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Biomedical subjects

C C Chamberlain

Publications and source records attributed to C C Chamberlain.

14 recordsLinked to original sources
PubMed2001

Radiation doses to infants and adults undergoing head CT examinations.

For routine noncontrast CT examinations of the head, we compared the radiation doses of infant patients aged no more than two years old, with those of "adults" defined as any patient whose weight was greater than 40 kg. Data were obtained for 23 infants, and an equal number of "adults," who underwent CT head examinations between May 1997 and March 1998. Patient CT data acquired included the x-ray tube potential (kVp), mAs, section thickness, and total number of sections. For radiation dosimetry purposes, the head was modeled as a uniform cylinder of water using patient size data obtained from a representative cross-sectional image. CT techniques and patient size data permitted the computation of the mean section doses in the head region, total energy imparted, and the corresponding effective doses. All CT scans were performed at 120 kVp, with an average current-exposure time product of 271 +/- 73 and 340 +/- 0 mAs for infants and "adults," respectively. The radius of the water cylinder used to model the patient head increased from 58 mm for 4 kg newborns to 70 mm for 8 kg infants. For "adults," there was little correlation between the weight of the patient and the mean water equivalent radius of 88 mm (r2 = 0.14). Mean section doses were 44.4 +/- 11.1 mGy for infants, and 44.2 +/- 1.5 mGy for "adults." The energy imparted to infants correlated with patient weight (r2= 0.35) much more than did that of "adults" (r2= 0.02). The average infant energy imparted (66.4 +/- 28.7 mJ) was approximately half the value obtained for "adults" (140 +/- 10 mJ). The average effective dose to the infants (7.6 +/- 3.1 mSv), however, was approximately six times higher than that for "adults" (1.3 +/- 0.1 mSv). There was no significant correlation between patient effective dose and patient mass for either the infant (r2 = 0.12) or the "adult" group of patients (r2= 0.02). Infant doses varied much more than "adult" doses, primarily because of a wider range of x-ray technique factors selected and secondarily due to the variation in infant head size. The observed variability in the computed radiation dose parameters indicates that it should be possible to reduce infant doses routinely in head CT examinations without any adverse effect on diagnostic imaging performance. For such routine head CT scans, the average dose reduction for infants weighing between 4 and 8 kg would be expected to range between 40% and 60%.

Adolescent↗
PubMed2000

Radiation doses to patients undergoing scoliosis radiography.

In this study we computed the radiation doses associated with scoliosis radiography and investigated how these radiation doses are influenced by the weight of the patient. We recorded the radiographic technique factors of 61 consecutive patients (46 females and 15 males) undergoing scoliosis radiography. A wedge-shaped aluminium filter attenuated the X-ray beam in the "chest region" relative to the "abdomen region". X-ray tube air kerma output factors (microGy mAs-1) and half value layers (HVLs) were determined experimentally for the "chest region" and "abdomen region". The energy imparted to each patient was computed from the air kerma area product, X-ray beam HVL and measured patient thickness. Values of patient effective dose were obtained using effective dose-to-energy conversion factors for specified radiographic projections, taking into account each patient's weight. The median patient age was 17 years, and the median patient weight was 53 kg. Entrance skin air kerma values in the "chest region" were approximately a factor of four lower than those in the "abdomen region". The air kerma values increased by a factor of two when the patient weight increased from 30 kg to 70 kg. Approximately 80% of the total energy imparted to a patient undergoing a scoliosis examination was in the "abdomen region", with the remaining 20% imparted to the "chest region". Energy imparted increased with patient weight, and was approximately 3 mJ for a 30 kg patient and approximately 8 mJ for a 70 kg adult patient. Effective doses showed little correlation with patient weight, with an average-sized patient (50 kg) receiving an effective dose of approximately 140 microSv. Patients undergoing scoliosis radiography receive effective doses that are low in comparison with other types of radiographic examination.

Adolescent↗
PubMed1997

Smaller format, laser camera-generated images: acceptability and cost savings.

