CT scan of the liver

Since its inception, CT scan has had a dominant role in hepatic imaging. Recent advances including helical CT scan and bolus-triggered scan initiation software packages have had a significant impact. Issues regarding volume, rate of administration, and type of intravenous contrast are being distilled. Workstations for three-dimensional data reconstructions are producing images that compete with conventional angiography in certain areas, while angiographically assisted CT scan is being refined in others.

Imaging of diffuse liver disease

Imaging can play an important role in the diagnosis and planning of treatment for patients with diffuse liver disease. In certain entities, such as iron overload disorders, fatty change, Budd-Chiari syndrome, and schistosomiasis, the imaging findings are characteristic and diagnostic. In others, the findings are less specific, but imaging still has utility in assessment for associated changes of cirrhosis and portal hypertension. In either case, familiarity with these diffuse hepatic diseases and their expected imaging findings enables an organized and thoughtful assessment, with careful attention paid to the key diagnostic features and the important sequlae, such as portal hypertension and the development of HCC.

Hepatic imaging. An overview

Recent advances in ultrasound, CT scan, MR imaging, and scintigraphy permit characterization of a variety of focal and diffuse liver diseases. Accurate clinical information, however, is of vital importance in selecting the optimal imaging modality and interpreting the study accurately. Using a combination of radiologic findings and clinical information, a correct diagnosis may be achieved noninvasively.

Superparamagnetic iron oxide particles (SH U 555 A): evaluation of efficacy in three doses for hepatic MR imaging

PURPOSE

To evaluate the efficacy of SH U 555 A in three doses for magnetic resonance (MR) imaging in the liver and to establish the best postinjection time point for liver MR imaging.

MATERIALS AND METHODS

Pre- and postcontrast image sets obtained in 169 patients after injection of SH U 555 A (randomly, 4, 8, or 16 mumol of iron per kilogram of body weight). Three blinded readers evaluated the precontrast and 10- and 40-minute postcontrast MR images of 54, 58, and 57 patients, respectively.

RESULTS

Statistically significant differences were observed in diagnostic confidence between images obtained with a dose of 4 or 16 mumol Fe/kg (P = .011) and in good or excellent improvement, respectively, in delineation of lesions on 10-minute postcontrast images (P = .001). No apparent differences in the efficacy evaluation were seen between the 10- and 40-minute postcontrast imaging time points.

CONCLUSION

There was a dose-dependent postcontrast improvement in evaluated efficacy parameters (diagnostic confidence, visual evaluations) after injection of SH U 555 A. Accumulation phase imaging could begin as early as 10 minutes after administration.

MRI of the gastrointestinal tract

This article reviews the application of magnetic resonance imaging (MRI) to study the gastrointestinal (GI) tract. A summary of the current MRI techniques is included, emphasizing the choice of pulsing sequences, imaging plane, surface coils and intravenous and oral contrast agents for each of the different segments of the GI tract. The multiple available oral contrast agents are reviewed, including the role of both positive and negative. Finally, the major clinical applications of MRI in the GI tract are discussed by major disease categories (congenital abnormalities, inflammatory disease and benign and malignant neoplasms). The latter is further subdivided by GI tract segments such as esophagus, stomach, small bowel and colon.

Low density barium and bentonite mixture versus high density barium: a comparative study to optimize negative gastrointestinal contrast agents for MRI

The purpose of this study was to compare the patient tolerance and efficacy, as magnetic resonance imaging negative oral contrast agents, of a mixture of clay compound bentonite and low density barium sulfate suspension with that of higher density barium sulfate. Twenty patients were randomized into two groups: 10 patients receiving a mixture of low concentration 60% w/v barium sulfate plus 2.5% w/v bentonite, and 10 patients receiving 220% w/v barium sulfate Liuqid-HD (E-Z-EM, Westbury, NY). Post-contrast Spin-echo (SE) T1- and T2-weighted images (WI) were obtained on a 1.0T magnet. Two independent readers scored the overall intraluminal signal intensity and delineation of the gastrointestinal tract and adjacent organs. Patient acceptance was evaluated via a short questionnaire, by recording spontaneous comments and documenting the quantity of contrast agent ingested. There was greater intraluminal bowel signal reduction and organ delineation with 220% w/v barium than with the barium-bentonite mixture on both SE T1WI (p = 0.03) and SE T2WI (p = 0.42). With both agents there was greater signal reduction on SE T2WI than SE T1WI. Higher scores for organ delineation for both contrast agents were seen with SE T1WI. With 220% w/v barium, there was significantly better delineation of the pancreatic body (p = 0.02) and pancreatic tail (p = 0.02) on T1WI compared with SE T2WI. With the barium-bentonite mixture, SE T1WI showed improved delineation of jejunum compared with SE T2WI (p = 0.03). There were no statistically significant differences between the volume of contrast ingested in the two groups. Abdominal cramps were recorded for one patient in each group. These results suggest that barium-bentonite mixture, although useful as a negative gastro-intestinal contrast agent, is not as effective as 220% w/v barium. Further studies with a larger patient population and concentration optimization studies are needed.

