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Biomedical subjects

L Ahlgren

Publications and source records attributed to L Ahlgren.

At least 19 recordsLinked to original sources
PubMed1999

A 252Cf-based instrument for in vivo body protein monitoring in cancer patients.

A hospital-based facility for in vivo prompt gamma neutron activation analysis of nitrogen for body protein determination is described. The patient is laid on a movable couch and is scanned with a vertically collimated neutron beam from a 252Cf neutron source (the amount of Cf varying from 120 to 40 microg due to the physical decay) positioned below the patient. Four large NaI(Tl) detectors are used to measure the 10.8 MeV gamma-rays from nitrogen. To check the long-term stability of the system, a solid phantom simulating the geometry of the adult human trunk, having similar elemental composition as tissue, was constructed. Repeated phantom measurements over 6 months gave a reproducibility in nitrogen determination of 2.9% (1 SD). Duplicate patient measurements carried out within a week showed a reproducibility of 5% (1 SD). A calibration method for absolute protein measurements in patients is presented. Patients are normally measured for 40 min; giving a mean whole-body equivalent dose of 0.25 mSv. Results from measurements on 13 cancer patients are presented.

Adult↗
PubMed1996

Skin plasma exudation and vasodilatation monitored by external detection of conversion electrons.

We have examined the plasma exudation response of inflammation in guinea pig skin by a noninvasive method and have evaluated the influence of vasodilatation. Indium radionuclides have been used to label plasma and blood and conversion electrons have been detected by an external detector. Transferrin (79,600 Da) was labeled by 111In or 113mIn in vivo and red blood cells were labeled by 111In in vitro. These tracers were given to separate groups of anesthetized guinea pigs and baseline activities were recorded from shaved skin surface areas. Skin prick tests with histamine and saline were performed and time-activity curves were recorded. The measurements with 111In-transferrin and 111In-labeled red blood cells demonstrated that histamine produced dose-dependent accumulation of plasma (up to a 6.5-fold increase) and blood (up to a 2.0-fold increase) in the skin. Hence, about one-third of accumulation of plasma induced by histamine may be explained by vasodilatation. With 113mIn-transferrin as plasma tracer greater effects of histamine were recorded, probably reflecting that the measurements also included deeper sections of the skin. We conclude that the intensity of accumulation of plasma in skin inflammation can be monitored by external detection of conversion electrons from 111In- and 113mIn-transferrin, and that the influence of vasodilatation can be estimated by detection of 111In-labeled red blood cells.

Animals↗
PubMed1996

Plasma exudation in the skin measured by external detection of conversion electrons.

A novel technique for measurement of plasma exudation in the skin is described. Transferrin labelled in vivo with indium-113m is used as a plasma tracer. The conversion electrons from 113mIn are detected with a polystyrene crystal mounted on a photomultiplier tube. Owing to the short range of the electrons in tissue, background radiation from tracer circulating in underlying tissue will be very small, allowing plasma exudation in the skin to be detected with a high signal to noise ratio. The characteristics of the detector system are described in model experiments using sheets of mylar to simulate soft tissue. The acute inflammatory response to histamine provocation was studied in guinea pig skin. A dose-related increase in count rate representing vasodilatation and plasma exudation was detected over the skin after histamine provocation. The electron radiation system appears suitable for detection of low levels of superficial radioactivity and for pathophysiological studies of the skin.

Animals↗
PubMed1993

Quantitative bone scintigraphy in prostatic carcinoma--long-term response to treatment.

Quantitative bone scintigraphy was performed in 24 patients with prostatic carcinoma before orchiectomy and up to one to four years after operation. The gamma camera count rate was recorded over the lower thoracic and all lumbar vertebrae 4 h after injection of 99mTc-MDP. Twelve patients had normal bone scintigrams throughout the study. They showed from two years after operation a slight increase in count rate values compared with the preoperative values, probably due to hormonal changes after orchiectomy and to age-related alterations in skeletal metabolism. Twelve patients had abnormal bone scintigrams. They showed as a response to treatment the flare phenomenon with an increase in count rate over the abnormal vertebrae when measured two weeks after operation followed by a decrease after two months. The lowest count rate values were obtained between six months and one year after operation. Thereafter the count rate seemed to remain on the same level. An increase in count rate was connected to progression of disease and the patients died of prostatic carcinoma within one year thereafter.

