Artefacts found in computed radiography.

Artefacts on radiographic images are distracting and may compromise accurate diagnosis. Although most artefacts that occur in conventional radiography have become familiar, computed radiography (CR) systems produce artefacts that differ from those found in conventional radiography. We have encountered a variety of artefacts in CR images that were produced from four different models plate reader. These artefacts have been identified and traced to the imaging plate, plate reader, image processing software or laser printer or to operator error. Understanding the potential sources of CR artefacts will aid in identifying and resolving problems quickly and help prevent future occurrences.

An auxiliary CT tabletop for radiography at the time of CT.

An auxiliary CT tabletop was designed and manufactured such that radiographic images might be acquired, with use of a ceiling-mounted X-ray tube, without removing the patient from the CT table. The tabletop required no modifications to the original CT table housing and did not produce artifacts in the CT images. Radiographs obtained with the overhead X-ray tube and auxiliary tabletop demonstrated image quality equivalent to traditional radiographs.

Motion artifacts in subsecond conventional CT and electron-beam CT: pictorial demonstration of temporal resolution.

To visually demonstrate the effective temporal resolution of subsecond conventional (slip-ring) and electron-beam computed tomographic (CT) systems, two phantoms containing high-contrast test objects were scanned with a slip-ring CT system (effective exposure time, 0.5 second) and an electron-beam CT system (exposure time, 0.1 second). Images were acquired of each phantom at rest, during translation along the x axis at speeds of 10-100 mm/sec, and during rotation about isocenter at speeds of 0.1 and 0.5 revolution per second. Motion artifacts and loss of spatial resolution were judged to be absent, noticeable, or severe. For 0.5-second conventional CT images, motion artifacts and loss of spatial resolution were noticeable at 10 mm/sec and 0.1 revolution per second and were severe at speeds greater than or equal to 20 mm/sec and at 0.5 revolution per second. For 0.1-second electron-beam CT scans, noticeable, but not severe, motion artifacts and loss of spatial resolution occurred at speeds between 40 and 100 mm/sec and at 0.5 revolution per second. Over the range of physiologic speeds examined, the images provide visually compelling evidence of the effect of improving temporal resolution in CT.

The radiodensity of medications seen on x-ray films.

OBJECTIVE: To analyze the radiodensity of commonly used medications and determine their ability to be seen on plan x-ray films. MATERIAL AND METHODS: Under conditions intended to simulate a patient undergoing radiography of the abdomen (including the use of a patient-equivalent phantom), 50 prescription and nonprescription drugs were tested. Their radiodensities were quantified, and their visibility on plain x-ray films was noted. The study drugs were then ranked in order of decreasing radiodensity. In addition, we report an illustrative case of ingested pills in the stomach that mimicked gallstones, a phenomenon we termed "pseudogallstones". RESULTS: In a 71-year-old woman with upper abdominal pain and nausea, a presumptive diagnosis of gallstones based on x-ray findings was subsequently found to be retained iron tablets. This case prompted our assessment of the radiodensity of medications frequently prescribed for elderly patients. Although all 50 medications studied were visible on plain x-ray films, a 13-fold difference was found in their relative radiodensities. Of the medications studied, potassium chloride was the most radiodense, and prednisone was the least radiodense. As a group, minerals were the most radiodense of all medications studied. CONCLUSION: Numerous commonly prescribed medications in their undissolved, undigested state are visible on plain x-ray films, as are mineral supplements, which have high radiodensities. At times, the appearance of these medications and supplements may be confused with organic pathologic conditions.

Spatial and temporal response characteristics of ionization chambers used in diagnostic radiology for exposure measurements and quality control.

The temporal and spatial (partial volume) response characteristics of ionization chambers used for measuring radiation exposures in x-ray quality control (QC) programs were evaluated. Five ionization chambers were evaluated using a pencil beam scanning x-ray source and a conventional radiographic system. The spatial response was determined by recording the exposure during scanning of the pencil beam or in increments using a slitted lead sheet on a conventional x-ray system. The temporal response was determined by recording x-ray wave forms using the different ionization chambers. The effects of partial volume irradiation of the chambers makes them unsuitable for use under these conditions, except those designed for exposure measurements in computed tomography. The temporal response of many chambers resembles that of a typical resistive-capacitive circuit, making them unsuitable for exposure time measurements or x-ray wave form evaluation. The appropriate ionization chamber must be selected for exposure measurements and quality control in diagnostic radiology.

Evaluation of mammographic viewbox luminance, illuminance, and color.

Twenty-three viewboxes were evaluated in six mammography facilities. Luminance and illuminance measurements were made with a recently calibrated photometer. Color temperatures were measured with a Minolta color meter. The average luminance for the 23 viewboxes was 2920 nit (lumen/Sr/m2), the lowest value was 1610 nit, and the highest value was 3630 nit. The average illuminance was 40 lux (lumen/m2), with 6 lux as the lowest value, and 97 lux as the highest. The average color temperature was 8400 K with the lowest value of 4900 K, and the highest of 10,900 K.