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  • 1
    Digitale Medien
    Digitale Medien
    Measurement of liver blood flow using oxygen-15 labelled water and dynamic positron emission tomography: Limitations of model description (1996)
    Springer
    European journal of nuclear medicine 23 (1996), S. 169-177 
    Details
    ISSN: 1619-7089
    Schlagwort(e): Positron emission tomography ; Liver perfusion ; Modelling ; Oxygen-15 labelled water
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract To date no satisfactory method has been available for the quantitative in vivo measurement of the complex hepatic blood flow. In this study two modelling approaches are proposed for the analysis of liver blood flow using positron emission tomography (PET). Five experiments were performed on three foxhounds. The anaesthetised dogs were each given an intravenous bolus injection of oxygen-15 labelled water, and their livers were then scanned using PET. Radioactivity in the blood from the aorta and portal vein was measured directly and simultaneously using closed external circuits. Time-activity curves were constructed from sequential PET data. Data analysis was performed by assuming that water behaves as a freely diffusible tracer and adapting the standard one-compartment blood flow model to describe the dual blood supply of the liver. Two particular modelling approaches were investigated: the dual-input model used both directly measured input functions (i.e. using the hepatic artery and the portal vein input, determined from the radioactivity detected in the aorta and portal vein respectively) whereas the single-input model used only the measured arterial curve and predicted the corresponding portal input function. Hepatic arterial flow, portal flow and blood volume were fitted from the PET data in several regions of the liver. The resulting estimates were then compared with reference blood flow measurements, obtained using a standard microsphere technique. The microspheres were injected in a separate experiment on the same dogs immediately prior to PET scanning. Whilst neither the single- nor the dual-input models accurately reproduced the arterial reference flow values, the flow values from the single-input model were closer to the microsphere flow values. The proposed single-input model would be a good approximation for liver blood flow measurements in man. The observed discrepancies between the PET and microsphere flow values may be due to the inherent temporal and spatial heterogeneity of liver blood flow. The results presented suggest that adaptation of the standard one-compartment blood flow model to describe the dual blood supply of the liver is limited and other flow tracers have to be considered for quantitative PET measurements in the liver.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01731841
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Whole-body positron emission tomography in clinical oncology: comparison between attenuation-corrected and uncorrected images (1997)
    Springer
    European journal of nuclear medicine 24 (1997), S. 1091-1098 
    Details
    ISSN: 1619-7089
    Schlagwort(e): Key words: Whole-body positron emission tomography ; Fluorine-18 fluorodeoxyglucose ; Attenuation correction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract. The clinical need for attenuation correction of whole-body positron emission tomography (PET) images is controversial, especially because of the required increase in imaging time. In this study, regional tracer distribution in attenuation-corrected and uncorrected images was compared in order to delineate the potential advantages of attenuation correction for clinical application. An ECAT EXACT scanner and a protocol including five to seven bed positions, emission scans of 9 min and post-injection transmission scans of 10 min per bed position were used. Uncorrected and attenuation-corrected images were reconstructed by filtered backprojection. In total, 109 areas of focal fluorine-18 fluorodeoxyglucose (FDG) uptake in 34 patients undergoing PET for the staging of malignancies were analysed. To measure focus contrast, a ratio of focus (target) to background average countrates (t/b ratio) was obtained from transaxial slices using a region of interest technique. Calculation of focus diameters by a distance measurement tool and visual determination of focus borders were performed. In addition, images of a body phantom with spheres to simulate focal FDG uptake were acquired. Transmission scans with and without radioactivity in the phantom were used with increasing transmission scanning times (2–30 min). The t/b ratios of the spheres were calculated and compared for the different imaging protocols. In patients, the t/b ratio was significantly higher for uncorrected images than for attenuation-corrected images (5.0±3.6 vs 3.1±1.4; P〈0.001). This effect was independent of focus localization, tissue type and distance to body surface. Compared with the attenuation-corrected images, foci in uncorrected images showed larger diameters in the anterior-posterior dimension (27±14 vs 23±12 mm; P〈0.001) but smaller diameters in the left-right dimension (19±11 vs 21±11 mm; P〈0.001). Phantom data confirmed higher contrast in uncorrected images compared with attenuation-corrected images. It is concluded that, although distortion of foci was demonstrated, uncorrected images provided higher contrast for focal FDG uptake independent of tumour localization. In most clinical situations, the main issue of whole-body PET is pure lesion detection with the highest contrast possible, and not quantification of tracer uptake. The present data suggest that attenuation correction may not be necessary for this purpose.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01254239
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Reproducibility of polar map generation and assessment of defect severity and extent assessment in myocardial perfusion imaging using positron emission tomography (1998)
    Springer
