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W Huda

Publications and source records attributed to W Huda.

At least 37 records · Page 2Linked to original sources
PubMed1997

Computation of energy imparted in diagnostic radiology.

Energy imparted is a measure of the total ionizing energy deposited in the patient during a radiologic examination and may be used to quantify the patient dose in diagnostic radiology. Values of the energy imparted per unit exposure-area product, omega (z), absorbed by a semi-infinite water phantom with a thickness z, were computed for x-ray spectra with peak x-ray tube voltages ranging from 50-140 kV and with added filtration, ranging from 1-6 mm aluminum. For a given phantom thickness and peak x-ray tube voltage, the energy imparted was found to be directly proportional to the x-ray beam half-value layer (HVL) expressed in millimeters of aluminum. Values of omega (z) were generated for constant waveform x-ray tube voltages and an anode angle of 12 degrees, and were fitted to the expression omega (z) = alpha x HVL + beta. Fitted alpha and beta parameters are provided that permit the energy imparted to be determined for any combination of tube voltage, half-value layer, and phantom thickness from the product of the entrance skin exposure (free-in-air) and the corresponding x-ray beam area. The results obtained using our method for calculating energy imparted were compared with values of energy imparted determined using Monte Carlo techniques and anthropomorphic phantoms for a range of diagnostic examinations. At 60, 80, and 120 kV, absolute values of energy imparted obtained using our method differed by 8%, 10%, and 12%, respectively, from the corresponding results of Monte Carlo computations obtained for an anthropomorphic phantom. The method described in this paper permits a simple determination of energy imparted for any type of diagnostic x-ray examination which may be used to compare the radiologic risks from differing types of x-ray examinations, optimize imaging techniques with respect to the patient dose, or estimate the patient effective dose equivalent.

Energy Transfer↗
PubMed1997

Relative speeds of Kodak computed radiography phosphors and screen-film systems.

Relative mAs values required to generate a constant plate readout signal for the Kodak Ektascan general purpose (GP-25) and high resolution (HR) photostimulable phosphors were measured as a function of x-ray beam quality and for a range of representative x-ray examinations. The signal intensity was determined from the exposure index (EI) generated during the read out of uniformly exposed phosphor imaging plates. These data were compared to the corresponding relative mAs values required to produce a constant film density of Lanex screen-film combinations with nominal speeds of 40, 400, and 600. The relative detection performance of the photostimulable phosphors generally decreased with increasing kVp and beam filtration. The relative response of GP-25 phosphors was independent of examination type, and modified by approximately 10% when scattered radiation was present. The HR phosphor was more efficient than a Lanex Single Fine extremity screen used with an EM-1 film. These relative response data will be useful for selecting the x-ray technique factors which minimize patient dose in x-ray examinations performed with photostimulable phosphors.

Biophysical Phenomena↗
PubMed1997

Effective dose and energy imparted in diagnostic radiology.

The patient effective dose, E, is an indicator of the stochastic radiation risk associated with radiographic or fluoroscopic x-ray examinations. Determining effective doses for radiologic examinations by measurement or calculation is generally very difficult. By contrast, the energy imparted, epsilon, to the patient may be obtained from the x-ray exposure-area product incident on the patient. As energy imparted is approximately proportional to the effective dose for any given x-ray radiographic view, the availability of E/epsilon ratios for common radiographic projections provides a convenient way for estimating effective doses. Ratios of E/epsilon were obtained for 68 projections using E and epsilon values obtained from published dosimetry data computed using Monte Carlo techniques on an adult anthropomorphic phantom. The average E/epsilon ratio for the 68 projections in adults was 17.8+/-1.4 mSv/J, whereas uniform whole body irradiation corresponds to 14.1 mSv/J. The major determinant of E/epsilon ratios was the projection employed (the body region irradiated and x-ray beam orientation), whereas the tube potential and beam filtration were of secondary importance. Adult E/epsilon ratios may also be used to obtain effective doses to pediatric patients undergoing x-ray examinations by application of a correction factor based on the patient mass.

Adult↗
PubMed1997

An approach for the estimation of effective radiation dose at CT in pediatric patients.

