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.     

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.     

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.     

Detecting bone marrow metastases at the time of examining the liver with radiocolloid

In a prospective study of 200 different consecutive patients with cancer, the bone marrow of the lumbar spine and pelvis has been examined at the time of obtaining a radiocolloid examination of liver and spleen. The images were examined "blind" by three observers who all agreed about the findings in 177 (89%) of the patients. Agreement by any two was considered to be definitive. The radiocolloid marrow examinations in this selected population had an accuracy of 0.97, sensitivity of 0.80, and specificity of 0.98 in diagnosing metastatic disease when validated by all other available evidence, or follow-up. Of the patients thus examined, 16 (8%) had abnormal marrow scan findings reflecting metastatic disease, eight (4%) at the time radiographs were normal, and two at the time bone scintigraphy was normal. Excluding patients with bowel cancer, in whom the detection rate was zero, 16 (12.4%) marrow examinations were abnormal. As a result we now obtain "saturated" images of the marrow incidental to radiocolloid examinations of the liver and spleen in patients with cancer other than that of the bowel.     

Examples of complementary roles of abdominal CT and radiocolloid liver imaging

Two cases are reported in which well-defined lesions of the liver were seen in radiocolloid liver imagings but not in the concurrent abdominal CT images. The results of autopsy confirmed the diagnosis of hepatoma in one and metastatic disease in the other. The third case, referred for a Tc-99m SC liver-spleen image because of a suboptimal abdominal CT owing to artifact, showed a normal liver. In certain clinical situations, radiocolloid imaging provides a complementary role to CT in the detection or confirmation of hepatic lesions and, in occasional patients, is superior to CT.     

同相位与反相位梯度回波T_1WI在肝脏的应用价值

目的　评估同相位与反相位梯度回波T1WI在肝脏应用的价值 ,尤其是评估其对肝内脂肪变的检测能力。方法　 76例病人采用屏气同相位与反相位T1W梯度回波序列对肝脏扫描。将76例病人分成 3组分析 :(1)肝内无占位病变组 ,8例 ;(2 )肝癌组 ,34例 ;(3)血管瘤或囊肿组 ,共 34例。对 2种序列的图像进行了定量分析。结果　 76例中发现 14例肝脂肪变 ,6 2例无脂肪变。在 14例肝脂肪变中 ,反相位MRI还显示了 4例低信号肿块周边环状高信号带 ,其中 3例肝癌 ,1例血管瘤。在肝脂肪变的反相位上显示肝与脾和病灶信噪比或对比信噪比值较同相位低 ,但肝与脾和病灶间信噪比 (SNR)或对比信噪比 (CNR)在同相位与反相位上均无显著性差异 (P >0 .0 5 )。结论　同相位与反相位对显示肝脏病变和对脂肪成分的诊断是有价值的。两者互补 ,缺一不可。为避免肝脏病变在T1WI上的误诊或漏诊 ,建议常规行同相位与反相位T1W扫描     

Role of scintigraphy in focally abnormal sonograms of fatty livers

Fatty infiltration of the liver may cause a range of focal abnormalities on hepatic sonography which may simulate hepatic nodular lesions. Discrete deposits of fat or islands of normal tissue which are uninvolved by fatty infiltration may stand out as potential space-occupying lesions on the sonograms. Twelve patients with such focally abnormal ultrasound images were referred for liver scintigraphy with 133Xe and 99mTc colloidal SPECT studies to clarify the issue. These examinations helped identify, in nine of 12 patients, the innocent nature of the sonographic abnormalities which were simply related to the fat deposition process. Further, [99mTc]RBC scans defined the additional pathologic process in three patients in whom actual space-occupying lesions were indeed present in the liver. Scintigraphy has an important role to play in the understanding of focal hepatic ultrasound abnormalities particularly in unsuspected hepatic steatosis.     

