Diagnosis of fatty liver with MR imaging.

The diagnosis of fatty liver with magnetic resonance (MR) imaging was evaluated in experimental rat models of simple fatty infiltration and fatty liver with hepatocellular injury. T1 and T2 were measured ex vivo and correlated with the histologic degree of fatty infiltration. Enhancement of fatty liver with four different cells-specific contrast agents was studied with ex vivo relaxometry and in vivo MR imaging. Quantitative analysis of conventional and chemical shift MR images was correlated with biochemically determined fat content of the liver. Diet-induced simple fatty infiltration of the liver caused a decrease in T1 of 15%, whereas the T1 of L-ethionine-induced fatty liver with hepatocellular injury increased by 12%. T2 showed a positive correlation with the degree of fatty infiltration in both models. Cell-specific hepatobiliary contrast agents showed the same liver uptake and relaxation enhancement in fatty livers as in normal livers. Conventional T1-weighted images and chemical shift images showed good correlation (r = .83 and .80, respectively) between signal intensity and the degree of fatty infiltration. However, only chemical shift imaging was reliable in the diagnosis of fatty liver.     

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.     

CT studies of the liver in vitro: a report on 82 cases with pathological correlation.

Eighty-two liver specimens were studied by both computed tomography (CT) and pathological examination with serial sectioning. In vitro CT studies showed low density structures within 57 normal livers to be due to portal and hepatic vessels but not to bile ducts. A liver with a minimum of 70% fatty infiltration could be diagnosed correctly on CT. Concerning the presence or absence of circumscribed liver disease, sensitivity was 80% and specificity was 84%. With respect to the total number of space occupying liver lesions (n = 364 in 18 specimens), sensitivity was 72%. The smallest metastases detectable on CT were 0.5 cm in diameter, but CT disclosed focal lesions of this small size in only 15% of the cases. In contrast to previously reported in vivo CT studies, metastases were often found to be of higher density than normal liver tissue in vitro.     

Imaging the pediatric liver: MRI and CT

The livers of 27 children, 2 weeks to 16 years old, were examined with MRI and CT. Fourteen children had normal livers, 9 had focal liver disease, and 4 had diffuse liver disease. Normal intrahepatic venous anatomy was visualized more frequently with MRI than with CT, regardless of presence of disease, type of disease, or age. Focal hepatic lesions were either iso- or hypointense on relatively T1-weighted images and were hyperintense on T2-weighted images regardless of the pathology. In three cases, lesions seen with MRI were not detected with CT. In two other cases, CT was interpreted as equivocal or abnormal, but the liver was normal on MRI. MRI was superior to CT for evaluation of patency of the intrahepatic portion of the inferior vena cava. Other than in cases of fatty infiltration, CT provided no information additional to MRI. MRI has the potential to replace CT as a technique for imaging the pediatric liver in many cases, especially for infants and young children.     

脂肪肝：MRI影像表现及MRI序列选择

目的：选择评估脂肪肝的MRI序列和认识脂肪肝的MRI影像表现以帮助鉴别诊断,方法：18例脂肪肝病人进行了肝脏平扫和增强MRI,采用屏气同,反相位T1加权梯度回波序列,2D FLASH加脂肪抑制T1WI以及HASTE T2WI。结论：18例肝脂肪变中伴有7例肝癌,2例血管瘤,1例囊肿,5例肝硬化;弥漫型脂肪浸润6例,局灶型脂肪浸润12例,脂肪肝影像表现,T1WI同相位表现为稍高或等信号,反相位或加压脂T1WI呈低信号;T2WI呈稍高或等信号,部分脂肪肝伴脂内肿块在反相位或加压脂TWI上可见低信号肿块周边全周或部分环状高信号带,在增强MRI上无明显强化,有时见少量小血管进入其内,结论：同与反相位MRI能较好鉴别诊断脂肪肝,两者互补,缺一不可,可避免脂肪肝的误诊或汤诊。建议对疑有脂肪肝患者行同,反相位T1加权MRI扫描。     

