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Biomedical subjects

J Doll

Publications and source records attributed to J Doll.

At least 19 recordsLinked to original sources
PubMed1991

Modification of a three-dimensional treatment planning system for the use of multi-leaf collimators in conformation radiotherapy.

The multi-leaf collimator of the DKFZ is designed as a low cost add-on device for conventional linear accelerators for radiotherapy. The technical specification of the computer controlled collimator is described briefly. A major limitation in the use of the wide capabilities of multi-leaf collimators in the clinic is still an appropriate treatment planning system. This paper describes treatment planning and dose calculation techniques for multi-leaf collimators and shows examples where the capabilities of the collimator are used extensively.

Dose-Response Relationship, Radiation↗
PubMed1991

Pharmacokinetics of molsidomine and its active metabolite, linsidomine, in patients with liver cirrhosis.

The pharmacokinetics of molsidomine were investigated in six healthy volunteers and in seven patients with alcoholic cirrhosis. After a 2 mg oral dose, molsidomine elimination half-life was prolonged in cirrhotic patients (13.1 +/- 10.0 h vs 1.2 +/- 0.2 h, P less than 0.01) because of a decrease in its apparent plasma clearance (CL/F) (39.8 +/- 31.9 ml h-1 kg-1 in patients with cirrhosis vs 590 +/- 73 ml h-1 kg-1 in volunteers). The elimination half-life of the active metabolite, linsidomine (SIN-1) was also prolonged in cirrhotic patients (7.5 +/- 5.4 h vs 1.0 +/- 0.19 h, P less than 0.05). The AUC values of both molsidomine and linsidomine were increased in the cirrhotic group, but the increase in the former was considerably greater than in the latter as shown by the significant decrease of the ratio AUClinsidomine/AUCmolsidomine x 100 (4.5 +/- 6.1 in cirrhotic patients vs 23.5 +/- 3.4 in healthy volunteers, P less than 0.001). These results suggest that liver cirrhosis profoundly alters the pharmacokinetics and metabolism of molsidomine.

Adult↗
PubMed1991

[Prediction of goal-directed behavior: attitude, subjective behavioral competence and emotions].

Ajzen's (1985) theory of planned behavior explaining and predicting goal-directed behavior is extended by an emotional component. The extended theory of planned behavior is tested experimentally. N = 64 subjects play with two video games (a speed- and a problem-oriented game) under an achievement-motivational orientation. One half of the subjects plays both games in an easy version, the other half in a difficult version. The verbal emotional reactions to playing video games are grouped factor-analytically into an "activity emotion" and a "security emotion". Subjects playing video games in the difficult condition feel significantly more insecure, and perceive their behavioral control as significantly lower than subjects playing in the easy condition. Tests of the extended theory of planned behavior lead to significant squared multiple correlations for the dependent variables within the range of R2 = .20 to .58. The activity emotion accounts predominantly for a significant part of the variance of the attitude and the security emotion accounts for a significant part of the variance of the perceived behavioral control. No predictive power was found for the intention to play the games successfully.

Achievement↗
PubMed1991

Non-uniformity measurements in PET.

To gain practical experience with the procedures suggested by the EEC task group on performance evaluation of positron tomographs, the non-uniformity of the Scanditronix PC 2048-7WB positron tomograph was measured. The test was performed using both a cylindrical head phantom and the EEC body phantom. According to the recommendation of the task group, 2 million counts were collected in each emission scan as a standard. As to be expected, non-uniformity decreased when more counts were collected or a wider reconstruction filter was used. Non-uniformity increased when going from the head phantom to the body phantom leaving all parameters unchanged. It was concluded that this effect was caused by increased noise due to the larger attenuation lengths but not to attenuation correction. The preliminary results of this study show that counting statistics dominates non-uniformity in the count range of about 2 million counts per image. Measured non-uniformity values are in the range of +/- 30%.

Equipment Design↗
PubMed1990

Three-dimensional photon radiotherapy planning for laryngeal and hypopharyngeal tumours.

Three-dimensional absorbed dose distributions have been computed for high-energy photon radiation therapy of laryngeal and hypopharyngeal cancers, using a coaxial pair of opposing lateral beams in fixed positions. Treatment plans obtained under various conditions of irradiation are analyzed and compared for a cobalt-60 gamma unit (GAMMATRON S80, Siemens), photon beams from a 6 MV (CLINAC 1800, VARIAN), an 8 MV (SATURNE, CGR) and a 15 MV (MEVATRON 77, Siemens) linear accelerator. Using open fields a somewhat non-uniform and partly insufficient dose in target volume of interest is obtained with all treatment units if sufficient protection of the spinal cord is provided. The x-ray plans are somewhat superior to the cobalt-60 ones. Depending on the quantum energy and wedge isodose angle, wedging only slightly improves or sometimes moderately decreases the homogeneity of the dose in the target volume. According to these small and/or controversial effects of wedges their application seems unnecessary and/or non-convenient. Simulations show that extreme care is needed in positioning the isocentre: an accuracy of +/- 3 mm is required in the median sagittal plane.

