Diagnostic accuracy of non-contrast magnetic resonance enterography in detecting active bowel inflammation in pediatric patients with diagnosed or suspected inflammatory bowel disease to determine necessity of gadolinium-based contrast agents.

BACKGROUND: Pediatric patients with inflammatory bowel disease (IBD) are at increased risk of gadolinium deposition given the potential need for multiple contrast-enhanced magnetic resonance enterography (MRE) exams over their lifetime. OBJECTIVE: To determine whether gadolinium-based contrast agents are necessary in assessing active bowel inflammation on MRE in pediatric patients with known or suspected IBD. MATERIALS AND METHODS: We conducted a retrospective study of 77 patients (7-18 years; 68.8% male) with known (n=58) or suspected (n=19) IBD and endoscopy with biopsy performed within 30 days of MRE without and with contrast evaluated bowel and non-bowel findings. During three visual analysis sessions, two radiologists reviewed pre-, post-, and pre-/post-contrast MRE images. A third radiologist independently reviewed 27 studies to assess inter-reader reliability. We used Cohen kappa (κ), Fleiss kappa, (κF), McNemar test, and sensitivity and specificity to compare MRE readings to combined endoscopic/histopathological findings (the reference standard). RESULTS: The pre- and pre-/post-contrast-enhanced MRE vs. combined endoscopic/histopathological results had moderate agreement (85.7%; κ 0.713, P<0.001; P-value 0.549). Compared to combined endoscopy/histopathology, pre- vs. pre-/post-contrast sensitivity (67%, confidence interval [CI] 0.53-0.79 vs. 67%, CI 0.53-0.79) and specificity (80%, CI 0.59-0.92 vs. 68%, CI 0.46-0.84) varied little (κ 0.42, P<0.001 and κ 0.32, P=0.003, respectively). The three readers had moderate agreement (85.2%; κ 0.695, P=0.001; P-value 0.625). More penetrating complications were identified following contrast administration (P-value 0.04). CONCLUSION: Use of a contrast agent does not improve the detection of active inflammation in the terminal ileum and colon compared to non-contrast MRE, although use of a contrast agent does aid in the detection of penetrating disease.

Acute side effects of three commonly used gadolinium contrast agents in the paediatric population.

OBJECTIVE: To determine the incidence of acute side effects of three commonly used gadolinium contrast agents in the paediatric population. METHODS: A retrospective review of medical records was performed to determine the incidence of acute adverse side effects of i.v. gadolinium contrast agents [MultiHance(®) (Bracco Diagnostics Inc., Princeton, NJ), Magnevist(®) (Bayer Healthcare Pharmaceuticals, Wayne, NJ) or Gadavist(®) (Bayer HealthCare Pharmaceuticals)] in paediatric patients. RESULTS: 40 of the 2393 patients who received gadolinium contrast agents experienced acute side effects, representing an incidence of 1.7%. The majority of the acute side effects (in 30 patients) were nausea and vomiting. The incidence was significantly higher in non-sedated patients (2.37% vs 0.7%; p = 0.0018). Furthermore, without sedation, the incidence of both nausea and vomiting was significantly higher in children receiving MultiHance, with a 4.48% incidence of nausea when compared with Magnevist (0.33%, p < 0.0001) and Gadavist (0.28%, p < 0.0001) and a 2.36% incidence of vomiting compared with those for Magnevist (0.50%, p = 0.0054) and Gadavist (0.28%, p = 0.014), whereas no difference was observed between Magnevist and Gadavist within the power of the study. In addition, there was no apparent difference between any of the three contrast agents for the incidence of allergy or other acute side effects detected, given the sample size. CONCLUSION: The gadolinium contrast agents MultiHance, Magnevist and Gadavist have a low incidence of acute side effects in the paediatric population, a rate that is further reduced in moderately sedated patients. MultiHance demonstrated significantly increased incidence of gastrointestinal symptoms compared with Magnevist and Gadavist. ADVANCES IN KNOWLEDGE: The incidence of acute side effects of three commonly used gadolinium contrast agents was determined in the paediatric population, which can have clinical implications.

Subtypes of renal cell carcinoma: MRI and pathological features.