Benign liver lesions: implications of detection in cancer patients

A review of liver sonograms obtained for cancer patients (excluding primary liver cancers) over a 12 year period found 829 benign lesions: non-parasitic cysts (427 cases), hemangiomas (216 cases), solitary calcifications (79 cases), focal fatty infiltration (62 cases), and miscellaneous lesions (45 cases). These benign pathologies represented 41.8% of the focal hepatic lesions observed during this period in this population; hepatic metastases accounted for the remaining 58.2%. Marked female predilection was noted for the nonparasitic cysts, hemangiomas, and focal fatty infiltration; 63–78.7% of these lesions were solitary, and first-line imaging by US was sufficient for diagnosis of 66.1–98.2% of cases. Analysis of lesion evolution over more than 5 years revealed modifications in 17% of hemangiomas, 23.9% of nonparasitic cysts, and 75% of cases of focal fatty infiltration. Systematic pretherapy liver sonography can be proposed owing to the high frequency of benign liver lesions that can create diagnostic problems during follow-up of cancer patients. Correspondence to: J. N. Bruneton     

CT and MR imaging of postnecrotic liver scars

Four cases of postnecrotic liver scar were examined by dynamic CT or MR imaging or both. Postnecrotic scars appeared as low-density areas on plain CT, showed marked and prolonged enhancement on single level dynamic CT, and became isodense on postcontrast scan. On T2-weighted images, postnecrotic scar were as hyperintense as the spleen. Postnecrotic liver scar is an example of localized attenuation or intensity difference not corresponding to mass lesion. It should be distinguished from mass lesions associated with lobar or segmental attenuation (or intensity) difference of the liver as well as nonmass lesions such as irregular fatty infiltration, radiation hepatitis, and hepatic infarction.     

Characteristic sonographic signs of hepatic fatty infiltration

Hepatic fatty infiltration sonographically appears as an area of increased echogenicity. When focal areas of fat are present in otherwise normal liver parenchyma, the fatty area may be masslike in appearance, leading to further imaging evaluation and sometimes even biopsy. This article discusses seven patients with focal fatty infiltration, who had sonographic signs that were highly suggestive of the fatty nature of the masses. These signs included angulated, geometric margins between normal and fatty tissue and interdigitating margins with slender fingers of normal or fatty tissue. These signs may be useful in diagnosing masslike areas of focal fatty infiltration and distinguishing these sonographically from other hepatic mass lesions.     

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.     

Rapid MR imaging with suspended respiration: clinical application in the liver

The authors demonstrate that it is possible to obtain highly T1-weighted images of the abdomen using a suspended respiration partial saturation (SRPS) method in a breath-holding interval. T2*-weighted images, which reflect tissue T2 as well as variations in the static magnetic field, can also be rapidly obtained. The authors studied five healthy subjects and 19 patients with a variety of liver abnormalities, including benign and malignant hepatic neoplasms, fatty liver infiltration, ascites, and hematoma. On T1-weighted multisection acquisitions, the entire liver can be screened for mass lesions in a single 20-second breath-holding interval. Phase-contrast SRPS images are sensitive to fatty infiltration of the liver. SRPS images are more sensitive to variations in magnetic susceptibility than spin-echo images are, which has been proved to be of value in the detection of hemorrhage. With continued pulse sequence development and clinical study, this method has the potential to become the method of choice for evaluation of the upper abdomen.     