PURPOSE: To estimate the effective radiation dose to pediatric and adult patients at head and abdomen computed tomography (CT). MATERIALS AND METHODS: Cylindrical water-equivalent phantoms were modeled for patients aged newborn to adult, and the energy imparted per unit axial exposure was computed. To determine the energy imparted to the simulated patients of different ages undergoing head and abdomen CT examinations, x-ray technique factors were combined with measured CT axial exposures. Body-region-specific ratios were calculated for effective dose per unit energy imparted, and these ratios were corrected for patient mass to obtain the effective dose to simulated patients. RESULTS: With use of standard techniques, the energy imparted to simulated patients at CT always increased with patient size, but the effective dose was higher in children than in adults. At CT in the head and abdomen, effective doses were highest in newborns. Effective doses ranged from 1.5 to 6.0 mSv in head CT examinations and from 3.1 to 5.3 mSv in abdomen CT examinations. CONCLUSION: The values for energy imparted at CT in pediatric patients were generally lower than in adults. The smaller mass of children, however, caused the corresponding effective doses to be higher than those in adults undergoing similar CT examinations.

Adolescent↗
PubMed1997

Evaluation of an on-line patient exposure meter in neuroradiology.

PURPOSE: To assess the clinical performance and usefulness of an on-line patient exposure meter installed on a neuroradiologic biplane imaging system. MATERIALS AND METHODS: A commercial on-line patient exposure meter was installed on each plane of a biplane neuroradiologic imaging system. The meter computed skin exposures on the basis of selected technique factors (tube potential and current) and information about patient location relative to the x-ray tube. Simulations were performed to measure the system accuracy with an angiographic anthropomorphic head phantom with the skin exposures measured with an ionization chamber. Skin doses were computed for 114 consecutive patients who underwent diagnostic and interventional neuroradiologic procedures. RESULTS: Agreement between measured and computed skin exposures in fluoroscopy, plain radiography, and digital imaging was generally within 5% of the true skin dose. For all fluoroscopic and radiographic procedures, total median skin doses were 1.20 and 0.64 Gy for the frontal and lateral planes, respectively. In both planes, patient skin doses resulted primarily from digital subtraction angiographic acquisitions. In 29 (25%) patients, the skin dose exceeded 2.00 Gy, but no radiation-induced deterministic effects were observed. CONCLUSION: An on-line patient exposure meter can provide accurate radiation skin dose data in patients undergoing diagnostic and therapeutic neuroradiologic procedures.

Angiography↗
PubMed1996

A cost-analysis of computed radiography and picture archiving and communication systems in portable radiography.

A total of 40,000 portable examinations are performed each year at Shands Hospital (Gainesville, FL), a 570-bed teaching hospital. Radiographs are obtained using a screen-film combination with the films digitized for transmission to displays in four intensive care units. A cost-analysis of replacing screen-film with computed radiography (CR) integrated into a filmless picture archiving and communication system (PACS) network was performed. Equipment requirements included two CR units, three high-resolution dual monitor displays, and an archive to store 3 months of image data. The capital costs were amortized over a 5-year period. Capital and operating costs of the proposed expansion to the existing PACS network, together with anticipated cost savings, were determined. The maximum data transfer rate for portable examinations was 150 MByte per hour and approximately 400 GByte of image data are generated each year. These figures were used to determine the hardware requirements for handling the acquisition, transfer, and display of the images. Annual costs of the proposed expansion were about $220,000. Cost savings were achieved by elimination of film, including its handling by technologists/library clerks, and amounted to about $200,000 per year.

Adult↗
PubMed1996

Picture archiving and communication system bandwidth and storage requirements.

The purpose of this work was to determine the requirements for image storage and network bandwidth for a total digital department in a moderate sized academic radiology department. Data from the radiology information system was combined with image production information to produce a model of image acquisition. Destinations of images to reading rooms were studied to determine the final distributions of film. All findings were used to model the flow of data that would be expected if the images in the department were completely digital. Using today's standards, the department would produce approximately 15.7 Gbytes of data per day or 3.5 Tbytes of data per year if all acquisitions were digital. The peak acquisition rate would be 1.8 Gbytes per hour with a sustained rate greater than 1 Gbyte per hour for most of the working day. The anticipated bandwidth for the total digital department exceeded the capabilities of the existing picture archiving and communication system equipment. A distributed networked archive solution was shown to optimize access to images by radiologists and referring clinicians.

Computer Storage Devices↗
PubMed1996

Computed radiography and film digitizer inputs to an intensive care unit teleradiology system: an image quality comparison.

