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Biomedical subjects

W Huda

Publications and source records attributed to W Huda.

At least 55 records · Page 3Linked to original sources
PubMed1995

CT doses in cylindrical phantoms.

A single CT scan of thickness T in a cylindrical phantom produces a three-dimensional dose distribution, which depends primarily on the photon energy spectrum, the x-ray beam shaping filter and the size and composition of the irradiated phantom. Monte Carlo simulations employing monoenergetic photons were employed to investigate the effect of each of these factors on phantom dose distributions. The fractional energies scattered, imparted and transmitted through the CT phantom were calculated. A dose index (D(r)), which is a function of phantom radius r, was computed. Phantom materials investigated included lung, fat, water, soft tissue, acrylic and bone with calculations performed for head (160 mm diameter) and body (320 mm diameter) phantoms. All dose and energy imparted data generated for CT phantoms were normalized using an 'in air' dose (Dair), which is defined as the axial dose (in acrylic) at the isocentre in the absence of any phantom. Results obtained show how CT parameters impact on doses in cylindrical phantoms. These dosimetry data are likely to be useful to estimate energy imparted to phantoms (and patients) undergoing CT examinations.

Biophysical Phenomena↗
PubMed1995

Energy imparted in computed tomography.

Monte Carlo techniques were used to study a generalized CT dose index D(r) as a function of the radius r of a cylindrical dosimetry phantom. The relationship between D(r) and the energy deposited in the phantom was investigated. For a specific x-ray spectrum, the energy imparted to head or body dosimetry phantoms can be obtained from measured D(r) values. This approach to CT dosimetry permits the energy imparted to phantoms (or patients) to be determined as CT technique parameters, or type of scanner, are changed.

Energy Transfer↗
PubMed1994

Radiation-induced temporary epilation after a neuroradiologically guided embolization procedure.

A 34-year-old woman underwent embolization of a left paraorbital arteriovenous malformation guided with a bi-plane x-ray system in two sessions separated by 3 days. Imaging included 110 minutes of fluoroscopy and 46 digital subtraction angiography acquisitions. Entrance skin dose rates were determined with measurements performed on a skull phantom. The maximum possible skin dose was estimated to be 6.6 Gy, which is consistent with the temporary epilation in the right occipital region of the skull reported by the patient approximately 5 weeks later.

Adult↗
PubMed1993

Film density calibration for computed radiography systems: is the standard three-point procedure accurate?

With computed radiography (CR) systems, laser printer-film processor combinations are normally checked daily by using test film three-point density measurements. In this study, the authors show that the recommended three-point quality assurance procedure can show satisfactory results even though the CR film output behaves in an anomalous manner. This problem can be corrected by using a 16-point calibration procedure. Regular 16-point calibrations should be performed to ensure satisfactory CR system performance.

Calibration↗
PubMed1992

A numerical method for electron transport calculations.

A numerical algorithm for calculating the penetration of electrons in dense media is presented. The numerical algorithm is intended for future application to radiotherapy dose calculations. The method is generic in the sense that it may be used with different theoretical models describing the angular scattering of electrons with depth. It is also general enough that it may be applied to electron dose calculations in heterogeneous as well as homogeneous media. The assumptions used in the algorithm are examined and equations describing the evolution of the distribution of electrons with depth are presented. Calculations have been performed for 10 MeV broad beams and pencil beams incident on water. It is shown that the Fermi-Eyges analytical solutions are recovered if the angular scattering process is assumed to be a Gaussian Markov process and the cumulative angle of electron travel remains small. In the case where the small angle approximation is not imposed, the numerical method qualitatively reproduces, at large depths, the wide angle scattering 'tails' seen in Monte Carlo generated profiles.

Algorithms↗
PubMed1991

Impact of gamma camera parameters on imaging performance, evaluated by receiver operating characteristic (ROC) analysis.

