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Patterns of specific absorption rates generated by interstitial, microwave antenna arrays must be experimentally ascertained and quantified to facilitate their clinical incorporation. Phantom studies involved the use of four single-gap, coaxial antennas oriented in a 2 cm square array. These dipoles were driven in phase by a microwave generator at a frequency of 915 MHz. The inherent limitations in modifying the specific absorption rate patterns were addressed with the addition of bolus to the phantom. These additions of Guy's muscle tissue-equivalent material were made either proximal or distal to the phantom proper. Experiments conducted in the presence and absence of tissue-equivalent material bolus showed the ability to achieve broader bands of 50% power deposition in certain bolus conditions. These heating patterns were sufficiently reproducible and predictable to warrant clinical application of the bolus addition. A through-and-through method of catheter implantation allowed for bolus addition when deemed necessary. Treatments with veterinary and human patients using the bolus method to modify heating patterns yielded augmented patterns of power deposition. The effective length of the antennas that would radiate efficiently was essentially broadened via introduction of a microwave-interacting medium. As a result of the tissue equivalent material's ability to absorb microwave power, it was necessary to interpose minimally-interactive styrofoam spacers to limit heat transfer effects at the tissue-bolus interfaces.

Medical licenses issued by the Nuclear Regulatory Commission contain the restriction that patients who are being treated with 131I should not be discharged from the hospital if the body burden is greater than 30 mCi (1,110 MB1). It is argued that there are no sound data supporting the theory that a patient receiving more than 30 mCi (1,110 MB1) of 131I is dangerous to others. This limitation may result in the use of lower, less effective doses of 131I, so that expensive, unnecessary hospitalization can be avoided. The need for adequate radiation safety programs that will advise patients and their families of the necessary precautions following therapy with 131I is discussed.

The spatial temporal distribution of radionuclides in children may differ greatly from that accepted for adults. Following injection of a bone-seeking agent (99mTc-EHDP), radioactivity in the metaphyseal growth complexes of the distal femur and proximal tibia was quantitated in a series of children 4 to 16 years of age, using a gamma camera/computer system. The dose to the growth plate was fount to range from 0.8 to 4.7 rads when adjusted to an administered activity of 200 muCi/kg, compared to approximately 0.6 rad to the adult skeleton for a corresponding study.

A new method for optimizing the design of multi-aperture parallel-hole collimators for the gamma scintillation camera is presented. The method takes into account the frequency spectrum of a plane source object distribution as well as the energy of the radiation. A frequency dependent statistical figure of merit is calculated and combined with a weighted object distribution frequency spectrum to obtain an objective function which, when maximized, yields the optimum collimator design according to the chosen criteria. The optimization is performed by means of a sequential pattern search technique. The results show a positive correlation between te objective function and an experimental performance index evaluated for existing collimators. The optimal designs obtained by maximizing the objective function, under the assumption of no scatter within the source, exhibit somewhat higher sensitivity and lower resolution than the commercial low energy collimators tested. It is concluded that much of the resolution capability of very high resolution collimators is unused because of the limitation imposed by the intrinsic resolution of the detector assembly.

Bone scintigraphy and radiography were performed in seven children with back pain. Six of the children with radiographic evidence of a pars interarticularis defect also had abnormal scintigrams. Increased uptake of the bone imaging agent occurred at six of the ten sites of radiographic pars interarticularis defects, implying increased bone metabolic activity. However, the location of scintigraphic abnormalities did not correspond to the location of radiographic abnormalities in several cases. Possible explanations for the discordant findings are: (a) normal bone metabolism at the site of an old spondylolysis and (b) radiographically inapparent stress fractures. Measurements of absorbed radiation dose indicate that plain radiography, including oblique views where appropriate, has a lower absorbed radiation dose than scintigraphy or tomography and should be performed prior to these studies.

