Low-dose unenhanced CT protocols according to individual body size for evaluating suspected renal colic: cumulative radiation exposures.

PURPOSE: The aim of this study was to assess the radiation dose of dose-reduced unenhanced abdominal multidetector computed tomography (MDCT) scan protocols for suspected renal colic in patients within normal weight range and overweight-obese patients and to record the cumulative dose of repeated examinations. MATERIALS AND METHODS: Over a 2-year period, we performed 1,026 unenhanced CT examinations for urolithiasis; among these, 675 were performed on 636 patients referred from the emergency department. Patients were divided into two groups on the basis of body mass index (BMI): normal weight (BMI <25 kg/m(2) group 1); overweight and obese (BMI >25 kg/m(2) group 2). For patients in group 1 and group 2, the protocols of our 64-row scanner prescribe tube current settings at 70 mAs and 150 mAs, respectively. The dose-length product (DLP) estimated by using the manufacturer's software was converted into effective dose (ED). RESULTS: Mean DLP and ED were 177 and 345 mGy/cm and 2.4 and 4.8 mSv for group 1 and group 2, respectively. A subset of 25 patients (3.7%) underwent two or more examinations, with estimated ED ranging from 4.8 to 19.2 mSv. CONCLUSIONS: Although radiation dose is nearly double in overweight-obese patients undergoing MDCT, it remains lower than that delivered by a standard-dose protocol. Patients with flank pain, who are often young, are at increased risk for serial CT examinations. Use of a low-dose protocol is mandatory in both normal-weight and obese patients to minimise radiation exposure.

Non-invasive measurement of water content in a lung phantom by neutrons.

A novel, non-invasive technique for measuring water content in lungs is described. This technique could find important medical applications such as real time monitoring of lung edema development in patients affected by cardiac insufficiency undergoing physical effort. The technique is based on the moderation (speed decrease) of fast neutrons crossing the lungs, due mostly to the water contained in lungs. In the application of this diagnostic method, the necessary dose given to the patient is lower than that associated with lung imaging techniques that do not use an image intensifier. The results so far obtained are encouraging, and the method appears to be an improvement over those so far reported in literature as it is able to detect a lung water increase equivalent to 25% of a full edema with a 20% standard error. Research is being performed in order to refine the technique, investigate geometry effects and make the method suitable to the medical field.

A method and apparatus for monitoring the level of tritiated water vapor in air using a solid scintillator.

Tritium is presently used in large quantities in laboratories for technological studies, as fuel for the process of nuclear fusion, and in the manufacture of radio-luminescent items. It is also produced in fission nuclear plants (with a yield of 10(-4) if the fuel is 235U and twice as much if the fuel is 239Pu), particularly in those which use D2O as moderator. The weak energy of beta particles (Emean=5.7 keV) produced by tritium implies that it is only harmful if internalized. In nature tritium in air is mainly present under two different chemical forms: elementary (HT, DT, T2) and oxidized (HTO, DTO, T2O). The latter is extremely more dangerous than the former as far as radioprotection is concerned; for this reason the derived air concentration limit (8 x 10(5) Bq m(-3)) for the gaseous form is 25,000 times higher than the value for the oxidized one. The purpose of the work presented here is to realize an area monitor that is able to discriminate in real time between the two chemical forms. Using the properties of zeolite as an absorber and scintillator, it was possible to construct such a detector. In 1 h the instrument can reveal HTO concentrations 40 times below the derived air concentration. A concentration equal to the derived air concentration can be revealed within the first minute of counting and the performance may be further improved. Moreover, the prototype realized is able to work automatically and continuously for 5 h. The capability of discriminating the oxidized chemical form, the sensitivity, and the possibility of obtaining real time information make this instrument a good monitor in those cases where there is a real risk of tritium air contamination.

A gas scintillation monitor for tritium gas in argon or in nitrogen.

For civilian purposes tritium is presently used in quantities of tens of PBq (MCi) in laboratories for the studies of tritium technology, at the Joint European Torus plant (Abingdon, Oxon, OX143A, UK) as fuel for the process of nuclear fusion, and in the manufacture of radio-luminescent items. Given the extreme mobility of tritium in most materials, it is necessary to use systems for double containment, such as glove boxes or spaces between primary and secondary containers, in which inert gas like argon or nitrogen flows. With these systems it is possible to recover tritium that escapes from the primary containment. Presently the gas flow is monitored continuously by means of ionization chambers which may present problems in particular applications ("memory effect" with high activity, strong dependence of the response on the presence of impurity, etc.). The aim of the work here presented is to determine the prospects for the realization of a new type of monitor mainly dedicated to the measurement of gas activity in isolation space of the containing systems of the high activity tritium plants. This monitor should have sufficient sensitivity, quick response, and should be easily decontaminated. As a detection technique we chose the scintillation produced in the inert gas by radioactive decay. With the first prototype, designed in cylindrical form, it was possible to observe gaseous scintillation events in mixture of tritium and argon or nitrogen. Following that, a spherical prototype was designed, of which we studied the performances and the dependence of the response varying the pressure, the concentration of tritium, the percentage of the impurity, and the gas flow rate. The results are satisfactory and suggest that the monitor could be used in glove boxes and double containment systems. The future research program will include tests involving large quantities of tritium and a study of the ideal dimensions and geometry of the detection chamber in order to optimize the detector response.

