Radiation doses and detriment from chest x-ray examinations.

Radiation dose distributions for chest x-ray examinations have been measured in a Rando phantom for three views (AP, PA and lateral) as a function of kVp. On the basis of these data, the relationship between the surface dose, energy imparted and the effective dose equivalent have been determined. The mean energy imparted in a typical chest examination (PA + lateral views at 100 kVp) is 1.7 mJ and the corresponding value of the effective dose equivalent, HE, is 42 muSv. The measured radiation doses associated with chest x-rays were compared with the predictions of Monte Carlo calculations. The average difference between Monte Carlo and measured data for the HE was only about 16%. Demographic features (age/sex) of patients undergoing chest x-rays were investigated, and a population irradiation factor (PIF) introduced to estimate the radiation detriment to this population. The probability of expressed radiation-induced detriment to the patient population from chest x-ray examinations was computed to be about one half of that expected for a normal adult (working) population receiving the same dose. The radiation risk associated with chest x-ray examinations for this population was estimated to be less than 0.3 fatal cancers plus serious genetic disorders in the first two generations per million patient examinations.

Some factors affecting the calibration of radionuclide calibrators--I. 99mTc.

In the Winnipeg area a centralized radiopharmacy serves several Nuclear Medicine departments supplying all their 99mTc radiopharmaceuticals on a daily basis. It was observed that there was very poor consistency between the assays as determined by the Radiopharmacy and those determined in the various Nuclear Medicine departments. An attempt to "correct" the various calibrators using a 57Co "mock" 99mTc source resulted in an aggravation of the problem, and an investigation of relative responses of various calibrators to the "mock" relative to a 99mTc source was undertaken, together with an investigation of the influences of various environmental conditions on the calibrator function. In many Nuclear Medicine departments technologists sensitive to concerns of radiation exposure have stacked lead shielding around the calibrator as added protection. However if the calibrator is not calibrated with sufficient lead shielding, such additional shielding will increase the ionization within the chamber, resulting in an elevated assay being obtained due to the lead X-rays and back-scattered radiation. In the absence of lead shielding, similar effects, although smaller in magnitude, are observed from other environmental factors such as the proximity of a wall or a person. Thus in selecting a calibrator, one which comes from the manufacturer, with a calibration certified by the manufacturer, incorporating an adequate amount of lead shielding to prevent additional back-scatter re-entering the ionization chamber should be considered essential unless a complete on-site recalibration using accurately calibrated samples of the radionuclides in question is planned.

Xenon-133 ventilation and perfusion studies in bronchiectasis.

Thirty-nine Xenon-133 ventilation and perfusion studies in 36 patients with bronchiectasis were analyzed retrospectively. These patients showed a marked reduction in ventilation with a less severe reduction in pulmonary arterial perfusion, resulting in areas of low ventilation-perfusion ratios. In those patients with bronchographic confirmation, xenon studies had greater sensitivity (0.89) than the chest radiographs (0.71). Where both the radiograph and the scan are normal, bronchiectasis is virtually excluded; therefore bronchography is not indicated.

Quantitation of fat in liver by xenon uptake.

Xenon uptake in fatty livers of seven patients has been quantitatively measured, and correlated with the amount of fat in the hepatic cells. Quantitation of the Xenon uptake correctly predicted the amount of fat seen histologically in six of the seven patients studied. In the seventh patient, analysis of the wash-in and wash-out curves showed that equilibrium conditions had not been reached. It is concluded that the establishment of equilibrium conditions is a prerequisite to the use of this test in a quantitative fashion.

Telephone line transmission of rectilinear radionuclide scans. Report of a pilot project.

The General Electric-Elscint system for telephone line transmission of rectillinear scans has been tested and with certain limitations found to be acceptable in terms of diagnostic accuracy for many scan procedures. The system tested had some logistic disadvantage requiring batch processing of the scans, and making quality control of the scans difficult with the one video data processor available at the reference centre.