Renal cell carcinoma (RCC) is the most common malignant tumor involving the kidney. Determining the subtypes of renal cell carcinoma is among the major goals of preoperative radiological work-up. Among all modalities, magnetic resonance imaging (MRI) has several advantages, such as inherent soft tissue contrast, detection of lipid and blood products, and excellent sensitivity to detect small amounts of intravenous contrast, which facilitate the discrimination of subtypes of RCC. In this article, we review MRI and pathological features used for determining the main histologic subtypes of RCC, including clear cell, papillary, collecting duct, chromophobe, multilocular cystic, and unclassified RCC.

Hepatobiliary MR imaging with gadolinium-based contrast agents.

The advent of gadolinium-based "hepatobiliary" contrast agents offers new opportunities for diagnostic magnetic resonance imaging (MRI) and has triggered great interest for innovative imaging approaches to the liver and bile ducts. In this review article we discuss the imaging properties of the two gadolinium-based hepatobiliary contrast agents currently available in the U.S., gadobenate dimeglumine and gadoxetic acid, as well as important pharmacokinetic differences that affect their diagnostic performance. We review potential applications, protocol optimization strategies, as well as diagnostic pitfalls. A variety of illustrative case examples will be used to demonstrate the role of these agents in detection and characterization of liver lesions as well as for imaging the biliary system. Changes in MR protocols geared toward optimizing workflow and imaging quality are also discussed. It is our aim that the information provided in this article will facilitate the optimal utilization of these agents and will stimulate the reader's pursuit of new applications for future benefit.

Magnetic resonance imaging of focal liver lesions: approach to imaging diagnosis.

This article is a review of magnetic resonance imaging (MRI) of incidental focal liver lesions. This review provides an overview of liver MRI protocol, diffusion-weighted imaging, and contrast agents. Additionally, the most commonly encountered benign and malignant lesions are discussed with emphasis on imaging appearance and the diagnostic performance of MRI based on a review of the literature.

Serial MR imaging of small arterially-enhancing liver lesions in patients with chronic liver disease.

OBJECTIVE: To determine the significance of small arterially-enhancing liver lesions seen with magnetic resonance imaging (MRI) in patients with chronic liver disease. MATERIAL AND METHOD: Our institutional review board approved this retrospective study, without requiring informed consent. Over a two-year period, 258 consecutive patients with cirrhosis or chronic hepatitis underwent multiphase three-dimensional, gadolinium-enhanced, breath-hold gradient-echo MRI. From this group, 29 patients underwent at least one follow-up MR study. When a small (< or = 20 mm) arterially-enhancing lesion was detected, the maximum diameter shape, signal intensities (T1-weighted and T2-weighted), and pattern of enhancement were evaluated to assess the associations between the imaging appearance on initial MR exam and subsequent behavior on follow-up imaging. Statistical testing was performed with JMP Statistical Software (SAS, Inc., Cary, NC) and StatXact 7 Statistical Software for Exact Nonparmetric Inference (Cytel, Inc., Cambride, MA). RESULTS: Sixty-five small (< or = 20 mm) arterially-enhancing lesions were detected in 29 patients. Ten of 65 lesions (15%) in nine patients were subsequently proven to represent hepatocellular carcinoma (HCC), while the remaining lesions either disappeared (46) or remained stable in size (9). Of the 10 lesions subsequently proven to represent HCC, eight lesions converted from hypo- or isointense to hyperintense on subsequent T2-weighted MRI (p < 0.001), seven lesions converted from hyper- or isointense to hypointense on subsequent T1-weighted images (p < 0.001), seven lesions demonstrated growth on subsequent MRI exam (mean increase in mean diameter = 1.4 cm), and five lesions subsequently developed rim enhancement that was not initially present. CONCLUSION: Small, arterially-enhancing lesions detected with MRI have a low likelihood of representing HCC, and MRI follow-up of such lesions is a reasonable approach. Lesions that increase in size, convert to hypointense on subsequent T1W images, convert to hyperintense in T2W images, or develop rim enhancement on follow-up MRI images are concerning and should prompt consideration of intervention.

Fat-suppressed dynamic and delayed gadolinium-enhanced volumetric interpolated breath-hold magnetic resonance imaging of cholangiocarcinoma.