Differentiation of hepatic metastases from hepatic hemangiomas and cysts by using MR imaging

T1-weighted and T2-weighted pulse sequences were employed for MR imaging of hepatic metastatic tumors (98 patients), hemangiomas (24 patients), and cysts (seven patients); a 0.6-T superconducting magnet was used. In a retrospective study, signal intensity and morphology were used to establish criteria for differentiating metastases from hemangiomas and cysts. The signal intensity of the lesion alone failed to be an etiologic discriminator because over 96% of all masses had a signal intensity less than that of liver on T1-weighted sequences, and at least 90% had a signal intensity greater than that of liver on T2-weighted sequences. Morphologic features depicted on T2-weighted images were more specific than those depicted on T1-weighted images in differential diagnosis. Amorphous, target, and halo signs and a change in morphology were present only in metastatic disease, with a frequency of 45%, 27%, 13%, and 12%, respectively. Two other morphologic patterns--doughnut and lightbulb signs--were found to have overlapping causes. Overall, at least one of the specific signs was observed in 92% of patients with metastatic disease. These data suggest that T2-weighted pulse sequences are essential for discriminating between hepatic metastases and hepatic hemangiomas and cysts. MR imaging is a promising technique for distinguishing these lesions.     

Focal hepatic masses and fatty infiltration detected by enhanced dynamic CT

A prospective evaluation of 185 consecutive patients with abdominal pain or suspected hepatic malignancy was performed to compare the diagnostic accuracy of contrast material-enhanced incremental dynamic computed tomography (IDCT) scans with plain CT scans for detection of hepatic masses and fatty infiltration of the liver. After a series of nondynamic plain CT scans, patients were examined at 7.5 scans/min during intravenous injection of 50 g of iodinated contrast material. Enhanced IDCT study was found to be an accurate, reproducible technique for liver evaluation. Of 155 neoplasms measured in 59 patients, liver-to-lesion differences of less than 10 HU were seen in only two tumors in IDCT scans as compared with 31 in plain CT scans. These differences were not significantly affected by lesion size for neoplasms greater than 6 mm in diameter. A confident diagnosis of fatty infiltration (23 patients) could be made when the spleen-minus-liver difference was 25 HU on enhanced IDCT scans and 10 HU on plain CT scans. In eight patients with liver metastases, there was little variation in the attenuation values of normal-appearing liver between serial examination studies (8 HU average).     

Nondiffuse fatty infiltration of the liver: does the uptake of iron-oxide increase or decrease at SPIO-enhanced MR imaging?

Purpose

To clarify whether the uptake of SPIO increases or decreases in areas of fatty change compared with surrounding areas of nonfatty change at SPIO-enhanced MR imaging.

Materials and methods

Approval for this retrospective study was obtained from our institutional review board. This study included 14 patients with nondiffuse fatty infiltration of the liver who underwent SPIO-enhanced MR imaging. Additionally, 30 patients without nondiffuse fatty infiltration of the liver were also evaluated.

Results

Among 14 patients, areas of fatty change showed relatively high signal intensity in 7 patents, indicating decreased uptake of SPIO in areas of fatty change. In these 7 patients, 4 had mild cirrhosis and 3 did not have cirrhosis. The mean percentage of signal intensity loss (42%) of fatty areas was significantly lower (p < 0.007) than that of adjacent areas of nonfatty change (52%). In the remaining 7 of 14 patients, areas of fatty change showed relatively low signal intensity, indicating increased uptake of SPIO in areas of fatty change. Among these 7 patients, 6 had advanced cirrhosis. The mean percentage of signal intensity loss (47%) of fatty areas was significantly higher (p < 0.008) than that of adjacent areas of nonfatty change (31%).

