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J Bojsen

Publications and source records attributed to J Bojsen.

At least 19 recordsLinked to original sources
PubMed1993

A semiconductor silicon PIN diode matrix detector for measurement of 133Xe washout in small regional skin areas.

Local variations in microvascularization are expected in lesions and lesion-free skin of patients with pressure sores. To investigate these variations, methods for studies of the regional blood flow rate within small skin areas are needed. Regional blood flow can be estimated by measuring the washout of 133Xe from the tissue. This study describes a 2 x 12 Si PIN diode matrix detector capable of 133Xe detection, and equipped with a collimator to improve the spatial resolution. Thus the regional blood flow in subcutaneous skin areas down to about 2 cm2 can be investigated when the atraumatic epicutaneous labelling technique is used. The capability of the matrix detector and its collimator is described by laboratory investigations. In pilot investigations three normal subjects and three paraplegics with pressure sores were studied. In each individual study the detector matrix was divided into six square areas containing four diode detectors each. Thus six 133Xe disappearance rate constants from adjacent subcutaneous tissue could be determined simultaneously.

Female↗
PubMed1992

A miniature silicon diode matrix detector for in vivo measurement of 133Xe disappearance following local tissue injection.

A variety of biological processes can be studied from the washout of compounds labelled with a gamma emitter. Conventional systems for measurement of gamma radiation can detect count rates at both the low and high energy range of the indicator in question, 133Xe. However, silicon (Si) photodiodes have the capability of measuring the lowest energies (25-40 keV) of gamma and x-ray emitters with sufficient efficiency when applied on the skin surface and close to the indicator depot. The purpose of the present study was firstly to evaluate a portable Si photodiode matrix detector system, composed of 16 photodiodes, for in vivo measurement of disappearance rate constants of 133Xe following injection into subcutaneous (SC) or skeletal muscle (SM) tissues as compared with a stationary sodium iodide single crystal detector. Secondly, from these results, to evaluate the contribution from intra-tissue indicator diffusion and indicate means of avoiding influence from local diffusion in the washout curve of 133Xe. From the recorded 133Xe distribution in the depot proper, Si photodiodes in the matrix were selected for calculation of the washout. The Si matrix detector was reliable with a constant linearity and sensitivity within the range 20-38 degrees C and calibrated to +/- 1% between diodes. The in vivo investigations comprised two SC injections on humans with four measuring periods for comparison, and four SC and five SM injections on dogs, resulting in eight and five measuring periods for comparison. Only when the results obtained from the Si photodiodes at the position just above the count rate maximum were selected, was the contribution from diffusion significant. The ability to detect geometry changes is advantageous in studies with potential motion artefacts, such as during exercise.

Americium↗
PubMed1992

Miniature silicon diode matrix-detector for in vivo measurement of 133xenon disappearance in the canine myocardium following local tissue injection.

After local tissue depositioning of 133Xenon (133Xe) the regional washout is usually registered by a NaI(Tl) detector. The residual radioactivity of 133Xe is usually measured at its 81 keV photopeak. However, using small Silicon (Si) photodiodes it is feasible to measure only the low-energy activity in the X-ray energy range. In the myocardium of open chest dogs 133Xe washout measurements by a matrix of Si diodes composed in a 4 x 4 array and a conventional NaI(Tl) detector were carried out simultaneously. Fourteen separate pairs of measurements were performed in 3 dogs. When the Si-diodes in the matrix were selected individually in accordance to the position with reference to the diode with maximum count rate or pooled, comparisons could be made between the corresponding washout rate constants measured by the reference detector. In the correlation between the rate constants the intercepts with the y axis were not significantly different from zero allowing the correlation lines to be fitted through (0.0). The slope of the correlation line was close to unity. The registration of the low-X-ray energy of 133Xe by the Si-detectors is an alternative to the conventional high energy activity recording appearing from the gamma-energy of the photopeak. The detector matrix concept allows elimination of motion artefacts and indicator distribution in the myocardial tissue. Due to the uniformity and low cost of Si-diodes the perspective may be the introduction as a disposable transducer useful during cardiac surgery for example.

