Publications (14)41.57 Total impact
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Article: An implementation of time-efficient respiratory-gated PET acquisition by repeated breath-holds.
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ABSTRACT: Background Respiratory gating in positron emission tomography (PET) is used to improve detection of small tumors in the lower lung regions and in the liver, and to obtain a better estimate of the standardized uptake value (SUV).PurposeTo develop a time-efficient method for acquisition of respiratory-gated PET/CT that would produce one single high quality image volume corresponding to a breath-hold state.Material and Methods An instrument was developed that displayed to the patient either red or green numbers, counting down from a chosen maximum to one at a rate of one dial per second. The patient was instructed to repeatedly hold the breath in moderate inspiration when red numbers were displayed and to breathe freely during display of green numbers. PET data were acquired in list mode and trigger signals were sent to the scanner and inserted into the list file each time the color of the countdown numbers switched from green to red. Data acquired during breath-holds were used to create one single image volume.ResultsHigh quality breath-hold images were obtained from 10 min data acquisition at one bed position. Improved image quality compared to standard whole-body PET was demonstrated by a significant reduction of noise (standard deviation) in regions of normal liver tissues.Conclusion The instruction to perform repeated breath-holds was well understood by patients and they cooperated satisfactorily. When the new procedure is used the duration of the data acquisition may typically be reduced by a factor of 4 compared to conventional respiratory-gated protocols where the patient breathes freely.Acta Radiologica 03/2013; · 1.37 Impact Factor -
Article: Quantitative dynamic (18)FDG-PET and tracer kinetic analysis of soft tissue sarcomas.
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ABSTRACT: Purpose. To study soft tissue sarcomas using dynamic positron emission tomography (PET) with the glucose analog tracer [(18)F]fluoro-2-deoxy-D-glucose ((18)FDG), to investigate correlations between derived PET image parameters and clinical characteristics, and to discuss implications of dynamic PET acquisition (D-PET). Material and methods. D-PET images of 11 patients with soft tissue sarcomas were analyzed voxel-by-voxel using a compartment tracer kinetic model providing estimates of transfer rates between the vascular, non-metabolized, and metabolized compartments. Furthermore, standard uptake values (SUVs) in the early (2 min p.i.; SUV(E)) and late (45 min p.i.; SUV(L)) phases of the PET acquisition were obtained. The derived transfer rates K(1), k(2) and k(3), along with the metabolic rate of (18)FDG (MR(FDG)) and the vascular fraction ν(p), was fused with the computed tomography (CT) images for visual interpretation. Correlations between D-PET imaging parameters and clinical parameters, i.e. tumor size, grade and clinical status, were calculated with a significance level of 0.05. Results. The temporal uptake pattern of (18)FDG in the tumor varied considerably from patient to patient. SUV(E) peak was higher than SUV(L) peak for four patients. The images of the rate constants showed a systematic pattern, often with elevated intensity in the tumors compared to surrounding tissue. Significant correlations were found between SUV(E/L) and some of the rate parameters. Conclusions. Dynamic (18)FDG-PET may provide additional valuable information on soft tissue sarcomas not obtainable from conventional (18)FDG-PET. The prognostic role of dynamic imaging should be investigated.Acta oncologica (Stockholm, Sweden) 12/2012; · 2.27 Impact Factor -
Article: A gel tumour phantom for assessment of the accuracy of manual and automatic delineation of gross tumour volume from FDG-PET/CT.