This paper describes a geometrically small NMR imaging system which has been developed and assembled within a university medical center environment. Consideration is given to the technical specifications and basic economics for the magnet system, NMR spectrometer, and computer configuration. Initial research objectives for the system are outlined which include (1) the signal-to-noise improvement potential of rotational gradient imaging, and (2) 19F tracer imaging considerations with a detailed discussion concerning the feasibility of in vivo NMR imaging of 19F-fluorodeoxyglucose (2-FDG and 3-FDG). Finally, potentially significant areas for research within the constraints of a small NMR imaging system are described.

Because of increasing concern over continuing medical and potential nonmedical exposure of the thyroid to radiation, risk estimates have been developed for acute thyroiditis, hypothyroidism, and both benign and malignant thyroid nodules following exposure of the human thyroid to external and internal sources of ionizing radiation. These estimates are unique in that they are based entirely on data in human subjects are included corrections for the spontaneous occurrence of thyroid disease in human populations not subjected to radiation whenever possible.

Indium-labeled lymphocytes were examined for response to a variety of mitogens, ability to synthesize immunoglobulins, mitotic index, and presence of chromosome aberrations at a range of exposures from 0.2 to 500 muCi/10(8) cells. Results of all four tests were found to be abnormal when the lymphocytes were labeled with 111In activities well within those employed for diagnostic testing.

Optical diffraction is used to study the structure of the Fourier transform of a thin suspension of human albumin microspheres. The intensity profile in the transform plane is then used to derive information about the particle size distribution.

A quantitative technique is described which allows the physician to predict more accurately whether a recurrent or metastatic well-differentiated thyroid carcinoma is amenable to radioiodine-131 therapy or is better treated by other means. A calibrated uptake probe and scaler system is used to obtain conjugate view (i.e., diametrically opposed) counting rates for both the whole body and for any areas of abnormal uptake (lesion) at 24,48 annd 72 hours following the administration of 2 mCi 131l. Quantitative calculations accounting for patient attenuation, lesion size and geometrical factors then provide a determination of the lesion uptake as well as the effective half-life of 131l in the lesion. The radiation dose which would be delivered to the lesion by a given therapeutic amount of 131l may then be calculated to help determine the desirability of 131l treatment. The results of patient studies indicate the potential benefit of such quantitative evaluation.

During a period of a little over ninety years, the use of radioactive materials has moved from the discovery of natural radioactivity by Becquerel to the use of highly sophisticated equipment for in-house production of biologically important molecules labeled with radionuclides, for the measurement of body functions. Radiation detectors have progressed from photographic plates and the gold leaf electroscope to the routine use of improved scintillation detectors for imaging the three-dimensional distribution of radioactive materials in the body as a function of space and time. It is expected that future improvements will be along the line of instruments with better spatial resolution, contrast, and sensitivity. Advances in hardware and software will be more than matched by developments in radiopharmaceuticals, including the use of monoclonal antibodies and receptor mapping agents which promise the exquisite specificity and sensitivity of radioimmunoassay procedures.

Knowledge of the normal liver size is essential for making the scintigraphic estimate of hepatomegaly. A nomogram for sonographic liver size versus height of the patient was developed for the normal pediatric patient. Liver size was measured as the longitudinal liver length in the plane midway between the xiphoid and the right lateral liver margin. Scintigraphic and sonographic measurements showed a good correlation. The scintigraphic nomogram was developed using the experimentally determined relationship between the two modalities.

Extrafocal radiation was investigated using four different rotating-anode radiographic units currently employed in a pediatric hospital. It was found to exhibit significant penetration, with an effective energy only slightly lower than that of the primary radiation. The percentage of extrafocal relative to focal radiation in pediatric procedures involving rare-earth screens ranged from 2 to 15%. The ratio of extrafocal to focal radiation tended to increase with increasing kVp, mA, and field size but was independent of focal spot size. Since extrafocal radiation may extend significantly outside of the primary collimated field, radiosensitive organs such as the gonads, thyroid, and eyes which are assumed to be shielded may actually receive as much as 25 mR per radiograph.