RATIONALE AND OBJECTIVES: To evaluate the use of laser-generated smaller images in neuroradiologic practice. MATERIALS AND METHODS: Computed tomographic (CT) scans of the heads of five subjects were obtained at bone and brain windows in three formats: 12:1 (12 images on a 35 x 43-cm film), 15:1 and 20:1. Two laser-camera systems were used. Images were measured, physically separated, and reconstructed as a 35 x 43-cm ensemble; they were presented randomly to seven radiologists who assessed image size and interpretability. Observer preference was also noted. One camera system was evaluated for contrast and spatial resolution by a medical physicist. RESULTS: These were negligible differences in image area between the 15:1 and 20:1 formats. No discernible differences in quality were found among the three formats. The 12:1 images were preferred by the radiologists, but the 20:1 images were deemed acceptable. Annualized cost savings of 46.7%, or $46,650, were projected for adoption of the 20:1 image format for neuroradiologic CT and magnetic resonance imaging. CONCLUSION: No major differences were detected in image area between the 15:1 and the 20:1 image formats or in image quality among the three formats. Use of a smaller image format may result in substantial cost savings.

Cost-Benefit Analysis↗
PubMed1997

Laser-based microfocused x-ray source for mammography: feasibility study.

A laser-produced plasma (LPP) x-ray source with possible application in mammography was created by focusing a laser beam on a Mo target. A Table-Top-Terawatt (TTT) laser operating at 1 J energy per pulse was employed. A dual pulse technique was used. Maximum energy transfer (approximately 10%) from laser light to hot electrons was reached at a 150 ps delay between pulses and the conversion efficiency (hard x-ray yield/laser energy input) was approximately 2 x 10(-4). The created LPP x-ray source is characterized by a very small focal spot size (tens of microns), Gaussian brightness distribution, and a very short pulse duration (a few ps). The spectral distribution of the generated x rays was measured. Images of the focal spot, using a pinhole camera, and images of a resolution pattern and a mammographic phantom were obtained. The LPP focal spot modulation transfer function for different magnification factors was calculated. We have shown that the LPP source in conjunction with a spherically bent, high throughput, crystal monochromator in a fixed-exit Rowland circle configuration can be used to created a narrow band tunable mammography system. Tunability to a specific patient breast tissue thickness and density would allow one to significantly improve contrast and resolution (exceeding 20 lp/mm) while lowering the exposure up to 50% for thicker breasts. The prospects for the LPP x-ray source for mammographic application are discussed.

Biophysical Phenomena↗
PubMed1996

Scatter reduction in mammography with air gap.

Scatter reduction by air gaps in mammography was investigated. We have experimentally demonstrated that, independently of the imaging geometry, scatter in air-gap mammography can be well described by a virtual source of scatter (VSS) model. This model postulates that scatter radiation originates from a virtual point source of scatter placed on the central axis between the x-ray source and the exit surface of a patient at distance delta and utilizes only two parameters: delta and (S/P)0. The (S/P)0 parameter represents scatter-to-primary ratio without an air gap and delta is the distance from the exit surface of a patient to the virtual source of scatter. We have experimentally determined the analytical form of the two independent parameters of the VSS model; delta exhibits a linear increase proportional to the radiation field size, does not depend on patient thickness, and is in the 10-30 cm range, while (S/P)0 increases with the field size as a power function and is in the 0.4-1.3 range. In the framework of the VSS model the selectivity, the contrast improvement factor, and the signal-to-noise improvement factor were employed to evaluate performance of air-gap mammography systems. We have demonstrated that selectivity of an air gap rapidly deteriorates at some well-defined critical value of scatter fraction that has profound consequences on air-gap performance. Assuming fixed patient exposure, the results shows that, if a contrast limited detection system (such as film/screen mammography) is used, an air gap system can outperform a grid system only if a very large source-to-patient (SPD) distance is utilized, which might be possible with new laser-based x-ray sources. For the noise limited detection systems (such as digital mammography) even a small SPD (70 cm) and a small air-gap (20 cm) system will outperform a grid system.

Air↗
PubMed1983

A surface bolus material for high-energy photon and electron therapy.

