30 results on '"Weitzel, Thilo"'
Search Results
2. Digital versus analogue PET in [68Ga]Ga-PSMA-11 PET/CT for recurrent prostate cancer: a matched-pair comparison
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Alberts, Ian, Prenosil, George, Sachpekidis, Christos, Weitzel, Thilo, Shi, Kuangyu, Rominger, Axel, and Afshar-Oromieh, Ali
- Published
- 2020
- Full Text
- View/download PDF
3. Exposure Stability of Quantitative Fluorine-18 Measurements On The Biograph Vision Quadra PET/CT System
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Prenosil, George Amadeus, primary, Hentschel, Michael, additional, Weitzel, Thilo, additional, Sari, Hasan, additional, Shi, Kuangyu, additional, and Rominger, Axel, additional
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- 2021
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- View/download PDF
4. PET/CT-guided biopsies of metabolically active bone lesions: applications and clinical impact
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Klaeser, Bernd, Wiskirchen, Jakub, Wartenberg, Jan, Weitzel, Thilo, Schmid, Ralph A., Mueller, Michel D., and Krause, Thomas
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- 2010
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5. Towards guidelines to harmonize textural features in PET: Haralick textural features vary with image noise, but exposure-invariant domains enable comparable PET radiomics
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Prenosil, George Amadeus, Weitzel, Thilo, Fürstner, Markus, Hentschel, Michael, Krause, Thomas, Cumming, Paul, Rominger, Axel, Klaeser, Bernd, Prenosil, George Amadeus, Weitzel, Thilo, Fürstner, Markus, Hentschel, Michael, Krause, Thomas, Cumming, Paul, Rominger, Axel, and Klaeser, Bernd
- Abstract
Purpose Image texture is increasingly used to discriminate tissues and lesions in PET/CT. For quantification or in computer-aided diagnosis, textural feature analysis must produce robust and comparable values. Because statistical feature values depend on image count statistics, we investigated in depth the stability of Haralick features values as functions of acquisition duration, and for common image resolutions and reconstructions. Methods A homogeneous cylindrical phantom containing 9.6 kBq/ml Ge-68 was repeatedly imaged on a Siemens Biograph mCT, with acquisition durations ranging from three seconds to three hours. Images with 1.5, 2, and 4 mm isometrically spaced voxels were reconstructed with filtered back-projection (FBP), ordered subset expectation maximization (OSEM), and the Siemens TrueX algorithm. We analysed Haralick features derived from differently quantized (3 to 8-bit) grey level co-occurrence matrices (GLCMs) as functions of exposure E, which we defined as the product of activity concentration in a volume of interest (VOI) and acquisition duration. The VOI was a 50 mm wide cube at the centre of the phantom. Feature stability was defined for df/dE → 0. Results The most stable feature values occurred in low resolution FBPs, whereas some feature values from 1.5 mm TrueX reconstructions ranged over two orders of magnitude. Within the same reconstructions, most feature value-exposure curves reached stable plateaus at similar exposures, regardless of GLCM quantization. With 8-bit GLCM, median time to stability was 16 s and 22 s for FBPs, 18 s and 125 s for OSEM, and 23 s, 45 s, and 76 s for PSF reconstructions, with longer durations for higher resolutions. Stable exposures coincided in OSEM and TrueX reconstructions with image noise distributions converging to a Gaussian. In FBP, the occurrence of stable values coincided the disappearance of negatives image values in the VOI. Conclusions Haralick feature
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- 2020
6. Ga-68-DOTATOC: Feasibility of high throughput screening by small animal PET using a clinical high-resolution PET/CT scanner
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Hofmann, Michael, Weitzel, Thilo, and Krause, Thomas
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- 2006
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7. Towards guidelines to harmonize textural features in PET: Haralick textural features vary with image noise, but exposure-invariant domains enable comparable PET radiomics
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Prenosil, George Amadeus, primary, Weitzel, Thilo, additional, Fürstner, Markus, additional, Hentschel, Michael, additional, Krause, Thomas, additional, Cumming, Paul, additional, Rominger, Axel, additional, and Klaeser, Bernd, additional
- Published
- 2020
- Full Text
- View/download PDF
8. Digital versus analogue PET in [68Ga]Ga-PSMA-11 PET/CT for recurrent prostate cancer: a matched-pair comparison
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Alberts, Ian, primary, Prenosil, George, additional, Sachpekidis, Christos, additional, Weitzel, Thilo, additional, Shi, Kuangyu, additional, Rominger, Axel, additional, and Afshar-Oromieh, Ali, additional
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- 2019
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9. Quantitative PET: Count Number Adaptations of Organ and Site specific Acquisition Protocols are a Key Determinant of comparable PET/CT Measurements
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Prenosil, George, Weitzel, Thilo, Hentschel, Michael, Krause, Thomas Michael, Rominger, Axel Oliver, and Klaeser, Bernd
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610 Medicine & health - Abstract
