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Biomedical subjects

L Brateman

Publications and source records attributed to L Brateman.

18 recordsLinked to original sources
PubMed1999

Proposition: a pregnant resident physician should be excused from training rotations such as angiography and nuclear medicine because of the potential exposure of the fetus.

It has been reasonably well documented that a pregnant resident physician can assume radiology rotations, including higher-exposure rotations such as angiography and nuclear medicine, without exposing the fetus to radiation levels that exceed national and international guidelines. Hence, many medical physicists support the contention that rotations should not be altered because a resident is pregnant. On the other hand, many if not most physicists subscribe to the ALARA (as low as reasonably achievable) principle, especially in cases of fetal exposure where increased radiation susceptibility is combined with an inability to decide for one-self. In addition, altered rotations usually can be accommodated by swapping rotations with other residents, with the pregnant resident taking high exposure rotations after delivery of the child. Policies on this issue vary among institutions, possibly because medical physicists have not come to closure on the issue. This issue of Point/Counterpoint is directed toward that objective.

Education, Medical, Graduate↗
PubMed1991

Left ventricular regional wall motion assessment by radionuclide ventriculography: a comparison of cine display with Fourier imaging.

Radionuclide ventriculography and contrast ventriculography were performed in two comparable projections on 50 patients with suspected coronary artery disease. The efficacy of conventional cine display and Fourier image analysis of the radionuclide ventriculogram was compared using contrast ventriculography as the gold standard. Of seven different combinations of Fourier images, the combination of left anterior oblique amplitude and phase and left posterior oblique amplitude and phase provided the highest sensitivity (87%), specificity (83%), accuracy (86%), and kappa coefficient (0.64). To increase statistical power, segment data were collapsed to global data in which a heart was considered normal if all segments were normal and abnormal if one or more segments were abnormal. Fourier images had higher sensitivity (Fourier 87%, cine 47%); lower specificity (Fourier 83%, cine 92%), higher accuracy (Fourier 86%, cine 58%), and higher kappa coefficient (Fourier 0.64, cine 0.25), and these differences were statistically significant (p less than 0.01).

Coronary Disease↗
PubMed1988

Magnetic field shimming by Fourier analysis.

The homogeneity of the magnetic field of an Oxford 85/310HR magnet was optimized with the use of passive shims (i.e., pieces of steel) and room-temperature electronic shims. Both the characteristics of the passive shims and the current settings for the room-temperature electronic shims were calculated with the goal of minimizing field inhomogeneities as assessed by Fourier analysis of data from circular field plots. The measurement techniques, the methods of data analysis, and the techniques employed in correcting the magnetic field are presented. Difficulties and constructive approaches are suggested in these descriptions. The final results show a field of excellent homogeneity over a 10-cm-diameter spherical volume, with a peak-to-peak variation of 3.2 ppm, which is better than the manufacturer's expected specification of 5 ppm. A water-filled sphere of 10 cm diameter gave a half-height linewidth of 0.14 ppm after a small amount of additional touch-up shimming. The field homogeneity as corrected is much improved over its original state, allowing the acquisition of improved spectra from samples of a size several centimeters in each linear dimension. Thus the field homogeneity is more useful for in vivo spectroscopy, the purpose for which the magnet was intended.

Fourier Analysis↗
PubMed1986

Chemical shift imaging: a review.

Chemical shift is the phenomenon that is seen when an isotope possessing a nuclear magnetic dipole moment resonates at a spectrum of resonance frequencies in a given magnetic field. These resonance frequencies, or chemical shifts, depend on the chemical environments of particular nuclei. Mapping the spatial distribution of nuclei associated with a particular chemical shift (e.g., hydrogen nuclei associated with water molecules or with lipid groups) is called chemical shift imaging. Several techniques of proton chemical shift imaging that have been applied in vivo are presented, and their clinical findings are reported and summarized. Acquiring high-resolution spectra for large numbers of volume elements in two or three dimensions may be prohibitive because of time constraints, but other methods of imaging lipid of water distributions (i.e., selective excitation, selective saturation, or variations in conventional magnetic resonance imaging pulse sequences) can provide chemical shift information. These techniques require less time, but they lack spectral information. Since fat deposition seen by chemical shift imaging may not be demonstrated by conventional magnetic resonance imaging, certain applications of chemical shift imaging, such as in the determination of fatty liver disease, have greater diagnostic utility than conventional magnetic resonance imaging. Furthermore, edge artifacts caused by chemical shift effects can be eliminated by certain selective methods of data acquisition employed in chemical shift imaging.

