Positron emission tomography (PET) is a nuclear medicine medical imaging technique which produces a three dimensional image or map of functional processes in the body.

Description

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A short-lived radioactive tracer isotope which decays by emitting a positron, chemically incorporated into a metabolically active molecule, is injected into the living subject (usually into blood circulation). There is a waiting period while the metabolically active molecule (usually a sugar) becomes concentrated in tissues of interest, then the subject is placed in the imaging scanner. The short-lived isotope decays, emitting a positron. After travelling up to a few millimeters the positron annihilates with an electron, producing a pair of annihilation photons (similar to gamma rays) moving in opposite directions. These are detected when they reach a scintillator material in the scanning device, creating a burst of light which is detected by photomultiplier tubes. The technique depends on simultaneous or coincident detection of the pair of photons: photons which do not arrive in pairs (i.e., within a few nanoseconds) are ignored.

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Magnetic Resonance Materials in Physics, Biology and Medicine

Echo-dephased steady state free precession
Sat, 16 May 2009 05:53:42 -0000
Abstract Objective  To introduce a novel positive contrast method for passive localization and visualization of paramagnetic susceptibility markers. Materials and methods  The novel approach is based on an echo-dephased steady-state free precession (SSFP) sequence. Gradients dephase any signal by ±π at the centered echo-time (TE = TR/2) and induce a total dephasing of ±2π per pixel within TR. This ensures that background tissues do not contribute to signal formation and thus appear dark. However, within the close vicinity of the paramagnetic marker, local gradient fields compensate for the intrinsic dephasing to form an echo. Conceptual issues of gradient compensation and its visualization characteristics are analyzed. The feasibility of the proposed technique for MR-guided intravascular interventions is demonstrated using flow phantom. Results  Echo-dephased SSFP is able to localize and visualize paramagnetic marker with excellent suppression of the background signals. The flow phantom experiments concluded that reliable tracking of the interventional guidewire is feasible using echo-dephased SSFP. Conclusion  With newly introduced echo-dephased SSFP approach, accurate and reliable visualization of paramagnetic interventional device is feasible. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0173-3Authors Sunil Patil, University of Basel Hospital Division of Radiological Physics, Department of Medical Radiology Petersgraben 4 4031 Basel SwitzerlandOliver Bieri, University of Basel Hospital Division of Radiological Physics, Department of Medical Radiology Petersgraben 4 4031 Basel SwitzerlandKlaus Scheffler, University of Basel Hospital Division of Radiological Physics, Department of Medical Radiology Petersgraben 4 4031 Basel Switzerland Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243
Monitoring the survival of islet transplants by MRI using a novel technique for their automated detection and quantification
Fri, 24 Apr 2009 06:56:02 -0000
Abstract Object  There is a clinical need to be able to assess graft loss of transplanted pancreatic islets (PI) non-invasively with clear-cut quantification of islet survival. We tracked transplanted PI in diabetic mice during the early post-transplant period by magnetic resonance imaging (MRI) and quantified the islet loss using automatic segmentation technique. Materials and methods  Magnetically labeled islet iso-, allo- and xenografts were injected into the right liver lobes. Animals underwent MRI scanning during 14 days after PI transplantation. MR images were processed using custom-made software, which automatically detects hypointense regions representing PI. It is based on morphological top-hat and bottom-hat transforms. Results  Manually and automatically detected areas, corresponding to PI, differed by 4% in phantoms. Signal loss regions due to PI decreased comparably in all groups during the first week post transplant. Throughout the second week post-transplant, the signal loss area continued in a steep decline in case of allografts and xenografts, whereas the decline in case of isografts slowed down. Conclusion  Automatic segmentation allows for the more reproducible, objective assessment of transplanted PI. Quantification confirms the assumption that a significant number of islets are destroyed in the first week following transplantation irrespective of allografts, xenografts or isografts. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0172-4Authors Daniel Jirak, Robarts Research Institute Imaging Research Laboratories London ON N6A 5K8 CanadaJan Kriz, Robarts Research Institute Imaging Research Laboratories London ON N6A 5K8 CanadaMichal Strzelecki, Technical University of Lodz Institute of Electronics Lodz PolandJiabi Yang, Robarts Research Institute Transplantation Group London ON CanadaCraig Hasilo, Robarts Research Institute Transplantation Group London ON CanadaDavid J. White, Robarts Research Institute Transplantation Group London ON CanadaPaula J. Foster, Robarts Research Institute Imaging Research Laboratories London ON N6A 5K8 Canada Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243
