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Biomedical subjects

J Persliden

Publications and source records attributed to J Persliden.

At least 37 records · Page 2Linked to original sources
PubMed1996

Transmission ionization chambers for measurements of air collision kerma integrated over beam area. Factors limiting the accuracy of calibration.

Kerma-area product meters (KAP meters) are frequently used in diagnostic radiology to measure the integral of air-collision kerma over an area A (integral of A Kc,air dA) perpendicular to the x-ray beam. In this work, a precise method for calibrating a KAP meter to measure integral of A Kc,air dA is described and calibration factors determined for a broad range of tube potentials (40-200 kV). The integral is determined using a large number of TL dosimeters spread over and outside the nominal field area defined as the area within 50% of maximum Kc,air. The method is compared to a simplified calibration method which approximates the integral by multiplying the kerma in the centre of the field by the nominal field area Anom. While the calibration factor using the precise method is independent of field area and distance from the source, that using the simplified method depends on both. This can be accounted for by field inhomogeneities caused by the heel effect, extrafocal radiation and scattered radiation from the KAP meter. The deviations between the calibration factors were as large as +/- 15% for collimator apertures of 5-100 cm2 and distances from the source of 50-160 cm. The uncertainty in the calibration factor using the precise method was carefully evaluated and the expanded relative uncertainty estimated to be +/- 3% with a confidence level of 95%.

Equipment Design↗
PubMed1996

Radiation dose at small intestinal biopsies in children: results of a national study.

The radiation dose delivered at small intestinal biopsies in children was investigated in a national study engaging 42 of 43 paediatric departments performing small intestinal biopsies. Measurements were performed with a thermoluminescence system at 257 biopsies. The results show a considerable variation of both duration of fluoroscopy (range 2-660 s; department medians) and radiation dose (range 0.1-14 mSv; department medians). The median of all absorbed doses was 0.69 mSv and the median duration of fluoroscopy 30 s. The observed variation cannot be explained by differences in X-ray equipment only. By optimization of all the technical conditions, such as X-ray equipment, biopsy device and method of sedation, at least a 6-fold reduction of radiation dose was obtained in one department. Especially if the operator is less experienced, it is worthwhile to optimize other factors to achieve the lowest possible radiation dose to the child. Children, coeliac disease, fluoroscopy, radiation dose, radiation risk, small intestinal biopsy.

Adolescent↗
PubMed1996

The morphology of ligament insertions after failure at low strain velocity: an evaluation of ligament entheses in the rabbit knee.

The morphology of failed rabbit knee entheses is described after in vitro load to failure testing at low strain velocity. Avulsion fracture was the dominant failure mode both for the cruciate ligaments and the medial collateral ligament. The patellar ligament became avulsed in most cases from the patellar insertion. The ligamentous anterior attachment of the medial meniscus failed by a midsubstance rupture and the posterior fibrocartilaginous attachment by a rupture near to the meniscal horn. On histological inspection the failure characteristics usually appeared more elaborate, involving to different degrees all portions of the bone-ligament-bone complexes. Avulsion fracture through subchondral bone was often combined with a partial ligament midsubstance rupture. In few cases avulsion from the cement line was combined with a rupture between the uncalcified fibrocartilage and the ligament. The medial collateral ligament failed in one case entirely at the cement line of its femoral insertion. Horizontal rupture through the calcified fibrocartilage and a vertical cleavage crossing the tidemark were also observed. The superficial portion of the patellar ligament failed with a midsubstance rupture, and the deeper part with an avulsion through the calcified fibrocartilage or an avulsion fracture. The complex failure characteristics may be attributed to uneven loading, nonuniformity of the structure, and specific anatomical location. Subchondral bone beneath femoral and tibial insertions seems to be weaker than the transitional zone between soft tissue and hard bone at the enthesis. The overall inferior structural quality of a ruptured ligament has to be taken into account when parts of the original structure are used for suturing or reconstruction.

Animals↗
PubMed1995

Transient local presence of nerve fibers at onset of secondary ossification in the rat knee joint.

