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Principles of Radiation Detection and Image Formation
Published in Ken Holmes, Marcus Elkington, Phil Harris, Clark's Essential Physics in Imaging for Radiographers, 2021
X-ray and gamma radiation detection is essentially a three-stage process:A solid scintillation crystal captures and converts X-rays into light.Light is then converted into a small electrical signal by the photocathode.Finally, a photomultiplier is used to amplify the signal into a much larger useful electronic signal.
Evaluation of the Potential of Microspherical Systems for Regional Therapy in the Tumor-Bearing Liver and Kidney Using Techniques in Nuclear Medicine
Published in Neville Willmott, John Daly, Microspheres and Regional Cancer Therapy, 2020
Jacqueline A. Goldberg, James H. McKillop, Colin S. McArdle
Rectilinear scanners have now been almost entirely replaced by the gamma camera. The gamma camera consists of a large radiation detector, in the form of a sodium iodide scintillation crystal.5 The scintillation crystal converts gamma rays emitted by the radiopharmaceutical into a light photon. The light photons are detected by photomultiplier tubes, which produce an electrical current. The electronic circuitry of the gamma camera then calculates the position of the incident gamma ray on the scintillation crystal. The distribution of the incident rays and their frequency are what constitutes the gamma camera image1 This image reflects the distribution of tracer in the field of view and thus provides information on the organ function under study (Figure 1).
X-ray Vision: Diagnostic X-rays and CT Scans
Published in Suzanne Amador Kane, Boris A. Gelman, Introduction to Physics in Modern Medicine, 2020
Suzanne Amador Kane, Boris A. Gelman
Inside the photomultiplier tube, visible photons hit a photocathode, a device that converts light to photoelectrons via the photoelectric effect. However, these photoelectrons are too few in number to produce an appreciable electrical signal. To overcome this problem, the photoelectrons are accelerated by a large voltage toward a positive electrode called a dynode. The collision between the energetic incoming electrons and the dynode metal frees many more electrons. These in turn are accelerated to the next dynode, further multiplying the signal when they in turn collide and release more electrons. After many such multiplications, a very large electrical signal has been produced from each original x-ray. These electrical signals can be digitized and stored on a computer for use with the digital image methods discussed later in Section 5.8.4.
Long axial field-of-view PET/CT devices: are we ready for the technological revolution?
Published in Expert Review of Medical Devices, 2022
Luca Filippi, Antonia Dimitrakopoulou-Strauss, Laura Evangelista, Orazio Schillaci
In last decades hybrid imaging, combining molecular and anatomical data in a unique, synergistic approach, has thoroughly changed the face of medical diagnostics [1,2]. In particular, positron emission computed tomography (PET/CT) has established itself as an essential tool in many oncological and non-oncological scenarios [3], providing the opportunity of investigating in vivo physio-pathological processes at a cellular and molecular level [4,5]. Notably, in recent years some technological improvements have been introduced in PET imaging, such as novel iterative reconstruction algorithms, or time-of-flight (TOF) PET/CT scanners operating in fully-3D mode [6]. Most importantly, the silicon photomultiplier (SiPM)-based detectors have been implemented instead of the ‘old-fashioned’ photomultiplier tubes (PMTs) [7,8], giving rise to the so-called digital PET/CT (dPET/CT). With respect to the PMT-equipped PET/CT, namely analogue PET/CT (aPET/CT), dPET/CT is characterized by higher sensitivity, spatial and temporal resolution, with a significantly greater detection rate of pathological lesions, also employing fast protocols [9–15].
Vitamin D deficiency is a risk factor for delayed tooth eruption associated with persistent primary tooth
Published in Acta Odontologica Scandinavica, 2021
Thaís Aparecida Xavier, Isabela Ribeiro Madalena, Raquel Assed Bezerra da Silva, Léa Assed Bezerra da Silva, Marcelo José Barbosa Silva, Andiara De Rossi, Erika Calvano Küchler, Sandra Yasuyo Fukada
Blood samples were collected at the Clinical Analysis Service of School of Pharmaceutical Sciences of Ribeirão Preto, University of São Paulo, and serum 25(OH)D levels were measured by chemiluminescence, using a LIAISON® 25 OH Vitamin D TOTAL Assay (DiaSorin, Saluggia, Italy) kit according to the manufacturer's instructions. After the introduction of the samples into the LIAISON® Analyser, there was the first incubation. The 25(OH)D was dissociated from its binding protein and bound to the solid phase’s antibody. At the end of 10 min, the vitamin D marker linked to an isoluminol derivative was added, and the unbound material was removed with a wash cycle. Subsequently, the initiator reagents were added, and the chemiluminescence reaction started. A photomultiplier measured the light signal as relative light units (RLUs), which is inversely proportional to 25(OH)D concentration.
Digital PET and detection of recurrent prostate cancer: what have we gained, and what is still missing?
Published in Expert Review of Medical Devices, 2021
Luca Filippi, Orazio Schillaci
It has to be highlighted that a further push to the applications of PET/CT in precision oncology has been determined by recent technological innovations. Until a few years ago PET/CT scanners were mainly based on photomultiplier tubes (PMTs) converting scintillation light into an electric current. In spite of several well-known advantages, such as high amplification, stability, and ruggedness, PMTs present several limitations, among whom their incompatibility with intense magnetic fields and limitations for the detection of small lesions [5]. A new type of PET detectors, the silicon photomultiplier (SiPM)-based detectors, has been recently developed and integrated into a novel PET/CT scanner, defined as digital PET/CT (dPET/CT). SiPM detectors consist of an array of microcells operating in a Geiger mode, as a single photon interacts with a microcell via photoelectric effects determining an electron/hole pair, which, in its turn, starts a self-sustaining cascade efficiently amplifying the original electron–hole pair into a macroscopic current flow. Passive quenching is obtained through a series of resistors integrated into the microcell [6]. With respect to conventional PMTs-based PET/CT scanners, namely analogue PET/CT (aPET/CT), dPET/CT is characterized by higher sensitivity, greater time resolution, and better spatial resolution [7].