Conclusion

The uptake of SPIO generally decreased in areas of fatty change compared with normal liver parenchyma at SPIO-enhanced MR imaging. However, in patients with advanced cirrhosis, areas of fatty change shows relatively low signal intensity because the uptake of SPIO in surrounding areas of nonfatty change severely decreased probably due to liver fibrosis.     

Asialoglycoprotein receptor function in benign liver disease: evaluation with MR imaging

An arabinogalactan-coated ultrasmall superparamagnetic iron oxide (AG-USPIO) preparation specific for asialoglycoprotein (ASG) receptors on hepatocytes was used as a magnetic resonance (MR) imaging contrast agent in the evaluation of a spectrum of benign liver diseases in animal models. The activity of hepatocyte ASG receptors, which directly reflects liver function, was directly assessed by measuring liver relaxation times in vitro and MR signal intensity in vivo. The following measurements allowed three-dimensional assessment of liver function: (a) liver relaxation time, (b) native MR signal intensities of liver, (c) response of liver to the AG-USPIO probe (percentage decrease of liver signal intensity after intravenous administration of 10 mumol/kg of AG-USPIO: normal liver 55%, fatty liver 57%, acute hepatitis 36%, chronic hepatitis 29%, and cirrhosis 46%), and (d) redistribution of hepatocyte-specific AG-USPIO to the spleen (present in hepatitis and cirrhosis but not in normal liver and fatty liver). The results of this study indicate that cellular hepatic abnormalities can be detected and quantitated with MR receptor imaging.     

Fatty liver. Chemical shift phase-difference and suppression magnetic resonance imaging techniques in animals, phantoms, and humans.

In vitro animal and human models were used to evaluate the potential of chemical shift magnetic resonance imaging (MRI) for assessing fatty liver. Phantoms of varying fat content were created from mayonnaise-agar preparations. Fatty liver was induced in eight rats by feeding them ethanol for three to six weeks (36% of total calories), whereas eight control rats were fed a normal diet. T1-weighted in-phase and opposed-phase MR images were obtained of the phantoms animals, and 28 human subjects. Additional images obtained in animals included long TR images with in-phase and opposed-phase technique, and hybrid chemical shift water and fat suppression. The rats were killed and histologic status was graded blindly by a hepatopathologist as normal, mild, moderate, or severe fatty change, for correlation with MR grading. Quantitative analysis of MR images included fat signal fraction for animals, and relative signal decrease between in-phase and opposed-phase images for phantom and human data. Phantom in-phase signal increased linearly with respect to fat content, whereas opposed-phase signal decreased linearly. MRI and histologic grading of rat livers were highly correlated, especially when based on water suppression images (r = 0.91, P = .0001). Opposed-phase images were also highly correlated, while fat suppression images were less effective. There was no overlap between MR-derived fat fractions for control (2.6%-5.7%) versus ethanol-fed rats (7.7%-17.9%, P = .0002). Human liver considered to be fatty by visual inspection (n = 8) had higher relative signal decrease than nonfatty liver (n = 22) (P less than .001). Phantom, animal, and human data demonstrate that comparison of T1-weighted in-phase and opposed-phase images is both practical and sensitive in the detection and grading of fatty liver.     

Fatty infiltration of the liver: demonstration by proton spectroscopic imaging. Preliminary observations

Two normal volunteers and three patients with CT evidence of fatty infiltration of the liver (two nonuniform, one diffuse) were studied to determine whether magnetic resonance imaging using a pulse sequence designed to differentiate fat and water could be used to detect fatty infiltration of the liver in human beings. The magnetic resonance technique used a modified spin echo technique (simple proton spectroscopic imaging) that was designed specifically to exploit the difference in the rate of precession between the protons in a water molecule and the protons in a fatty acid molecule. Images were obtained using in-phase and opposed techniques and were added or subtracted in order to obtain pure water and pure fat images. Quantitative data showed that fatty liver can be separated from normal liver using the spin echo technique, and that the opposed image of the proton spectroscopic technique is more sensitive to small changes in hepatic fatty content than in-phase images with any echo time.     