Proton spectroscopic imaging (Dixon method) of the liver: clinical utility

The contribution of proton spectroscopic (PS) imaging to magnetic resonance (MR) imaging of the liver was assessed at 0.5 T in 55 patients with known or suspected hepatic malignancy. PS images were compared subjectively with T1- and T2-weighted spin-echo (SE) images for hepatic lesion detection and conspicuity. For hepatic metastases (n = 27), PS images were equal to T1-weighted images in lesion detection in 17 patients but showed fewer lesions in five patients and false-negative results in two. When compared with T2-weighted images, PS images depicted more lesions in six patients, an equal number of lesions in 18, and fewer lesions in two. Hepatomas (n = 8) were detected with each sequence in all patients. Hepatomas were often more conspicuous on PS images than on T2-weighted images; they were of equal conspicuity on PS and T1-weighted images in most cases. Whereas fatty infiltration (n = 16) appeared on PS images as areas of low signal intensity similar to that of paraspinal muscle, it produced no detectable abnormality on either T1- or T2-weighted images. PS imaging is inferior to T1-weighted SE imaging in the detection of hepatic metastases. The major role of PS imaging at intermediate field strength is to differentiate focal fatty infiltration from hepatic metastases.     

基于纹理分析的脂肪肝B超图像识别

目的 为B超诊断脂肪肝建立计算机辅助诊断手段。方法 通过分析正常肝和脂肪肝B超图像的纹理特征,包括灰度共生矩阵的角二阶矩、熵和反差分矩统计特征,组成特征矢量,再用k-平均聚类算法和自组织特征映射人工神经网络算法对特征矢量进行分类处理。结果 k-平均聚类算法对正常肝的识别率为63．6％,对脂肪肝的识别正确率达90．9％;自组织特征映射人工神经网络对正常肝的识别正确率达84.8％,对脂肪肝的识别正确率达90．9％。结论 本文中建立的方法能较肉眼更精确地反映正常肝和脂肪肝B超图像的特征,如果再结合医生的临床经验能大大提高脂肪肝的诊断准确性。     

Quantitative estimation of attenuation in ultrasound video images: correlation with histology in diffuse liver disease

RATIONALE AND OBJECTIVES: To determine the relationship between the attenuation of backscatter intensity in B-scan images of the liver and diffuse liver disease in order to assess the usefulness of this method in providing quantitative objective characterization of diffuse liver diseases in general and in fatty liver in particular. METHODS: Twenty-four healthy volunteers and 28 patients with elevated liver enzyme levels who underwent liver biopsy were included in this study. An automatic far-field slope (FFS) algorithm that estimates the decrease in amplitude of the backscattered echo as a function of beam depth was implemented on the noncompensated image that was acquired on a commercial phased-array ultrasound system fitted to a custom-built interface card. The images were processed at a work-station. All scans were acquired repeatedly, read, and graded blindly by experienced ultrasound radiologists. Histology obtained via needle biopsy was reviewed without knowledge of the ultrasound findings. RESULTS: Analysis of the FFS data for fatty infiltration in all patient groups yielded a sensitivity of 67%, a specificity of 77%, a positive predictive value (PPV) of 77%, negative predictive value (NPV) of 67%, and an accuracy of 71%. The mean score of the ultrasound reviewers showed a sensitivity of 82%, a specificity of 66%, a PPV% of 68%, an NPV of 81%, and an accuracy of 72%. Normal FFS values (false-negative) were found in five patients with proved fatty infiltration. All of these patients had coexistent moderate to severe hepatic inflammation. However, FFS data in patients with uncomplicated (pure) fatty infiltration revealed a sensitivity of 100%, a specificity of 80%, a PPV of 89%, an NPV of 100%, and an accuracy of 92%. The best ultrasound score yielded a sensitivity of 100%, a specificity of 60%, a PPV of 80%, an NPV of 100%, and an accuracy of 85% in the same patients. CONCLUSIONS: The data demonstrate an excellent sensitivity (100%) of the FFS values in patients with uncomplicated fatty infiltration. This was also the only group of patients in whom the FFS score was superior to the radiologists' best score. The FFS method can be used as a tool to follow up the response to a clinical or research treatment and to obtain standardization of pattern interpretation independently of the individual reader.     