Aim: The ever-growing diversity and complexity of PET/CT systems make it increasingly difficult to define common acquisition protocols for quantifiable and comparable PET measurements in clinical routine and, above all, in multicenter clinical trials. We aimed to analyze the dependency of quantitative PET on technical variability, in order to improve acquisition and reconstruction protocols. The results formed the base for selected clinical acquisitions protocols, tailored to particular PET/CT systems. Materials and Methods: Image noise was examined in 422 PET/CT datasets from 18 PETCT systems participating in a Swiss multicenter phantom study. 215 of these measurements contained also hot spheres for recovery curve (RC) analysis. The study protocol combined different acquisition durations and low- and high-resolution image reconstructions with filtered back projection (FBP), ordered subset expectation maximization (OSEM), and vendor specific point spread function (PSF) based reconstruction. Data was analyzed with regard to exposure, defined as the product of background activity concentration and acquisition time. This produced results comparable in relation to the number of available decays per volume, independently from the actual activity concentration. Quality assurance (QA) limits for RCs were taken from guidelines issued by the Federal Office of Public Health in Switzerland. Additionally, RC shapes were quantitatively analyzed. Results: Passing the given QA limits depended highly on adequate exposure by keeping image noise levels low. Also, the minimal exposures required to fulfill the given QA limits differed between PET/CT systems, acquisition protocols and reconstruction algorithms. Despite higher image noise levels, quantifiability of FBP data was affected less by low count numbers than OSEM or PSF data. Insufficient count numbers led to faulty and incomparable image quantification,and consequently also erratic RCs. From the gathered data, we were able to propose limits for minimal exposure for ten different PET/CT devices and for common clinical protocols, suitable for whole body and organ-specific high-resolution acquisitions. Conclusions: In order to reproducibly generate comparable and quantitative data, count numbers in PET/CT acquisitions must be specifically adapted to the clinically necessary image resolution, reconstruction method and the PET/CT system used. Therefore, optimal PET/CT acquisition times vary with the required exposure and with the expected activity uptake in target organs. This in turn argues against fixed acquisition times and mandates site and organ specific acquisitions protocols. Adapting exposure to a site’s distinct technical factors appears to be a relevant element of PET/CT standardization in the context of multi-center trials.
- Published
- 2018
10. Evaluation of Multi-Center PET/CT Quality Assurance: Multi-Paradigm Software Enables Automated PET Quality Control
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Weitzel, Thilo, Prenosil, George, Hentschel, Michael, Fürstner, Markus, Krause, Thomas Michael, Rominger, Axel Oliver, and Klaeser, Bernd
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610 Medicine & health - Abstract
Context: PET quality assurance (QA) is becoming increasingly important as well as more complex, following the technological and radiopharmaceutical progress in PET imaging. Consequently, PET quality control (QC) has to handle an increasing heterogeneity of devices and diversity of clinical applications. However, actual PET QC focuses on equipment and good practice, while QC of individual datasets stays costly in terms of time and resources, and thus often lacks adequate diligence. Aim: Our aim is to promote automated PET QC of individual datasets and demonstrate its importance and feasibility as integral part of PET imaging. First objective was to develop a software prototype for automated PET QC on diverse data sets. Second objective was to demonstrate feasibility and benefits of such software. In particular, the automated QC should enable an in depth evaluation of data from a nationwide PET survey organized by the Swiss Society of Nuclear Medicine (SGNM-SSMN). Materials and Methods: The software implements a multi-paradigm approach based on an in-house software development tool. Among a range of modern design patterns, the software implements an embedded rule-based system to support decisions and reconfigurations of itself at runtime. A total of 453 datasets originating from 18 different PET/CT systems at 14 Swiss sites was available for QC. According to a detailed study protocol, each site was requested to provide a range of various image reconstructions from multiple acquisitions of two differing phantoms. The software was applied in a single run to all datasets, producing an individual quality report for each dataset and a database making all results available for further evaluation. Results: The automated QC correctly classified the diverse datasets according to acquisition protocol, reconstruction protocol and type of phantom used. Corresponding protocol adherence verification and quantitative evaluations were performed. The system rejected 7% of the data sets because of serious violations of protocol. Another 57% of the datasets were categorized as of restricted use, because of a variety of minor violations of protocol or a mismatch between quantitative specifications and actual data. Only 36% of the data sets fully passed QC. The resulting database proved to be essential for further evaluations as published elsewhere. Conclusion: The results indisputably prove the need, the feasibility and the benefits of automated PET QC. More intelligent software is a prerequisite for rigorous PET QC of individual datasets, especially given the increasing diversity of PET imaging applications.