The relationship between gamma camera variables (total counts in image, collimator type, etc) and diagnostic imaging performance was quantitatively investigated using receiver operating characteristic (ROC) curve analysis. A College of American Pathologists (CAP) liver phantom was used with a 99Tcm flood source to generate anterior and lateral liver images containing 'cold lesions'. These images were interpreted by four nuclear medicine physicians, and the areas under the corresponding ROC curves computed. These medicine physicians, and the areas under the corresponding ROC curves computed. These areas were taken as a quantitative estimate of the imaging performance of the system. The average area under the ROC curve for the four physicians reading the same 'standard' image six times was computed to be 66.8 +/- 5.8. Experiments were performed to show the effect on diagnostic performance of (i) increasing the total image counts from 200k to 2000k, (ii) varying the phantom-to-collimator separation from 0 to 8 cm and (iii) changing the collimator type. In all cases, data were generated which demonstrated the quantitative improvement (or deterioration) resulting from these changes. These data may be used in the design of clinical imaging protocols, for which choices have to be made for each gamma camera variable.

Gamma Cameras↗
PubMed1991

Occupational doses to medical radiation technologists in Manitoba (1978-1988).

In Canada, occupational exposure to medical technologists accounts for about 8 per cent of all occupational exposure. In this paper, occupational doses to Manitoban radiation technologists (RTs) in diagnostic radiology, nuclear medicine and radiotherapy are presented for the period 1978-1988. Particular attention is paid to the distribution of dose among this population. The importance of age and sex demographics on radiation detriment is also estimated.

Data Collection↗
PubMed1991

Doses and population irradiation factors for Canadian radiation technologists (1978 to 1988).

Individual and collective radiation doses received by Canadian radiation technologists (RTs) working in diagnostic radiology, nuclear medicine and radiotherapy are summarized for the period 1978 to 1988. The data were obtained directly from the National Dose Registry, Department of National Health and Welfare. Over the 11-year study period the mean annual dose equivalent fluctuated around 0.2, 1.8 and 1.1 mSv for RTs working in diagnostic radiology, nuclear medicine and radiotherapy respectively. Over the same period the occupational collective dose equivalent decreased in diagnostic radiology (by 44%) and radiotherapy (by 35%) and increased in nuclear medicine (by 45%). Approximately 10,000 RTs are monitored each year, with an estimated total occupational collective dose equivalent of about 3.6 person-sieverts. Analysis of dose distribution data showed that only 1.3% of all monitored RTs received an annual whole-body dose equivalent greater than the current legal limit for members of the public (5 mSv). Approximately half of the RTs working in nuclear medicine and radiotherapy received an annual dose equivalent in excess of 0.5 mSv; only 7.3% of their diagnostic radiology counterparts exceeded this level. Demographic data showed a high preponderance of young women in all three RT classifications, and an analysis of the radiation risks to this occupational group revealed increases of up to 12% above the risk associated with a "standard" adult working population exposed to the same collective dose equivalent.

Adult↗
PubMed1990

Estimates of the effective dose equivalent, HE, in positron emission tomography studies.

The effective dose equivalent, HE, can be used as a standard radiation dose parameter in all imaging modalities that use ionizing radiation, including positron emission tomography (PET). A simplified method for evaluating approximate HE values for the positron emitters carbon 11, nitrogen 13, oxygen 15 and fluorine 18 is presented. HE values for a range of PET studies have been computed based on biodistribution data available in the scientific literature. Low-dose PET studies include a bolus administration of 1030 MBq CO15O (HE = 1 mSv) and 74 MBq [18F]-L dopa (HE = 1.3 mSv). High-dose PET studies include a 1-h (steady-state) inhalation of a total of 9250 MBq C15OO (HE = 9.4 mSv). The mean HE value of 13 diverse PET studies was computed to be 4.5 mSv.

Female↗
PubMed1990

Radiation doses due to breast imaging in Manitoba: 1978-1988.

The number of mammographic examinations performed annually in the province of Manitoba, Canada, and their associated radiation doses (total collective breast dose and average glandular dose [AGD] per view) are reported for the period 1978-1988. These data indicate that the total number of examinations performed annually increased by a factor of five during the 11-year study. The total annual collective breast dose, meanwhile, increased at a much slower rate, from 40 person-Gy in 1978 to 97 person-Gy in 1988; this difference is attributable to the gradual replacement of xeroradiography by screen-film mammography and to changes in technique. In the late 1980s, the AGD due to xeroradiography for a craniocaudal view was 3.3 mGy, a factor of 2.4 greater than the corresponding dose associated with dedicated screen-film units.

Canada↗
PubMed1990

Diagnostic thyroid procedures and corresponding radiation doses in Manitoba: 1981-1985.