In view of recent evidence that nerves may be involved in bone formation, the present study examines the local occurrence of axons at the onset of secondary ossification center formation in the knee region of developing rats. Radiographic and histological examination showed that secondary ossification center formation commenced at day 10. At day 15 the epiphyseal ossification had reached a relatively mature state. As seen by light microscopy, cartilage canals first appeared at day 5, reaching the epiphyseal center by day 9. Axons exhibiting a neurofilament-like immunoreactivity emerged from the perichondrial plexa into the cartilage canals. Many calcitonin gene-related peptide (CGRP)-immunoreactive axons were found in the canals, as well as in the perichondrium. Axons with tyrosine hydroxylase-like immunoreactivity were not found in the canals, but such fibers occurred in relation to blood vessels at other sites. The canal-related axons disappeared between days 13 and 15, and the canals themselves did not persist beyond bone formation. As seen in the electron microscope, an individual canal contained 3-10 unmyelinated Schwann cell-enclosed axons with diameters of 0.1-2.0 microM. These observations show that putative sensory unmyelinated axons with CGRP-and SP-like immunoreactivity are transiently present during initiation of bone formation in developing epiphyses. Whether there is a causal relation between transient innervation and osteogenesis remains to be determined.

Animals↗
PubMed1995

Delivery and retention of an insulin aerosol produced by a new jet nebulizer.

UNLABELLED: This study describes the delivery and distribution of an aerosol generated by a jet nebulizer (MAXIN) in an experimental animal model. Anesthetised, intubated and ventilated piglets inhaled radiolabeled technetium diethylene-triamine-penta-acetic acid (99mTc-DTPA) through the endotracheal tube. The lungs were excised en bloc and scintigraphed, using a computerized gamma camera to evaluate the pattern of distribution. By nebulizing radiolabeled 125I-insulin and comparing the activity deposited on inspiratory and expiratory electrostatic filters, delivery and retention of nebulized insulin was assessed. The distribution of aerosol in the lungs was very even and reached the most peripheral parts. The delivery of nebulized insulin was calculated to be 88.9 +/- 5.3% and 36.1 +/- 8.8% of the insulin delivered to the respiratory tract was retained. The immediate local effects of insulin aerosol administration on the lungs were evaluated using light microscopy. No adverse effects were observed at histopathologic examination of the lung tissue. CONCLUSION: This study shows a high penetration of aerosol to the peripheral parts of the lung and efficient delivery of nebulized insulin when using the MAXIN-nebulizer.

Aerosols↗
PubMed1995

AMBER chest radiography and patient dose measurements.

PURPOSE: Improved chest imaging has been reported with the usage of AMBER (advanced multiple-beam equalization radiography) equipment but with a higher patient radiation dose compared with conventional chest radiography. Most studies, however, describe dose measurements from phantoms. This study presents a comparison of radiation dose measurements in 57 patients for p.a. projections from an AMBER unit with and without an extra Cu filtration and from a formerly used conventional Siemens chest stand. MATERIAL AND METHODS: Dose measurements were performed with thermoluminescence dosimetry. Entrance surface doses were recorded from 5 dosimeters, placed on the patient's back. Four were placed over the upper and lower lung fields, respectively, and 1 over the mediastinal area. The dose values were then compared with the values obtained from the conventional chest stand and from the measurements with the extra filtration on the AMBER system. RESULTS: The mean entrance dose for the mediastinal area was 0.25 mSv (range 0.15-0.49). With the extra Cu filtration it was 0.16 mSv (0.07-0.29). For the lung fields the values were 0.19 mSv (0.07-0.44) and 0.10 mSv (0.02-0.31), respectively. For the conventional chest stand the entrance dose to the patient was 0.23 mSv. CONCLUSION: AMBER entrance surface doses for the p.a. projection without extra Cu filtration were comparable to the doses obtained with the formerly conventional Siemens chest stand and were well within European recommendations. With extra Cu filtration the AMBER entrance surface doses were reduced by a factor of almost 2.