- Published
- 2018
11. Results of a nationwide phantom based PET-Survey in Switzerland before harmonization
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Klaeser, Bernd, Prenosil, George, Hentschel, Michael, Fürstner, Markus, Krause, Thomas Michael, Rominger, Axel Oliver, and Weitzel, Thilo
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610 Medicine & health - Abstract
Aim: To gain an overview about the variability of PET measurements with diverse PET/CT-systems used in Switzerland, and to provide an inventory on acquisition protocol adherence in a multi-centre setting. Materials and methods: A total of 28 PET/CT sites in Switzerland was invited to participate in a PET phantom survey. Based on obligatory semiannual phantom measurements as prescribed by the Federal Office of Public Health in Switzerland, a detailed study protocol defined PET acquisitions of two different durations with a homogeneous cylinder phantom (activity concentration (AC) 10 kBq/ml) and a fillable “hot spheres” (18F) phantom (3.5 kBq background AC; sphere to background ratio 5:1). At least 7 image reconstructions for each acquisition (28 per study site) were requested. Reconstructions included sets of standard (4mm, isotropic) and high resolution (2mm, isotropic) reconstructions, using filtered back-projection (FBP), ordered subset expectation maximization (OSEM) and vendor specific point spread function (PSF) based reconstructions. Data of all sites underwent automatic quality control (QC) utilizing an in-house developed multi-paradigm software and were analyzed with regard to comparability of measured AC. Results: Phantom data was provided by 14 of 28 PET sites (5/5 university hospitals, 7/13 cantonal hospitals, 2/9 private hospitals). From 18 PET devices, 459/504 expected datasets (92%) were received and underwent QC. Of these, 6 datasets were not readable, and 31 datasets were not accepted (e.g. no attenuation correction), resulting in 422 evaluated datasets. 257/422 (61%) datasets were of restricted use for quantification because of protocol violations (e.g. strongly anisotropic voxels, filter parameters or AC out of proposed range, faulty exposure and axial or radial offset of phantom spheres), and/or actual background AC was not provided in 160/422 datasets (38 %). We found high variations in prepared actual or presupposed phantom AC and in recovery of AC, latter depending on reconstruction methods and reconstruction parameters (e.g. isotropy of voxels). Device-specific acquisition parameters - in terms of exposure per reconstructed voxel size - had a major influence on inter-site comparability of quantitative PET measurements. Underexposed PET acquisitions lead to faulty quantification of AC. Conclusions: As expected from comparable studies, the nationwide Swiss phantom survey also found considerable variation in PET AC quantification. In the context of multi-centre trials, protocol compliance may not be assumed. Thus, a throughout QC of all datasets appears to be mandatory to assure data quality and comparability. In addition, quantitative PET data may only be used after check of adequate image exposure.
- Published
- 2018
12. PET/CT-guided biopsies of metabolically active bone lesions: applications and clinical impact
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Klaeser, Bernd, Wiskirchen, Jakub, Wartenberg, Jan, Weitzel, Thilo, Schmid, Ralph, Mueller, Michel, Krause, Thomas, Klaeser, Bernd, Wiskirchen, Jakub, Wartenberg, Jan, Weitzel, Thilo, Schmid, Ralph, Mueller, Michel, and Krause, Thomas
- Abstract
Purpose: In a minority of cases a definite diagnosis and stage grouping in cancer patients is not possible based on the imaging information of PET/CT. We report our experience with percutaneous PET/CT-guided bone biopsies to histologically verify the aetiology of hypermetabolic bone lesions. Methods: We retrospectively reviewed the data of 20 consecutive patients who underwent multimodal image-guided bone biopsies using a dedicated PET/CT system in a step-by-step technique. Technical and clinical success rates of PET/CT-guided biopsies were evaluated. Questionnaires were sent to the referring physicians to assess the impact of biopsies on patient management and to check the clinical need for PET/CT-guided biopsies. Results: Clinical indications for biopsy were to histologically verify the aetiology of metabolically active bone lesions without a morphological correlate confirming the suspicion of metastases in 15 patients, to determine the origin of suspected metastases in 3 patients and to evaluate the appropriateness of targeted therapy options in 2 patients. Biopsies were technically successful in all patients. In 19 of 20 patients a definite histological diagnosis was possible. No complications or adverse effects occurred. The result of PET/CT-guided bone biopsies determined a change of the planned treatment in overall 56% of patients, with intramodality changes, e.g. chemotherapy with palliative instead of curative intent, and intermodality changes, e.g. systemic therapy instead of surgery, in 22 and 50%, respectively. Conclusion: PET/CT-guided bone biopsies are a promising alternative to conventional techniques to make metabolically active bone lesions—especially without a distinctive morphological correlate—accessible for histological verification. PET/CT-guided biopsies had a major clinical impact in patients who otherwise cannot be reliably stage grouped at the time of treatment decisions
- Published
- 2018
13. Isotope independent determination of PET/CT modulation transfer functions from phantom measurements on spheres
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Prenosil, George, Klaeser, Bernd, Hentschel, Michael, Fürstner, Markus, Berndt, Michael, Krause, Thomas Michael, and Weitzel, Thilo
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610 Medicine & health - Abstract