Hepatic artery injection of I-131-labeled lipiodol. Part I. Biodistribution study results in patients with hepatocellular carcinoma and liver metastases

Biodistribution of iodine-131-labeled Lipiodol Ultra-Fluide (I-131 LUF) injected into the hepatic artery was studied scintigraphically in 47 patients with hepatocellular carcinoma (n = 23), hepatic metastases (n = 14), or normal livers (n = 10). The investigation was extremely well tolerated. I-131 LUF concentrated mainly in the liver (L) and the lungs (l), with L/L + l activity ratios greater than 75% for all three groups of patients. I-131 LUF distribution was homogeneous in normal livers and heterogeneous in cirrhotic livers. I-131 LUF concentrated in the tumor with a tumorous (T) to nontumorous (NT) activity ratio (T/NT) of 4.3 +/- 3.6 for hepatocellular carcinoma and 2.4 +/- 0.7 for hepatic metastases. The effective half-life of I-131 LUF is more than 4.5 days for the three groups. It was eliminated mainly through the urine. Clearance from tumor is slower than from normal liver, as shown by the increase in T/NT at day 18. Biodistribution did not change in patients who had a second injection, which indicates that there is no saturation phenomenon. The results of this study suggest that LUF may be considered as a potential carrier vehicle for therapeutic agents.     

Value of MR imaging in evaluating focal fatty infiltration of the liver: preliminary study.

Focal fatty infiltration of the liver is a well-known entity that occasionally mimics metastatic disease on ultrasonographic (US) and computed tomographic (CT) scans and requires biopsy for diagnosis. To determine if high-field-strength magnetic resonance (MR) imaging might be useful in the differential diagnosis of the lesions, the authors compared US, CT, and MR findings in three patients with biopsy-proved fatty hepatic lesions. Areas of focal fatty infiltration were hyperechoic on US scans and had low attenuation on CT scans. No mass effect of the lesions on vascular structures or liver contours was observed, particularly on contrast material-enhanced CT scans. For all three patients, MR findings suggested the correct diagnosis by demonstrating focal high signal intensity on spin-echo T1- and T2-weighted images. On the basis of these preliminary findings, it appears that focal fatty infiltration of the liver may be differentiated from metastatic disease by means of high-field-strength MR imaging.     

Macrovesicular hepatic steatosis in living related liver donors: correlation between CT and histologic findings

PURPOSE: To assess degree of macrovesicular steatosis with unenhanced computed tomography (CT) and correlate it with histologic findings in potential donors for living related liver transplantation. MATERIALS AND METHODS: Forty-two candidates underwent unenhanced CT within 4 weeks of core liver biopsy. An experienced liver pathologist, blinded to both CT and surgical findings, retrospectively reviewed biopsy specimens and determined degree of macrovesicular steatosis. A radiologist blinded to histologic grading calculated mean hepatic attenuation in each donor liver by averaging 25 region-of-interest (ROI) measurements on five sections (five ROIs per section). Mean splenic attenuation was calculated with three separate ROI measurements. Liver attenuation index (LAI) was derived and defined as the difference between mean hepatic and mean splenic attenuation. Body mass index (BMI) was determined for each patient. Linear regression analysis was used to correlate degree of macrovesicular steatosis with both LAI and BMI. RESULTS: LAI correctly predicted degree of macrovesicular steatosis in 38 (90%) of 42 cases. In four of four livers, LAI below -10 HU correlated with greater than 30% macrovesicular steatosis (unacceptable for liver transplantation). In nine of 11 livers, LAI was between -10 and 5 HU and correctly predicted 6%-30% steatosis (relative contraindication). In two of 11 cases, LAI overestimated degree of hepatic steatosis. LAI above 5 HU correctly predicted 0%-5% steatosis in 25 of 27 livers. In two of 27 cases, parenchymal hemosiderin deposition led to an increase in LAI into the normal range, despite mild histologically confirmed steatosis. Degree of histologic macrovesicular steatosis correlated well with LAI (r = 0.92) and marginally with BMI (r = 0.45). Of 27 potential donors with normal livers at CT and acceptable LAI levels, four (15%) were deemed poor donor candidates because core biopsy revealed subtle hepatic necrosis and nonspecific hepatitis. CONCLUSION: Although unenhanced CT quantifies the degree of macrovesicular steatosis relatively well, it may preclude a liver biopsy only in a small percentage of potential donors with low LAI (unacceptable degree of steatosis). Core liver biopsy is still necessary in the majority of donors with normal LAI to identify those with both fatty liver and coexistent hemosiderin deposition or radiologically occult diffuse liver diseases.     