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ABSTRACT: Introduction. Our primary aim was to make a phantom for PET that could mimic a highly irregular tumour and provide true tumour contours. The secondary aim was to use the phantom to assess the accuracy of different methods for delineation of tumour volume from the PET images. Material and methods. An empty mould was produced on the basis of a contrast enhanced computed tomography (CT) study of a patient with a squamous cell carcinoma in the head and neck region. The mould was filled with a homogeneous fast-settling gel that contained both (18)F for positron emission tomography (PET) and an iodine contrast agent. This phantom (mould and gel) was scanned on a PET/CT scanner. A series of reference tumour contours were obtained from the CT images in the PET/CT. Tumour delineation based on the PET images was achieved manually, by isoSUV thresholding, and by a recently developed three-dimensional (3D) Difference of Gaussians algorithm (DoG). Average distances between the PET-derived and reference contours were assessed by a 3D distance transform. Results. The manual, thresholding and DoG delineation methods resulted in volumes that were 146%, 86% and 100% of the reference volume, respectively, and average distance deviations from the reference surface were 1.57 mm, 1.48 mm and 1.0, mm, respectively. Discussion. Manual drawing as well as isoSUV determination of tumour contours in geometrically irregular tumours may be unreliable. The DoG method may contribute to more correct delineation of the tumour. Although the present phantom had a homogeneous distribution of activity, it may also provide useful knowledge in the case of inhomogeneous activity distributions. Conclusion. The geometric irregular tumour phantom with its inherent reference contours was an important tool for testing of different delineation methods and for teaching delineation.Acta oncologica (Stockholm, Sweden) 10/2012; · 2.27 Impact Factor -
Article: Dynamic FDG PET for assessing early effects of cerebral hypoxia and resuscitation in new-born pigs.
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ABSTRACT: Changes in cerebral glucose metabolism may be an early prognostic indicator of perinatal hypoxic-ischaemic injury. In this study dynamic ¹⁸F-FDG PET was used to evaluate cerebral glucose metabolism in piglets after global perinatal hypoxia and the impact of the resuscitation strategy using room air or hyperoxia. New-born piglets (n = 16) underwent 60 min of global hypoxia followed by 30 min of resuscitation with a fraction of inspired oxygen (FiO₂) of 0.21 or 1.0. Dynamic FDG PET, using a microPET system, was performed at baseline and repeated at the end of resuscitation under stabilized haemodynamic conditions. MRI at 3 T was performed for anatomic correlation. Global and regional cerebral metabolic rates of glucose (CMRgl) were assessed by Patlak analysis for the two time-points and resuscitation groups. Global hypoxia was found to cause an immediate decrease in cerebral glucose metabolism from a baseline level (mean ± SD) of 21.2 ± 7.9 to 12.6 ± 4.7 μmol/min/ 100 g (p <0.01). The basal ganglia, cerebellum and cortex showed the greatest decrease in CMRgl but no significant differences in global or regional CMRgl between the resuscitation groups were found. Dynamic FDG PET detected decreased cerebral glucose metabolism early after perinatal hypoxia in piglets. The decrease in CMRgl may indicate early changes of mild cerebral hypoxia-ischaemia. No significant effect of hyperoxic resuscitation on the degree of hypometabolism was found in this early phase after hypoxia. Cerebral FDG PET can provide new insights into mechanisms of perinatal hypoxic- ischaemic injury where early detection plays an important role in instituting therapy.European Journal of Nuclear Medicine 02/2012; 39(5):792-9. · 4.53 Impact Factor -
Article: Dynamic respiratory gated (18)FDG-PET of lung tumors - a feasibility study.
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ABSTRACT: (18)FDG-PET/CT imaging is well established for diagnosis and staging of lung tumors. However, more detailed information regarding the distribution of FDG within the tumor, also as a function of time after injection may be relevant. In this study we explore the feasibility of a combined dynamic and respiratory gated (DR) PET protocol. A DR FDG-PET protocol for a Siemens Biograph 16 PET/CT scanner was set up, allowing data acquisition from the time of FDG injection. Breath-hold (BH) respiratory gating was performed at four intervals over a total acquisition time of 50 minutes. Thus, the PET protocol provides both motion-free images and a spatiotemporal characterization of the glucose distribution in lung tumors. Software tools were developed in-house for tentative tumor segmentation and for extracting standard uptake values (SUVs) voxel by voxel, tumor volumes and SUV gradients in all directions. Four pilot patients have been investigated with the DR PET protocol. The procedure was well tolerated by the patients. The BH images appeared sharper, and SUV(max)/SUV(mean) was higher, compared to free breathing (FB) images. Also, SUV gradients in the periphery of the tumor in the BH images were in general greater than or equal to the gradients in the FB PET images. The DR FDG-PET protocol is feasible and the BH images have a superior quality compared to the FB images. The protocol may also provide information of relevance for radiotherapy planning and follow-up. A patient trial is needed for assessing the clinical value of the imaging protocol.Acta oncologica (Stockholm, Sweden) 08/2011; 50(6):889-96. · 2.27 Impact Factor -
Article: Monitoring the effect of targeted therapies in a gastrointestinal stromal tumor xenograft using a clinical PET/CT.