Magnetic resonance imaging evaluation of a case of von Hippel-Lindau disease

We present a case of von Hippel-Lindau disease with special reference to the findings in MR imaging of visceral abdominal manifestations.

Hepatic metastases: computed tomography versus magnetic resonance imaging in 1997

The developments in computed tomography (CT) and magnetic resonance (MR) imaging that have taken place over the last two decades have dramatically increased our ability to detect and characterize focal liver lesions, and have led to the liver becoming the primary focus of interest in abdominal imaging. At the same time, advances in the medical and surgical treatment of secondary liver tumors have continued to be a challenge to these advances in radiology. It is clear that a successful outcome depends on knowledge of the size and location of the tumor burden, and accurate radiological assessment is crucial in identifying the subgroups of patients who may benefit from surgery and, at the same time, in preventing unnecessary radical surgery, with its high morbidity, in those likely to gain only a short-term benefit. The current period of limited resources, along with increased awareness of the effects of ionizing radiation, has led to competition between the two modalities, with considerable debate as to which offers the better noninvasive examination of the liver, particularly with regard to the detection and characterization of focal liver lesions. Arguments over each method's relative merits have tended to be overstated, but the parallel use of different diagnostic techniques is costly and inefficient. Each needs to be placed in an appropriate position on diagnostic pathways.

Undifferentiated (embryonal) sarcoma of the liver: pathologic basis of imaging findings in 28 cases

PURPOSE

To correlate the imaging and pathologic features of undifferentiated (embryonal) sarcoma (UES) and account for the discrepancy between the solid appearance at ultrasound (US) and the almost cystlike appearance at computed tomography (CT) and magnetic resonance (MR) imaging.

MATERIALS AND METHODS

The clinical, pathologic, and imaging findings in 28 patients (age range, 3-49 years) with pathologically proved UES were retrospectively reviewed. All patients underwent at least one cross-sectional imaging study to include CT (27 patients), US (21 patients), and MR imaging (six patients). Tumor size, gross morphology (n = 27), histologic features, and proportion of solid and cystlike components were evaluated and correlated to the imaging findings.

RESULTS

The mean transverse diameter of the tumors was 14 cm (range, 10-25 cm). At gross examination, the tumors were predominantly solid (mean, 83% of tumor volume), and pathologic and US findings were concordant. Conversely, CT scans showed low attenuation (approximately that of water) in 88% of the tumor volume and T2-weighted MR images showed high signal intensity (approximately equal to that of cerebrospinal fluid) in 89% of the tumor volume.

CONCLUSION

UES shows a misleading cystlike appearance at CT and MR imaging compared with US and pathologic findings. In a child or young adult with a liver tumor, this finding is useful in making a prospective diagnosis and avoiding misguided attempts at drainage.

MR imaging of inflammatory disease of the liver

Although MR imaging has achieved a clear role in the assessment of focal benign and malignant hepatic lesions, its role in the evaluation of inflammatory processes in the liver is less well defined and studied. Many inflammatory diseases in the liver have no characteristic or specific imaging findings with MR imaging. Familiarization with these entities and their respective imaging findings is important, however, to aid in their identification and distinction from the more commonly studied neoplastic disease.

MR imaging of the liver--a practical approach

Clinical information must be combined with radiologic features to evaluate focal or diffuse liver disease effectively, and MR examinations need to be tailored appropriately. If there are characteristic radiologic findings, in many cases a correct diagnosis is possible; however, radiologic methods may provide an exact description of disease extent, vascular supply, infiltration, metastases, and tumor changes like necrosis or hemorrhage, without providing a definitive diagnosis. In these situations interventional radiologic techniques (such as percutaneous biopsy) have a potential role in diagnosis.

Rectal perflubron: new application in MRI of perirectal fistulae

PURPOSE

Our goal was to determine the efficacy of MRI with rectal administration of perflubron in the evaluation of perirectal and pelvic fistulae, with an emphasis on development of an improved method for fistula visualization.