Cobalt Radioisotopes↗
PubMed1990

[Psychosocial factors of participation in HIV testing].

The relevance of the attitude toward the HIV test, the subjectively perceived infection risk, the expected consequences of testing, and the perceived reference group influences for HIV antibody testing is studied. 211 persons, who were tested for AIDS in an AIDS consulting institution, and 86 controls, who had not been tested, participated in the study. The significance of the results for AIDS prevention is discussed.

AIDS Serodiagnosis↗
PubMed1989

Measured attenuation correction methods.

Accurate attenuation correction is a prerequisite for the determination of exact local radioactivity concentrations in positron emission tomography. Attenuation correction factors range from 4-5 in brain studies to 50-100 in whole body measurements. This report gives an overview of the different methods of determining the attenuation correction factors by transmission measurements using an external positron emitting source. The long-lived generator nuclide 68Ge/68Ga is commonly used for this purpose. The additional patient dose from the transmission source is usually a small fraction of the dose due to the subsequent emission measurement. Ring-shaped transmission sources as well as rotating point or line sources are employed in modern positron tomographs. By masking a rotating line or point source, random and scattered events in the transmission scans can be effectively suppressed. The problems of measured attenuation correction are discussed: transmission/emission mismatch, random and scattered event contamination, counting statistics, transmission/emission scatter compensation, transmission scan after administration of activity to the patient. By using a double masking technique simultaneous emission and transmission scans become feasible.

Humans↗
PubMed1979

Calculation of residence time distributions of intravascular radioactive tracers in fields of external registration.

Because of the physiological significance of the mean velocity of blood flow, indicator dispersion models are of special interest and possess practical relevance, if biological and extraneous variables can be altered. The variables being considered are flow characteristics of the streaming blood, tracer distribution at the entrance into the flow system, and the area in which impulses are collected to form the time-activity curve. Using a simplified version of the general convective diffusion equation (diffusion model) in which the diffusion constant D includes all propagation and mixing of the tracer, a simple numerical method can be applied. The method is used to determine influences of injection and changed regions of interest on the time-activity curve and the following parameters: appearance times, peak times, mean circulation times, and the times of the first inflection points. For this purpose, the range of D was determined in 14 patients by applying experimental data to the model. The calculations on the variables show, that the advantage of this method is its applicability to any experimental case by simply adapting the input data to the recordings.

Blood Circulation↗
PubMed1977

[Automated method of determining blood circulation time in nuclear medicine cardiology].

In this paper a method of computer-assisted evaluation of circulation times using a scintillation camera is described. Eight segments of the central circulation are defined on a graphic display unit. Then the analysis of time-activity curves and the normalization of circulation times to hear rate is performed. The automatic analysis is based upon the hydrodynamic meaning of the first inflection point of a time-activity curve. The differences between inflection points are nearly identical with appearance time differences under the experimental conditions used in 131 cases. A mathematical model is presented to defined the conditions for this behaviour and to explain some deviations observed if time differences exceeded a certain value. It can be shown that the method described is largely independent of extraneous influences. It offers haemodynamically relevant parameters that correspond to the minimal cardiac transit times.

Blood Circulation Time↗
PubMed1976

[Clinical significance of kidney imaging in bone scintigraphy].

The results of the examination of 62 patients who had undergone skeletal scintigraphy with 18-F and a urologic examination, were evaluated to determine whether the 18-F incorporation in the kidneys might indicate the presence of renal disease. Patients with and without renal disease demonstrated a similar 18-F incorporation in the kidneys. Our data indicate that a side different 18-F renal activity is without clinical significance.

Bone Diseases↗
PubMed1975

[Three-stage method in lung scintigraphy: ventilation, diffusion and perfusion (author's transl)].

A combination of three stages--ventilation, "perfusion" and diffusion-- has proved to be the optimal method in the scientigraphic exmaination of the lung. 85mCrypton is preferred for ventilation studies compared with 133Xenon, in view of its more suitable radiation energy and lower solubility. In the pre and post-operative investigation of the lungs, ventilation estimations are essential, providing a more reliable perameter than "perfusion estimations". The results from "perfusion" measurements with MAA or microspheres frequently do not correspond with those obtained by 133Xenon. It is still debatable whether the use of MAA or microspheres provide perfusion values and it would be better at present to speak of MAA fixation results.

Adult↗