A new low-dose chest radiographic system for use in the neonatal nursery was evaluated. This test system, composed of a Du Pont Kevlar fiber-front cassette, Quanta fast-detail screen, Cronex 4L film (wide latitude), and additional yttrium filtration (0.1 mm), reduced the radiation dose in neonatal chest radiography by 69% (0.9 vs 2.9 mrad [0.009 vs 0.029 mGy]) as compared with a conventional system without added yttrium filtration; the thyroid dose was reduced by 76% (0.9 vs 3.7 mrad [0.009 vs 0.037 mGy]). The cumulative dose reduction was achieved through a combination of factors, including (1) beam hardening by the added yttrium filter, (2) increased X-ray transmission through the Kevlar cassette, and (3) a fast film-screen combination. Scatter radiation at distances of 1 and 6 ft. (0.3 and 1.8 m) was negligible for both systems. Image sharpness was compared for the conventional system with and without added yttrium filtration and for the Kevlar system with yttrium. Although sharpness of bony detail was unchanged by adding yttrium filtration to the conventional system, a decrease in sharpness was noted with the Kevlar system. Because image sharpness was affected in the test system, we are not using the Kevlar-Cronex 4L system for mobile chest radiography in the neonatal intensive care unit, despite dose reductions. However, further study is recommended to determine if there is a slower film-screen combination with yttrium filtration that will not degrade image sharpness.

A method of determining intracranial blood vlot volumes from CT images data is presented. This technique avoids dependence on regular geometric volume approximations. Studies are presented on phantoms of known volume (ranging from 3.5 to 108 cm3) but with varying size, shape, and density relative to the surrounding medium. For a wide range of differential densities across the boundary, these phantom results indicate that volumes may be calculated to an accuracy generally better than +/- 2 cm3. A series of clinical cases, principally hypertensive intracranial hemorrhages, have been studied to demonstrate the technique. Three-dimensional axes, which allow clot localization relative to cerebral anatomy, are defined using the anterior/posterior falx attachment points and the dorsum sellae. Clot volume, center of mass, vector of clot expansion, and shift of anatomical structures are determined. Correlation of these data with clinical outcome and surgery is discussed.

The authors show that the intrinsic ultrasonic attenuation of a gallstone is an important factor in determining the degree of shadowing. B scans in vivo and in vitro demonstrated that stones with higher attenuation also show the most shadowing. In addition, attenuation can be correlated with physical structure: more highly attenuating stones tend to have the largest percentage of crystalline material, a larger average crystal size, and a more rigid structure. The authors recommend that higher-frequency transducers be used where possible if nonshadowing structures are seen in the gallbladder.

Cystourethrography was used by the referring physician in 53 children with urinary tract disease. The benefits of this technique were evaluated using Bayesian methods. Prior and subsequent odds of the accuracy of the clinical diagnosis being affected by the radiological procedure were estimated. Marked benefits were found in 12 cases, which were used as the basis for the most conservative estimate of benefits. The genetic benefit-risk ratio is 140 for boys and 8.3 for girls. The somatic benefit-risk ratio is 10,000 for boys and 4,200 for girls.

The radiation incident at Chernobyl, USSR, on April 26, 1986 was first detected in Sweden on April 29, when increased radioactivity was observed at a nuclear facility in that country. Subsequently, higher levels of radioactivity were observed in most of Eastern Europe and then in Western Europe. Increased radioactivity was eventually noted in the United States beginning about May 5. The three-day interval between the incident and its discovery outside the USSR caused great apprehension. This chain of events indicates the very important role for the nuclear medicine physician, the medical physicist and their colleagues. It is likely that this medical specialty area is staffed by personnel who are best qualified to interpret these findings and to determine the necessary course of action both for patients and the general public. The nuclear medicine specialist can provide valuable input in estimating the radiation dose impact resulting from such an incident. This estimate may be accomplished either by combining measured activity levels with the physiological and physical factors involved; or by actual in vivo counting and quantitation of radioactivity in individuals exposed to radionuclides. From the measured activities in air, water and food, and assumed intakes for various age groups, doses can be estimated both for inhalation and ingestion of radionuclides. In vivo measurements of radionuclides can be performed with conventional instrumentation used routinely in nuclear medicine laboratories.