Animals↗
PubMed1986

Local variation in cutaneous and subcutaneous blood flow measured by CdTe(C1) minidetectors in normal and psoriatic skin.

The accuracy of the 133Xe washout method and the validity of newly developed cadmium telluride CdTe(Cl) minisemiconductor detectors were estimated by performing comparative, simultaneous measurements of both cutaneous (CBF) and subcutaneous (SBF) blood flow using 2 conventional scintillation sodium iodide NaI(Tl) and CdTe(Cl) detectors over the same radioactive depot in each of 10 individuals. The accuracy of the 133Xe washout method was found to be 13-15% (C.V.) for the CBF measurements and 9-12% (C.V.) for the SBF measurements. The CdTe(Cl) detectors, which have a weight of 20 g and were attached directly over the radioactive depot, may replace stationary NaI(Tl) detectors placed 20 cm from the depot for measurements of both CBF and SBF. Two CdTe(Cl) detectors were used for estimations of the local variation in CBF and SBF within a distance of 5 cm in normal skin of 10 individuals. The C.V. was 7% for the CBF measurements and 18% for the SBF measurements. Measurements of CBF and SBF were performed in 6 psoriatic patients who, after about 1 week of antipsoriatic treatment with beech tar, developed typical Woronoff rings. The local CBF differed significantly from the center of psoriatic plaques to the margin, in the Woronoff ring, and in nonlesional skin. In contrast, SBF was remarkably equal within the plaque and in the Woronoff ring. The color of the Woronoff ring cannot be ascribed to a local cutaneous vasoconstriction. Cutaneous blood flow in chronic stable, lesional psoriatic skin was significantly lower than previously published values for active lesional psoriatic skin, but significantly higher than CBF in normal individuals. Measurements of CBF in tetrahydrofurfuryl nicotinic acid (Trafuril)-treated skin showed higher values than measurements of CBF in the postischemic hyperemia period both in normal and in lesional psoriatic skin. Trafuril induced a significant increase of CBF in both lesional and nonlesional skin. The high CBF rates in lesional psoriatic skin are not due to a maximally, passively dilated vascular bed.

Adult↗
PubMed1984

Portable detectors for 125I-insulin absorption measurement during subcutaneous infusion with portable pumps.

Programmed subcutaneous insulin infusion is a promising method for normalisation of the blood glucose concentration in insulin-dependent diabetics. To evaluate insulin availability the absorption rate from the depot is usually measured intermittently by radioactively-labelled insulin and stationary scintillation detectors. Small portable detectors are an alternative, however, and continuous absorption measurements could be made during normal life conditions. Contrary to conventional single injection therapy, the insulin depot initially expands during infusion treatment, changing the geometry during measurements. In the present study the methodological aspects and geometrical dependences were investigated. Simulated studies were made with various plane disc 125I sources in Perspex phantoms as well as 125I-insulin absorption studies in short-term subcutaneous infusion experiments with anaesthetised rabbits. Results from portable, end-window Geiger-Müller (GM) detectors fixed above the depots and close to the surfaces of phantom or skin were compared with results obtained by a conventional stationary NaI(Tl) detector 15 cm from the phantom or skin surface. With a 125I-insulin infusion site at 5 mm depth in the subcutaneous tissue of rabbits, an overall linear proportionality was found between the results obtained with a NaI(Tl) detector and a GM detector raised 15 mm above the skin surface inside the detector housing.

Animals↗
PubMed1984

Subcutaneous measurements of 133Xe disappearance with portable CdTe(Cl) detectors: elimination of interference from combined convection and diffusion.

