULTS

The incidence of monophasic and biphasic hepatic vein waveform was 2 (10%) for group B, 11 (55%) for group C, 16 (80%) for group D, and none for group A. The difference in the distribution of triphasic Doppler waveform pattern between the patients and the control group was significant (p < 0.001). Hepatic artery resistance index was 0.81 (+ or - 0.02), 0.78 (+ or - 0.03), 0.73 (+ or - 0.03), and 0.68 (+ or - 0.05), respectively, in groups A, B, C, and D and was significantly different between groups (p < 0.001).

CONCLUSION

As the severity of nonalcoholic fatty infiltration increases, the incidence of abnormal hepatic vein waveforms increases and hepatic artery resistance index decreases.

The natural history of Shwachman-Diamond syndrome-associated liver disease from childhood to adulthood

OBJECTIVES

In order to characterize the natural course of Shwachman-Diamond syndrome (SDS)-associated hepatopathy we evaluated liver biochemistry and imaging findings, and their evolution with age, in patients with SDS and verified SBDS mutations.

STUDY DESIGN

Retrospective and cross-sectional liver imaging, biochemical and histologic data of 12 patients (age range 2.1 to 37 years) with SBDS mutations were analyzed. Hepatic volume and parenchymal structure were determined from magnetic resonance imaging data.

RESULTS

Hepatomegaly and aminotransaminase elevation was observed in most of the patients with SDS at an early age; values normalized by age 5 years and remained normal over extended follow-up. Mild to moderate serum bile acid elevation was noted in 7 patients (58%). On magnetic resonance imaging, no patients (n = 11) had evidence of hepatic steatosis, cirrhosis, or fibrosis. Three middle-aged patients had hepatic microcysts.

CONCLUSIONS

SDS-associated hepatopathy has overall good prognosis. No major hepatic abnormalities developed during extended follow-up to adulthood. Mild cholestasis in follow-up even after normalization of transaminase levels may reflect primary alterations in liver metabolism in SDS.

Nonalcoholic fatty liver disease: quantitative assessment of liver fat content by computed tomography, magnetic resonance imaging and proton magnetic resonance spectroscopy

OBJECTIVE

The purpose of this study was to evaluate the clinical application of imaging technology in the quantitative assessment of fatty liver with magnetic resonance imaging (MRI) and proton MR spectroscopy.

METHODS

Overall 36 patients with diffuse fatty liver who had undertaken the computed tomography (CT) scan, MRI and proton MR spectroscopy (1H MRS) were analyzed. Their body mass index (BMI) was measured and their liver to spleen CT ratio (L/S) calculated on the plain CT scan. MR T1-weighted imaging (T1WI) was obtained with in-phase (IP) and out-of-phase (OP) images. T2-weighted imaging (T2WI) was acquired with or without the fat-suppression technique. The liver fat content (LFC) was quantified as the percentage of relative signal intensity loss on T1WI or T2WI images. The intrahepatic content of lipid (IHCL) was expressed as the percentage of peak value ratio of lipid to water by 1H MRS.

RESULTS

The results of BMI measurement, CT L/S ratio, LFC calculated from MR T1WI and T2WI images, as well as IHCL measured by 1H MRS were 27.26 +/- 3.01 kg/m2, 0.88 +/- 0.26, 13.80 +/- 9.92%, 40.67 +/- 16.04% and 30.98 +/- 20.43%, respectively. The LFC calculated from MR T1WI, T2WI images and IHCL measured by 1H MRS correlated significantly with the CT L/S ratio (r = -0.830, P = 0.000; r = -0.736, P = 0.000; r = -0.461, P = 0.005, respectively). BMI correlated significantly only with the liver fat contents measured by T1WI IP/OP and 1H MRS (r = -0.347, P = 0.038; r = -0.374, P = 0.025, respectively).

CONCLUSION

CT, MR imaging and 1H MRS were effective methods for the quantitative assessment of LFC. The MR imaging, especially 1H MRS, would be used more frequently in the clinical evaluation of fatty liver and (1)H MRS could more accurately reflect the severity of fatty liver.

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 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.

Usefulness of chemical-shift MRI in discriminating increased liver echogenicity in glycogenosis

BACKGROUND

Glycogen storage diseases are inherited defects which cause accumulation of glycogen in the tissues. Hepatic steatosis is defined as accumulation of fat within hepatocytes. On sonography, liver shows increased echogenicity both in glycogen storage diseases and steatosis. Liver hyperechogenicity in glycogen storage diseases may depend on accumulation of glycogen and/or fat. Chemical-shift magnetic resonance imaging can discriminate tissues only containing water from those containing both fat and water.

