1,720,987 research outputs found
Achieving 10 ps coincidence time resolution in TOF-PET is an impossible dream
No full textGreen Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.RST/Radiation, Science and TechnologyRST/Medical Physics & Technolog
Physics and technology of time-of-flight PET detectors
No full textThe imaging performance of clinical positron emission tomography (PET) systems has evolved impressively during the last ∼15 years. A main driver of these improvements has been the introduction of time-of-flight (TOF) detectors with high spatial resolution and detection efficiency, initially based on photomultiplier tubes, later silicon photomultipliers. This review aims to offer insight into the challenges encountered, solutions developed, and lessons learned during this period. Detectors based on fast, bright, inorganic scintillators form the scope of this work, as these are used in essentially all clinical TOF-PET systems today. The improvement of the coincidence resolving time (CRT) requires the optimization of the entire detection chain and a sound understanding of the physics involved facilitates this effort greatly. Therefore, the theory of scintillation detector timing is reviewed first. Once the fundamentals have been set forth, the principal detector components are discussed: the scintillator and the photosensor. The parameters that influence the CRT are examined and the history, state-of-the-art, and ongoing developments are reviewed. Finally, the interplay between these components and the optimization of the overall detector design are considered. Based on the knowledge gained to date, it appears feasible to improve the CRT from the values of 200-400 ps achieved by current state-of-the-art TOF-PET systems to about 100 ps or less, even though this may require the implementation of advanced methods such as time resolution recovery. At the same time, it appears unlikely that a system-level CRT in the order of ∼10 ps can be reached with conventional scintillation detectors. Such a CRT could eliminate the need for conventional tomographic image reconstruction and a search for new approaches to timestamp annihilation photons with ultra-high precision is therefore warranted. While the focus of this review is on timing performance, it attempts to approach the topic from a clinically driven perspective, i.e. bearing in mind that the ultimate goal is to optimize the value of PET in research and (personalized) medicine. </p
Sealed catheter-based beta sources for intravascular brachytherapy: Novel designs and dosimetric characterization
No full textAbstract not availableApplied Science
Determining scintillation pulse shapes of fast PET scintillators
No full textDetermining the scintillation pulse shapes of PET scintillation crystals, especially the rise time of the pulse, will yield valuable information for making choices in the design of time of flight-PET scanners, with respect to e.g. scintillator crystal material and the detector trigger schemes. This can eventually improve the image quality of PET scans by noise reduction and/or reduce the image acquisition time and the dose to the patient. Knowledge of the rise time of the scintillation pulse is also of great importance in the modelling of the physical processes involved in scintillations. Several setups are presented and assessed with the intention to develop a procedure that is relatively easy to implement and is suitable for determining scintillation pulse shapes of PET scintillation crystals, excited by 511 keV photons, with sub-nanosecond timing resolution. The emphasis is on characterizing the rising edge of the scintillation pulse. The time correlated single photon counting method was employed in all of the setup variations. A proof-of-principle of the applicability of a suitable measurement procedure is given, which achieves a timing resolution of 120 ps FWHM and was used to determine the exponential rise time of a lutetium-yttrium oxyorthosilicate (LYSO) scintillator to be 81 ps with an estimated uncertainty interval of [50,120] ps. Also recommendations for further work on the basis of this procedure are made.Radiation, Detection & Medical ImagingRadiation, Radionuclides & ReactorsApplied Science
Magnetic detection of tumors using nanoparticles
No full textThe aim of this thesis is to explore the technical possibilities to develop a technique to detect tumors based on the magnetic detection of magnetic nanoparticles, targeted at tumor tissues. The report describes the main principles from magnetism, nano-medicine, nanotechnology and magnetic sensors that underlay the proposed technique. The focus and uniqueness of the thesis lays on the behaviour of the MNP’s and how they can be manipulated in order to be measured. The experimental part of the thesis demonstrates the proof of principle of the detection and localisation of the MNP’s in a sample. No real tissues or biological materials are used for the experiment. Cancer is the highest cause of dead nowadays. The survival rates strongly depend on the detection phase at which the cancer is detected. Currently the most accurate medical imaging technique for the localisation of tumors is MRI. MRI equipment is quite expensive and therefore the MRI scans are reserved for specific medical indications. The development of cheaper, non-invasive imaging techniques has gained a lot of attention in the bio-medical sector. Cheaper imaging techniques are not only interesting for the developed countries, but specially for developing countries. I aim that further development of the of a scanning technique based on the proof of principle demonstrated in this report can provide a cheap technique for the detection and localisation of tumors. The technique can be made cheap because its main physical components are magnetic nanoparticles and magnets, both of which can be produced by cheap processes.The measurements done for the experiment have been done with an Ipad, which demonstrates that no high sophisticated measurement tools are required to build the proposed technique.Mechanical, Maritime and Materials EngineeringMicroelectronic