Adult↗
PubMed1994

A Monte Carlo program for the calculation of contrast, noise and absorbed dose in diagnostic radiology.

A Monte Carlo computer program has been developed for the simulation of X-ray photon transport in diagnostic X-ray examinations. The simulation takes account of the incident photon energy spectrum and includes a phantom (representing the patient), an anti-scatter grid and an image receptor. The primary objective for developing the program was to study and optimise the design of anti-scatter grids. The program estimates image quality in terms of contrast and signal-to-noise ratio, and radiation risk in terms of mean absorbed dose in the patient. It therefore serves as a tool for the optimisation of the radiographic procedure. A description is given of the program and the variance-reduction techniques used. The computational method was validated by comparison with measurements and other Monte Carlo simulations.

Computer Simulation↗
PubMed1994

A Monte Carlo study of grid performance in diagnostic radiology: task-dependent optimization for digital imaging.

A Monte Carlo computational model has been used to optimize grid design in digital radiography. The optimization strategy involved finding grid designs that, for a constant signal-to-noise ratio, resulted in the lowest mean absorbed dose in the patient. Different examinations were simulated to explore the dependence of the optimal scatter-rejection technique on the imaging situation. A large range of grid designs was studied, including grids with both aluminium and fibre interspaces and covers, and compared to a 20 cm air gap. The results show that the optimal tube potential in each examination does not depend strongly on the scatter-rejection technique. There is a significant dose reduction associated with the use of fibre-interspaced grids, particularly in paediatric radiography. The optimal grid ratio and strip width increase with increasing scattering volume. With increasing strip density, the optimal strip width decreases, and the optimal grid ratio increases. Optimal grid ratios are higher than those used today, particularly for grids with large strip density. It is, however, possible to identify grids of good performance for a range of strip densities and grid ratios provided the strip width is selected accordingly. The computational method has been validated by comparison with measurements with a caesium iodide image receptor.

Algorithms↗
PubMed1994

Monte Carlo study of grid performance in diagnostic radiology: task dependent optimization for screen-film imaging.

An optimization of anti-scatter grid design using Monte Carlo techniques in diagnostic radiology is presented. The criterion for optimization was to find the combinations of the grid parameters (lead strip width, grid ratio and strip density) and tube potential which result in the lowest mean absorbed dose in the patient at fixed image contrast. The optimization was performed in three irradiation geometries, representing different scattering conditions (paediatric examinations, and two adult lumbar spine examinations) and was restricted to grids using fibre materials in covers and interspaces. Grid designs currently available were studied, as were designs which use thinner strips (< 30 microns) and higher grid ratios (> 18). It was found that grids with widely different strip densities (strips cm-1) and grid ratios can have good performance provided that they are used with appropriate strip width and tube potential. With increasing amounts of scatter, the optimal grid requires thicker strips and higher grid ratios. Increasing the strip density and using thinner strips and higher grid ratios are generally required. Grids with low strip density (25 strips cm-1) were found to be less sensitive to alterations in strip width. Optimal grids for paediatric radiology require thinner strips (10-20 microns) than those in currently available grids. Grids on the market are best suited for examinations of the adult body in anteroposterior (AP) view. In the adult lateral view, representing the largest scattering volume, higher grid ratios (> 18) than those in existing grids would be optimal. Examples of good grid designs are given for each examination.

Adult↗
PubMed1993

Small intestinal biopsy in children with coeliac disease: measurement of radiation dose and analysis of risk.

To verify the diagnosis of coeliac disease in childhood, three consecutive small intestinal biopsies are performed under fluoroscopic control. To assess the amount of radiation dose absorbed during biopsy, dose measurements were performed both in patients and in a phantom model. These measurements were used for a theoretical assessment of cancer risk and shortening of life due to radiation exposure. The cancer excess lifetime mortality risk (CELMR) was 0.001, i.e. 1 case per 1000 children with a diagnosis of coeliac disease. The loss of life expectancy after three small intestinal biopsies in childhood was approximately 15% of the risk due to lifetime exposure to natural background radiation. These results should be compared with the reported increased risk of malignancy for undiagnosed coeliac disease in adult age. Although the excess risk of the biopsies was small, all efforts should be made to use a technique and equipment giving the least radiation dose.