The authors describe a useful bolus material for therapy with high-energy photons and electrons (greater than 1 MeV). Qualities evaluated included flexibility, transparency, tissue equivalence (re radiation interactions), stability at high doses, durability, lack of toxicity, ease in cleaning, low flammability, and cost. Using a parallel-plate ionization chamber and 60Co, 4-, and 10-MV photons as well as 6- and 18-MeV electrons, maximum deviation from water-equivalent values was approximately 2 mm for 6-MeV electrons. The material comes in large sheets of precise thickness (+/- 0.5 mm) which can be cut and layered to form more complex shapes.

Elastomers↗
PubMed1980

Density patterns in the normal lung as determined by computed tomography.

Lung density patterns in a group of randomly selected, normal individuals were determined by computed tomography, using two methods: one measuring the density of the peripheral lung (parenchyma), and the other determining the density of the whole lung field. The effects of body position and respiratory phase, as well as patient age were assessed. The potential use for this information in clinical settings and in physiological investigation is suggested.

Age Factors↗
PubMed1979

Transmission computed tomography, Tc-99m MAA scintigraphy, and plain chest radiography after experimentally produced acute pulmonary arterial occulusion in the dog.

We have occluded segmental and subsegmental pulmonary arteries in the dog with Swan-Ganz balloon catheters or i.v. injection of autologous clot, and have studied the chest with transmission computed tomography (TCT), Tc-99m-MAA gamma imaging, and plain radiographs. The arterial occlusions were between 1 and 5 hr old at the time of imaging. Radiographs revealed no lesions. Tc-99m MAA scanns revealed ten of 11 lesions. When a TCT image was made before i.v. injection of Renografin-60, two of 11 lesions were identified; after Renografin the score was four out of ten. The appearance of lesions on TCT was highly variable. Tc-99m-MAA gamma imaging, therefore, is far more accurate than TCT in the identification of small experimentally produced acute pulmonary arterial occlusions in the dog, and our study fails to suggest a secure place for TCT in the diagnosis of small, acute human pulmonary emboli. The commonly-held assumption that postembolic lung is oligemic is questioned.

Animals↗
PubMed1977

Physical, performance, and dosimetric characteristics of the delta-Scan 50 whole-body/brain scanner.

The delta-Scan 50 computed tomographic (CT) scanner has the ability to determine x-ray attenuation coefficients with a precision ranging from 0.3 to 2.6% depending upon such factors as patient size and scan diameter. Resolution is 20-80% greater than the pixel width, with values ranging from 1.2 to 2.1 mm. The collimating system determines certain characteristics of the image and affects the dose to the patient: doses for typical procedures are on the order of 1 rad, and gonadal doses are in the millirad range. Potential improvements are discussed.

Brain Diseases↗
PubMedDate not supplied

Paravertebral muscle metastases as imaged by magnetic resonance venography: a brief report.

Paraspinal muscle metastasis as initially suggested by an electromyographic pattern of isolated posterior primary ramus denervation and subsequently confirmed by magnetic resonance imaging has been reported. However, despite widespread systemic tumor dissemination, metastases to other skeletal muscle occurs infrequently. Uniquely, the paraspinal muscles are drained by the paravertebral plexus of veins. Valveless and at very low pressures, they communicate directly by collaterals with the portal system. Valsalva maneuvers with sudden increases of pressure within the intra-abdominal and intrathoracic cavities can force venous blood from the systemic circulation into the paravertebral plexus of veins. These same venous surges potentially carry tumor emboli to the vertebrae and/or from the vertebral medulla to the adjacent paravertebral muscle by the venous communicators. The inherent increased vascularity of metastatic tumor relative to the surrounding paraspinal muscle as demonstrated by magnetic venous angiography for the first time now permits earlier confirmation and biopsy of the electromyographic-suspected metastatic lesion. In this reported instance of a magnetic resonance imaging-recognized primary lung metastasis confirmed by magnetic resonance venography, there is the future promise of identifying earlier and smaller lesions by this technique.

Aged↗