METHOD

Fourteen pelvic and/or perirectal fistulae were evaluated in nine patients with MRI after the rectal administration of 200 ml of perflubron. Images were reviewed by two independent readers and evaluated for the presence or absence of fistulae. Qualitative assessment was also performed, rating the examinations for the ability to visualize the fistulae. Comparison was made with the clinical examination and/or operative findings, as well as available preperflubron imaging studies (CT = 10; fluoroscopy = 1; preperflubron MRI = 4).

RESULTS

MRI with rectal perflubron demonstrated all 14 fistulae (100%), while preperflubron imaging demonstrated only 7 of 14 (50%) fistulae (p < or = 0.008, Wilcoxon signed rank test). In addition, MRI with perflubron resulted in significantly improved qualitative visualization of fistulae (overall very good rating versus poor rating for preperflubron imaging, p < or = 0.006, Wilcoxon signed rank test).

CONCLUSION

MRI with rectal perflubron is a superior modality for imaging of fistulae, compared with conventional methods, since it allows a noninvasive means of demonstrating the presence of a fistula as well as offers improved qualitative assessment of fistulous disease.

MR imaging measurement of the femoral antetorsional angle as a new technique: comparison with CT in children and adults

OBJECTIVE

Our objective was to determine the accuracy, precision, and reliability of MR imaging as a technique for measurement of the femoral antetorsional angle.

SUBJECTS AND METHODS

We used MR imaging to measure anteversion of the femoral neck in 44 patients: 19 children (range, 3-17 years old; mean, 11 years old) and 25 adults (range, 18-83 years old; mean, 29 years old).

RESULTS

We found a high correlation between MR imaging and CT measurements (r = 77). On CT, the mean angle for children was 34 degrees and for adults it was 22.2 degrees. On MR imaging, the mean angle for children was 23.22 degrees and for adults it was 15.71 degrees. The mean anteversion angles obtained by CT exceeded those obtained by MR imaging. Mean interobserver and intraobserver agreements were high for MR imaging (r = .97 and r = .97, respectively) and for CT (r = .99 and r = .96, respectively).

CONCLUSION

Compared with CT as the gold standard, MR imaging measurement of femoral anteversion allows precise anatomic measurements and produces reliable, reproducible results. MR imaging is recommended for preoperative planning in pediatric patients with femoral rotation osteotomies.

Pancreatic neoplasms: MR imaging and pathologic correlation

Magnetic resonance (MR) imaging can aid in the detection and characterization of many pancreatic neoplasms. The MR imaging appearances of common pancreatic neoplasms such as ductal adenocarcinoma are well-known. However, MR imaging features of more unusual pancreatic neoplasms are not well understood. Such tumors include mucin-hyper-secreting carcinoma, serous microcystic neoplasm, mucinous macrocystic neoplasm, solid and papillary epithelial neoplasm, multiple cysts associated with von Hippel-Lindau disease, acinar cell carcinoma, pancreaticoblastoma, and endocrine neoplasms (eg, nonfunctioning islet cell tumors, insulinoma, and gastrinoma). In general, pancreatic neoplasms demonstrate high signal intensity on T2-weighted images; the signal intensity on T1-weighted images is more variable but is often intermediate or low. Gadolinium enhancement is often helpful in further characterizing pancreatic neoplasms. The gross and histologic features of pancreatic neoplasms are also not well-known. Correlation with the underlying pathologic features enhances understanding of the MR imaging characteristics of both common and unusual pancreatic neoplasms.

Retroperitoneal MR imaging

Although CT is usually the first imaging study used to evaluate for retroperitoneal disease, MR imaging is increasingly chosen to further characterize lesions. In addition, MR imaging is the ideal modality for evaluating the extent of retroperitoneal tumors as well as their relationship to adjacent structures and organs. The multiplanar capabilities and soft-tissue contrast resolution are significant advantages of MR over CT. This article reviews the retroperitoneal anatomy and our current imaging techniques. Disease processes that commonly affect the retroperitoneum are discussed along with their MR imaging characteristics.

High-density oral barium sulfate in abdominal MRI: efficacy and tolerance in a clinical setting

Bowel and anatomic delineation were evaluated on abdominal magnetic resonance imaging scans in patients who received high-density barium sulfate orally (n = 16, BA+ group) or underwent magnetic resonance imaging without oral contrast (n = 14, BA- group). On T1-weighted images, the BA+ group had better delineation of gastric fundus, duodenum, jejunum, and ileum (p < .005) and pancreatic head (p < .02) than did the BA- group. On T2-weighted images, gastric fundus (p < .005), jejunum (p < .02), and ileum (p < .02) were better delineated in the BA+ group than in the BA- group. Analysis of patients' prior CT scans, used to control for selection bias, showed no differences in anatomic or bowel delineation between BA+ and BA- groups that would account for the differences seen in magnetic resonance imaging. One-fourth of patients could tolerate only 150 cc of contrast. High-density oral barium sulfate is recommended in patients undergoing magnetic resonance imaging for pancreatic or gastrointestinal tract disease, although patient intolerance may limit its widespread use in abdominal magnetic resonance imaging.