Detection and quantification of d-glucuronic acid in human bile using 1H NMR spectroscopy: relevance to the diagnosis of pancreatic cancer
Fri, 24 Apr 2009 06:56:02 -0000
Abstract Objective  There are no specific biomarkers available for the definitive diagnosis of pancreatic cancer. Analysis of d-glucuronic acid (GlcUA) in bile could be valuable in this regard. Materials and methods  Bile samples obtained from patients with pancreatic cancer (n = 4), chronic pancreatitis (n = 3) and control patients with biliary obstruction (n = 10) were analyzed by 1H NMR spectroscopy. GlcUA was quantified from the peak area of the α-1CH signal (at 5.24 ppm) obtained by deconvolution. Results  GlcUA was detected in human bile by one-dimensional 1H NMR and two-dimensional 1H–1H COSY and TOCSY experiments. Quantification of GlcUA was achieved by measuring the peak area of the α-1CH signal using CPMG experiment, and the quantities of GlcUA were calibrated to account for the attenuation due to T 2 relaxation. GlcUA was observed at elevated levels in bile samples obtained from pancreatic cancer patients, whereas it was either absent or found in negligible amounts in control and chronic pancreatitis patients. The reason for the presence of elevated levels of GlcUA could be the hydrolysis of biliary bilirubin diglucuronide by β-glucuronidase, released excessively from pancreatic tissue during the course of malignancy. Conclusion  Analysis of d-glucuronic acid in bile could be valuable in the detection of pancreatic cancer, and detecting GlcUA by in vivo 1H MRS has the potential to help in the non-invasive diagnosis of pancreatic cancer. Given that only four cancer patients have been studied so far, the new biomarker is regarded as a preliminary finding, but one that warrants further investigation. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0171-5Authors Tedros Bezabeh, National Research Council Institute for Biodiagnostics 435 Ellice Avenue Winnipeg MB R3B 1Y6 CanadaOmkar B. Ijare, National Research Council Institute for Biodiagnostics 435 Ellice Avenue Winnipeg MB R3B 1Y6 CanadaNils Albiin, CLINTEC, Karolinska Institutet Division of Radiology Stockholm SwedenUrban Arnelo, CLINTEC, Karolinska Institutet Division of Surgery Stockholm SwedenBo Lindberg, CLINTEC, Karolinska Institutet Division of Radiology Stockholm SwedenIan C. P. Smith, National Research Council Institute for Biodiagnostics 435 Ellice Avenue Winnipeg MB R3B 1Y6 Canada Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243
Extraction of the first bolus passage in dynamic susceptibility contrast perfusion measurements
Tue, 21 Apr 2009 10:05:53 -0000
Abstract Object  The processing of dynamic susceptibility contrast perfusion measurements requires an extraction of the first bolus passage of the injected contrast agent. State-of-the-art methods employ the fit of a gamma variate function to the measured data. The use of a gamma variate function is motivated by its shape similarity to the expected relaxation rate time-course during the first bolus passage. However, the quality of this result is strongly influenced by the amount of overlap of the first and second bolus passage. In this work we present an alternative, data-driven method for the extraction of the first bolus passage from a measured relaxation time-course. Materials and methods  By using prior knowledge of the injection function, the measured time-courses can be transformed to time-courses that would occur at a shorter injection duration where the two bolus passages have less overlap. This time-course is found by Tikhonov regularized deconvolution of the measured time-courses with an injection function that bases on the measurement protocol. A minimum search yields the cut-off point at which the first bolus can be extrapolated to zero. The gamma variate fit is performed using Powells algorithm. The proposed approach is compared to the gamma variate fit approach using simulations and an exemplary dataset from one healthy volunteer. Results  The new method performs comparably stable as the gamma variate function fit approach in simulations. Both methods are superior to a simple exponential extrapolation approach. Applied to volunteer data, the new method performs much faster than the gamma variate fit approach. The results obtained from both methods correspond well. Conclusion  The new method offers a conceptual understanding of the first bolus passage and yields similar results to the gamma variate function fit approach but performs much faster. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0170-6Authors Peter Gall, University Medical Center Freiburg Department of Diagnostic Radiology, Medical Physics Hugstetterstrasse 55 79106 Freiburg GermanyIrina Mader, University Medical Center Freiburg Department of Neuroradiology Breisacher Strasse 64 79106 Freiburg GermanyValerij G. Kiselev, University Medical Center Freiburg Department of Diagnostic Radiology, Medical Physics Hugstetterstrasse 55 79106 Freiburg Germany Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243