RATIONALE AND OBJECTIVES: We compared computed radiography (CR) with a film digitizer as an image input device for transmitting radiographs to intensive care unit (ICU) displays. METHODS: Limiting spatial resolution and low-contrast detectability performance were determined for a 600-speed screen-film combination and CR films. The same image data were transmitted to ICU displays directly from the CR or by digitizing the conventional film. RESULTS: CR resolution ranged from 2.5 to 3 line pairs per millimeter (Ip/ mm) depending on cassette size. Display station resolution for the CR image data was 1.5-1.9 lp/mm, but improved resolution could be achieved using display magnification modes. Film digitization resulted in a loss of resolution. Direct transmission of CR image data to display stations gave low-contrast detectability similar to that obtained with CR film. CONCLUSION: ICU teleradiology displays that use CR, rather than film digitizers, offer improved image quality and superior operational efficiency.

Intensive Care Units↗
PubMed1996

Comparison of trained and untrained observers using subjective and objective measures of imaging performance.

RATIONALE AND OBJECTIVES: We compared subjective and objective measures of imaging performance using variations of Rose- and Burger-type low-contrast phantoms with trained (radiology residents) and untrained (graduate students) observers. METHODS: With one phantom variant, observers indicated the total number of objects seen when test objects were presented in a regular pattern (subjective). With the second phantom variant, observers stated whether a low-contrast disk was present in each locale, thereby permitting the true-positive fraction and false-positive fraction to be determined (objective). RESULTS: The untrained-observer group had a significantly lower imaging performance than the trained observer group in subjective tests. These differences were not found on objective tests. For the trained-observer group, similar contrast levels were required in subjective and objective tests to yield a 50% rate of detection. CONCLUSION: Trained observers are superior subjects compared with untrained observers for assessing imaging performance using subjective low-contrast phantoms. In experiments using phantoms that allowed objective testing, both groups of observers yield similar results.

Educational Status↗
PubMed1996

Energy imparted and effective doses in computed tomography.

The radiation risk to patients undergoing computed tomography (CT) examinations may be characterized by using the dose descriptors of effective dose equivalent (HE) and effective dose (E). Values of HE and E, however, are much more difficult to obtain than the total energy imparted (epsilon) to the patient. In this study, representative values of the ratios HE/epsilon and E/epsilon were obtained using published Monte Carlo organ dose computations for typical CT x-ray spectra. Values of patient dose per unit energy imparted can be combined with independent estimates of energy imparted to quantify the dose to a patient undergoing any type of CT examination.

Head↗
PubMed1996

Medical physics.

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Biophysics↗
PubMed1996

Technical exhibits.

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Exhibitions as Topic↗
PubMed1996

Mottle on computed radiographs of the chest in pediatric patients.

PURPOSE: To investigate the relationship between radiation exposure and perceived mottle at bedside pediatric chest examinations performed with screen-film and computed radiographic techniques. MATERIALS AND METHODS: In a pediatric intensive care unit, chest radiographs were obtained with both computed radiography (60 radiographs) and a 600-speed screen-film system (14 radiographs). The relative radiation exposure was estimated by using the sensitivity value obtained in the processing of each computed radiograph. Five radiologists assessed the mottle present in the computed radiographs and screen-film images. RESULTS: For computed radiographs, the perceived level of mottle was inversely related to radiation exposure. For the same radiation exposure, the perceived mottle on computed radiographs was significantly higher than that on screen-film images (P < .001 for small cassettes; P < .01 for large cassettes). CONCLUSION: Pediatric computed radiography of the chest requires approximately twice the exposure of a 600-speed screen-film system to attain the same level of mottle.

Child↗
PubMed1996

Patient doses in bone mineral densitometry.

Procedures were developed to compute effective dose equivalent (H(E)) values for patients undergoing bone mineral densitometry (BMD) measurements such as dual energy X-ray absorptiometry (DEXA) and quantitative computed tomography (QCT). Representative values of H(E) were determined for patients undergoing each type of BMD procedure. Typical DEXA measurements are associated with an H(E) of about 2.5 microSv. For QCT, the values of H(E) are 300 microSv for single energy techniques and 1 mSv for dual energy techniques, respectively. By comparison, a single well collimated abdominal X-ray examination often taken in conjunction with DEXA studies results in an H(E) of about 100 microSv. BMD patient doses are at the lower end of the exposure range encountered in diagnostic radiology. As a result, radiation dose is not a primary factor in choosing the method for BMD determination.

Absorptiometry, Photon↗
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↗