Quantitative external counting methods for the in vivo determination of the activity uniformly distributed in an area of interest (lesion) have been developed. The theoretical work has been extended to include the effects of regions of differing attenuation coefficient and of non-target organ activity in the tissue surrounding the lesion. A clinical quantitative procedure utilizing a "calibrated" gamma camera and associated computer system is described. Studies including a bone substitute material in a water phantom confirmed the basic theoretical work.

Previous studies on pulse-height selection for scintillation cameras have been concerned with static imaging or asymmetric window settings around the photo peak. For count densities typical of those encountered in flow studies and for the customary symmetric window it is shown here, both computationally and experimentally, that a window setting in the range of 25-35% provides the maximum lesion detectability rate for lesions of 0.5- to 2.0-cm diameter.

An adjustable portal film cassette holder has been designed and constructed. The holder provides for: holding portal film perpendicular to and centered with the central axis of the beam film-to-patient distance to minimize magnification; angling (swivel) film to match collimator angle; and ease of correct repositioning of arrangement when frequent filming is required. This device has now been in use for several months with good results.

We used a combination of radioiodine scanning and quantitative radiation dosimetry to evaluate responses to therapeutic irradiation with 131I in 76 patients with thyroid adenocarcinoma. Fifty patients received 131I treatment for ablation of residual thyroid tissue after surgical thyroidectomy, and 26 had 131I treatment for metastatic thyroid cancer. Successful ablation was observed in patients receiving higher radiation doses to the thyroid--about 4.4 times those in patients whose lesions were not ablated--largely because of a longer effective half-life of 131I in residual thyroid tissue in the patients with ablated lesions. Patients with metastases that persisted after 131I therapy tended to have more advanced disease and received significantly lower radiation doses per millicurie of administered 131I than did persons whose lesions responded to treatment. Initial 131I treatment resulting in radiation doses of at least 30,000 rad to thyroid remnants and 8000 rad to metastases was associated with a significant increase in the rate of response to therapy.

The characteristics of various types of collimators have been studied systematically for the EMI Mark I brain scanner. The degree of collimation ranged from the 13-mm adjacent A and B slices to 3-mm separated slices. Multiple phantom studies (including variable density immiscible liquid interfaces) have been performed to evaluate the effect of collimation on (a) the line-spread function, (b) the change in effective absorption number, and (c) volume averaging. Effects associated with the technique settings involving the kVp, the mA, and the scan time were also investigated. The results of TLD dose measurements as a function of collimation are presented. The significance of collimation in specific clinical studies involving small, fairly well-circumscribed lesions is discussed.

Quantitative conjugate view external counting techniques were applied to determine radiation dose to the liver and spleen in pediatric patients undergoing 99mTc-sulfur colloid (Tc-SC) liver scans. The effective half-life of 99mTc-SC was 5.8 +/- 0.23 hours and 5.2 +/- 0.68 hours in the liver and spleen, respectively. Dose per administered activity ranged from 0.34 to 0.63 rad/mCi (92 to 170 muGy/MBq) for the liver and 0.35 to 1.96 rad/mCi (95.0 to 530.0 muGy/MBq) for the spleen. The spleen to liver dose ratio ranged from 1.0 to 4.9. These values are compared with results extrapolated from published adult data to the pediatric population.

The sensitivity to ionizing radiation of three human bladder transitional cell carcinomas grown in the nude mouse was investigated at four different radiation levels, 500, 1,000, 2,000 and 4,000 rad. Each tumor line exhibited a response pattern which reflected to a certain degree tumor differentiation and growth rate in the nude mouse. Exposure to 1,000 rad was the minimum amount of radiation required to produce a distinct, although transient, tumor response in all three tumor lines characterized by a growth delay of 3-4 weeks, whereas maximum tumor response was observed at the 4,000 rad radiation level. These studies would permit a better understanding of the behavior of human bladder cancer to ionizing radiation and may further facilitate efforts at identifying effective radiosensitizing agents that may result in maximizing tumor response.