From detectors towards systems: enabling clinical TOF-PET with monolithic scintillators
No full textNuclear medical imaging (NMI) is the branch of nuclear medicine aimed at imaging the in-vivo distribution of specific compounds labeled with radioactive elements (radiotracers) inside animals (preclinical applications) or patients (clinical applications). These compounds are developed to follow metabolic pathways or for binding to receptor systems of interest and are administered to the imaged subject to obtain diagnostic information, such as the functionality of certain organs or the presence of tissues with altered metabolism, e.g. tumors or inflamed tissues. The estimation of the radiotracer distribution is obtained by externally detecting the radiations emitted by the radioactive element attached to the tracer...RST/Medical Physics & Technolog
Improving the Time Resolution of TOF-PET Detectors by Double-Sided Readout
No full textState-of-the-art scintillation detectors for time-of-flight positron emission tomography (TOF-PET) typically employ scintillation crystals with a high aspect ratio (e.g. 4 ×4 ×22 mm3) read out on one of the small crystal surfaces. This single-sided readout (SSR) geometry may be unfavorable in terms of the coincidence resolving time (CRT) that can be achieved because of its effect on the light collection efficiency; the spread in the scintillation photon propagation times; and depth-of-interaction (DOI) related, variable detection delays. In this work it is investigated to which extent these effects can be mitigated by applying a fast photosensor on each of the small crystal surfaces. Such double-sided readout (DSR) has been introduced previously to counter the issue of DOI-related parallax errors. For the present purpose, we used Hamamatsu MPPC-S10362-33-050 C silicon photomultipliers (SiPMs) optically coupled to LSO:Ce,Ca scintillators. For polished 3 ×3 ×20 mm3 crystals with SSR, CRT values of 184 ±6 ps FWHM and 215 ±6 ps FWHM were determined for irradiation head-on and from the side, respectively. In this case, DSR improved the CRT measured under side irradiation to 174 ±6 ps FWHM. A much more substantial improvement was observed for equally sized crystals having etched side surfaces. For these crystals the CRT changed from 358 ±5 ps FWHM (head-on irradiation) and 343 ±6 FWHM (side irradiation) with SSR to 180 ±5 ps FWHM with DSR (side irradiation). These values are compared with the time resolution of detectors employing LSO:Ce,Ca crystals with a size of 3 ×3 ×5 mm3 ( CRT = 121 ±2 ps FWHM) and 3 ×3 ×10 mm3 ( CRT = 162 ±9 ps FWHM and CRT = 183 ±3 ps for polished and etched crystals, respectively).RST/Radiation, Science and TechnologyApplied Science
BGO as a hybrid scintillator / Cherenkov radiator for cost-effective time-of-flight PET
No full textDue to detector developments in the last decade, the time-of-flight (TOF) method is now commonly used to improve the quality of positron emission tomography (PET) images. Clinical TOF-PET systems based on L(Y)SO:Ce crystals and silicon photomultipliers (SiPMs) with coincidence resolving times (CRT) between 325 ps and 400 ps FWHM have recently been developed. Before the introduction of L(Y)SO:Ce, BGO was used in many PET systems. In addition to a lower price, BGO offers a superior attenuation coefficient and a higher photoelectric fraction than L(Y)SO:Ce. However, BGO is generally considered an inferior TOF-PET scintillator. In recent years, TOF-PET detectors based on the Cherenkov effect have been proposed. However, the low Cherenkov photon yield in the order of ∼10 photons per event complicates energy discrimination-a severe disadvantage in clinical PET. The optical characteristics of BGO, in particular its high transparency down to 310 nm and its high refractive index of ∼2.15, are expected to make it a good Cherenkov radiator. Here, we study the feasibility of combining event timing based on Cherenkov emission with energy discrimination based on scintillation in BGO, as a potential approach towards a cost-effective TOF-PET detector. Rise time measurements were performed using a time-correlated single photon counting (TCSPC) setup implemented on a digital photon counter (DPC) array, revealing a prompt luminescent component likely to be due to Cherenkov emission. Coincidence timing measurements were performed using BGO crystals with a cross-section of 3 mm × 3 mm and five different lengths between 3 mm and 20 mm, coupled to DPC arrays. Non-Gaussian coincidence spectra with a FWHM of 200 ps were obtained with the 27 mm3 BGO cubes, while FWHM values as good as 330 ps were achieved with the 20 mm long crystals. The FWHM value was found to improve with decreasing temperature, while the FWTM value showed the opposite trend.RST/Radiation, Science and TechnologyRST/Applied Radiation & Isotope
Ex vivo Validation of PET Imaging by 3D-printed Phantoms
No full textBiomedical Engineering | Medical Physic
Artificial Intelligence in Radiotherapy: Probabilistic Deep Learning for Dose Prediction and Anatomy Modeling
No full textRST/Medical Physics & Technolog
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