PURPOSE A PET/CT system's imaging capabilities are best described by its point spread function (PSF) in the spatial domain or equivalently by its modulation transfer function (MTF) in the spatial frequency domain. Knowing PSFs or MTFs is a prerequisite for many numerical methods attempting to improve resolution and to reduce the partial volume effect. In PET/CT, the observed PSF is a convolution of the system's intrinsic imaging capabilities including image reconstruction (PSF0) and the positron range function (PRF) of the imaged β(+) emitting isotope. A PRF describes the non-Gaussian distribution of β(+) annihilation events around a hypothetical point source. The main aim was to introduce a new method for determining a PET/CT system's intrinsic MTF (MTF0) from phantom measurements of hot spheres independently of the β(+) emitting isotope used for image acquisition. Secondary aim was to examine non-Gaussian and nonlinear MTFs of a modern iterative reconstruction algorithm. METHODS PET/CT images of seven phantom spheres with volumes ranging from 0.25 to 16 ml and filled either with (18)F or with (68)Ga were acquired and reconstructed using filtered back projection (FBP). MTFs were modeled with linear splines. The spline fit iteratively minimized the mean squared error between the acquired PET/CT image and a convolution of the thereof derived PSF with a numerical representation of the imaged hot phantom sphere. For determining MTF0, the numerical sphere representations were convolved with a PRF, simulating a fill with either (18)F or (68)Ga. The MTFs determined by this so-called MTF fit method were compared with MTFs derived from point source measurements and also compared with MTFs derived with a previously published PSF fit method. The MTF fit method was additionally applied to images reconstructed by a vendor iterative algorithm with PSF recovery (Siemens TrueX). RESULTS The MTF fit method was able to determine (18)F and (68)Ga dependent MTFs and MTF0 from FBP reconstructed images. Root-mean-square deviation between fit determined MTFs and point source determined MTFs ranged from 0.023 to 0.039. MTFs from Siemens TrueX reconstructions varied with size of the imaged sphere. CONCLUSIONS MTF0 can be determined regardless of the imaged isotope, when using existing PRF models for the MTF fit method presented. The method proves that modern iterative PET/CT reconstruction algorithms have nonlinear imaging properties. This behaviour is not accessible by point source measurements. MTFs resulting from these clinically applied algorithms need to be estimated from objects of similar geometry to those intended for clinical imaging.
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- 2016
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14. Technical Note: Transconvolution based equalization of positron energy effects for the use of 68 Ge/68 Ga phantoms in determining 18 F PET recovery
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Prenosil, George A., primary, Hentschel, Michael, additional, Fürstner, Markus, additional, Krause, Thomas, additional, Weitzel, Thilo, additional, and Klaeser, Bernd, additional
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- 2017
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15. Isotope independent determination of PET/CT modulation transfer functions from phantom measurements on spheres
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Prenosil, George A., primary, Klaeser, Bernd, additional, Hentschel, Michael, additional, Fürstner, Markus, additional, Berndt, Michael, additional, Krause, Thomas, additional, and Weitzel, Thilo, additional
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- 2016
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16. T2-relaxometry predicts outcome of DBS in idiopathic Parkinson's disease
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Lönnfors-Weitzel, Tarja, primary, Weitzel, Thilo, additional, Slotboom, Johannes, additional, Kiefer, Claus, additional, Pollo, Claudio, additional, Schüpbach, Michael, additional, Oertel, Markus, additional, Kaelin, Alain, additional, and Wiest, Roland, additional
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- 2016
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17. Transconvolution and the virtual positron emission tomograph--a new method for cross calibration in quantitative PET∕CT imaging
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Klaeser, Bernd, Krause, Thomas Michael, Prenosil, George, Hentschel, Michael, and Weitzel, Thilo
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610 Medicine & health - Abstract
PURPOSE Positron emission tomography (PET)∕computed tomography (CT) measurements on small lesions are impaired by the partial volume effect, which is intrinsically tied to the point spread function of the actual imaging system, including the reconstruction algorithms. The variability resulting from different point spread functions hinders the assessment of quantitative measurements in clinical routine and especially degrades comparability within multicenter trials. To improve quantitative comparability there is a need for methods to match different PET∕CT systems through elimination of this systemic variability. Consequently, a new method was developed and tested that transforms the image of an object as produced by one tomograph to another image of the same object as it would have been seen by a different tomograph. The proposed new method, termed Transconvolution, compensates for differing imaging properties of different tomographs and particularly aims at quantitative comparability of PET∕CT in the context of multicenter trials. METHODS To solve the problem of image normalization, the theory of Transconvolution was mathematically established together with new methods to