Detection of hepatic metastases by proton spectroscopic imaging. Work in progress

Fourteen patients with hepatic metastases underwent magnetic resonance (MR) imaging using both the conventional spin-echo (SE) technique and the opposed phase of the proton spectroscopic imaging method. The opposed image showed more lesions than the conventional SE image in five patients and provided better contrast between the liver parenchyma and metastases in two patients. Four of these seven patients had associated fatty infiltration of the liver. When compared with the computed tomography (CT) scan, the opposed image either showed more lesions or provided better contrast in six patients, four of whom had fatty infiltration. More significantly, the MR image showed several 1-cm lesions not shown by the CT scan in one patient. Our study discloses the possible explanations for the increased sensitivity of the opposed image in detecting hepatic metastases.     

Diagnosis of cirrhosis and hepatitis by quantitative hepatic and other reticuloendothelial clearance rates.

Although methods for measuring colloid clearance rates have been described, they are not commonly used. Rather, most clinicians rely on the relative radiocolloid accummulation in the liver and spleen as estimated by visual inspection of liver scans. This method lacks objectivity, however, and only indirectly reflects the rate of radiocolloid clearance. We have developed a noninvasive kinetic technique for measuring radiocolloid clearance by the liver, spleen, and other reticuloendothelial tissues. The clerance-rate constants obtained by this technique appear to differentiate among cirrhosis, fatty metamorphosis, hepatitis, and normal function. In normal subjects, the mean clearance-rate constants for the liver, spleen, and extrahepatosplenic reticuloendothelial system were 16.0, 1.4, and 3.4 ml/min per 100 ml of plasma, respectively. The mean hepatic clearance-rate constant was normal in hepatitis (16.8 ml/min per 100 ml), reduced in cirrhosis (5.7), and slightly reduced in fatty metamorphosis (10.4). Both the hepatic-to-splenic and the hepatic-to-extrahepatosplenic ratios of clearance-rate constants were reduced in cirrhosis and slightly reduced in fatty metamorphosis and hepatitis. Interestingly, the splenic clearance-rate constants were normal in these three diseases.     

Fatty infiltration of the liver: evaluation by proton spectroscopic imaging

The reliability of proton spectroscopic imaging in evaluating fatty infiltration of the liver was investigated in 35 subjects (12 healthy volunteers and 23 patients with fatty livers). With this modified spin-echo technique, fatty liver could be separated from normal liver both visually and quantitatively. On the opposed image, normal liver had an intermediate signal intensity, greater than that of muscle, whereas fatty liver had a lower signal intensity, equal to or less than that of muscle. In normal livers, the lipid signal fraction was less than 10%, while in fatty livers it was greater than 10% and usually exceeded 20%. With this technique, nonuniform fatty infiltration of the liver can be differentiated from hepatic metastases, and the technique may prove useful in the differentiation of some hepatic disorders.     

Detection of hepatic metastases in diffuse fatty infiltration by CT: the complementary role of imaging

Six patients undergoing computed tomographic (CT) evaluation for possible abdominal and pelvic metastases were shown to have diffuse fatty infiltration of the liver and findings indeterminate for hepatic metastases. In two patients with diffuse fatty infiltration and no focal hepatic lesions on CT, technetium-99m sulfur colloid imaging demonstrated focal hepatic defects confirmed to represent metastases. In four patients with diffuse fatty infiltration and hyperdense liver foci on CT, radionuclide imaging demonstrated normal uptake in the hyperdense foci confirmed to represent areas of normal liver spared by fatty infiltration. In each of the six patients, clinical management was altered by the radionuclide findings.     

Loss of echogenic lesion of focal fatty infiltration in fibrotic liver

Five alcoholics with chronic liver disease showed focal low density areas of the liver that varied in distribution on computed tomography (CT) but no corresponding lesions on ultrasonography. The densities of these areas on CT were much lower than that of spleen. All the areas disappeared 2 days to 4 weeks after patients entered the hospital, suggesting that they were focal areas of fatty liver. Four patients had liver cirrhosis and one liver fibrosis. These observations may add further evidence to our previous finding that increased echogenecity of the liver produced by fatty infiltration is attenuated by complicating fibrosis.