Cystic fibrosis: spectrum of thoracic and abdominal CT findings in the adult patient.

Cystic fibrosis (CF) is an autosomal recessive disorder that is characterized by an abnormality of exocrine gland function. Adult patients represent a rapidly growing percentage of the CF population. Pulmonary changes are seen in nearly every case and are the most serious complication of CF. In advanced lung disease, bronchiectasis, emphysematous bullae, and subpleural blebs can frequently develop. Although pulmonary disease is the most common cause of death and morbidity among CF patients, there also can be involvement of other groups, particularly in adults, which show characteristic signs on CT and spiral CT. Pancreatic abnormalities are present in 85-90% of CF patients. The degree of pancreatic involvement varies, ranging form accumulations of mucus in the small ducts to totally plugged ducts, which can cause atrophy of the exocrine glands and progressive fibrosis. Pancreatic dysfunction on CT is demonstrated as fatty replacement and fibrosis of the pancreas. However, there may be scattered foci of pancreatic calcifications that can be detectable on plain radiographs. Hepatobiliary involvement follows the same pattern as pancreatic abnormalities. Bile canaliculi are plugged by mucinous material and when this plugging is of long duration, biliary cirrhosis with diffuse hepatic nodularity may develop. Such severe hepatic involvement is see in only about 2-5% of patients, although minor hepatic alterations, such as diffuse fatty changes, are fairly common. Hepatobiliary involvement is characterized by hepatic nodularity, compatible with cirrhosis, splenomegaly, and ascites. Complete obstruction of the ileum by meconium occurs in approximately 10% of newborns with CF. Intestinal findings on CT include obstruction, although this is more common in children. These CT signs should be evaluated carefully in adult patients since they may be suggestive of CF. Computed tomography offers unique information about organ involvement (other than pulmonary) that can alter diagnosis and patient management.

Nonneoplastic liver disease: evaluation with CT and MR imaging.

A wide range of nontumorous hepatic diseases may have an impact on liver function and serve as indications for computed tomographic (CT) or magnetic resonance (MR) imaging. New imaging techniques such as spiral CT and fast MR imaging aid in detecting and characterizing these disease processes and in assessing the extent of disease. Infectious liver disease (eg, hepatic abscess, echinococcal disease, fungal infection) typically has low attenuation at CT and high signal intensity at T2-weighted MR imaging. Cholangitis is characterized by ductal dilatation at both CT and MR imaging. In acute portal vein thrombosis, the thrombus has low attenuation at CT and is hyperintense relative to liver at MR imaging. Hepatic infarcts usually appear as well-circumscribed, peripheral, wedge-shaped areas of decreased attenuation at CT. The causes or complications of cirrhosis can be most readily identified with MR imaging. In patients with chronic radiation-induced hepatitis, CT shows the irradiated parenchyma as a region of increased attenuation, whereas T1- and T2-weighted MR imaging demonstrate geographic areas of low and high signal intensity, respectively. Hemachromatosis has homogeneously increased liver attenuation at CT and decreased signal intensity at gradient-echo MR imaging in particular. Familiarity with the CT and MR imaging features of the spectrum of nonneoplastic conditions of the liver is essential in making an accurate diagnosis.

An interactive computer-based tool for teaching the segmental anatomy of the liver: usefulness in the education of residents and fellows.

OBJECTIVE: The purpose of this study was to develop an interactive computer-based tool for teaching hepatic segment anatomy and to evaluate its usefulness for radiology education. CONCLUSION: An interactive computer-based teaching tool has been developed that effectively teaches the segmental anatomy of the liver to radiology residents and fellows who have a wide range of baseline knowledge of hepatic anatomy.

Three-dimensional spiral CT during arterial portography: comparison of three rendering techniques.

The three most common techniques for three-dimensional reconstruction are surface rendering, maximum-intensity projection (MIP), and volume rendering. Surface-rendering algorithms model objects as collections of geometric primitives that are displayed with surface shading. The MIP algorithm renders an image by selecting the voxel with the maximum intensity signal along a line extended from the viewer's eye through the data volume. Volume-rendering algorithms sum the weighted contributions of all voxels along the line. Each technique has advantages and shortcomings that must be considered during selection of one for a specific clinical problem and during interpretation of the resulting images. With surface rendering, sharp-edged, clear three-dimensional reconstruction can be completed on modest computer systems; however, overlapping structures cannot be visualized and artifacts are a problem. MIP is computationally a fast technique, but it does not allow depiction of overlapping structures, and its images are three-dimensionally ambiguous unless depth cues are provided. Both surface rendering and MIP use less than 10% of the image data. In contrast, volume rendering uses nearly all of the data, allows demonstration of overlapping structures, and engenders few artifacts, but it requires substantially more computer power than the other techniques.

Spiral CT during arterial portography: technique and applications.

Spiral computed tomography during arterial portography (CTAP) combines rapid scanning with selective imaging during the portal phase of enhancement of the liver, resulting in an effective method for evaluation of liver neoplasms prior to partial hepatic resection. Compared with dynamic incremental CTAP, spiral CTAP results in improved quality of three-dimensional and multiplanar reconstructions, facilitating presurgical planning. Accurate volumetric analysis of the tumor can be performed, and subsegmental tumor localization is facilitated by the high levels of hepatic and portal venous enhancement. Additional advantages of spiral CTAP include small reconstruction intervals for improved lesion detection. However, the specificity of spiral CTAP is low because both benign and malignant tumors appear as hypoattenuating perfusion defects. In addition, both focal and geographic nontumorous perfusion defects may be seen more frequently with spiral CTAP than with dynamic CTAP. Knowledge of common diagnostic pitfalls is necessary for accurate interpretation of spiral CTAP images.