handle point spread functions of different PET∕CT systems. Knowing the point spread functions of two different imaging systems allows determining a Transconvolution function to convert one image into the other. This function is calculated by convolving one point spread function with the inverse of the other point spread function which, when adhering to certain boundary conditions such as the use of linear acquisition and image reconstruction methods, is a numerically accessible operation. For reliable measurement of such point spread functions characterizing different PET∕CT systems, a dedicated solid-state phantom incorporating (68)Ge∕(68)Ga filled spheres was developed. To iteratively determine and represent such point spread functions, exponential density functions in combination with a Gaussian distribution were introduced. Furthermore, simulation of a virtual PET system provided a standard imaging system with clearly defined properties to which the real PET systems were to be matched. A Hann window served as the modulation transfer function for the virtual PET. The Hann's apodization properties suppressed high spatial frequencies above a certain critical frequency, thereby fulfilling the above-mentioned boundary conditions. The determined point spread functions were subsequently used by the novel Transconvolution algorithm to match different PET∕CT systems onto the virtual PET system. Finally, the theoretically elaborated Transconvolution method was validated transforming phantom images acquired on two different PET systems to nearly identical data sets, as they would be imaged by the virtual PET system. RESULTS The proposed Transconvolution method matched different PET∕CT-systems for an improved and reproducible determination of a normalized activity concentration. The highest difference in measured activity concentration between the two different PET systems of 18.2% was found in spheres of 2 ml volume. Transconvolution reduced this difference down to 1.6%. In addition to reestablishing comparability the new method with its parameterization of point spread functions allowed a full characterization of imaging properties of the examined tomographs. CONCLUSIONS By matching different tomographs to a virtual standardized imaging system, Transconvolution opens a new comprehensive method for cross calibration in quantitative PET imaging. The use of a virtual PET system restores comparability between data sets from different PET systems by exerting a common, reproducible, and defined partial volume effect.
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- 2013
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18. Technical Note: Transconvolution based equalization of positron energy effects for the use of 68Ge/68Ga phantoms in determining 18F PET recovery.
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Prenosil, George A., Hentschel, Michael, Fürstner, Markus, Krause, Thomas, Weitzel, Thilo, and Klaeser, Bernd
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POSITRON emission tomography ,COMPUTED tomography ,QUALITY assurance in radiotherapy ,IMAGING phantoms ,DIAGNOSTIC imaging - Abstract
Purpose Avoiding measurement variability from
18 F phantom preparation by using68 Ge/68 Ga phantoms for the determination of18 F recovery curves ( RC) in clinical quality assurance measurements and for PET/ CT site qualification in multicentre clinical trials. Methods RCs were obtained from PET/ CT measurements of seven differently sized phantom spheres filled either with18 F or with68 Ga. RCs for the respective other isotope were then determined by two different methods: In the first method, images were convolved with positron range transconvolution functions derived from positron annihilation distributions found in literature. This method generated recasted images matching images using the respective other isotope. In the second method, the PET/ CT system's isotope independent (intrinsic) point spread function was determined from said phantom measurements and convolved with numerical representations simulating hot spheres filled with the respective other isotope. These simulations included the isotope specific positron annihilation distributions. Recovered activity concentrations were compared between recasted images, simulated images, and the originally acquired images. Results18 F and68 Ga recovery was successfully determined from image acquisitions of the respective opposite isotope as well as from the simulations.68 Ga RCs derived from18 F data had a normalized root-mean-square deviation ( NRMSD) from real68 Ga measurements of 0.019% when using the first method and of 0.008% when using the second method.18 F RCs derived from68 Ga data had a NRMSD from real18 F measurements of 0.036% when using the first method and of 0.038% when using the second method. Conclusions Applying the principles of transconvolution,18 F RCs can be recalculated from68 Ga phantom measurements with excellent accuracy. The maximal additionally introduced error was below 0.4% of the error currently accepted for RCs in the site qualification of multicentre clinical trials by the EARL program of the European Association of Nuclear Medicine ( EANM). Therefore, our methods legitimately allow for the use of long-lived solid state68 Ge/68 Ga phantoms instead of manually prepared18 F phantoms to characterize comparability of18 F measurements across different imaging sites or of longitudinal18 F measurements at a single PET/ CT system. [ABSTRACT FROM AUTHOR]- Published
- 2017
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19. Volumen-Hologramme in photochromen Medien
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Weitzel, Thilo
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PHOTOCHROMIE (STEREOCHEMIE) ,COMPUTER SIMULATION ,Chemistry ,HOLOGRAPHIE (OPTIK) ,HOLOGRAPHY (OPTICS) ,PHOTOCHROMISM (STEREOCHEMISTRY) ,COMPUTERSIMULATION - Published