AIM

The primary aim of the present study was to evaluate the usefulness of liver chemical-shift magnetic resonance imaging for detecting liver steatosis in patients with metabolic impairment due to glycogen storage diseases.

SUBJECTS

Twelve patients with type I (n=8) or type III (n=4) glycogen storage diseases were studied and compared to 12 obese-overweight subjects with known liver steatosis. As control group 12 lean normal voluntary subjects were recruited.

METHODS

Liver was evaluated by sonography and chemical-shift magnetic resonance imaging to calculate hepatic fat fraction.

RESULTS

A significant difference in echogenicity between patients with glycogen storage diseases and normal subjects was observed (p<0.05), while this difference was not present between overweight-obese and glycogen storage diseases patients. On the contrary, fat fraction was similar between glycogen storage diseases patients and normal subjects and different between glycogen storage diseases patients and overweight-obese (p<0.05).

CONCLUSION

The present data suggest that chemical-shift magnetic resonance imaging may exclude fat deposition as a cause of liver hyperechogenicity in subjects with glycogen storage diseases.

Role of radiologic modalities in the management of non-alcoholic steatohepatitis

During the last decade, the role of radiologic modalities in management of patients who have fatty liver disease has expanded. Ultrasonography has been used as a noninvasive alternative to biopsy for monitoring patients who have hepatic steatosis, but MRI is more appealing than ultrasonography to denote minor changes in hepatic fat content. Distinguishing patients who have non-alcoholic steatohepatitis from steatosis alone has become of clinical importance; however, the differences are not apparent with any radiologic modalities. Several modalities have been developed to noninvasively and accurately quantify hepatic fat content and diagnose steatohepatitis. In the future, radiologic modalities might be used to monitor the natural history of the disease or evaluate therapeutic interventions in patients who have non-alcoholic fatty liver disease.

Artifacts in body MR imaging: their appearance and how to eliminate them

A wide variety of artifacts can be seen in clinical MR imaging. This review describes the most important and most prevalent of them, including magnetic susceptibility artifacts and motion artifacts, aliasing, chemical-shift, zipper, zebra, central point, and truncation artifacts. Although the elimination of some artifacts may require a service engineer, the radiologist and MR technologist have the responsibility to recognize MR imaging problems. This review shows the typical MR appearance of the described artifacts, explains their physical basis, and shows the way to solve them in daily practice.

Fatty Liver: Imaging Patterns and Pitfalls

Fat accumulation is one of the most common abnormalities of the liver depicted on cross-sectional images. Common patterns include diffuse fat accumulation, diffuse fat accumulation with focal sparing, and focal fat accumulation in an otherwise normal liver. Unusual patterns that may cause diagnostic confusion by mimicking neoplastic, inflammatory, or vascular conditions include multinodular and perivascular accumulation. All of these patterns involve the heterogeneous or nonuniform distribution of fat. To help prevent diagnostic errors and guide appropriate work-up and management, radiologists should be aware of the different patterns of fat accumulation in the liver, especially as they are depicted at ultrasonography, computed tomography, and magnetic resonance imaging. In addition, knowledge of the risk factors and the pathophysiologic, histologic, and epidemiologic features of fat accumulation may be useful for avoiding diagnostic pitfalls and planning an appropriate work-up in difficult cases.

Pediatric nonalcoholic fatty liver disease: a critical appraisal of current data and implications for future research

Although population prevalence is very difficult to establish, nonalcoholic fatty liver disease (NAFLD) is probably the most common cause of liver disease in the preadolescent and adolescent age groups. There seems to be an increase in the prevalence of NAFLD, likely related to the dramatic rise in the incidence of obesity during the past 3 decades. Despite an increase in public awareness, overweight/obesity and related conditions, such as NAFLD, remain underdiagnosed by health care providers. Accurate diagnosis and staging of nonalcoholic steatohepatitis (NASH) requires liver biopsy. The development of noninvasive surrogate markers and the advancements in imaging technology will aid in the screening of large populations at risk for NAFLD. Two distinct histological patterns of NASH have been identified in the pediatric population, and discrete clinical and demographic features are observed in children with these 2 patterns. The propensity for NASH to develop in obese, insulin-resistant pubertal boys of Hispanic ethnicity or a non-Hispanic white race may provide clues to the pathogenesis of NAFLD in children. The natural history of pediatric NASH has yet to be defined, but most biopsies in this age group demonstrate some degree of fibrosis. In addition, cirrhosis can be observed in children as young as 10 years. While the optimal treatment of pediatric NAFLD has yet to be determined, lifestyle modification through diet and exercise should be attempted in children diagnosed with NAFLD. A large, multicenter trial of vitamin E and metformin is underway as part of the NASH clinical research network.