In vivo animal tests of an artifact-free contrast agent for gastrointestinal MRI

A variety of shortcomings are associated with most currently used gastrointestinal contrast agents for magnetic resonance imaging (MRI). Artifacts resulting from peristalsis and other motions in the abdominal region are produced by many positive contrast agents (which increase signal intensity). Although this is not a problem for negative contrast agents (which decrease signal intensity), some negative contrast agents produce magnetic susceptibility artifacts that are especially pronounced at high field strength and with gradient echo pulse sequences. These susceptibility artifacts are produced by both paramagnetic and diamagnetic agents. It has been demonstrated in phantoms, however, that susceptibility matching can be used to produce contrast agents with desirable relaxation and contrast properties but without deleterious susceptibility artifacts. We now report results of animal tests of such an oral contrast agent, consisting of a suspension of superparamagnetic iron oxide particles and diamagnetic barium sulfate particles, compared to individual suspensions of the iron oxide and of the barium sulfate. Iron oxide was the least effective and the matched susceptibility mixture was the most effective for the intestine, which has traditionally been the most difficult region of the GI tract to visualize clearly. Matched susceptibility mixtures, which are inherently able to yield images free of susceptibility artifacts without compromising contrast, show promise of being improved oral negative contrast agents for use in gastrointestinal MRI.

The leaking esophagus: CT patterns of esophageal rupture, perforation, and fistulization

Esophageal perforation can be a catastrophic event for a patient regardless of the etiology of the perforation. Contrast esophagrams can typically diagnose an esophageal perforation if the clinical symptoms or history suggest the diagnosis. Often, however, the clinical features are atypical and a CT scan is performed early in the patient's workup. It is, therefore, essential to recognize the CT features seen in esophageal perforation. The various etiologies and CT findings of esophageal perforation are reviewed in this article. The CT abnormalities include extraluminal air, periesophageal fluid, esophageal thickening, and extraluminal contrast. These CT findings may be the first clue to the correct diagnosis of esophageal perforation.

Solid and papillary epithelial neoplasm of the pancreas: imaging-pathologic correlation on 56 cases

PURPOSE

To evaluate the clinical, pathologic, and imaging findings of solid and papillary epithelial neoplasm (SPEN) of the pancreas and to correlate imaging and gross pathologic features.

MATERIALS AND METHODS

A retrospective review was performed in 56 patients (53 female and three male patients aged 10-74 years [mean age at diagnosis, 25 years]) with pathologically proven SPEN of the pancreas. All patients underwent computed tomography (n = 49), ultrasonography (n = 31), or magnetic resonance (MR) imaging (n = 9). Tumor size, location, and imaging features were evaluated and correlated with gross pathologic and histologic features.

RESULTS

Mean transverse diameter of these tumors was 9.0 cm (range, 2.5-17.0 cm). They were localized to the tail (n = 30), head (n = 18), and body (n = 8) of the pancreas. All tumors contained some degree of internal hemorrhage or cystic degeneration, and all were well encapsulated. Areas of hemorrhagic degeneration ranged from solid friable tumor to gelatinous or cystic cavities and therefore demonstrated variable imaging features. Calcification was noted in 16 patients. Fluid-debris levels were noted in 10 patients.

CONCLUSION

Imaging studies of SPEN of the pancreas consistently demonstrate variable degrees of hemorrhagic degeneration. Calcification is common. Characteristic fluid-debris levels and signal intensities seen with MR imaging indicate blood products. In the appropriate clinical setting, these findings are useful in making a prospective diagnosis.

Intussuscepted colonic lipomas: loss of fat attenuation on CT with pathologic correlation in 10 cases

BACKGROUND

To determine if infarction and necrosis is the cause of the confusing soft tissue density on CT within intussuscepting lipomas of the colon.

METHODS

The clinical records, radiologic examinations, and pathologic specimens of all 13 cases of colonic lipomas collected from 1988 to 1994 studied by CT and surgically resected were retrospectively reviewed. Ten of these cases were associated with intussusception; the CT attenuation of the lead point was graded according to its relative fat/soft tissue density. Pathologic specimens were graded independently by a GI pathologist and graded according to the degree of infarction/fat necrosis.