- 2001
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20. Metabolic pathway and distribution of superparamagnetic iron oxide nanoparticles: in vivo study
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Schlachter,Eva Katharina, Widmer,Hans Ruedi, Bregy,Amade, Lönnfors, Vajtai, Corazza,Nadia, Bernau, Weitzel,Thilo, Mordasini, Slotboom, Herrmann, Bogni, Hofmann,Heinrich, Frenz,Martin, Reinert,Michael, Schlachter,Eva Katharina, Widmer,Hans Ruedi, Bregy,Amade, Lönnfors, Vajtai, Corazza,Nadia, Bernau, Weitzel,Thilo, Mordasini, Slotboom, Herrmann, Bogni, Hofmann,Heinrich, Frenz,Martin, and Reinert,Michael
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Eva K Schlachter1, Hans Ruedi Widmer1, Amadé Bregy1, Tarja Lönnfors-Weitzel2, Istvan Vajtai3, Nadia Corazza3, Vianney JP Bernau6, Thilo Weitzel2, Pasquale Mordasini2, Johannes Slotboom2, Gudrun Herrmann4, Serge Bogni5, Heinrich Hofmann6, Martin Frenz5, Michael Reinert11Department of Neurosurgery, 2Institute for Diagnostic and Interventional Neuroradiology, 3Department of Pathology, 4Institute of Anatomy, 5Institute of Applied Physics, University of Bern, Berne, Switzerland; 6Laboratory of Powder Technology, Ecole Polytechnique Fédérale de Lausanne, Lausanne, SwitzerlandBackground: Experimental tissue fusion benefits from the selective heating of superparamagnetic iron oxide nanoparticles (SPIONs) under high frequency irradiation. However, the metabolic pathways of SPIONs for tissue fusion remain unknown. Hence, the goal of this in vivo study was to analyze the distribution of SPIONs in different organs by means of magnetic resonance imaging (MRI) and histological analysis after a SPION-containing patch implantation.Methods: SPION-containing patches were implanted in rats. Three animal groups were studied histologically over six months. Degradation assessment of the SPION-albumin patch was performed in vivo using MRI for iron content localization and biodistribution.Results: No SPION degradation or accumulation into the reticuloendothelial system was detected by MRI, MRI relaxometry, or histology, outside the area of the implantation patch. Concentrations from 0.01 µg/mL to 25 µg/mL were found to be hyperintense in T1-like gradient echo sequences. The best differentiation of concentrations was found in T2 relaxometry, susceptibility-sensitive gradient echo sequences, and in high repetition time T2 images. Qualitative and semiquantitative visualization of small concentrations and accumulation of SPIONs by MRI are feasible. In histological liver samples, Kupffer cells were significantly correlated with posti
- Published
- 2011
21. Erratum: “Transconvolution and the virtual positron emission tomograph-A new method for cross calibration in quantitative PET/CT imaging” [Med. Phys. 40(6), 062503 (15pp.) (2013)]
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Prenosil, George A., primary, Weitzel, Thilo, additional, Hentschel, Michael, additional, Klaeser, Bernd, additional, and Krause, Thomas, additional
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- 2013
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22. Response to “Comment on ‘Transconvolution and the virtual positron emission tomograph (vPET): A new method for cross calibration in quantitative PET/CT imaging’ ” [Med. Phys. 40, 062503 (15pp.) (2013)]
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Weitzel, Thilo, primary, Prenosil, George A., additional, Hentschel, Michael, additional, Klaeser, Bernd, additional, and Krause, Thomas, additional
- Published
- 2013
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23. Transconvolution and the virtual positron emission tomograph-A new method for cross calibration in quantitative PET/CT imaging
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Prenosil, George A., primary, Weitzel, Thilo, additional, Hentschel, Michael, additional, Klaeser, Bernd, additional, and Krause, Thomas, additional
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- 2013
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24. A navigation system for percutaneous needle interventions based on PET/CT images: Design, workflow and error analysis of soft tissue and bone punctures
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Oliveira-Santos, Thiago, primary, Klaeser, Bernd, additional, Weitzel, Thilo, additional, Krause, Thomas, additional, Nolte, Lutz-Peter, additional, Peterhans, Matthias, additional, and Weber, Stefan, additional
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- 2011
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25. New Photochromic Materials for Holographic Recording
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Weitzel, Thilo, primary, Wild, Urs, additional, Amlung, Martin, additional, Dürrb, Heinz, additional, and Irie, Mashiro, additional
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- 2000
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26. DEVICE FOR DETECTING OR GENERATING OPTICAL SIGNALS
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CAMPUS TECHNOLOGIES AG and WEITZEL THILO
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G01B9/02 - Abstract
The invention relates to a device for detecting optical signals or for generating optical signals by the modulation of optical carriers. Said device comprises the following: elements for generating at least one reference light beam, whose frequency or phase has been shifted and/or modulated or whose timing has been shifted, in relation to the optical signal which is to be detected; elements which allow the optical signal which is to be detected and/or the reference light beam(s) to be aligned in such a way, that they can be used for interference; at least one detector with a demodulator which can detect an amplitude modulation.