OBJECTIVE: To determine the enhancement phase providing the highest contrast-to-noise ratio (CNR) between cholangiocarcinoma and liver or portal vein on dynamic and delayed gadolinium-enhanced magnetic resonance imaging (MRI). SUBJECTS AND METHODS: Precontrast, 3-phase dynamic postcontrast, and delayed postcontrast MRI of the liver was performed in 25 patients with cholangiocarcinoma and correlated with surgical findings, pathology, and other imaging studies. Contrast-to-noise ratios for tumor relative to adjacent liver and portal vein were calculated from signal intensities determined from regions of interest obtained for each phase of enhancement. A subjective assessment of the signal intensity of the periportal tissues relative to the portal vein was made for each set of delayed images. RESULTS: A mass was visible in 24 of 25 patients. Tumor masses were hypointense in 92%, 67%, 75%, and 21%; isointense in 8%, 8%, 17%, and 12%; and hyperintense in 0%, 25%, 8%, and 67% of patients relative to liver on precontrast, arterial, portal venous, and delayed images, respectively. No single phase of gadolinium enhancement demonstrated consistently superior tumor-versus-liver CNR. Delayed imaging demonstrated the highest tumor-versus-liver CNR in 25% of patients and the lowest in 33%. The portal venous phase demonstrated the highest tumor-versus-portal vein CNR in 75% of patients. Delayed postcontrast images demonstrated the lowest tumor-versus-portal vein CNR in 38% of patients. Periportal tissues were isointense to portal vein in all but 1 patient on delayed images. CONCLUSION: No single phase of dynamic and delayed gadolinium-enhanced MRI demonstrates superior CNR between cholangiocarcinoma and normally enhancing liver, although the portal phase provides the best CNR between tumor and portal vein in most cases. Although delayed enhancement is typical of cholangiocarcinoma, delayed imaging does not necessarily offer superior contrast between tumor and liver parenchyma compared with other phases of enhancement. Differentiation between tumor and portal vein and periportal tissues may be difficult on delayed images.

Clinical and economic impact of falsely decreased calcium values caused by gadoversetamide interference.

OBJECTIVE: Gadolinium is administered as a contrast agent in MRI procedures. Two gadolinium-based contrast agents, gadodiamide and gadoversetamide, interfere with colorimetric total serum calcium methods. The purpose of this prospective observational study was to examine the incidence of calcium interference after gadoversetamide procedures, associated clinical outcomes, and costs 20 months after implementation of quality assurance and physician education programs. MATERIALS AND METHODS: Records of patients who received gadoversetamide from June 24, 2006, to October 7, 2006, were reviewed to determine if a routine calcium test had been performed after the injection. Calcium values were repeated with an alternate method that is less susceptible to gadoversetamide interference. If the difference was > or = 2.0 mg/dL or if the initial test value was < or = 7.0 mg/dL, patient charts were reviewed for any related treatment. Costs associated with this algorithm were tracked. RESULTS: The initial calcium test was performed after gadoversetamide in 766 of 3,439 instances. The alternate test was performed in 633 of 766. One hundred twenty-five of 633 (20%) showed a difference in calcium values that was > or = 0.7 mg/dL, with 16 showing differences of > or = 1.6 mg/dL. Chart review for 56 instances revealed that calcium supplements were administered in 22 of 56 around the time of gadoversetamide injection. However, none appeared to be related to the spurious hypocalcemia. The total additional cost (reagent and technologist) for following this algorithm for just over 3 months was $6,807. CONCLUSION: Approximately 20% of patients receiving gadoversetamide exhibited spurious hypocalcemia. No patients were identified who received inappropriate calcium because of this interference. This may be attributable to the quality assurance and physician education programs.

MR imaging of the gallbladder: a pictorial essay.

The gallbladder serves as the repository for bile produced in the liver. However, bile within the gallbladder may become supersaturated with cholesterol, leading to crystal precipitation and subsequent gallstone formation. The most common disorders of the gallbladder are related to gallstones and include symptomatic cholelithiasis, acute and chronic cholecystitis, and carcinoma of the gallbladder. Other conditions that can affect the gallbladder include biliary dyskinesia (functional), adenomyomatosis (hyperplastic), and postoperative changes or complications (iatrogenic). Ultrasonography (US) has been the traditional modality for evaluating gallbladder disease, primarily owing to its high sensitivity and specificity for both stone disease and gallbladder inflammation. US performed before and after ingestion of a fatty meal may also be useful for functional evaluation of the gallbladder. However, US is limited by patient body habitus, with degradation of image quality and anatomic detail in obese individuals. With the advent of faster and more efficient imaging techniques, magnetic resonance (MR) imaging has assumed an increasing role as an adjunct modality for gallbladder imaging, primarily in patients who are incompletely assessed with US. MR imaging allows simultaneous anatomic and physiologic assessment of the gallbladder and biliary tract in both initial evaluation of disease and examination of the postoperative patient. This assessment is accomplished chiefly through the use of MR imaging contrast agents excreted preferentially via the biliary system.