Fast multiecho balanced SSFP metabolite mapping of 1H and hyperpolarized 13C compounds
Wed, 15 Apr 2009 08:04:00 -0000
Abstract Object  To investigate the feasibility of multiecho balanced steady-state free precession (bSSFP)-based fast chemical shift mapping hyperpolarized 13C metabolites. The overall goal was to reduce total imaging time and to increase spatial resolution compared to common chemical shift imaging (CSI). Materials and methods  A multiecho bSSFP sequence in combination with an iterative reconstruction algorithm was implemented. 1H experiments were performed on phantoms and on a human volunteer in order to investigate the feasibility of the method on a system with metabolite maps that are known beforehand. 13C experiments were performed in vivo on pigs, where CSI images were acquired also for comparison. Results  Chemical shift images of three and four distinct 1H resonance frequencies as well as chemical shift images of up to five hyperpolarized 13C metabolites were successfully obtained. Conclusion  Fast metabolite mapping based on multiecho balanced SSFP in combination with an iterative reconstruction approach could successfully separate several 1H resonances and hyperpolarized 13C metabolites. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0169-zAuthors Jochen Leupold, University Hospital Freiburg Department of Diagnostic Radiology, Medical Physics Freiburg GermanySven Månsson, Lund University, Malmö University Hospital Medical Radiation Physics and Radiology, Department of Clinical Sciences Malmö Malmö SwedenJ. Stefan Petersson, GE Healthcare Helsingborg SwedenJürgen Hennig, University Hospital Freiburg Department of Diagnostic Radiology, Medical Physics Freiburg GermanyOliver Wieben, University of Wisconsin-Madison Departments of Medical Physics and Radiology, Wisconsin Institutes for Medical Research (WIMR) 1111 Highland Ave. Madison WI 53705-2275 USA Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243
Voxel-based reproducibility of T2 relaxation time in patellar cartilage at 1.5 T with a new validated 3D rigid registration algorithm
Wed, 01 Apr 2009 05:53:10 -0000
Abstract Object  T2 relaxation time is a promising MRI parameter for the early diagnosis and follow-up of osteoarthritis. Assessing the evolution of osteoarthritis needs exact comparison of datasets acquired at different times and knowledge of the T2 reproducibility. The aims of this work were to establish a method for voxel-wise comparison of T2 datasets and to assess voxel-based T2 reproducibility in healthy patellar cartilage. Materials and methods  A new rigid 3D-registration algorithm was developed. The precision of the registration algorithm was calculated with numerical simulations and in vitro measurements. In vivo T2 reproducibility was assessed in six volunteers measured at seven different times. The voxel-based reproducibility was characterized with the coefficient of variation (CV) of T2, and its regional variations were analyzed. Results  The registration algorithm showed an average registration precision lower than 25% of the voxel size. In vivo voxel-based T2 reproducibility exhibited a median CV of 10.1%. Reproducibility showed significant regional differences. Largest CVs (15.4%) were found near the articular surface. The central regions showed the lowest CVs (7.2%) and the lateral regions intermediate CVs (11.2%). Conclusion  Using a rigid 3D-registration algorithm provides voxel-based T2 reproducibility errors comparable to former, 2D region-based approaches, thus opening the possibility of voxel-based monitoring of cartilage degradation in osteoarthritis. Content Type Journal ArticleCategory Research ArticleDOI 10.1007/s10334-009-0168-0Authors José G. Raya, Ludwig Maximilian University of Munich Josef Lissner Laboratory for Biomedical Imaging, Department of Clinical Radiology, Großhadern Marchioninistr. 15 81377 Munich GermanyAnnie Horng, Ludwig Maximilian University of Munich Department of Clinical Radiology, Großhadern Munich GermanyOlaf Dietrich, Ludwig Maximilian University of Munich Josef Lissner Laboratory for Biomedical Imaging, Department of Clinical Radiology, Großhadern Marchioninistr. 15 81377 Munich GermanyJürgen Weber, Ludwig Maximilian University of Munich Josef Lissner Laboratory for Biomedical Imaging, Department of Clinical Radiology, Großhadern Marchioninistr. 15 81377 Munich GermanyJulia Dinges, Klinikum rechts der Isar der Technischen Universität München Institut für Röntgendiagnostik Munich GermanyElisabeth Mützel, Ludwig Maximilian University of Munich Department of Forensic Medicine Munich GermanyMaximilian F. Reiser, Ludwig Maximilian University of Munich Josef Lissner Laboratory for Biomedical Imaging, Department of Clinical Radiology, Großhadern Marchioninistr. 15 81377 Munich GermanyChristian Glaser, Ludwig Maximilian University of Munich Department of Clinical Radiology, Großhadern Munich Germany Journal Magnetic Resonance Materials in Physics, Biology and MedicineOnline ISSN 1352-8661Print ISSN 0968-5243

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