Biomedical subjects

P S Calhoun

Publications and source records attributed to P S Calhoun.

7 recordsLinked to original sources

PubMed1995

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.

Adult↗

PubMed1995

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.

Algorithms↗

PubMed1995

CT of the esophagus: spectrum of disease with emphasis on esophageal carcinoma.

The esophagus is involved by a wide range of pathologic processes that can be detected, defined, and staged with computed tomography (CT). These processes include esophageal carcinoma; benign esophageal tumors; inflammatory and infectious diseases; miscellaneous conditions such as Barrett esophagus, achalasia, and varices; and trauma and perforation. CT is usually performed to clarify findings seen with other imaging modalities or to stage a pathologic condition; however, it may be the primary imaging modality in some cases. Because of the critical location of the esophagus, it can be involved secondarily by other disease processes or as part of a systemic process. By being aware of the appearances of the various entities that affect the esophagus, the radiologist can play an important role in detecting and staging esophageal disease. Although the role of CT in the evaluation of esophageal disease has been controversial, recent developments such as spiral CT have the potential to renew interest in this application.

Adult↗

PubMed1995

Imaging of intrahepatic cholangiocarcinoma: 1. Peripheral cholangiocarcinoma.

Cholangiocarcinoma is the second most common primary hepatic malignant tumor after hepatocellular carcinoma, accounting for 5-30% of all primary hepatic malignant tumors [1]. Intrahepatic cholangiocarcinomas can be classified as peripheral cholangiocarcinoma, which originates from an interlobular biliary duct, or as hilar cholangiocarcinoma, which originates from a main hepatic duct or from the bifurcation of the common hepatic duct. Intrahepatic cholangiocarcinomas account for only about half of cholangiocarcinomas, and this pictorial essay focuses only on the peripheral form of the disease. Clinically, therapeutically, and radiologically, these two types of cholangiocarcinomas differ. Features suggestive of the diagnosis of peripheral cholangiocarcinoma can be shown by sonography, CT, and MR imaging. Cholangiography and angiography have a limited role in evaluating this neoplasm that manifests as a focal mass. This essay reviews the appearances of peripheral cholangiocarcinoma and discusses the various imaging techniques that can be used to evaluate this unusual tumor that is often resectable and potentially curable.

Adult↗

PubMed1995

Imaging of intrahepatic cholangiocarcinoma: 2. Hilar cholangiocarcinoma.

Hilar cholangiocarcinoma (also called Klatskin's tumor) is more common than peripheral cholangiocarcinoma. Sonography, CT, MR imaging, angiography, and cholangiography can suggest the diagnosis, but the major issue of imaging with this tumor is to determine whether the tumor is resectable. The anatomic location of hilar cholangiocarcinoma makes resection difficult, so that surgical exploration of patients with this condition should be undertaken only when preoperative evaluation has shown a potential for curative resection. Preoperative assessment of resectability of hilar cholangiocarcinoma is often extensive, requiring several types of imaging. This pictorial essay reviews the imaging features of hilar cholangiocarcinoma. The role of imaging in the preoperative planning, with specific emphasis on staging extent of disease, including hepatic and vascular involvement, is discussed and illustrated.

Adult↗

PubMed1994

Interactive multimedia program for imaging the spleen: concept, design, and development.

The authors present some of the decision making and design goals that guided the development of computer-based educational programs, specifically a module to teach the role of computed tomography in detection and evaluation of splenic disease. One goal was that the program would take advantage of the computer yet allow users to recognize or learn quickly the techniques used to navigate through the program. A game interface was chosen as a means to aid retention of the material being taught, as well as to make use of the module enjoyable. The structure used to present the program content was based on the common means by which radiology has traditionally been taught. The four sections of the module consist of the slide lecture, traditional text, a quiz, and teaching files. Each question in the quiz section is linked to the relevant text section for review, and the teaching file section can be used as a self-test by hiding the text and diagnosis fields. Computer-based educational programs are an important resource for residents and practicing professionals, and they will continue to evolve with developments in technology. However, it should be the goal of all new projects to find a balance of form, in which the value of traditional teaching methods can be preserved with the maximum opportunity for innovation.

CD-ROM↗

PubMedDate not supplied

The GI Project: a prototype electronic textbook for high school biology.

A prototype electronic science textbook for secondary education was developed to help bridge the gap between state-of-the-art medical technology and the basic science classroom. The prototype combines the latest in radiologic imaging techniques with a user-friendly multimedia computer program to teach the anatomy, physiology, and diseases of the gastrointestinal (GI) tract. The program includes original text, illustrations, photographs, animations, images from upper GI studies, plain radiographs, computed tomographic images, and three-dimensional reconstructions. These features are intended to create a stimulus-rich environment in which the high school science student can enjoy a variety of interactive experiences that will facilitate the learning process. The computer-based book is a new educational tool that promises to play a prominent role in the coming years. Current research suggests that computer-based books are valuable as an alternative educational medium. Although it is not yet clear what form textbooks will take in the future, computer-based books are already proving valuable as an alternative educational medium. For beginning students, they reinforce the material found in traditional textbooks and class presentations; for advanced students, they provide motivation to learn outside the traditional classroom.

Biology↗