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Biomedical subjects

G Wickman

Publications and source records attributed to G Wickman.

33 records · Page 2Linked to original sources
PubMed1978

Mean energy imparted in relation to the focus to object distance.

The relationship between the energy absorbed by the patient at the exposure of a radiographic image and the focus to object distance is analysed. It is found that the mean energy imparted, or the integral absorbed dose, is the same irrespective of the focus to object distance when the energy fluence and the field size are both normalized at the film plane. When the field size is kept constant within the object whilst the focus to object distance is varied a limited increase in the mean energy imparted occurs when the focus to object distance is decreased; this statement is valid for the focus to object distances which are usually applied in diagnostic radiology. When estimating radiation risks the importance of the focus to object distance is found to be of limited interest.

Absorption↗
PubMed1978

Elliptical narrow beam rotation radiography.

The basic mathematics for elliptical narrow beam rotation radiography are deduced and exemplified. An analysis of the functioning principle of elliptical systems shows that the essential factor in the image formation is the form of the evolute of the ellipse, which determines the projection of the object. The image layer does not necessarily coincide with the ellipse.

Health Physics↗
PubMed1977

Blurring and layer thickness in narrow beam rotation radiography.

The definition of the blurring of narrow beam rotation radiography is revived. The relative value of the blurring is considered to be the most reliable measurement. Calculations of the layer thickness should be based on the definition of the relative blurring. Experimental tests were performed, which confirm the mathematically presented hypothesis and also confirm the validity of the mathematical model of narrow beam rotation radiography presented by WELANDER (1974).

Mathematics↗
PubMed1976

Experimental evaluation of tube potential and contrast medium concentration for cholangiography.

Model cholangiographic experiments were performed in which the relationship between contrast medium concentration, duct diameter, calculus size and tube potential was analysed. The same degree of diagnostic reliability was obtained by increasing the tube potential as by diluting the contrast medium. A tube potential of 100 to 110 kV and a contrast medium concentration of 45 per cent were found to give the best result if the background density of the film was held constant.

Bile Ducts↗
PubMed1976

Absorbed dose in mammary radiography.

By exposure measurements in an alcohol-water mixture simulating breast tissue, the absorbed dose, and dose distribution in the breast at the radiation qualities commonly used in mammary radiography have been calculated. The absorbed doses for different recording media have been compared at those radiation qualities which result in similar image qualities in the different recording media.

Ethanol↗
PubMedDate not supplied

Low field (0.02 T) MR imaging of the whole body.

The diagnostic utility of extremely low field magnetic resonance (MR) (0.02 T) was evaluated in various parts of the body outside the head. The areas investigated included the spine (104 patients), kidneys (19 patients), female pelvis (21 patients), and hips (15 patients). The results were compared with those of other imaging modalities, e.g., ultrasound, CT, and scintigraphy. Available pulse sequences and typical examination times for different types of studies are reported. Poor spatial resolution and long imaging times limit the application of this technique to the whole body. Due to poor signal-to-noise ratio, image quality is not comparable with that obtained at higher field strengths. In spite of these restrictions it was possible to demonstrate lumbar disk herniations, to differentiate renal and ovarian cysts from tumors, and to detect early avascular necrosis of the femoral head. Extremely low field MR imaging may eventually be used in screening spinal pathology and in the diagnosis of early avascular necrosis of the femoral head. At present, this technique can not replace ultrasound or CT in abdominal examinations.

Adolescent↗
PubMedDate not supplied

Polarity effect in plane-parallel ionization chambers using air or a dielectric liquid as ionization medium.

A plane-parallel ionization chamber having a sensitive volume of 2 mm3 and using the dielectric liquid tetramethylsilane as the sensitive medium instead of air is described. In the design of the chamber special attention was given to the factors that can cause unwanted currents in the cable, stem, or the chamber dielectric material. The chamber has been tested with respect to the polarity effect in regions of radiation fields where ordinary plane-parallel ionization chambers will often fail. These regions are the build-up region in photon fields, and the region close to the practical range for electrons where nonelectronic equilibrium is significant. Experimental results show that, despite the extremely small ionization volume in the liquid ionization chamber, the polarity effect never exceeds a few tenths of a percent in field positions where well-known commercially available chambers with much less spatial resolution designed for measurements in radiation therapy fields can show polarity effects of 5% to 30%. The origin of spurious currents and how they must be minimized in the design of either a liquid- or gas-filled ionization chamber is discussed.

Electrons↗
PubMedDate not supplied

Low dose pelvimetry with biplane digital radiography.

The digital moving slit technique as used by most CT scanners for overview images, was used for antero-posterior and lateral views of the pelvis for pelvimetry. The method was evaluated in phantom experiments and clinical examinations were performed in 23 patients. The method was compared with conventional pelvimetry in 14 patients. Estimated ovarian dose was reduced by a factor of 14.2. The discrepancy in measurements of the pelvic diameters by computed tomography compared with conventional pelvimetry was considered to be without practical importance from an obstetric point of view. Digital pelvimetry is easier for the patient, faster and the need for repeated exposures is eliminated. Based on these facts it is suggested that digital pelvimetry should replace the conventional method whenever possible.

Female↗
PubMedDate not supplied

Magnetic resonance imaging of renal masses at 0.02 tesla.

To determine the usefulness of extremely low field magnetic resonance imaging (MRI) in the evaluation of renal masses 19 patients with 15 tumors (13 renal and 2 renal pelvic carcinomas) and 8 cysts were examined in a 0.02 tesla MRI unit. The findings were compared with results of computed tomography (CT) and ultrasound. Cavography was performed in 6 patients. MRI enabled differentiation between cysts and solid tumors. Tumor extension into the inferior vena cava could be demonstrated in one case and liver metastases in two patients. The image quality was inferior to that reported at higher field strengths and the tumors were more precisely staged by CT and ultrasound. At present, it is unlikely that low field MRI will play any substantial role in the evaluation of renal masses.

Carcinoma, Renal Cell↗