Acid Phosphatase↗
PubMed1992

Quantitative bone scintigraphy and 24-hour whole-body counting of 99mTc-methylene diphosphonate in patients with prostatic carcinoma.

Thirty-four patients with prostatic carcinoma were studied with quantitative bone scintigraphy and whole-body counting (WBC) 1 and 24 h after injection of 99mTc-MDP before as well as two weeks and two months after orchiectomy. Thirteen of the patients had normal bone scintigrams and WBR at the three different investigations; 21 had skeletal metastases. The latter showed throughout the study higher local gamma camera count rates as well as WBR values than the patients with normal scintigrams. In these patients a "flare phenomenon", with an increase in count rate two weeks after orchiectomy followed by a decrease two months post-operatively, was seen with quantitative bone scintigraphy but not with WBC. However, WBC may be a valuable method indicating the total extent of skeletal metastases in the body, while quantitative bone scintigraphy is more accurate in the interpretation of individual skeletal metastases.

Aged↗
PubMed1991

Absorbed dose to technicians due to induced activity in linear accelerators for radiation therapy.

Absorbed dose to the trunk and to the hands of technicians working with accelerators for radiotherapy have been measured with TL dosimeters for seven different accelerators. The contribution from induced activity in the accelerator and from radiation transmitted through the walls of the treatment room have been estimated separately. The total annual absorbed dose to the trunk and to the hands have been estimated to be 2 mGy, of which the induced activity contributes one-third (0.7 mGy). The exposure of the technicians was found to be dominated by radiation penetrating the walls of the treatment room. For one accelerator the absorbed dose rate in the treatment room was measured continuously between 0.5 min and 48 h after end of treatment. Immediately after irradiation with high-energy photons the radiation is dominated by 28Al and 62Cu T1/2 = 2.3 and 9.7 min respectively) and later by radionuclides with longer half-lives, 187W and 57Ni (T1/2 = 24 and 36 h respectively). Due to these radionuclides the radioactivity in the accelerator will build up and the technicians will therefore be irradiated every time they enter the treatment room and not only directly after a treatment with high-energy photons.

Electrons↗
PubMed1991

Relationship between 99Tcm-MDP uptake and bone mineral density in patients with prostatic carcinoma.

Seventeen men with prostatic carcinoma were investigated with quantitative bone scintigraphy and quantitative computed X-ray tomography before orchiectomy and up to 6 months after this operation. The uptake of 99Tcm-labelled methylene disphosphonate (99Tcm-MDP) and bone mineral density (BMD) were determined for each vertebra from Th10 to L4. Ten patients had normal scintigrams. No change in MDP uptake or BMD was seen after 6 months in these patients. Of the seven patients with abnormal scintigrams, one patient had a clinical sign of progression with an increase in both MDP uptake and BMD. The remaining six patients showed stable or improved clinical status. For their abnormal vertebrae a decrease in MDP uptake was seen, while BMD varied in different ways after 6 months. For the normal vertebrae in these patients with metastatic involvement, no change in MDP uptake was seen. However, the BMD values showed a decrease, indicating a generalized increase in bone resorption at sites distant from the metastases.

Aged↗
PubMed1991

Kinetics of lead in bone and blood after end of occupational exposure.

In 14 retired lead workers, followed for over 18 years after end of exposure, repeated analyses of lead levels in finger bone by an in vivo X-ray fluorescence method revealed a decrease of lead concentration. The data were analysed using an exponential retention model. For the whole group the biological half-time was 16 (asymptotic 95% confidence interval, CI 12,23) years. The median of the estimated bone lead levels at the end of exposure was 85 micrograms.g-1 above the "background" (3 micrograms.g-1). A simultaneous follow-up of blood lead levels displayed a decrease, which could be described by a tri-exponential retention model with group half-times of 34 (CI 29,41) days, 1.2 (CI 0.9,1.8) years, and 13 (CI 10,18) years, respectively. The median of the estimated blood lead levels at the end of exposure for the three components were 0.49, 0.61, and 1.1 mumol.l-1 above the "background" (0.38-0.56 mumol.l-1), respectively. The well-documented decrease of lead exposure in the general population over the years, urged the use of a decreasing "background" of blood lead during the time of the study. The slowest of the three components represented the skeleton (probably mainly cortical bone), as did mainly probably also the intermediate one (trabecular bone). The data show the rather slow turnover of lead in the skeleton, the usefulnes of in vivo skeletal lead measurements as a long-term exposure index, and the importance of bone as a source of "endogenous" lead exposure.