Portable, solid state, cadmium telluride [CdTe(C1)] detectors were used for measurements of 133Xe-disappearance rate constants as a measure of subcutaneous (s.c.) blood flow. To eliminate the disturbance on the measurements from combined local convection and diffusion of xenon in the s.c. tissue, two methods were demonstrated to be feasible in both control persons and anaesthetized rabbits. A small volume (50-80 microliters) was injected into the s.c. tissue at a depth of 5 mm and the CdTe(C1) detector elevated 20 mm above the skin surface. In this situation identical disappearance rate constants were recorded by the CdTe(C1) detector and the NaI(T1) reference detector at 15-20 cm from the depot. Similiar results were obtained when either a large volume (greater than or equal to 800 microliters of Xe in humans) was injected into the s.c. tissue or the labelling was performed with a smaller volume in an atraumatic uniform manner to obtain a constant Xe concentration exceeding the field of view of the CdTe(C1) detector, which in these cases was attached directly to the skin surface. The coefficients of variation (CV) of the disappearance rate constants measured by the CdTe(C1) detector were 9% and 11%, and these values did not differ significantly from each other (P greater than 0.2), or from CV-values calculated from measurements with NaI(T1) detectors.

Adolescent↗
PubMed1983

Clinical factors influencing the absorption of 125I-NPH insulin in diabetic patients.

Clinical factors which might influence the absorption of subcutaneously injected 125I-NPH insulin were studied in 101 diabetics. The disappearance curve was monoexponential after a delay period of 1.5 +/- 0.8 h (mean +/- SD). Lipohypertrophy significantly prolonged insulin absorption (half life (T1/2) = 11.2 +/- 3.1 h, p = 0.0001). Low bicarbonate levels increased the absorption (T1/2 3.9 +/- 2.3 h, p less than 0.05). Lean diabetics had a faster absorption (6.2 +/- 1.9 h) than normal weight diabetics (7.5 +/- 2.0 h, p less than 0.02). Sex, age, diabetes duration and injection depth did not influence T1/2. The half life was significantly inversely correlated to the resting subcutaneous blood flow (r = 0.882, p less than 0.01). The overall interindividual coefficient of variation for insulin absorption in nonketotic diabetics was 27.4%. Also considerable intra-patient day-to-day variation was found (24.5%), and between different injection sites (30.2%). These variations emphasize the drawbacks of conventional insulin therapy in the management of insulin-requiring diabetics.

Absorption↗
PubMed1983

Comparison of portable CdTe(Cl) detectors with stationary NaI(Tl) detectors for subcutaneous 133Xe disappearance measurements.

133Xe washout measurements from locally injected depots in the subcutaneous tissue of the thigh have been performed intermittently by a NaI(Tl) detector placed 15 cm from the depot and a cadmium telluride [CdTe(Cl)] detector fixed to the skin surface above the depot. In 19 experiments, the measurements were performed during rest, before and after bicycling and during circulatory arrest during an occlusion cuff pressure of 240-250 mmHg. The disappearance rates measured by the two detector systems showed a linear correlation (r = 0.934, P less than 0.001). However, the rate constants measured by the CdTe(Cl) detector were an average of 1.48 times the values obtained by the NaI(Tl) detector during a period of 1-4 h after the injection. The coefficient of variation of the proportionality factor is 3.3%. Only the central part of the local depot area is exposed to the CdTe(Cl) detector. Using the NaI(Tl) detector and lead shielding of the peripheral or central part of the depot area, it was demonstrated that the disappearance rates obtained reflect the measuring geometries. The correction itself is therefore due to differences in the measuring geometries of the two detector types, and possibly to diffusion and convection of xenon. For quantitative determination of the subcutaneous blood flow, the disappearance rate constants determined by the CdTe(Cl) detector thus have to be corrected by division with the factor 1.48.

Adolescent↗
PubMed1983

The glomerular filtration rate in unrestrained rabbits determined by means of an implanted telemetrical device.