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ABSTRACT: The purpose of this study is to assess treatment responses induced by the two tyrosine kinase inhibitors, Imatinib and Sunitinib, in a gastrointestinal stromal tumor (GIST) xenograft using a clinical positron emission tomography/computed tomography (PET/CT) scanner. Nude mice bearing human GIST xenografts with mutations in exons 11 and 17 were randomly allocated to treatment with Imatinib, Sunitinib, or placebo daily for seven consecutive days. 2-deoxy-2-[(18)F]fluoro-D: -glucose PET ((18)F-FDG-PET/CT) was performed in a clinical PET/CT scanner at baseline (day 0) and 1 and 7 days after onset of treatment. Treatment response was assessed by measuring tumor volumes and by calculation of tumor-to-liver (18)F-FDG uptake ratios. Minor reductions in tumor volume were observed in both treatment groups. For the two treatment groups, significantly decreased tumor-to-liver uptake ratios were observed both at day 1 (Imatinib, -41%, p = .002; Sunitinib, -55%, p < .001) and at day 8 (Imatinib, -35%, p < .001; Sunitinib, -50%, p < .001), when compared to individual baseline values. For the control tumors, neither tumor volumes nor tumor-to-liver uptake ratios were altered during the 8 days the experiment lasted. Significant anti-tumor effects were demonstrated following treatment with both Imatinib and Sunitinib. Decreased tumor-to-liver uptake ratios were more pronounced than tumor volume reductions. Effects of novel targeted therapies can be evaluated in the GIST xenograft model using a clinical PET/CT scanner.Molecular imaging and biology: MIB: the official publication of the Academy of Molecular Imaging 12/2010; 13(6):1234-40. · 2.47 Impact Factor -
Article: A method for on-site measurements of the effective spatial resolution in PET image volumes reconstructed with OSEM and Gaussian post-filters.
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ABSTRACT: When PET image volumes are reconstructed with ordered subset expectation-maximization (OSEM) and subjected to filtration with a 3D Gaussian filter the effective spatial resolution is a function of both the intrinsic scanner resolution and the user-selectable spatial width of the filter. A method was developed to derive the effective spatial resolution from such volumes obtained after acquisitions with a line source on a Siemens Biograph 64 PET/CT scanner. Assuming Gaussian distributions, the full widths at half maximum (FWHM) were derived from probit plots of cumulative spatial distributions across the line source. The effective FWHM values were also used to estimate the FWHM of the intrinsic resolution by extrapolation to a zero filter width.Radiation Protection Dosimetry 02/2010; 139(1-3):195-8. · 0.82 Impact Factor -
Article: Integrin scintimammography using a dedicated breast imaging, solid-state gamma-camera and (99m)Tc-labelled NC100692.
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ABSTRACT: Integrin scintimammography with NC100692 and a dedicated gamma-camera, LumaGEM, based on semi-conductor technology, was performed to investigate the detection ability of this combination in breast cancer. Eight patients with a high suspicion of breast cancer were administered 600-750 MBq (99m)Tc-labelled NC100629. Two acquisitions using a cranio-caudal and a lateral view were used, with moderate compression of the breast. LumaGEM scintigraphy revealed 9 of 11 malignancies, sized 6-20 mm. Two lesions in patients with multicentric disease were not diagnosed, one of which measured only 2.5 mm. In one patient, the procedure was inconclusive, due to major breast hypertrophy. The combined use of NC100629 and a dedicated gamma-camera for breast imaging was highly effective in diagnosing breast cancer.Clinical physiology and functional imaging 08/2008; 28(4):235-9. · 1.21 Impact Factor -
Article: A simulation of MRI based dose calculations on the basis of radiotherapy planning CT images.