Animals↗
PubMed1985

Chemical shift artifact in clinical magnetic resonance images at 0.35 T.

A thin, low-intensity line, which partially surrounds many structures on magnetic resonance imaging (MRI), is an artifact due to the phenomenon of chemical shift and should not be mistaken for a normal or abnormal morphologic structure. This artifact can be recognized by its characteristic appearance perpendicular to the direction of the frequency-encoding gradient at the interface of tissues with different chemical shift properties. Confinement within or extension beyond this thin, low-intensity line cannot be used as a criterion for staging neoplasms. Once recognized, the chemical shift artifact should not impede the use of MRI for clinical imaging at 0.35 T.

Diagnostic Errors↗
PubMed1984

Compton scatter axial tomography with x-rays: SCAT-CAT.

A method of extracting information from the backscattered field produced in parallel beam x-ray computed tomography (CT) is presented. A calculational model to predict the backscattered field based on Compton scattering is described, and the model is verified by measurements of simple phantoms. The phantoms tested--cylinders of polymethylmethacrylate (PMM) with air gaps and aluminium rods placed internally--are irradiated on a scanning assembly, built to simulate a first generation CT scanner with a transmission and a scatter detector (the SCAT-CAT). Data from the transmission detector are reconstructed by traditional CT methods to provide a transmission image; it is the data from the backscatter detector which are analysed in this study. After verification of the model for the scattered field calculations, a method of extracting information from the scattered field is developed, based on ratios of scatter signals from non-uniform to uniform phantoms. This method is demonstrated for predicted data of a simulated phantom and for measured data of the same and two additional phantoms. The method is very sensitive to air gaps in the phantoms because of the relative electron density of air with respect to PMM; it is not as sensitive to aluminium rods for the same reason. Various methods of applying the scattered field information to produce an image representing a simulated phantom are considered, and a preferred method is chosen to reconstruct scattered field data into an image for the three phantoms studied.

Humans↗
PubMed1984

Magnetic resonance imaging of hepatic lymphoma.

The livers of 13 patients with histologically proven hepatic lymphomatous involvement were studied with both magnetic resonance imaging (MRI) and computed tomography (CT). MRI and CT demonstrated a focal abnormality in only one case. In the other 12 cases in which a focal abnormality was not demonstrated with MRI or CT, calculated T1 and T2 relaxation times in regions of interest in the liver were within 1 SD of their respective normal means. The inability to detect hepatic involvement in most cases was probably due to the diffuse microscopic distribution of lymphoma in the liver and the methodology used for calculating relaxation factors. Thus, with current imaging technology, MRI does not seem to be better than CT for evaluating the liver for lymphomatous involvement.

Adult↗
PubMed1980

Potential hazard to ultrasonographers from previously administered radionuclides.

The authors discuss the potential radiation hazard to the ultrasonographer from patients who have received radionuclides for nuclear medicine studies. Data are presented for 24 of the more than 30 patients measured, and radiation levels of 10 mR/hr (0.72 nA/kg) over the abdomen and 5 mR/hr (0.358 nA/kg) at the tableside were obtained from some patients. In one unusual case, 40 mR/hr (2.88 nA/kg) and 8 mR/hr (0.58 nA/kg) at the position of the sonographer's hands and gonads, respectively, were recorded. These levels indicate that ultrasonographers should be considered radiation workers and should be monitored for radiation exposure.

Allied Health Personnel↗
PubMedDate not supplied

Edge artifacts in MR images: chemical shift effect.

The boundaries of some organs as seen in clinical magnetic resonance images appear to be asymmetric. This effect is caused by chemical shift differences between the resonant frequencies of the hydrogen nuclei of water and fat. The zeugmatographic technique maps resonant frequencies to unique spatial locations. These differences in resonant frequencies can appear as artifactual misplacement of information as this one-to-one correspondence is lost. Various phantoms are used to demonstrate that the boundary artifact appears only in the direction of the read (frequency-encoding) gradient when media of two different chemical shifts are separated by an interface. When the relative shift is less than the width of the interface, the boundary appears to be asymmetric; when the relative shift is greater than the width of the interface, a bright band is seen along one edge with a dark band along the other. This artifact is more pronounced in low resolution images than in high resolution images, and these effects are seen even when the relative chemical shift is smaller than a pixel bandwidth. These effects are explained both conceptually and analytically. The clinician should be aware of the potential presence of this artifact at boundary interfaces that bear diagnostic significance.

