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Immediately following the discovery of x rays they were applied to medical diagnosis and therapy. These early medical applications were soon shown to be accompanied by rather severe biologic responses and injuries. This resulted in the development of standards. Radiation standards were developed to properly control the application of x rays in medicine by controlling equipment and how it was used. Control of personnel occurred later with first certification and then licensure.

One of the important characteristics of a computed tomography scanner is the image slice thickness. Most phantoms designed to measure this parameter do so with a ramp or tilted wire. Such a phantom must be precisely aligned to avoid possible significant inaccuracy. We present here a procedure for measuring the image slice thickness using a phantom containing two crossed ramps. The procedure produced consistent and accurate measurements of slice thickness without having to carry out a time consuming alignment procedure.

The precise slice geometry of a CT scanner is an important, albeit tedious to determine, characteristic. A series of computer programs have been developed to analyze the slice thickness insert of the AAPM phantom. Without operator assistance they generate the beam profiles and slice thicknesses at three points in the scan field. A representative analysis is done on an AS&E scanner with slice thickness settings of 2 to 10 mm. The resulting discrepent measured thicknesses, ranging from 3 to 8 mm, indicate the need to perform such slice thickness measurements as part of a regular quality assurance program.

Two of the AAPM CT performance phantom inserts require precise alignment. We present a method for aligning an insert which makes use of the partial volume effect. We demonstrate that the procedure is sensitive to tilts of less than one degree and, using the slice thickness insert, allows reproducible positioning.

Five months old male opossums were exposed to 5000 rd wholebody 60Co gamma-radiation. Testes tissues from animals sacrificed at 16, 40 and 90 hours post-irradiation and from nonirradiated animales were used for enzymatic and histological studies. Electrophoretic pattern of lactate dehydrogenase and glucose-6-phosphate dehydrogenase was slightly disturbed in early hours in irradiated animals, but it did not persist beyond 40 hours postirradiation. Histological study indicates 31% survival of type A spermatogonia suggesting high radioresistance of testes tissue in comparison to other animals.

The dose to active bone marrow resulting from anteroposterior (AP) and posteroanterior (PA) chest examinations was estimated using an Alderson Rando phantom and extruded lithium fluoride dosimeters. The AP projections resulted in a mean marrow dose range of 1.9-2.6 mrad (0.019-0.026 mGy) as compared to doses for PA projections of 3.4-3.8 mrad (0.034-0.038 mGy) for optimally diagnostic exposure taken at 70, 90, and 120 kVp.

The effect of orientation on extruded thermoluminescent dosimeters has been investigated. TLD's placed on the surface and within a phantom were exposed separately to five diagnostic beam qualities and to 60Co gamma rays. The resulting data were subjected to analysis of variance and examined for significant correlations. The response of dosimeters on the phantom surface varied with orientation and was energy dependent. In the phantom and with 60Co, no orientation effects were observed.

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.

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.

Extracorporeal shock wave lithotripsy (ESWL) has provided a nonsurgical approach to treatment of renal stones. The Dornier lithotripter uses dual image intensified x-ray systems to center the stone before treatment. Three imaging modes are offered: a fluoroscopic mode and two video spot filming modes. The average entrance exposure to the stone side of the typical patient at our facility is 2.6 X 10(-3) C kg-1 (10 R) [range: 0.5-7.7 X 10(-3) C kg-1 (2-30 R)] which is comparable and often much less than that reported for percutaneous lithotripsy. Recommendations are made for minimizing patient exposure. Scattered radiation levels in the lithotripter room are presented. We have determined that Pb protective apparel is not required during this procedure provided x-ray operation is temporarily halted should personnel be required to lean directly over the tub to attend to the patient. If the walls of the ESWL room are greater than 1.83 m (6 feet) from the tub, shielding in addition to conventional construction is not required.

Three groups of six male Balb/c mice, subjected to 30 MHz continuous wave NMR exposure in a static magnetic field of 7.05 K Gauss for one hour, were each compared to another group of ten unexposed mice with respect to chromatid and chromosomal aberrations. The exposed groups were sacrificed at two hours, 24 hours and 48 hours following NMR exposure respectively. Control mice were sacrificed 24 hours after sham-exposure. All groups had approximately 0.02 apparent aberrations per cell. These apparent aberrations were in the form of metacentric chromosomes, possibly resulting from a union of chromosomes at their centromeres or possibly simply chromosomes in association. The results are consistent with earlier in vitro findings that NMR exposure causes no adverse cytogenetic effects.

A method is presented whereby the modulation transfer function can be calculated directly from the edge response function without having to find the line spread function as an intermediate step.

Inbred strains of C57BL mice were exposed to either 100, 500, or 1000 rads of whole-body irradiation. Another group of mice were given injections of 3-methylcholanthrene only, and a control group had no treatment. Forty-eight hr after treatment, the animals were killed and hepatic aryl hydrocarbon hydroxylase (AHH) activity was measured by spectrophotofluorometer. A comparison of hepatic AHH activity in treated and nontreated groups of mice showed that each treated group had a significantly increased AHH induction compared with the control group. Although radiation appeared to have a dose-related effect on AHH induction, the increase with dose level was not statistically significant.

To determine the effect of MR imaging on the immune system, 21 male C57BL/6 X DBA/2 F1 mice were exposed to MR imaging at a field strength of 0.15 T for 2 hr. Another nine mice (controls) were sham exposed for the same amount of time. Mice were sacrificed and their spleens removed 24, 72, and 144 hr after the exposure (MR or sham). Spleen cell suspensions were passed over nylon wool columns and then used as effector cells in a short-term natural killer cell cytotoxicity assay with 51Cr-labeled YAC-1 cells as target cells. The results showed no evidence of decreased cytotoxicity due to exposure to MR. On the contrary, at all three times after exposure and for all target-to-effector cell ratios, mean cytotoxicity was greater for MR-exposed groups than for sham-exposed groups. The results show that MR exposure has no adverse effect on the immune system, as evidenced by natural killer cell activity.