Thirty-one observers (five radiologists, five radiology residents, and 21 nonradiologists) examined low-contrast images of 13 polyvinylchloride cylinders. Image density ranged from 1.91 to 2.05 OD units with a background density of 2.09 OD units. The experiment tested visual performance under various clinically relevant lighting conditions by asking the observers to locate a groove in each cylinder. Use of low ambient light and restricting light from surrounding veiwboxes significantly improved performance (P less than 0.0001). In general, the less the amount of extraneous light, the higher was the detection rate. Some observers did significantly better than others. Reduced scattering of light within the eye is suggested as an explanation for their increased performance.

Humans↗

PubMedDate not supplied

Test cassette for measuring peak tube potential of diagnostic x-ray machines.

A test cassette employing a modification of the Ardran-Crooks attenuation technique for measuring peak tube potential (and half-value layer) is described. The technique employs a radiographic intensifying screen which is exposed to a hardened x-ray beam. Copper penetrameters are used to determine the attenuator thickness which reduces the light output from the screen to that transmitted by an optical attenuator over an adjacent area of the screen. The test cassette was calibrated by using x-ray machines whose high voltages were measured electrically. The test cassette has a measurement precision of +/- 1 kVp and an accuracy of +/- 3 kVp or better in the range 50-130 kVp for x-ray generators with the same voltage waveform.

Quality Control↗

PubMedDate not supplied

A scanning-slit x-ray videoabsorptiometric technique for bone mineral measurement.

An x-ray videoabsorptiometric technique was developed for measurement of bone mineral content (BMC) in vivo. The principle utility of this technique is the precise measurement of commonly fractured bones, such as the femoral neck, that are difficult to measure by other techniques because of repositioning problems. Scanning slits reduce scattered radiation and improve linearity of measurements. Heavily filtered, high-kVp beams are used to minimize errors from beam hardening, and data renormalization is employed to compensate for spatial nonuniformities of the beam and detector. Linearity of measured BMC over the range 0.8 to 5 g/cm2 is very good (r = 0.998) and compares well to single- and dual-photon absorptiometry. A 1.6% change in measured BMC is observed for a 10% change (approximately 2 cm) in tissue thickness while a 10% change in marrow type causes a 0.6%-0.8% change in BMC. Manual repositioning of a femur phantom revealed a variation of 0.84% over ten measurements when femur values were referenced to standards. A computer repositioning algorithm provides much easier identification of the region for analysis and yields comparable variation (0.9%).

Aged↗

PubMedDate not supplied

An inexpensive kVp penetrameter.

In this report we describe an improvement upon the design by Stanton and Lightfoot for a simple photographic null method to determine the kVp of a diagnostic region x-ray source. The new version has two primary advantages over the Ardran and Crooks design in that it is both simpler and less expensive to produce.

Costs and Cost Analysis↗

PubMedDate not supplied

Two thermal methods to measure the energy fluence of a brief exposure of diagnostic x rays.

This paper describes two simple thermal methods for measuring the energy fluence in J/cm2 from a diagnostic x-ray exposure. Both detectors absorb essentially 100% of the radiation and give a signal that is directly proportional to the energy fluence of the x-ray beam. One detector measures the thermal effect when a pulse of x rays is totally absorbed in the pyroelectric detector of lead-zirconium-titanate (PZT). The other detector measures the expansion of a gas surrounding a lead disk detector in a photoacoustic chamber. The increased pressure of the gas is transmitted through a 1-mm duct to a sensitive microphone. Both detectors have previously been used to measure the energy fluence rate of continuous x-ray beams in the same energy region using a chopped beam and a lock-in amplifier. Measurement of the energy fluence of a pulse of radiation eliminates the need for the beam chopper and lock-in amplifier and results in a simple, rugged, and inexpensive dosimeter. Either method can be combined with the area of the beam to give an estimate of the imparted energy to the patient from a diagnostic x-ray exposure.

Energy Transfer↗

PubMedDate not supplied

Absorption edge fluoroscopy using quasi-monoenergetic x-ray beams.

Explore the source record for details and available documents.

Filtration↗

PubMedDate not supplied

Effect of operator training on patient exposure: an analysis of the NEXT data.

The Nationwide Evaluation of X-ray Trends (NEXT) program has obtained data from various states on the physical factors related to patient radiation exposure from several common radiographs. Data from two years were examined for exposure, beam area/film area and exposure area product delivered to a "standard patient." The data were examined for differences as a function of operator training.

Humans↗