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Biomedical subjects

D W Anderson

Publications and source records attributed to D W Anderson.

170 records · Page 10Linked to original sources
PubMedDate not supplied

Measurement of accelerator bremsstrahlung spectra with a high-efficiency Ge detector.

A Compton spectrometer with a high-efficiency Ge detector was used to measure photon spectra from clinical accelerators. The response-function matrix for the detector system was determined using ten radioactive sources that emitted gamma rays of single energy ranging from 279-1525 keV. The system was tested by measuring the spectrum from a 60Co teletherapy machine. The energy distribution of tungsten target bremsstrahlung produced by 2.2, 2.5, 15, 20, and 25 MeV electrons in two clinical accelerators were determined. Theoretical thin-target calculations overestimate the number of photons in the high-energy regions of the spectra, as was expected. However, theoretical thick-target calculations underestimate the numbers of high-energy photons.

Germanium↗
PubMedDate not supplied

Contrast testing for magnetic resonance imaging.

A test phantom for evaluating magnetic resonance image contrast was constructed using separate chambers filled with manganese chloride (MnCl2) solutions of different concentrations. The concentrations were chosen so that the relaxation times produced were distributed over the range appropriate for human tissues in brain imaging. Specific solutions had relaxation properties similar to those of white matter, gray matter, and brain tumors. The region surrounding the chambers was filled with a sodium chloride solution with conductivity similar to that of brain tissue so that radiofrequency signal absorption would be appropriate. When magnetic resonance relaxation response curves were obtained with the phantom, relaxation contrast and latitude could be compared for different imaging pulse sequences. Contrast responses for gradient echo sequences differed considerably when the flip angle was changed.

Image Enhancement↗
PubMedDate not supplied

A survey approach for finding cases of epilepsy.

Identify persons with epilepsy by first looking for prescriptions for particular antiseizure drugs. Follow these prescriptions from the pharmacies to the physicians who wrote them for patients. Ask the physicians whether the patients have epilepsy. Finally, contact the patients who do have epilepsy to elicit information about the impact of that condition on their lives. With these steps, it may be possible to carry out successfully a probability survey of epilepsy in the United States population. To learn more about this approach, a field test was funded by the National Institute of Neurological and Communicative Disorders and Stroke (NINCDS) of the Public Health Service. From 1978 through 1982, the work was planned, carried out, and evaluated by Research Triangle Institute, Research Triangle Park, NC. Epilepsy is a sensitive topic to ask about in a survey. Also, the condition is sufficiently rare to render ordinary survey approaches inefficient. Even if rarity were not an issue, there would be the problem of response error because a person with epilepsy does not, as a rule, have much clinical information on his or her condition. Better information lies with the physician who provides the care, but many physicians are busy with their practices. Furthermore, their record systems are usually not designed for easy retrieval of information, unless the names of patients are available. In the survey approach considered here, the names of patients are obtained through a random sampling of prescriptions for antiseizure drugs. The field test was divided into three phases with special activities reserved for each. The most important problem confronted was how to safeguard the confidentiality of relationships between pharmacist and patient and between physician and patient.Special guidelines on confidentiality were put into effect for the data collection. These guidelines,however, contributed to serious problems of nonresponse-especially for physicians. This article provides a brief account of the field test, including a rationale for the survey strategy of finding cases of epilepsy through prescriptions for antiseizuredrugs.

Anticonvulsants↗
PubMedDate not supplied

Field-focusing hyperthermia and magnetic resonance imaging (MRI) with a grounded probe and a commercial MRI scanner.

A method for performing magnetic resonance imaging (MRI) and producing field-focusing hyperthermia sequentially in phantoms and rat tissues with a grounded hyperthermic probe and a commercial MRI scanner was demonstrated. In the treatment mode the MRI scanner was used as a radiofrequency (RF) power source, and an invasive, electrically grounded, tuned probe was used to produce hyperthermia in phantoms via induced eddy current convergence. Temperature increases of 4.5 degrees C/5 minutes in a dielectrically uniform phantom and 5.0 degrees C/6 minutes in the peritoneum of a rat were measured in the vicinity (3-5 mm) of the grounded probe with the transmitter of the MRI scanner working at 2 per cent duty cycle. The advantage of this combined diagnostic and therapeutic approach is that the position of the hyperthermic probe can be monitored before each treatment, with observation of the tumor during and after treatment, if desired. In addition, the total cost is significantly less than that of both an MRI scanner and an RF hyperthermia treatment system.

Animals↗
PubMedDate not supplied

Findings from a major U.S. survey of persons hospitalized with head injuries.

In 1974, work began on the first national survey of head and spinal cord injuries in the United States. The survey was a project of the National Institute of Neurological and Communicative Disorders and Stroke of the Public Health Service. This article presents highlights of the survey, particularly the findings about head injuries (that is, brain injuries). The survey population consisted of people admitted to U.S. hospitals as inpatients between January 1, 1970, and December 31, 1974. To be medically eligible, patients must have experienced physical injury (except birth trauma) caused by an external, mechanical force. Probability sampling was used in a three-stage plan to select appropriate hospital records. Findings of the head and spinal cord injury survey follow: Of all age groups, 15- to 24-year-olds had the highest rate of head injuries. Males had a rate of head injuries more than twice that of females. Head injuries occurred most often on Fridays, Saturdays, and Sundays. The chief cause of head injuries was motor vehicle accidents.

Accidents, Traffic↗
PubMedDate not supplied

Ultrastructural evidence of intrahepatic cholestasis before and after chenodeoxycholic acid therapy in patients with cholelithiasis: the national cooperative gallstone study.

Electron microscopy was performed to assess potential hepatotoxicity before and after 9 and 24 months of chenodeoxycholic acid (CDCA) therapy (375 or 750 mg, daily) in 103 patients with cholelithiasis. Prior to treatment, 64% of the biopsies demonstrated ultrastructural evidence of intrahepatic cholestasis, manifested by abnormal bile canaliculi, thickened pericanalicular ectoplasm, and retention of biliary material within liver cells or pericellular spaces. After 9 months of CDCA therapy, several changes (including increased free cytoplasmic "biliary pigment," decreased canalicular microvilli, and increased pericanalicular ectoplasm) consistent with intrahepatic cholestasis became more prevalent (63% prior to therapy, 89% at 9 months, p less than 0.01) regardless of CDCA dose. After 24 months of therapy, canalicular microvilli and pericanalicular ectoplasm continued to be abnormal (p less than 0.01). This study indicates that ultrastructural evidence of intrahepatic cholestasis is a common subclinical abnormality in patients with cholelithiasis which increases during CDCA therapy, changes which could represent either the natural history of cholelithiasis or CDCA toxicity. A drug effect is suggested by the lack of correlation of these abnormalities with the duration of cholelithiasis prior to CDCA treatment and their "increasing" prevalence after only 9 months of therapy. In addition, canalicular membrane lesions developed in two patients which were similar to lithocholate toxicity in animals. It is not known whether these abnormalities would result in clinically significant hepatoxicity if therapy is continued for longer than 24 months.

Bile Canaliculi↗
PubMedDate not supplied

A system for checking radiation therapy calculations for treatment time or monitor setting.

Errors in the calculation of radiation therapy treatment time or monitor setting are likely to occur with regularity unless adequate quality control procedures are utilized. These errors can be greatly reduced if appropriate computer systems are employed with programs which utilize analytical representations of dosimetric quantities. A system wherein dosimetry technologists routinely check treatment calculations using a computer terminal has been in operation in our department for several years and has proved helpful in uncovering calculation errors.

Computers↗