1.
Sjöholm, H, et al.
(författare)
Necrosis of malignant gliomas after intratumoral injection of 201Tl in vivo in the rat
1995
Ingår i: Anti-Cancer Drugs. - 0959-4973. ; 6:1, s. 109-114
Tidskriftsartikel (refereegranskat) abstract
Fourteen adult Fischer 344 rats were inoculated in vivo unilaterally in the caudate nucleus in the brain with malignant RG 2 glioma cells. By 3 weeks a tumor with a diameter of 3-6 mm normally develops. Ten animals which survived the repeated periods of anesthesia and thallium (Tl) injections (intratumorally three times of 201Tl, 15-23 days after inoculation) showed a prolonged retention of radioactivity at the site of injection with no uptake in other organs except for the kidneys. Singular circumscribed necroses were found post-mortem at the site of injection, comprising malignant glioma tumor tissue, which in six animals was absent, in three animals was markedly reduced in size compared with controls and in one animal had the expected size. In four animals metastases were found in distant locations in the brain; in three of these cases there was a retention of radioactivity in the tumor. The selective necrotizing effect on the tumor cells is interpreted as mainly due to emission of Auger electrons from intracellularly accumulated 201Tl, giving rise to very high energy deposition in the vicinity of the cell nucleus. The results should also have implications for the treatment of human malignant gliomas.
2.
Persson, Bertil R, et al.
(författare)
Blood-brain barrier permeability in rats exposed to electromagnetic fields used in wireless communication
1997
Ingår i: Wireless Networks. - 1022-0038. ; 3, s. 455-461
Tidskriftsartikel (refereegranskat) abstract
iological effects of radio frequency electromagnetic fields (EMF) on the blood-brain barrier (BBB) have been studied in Fischer 344 rats of both sexes. The rats were not anaesthetised during the exposure. All animals were sacrificed by perfusion–fixation of the brains under chloralhydrate anaesthesia after the exposure. The brains were perfused with saline for 3–4 minutes, and thereafter perfusion fixed with 4% formaldehyde for 5–6 minutes. Whole coronal sections of the brains were dehydrated and embedded in paraffin and sectioned at 5 m. Albumin and fibrinogen were demonstrated immunohistochemically and classified as normal versus pathological leakage. In the present investigation we exposed male and female Fischer 344 rats in a Transverse Electromagnetic Transmission line chamber to microwaves of 915 MHz as continuous wave (CW) and pulse-modulated with different pulse power and at various time intervals. The CW-pulse power varied from 0.001 W to 10 W and the exposure time from 2 min to 960 min. In each experiment we exposed 4–6 rats with 2–4 controls randomly placed in excited and non-excited TEM-cells respectively. We have in total investigated 630 exposed rats at various modulation frequencies and 372 controls. The frequency of pathological rats is significantly increased (p < 0:0001) from 62=372 (ratio: 0:170:02) for control rats to 244=630 (ratio: 0:390:03) in all exposed rats. Grouping the exposed animals according to the level of specific absorbed energy (J/kg) give significant difference in all levels above 1.5 J/kg. The exposure was 915 MHz microwaves either pulse modulated (PW) at 217 Hz with 0.57 ms pulse width, at 50 Hz with 6.6 ms pulse width or continuous wave (CW). The frequency of pathological rats (0:17) among controls in the various groups is not significantly different. The frequency of pathological rats was 170=481 (0:350:03) among rats exposed to pulse modulated (PW) and 74=149 (0:500:07) among rats exposed to continuous wave exposure (CW). These results are both highly significantly different to their corresponding controls (p < 0:0001) and the frequency of pathological rats after exposure to pulsed radiation (PW) is significantly less (p < 0:002) than after exposure to continuous radiation (CW).
3.
Salford, Leif, et al.
(författare)
Brain tumour development in rats exposed to electromagnetic fields used in wireless cellular communication
1997
Ingår i: Wireless Networks. - 1022-0038. ; 3, s. 463-468
Tidskriftsartikel (refereegranskat) abstract
It has been suggested that electromagnetic fields (EMF) act as promoters late in the carcinogenesis process. To date, however, there is no convincing laboratory evidence that EMFs cause tumour promotion at non-thermal exposure levels. Therefore the effects of exposure to electromagnetic fields were investigated in a rat brain glioma model. Some of the exposures correspond to electromagnetic fields used in wireless communication. Microwaves at 915 MHz were used both as continuous waves (1 W), and pulse-modulated at 4, 8, 16 and 217 Hz in 0.57 ms pulses and 50 Hz in 6.67 ms pulses (2 W per pulse). Fischer 344 rats of both sexes were used in the experiments. By stereotaxic technique rat glioma cells (RG2 and N32) were injected into the head of the right caudate nucleus in 154 pairs of rats, exposed and matched controls. Starting on day 5 after inoculation, the animals were exposed for 7 hours a day, 5 days a week during 2–3 weeks. Exposed animals were kept unanaesthetized in well-ventilated TEM cells producing 915 MHz continuous or modulated microwaves. Their matched controls were kept in identical TEM cells without EMF exposure. All brains were examined histopathologically and the tumour size was estimated as the volume of an ellipsoid. Our study of 154 matched pairs of rats does not show any significant difference in tumour size between animals exposed to 915 MHz, and those not exposed. Thus our results do not support that even an extensive daily exposure to EMF promotes tumour growth when given from the fifth day after the start of tumour growth in the rat brain until the sacrifice of the animal after about 16 days.