Data on nuclear medicine thyroid examinations performed in Manitoba (population 1 million) from 1981-1985 were collected, with more detailed demographic data obtained on 1,100 consecutive patients between June 1987 and January 1988. An average of 2,081 patients were examined per year, 81% female and 19% male, representing 8.4% of all nuclear medicine procedures. Typical administered activity and associated HE per patient were 238.0 MBq and 1.5 mSv for 99mTc, 7.4 MBq and 1.2 mSv for 123I, and 0.33 MBq and 3.9 mSv for 131I. Based on NCRP risk estimates with explicit corrections for age, sex, and radionuclide used, it is estimated that the rate of thyroid cancer induction is unlikely to exceed 0.56 y-1, of which about 10% would be fatal. This estimate is about a factor of 4 less than that generated using more generally applicable radiation protection risk estimates averaged over both sexes and all ages in the general population. The replacement of 131I with the present mix of radiotracers used for thyroid evaluation has resulted in a reduction of the estimated population detriment by a factor of 3.6.

Adolescent↗
PubMed1989

The use of the effective dose equivalent, HE, for 99mTc labelled radiopharmaceuticals.

Using the concept of effective dose equivalent, HE, it is shown that a knowledge of the detailed biodistribution data in most organs and tissues taking up 99mTc labelled radiopharmaceuticals is unnecessary for the calculation of radiation risk. Reasonably precise dosimetry (+/- 25%) can be obtained from urine excretion data alone providing there is no significant uptake within the gonads or the thyroid. Special attention should only be paid to absorbed dose measurements in red bone marrow, skin, lungs, gonads and thyroid, with the greatest attention directed toward the retention and dosimetric aspects of radioactivity in the latter two organs. An example HE calculation for 99mTc labelled d,1-HMPAO is presented to illustrate the importance of these specific five organs to radiation risk.

Adult↗
PubMed1989

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.

Adult↗
PubMed1989

Nuclear medicine staff and patient doses in Manitoba (1981-1985).

The number of diagnostic in vivo nuclear medicine (NM) procedures in the Province of Manitoba (population 1 million) has been examined over the period 1981 to 1985. The annual number of procedures performed has remained relatively constant at about 25 per thousand population. The isotope 99mTc accounted for 86% of all the studies performed and the number of NM procedures per imaging system was approximately 1,300 per annum. The total number of NM operators in the province increased from 30 in 1981 to about 40 in 1985. The mean NM operator dose was reduced from 3.8 mSv to 2.5 mSv over this five-year period and the collective operator dose underwent a smaller reduction of 13% to about 100 person-mSv in 1985. The value of the mean patient effective dose equivalent (HE) was relatively constant at 5.2 mSv. The contribution of diagnostic NM procedures to the annual per caput population dose in Manitoba was 0.13 mSv. Three diagnostic procedures (brain, bone and cardiac) accounted for approximately 80% of the collective patient HE. Patient profiles (age, sex and medical history) were obtained for the patients undergoing these three procedures, which showed them to be atypical in comparison to a normal working population. These data suggested that the application of the International Commission on Radiological Protection risk factor of 1.65 X 10(-2) Sv-1 to this patient population would have significantly overestimated the expected radiation detriment.

Female↗
PubMed1989

Occupational doses in radiation oncology in Manitoba--1980 to 1986.

The province of Manitoba (population of 1.0 million) has two radiotherapy centers employing a number of people, of whom about 60 are exposed to radiation during the course of their work. The individual and collective radiation doses to these workers, as recorded by thermoluminescent dosimeter plaques, were reviewed for the period 1980 to 1986. Whole-body doses to radiotherapy technologists responsible for operating the treatment machines and brachytherapy afterloading procedures ranged from 0.5 to 2.5 mSv y-1, whereas the corresponding doses to nursing staff working on a hospital brachytherapy ward were about 1.0 mSv y-1. The collective occupational dose from radiotherapy in Manitoba was approximately 70 person-mSv. Trends show individual operator and collective doses to be increasing at a higher rate than the number of patients undergoing radiotherapy. Occupational exposure in radiotherapy in this province was found to be comparable to that encountered in nuclear medicine in Manitoba and greater than that in diagnostic radiology.

Brachytherapy↗