Scintigraphic recording of blood volume shifts.

UNLABELLED: A scintigraphic device consisting of small scintillation probes tightly fixed to the skin was developed to record intravascular blood volume shifts continuously and simultaneously at several sites. The aim of the present study was to ascertain the reliability of the measurements obtained, show the blood shifts induced by common daily activities in healthy subjects and clarify the mechanisms responsible for hemodynamic changes. METHODS: Measurements were made in three fields of the right lung, the liver, thighs and calves of 16 men during Valsalva maneuver, hyperventilation, various posture changes and treadmill walking. Some tests were repeated. RESULTS: The measured blood volume shifts were always in the expected direction and in accordance with those reported in the literature; they also were reproducible. Therefore, the measurements were reliable. A pattern of blood volume changes peculiar to some common daily activities was recorded in subjects moving freely. Insights were obtained on the mechanisms responsible for the blood volume shifts. CONCLUSION: Our noninvasive technique provides reliable continuous measurements of blood volume changes at several sites during common daily activities and could be applied not only in healthy subjects but also in patients.

Radiation transport in a radiotherapy room.

The photoneutron dose equivalent in a linac radiotherapy room and its entrance maze was investigated by means of Monte Carlo simulations under different conditions. Particularly, the effect of neutron absorbers and moderator layers placed on the maze walls was considered. The contribution of prompt gamma rays emitted in absorption reactions of thermal neutrons was also taken into account. The simulation results are compared with some experimental measurements in the therapy room and in the maze.

Gastric emptying of radionuclide-labeled solid meal in beagle dogs using a scintigraphic method.

A scintigraphic method for in vivo radiotracers measurement is described to investigate the gastrointestinal emptying rate in beagle dogs. The proposed method has been applied to study the effect of a pharmacological compound in enhancing stomach emptying and involves the following steps: 1) 131I-labeled anion exchange resin grains preparation, as solid food markers to be ingested by the dogs; 2) continuous recording of gastric emptying evolution over a period of 5 h with fast data-gathering instrumentation employing small size and light-weight CsI scintillation detectors coupled to a photodiode, equipped with a lead shield and collimator; 3) comparison of results obtained with drugs to previous standard emptying curves. The purpose of this study was to evaluate the prokinetic activity of a recent synthesized compound (BIMU 1).

Simultaneous recording of blood volume shifts in different vascular beds in man by a versatile scintigraphic method.

A device was developed to record the blood volume changes occurring in the lung and calf during postural changes, physical exercise, and the Valsalva maneuver in man. The changes in regional counting rates from the right middle lung and the calf mirrored the well-known changes in venous return that are expected to occur in response to the above-mentioned external stimuli. Thus a sustained decrease in lung blood volume was noted on assumption of the erect posture as well as during the forced expiration of the Valsalva maneuver. In addition a rapid increase and a sharp decrease in lung blood volume took place at the very onset and at the very end of walking, respectively. The calf blood volume declined immediately at the onset of walking, increased slightly in the ensuing two minutes, and returned to baseline quickly at the termination of walking. The authors' method enables real-time equilibrium blood pool scintigraphy to be recorded continuously and simultaneously from different districts over sustained periods of time irrespective of the posture and the physical activity performed by the patient. Their method might improve knowledge of the systemic circulatory responses to selective physiologic and therapeutic interventions in health and disease.

A new method for evaluating lung uptake of thallium-201 during stress myocardial scintigraphy.

A novel, multipurpose device has been designed that allows thallium activity to be continuously studied from a given lung area at rest and at peak exercise. The information gained from this technique proves to be relevant and reliable because lung thallium activity is displayed in real time and the interpretation of thallium distribution is not based on qualitative or quantitative comparison with that in the myocardium or mediastinum. The time-activity curves obtained in our study group are reported and the relation of peak activity to plateau activity (peak/plateau ratio) is proposed as an index that is easy to obtain for identifying patients with normal and impaired left ventricular function.

Total tritium measurement in atmosphere.

Measurement of tritium in the atmosphere is of strong interest wherever this radionuclide is used. Therefore, a method is proposed for the joint measurement of burnable tritium, independently from its physico-chemical form, and of tritiated water. The method consists of transforming the tritiated molecules of the gases present in the air volume into tritiated water by burning them together with a known quantity of hydrogen. The water vapor is condensed and added to a liquid scintillator. The scintillator is also able to dissolve conventional filters so that the tritium attached to particulate and concentrated on these filters can be jointly measured, as will be discussed in a future report. The overall detection limit of the method is approximately 64 Bq m-3 for a combustion period of 10 min (which corresponds to sampling an air volume of 15 L) and a counting period of 10 min. This limit, much lower than the derived air concentrations in the most unfavorable cases, allows the application of the method for safety purposes. Moreover, the method can be integrated into a general procedure for the measurement of tritium in different chemical forms, to be applied in case of necessity.