Nuclear magnetic resonance imaging of experimentally induced liver disease

Experimental animal models of hepatitis, fatty liver, and hepatic iron overload were evaluated using a 3.5-kGauss nuclear magnetic resonance (NMR) imaging system. Increases in image intensity measurements and in T2 relaxation times equalled the sensitivity of histologic findings for the detection of early stages of hepatitis. A significant shift in T1 relaxation times characterized the early stages of hepatic necrosis. Liver triglyceride content correlated significantly with increases in NMR intensity measurements (p less than 0.01); however, changes in liver water content had a much greater influence on intensity, T1, and T2. Thus, it may be possible to distinguish hepatitis from benign fatty liver. Liver iron content correlated with decreases in NMR intensity measurements (p less than 0.001), and iron levels as low as 1.2 mg/g were detected. NMR may more specifically identify hepatocellular iron overload than do other techniques that do not distinguish hepatocellular from reticuloendothelial iron.     

Value of dual-energy CT in differentiating focal fatty infiltration of the liver from low-density masses

Focal (irregular, partial) fatty infiltration of the liver may simulate neoplastic or other hypodense masses on CT. On the basis of previous observations of the phenomenon that differences in X-ray attenuation diminish with increasing energy of X-rays used, we performed a preliminary study to determine if dual-energy CT could be used to discriminate between fatty infiltration and hypodense liver masses. Dual-energy CT at 140 and 80 kVp was performed in 14 patients undergoing liver biopsy and in seven control subjects with presumedly normal liver. Attenuation measurements were taken, and the changes in attenuation between 140 and 80 kVp were calculated. The mean changes in attenuation were 3.5 H for normal liver (n = 7), 2.5 H for hypodense liver masses (n = 6), 13 H for fatty liver (n = 5), 0.3 H for fatty liver combined with hemochromatosis or hemosiderosis (n = 3), and 2 H for the spleen (n = 18). The change in attenuation increased as the fat content in the liver increased. Analysis of variance showed a statistically significant difference (p less than .001) between fatty liver and the other groups. A difference greater than 10 H was unique to fatty infiltration. These results suggest that dual-energy CT may help to differentiate focal fatty infiltration of the liver from low-density neoplastic or other lesions, but only if the iron content of the liver is not increased.     

Focal hepatic lesions: differentiation with MR imaging at 0.5 T

Magnetic resonance (MR) examinations of 43 patients with 95 focal hepatic lesions (diameter, greater than 1 cm) were analyzed for lesion shape, homogeneity, and relative signal intensity compared with normal liver parenchyma, spleen, and skeletal muscle. On T1-weighted, balanced, and T2-weighted images, most metastases (74%), cavernous hemangiomas (76%), and cysts (82%) were smooth and round or oval, while the hepatocellular carcinomas all had irregular borders (40%) or were lobulated (60%). All lesions with irregular borders were malignant. Seventy percent of metastatic lesions, 85% of cavernous hemangiomas, and 100% of simple hepatic cysts were of homogeneous signal intensity, while 60% of hepatocellular carcinomas were inhomogeneous. Logistic regression analysis of multiple lesion characteristics showed that inhomogeneous lesions had a high likelihood of malignancy, while markedly hyperintense lesions had a very low probability of being malignant, regardless of other traits. Homogeneous lesions that were isointense or hyperintense compared with spleen on balanced images but were not markedly hyperintense on T2-weighted images also had a high likelihood of malignancy.     