Biopsy↗
PubMed1993

Selection of anti-scatter grids for different imaging tasks: the advantage of low atomic number cover and interspace materials.

A Monte Carlo computer program has been developed for the study of anti-scatter grids used in diagnostic radiology. The program estimates the scatter from soft tissue phantoms representative of either adult or paediatric examinations and uses dose increase, signal-to-noise ratio improvement and contrast improvement factors to study grid performance. It has been used to quantify the advantage of replacing grids with aluminium covers and interspaces by grids using materials of low atomic number for these components. Two approaches are used. First, the aluminium and low atomic number alternatives are compared for five grid ratios at fixed strip density and width and for tube potentials of 50, 70, 100 and 150 kV. Second, 44 commercially available grids are compared for three different imaging situations (lumbar spine, chest and paediatric). The results demonstrate that grids made with carbon fibre cover and cotton fibre interspace result in greater improvements in contrast and signal-to-noise ratio, and lower dose increase factors, than do grids made with aluminium. The dose reduction varies with irradiation conditions and is generally larger at lower tube potentials, higher grid ratios and lower strip densities. A typical reduction in mean absorbed dose in the patient is 30% in an adult lumbar spine (AP view) at 70 kV with a grid with 36 strips per centimetre and ratio 12.

Adult↗
PubMed1993

Monte Carlo study of grid performance in diagnostic radiology: factors which affect the selection of tube potential and grid ratio.

A Monte Carlo computational model has been developed for the study of the performance of anti-scatter grids in diagnostic radiology. It is used here to estimate the scatter in the image plane from soft tissue phantoms (representing the patient) and to calculate image contrast and the mean absorbed dose in the phantom. Different scattering conditions, representative of various examinations, have been investigated: adult lumbar spine; small field radiography and fluoroscopy; adult chest and paediatric pelvis and chest. For each scattering condition, the combinations of tube potential and grid ratio have been found which, for a well designed grid, result in the lowest mean absorbed dose in the phantom for a fixed contrast level. In examinations which generate large amounts of scatter, the use of high grid ratios in combination with high tube potentials is favourable with regard to both mean absorbed dose in the phantom and tube charge. When less scatter is generated, either the grid ratio or the tube potential can be varied to achieve the desired contrast level. High grid ratios require shorter exposure times, but need careful alignment in the beam to prevent primary radiation cut-off. It is shown that the air gap technique can be used to reduce patient dose in examinations with small amounts of scatter, but in combinations with a lower tube potential than when a grid is used.

Adult↗
PubMed1993

Comparison of image quality and mean absorbed dose to the breast for two mammographic films.

A film intended for mammography (Kodak SO 155 MRH-1) was tested and compared to one (Kodak SO 177 Ortho M) used earlier. Both films including the cassette could resolve 20 lp/mm. For a processing time of 90 s the new film gave the same overall image quality and irradiation dose to the breast as the old system. If, instead, the processing time was increased to 150 s, a 43% reduction in kerma could be attained with the new film. With a developing temperature of 36 degrees C and 150 s processing time, the noise is clinically acceptable. A nonparametric test showed no significant difference between the 2 films on the 0.01 level. At an X-ray tube potential difference of 25 kV, the mean absorbed dose to a 4.5-cm-thick breast was reduced from 1.7 mGy with the old combination to 1.0 mGy with the new one. The measurements were made with a moving grid.

Humans↗
PubMed1993

Conversion factors between energy imparted to the patient and air collision kerma integrated over beam area in pediatric radiology.