An implanted radio-telemetrical device, which consists of a Geiger-Müller detector, a high voltage supply and a FM transmitter, incapsulated in araldite (weight 130 g) was used to measure the body disappearance rate of 125I-iothalamate following a single i.v. bolus in unrestrained and undisturbed rabbits. The disappearance curve is practically monoexponential from 10 to 60 minutes after administration of the indicator and the disappearance rate constant (Ke) is closely correlated to the "final slope" of the plasma disappearance curve of 125I-iothalamate (kp) r=0.99). A linear correlation was also found between Ke and GFR measured simultaneously by constant infusion clearance technique, using an indicator not detected by the Geiger-Müller detector (51Cr-EDTA) (r=0.98). The ratios between the renal clearances of 125I-iothalamate, 51Cr-EDTA and inulin were determined by constant infusion clearance technique in a separate series of experiments since no data were available in the present literature. The results show that GFR can be determined by means of the telemetrical method and in a series of experiments in undisturbed rabbits GFR was found to be on average 4.7 ml . min-1 . kg-1 (expressed as inulin clearance). Using the same technique in lightly pentobarbital anesthetized rabbits GFR was on average 3.5 ml . min-1 . kg-1.

Animals↗
PubMed1982

Evidence for growth inhibition by platinum electrodes at low current levels.

Platinum is considered to be a noble metal and is often used for electrodes in biological investigations. However, platinum electrodes can form inhibitory compounds, as pointed out by Rosenberg et al. 1965. The aim of this study was to investigate whether platinum electrodes are inert in the extremely low frequency (ELF) range of currents. Human bone marrow cells cultured in agar were used as target cells and were grown under various electrical conditions. A 50% reduction in growth compared with controls was obtained by average currents of 2300 microA at 8 Hz and 110 microA at 80 Hz, the current being derived from a square bipolar voltage waveform. D.c. currents were also inhibitory, with a value of 50% at the 1.4 microA level. The cells were probably not affected directly by the current, since inhibitory properties could be stored in agar and saline and because titanium electrodes at equal current levels did not produce the same effect.

Bone Marrow↗
PubMed1982

Kinetics of subcutaneous NPH insulin in diabetics.

Kinetics of subcutaneous NPH insulin were studied in newly diagnosed insulin-dependent diabetics. Using a biotelemetric technique with small Geiger-Müller detectors applied to the skin surface, the disappearance of 125I-NPH insulin fron subcutis was monoexponential with a mean half-life of 6.6 +/- 3.3 (SD) hr. A model is presented to compare the disappearance rates of subcutaneous 125I-NPH insulin and the calculated plasma appearance insulin curve derived from the actual plasma insulin concentration measurements, assuming a one-compartment model and first-order kinetics. Areas under the absorption- and appearance-time curves calculated from external measurements and from plasma insulin concentrations were identical. There was a strong correlation between plasma concentrations and absorbed amounts of labeled insulin (r = 0.8782, P less than 0.001), as there was between the blood glucose-lowering effects and percent absorbed insulin per hour (r = 0.7659, P less than 0.001). Our results indicate that the disappearance rate of iodine-labeled insulin was a relevant biological expression of insulin absorption from subcutis and a reliable noninvasive method of quantitative determination of insulin concentration in blood.

Absorption↗
PubMed1982

Biotelemetric detection of the disappearance of subcutaneously injected 125I-NPH insulin.

A biotelemetric method with Geiger-Müller (GM) detectors fixed to the skin surface was used for continuous registration of the disappearance rate of subcutaneously injected 125I-NPH insulin. Methodological problems concerning counting geometry were investigated by comparing the disappearance of radioactivity, measured the GM- and NaI-detectors, respectively, and by scanning of the radioactive source. The size and position of the subcutaneous depot was unchanged throughout the study. Movement artifacts could be avoided. The coefficient of variation for distribution of ratios between count rates for GM- and NaI-detectors was 3.0% +/- 1.1 (SD) (range 0.9-4.0%) over periods of 24 h. It is concluded that the biotelemetry technique proved to be a clinically useful procedure for insulin absorption studies.

Adult↗
PubMed1982

Biotelemetry in local clearance studies with radionuclides using cadmium telluride detectors.