Adult↗
PubMed1991

Additional information from quantitative 24-hour 99mTc-MDP bone scintigraphy in patients with prostatic carcinoma.

Quantitative bone scintigraphy was performed at 4 and 24 h after injection of 99mTc-MDP. The lower thoracic and all the lumbar vertebrae were recorded in 37 patients with prostatic carcinoma before orchiectomy as well as two weeks, two and six months postoperatively. Fourteen patients had normal bone scintigrams. By means of the measured variation in the count rate between normal vertebrae, the criterion for a vertebra to be considered as abnormal was determined using the 4 h-uptake values. For patients with normal scintigrams the count rate at 24 h was below the 4 h level and the mean 24 h/4 h ratio was determined to be 0.85 +/- 0.09 (1 SD). Normal vertebrae in patients with skeletal metastases had only slightly lower count rate values at 24 h than at 4 h. Abnormal vertebrae showed a higher count rate at 24 h, especially two weeks postoperatively, while a tendency towards lower values than at 4 h was seen after 6 months. If the 24 h/4 h ratio is used as an extra criterion to the count rate at 4 h, the vertebrae will be more accurately defined as normal or abnormal.

Aged↗
PubMed1990

Dynamic quantitative bone scintigraphy in patients with prostatic carcinoma treated by orchiectomy.

Dynamic quantitative bone scintigraphy was performed on 31 men with prostatic carcinoma before orchiectomy as well as 2 weeks, 2 and 6 months postoperatively. After injection of technetium methylene diphosphonate Tc 99m (99mTc-MDP) the count rate was recorded as serial images over the lower thoracic and all the lumbar vertebrae from 1 to 240 min post-injection. Thirteen men had normal bone scintigrams with no changes in 99mTc-MDP content at the four different investigation times. Eighteen men had skeletal metastases. Throughout the study half of the abnormal vertebrae in these patients showed an abnormal count rate after only 6 min post-injection. After 1 h it was possible in almost all abnormal vertebrae to predict abnormal bone uptake. In response to therapy a "flare phenomenon" with an increase in count rate was seen 2 weeks after orchiectomy followed by a decrease 2 months postoperatively in most of the abnormal vertebrae. The count rate decreased even below the pre-operative level after 6 months. Also, the normal vertebrae in the patients with skeletal metastases showed a tendency towards the flare phenomenon, which was not seen in patients with normal bone scintigrams.

Aged↗
PubMed1990

Tomographic scintigraphy using a pinhole collimator and a rotating gamma camera.

When a pinhole collimator is to be used for tomographic studies the standard SPECT software has to be modified so as to avoid serious image distortion outside the axis of rotation. The MTF measured at the axis of rotation shows that the better resolution of the pinhole collimator as compared with that of a parallel-hole collimator improves the tomographic image. The low sensitivity of the pinhole collimator excludes the use of an aperture smaller than 6 mm for patient tomographic studies where the activity which may be administered is restricted.

Adenoma↗
PubMed1989

Ferrous sulphate gels for determination of absorbed dose distributions using MRI technique: basic studies.

Two gels have been found to be suitable to load with ferrous sulphate solution. In these soft tissue equivalent phantoms, the absorbed dose distribution can be measured after irradiation in clinically used MR imaging equipment. The present studies were carried out using a 0.25 T NMR analyser without imaging properties. A ferrous sulphate solution, 0.05 M with respect to sulphuric acid, can be gelled with 4% gelatin to give a dosemeter which has a response which is linearly correlated (r = 0.998) with the absorbed dose in the interval 0-40 Gy. Ferrous sulphate solution can also be gelled with 1% agarose, but this gel has to be purged with oxygen to obtain a linear relationship (r = 0.997) in the same absorbed dose interval. The ferrous sulphate loaded gels have a sensitivity which is a factor of 2.2 or 4.0 times higher for gelatin and agarose, respectively, than the ordinary dosemeter solution. Because the standard deviation of background measurements is higher for the gels than for the dosemeter solution, the minimum detectable absorbed dose is about the same, or 1.0 Gy, for the two gels and the dosemeter solution. The sensitivity of the ferrous sulphate loaded gels shows no dependence on dose rate if the mean dose rate and the absorbed dose per pulse are within the limits normally used by accelerators for radiotherapy.