Imaging Features of Perivascular Fatty Infiltration of the Liver: Initial Observations

PURPOSE

To retrospectively identify and describe the imaging features that represent perivascular fatty infiltration of the liver.

MATERIALS AND METHODS

The institutional review board approved the study and waived informed consent. The study complied with the Health Insurance Portability and Accountability Act. Ten patients (seven women, three men; mean age, 78 years; range, 31-78 years) with fatty infiltration surrounding hepatic veins and/or portal tracts were retrospectively identified by searching the abdominal imaging teaching file of an academic hospital. The patients' medical records were reviewed by one author. Computed tomographic (CT), magnetic resonance (MR), and ultrasonographic (US) imaging studies were reviewed by three radiologists in consensus. Fatty infiltration of the liver on CT images was defined as absolute attenuation less than 40 HU without mass effect and, if unenhanced images were available, as relative attenuation at least 10 HU less than that of the spleen; on gradient-echo MR images, it was defined as signal loss on opposed-phase images compared with in-phase images; and on US images, it was defined as hyperechogenicity of liver relative to kidney, ultrasound beam attenuation, and poor visualization of intrahepatic structures. Perivascular fatty infiltration of the liver was defined as a clear predisposition to fat accumulation around hepatic veins and/or portal tracts. For multiphase CT images, the contrast-to-noise ratio was calculated for comparison of spared liver with fatty liver in each imaging phase.

RESULTS

Fatty infiltration surrounded hepatic veins in three, portal tracts in five, and both hepatic veins and portal tracts in two patients. Six of the 10 patients had alcoholic cirrhosis, two reported regular alcohol consumption (one of whom had acquired immunodeficiency syndrome and hepatitis B), one was positive for human immunodeficiency virus, and one had no risk factors for fatty infiltration of the liver. In three of the 10 patients, fatty infiltration was misdiagnosed as vascular or neoplastic disease on initial CT images but was correctly diagnosed on MR images.

CONCLUSION

Perivascular fatty infiltration of the liver has imaging features that allow its recognition.

Hepatic MRI for fat quantitation: its relationship to fat morphology, diagnosis, and ultrasound

PURPOSE

The value of MRI and ultrasound in quantifying hepatic steatosis is assessed and the results compared with those obtained by liver biopsies.

METHODS

A total of 38 patients undergoing hepatic biopsy for a variety of liver diseases were recruited for this study. Hepatic fat morphology and severity were assessed visually in each biopsy specimen. Steatosis pattern included macrovesicular, microvesicular, or mixed. The severity of hepatic steatosis was assessed by MRI through chemical shift imaging (n = 38) and by ultrasound through echogenicity (n = 31).

RESULTS

MRI had a better correlation than ultrasound for microscopic fat content (r = 0.77, P < 0.001 vs. r = 0.41, P < 0.05). In macrovesicular steatosis, MRI and ultrasound both correlated well with microscopic fat content (r = 0.92, P < 0.001 vs. r = 0.90, P < 0.001). In nonalcoholic fatty liver disease, ultrasound revealed severe steatosis in all instances, but MRI fat content ranged greatly (19%-40%). In diagnoses excluding nonalcoholic fatty liver disease, increasing ultrasound severity did not correspond to advanced MRI fat content.

CONCLUSION

Hepatic MRI and ultrasound are both useful in identifying heavy fat accumulation associated with nonalcoholic fatty liver disease. MRI is superior to ultrasound in detecting and quantifying minor degrees of fatty metamorphosis in the liver.

Effect of diffuse fatty infiltration of the liver on hepatic artery resistance index

PURPOSE

This study was conducted to evaluate the effect of various degrees of diffuse fatty infiltration of the liver on the hepatic artery resistance index.

METHODS

One-hundred forty subjects were examined using standard color and spectral Doppler sonography protocols. Fatty infiltration of the liver was identified and graded sonographically. The patients were grouped (n = 35 in each of 4 groups) according to the degree of diffuse fatty infiltration of the liver as follows: normal (group 1), mild (group 2), moderate (group 3), and severe (group 4). The resistance index calculated for each patient was the mean of 3 measurements. Mean resistance index of the hepatic artery was then calculated for each group.

RESULTS

The mean resistance index was 0.81 +/- 0.04 for group 1, 0.79 +/- 0.06 for group 2, 0.75 +/- 0.05 for group 3, and 0.73 +/- 0.05 for group 4. We found a statistically significant (p < 0.05) decrease in resistance index when comparing groups 3 and 4 with groups 1 and 2 separately.

CONCLUSIONS

Hepatic artery resistance index decreases as the severity of diffuse fatty infiltration increases.