Efficacy and safety of gadodiamide (Gd-DTPA-BMA) in renal 3D-magnetic resonance angiography (MRA): a phase II study.

PURPOSE: To determine the most efficacious dose of gadodiamide for three-dimensional (3D) contrast-enhanced (CE) magnetic resonance angiography (MRA) of the renal arteries on a patient level based on the sensitivity in detecting the main hemodynamically relevant (> or =50% or occlusion) renal artery stenosis (RAS) using intra-arterial digital subtraction angiography (IA DSA) as the gold standard. MATERIALS AND METHODS: This prospective, randomized, double-blind, parallel-group, multicenter study included 273 patients referred to IA DSA for suspected RAS. Patients underwent 3D CE MRA after injection of 0.01, 0.05, 0.1, or 0.2mmol/kg of body weight gadodiamide (0.5mmol/ml). The images were assessed for location and degree of RAS by independent blinded readers (MRA: three readers, IA DSA: one reader). Hypothesis testing for a significant trend in sensitivity across dose groups was based on the one-sided Cochran-Armitage style trend test for each independent MRA reader. RESULTS: The lowest dose group (0.01mmol/kg) proved non-efficacious in detecting hemodynamically relevant (i.e., > or =50% or occlusion) RAS. A statistically significant dose trend (p<0.001) was shown for each of the three independent readers. Depending on reader, the sensitivity obtained with 0.05, 0.1, and 0.2mmol/kg was 63.9-86.1%, 75.8-91.4% and 80.6-90.6%, the specificity was 66.7-73.9%, 59.3-75.0%, and 59.3-75.0% and accuracy was 67.8-78.9%, 75.4-77.4%, and 76.3-81.0%, for the three dose groups, respectively. There were eight non-severe adverse events (AEs). Three serious AEs occurring in one patient were judged not related to gadodiamide by the on-site investigator. CONCLUSION: A significant dose trend between the four doses examined was observed. The lowest dose (0.01mmol/kg) differed significantly from those of the other three doses. Based on the analysis of the primary and secondary endpoints, 0.1mmol/kg gadodiamide appears to be the most suitable dose in diagnosing hemodynamically relevant RAS. The present study also demonstrated gadodiamide to be safe and well tolerated.

MR contrast agents: physical and pharmacologic basics.

Since approval of the first magnetic resonance (MR) contrast agent was granted in 1988, there has been remarkable growth in the utilization of intravenous gadolinium (Gd)-based agents. Currently it is estimated that nearly half of all MR studies performed are contrast-enhanced. Despite containing a toxic heavy metal, these agents have proven to be not only an effective diagnostic adjunct to non-enhanced MRI, but also remarkably well tolerated and safe. As a result, conventional wisdom has been that MR contrast media are "biologically inert," a notion that is clearly false. Ultimately, it is the radiologist's responsibility to understand the potential adverse effects of Gd-based agents and the special situations in which they are likely to occur; however, the basic pharmacology of contrast agents is generally not included in medical school curricula or formally taught in residency. The purpose of this review is to discuss the mechanism of action of MR contrast agents and relevant aspects of their clinical pharmacology, including effects on the cardiovascular and renal systems, potential laboratory errors, and special situations involving women and children. We also briefly discuss the issue of nephrogenic systemic fibrosis (NSF).

MRI characterization of 124 CT-indeterminate focal hepatic lesions: evaluation of clinical utility.