27. PET/CT-guided biopsies of metabolically active bone lesions: applications and clinical impact
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Klaeser, Bernd, Wiskirchen, Jakub, Wartenberg, Jan, Weitzel, Thilo, Schmid, Ralph, Mueller, Michel, Krause, Thomas, Klaeser, Bernd, Wiskirchen, Jakub, Wartenberg, Jan, Weitzel, Thilo, Schmid, Ralph, Mueller, Michel, and Krause, Thomas
- Abstract
Purpose: In a minority of cases a definite diagnosis and stage grouping in cancer patients is not possible based on the imaging information of PET/CT. We report our experience with percutaneous PET/CT-guided bone biopsies to histologically verify the aetiology of hypermetabolic bone lesions. Methods: We retrospectively reviewed the data of 20 consecutive patients who underwent multimodal image-guided bone biopsies using a dedicated PET/CT system in a step-by-step technique. Technical and clinical success rates of PET/CT-guided biopsies were evaluated. Questionnaires were sent to the referring physicians to assess the impact of biopsies on patient management and to check the clinical need for PET/CT-guided biopsies. Results: Clinical indications for biopsy were to histologically verify the aetiology of metabolically active bone lesions without a morphological correlate confirming the suspicion of metastases in 15 patients, to determine the origin of suspected metastases in 3 patients and to evaluate the appropriateness of targeted therapy options in 2 patients. Biopsies were technically successful in all patients. In 19 of 20 patients a definite histological diagnosis was possible. No complications or adverse effects occurred. The result of PET/CT-guided bone biopsies determined a change of the planned treatment in overall 56% of patients, with intramodality changes, e.g. chemotherapy with palliative instead of curative intent, and intermodality changes, e.g. systemic therapy instead of surgery, in 22 and 50%, respectively. Conclusion: PET/CT-guided bone biopsies are a promising alternative to conventional techniques to make metabolically active bone lesions—especially without a distinctive morphological correlate—accessible for histological verification. PET/CT-guided biopsies had a major clinical impact in patients who otherwise cannot be reliably stage grouped at the time of treatment decisions
28. Technical Note: Transconvolution based equalization of positron energy effects for the use of 68 Ge/ 68 Ga phantoms in determining 18 F PET recovery.
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Prenosil GA, Hentschel M, Fürstner M, Krause T, Weitzel T, and Klaeser B
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- Electrons, Humans, Positron-Emission Tomography, Image Processing, Computer-Assisted, Phantoms, Imaging, Positron Emission Tomography Computed Tomography
- Abstract
Purpose: Avoiding measurement variability from
18 F phantom preparation by using68 Ge/68 Ga phantoms for the determination of18 F recovery curves (RC) in clinical quality assurance measurements and for PET/CT site qualification in multicentre clinical trials., Methods: RCs were obtained from PET/CT measurements of seven differently sized phantom spheres filled either with18 F or with68 Ga. RCs for the respective other isotope were then determined by two different methods: In the first method, images were convolved with positron range transconvolution functions derived from positron annihilation distributions found in literature. This method generated recasted images matching images using the respective other isotope. In the second method, the PET/CT system's isotope independent (intrinsic) point spread function was determined from said phantom measurements and convolved with numerical representations simulating hot spheres filled with the respective other isotope. These simulations included the isotope specific positron annihilation distributions. Recovered activity concentrations were compared between recasted images, simulated images, and the originally acquired images., Results:18 F and68 Ga recovery was successfully determined from image acquisitions of the respective opposite isotope as well as from the simulations.68 Ga RCs derived from18 F data had a normalized root-mean-square deviation (NRMSD) from real68 Ga measurements of 0.019% when using the first method and of 0.008% when using the second method.18 F RCs derived from68 Ga data had a NRMSD from real18 F measurements of 0.036% when using the first method and of 0.038% when using the second method., Conclusions: Applying the principles of transconvolution,18 F RCs can be recalculated from68 Ga phantom measurements with excellent accuracy. The maximal additionally introduced error was below 0.4% of the error currently accepted for RCs in the site qualification of multicentre clinical trials by the EARL program of the European Association of Nuclear Medicine (EANM). Therefore, our methods legitimately allow for the use of long-lived solid state68 Ge/68 Ga phantoms instead of manually prepared18 F phantoms to characterize comparability of18 F measurements across different imaging sites or of longitudinal18 F measurements at a single PET/CT system., (© 2017 The Authors. Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.)- Published
