CT alignment probe for the dose profile insert.

One of the most accepted methods of characterizing the dose in computed tomography (CT) is by measuring the dose profile. Thermoluminescent dosimeters (TLD's) arranged in a stack are scanned in a plexiglass phantom. Unfortunately with this system there is no assurance that the scan properly intercepts the stack. Mispositioning will not be apparent until the TLD's are read, entailing at least a 24 h delay before rescanning. We have designed a simple alignment probe that insures that the scan will be centered on the stack to within 1 mm.

Radiographic workload and use factors for orthopedic facilities.

Observations of technique factors at 9 radiographic installations dedicated to orthopedic radiography have been made. Monthly area radiation measurements with thermoluminescent dosimeters were made at three of these facilities. The results of these observations and measurements suggest that current NCRP recommended assumptions utilized in protective barrier computations result in considerably more shielding than is necessary. We observed an average workload of 224 mA min/wk and a maximum weekly average of 670 mA min/wk. The use factor for the chest wall averaged 5%. That for all other vertical barriers was less than 1%. The average operating potential was 75 kVp. Room radiation measurements confirm the suggestion that at least two of the walls and the control booth barrier in an orthopedic radiographic facility may be considered secondary barriers.

Radiation dose in neurological computed tomographic scanning.

Patient dose and dose distribution during neurological computed tomography examinations were determined with five different computed tomography scanners. Maximum intracranial doses ranged from 1.17 to 2.67 rads. Doses to the lens of the eye ranged from 0.23 to 2.81 rads. These levels are considered and compared with patient doses reported for other computed tomography studies and for conventional tomographic examinations. In general, patient dose during computer tomographic examinations is less than one quarter of that during conventional tomography of the head.

Attenuation properties of lead composite aprons.

Traditionally, the absorption properties of protective aprons used in diagnostic radiology have been specified in units of lead equivalent thickness. This is appropriate and accurate when lead is the only high-atomic-numbered component in the apron. In an attempt to manufacture light-weight protective apparel, however, some manufacturers have included other elements with k absorption edges in the energy range of interest, to provide equivalent absorption properties with less weight. With these other high-atomic-numbered elements added, the lead equivalence of the apparel becomes a function of the photon energy. This must be recognized and specified by the supplier, because lead apparel is used in environments other than diagnostic radiology, where the shielding benefits may be substantially less than expected when specifications are based on the diagnostic x-ray energy range.

The AAPM/RSNA physics tutorial for residents. Typical patient radiation doses in diagnostic radiology.

Factors affecting patient dose in all x-ray imaging modalities include beam energy, filtration, collimation, patient size, and image processing. In conventional radiography, the most important determinant of acceptable patient dose is use of the highest peak kilovoltage that results in diagnostic images. Digital radiography allows a much wider range of exposures than conventional radiography for producing diagnostic images. However, operators must be aware of the subtle differences in techniques used with digital systems to avoid unnecessary increases in patient dose. Low-dose mammography requires lower ranges of peak kilovoltage; different target materials, filters, and screen-film combinations; special attention to breast thickness, composition, and compression during the study; and different standards for grids, magnification, and optical density. Although peak kilovoltage and tube current are important for controlling patient dose in fluoroscopy, collimation, source-to-skin and patient-to-image intensifier distances, and control of beam-on time have perhaps greater importance. Computed tomography (CT) involves greater patient dose than conventional radiography, and, although the primary radiation dose is delivered to smaller volumes, dose calculations must account for dose received by adjacent tissue sections. Many variables are involved in fetal exposure and fetal dose effects, but a solid understanding of them can help in developing responsible patient management practices.

Patient radiation dose in conventional and xerographic cephalography.

A comparison of the radiation doses for xeroradiographic and conventional film screen cephalography was made. Alderson tissue-equivalent phantoms were used for patient stimulation. An optimum technique in terms of patient dose and imaqe quality was established for the xeroradhe data indicated that the dose for the Xerox process ranged from five to eleven times greater than that for the conventional process for entrance and exit exposures, respectively. The most commonly reported dose, the entrance dose, was found to be 206 mrad, which is five Imes that for the conventional cephalogram. This dose, however, falls within an acceptable range for other dental and medical radiation doses. It is recommended that conventional cephalography be used for routine purposes and that xeroradiography be reserved for situations requiring the increased image quality that the process affords.