We evaluated 1,266 persons who had received external radiotherapy for benign diseases in childhood. The evaluation used detailed questionnaires completed by trained interviewers and neoplastic disease registry data. The control population included 958 age-, sex-, race-, and disease-matched persons who had not received radiotherapy and 9,865 family members of the two study groups. An excess number of clinically important thyroid neoplasms, both benign and malignant, was noted in the irradiated group.

Many technical and logistical questions must be addressed when planning the installation of an NMR imaging system. These considerations become particularly significant when the facility is being established within an existing medical center complex. This paper presents a report on the practical aspects and experience obtained in siting a 6-coil 0.15 T resistive magnet system. The topics discussed include: floor loading; ferromagnetic environment; the effect of iron on the magnet field strength and homogeneity characteristics; shimming procedures; temperature stability requirements; rf shielding; and effects of the magnetic field on common medical instrumentation and magnetic media. It was found that the field shift as a function of the distance of a steel mass from the center of the magnet exhibited an (1/r)5.2 +/- 0.5 to (1/r) 4.2 +/- 0.3 dependence for axial and radial positions respectively which, as expected, is somewhat weaker than the (1/r)6 dependence expected by point dipole approximations. Field distortions caused by the presence of ferromagnetic material in radial positions may be essentially fully compensated with first order transverse shim coils (most conveniently, the x and y imaging gradient coils could be used). Axially distributed material requires, in addition to first order z-gradient correction, higher order axial shim compensation. The temperature stability of the magnet system over the scan period must be better than 0.2 degrees C to insure that temperature-induced field fluctuations are less than the intrinsic static inhomogeneity: and, ideally, below 0.01 degrees C to reduce these fluctuations to less than those caused by power supply instability.

A study was performed to determine the accuracy of 99Mo measurements using three commercial dose calibrators with their 99Mo assay shields. One 99Mo assay shield allowed excessive penetration by the lower energy 99mtc photons, resulting in the calibrator's falsely high interpretation of the activity of 99Mo present in the high-activity 99mTc eluates. All three calibrators performed adequately with a National Bureau of Standards 99Mo standard in equilibrum with 99mTc. By using low-activity aliquots of 99Mo and 99mTc, a low-level linearity test was performed. Two of the calibrators were found to have a threshold of approximately 10 microCi (370 kBq) for a nonzero 99Mo response, although one of these occasionally produced variable nonzero responses below its threshold. Only one of the calibrators was found to reflect accurately the activity of 99Mo present under all conditions tested.

The effectiveness of three methods of assessing the patient body burden following 131I therapy was compared: (a) urine assay, (b) external exposure rate measurements, and (c) predictions based on a pretherapy diagnostic work-up. The urine assay method exhibited the greatest potential for error and personnel risk. The diagnostic work-up provided predictions of the body burden as a function of time, which may be applied to estimate the expected hospital stay. The direct external exposure rate survey showed the potential for being an accurate, reliable, and relatively safe method of monitoring the patient body burden.

The effect of cis-diamminedichloroplatinum II (DDP) and ionizing radiation on human bladder transitional cell carcinoma (TCC) was evaluated in nude mouse-grown human tumors following administration of single-agent and combination treatment. Combination of DDP and radiation resulted in accelerated tumor regression and substantially delayed tumor regrowth. The potentiating effect of DDP on ionizing radiation was related to timing and sequence of treatments and was independent of tumor sensitivity to DDP. Best results, as judged by tumor growth curve characteristics, histopathologic changes, and absence of tumor metastases, were obtained when DDP was administered at an early stage following radiation treatment.

A method of experimentally obtaining both neutron and gamma-ray spectra in a scattering medium is described. The method utilizes a liquid-organic scintillator (NE-213) coupled with a pulse-shape discrimination circuit. This allows the separation of the neutron-induced pulse-height data from the gamma-ray pulse-height data. Using mathematical unfolding techniques, the two sets of pulse-height data were transformed to obtain the neutron and gamma-ray energy spectra. A small spherical detector was designed and constructed to reduce the errors incurred by attempting spectral measurements in a scattering medium. Demonstration of the utility of the system to obtain the neutron and gamma-ray spectra in a scattering medium was performed by characterizing the neutron and gamma-ray spectra at various sites about a 3.7-microgram (1.5 cm active length) californium-252 source in a tissue-equivalent medium.