- 2017
- Full Text
- View/download PDF
29. Metabolic pathway and distribution of superparamagnetic iron oxide nanoparticles: in vivo study.
- Author
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Schlachter EK, Widmer HR, Bregy A, Lönnfors-Weitzel T, Vajtai I, Corazza N, Bernau VJ, Weitzel T, Mordasini P, Slotboom J, Herrmann G, Bogni S, Hofmann H, Frenz M, and Reinert M
- Subjects
- Animals, Ferric Compounds metabolism, Histocytochemistry, Implants, Experimental, Magnetic Resonance Imaging, Magnetite Nanoparticles chemistry, Male, Rats, Rats, Wistar, Tissue Distribution, Ferric Compounds pharmacokinetics, Magnetite Nanoparticles administration & dosage
- Abstract
Background: Experimental tissue fusion benefits from the selective heating of superparamagnetic iron oxide nanoparticles (SPIONs) under high frequency irradiation. However, the metabolic pathways of SPIONs for tissue fusion remain unknown. Hence, the goal of this in vivo study was to analyze the distribution of SPIONs in different organs by means of magnetic resonance imaging (MRI) and histological analysis after a SPION-containing patch implantation., Methods: SPION-containing patches were implanted in rats. Three animal groups were studied histologically over six months. Degradation assessment of the SPION-albumin patch was performed in vivo using MRI for iron content localization and biodistribution., Results: No SPION degradation or accumulation into the reticuloendothelial system was detected by MRI, MRI relaxometry, or histology, outside the area of the implantation patch. Concentrations from 0.01 μg/mL to 25 μg/mL were found to be hyperintense in T1-like gradient echo sequences. The best differentiation of concentrations was found in T2 relaxometry, susceptibility-sensitive gradient echo sequences, and in high repetition time T2 images. Qualitative and semiquantitative visualization of small concentrations and accumulation of SPIONs by MRI are feasible. In histological liver samples, Kupffer cells were significantly correlated with postimplantation time, but no differences were observed between sham-treated and induction/no induction groups. Transmission electron microscopy showed local uptake of SPIONs in macrophages and cells of the reticuloendothelial system. Apoptosis staining using caspase showed no increased toxicity compared with sham-treated tissue. Implanted SPION patches were relatively inert with slow, progressive local degradation over the six-month period. No distant structural alterations in the studied tissue could be observed., Conclusion: Systemic bioavailability may play a role in specific SPION implant toxicity and therefore the local degradation process is a further aspect to be assessed in future studies.
- Published
- 2011
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30. Multimodal target correction by local bone registration: a PET/CT evaluation.
- Author
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Oliveira-Santos T, Weitzel T, Klaeser B, Krause T, Nolte LP, Weber S, and Reyes M
- Subjects
- Humans, Reference Standards, Reproducibility of Results, Bone and Bones diagnostic imaging, Image Processing, Computer-Assisted methods, Positron-Emission Tomography methods, Tomography, X-Ray Computed methods
- Abstract
PET/CT guidance for percutaneous interventions allows biopsy of suspicious metabolically active bone lesions even when no morphological correlation is delineable in the CT images. Clinical use of PET/CT guidance with conventional step-by-step technique is time consuming and complicated especially in cases in which the target lesion is not shown in the CT image. Our recently developed multimodal instrument guidance system (IGS) for PET/CT improved this situation. Nevertheless, bone biopsies even with IGS have a trade-off between precision and intervention duration which is proportional to patient and personnel exposure to radiation. As image acquisition and reconstruction of PET may take up to 10 minutes, preferably only one time consuming combined PET/CT acquisition should be needed during an intervention. In case of required additional control images in order to check for possible patient movements/deformations, or to verify the final needle position in the target, only fast CT acquisitions should be performed. However, for precise instrument guidance accounting for patient movement and/or deformation without having a control PET image, it is essential to be able to transfer the position of the target as identified in the original PET/CT to a changed situation as shown in the control CT.
- Published
- 2010
- Full Text
- View/download PDF
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