    European journal of nuclear medicine 25 (1998), S. 1313-1321 
    Details
    ISSN: 1619-7089
    Schlagwort(e): Key words: Myocardial perfusion ; Automated polar map generation ; Defect size ; Cardiac phantom
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract. The purpose of this study was to determine the reliability of new software developed for the analysis of cardiac tomographic data. The algorithm delineates the long axis and defines the basal plane and subsequently generates polar maps to quantitatively and reproducibly assess the size and severity of perfusion defects. The developed technique requires an initial manual estimate of the left ventricular long axis and calculates the volumetric maximum myocardial activity distribution. This surface is used to map three-dimensional tracer accumulation onto a two-dimensional representation (polar map), which is the basis for further processing. The spatial information is used to compute geometrical and mechanical properties of a solid model of the left ventricle including the left heart chamber. A new estimate of the axis is determined from this model, and the previously outlined procedure is repeated together with an automated definition of the valve plane until differences between the polar maps can be neglected. This quantitative analysis software was validated in phantom studies with defects of known masses and in ten data sets from normals and patients with coronary artery disease of various severity. We investigated the reproducibility of the maps with the introduction of a similarity criterion where the ratio of two corresponding polar map elements lies within a 10% interval. The maps were also used to measure intra–and interobserver variability in respect of defect size and severity. In the phantom studies, it was possible to reliably assess mass information over a wide range of defects from 5 to 60 g (slope: 1.02, offset –0.68, r = 0.972). Patient studies revealed a statistically significant increase in the reproducibility of the automatic technique compared with the manual approach: 54%±19% (manual) compared with 88%±9% (automatic) for observer 1 and 61%±20% vs 82%±5% for observer 2, respectively. The intervariability analysis showed a significant improvement from 59%±14% to 83%±7% in similar polar map elements and a significantly improved correlation in the calculation of severity (from r = 0.908 to 0.989) and extent (from r = 0.963 to r = 0.992) of the perfusion defects when the automated procedure was applied. It is concluded that, assuming a constant wall thickness and tissue density, absolute defect mass can be reliably estimated. Furthermore, the proposed software demonstrates a significant improvement in the generation of volumetric polar maps for the quantitative assessment of perfusion defects.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002590050301
    Standort Signatur Einschränkungen Verfügbarkeit
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    Artikel (Nationallizenzen)
    Volltext
  • 4
    Digitale Medien
    Digitale Medien
    Whole-body positron emission tomography in clinical oncology: Comparison between attenuation-corrected and uncorrected images (1997)
    Springer
    European journal of nuclear medicine 24 (1997), S. 1091-1098 
    Details
    ISSN: 1619-7089
    Schlagwort(e): Whole-body positron emission tomography ; Fluorine-18 fluorodeoxyglucose ; Attenuation correction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract The clinical need for attenuation correction of whole-body positron emission tomography (PET) images is controversial, especially because of the required increase in imaging time. In this study, regional tracer distribution in attenuation-corrected and uncorrected images was compared in order to delineate the potential advantages of attenuation correction for clinical application. An ECAT EXACT scanner and a protocol including five to seven bed positions, emission scans of 9 min and post-injection transmission scans of 10 min per bed position were used. Uncorrected and attenuation-corrected images were reconstructed by filtered backprojection. In total, 109 areas of focal fluorine-18 fluorodeoxyglucose (FDG) uptake in 34 patients undergoing PET for the staging of malignancies were analysed. To measure focus contrast, a ratio of focus (target) to background average countrates (t/b ratio) was obtained from transaxial slices using a region of interest technique. Calculation of focus diameters by a distance measurement tool and visual determination of focus borders were performed. In addition, images of a body phantom with spheres to simulate focal FDG uptake were acquired. Transmission scans with and without radioactivity in the phantom were used with increasing transmission scanning times (2–30 min). The t/b ratios of the spheres were calculated and compared for the different imaging protocols. In patients, the t/b ratio was significantly higher for uncorrected images than for attenuation-corrected images (5.0±3.6 vs 3.1±1.4;P〈0.001). This effect was independent of focus localization, tissue type and distance to body surface. Compared with the attenuation-corrected images, foci in uncorrected images showed larger diameters in the anterior-posterior dimension (27±14 vs 23±12 mm;P〈0.001) but smaller diameters in the leftright dimension (19±11 vs 21±11 mm;P〈0.001). Phantom data confirmed higher contrast in uncorrected images compared with attenuation-corrected images. It is concluded that, although distortion of foci was demonstrated, uncorrected images provided higher contrast for focal FDG uptake independent of tumour localization. In most clinical situations, the main issue of whole-body PET is pure lesion detection with the highest contrast possible, and not quantification of tracer uptake. The present data suggest that attenuation correction may not be necessary for this purpose.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01254239
    Standort Signatur Einschränkungen Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
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