| 1. |
- Ceberg, Crister, et al.
(författare)
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A new method for quantification of image distortion due to pile-up in scintillation cameras
- 1991
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Ingår i: European Journal Of Nuclear Medicine. - 1432-105X. ; 18:12, s. 959-963
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Tidskriftsartikel (refereegranskat)abstract
- Characterization of the count-rate performance of scintillation cameras should include not only the specification of count losses. At high count rates, there is also an image distortion due to the mispositioning of pile-up events. In this paper a simple and clinically relevant procedure to quantify this distortion is presented. The images of a square uniform technetium-99m phantom at high and low count rates are used. The fraction of the total counts being correctly positioned is determined as the peripheral count density divided by the total average count density. This ratio, corrected for the camera non-uniformity at low count rates, is called the 'positioning ability'. According to the National Electrical Manufacturers' Association (NEMA), the 'system count rate performance with scatter' should be reported as the measured count rate giving 20% count losses. In this paper it is suggested that this measure be complemented by a measure of the fraction correct positioned events at this count rate. This fraction, the 'high count rate positioning ability', can be easily and accurately measured using our method. The method has been tested on two different scintillation cameras. For one of them the high count rate positioning ability was determined as 91% at a measured count rate of 30,000 s-1 with 20% count losses. For the other camera, the corresponding figures were 88% at 59,000 s-1 and close to 100% at 38,000 s-1, before and after the installation of a new pile-up rejection circuit, respectively.
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| 2. |
- Ceberg, Crister, et al.
(författare)
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Photon activation therapy of RG2 glioma carrying Fischer rats using stable thallium and monochromatic synchrotron radiation.
- 2012
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 57:24, s. 8377-8391
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Tidskriftsartikel (refereegranskat)abstract
- 75 RG2 glioma-carrying Fischer rats were treated by photon activation therapy (PAT) with monochromatic synchrotron radiation and stable thallium. Three groups were treated with thallium in combination with radiation at different energy; immediately below and above the thallium K-edge, and at 50 keV. Three control groups were given irradiation only, thallium only, or no treatment at all. For animals receiving thallium in combination with radiation to 15 Gy at 50 keV, the median survival time was 30 days, which was 67% longer than for the untreated controls (p = 0.0020) and 36% longer than for the group treated with radiation alone (not significant). Treatment with thallium and radiation at the higher energy levels were not effective at the given absorbed dose and thallium concentration. In the groups treated at 50 keV and above the K-edge, several animals exhibited extensive and sometimes contra-lateral edema, neuronal death and frank tissue necrosis. No such marked changes were seen in the other groups. The results were discussed with reference to Monte Carlo calculated electron energy spectra and dose enhancement factors.
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| 3. |
- Ljunggren, Kaj, et al.
(författare)
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Beta camera low activity tumor imaging
- 1993
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Ingår i: Acta Oncologica. - : Informa UK Limited. - 1651-226X .- 0284-186X. ; 32:7-8, s. 869-872
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Tidskriftsartikel (refereegranskat)abstract
- A new technique, the beta camera, to complement film autoradiography, with fast quantitative imaging of beta particle-emitting radionuclides has been developed. It consists of a thin plastic scintillator and a light-sensitive microchannel plate detector. The thin tissue sample is mounted on the scintillator. Our first system had a high background and a moderate spatial resolution of 900 microns. We now report an improved system with a photomultiplier tube mounted on the scintillator of the microchannel plate detector. Only events registered by both detectors are accepted. A fast coincidence unit processes the signals, and if a time overlap exists, an event is generated in the beta camera. In the coincidence mode, images with low activity distribution of 201Tl (count rate 1 s-1) in 50 microns-thick slices of a human glioma tumor could be recorded with a spatial resolution of 500 microns.
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| 4. |
- Sjöholm, H, et al.
(författare)
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Necrosis of malignant gliomas after intratumoral injection of 201Tl in vivo in the rat
- 1995
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Ingår i: Anti-Cancer Drugs. - 0959-4973. ; 6:1, s. 109-114
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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.
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| 5. |
- Wanying, Q, et al.
(författare)
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Radio-iodinated and internally labelled (35S) IgM monoclonal antibodies in a syngenic rat model
- 1991
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Ingår i: Acta Oncologica. - : Informa UK Limited. - 1651-226X .- 0284-186X. ; 30:3, s. 379-383
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Tidskriftsartikel (refereegranskat)abstract
- To simulate the human situation concerning human monoclonal antibodies (MAbs), we have introduced a new syngenic rat model with an implanted rat colon carcinoma. Rat IgM MAbs (10B12), labelled by the chloramine-T method with 125I or internally with 35S, were injected intravenously into the rats and the biodistribution was studied for 8 days. The radioactivity uptake in the tumours of the 35S label was higher than that of the 125I label and the retention of 35S in the tumours gave tumour/blood ratios 8 times higher than those of 125I at 48 and 96 h after injection. In this model we have shown that dehalogenation of iodinated IgM MAbs is a serious problem. We therefore suggest that internally labelled MAbs should be used and that further investigations should be carried out in a syngenic rat model, since this probably reflects the clinical situation better than the nude mouse model.
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