Ferrous Compounds↗
PubMed1988

Repeated quantitative bone scintigraphy in patients with prostatic carcinoma treated with orchiectomy.

Bone scintigraphy was performed in 16 men with newly diagnosed prostatic carcinoma before orchiectomy as well as 2 weeks and 2 months after operation. The uptake in the lower thoracic and lumbar vertebrae was registered up to 240 min after injection of 99mTc-MDP and was then calculated for each patient and vertebra. The relative standard deviation in measured uptake due to measuring technique was estimated to be +/- 7%. In eight patients, who had normal bone scintigraphies before orchiectomy, there were no changes in the uptake values after operation. The remaining eight patients had widespread metastatic involvement prior to treatment. Six of these patients showed a so called "flare phenomenon" in the abnormal vertebrae which means an initial increase in uptake after operation followed by a decreased uptake in response to therapy. One patient had a continuously increased uptake in all the abnormal vertebrae which correlated well with the clinical progression of the disease, while in another patient both reactions were seen. Thus, repeated quantitative bone scintigraphies using 99mTc-MDP can be made in a reproducible way and can be a useful tool to follow a patient's response to treatment.

Aged↗
PubMed1987

Radionuclide left ventricular volume determination. Influence of scattered radiation and surrounding activity.

Radionuclide measurements of left ventricular volumes, ejection fractions and stroke volumes were performed by an equilibrium technique in nine patients using left anterior oblique projection and individual depth correction. Phantom studies were made in order to evaluate attenuation and scattering of the radiation. It was found that a simple depth correction factor, k(d) = e mu d, can be used under certain conditions. However, the determination of left ventricular volume by radionuclide techniques is not a truly absolute method. The depth correction factor to be used is dependent on the condition of measuring and evaluation, for instance how the region of interest for the left ventricle is selected. Therefore, this method should be carefully standardized, evaluated and compared to other techniques. Stroke volume measured by radionuclide and dye-dilution technique showed a correlation coefficient of 0.76 (nine patients) at rest and 0.77 (seven patients) at work. This method can be easily performed during routine ejection fraction determination and can thus be useful in clinical studies.

Adult↗
PubMed1986

Comparison of measured and calculated absorbed doses from tangential irradiation of the breast.

Calculated absorbed dose distributions from tangential irradiation of the breast have been compared with TLD measurements in a anthropomorfic body-shaped phantom which has gone through all phases of the radiation treatment planning cycle, including mapping of electron densities with a CT scanner, simulation of beam set-up and several treatments with an accelerator. The absorbed doses, measured in the breast are 2-6% lower than those calculated with the clinically used treatment planning system. The deviation is slightly higher when wedges are used. The main source for this deviation is shown to be the limitations in the loss-of-scatter correction in the dose calculation algorithm used. It has also been noted that the variation of the absorbed dose in the target volume is in general smaller than predicted by the calculations.

Breast Neoplasms↗
PubMed1986

A method for conversion of Hounsfield number to electron density and prediction of macroscopic pair production cross-sections.

A method for the determination of electron density using a narrow beam attenuation geometry is described. The method does not require that the elemental composition of the phantom materials is known. The Hounsfield numbers for the phantom materials used were determined using five different CT scanners. A relationship between Hounsfield number and electron density can thus be established, which is of considerable value in radiation therapy treatment planning procedures. Measurements of the ratio coherent/incoherent scattering of low energy photons in a certain geometry has proven valuable for determination of atomic number, which in its turn can be used for estimation of macroscopic pair production coefficients for high energy photons. The combination of knowledge of electron density with methods for determination of processes, dependent on atomic number, can form a base for adequate composition of phantom materials for purposes of testing dose calculation algorithms for photons and electrons.

Electrons↗