Kidney↗
PubMedDate not supplied

Energy dependence of correction factors for some Victoreen Model 570 Condensor R-Meter medium-energy chambers.

The energy dependence of each of six models of medium-energy Victoreen 570 Condenser R-Meter chambers was determined by measurement of the exposure correction factors over the diagnostic x-ray beam-quality range (0.4-4.1 mm A1 HVL) for several samples of each model. The results of an analysis of variance performed by model on the correction factors are reported as mean correction factors for the x-ray beams evaluated, with a relative standard error less than 0.8% in all cases. Energy-dependence curves for the six chamber models are given; their use is described.

Calibration↗
PubMedDate not supplied

Energy dependence of correction factors for some low-energy direct-reading pocket dosimeters.

The energy dependence for each of five models of low-energy direct-reading pocket dosimeters was characterized through an examination of the exposure correction factors determined over the diagnostic x-ray range (0.4-4.1-mm Al HVL) for many samples of each model. The results of an analysis of variance performed by model on the correction factors are reported as mean correction factors for the x-ray beams evaluated, the relative standard error being less than 0.8% in all cases. Energy-dependence curves for the dosimeter models are given, and their use is described.

Radiography↗
PubMedDate not supplied

Energy dependence of correction factors for two models of Keithley diagnostic ion chambers.

The energy dependence for each of two models of ionization chambers compatible with the Keithley model 35020 Digital Dosimeter, is determined by measurement of the exposure correction factors determined over the diagnostic x-ray range (0.4--4.9 mm AL HVL) for several for several samples of each model. The results of an analysis of variance performed by model on the correction factors are reported as mean correction factors for the x-ray beams evaluated, with a relative standard error of less than 1% for both cases. Energy-dependence curves for the two chamber models are given, and their use is described.

Evaluation Studies as Topic↗
PubMedDate not supplied

Evaluations of magnetic resonance imaging parameters with simple phantoms.

Imaging parameters associated with a clinical magnetic resonance imaging (MRI) system, evaluated with the use of simple and inexpensive phantoms, are described in evaluation of a clinical MRI system. Images, obtained with a Diasonics 0.35-T MRI system using an elliptical whole-body radio frequency coil, are presented which demonstrate geometric distortion, inaccuracy of image dimensions, and artifacts. Measurements of reproducibility and uniformity of both signal intensity and spin-lattice relaxation times are presented for uniform phantoms. Replicate measurements are analyzed by two-way analyses of variance to determine the significance of variations as a function of position and slice. Apparent T1's are not significantly different among the slices for the images analyzed, but there is a significant effect due to position in the field. Direct measurement of the radio frequency field for the center slice follows a pattern which is similar. Spin-lattice relaxation times are compared among two-point calculations and nonlinear four-point calculations, and the effects of pooling data are found to increase the precision of T1 measurements.

Humans↗
PubMedDate not supplied

Radiation safety considerations for diagnostic radiology personnel.

In radiation protection, the guiding philosophy is ALARA (as low as reasonably achievable), and states have regulatory authority. Dose limits are in part based on effective dose equivalent and differences in tissue sensitivities. In diagnostic radiology, the main source of occupational dose is scattered radiation from the patient--particularly from fluoroscopically guided procedures. Personnel stand near patients for long times, and angulated geometries with C-arm equipment may result in high personnel doses from backscatter. For all procedures, judicious applications of time, distance, and shielding affect dose. Appropriate use includes collimating properly, optimizing beam-on time, minimizing distances between image intensifier and patient, ensuring sufficient distance between patient and x-ray tube, and optimizing exposure rates for image quality and dose. Although dose limits typically regulate maximum whole-body dose, protective clothing worn by fluoroscopists reduces personnel risks; weighting factors can be applied to estimate effective dose equivalent. Pregnant personnel have lower limits, which apply only with voluntary declaration of pregnancy. With appropriate precautions, fetal doses can typically remain within recommended limits without changes in occupational tasks. Radiation workers in each state must ensure that regulations are appropriate. Then, for protection of both employee and employers, the rules can and must be followed.

Diagnostic Imaging↗