Small, gamma-sensitive, cadmium-telluride [CdTe(C1)] detectors are evaluated for biotelemetry of the local clearance of an injected radioactive depot in tissue. The lateral displacement dependence and depth dependence are determined with 99mTc as radiation source. Perspex is used as attenuation and scattering medium. With 133Xe injected into subcutaneous tissue the effect of a geometrical adjustment of the CdTe(C1) detector prior to measurement is studied. Examples of 133Xe disappearance curves are shown during rest and ergometry bicycling.

Cadmium↗
PubMed1982

An implantable, externally powered radiotelemetric system for long-term ECG and heart-rate monitoring.

An externally inductive powered implantable ECG radiotelemetry unit has been developed for continuous long-term measurements of cardiophysiological changes following administration of cardiotoxic drugs. The power density distribution (320 kHz) inside the cage has been measured to be 3-11 mW/cm2. The implantable unit has a volume of 38 X 22 X 8 mm and a mass of 9 g, and has been tolerated by the animal (guinea pig) during a continuous registration period of 6 months.

Animals↗
PubMed1981

Determination of 24-hour insulin infusion pattern by an artificial endocrine pancreas for intravenous insulin infusion with a miniature pump.

UNLABELLED: Intravenous insulin infusion with a glucose controlled insulin infusion system (GCIIS) is known to restore glucose homeostasis. A simpler approach to improve blood glucose regulation is preprogrammed intravenous insulin infusion with portable pumps without sensor-mediated feedback. We report a study designed to evaluate whether the preprogrammed insulin infusion pattern to be used in the miniature insulin infusion pump (MIIP) could be optimized by concomitant employment of the GCIIS for blood glucose control. Six juvenile-onset insulin-dependent diabetics (mean age 31 yrs) were studied. Mean blood glucose (MBG) was 6.2 mmol/l +/- 0.5 (SD) during glucose controlled infusion and 5.3 +/- 0.6 during the combined MIIP + GCIIS-day. The insulin requirements calculated from the s.c. regimen (56 U +/- 10 SD) were identical to the GCIIS-measured (51 U +/- 14) and to the amounts delivered during the combined MIIP-GCIIS infusion day (54 U +/- 13). A mean surplus of 3 U was given by the GCIIS. Mean amplitude of glycaemic excursions (MAGE) was 3.0 mmol/l during GCIIS-control, and 3.3 mmol/l during combined infusion. IN CONCLUSION: The GCIIS was found capable of calculating the 24-hour insulin dose in well-known, unstable diabetics; however, it did not improve the preprogrammed insulin infusion profile obtained by the MIIP.

Artificial Organs↗
PubMed1981

Assessment of cadmium telluride detector system for measurement of muscle blood flow during dynamic exercise in man.

We have used a miniature cadmium telluride detector in the assessment of muscle blood flow during dynamic exercise in man following local injection of 133Xenon. The results obtained were compared with those using a conventional sodium iodide detector. There was no significant difference between the results obtained with the two detectors. The reproducibility of results was greater with cadmium telluride than with sodium iodide. The cadmium telluride system has the advantage of being small, lightweight and portable and enables measurements to be made during dynamic exercise.

Cadmium↗
PubMed1981

A mercuric iodide detector unit implantable and externally powered for use in radionuclide tracer studies in small animals.

A small externally powered implantable gamma-radiation detector unit (35 X 12 mm diameter containing a mercuric iodide detector (HgI2), charge amplifier, radiotransmitter and an inductive power supply has been constructed. Since the total weight of the device is 5 g, it is suitable for implantation in laboratory animals such as rats or hamsters. A comparison between the implanted HgI2 detector unit and a conventional stationary 2 X 2 inch NaI(TI) detector has been performed by simultaneous measurements of the 133Xe clearance from a depot. Using 125I-iothalamate a kidney function study of an unrestrained hamster is shown as an example of measurements in the unrestrained animal.

Animals↗