4.
Brockstedt, Sara, et al.
(författare)
Use of an enhanced gradient system for diffusion MR imaging with motion-artifact reduction
1995
Ingår i: Acta Radiologica. - 1600-0455. ; 36:6, s. 662-670
Tidskriftsartikel (refereegranskat) abstract
PURPOSE: A spin-echo diffusion-sensitized pulse sequence using high gradients (23 mT/m) is introduced. MATERIAL AND METHODS: In order to minimize motion artefacts, velocity-compensating gradients, ECG-triggering and post-processing with phase correction and raw data averaging using navigator echoes was performed. The in vitro ratio of diffusion coefficients for water and acetone was determined and the water self-diffusion coefficient at different temperatures was evaluated. The pulse sequence was tested in 7 healthy volunteers and in 2 tumour patients with astrocytomas of grades I-II and III-IV. Both single-slice and multi-slice techniques were used. RESULTS: The incorporation of phase correction clearly improved the quality of both diffusion-encoded images and the calculated diffusion maps. Mean values of the diffusion coefficients in vivo were for CSF 2.66 x 10(-9) m2/s and for white and grey matter 0.69 x 10(-9) m2/s and 0.87 x 10(-9) m2/s, respectively. CONCLUSION: Velocity-compensating gradients in combination with a high gradient strength were shown to be useful for in vivo diffusion MR imaging.
5.
Ceberg, Crister, et al.
(författare)
A stochastic model for subcellular dosimetry in boron neutron capture therapy
1995
Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 40:11, s. 1819-1830
Tidskriftsartikel (refereegranskat) abstract
The therapeutic effectiveness of boron neutron capture therapy is highly dependent on the microscopic distribution of the administered boron compound. Two boron compounds with different uptake mechanisms in the tumour cells may thus cause effects of different degrees even if the macroscopic boron concentrations in the tumour tissue are the same. This difference is normally expressed quantitatively by the so-called relative local efficiency (RLE). In this work, a stochastic model for the subcellular dosimetry has been developed. This model can be used to calculate the probability for an energy deposition above a certain threshold level in the cell nucleus due to a single neutron capture reaction. If a threshold cell-kill function is assumed, and if the dose is low enough that multiple energy depositions are rare, the model can also be applied to calculations of the survival probability for a cell population. Subcellular boron distributions in rats carrying RG 2 rat gliomas were measured by subcellular fractionation after administration of two different boron compounds: a sulphydryl boron hydride (BSH) and a boronated porphyrin (BOPP). Based on these data, the RLE factors were then calculated for these compounds using the stochastic model.
6.
Wirestam, Ronnie, et al.
(författare)
Quantification of low-velocity motion using a navigator-echo supported MR velocity-mapping technique: application to intracranial dynamics in volunteers and patients with brain tumours
1997
Ingår i: Magnetic Resonance Imaging. - 1873-5894. ; 15:1, s. 1-11
Tidskriftsartikel (refereegranskat) abstract
Gradient-echo pulse sequences with velocity-encoding gradients of 22.5-25 mT/m, were used for brain-motion and CSF-flow studies. To reduce motion artifacts, a phase-correction technique based on navigator echoes was evaluated. Three patients with right-sided parietal tumours were investigated; one astrocytoma grade III-IV, one astrocytoma grade I-II and one benign meningioma. In healthy volunteers, a maximal brain-tissue velocity of (0.94 +/- 0.26) mm/s (mean +/- 1SD) was observed, which is consistent with previously presented results. The phase correction was proven useful for reduction of artifacts due to external head movements in modulus and phase images, without loss of phase information related to internal motion. The tissue velocity within the astrocytomas was low during the entire cardiac cycle. An abnormally high rostral velocity component was, however, observed in the brain tissue frontal to the astrocytomas. In all patients, an abnormal CSF flow pattern was observed. The study of brain motion may provide further understanding of the effects of tumours and other pathological conditions in the brain. When considering intracranial motion as a source of error in diffusion/perfusion MRI, the present study suggests that a pathology can alter the properties of brain motion and CSF flow considerably, leading to a more complex impact on diffusion/perfusion images.