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ABSTRACT: The advantage of MRI-based radiotherapy planning is the superior soft tissue differentiation. However, for accurate patient dose calculations, a conversion of the MR images into Hounsfield CT maps is necessary. The aim of the present study was to investigate the dose accuracy that can be achieved with segmented MR-images derived from the planning CT images by assigning fixed densities to different classes of tissues. Treatment plans for ten prostate cancer patients were selected. A collapsed cone algorithm was used to calculate patient dose distributions. The dose calculations were based on four different image sets: (1) the original CT-series (DD(DP)), (2) a simulated MR series with all tissue set to a homogenous water equivalent material of density 1.02 g/cm(3) (DD(W)), (3) a simulated MR series with soft tissue set to a water equivalent material with density 1.02 g/cm(3) and the bone set to a density of 1.3 g/cm(3) (DD(W+B1.3)), and (4) a simulated MR series identical to (3) but with a bone density equal to 2.1 g/cm(3) (DD(W+B2.1)). The dose distributions were compared by analysing dose difference histograms as well as through a visual display of spatial dose deviations. The population based minimum, mean and maximum dose difference between the DD(DP) and DD(W) in the target volume was -2.8, -1.0 and 0.6%, respectively. Corresponding differences between DD(DP) and DD(W+B1.3) were -1.6, 0.2 and 1.5%, respectively, and between DD(DP) and DD(W+B2.1) -4.3, 4.2 and 9.7%, respectively. For the rectum, the differences between CT(DP) and the other image sets were in the range of -19.5 to 8.8%. For the bladder, the differences were in the range of -9.6 to 7.0%. A systematic study using segmented MR images was undertaken. To achieve an acceptable accuracy in the CTV dose, the MR images should be segmented into bone and water equivalent tissue. Still, significant dose deviation for the organs at risk may be present. As tissue segmentation in real MR images is introduced, segmentation errors and errors that stem from geometrical non-linearities may further reduce the accuracy.Acta oncologica (Stockholm, Sweden) 02/2008; 47(7):1294-302. · 2.27 Impact Factor -
Article: Early changes in apparent diffusion coefficient predict the quantitative antitumoral activity of capecitabine, oxaliplatin, and irradiation in HT29 xenografts in athymic nude mice.
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ABSTRACT: The purpose of this study was to evaluate the possible use of changes in apparent diffusion coefficient (ADC) measured by magnetic resonance imaging for pretreatment prediction and early detection of tumor response in a mouse model during fractionated chemoradiotherapy. Athymic mice with bilateral HT29 xenografts on rear flanks were allocated into three groups: control, capecitabine, and capecitabine and oxaliplatin. The left flanks of the mice received daily irradiation. T2 and diffusion images were acquired before therapy and weekly for the following 9 weeks. Pretreatment and changes in ADC were calculated and compared with tumor doubling growth delay. No correlations between pretreatment ADC and changes in tumor volumes after therapy were seen. All treated tumors, except those receiving capecitabine (P = .06), showed increased mean tumor ADC values 11 days after initialization of therapy (P < .05) before returning to pretreatment values within 5 days posttherapy (day 18 after onset of therapy). This increase in mean tumor ADC showed a strong positive correlation (r = 0.92, P < .01) with mean tumor doubling growth delay. Pretreatment ADC values did not predict the effectiveness of therapy, whereas early changes in mean ADC quantitatively correlated with treatment outcome.Neoplasia (New York, N.Y.) 05/2007; 9(5):392-400. · 5.48 Impact Factor -
Article: Localized internal radiotherapy with 90Y particles embedded in a new thermosetting alginate gel: a feasibility study in pigs.
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ABSTRACT: Internal radiotherapy requires the localization of the radionuclide to the site of action. A new injectable alginate gel formulation intended to undergo immediate gelation in tissues and capable of encapsulating radioactive particles containing 90Y was investigated. The formulation was injected intramuscularly, into the bone marrow compartment of the femur and intravenously, respectively, in pigs. The distribution of radioactivity in various tissues was determined. Following intramuscular injection, more than 90% of the radioactivity was found at the site of injection. Following injection into bone marrow, 30-40% of the radioactivity was retained at the site of injection, but a considerable amount of radioactivity was also detected in the lungs (35-45%) and the liver (5-18%). Following intravenous injection, 80-90% of the radioactivity was found in the lungs. The present formulation appears suitable for localized radiotherapy in organs and tissues having low perfusion.Nuclear Medicine Communications 03/2006; 27(2):185-90. · 1.40 Impact Factor -
Article: Effects of photon attenuation on the determination of cardiac volumes from reconstructed counts in gated blood pool SPET.