RESULTS

The lipomas ranged from 4 to 7 cm in diameter (mean = 5 cm). Only one case with intussusception, and all three cases without, demonstrated pure fat attenuation on CT and demonstrated pure fat histologically. One case demonstrated soft tissue attenuation and corresponded with the most severely infarcted specimen histologically; two cases with similar but less severe infarction/fat necrosis corresponded with less than 25% fat attenuation. These latter three cases were originally misinterpreted as malignancies rather than lipomas. Six cases maintained greater than 50% fat density and intermediate amounts of infarction/fat necrosis.

CONCLUSION

Lipomas may have an atypical appearance when intussuscepted due to varying degrees of infarction/fat necrosis.

Focal nodular hyperplasia of the liver: radiologic-pathologic correlation

Focal nodular hyperplasia (FNH) is a benign hepatic tumor that likely represents a local hyperplastic response of hepatocytes to a congenital vascular anomaly. It is most commonly seen in middle-aged women and is typically a solid mass measuring less than 5 cm in diameter. Most lesions have central scars that contain thick-walled vessels that provide excellent arterial blood supply; hemorrhage, necrosis, and infarction are, therefore, extremely unusual. Characteristic imaging features include a hypervascular homogeneous tumor with a central scar and with both hepatocellular and reticuloendothelial function. Ultrasonography, computed tomography, scintigraphy, and magnetic resonance imaging all offer different advantages in the detection and characterization of FNH. There is excellent correlation between the pathologic and imaging features of FNH. In many cases, it is possible to obtain a prospective imaging diagnosis of FNH; however, in some cases, the distinction between FNH and other primary hepatic neoplasms is not possible. In these latter cases, close imaging follow-up, needle biopsy, or even surgical resection may be necessary.

Ring enhancement in ultrasmall superparamagnetic iron oxide MR imaging: a potential new sign for characterization of liver lesions

OBJECTIVE

We performed this study to evaluate the incidence and significance of ring enhancement after i.v. administration of an ultrasmall superparamagnetic iron oxide (USPIO) particle (Code 7227), a reticuloendothelial contrast agent with potential use as a blood-pool agent, for characterizing focal hepatic lesions.

SUBJECTS AND METHODS

Conventional T1-weighed imaging, fat-suppressed T1-weighted imaging, conventional T2-weighted imaging, and fast T2-weighted imaging of the liver were obtained in 27 patients with 43 liver lesions before and after i.v. administration of a USPIO preparation. All lesions were larger than 1 cm; 29 were malignant and 14 were benign. Diagnosis was confirmed in all cases, either pathologically (19 patients) or by follow-up examination (eight patients). Two readers independently evaluated each pulse sequence for the presence of ring enhancement of hepatic lesions.

RESULTS

Ring enhancement was noted only on T1-weighted images, with no ring enhancement evident on T2-weighted images. Twenty of 43 (47%) lesions showed ring enhancement, including 18 of 29 (62%) malignant lesions and two of 14 (14%) benign lesions (p < .011); Wilcoxon signed rank test). Fat-suppressed T1-weighted imaging showed ring enhancement better than or equal to conventional T1-weighted imaging in all cases, with ring enhancement of 15 of 18 (83%) malignant lesions and two of two benign lesions better demonstrated on fat-suppressed T1-weighted imaging sequences (p < or = .025).

CONCLUSION

Ring enhancement after i.v. administration of Code 7227 is a frequent finding seen more often with malignant than benign lesions, potentially identifying a new MR imaging feature for the characterization of liver lesions. The identification of ring enhancement on T1-weighted images attests to the significant blood-pool effects of USPIO particles.

Superparamagnetic iron oxide (SPIO) as an oral contrast agent in gastrointestinal (GI) magnetic resonance imaging (MRI): comparison with state-of-the-art computed tomography (CT)

This study was conducted to compare the sensitivity and specificity of abdominal magnetic resonance imaging using oral superparamagnetic iron oxide with oral contrast-enhanced computed tomography in the detection of GI pathology. Overall sensitivity was calculated to be 83% for OECT compared to 67% by SPIO MRI. Specificity for OECT was 68% compared to 89% for SPIO MRI. The results from imaging with superparamagnetic iron oxide and imaging with oral contrast-enhanced computed tomography were in agreement in 14 subjects who had normal gastrointestinal tracts. In the remaining 16 patients, eight pathologic entities were detected by both modalities whereas 15 abnormalities were seen by only one modality. Superparamagnetic iron oxide magnetic resonance imaging was helpful in discriminating normal bowel from solid lesions and in detecting subtle gastrointestinal tract mass effect. In 30 consecutively studied patients suspected of having GI pathology, OECT was more sensitive than SPIO MRI in detecting abdominal pathology. Conversely, SPIO MRI was more specific than OECT.