Objective criteria for judging the uniformity of field floods are developed and the effects of the energy window and scatter material on uniformity are examined. There is a highly significant correlation (p = 0.99) between a 14% difference in average count among adjacent photomultiplier tube regions and observer detection of detuned areas. Similarly, a 10% average count difference is not significantly recognized as a nonuniform area. Results indicate that there is a complex interaction between uniformity, energy window (15-30% symmetrical) and 0-7.6 cm of tissue-equivalent scatter medium interposed between the flood source and the collimator. Quantitation of the flood should be performed to indicate which regions need retuning.

The use of hyperthermia in combination with radiotherapy is currently being investigated at many cancer treatment facilities. Several different types of heating modalities are presently being used and for each of these systems it is important to determine the power distributions of their hyperthermia applicators in tissue-equivalent phantoms. This information will be used for treatment planning, routine quality assurance, and acceptance testing as well as for comparison between these various modalities and systems. This report describes the power distribution characteristics of the Clini-Therm 10 x 10 cm 915-MHz waveguide applicator measured within muscle tissue phantom materials arranged in several clinically relevant treatment configurations. The net increase in temperature that resulted from 20-s pulses of microwave power was measured at various points within each phantom by the system's implantable fiberoptic temperature sensors. From these temperature measurements the distribution of power was calculated as specific absorption rates (SAR). The results are displayed as two-dimensional ISO-SAR maps which relate power levels throughout the irradiated volume to those obtained on the central axis of the applicator. When the applicator was in direct contact with the muscle phantom the highest SAR measured was 2 cm lateral to its central axis along the muscle surface. On the central axis approximately 50% of the power was attenuated by each centimeter of muscle material. The introduction of either fat, bone, or a water-filled pad between the applicator and the muscle altered the pattern of power distribution within the irradiated volume without substantially altering the relative distribution of power along the central axis.(ABSTRACT TRUNCATED AT 250 WORDS)

The surface topography of a patient can be determined by photogrammetry before beginning radiotherapy. The source light of the therapy unit or simulator is used to project a grid pattern onto the patient, and this is then photographed together with control points consisting of miniature light bulbs mounted on a frame suspended from the wedge slot of the therapy machine. When the photograph is projected onto a graphics terminal for data entry into a computer, the three-dimensional topography of the patient's surface can be reconstructed as a two-dimensional matrix of discrete points. A computer algorithm can then design a tissue compensator to fit the individual patient.

It is customary to use the LD50 response as a criterion for the evaluation of chemical radioprotection. The increased urinary excretion of deoxycytidine (CdR) in irradiated rats has been shown to be a linear dose--response relationship up to 200 R, thus making it possible to consider such a response as a criterion for chemical radioprotection evaluation at sub-lethal irradiation levels. Rats were subjected to 200 R X-irradiation with various chemical protectors and without chemical protectors, urine was collected 24 hours after irradiation, and the CdR levels in the urine analysed. A dose-reduction factor (DRF) was determined for 24-hour urinary excretions of CdR for chemically protected and non-protected rats. The DRF values are within 6 per cent of those reported by other investigators using LD50 as the response criterion for serotonin, cysteine, MEA and PAPP but differ for WR-2721 and WR-2823. Agreement using WR-2721 and WR-2823 compounds is only obtained when the toxicity effect of the compound is taken into consideration.

The results of neutron-transport flux-density and dose rate calculations for implantable Californium-252 point and line sources in essentially infinite tissue-equivalent material are presented. The point-source flux densities were obtained from a discrete ordinates calculation, and the point dose rates were established by multiplying the flux densities by their appropriate kerma factors. Line-source dose rates were evaluated by integrating the point dose rates over the length of the line source. Dose-rate data are given within a 20 X 20-cm region from the source center for source lengths of 1.5, 2, and 3 cm. The dose rates established by these calculations showed good agreement with an independent Monte Carlo calculation. Detailed point-source flux-density data as a function of energy and position are also given.