Pseudotumor of the quadrate lobe in hepatic sonography: a sign of generalized fatty infiltration

Sonograms of 43 patients demonstrated a focal area of decreased echogenicity in the medial segment of the left hepatic lobe (quadrate lobe). The shape ranged from ovoid to sheetlike, and the diameter ranged from 0.7 to 8.6 cm. The echogenicity of the right hepatic lobe was abnormally increased in 34 of 37 scans graded. In 20 patients with follow-up sonograms, 11 showed no change, six disappeared and three decreased in size. In 12 patients with unenhanced CT scans, 10 had decreased attenuation of the hepatic parenchyma and normal attenuation in the observed quadrate lobe focus. The hypoechoic focus in the quadrate lobe represents focal sparing in generalized fatty infiltration of the liver. When present, this focus represents a useful qualitative sign of generalized fatty infiltration in the rest of the liver.     

100名健康者肾上腺18F-FDG PET/CT显像分析

目的 探讨正常肾上腺18F-脱氧葡萄糖(FDG) PET显像特征,为在18F-FDG PET或PET/CT显像中判断肾上腺是否有高代谢灶提供依据.方法 选择行PET/CT体格检查的健康者100名.图像分析采用目测计分和测定标准摄取值(SUV)2种方法.目测计分法以肝为对照,肾上腺未显影为0分,放射性摄取低于肝放射性为1分,等于肝放射性为2分,高于肝放射性为3分;SUV由图像横断面测量,依据CT所显示的肾上腺和肝,手动勾画感兴趣区(ROI),获得左右两侧肾上腺、肝的SUV平均值(SUVmax)、SUV最大值(SUVmax),再计算肾上腺与肝SUV的比值.结果 (1)目测分析:左、右侧正常肾上腺放射性摄取分别有94%和91%等于或低于肝.(2)左、右侧正常肾上腺95%可信区间(CI)上限,SUVmax分别为1.39和1.65, SUVmax分别为1.98和2.19.(3)左、右侧正常肾上腺/肝比值的95%CI上限,SUVmax分别为0.65和0.75, SUVmax分别为0.76和0.83.(4)左、右侧肾上腺对18F-FDG摄取有一定差异,右侧肾上腺SUVmax和SUVmax均高于左侧.(5)除右侧SUVmax男性高于女性外,余各组性别差异无统计学意义.(6)正常肾上腺对18F-FDG摄取在＜60岁组和≥60岁组的差异无统计学意义.结论 正常肾上腺18F-FDG生理性摄取程度的主要表现为低于肝.     

Model-based analysis of Gd-BOPTA-induced MR signal intensity changes in cirrhotic rat livers

OBJECTIVE: To quantify the hepatic transport of the hepatobiliary contrast agent gadobenate dimeglumine (Gd-BOPTA) in rats with biliary cirrhosis of various severity degrees from magnetic resonance (MR) signal intensities using a population pharmacokinetic approach. MATERIALS AND METHODS: MR signal intensity was recorded during the Gd-BOPTA perfusion of normal and cirrhotic isolated rat livers. Similar experiments were conducted with Gd-labeled Gd-BOPTA to quantify Gd-BOPTA content in liver, bile, and perfusate. All experimental data were analyzed together according to a population pharmacokinetic approach. RESULTS: A 6-compartment model developed from the radioactivity data adequately fit all MRI data when 4 image parameters were added to describe the relationship between the amount of contrast agent and the signal intensity. The model showed that entry of Gd-BOPTA into hepatocytes was decreased in cirrhotic livers when compared to normal livers. CONCLUSIONS: Although the MR signal intensity is similar in normal and cirrhotic livers, the population pharmacokinetic approach developed in this study shows a decreased entry of Gd-BOPTA into cirrhotic hepatocytes.