OBJECTIVE: To evaluate the diagnostic yield of MRI performed for characterization of focal hepatic lesions that are interpreted as indeterminate on CT. PATIENTS AND METHODS: In a retrospective investigation, 124 indeterminate focal hepatic lesions in 96 patients were identified on CT examinations over 5 years from 1997 to 2001. All patients had MRI performed for the liver within 6 weeks of their CT examination. CT and MR images were reviewed independently by two separate groups of two radiologists. The value of MRI in characterizing these lesions was assessed. Diagnoses were confirmed based on histology, characteristic imaging features, and clinical follow-up. RESULTS: MRI definitely characterized 73 lesions (58%) that were indeterminate on CT. MRI was accurate in 72/73 of these lesions. MRI could not definitely characterize 51 lesions (42%). Ten lesions were not visualized on MRI, and follow-up imaging confirmed that no lesion was present in eight of these cases (pseudolesions). CONCLUSION: MRI is valuable for the characterization of indeterminate focal hepatic lesions detected on CT.

MR and MRCP in the evaluation of primary sclerosing cholangitis: current applications and imaging findings.

Primary sclerosing cholangitis is a progressive cholestatic disease of unknown etiology leading to cirrhosis and liver failure. Several imaging modalities have been used to study this disease, including ultrasonography, computed tomography and hepatobiliary scintigraphy, but accurate diagnosis was found to be best made with endoscopic retrograde cholangiopancreatography or direct cholangiography. However, these 2 methods are invasive and may produce serious complications. Magnetic resonance cholangiopancreatography is a noninvasive imaging technique that has become very useful for diagnosing primary sclerosing cholangitis. Contrast enhanced magnetic resonance imaging provides pertinent information of extraductal abnormalities in addition to biliary ductal changes.

Hybrid peripheral 3D contrast-enhanced MR angiography of calf and foot vasculature.

OBJECTIVE: The objective of our study was to describe hybrid peripheral (HyPer) 3D contrast-enhanced MR angiography (CE-MRA) using sagittal acquisition with parallel imaging of the calf and foot station. The benefit of a dedicated sagittal 3D CE-MRA acquisition of the calf and foot was evaluated by assessing the degree of venous contamination and its diagnostic quality compared with standard bolus chase 3D CE-MRA alone. MATERIALS AND METHODS: Fifty-three patients (99 legs) were scanned with a 1.5-T MR system equipped with a dedicated bilateral lower extremity phased-array coil. First, high-resolution 3D CE-MRA images of the calves and feet were obtained using two separate sagittal slabs with parallel imaging, with a resulting voxel size of 1.4 x 1.0 x 1.0 mm3. Second, standard bolus chase 3D CE-MRA was performed from the abdomen and pelvis station to the calf-foot station. Images were interpreted by two radiologists. The calf-foot arterial trees were divided into 12 segments. Each segment was characterized as diagnostic or nondiagnostic. The degree of venous contamination was assessed as interfering with the diagnosis or not. Paired Student's t test and Wilcoxon's signed rank test were used to test for statistically significant differences between the techniques. RESULTS: For the left leg (n = 48), the mean number (+/- SD) of diagnosed arterial segments for HyPer 3D CE-MRA was 9.2 +/- 2.3 and for bolus chase 3D CE-MRA, 7.1 +/- 4.2 (p < or = 0.0004). For the right leg (n = 51), the corresponding values were 9.4 +/- 2.2 and 7.6 +/- 3.5 (p < or = 0.0005), respectively. For bolus chase 3D CE-MRA, venous contamination interfered with the diagnosis in 24 of 99 legs, whereas with HyPer 3D CE-MRA, there was no interference. Selective analysis of the dorsalis pedis arteries showed that the number of diagnostic vessels was 62 (62.6%) of 99 for HyPer 3D CE-MRA and 13 (13.1%) of 99 for bolus chase 3D CE-MRA. CONCLUSION: HyPer 3D CE-MRA is an alternative method for time-resolved high-resolution peripheral CE-MRA in evaluating the trifurcation and feet vessels with no venous contamination.

MRI of the peritoneum: spectrum of abnormalities.

OBJECTIVE: Our objective was to detail peritoneal anatomy, techniques for optimizing peritoneal MRI, and the MRI characteristics of several disease processes that frequently involve the peritoneum. CONCLUSION: Homogeneous fat suppression and dynamic contrast-enhanced imaging, including delayed imaging, are critical technical factors for successful lesion detection and characterization on peritoneal MRI.

Endovaginal magnetic resonance imaging of the female urethra.