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ABSTRACT: In gated cardiac blood pool single-photon emission tomography (SPET), the volume of a ventricle may be determined by a method that exploits the proportionality between that volume and the total reconstructed counts within a larger volume of interest that includes the actual ventricle. The present work was carried out to determine how the attenuation of photons modifies the reconstructed counts obtained with this technique, and how this affects the accuracy of volume determination. Furthermore, we wanted to investigate how count-based determination of ventricle volumes is affected by the total SPET rotation angle and by different arm positions. We used micro -maps derived from computed tomography (CT) series of nine arbitrarily chosen patients to calculate a volume correction factor for each cardiac volume manually drawn on the CT images. An anthropomorphic chest phantom was used to confirm the calculation of correction factors. For the regions of the ventricles contained within a CT slice through the central part of the heart, the left to right volume ratio needed to be corrected by factors of 1.21 and 1.12 for 180 degrees and 360 degrees rotation, respectively. When all voxels within the left and right ventricles were included, the required volume ratio correction factor was close to 1. However, the variation among patients was larger for a 180 degrees (range 0.97-1.08) than for a 360 degrees rotation arc (range 1.0-1.03).European journal of nuclear medicine and molecular imaging 04/2004; 31(3):399-402. · 4.99 Impact Factor -
Article: Studies on the synthesis and biological properties of non-carrier-added [(125)I and (131)I]-labeled arylalkylidenebisphosphonates: potent bone-seekers for diagnosis and therapy of malignant osseous lesions.
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ABSTRACT: Arylalkylidenebisphosphonates labeled with nca [(125)I or (131)I] have been synthesized and their biological function investigated. The label was attached to the aromatic group in high yield and under mild conditions by means of iododesilylation. The bone affinities of the radioactive compounds were investigated in normal Balb/C mice. The compound 1-hydroxy(m-iodo[(125,131)I]-phenylethylidene)-1,1-bisphosphonate was found to possess superior bone affinity compared to others, and its in vivo deiodination was insignificant. The uptake in femur 24h after injection was 850 +/- 265% and 986 +/- 118% of injected dose per gram tissue times gram body weight in mice and rats, respectively. The therapeutic potential of the compound was investigated in two tumor models in athymic (nude) rats, one model for mixed lytic/sclerotic metastatic bone-lesions originating from breast cancer and the other model simulating osseous osteosarcoma. The effects in these models compare favorably to those observed for established treatment modalities. The experiments demonstrate that radioiodinated bisphosphonates may have a potential for diagnosis and therapy of malignant osseous lesions.Journal of Medicinal Chemistry 08/2003; 46(14):3021-32. · 5.25 Impact Factor -
Article: A method for measurement of the uptake patterns of two beta-emitting radionuclides in the same tissue section with a digital silicon detector: application to a study of 89SrCl2 and 153Sm-EDTMP in a dog with spontaneous osteosarcoma.
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ABSTRACT: The biological effect of a radiopharmaceutical depends heavily on the heterogeneity of the uptake in the various tissues. A comparative study of two radiopharmaceuticals should therefore include a comparison of the uptake patterns in different tissues. To eliminate the problems caused by variation in kinetics and tumour characteristics between individuals, such a comparison should be based on measured distributions of the radiopharmaceuticals in the same tissue sample. The excellent linearity between activity and counts in images obtained with a digital silicon strip detector allows such distributions to be derived from two autoradiographs acquired at different time points. This method was applied in a comparison of the uptake patterns of 153Sm-EDTMP and 89SrCl2 in sections obtained from a dog with spontaneous osteosarcoma, containing both tumour and normal bone tissues. As the areas of the section were larger than the detector area, the section had to be cut into smaller parts. Images of these were later merged by means of image processing techniques. There were significant differences in the uptake patterns of the two nuclides. In the primary tumour, the uptake of 153Sm was highly heterogeneous, while 89Sr was more uniformly distributed. In trabecular bone, the accumulation of 153Sm was higher than that of 89Sr. In solid cortical bone, 89Sr had the highest uptake.European journal of nuclear medicine and molecular imaging 03/2002; 29(2):191-7. · 4.99 Impact Factor
Top co-authors
Top Journals
Institutions
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2013
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Oslo University Hospital
- Intervention Centre
Oslo, Oslo, Norway
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2008
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University of Bergen
Bergen, Hordaland Fylke, Norway
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2002
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University of Oslo
- Department of Radiology and Nuclear Medicine (ARN)
Oslo, Oslo, Norway
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