Conversion factors between the energy imparted to the patient in pediatric radiography and air collision kerma integrated over beam area are presented. The values have been derived from Monte Carlo calculations in soft tissue phantoms and extend results published earlier to cover children from early infancy to the age of 15 years. Variations related to phantom size as well as to focus-phantom distance, radiation field size, orientation of view (a.p., lateral), tube potential, and beam filtration are given. We show that the conversion factor increases with increasing half-value layer of the X-ray beam and the anterioposterior width of the simulated child. Increasing the focus-phantom distance increases the conversion factor, while increasing the field size decreases the factors due to more scattered radiation escaping laterally from the phantom.

Adolescent↗
PubMed1992

Calculation of dose and contrast for two mammographic grids.

To aid in selecting optimal conditions for screening mammography practice in Sweden, the performance of two mammographic grids (one moving and one stationary) has been investigated. Monte Carlo techniques were used to simulate photon transport in the breast. Transport through the breast support, grid covers, grid and image receptor (33.9 mg cm-2 Gd2O2S) was treated analytically. The contrast of a 100 microns calcification has been evaluated for three tissue compositions (adipose, glandular, 50:50 fractions by weight of adipose and glandular tissue) as a function of breast thickness (2-8 cm) and potential difference (25-30 kV, Mo anode). Contrast for a 5 cm 'average' breast at 28 kV was improved by 40% using the moving grid and by 30% using the stationary one; the corresponding increases in breast absorbed dose, keeping the energy imparted to the image receptor constant, were 90% and 150%, respectively. The superior properties of the moving grid were due to (i) equal scatter rejection ability and higher transmission of primary photons yielding lower scatter-to-primary ratios behind the grid, and (ii) less attenuation and filtering of the primary photons in the interspace material yielding lower degradation of primary contrast.

Breast Neoplasms↗
PubMed1992

Monte Carlo simulation of multiple scattering in Compton spectroscopy.

The Compton scattered photons from a scattering medium can be analyzed in a Compton spectrometer and the primary energy spectrum derived using the Compton equation. Since the reconstruction algorithm assumes that only singly-scattered photons from the scatterer are detected, multiply-scattered photons introduce errors into the measurements unless they can be accurately corrected for. In this work, a Monte Carlo collision density estimator was used to determine the contribution from photons multiply-scattered from a Lucite scatterer in the form of a square rod. The ratio of multiply- to singly-scattered photons was determined for rod thicknesses from 0.5 to 5 mm and photons of energy 20 to 110 keV. The ratio in percent can be well approximated as a linear function of energy with slope 2.2. For thicknesses below 2 mm, the ratio is less than 5% at all energies.

Monte Carlo Method↗
PubMed1987

Effects of thyroid stimulating immunoglobulin on function and morphology of xenotransplanted toxic diffuse, toxic nodular and normal thyroid tissue.

In order to examine the properties of human thyroid tissue, toxic diffuse goiter (TDG), toxic nodular goiter (TNG) and normal thyroid tissue were transplanted to nude mice. Starting 3 and 10 weeks after the transplantation the mice were given 14 daily injections of control serum or serum containing thyroid stimulating immunoglobulin (TSI). The uptake and release of 125I were repeatedly measured externally. The uptake and unstimulated release of 125I was lowest in TDG transplants, highest in TNG transplants, and intermediate in transplants of normal thyroid tissue. The findings were similar at both 3 and 10 weeks. Injections of TSI reduced the biological half-time of the tracer in TDG and normal transplants, but had no significant effect on TNG transplants. Light and electron microscopic studies showed that hyperplastic TDG tissue underwent involution after transplantation, whereas TNG and normal thyroid tissue remained unchanged. Injection of TSI reactivated TDG tissue; morphometry showed that the absolute and relative volumes of the follicle cells were more than doubled, with a corresponding decrease in the volume of the follicle lumen, and mitotic figures were common. Similar findings were seen in normal transplants, whereas the effect of TSI on TNG tissue was less pronounced. In summary, our observations show that serum from a patient with Graves' disease stimulated iodine release and induced follicle cell hyperplasia and probably also follicle cell multiplication in transplanted normal and TDG tissue, but had a lesser effect on TNG tissue.

Animals↗