Magnetic resonance imaging (MRI) is playing an important role in the clinical evaluation of women presenting with urethral symptoms. Voiding cystourethrography, direct urethrography, and pelvic sonography provide limited information on abnormalities that are in continuity with the urethra. On the other hand, urethra and periurethral tissues can be noninvasively evaluated by high-resolution endocavitary MRI. Because of its multiplanar capability and high tissue contrast, endovaginal MRI is an extremely reliable diagnostic test in the evaluation of urethral abnormalities. In this article, the utility of endovaginal MRI in the detection and characterization of a wide spectrum of urethral pathologic conditions, such as congenital anomalies, diverticula, urethritis, and benign and malignant neoplasms, is discussed.

Costs of a medical education: comparison with graduate education in law and business.

INTRODUCTION: The costs of graduate school education are climbing, particularly within the fields of medicine, law, and business. METHODS: Data on graduate level tuition, educational debt, and starting salaries for medical school, law school, and business school graduates were collected directly from universities and from a wide range of published reports and surveys. RESULTS: Medical school tuition and educational debt levels have risen faster than the rate of inflation over the past decade. Medical school graduates have longer training periods and lower starting salaries than law school and business school graduates, although physician salaries rise after completion of post-graduate education. CONCLUSIONS: Faced with an early debt burden and delayed entry into the work force, careful planning is required for medical school graduates to pay off their loans and save for retirement.

Role of imaging in pretreatment evaluation of early invasive cervical cancer: results of the intergroup study American College of Radiology Imaging Network 6651-Gynecologic Oncology Group 183.

PURPOSE: To compare magnetic resonance imaging (MRI) and computed tomography (CT) with each other and to International Federation of Gynecology and Obstetrics (FIGO) clinical staging in the pretreatment evaluation of early invasive cervical cancer, using surgicopathologic findings as the reference standard. PATIENTS AND METHODS: This prospective multicenter clinical study was conducted by the American College of Radiology Imaging Network and the Gynecologic Oncology Group from March 2000 to November 2002; 25 United States health centers enrolled 208 consecutive patients with biopsy-confirmed cervical cancer of FIGO stage > or = IB who were scheduled for surgery based on clinical assessment. Patients underwent FIGO clinical staging, helical CT, and MRI. Surgicopathologic findings constituted the reference standard for statistical analysis. RESULTS: Complete data were available for 172 patients; surgicopathologic findings were consistent with FIGO stages IA to IIA in 76% and stage > or = IIB in 21%. For the detection of advanced stage (> or = IIB), sensitivity was poor for FIGO clinical staging (29%), CT (42%), and MRI (53%); specificity was 99% for FIGO clinical staging, 82% for CT, and 74% for MRI; and negative predictive value was 84% for FIGO clinical staging, 84% for CT, and 85% for MRI. MRI (area under the receiver operating characteristic curve [AUC], 0.88) was significantly better than CT (AUC, 0.73) for detecting cervical tumors (P = .014). For 85% of patients, FIGO clinical staging forms were submitted after MRI and/or CT was performed. CONCLUSION: CT and MRI performed similarly; both had lower staging accuracy than in prior single-institution studies. Accuracy of FIGO clinical staging was higher than previously reported. The temporal data suggest that FIGO clinical staging was influenced by CT and MRI findings.

Focal hepatic lesions: diagnostic value of enhancement pattern approach with contrast-enhanced 3D gradient-echo MR imaging.

Focal hepatic lesions constitute a daily challenge in the clinical setting. However, noninvasive methods can be useful in the detection and characterization of these lesions. The noninvasive diagnosis of liver lesions is usually achieved with contrast material-enhanced computed tomography and magnetic resonance (MR) imaging. Dynamic three-dimensional gradient-recalled-echo MR imaging provides dynamic contrast-enhanced thin-section images with fat saturation and a high signal-to-noise ratio and is excellent for the evaluation of various focal hepatic lesions. A comprehensive MR imaging examination in this setting includes T2-weighted and chemical shift T1-weighted imaging and demonstrates characteristic enhancement patterns that can be helpful in the diagnosis of most of these lesions. These enhancement patterns are seen during particular phases of contrast-enhanced imaging and include arterial phase enhancement, delayed phase enhancement, peripheral washout, ring enhancement, nodule-within-a-nodule enhancement, true central scar, pseudocentral scar, and pseudocapsule. Familiarity with these enhancement patterns can help in the identification of specific focal lesions of the liver.