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Scintillation Detectors
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
Although photomultiplier tubes still are very common as light sensors for scintillation detectors, the use of photodiodes in various forms offers some advantages apart from being smaller. Many scintillator materials (e.g. CsI(Tl), BGO and Gd2O5S (GOS)) have a significant photon emission in the long wavelength region not energetic enough to produce electrons in the photocathode of a PM tube, while photodiodes have a significantly better sensitivity for long wavelength photons. PM tubes are very sensitive to magnetic fields and must be shielded by a thin layer of mu-metal. This is however not enough when applied in strong magnetic fields that prevent them being used in coupled MR-PET systems or similar. Further advantages in using photodiodes are the higher quantum efficiency, lower power consumption, compact size, and the rugged design. All of which are factors of importance when designing compact, robust detector systems like hand-instruments or CT-systems. Due to their compact design, they are in general faster than PM tubes, which is an advantage in coincidence-based systems (e.g. PET).
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.
Intrinsic Optical Properties of Brain Slices: Useful Indices of Electrophysiology and Metabolism
Published in Avital Schurr, Benjamin M. Rigor, BRAIN SLICES in BASIC and CLINICAL RESEARCH, 2020
Thomas J. Sick, Joseph C. LaManna
Choice of a light detection device depends almost entirely on the type of optical information required. It is beyond the scope of this chapter to review this instrumentation, but important considerations will include sensitivity, spectral response, speed, and spatial resolution. Photomultiplier tubes and photon counting systems provide the highest sensitivity but have little spatial resolution and, for spectral studies, require additional instrumentation for optical filtering. For spectral analysis of brain slices, a number of instruments may be used. Conventional spectrophotometers and fluorometers offer the advantage of high sensitivity, but they generally are not easily adapted for use with brain slices and spectral acquisition is slow due to the mechanical nature of the spectral scan. The more recent development of solid-state spectrometers using cooled photodiode or charge-coupled-device (CCD) detectors, while perhaps not as sensitive, provides rapid spectral acquisition, and they can be easily adapted for use with standard brain slice recording chambers. Like photomultiplier tubes, spectroscopy techniques are often limited in spatial resolution. A variety of ultrasensitive solid-state camera systems are commercially available for imaging (high spatial resolution) optical signals from brain slices. However, there must always be a trade-off between spatial resolution, speed, and the requirement for spectral information which will dictate the optical instrumentation most applicable for any given experimental procedure.
The effect of the third dose of the BNT162b2 vaccine on anti-SARS-CoV-2 spike antibody levels in healthcare workers with and without COVID-19 infection
Published in Annals of Medicine, 2023
Blanka Wolszczak-Biedrzycka, Anna Bieńkowska, Beata Cieślikiewicz, Elwira Smolińska-Fijołek, Grzegorz Biedrzycki, Justyna Dorf
Antibody levels were measured using the Elecsys anti-SARS-CoV-2 S assay (Roche S-RBD tAb). This electrochemiluminescence immunoassay (ECLIA) is used forth in vitro quantification of total antibodies (IgG/IgA/IgM) to SARS-CoV-2 S-RBD proteins inhuman serum and is performed on a Roche Cobas E411 fully automated analyzer (Roche Diagnostics). The assay is performed on the Roche Cobas E411(Roche Diagnostics). This assay is a dual antigen assay format using a recombinant protein representing the RBDS antigen. The three-step procedure favors the detection of high-affinity antibodies to SARS-CoV-2. Samples are incubated with a mixture of biotinylated and ruthenylated RBD antigen to create an immune complex with the dual antigen. Streptavidin-coated microparticles are then added to bind the DAGS complexes to the solid phase. The reagent mixture is transferred to a measuring cell, and the microparticles are trapped magnetically. The application of a voltage induce chemiluminescence, which is measured with a photomultiplier tube. The signal output increases as the antibody titer increases. The detection range is 0.40–250 U/ml (up to 25,000 U/ml at a dilution of 1:100), with values below 0.80 U/ml being considered negative and values above 0.80 U/ml being positive [1,16].
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].
Scanning transmission X-ray microscopy study of subcellular granules in human platelets at the carbon K- and calcium L2,3-edges
Published in Platelets, 2022
Jeonghee Shin, Sehee Park, Tung X. Trinh, Sook Jin Kwon, Jiwon Bae, Hangil Lee, Eugenia Valsami-Jones, Jian Wang, Jaewoo Song, Tae Hyun Yoon
STXM images of the human platelets were acquired at the SM beamline of the Canadian light source (CLS, Saskatoon, Canada). The maximum current of 220 mA at the CLS was operated in the decay mode. The synchrotron-based monochromatic soft X-ray was focused on ~30 nm using a Fresnel zone plate (outermost zone width of 25 nm). The first order of the diffractively focused X-ray was selected using the order-sorting aperture (OSA, pinhole diameter of 50 µm). The sample was mounted on the interferometrically controlled piezo stage and raster-scanned. The intensity of the transmitted X-rays was measured using a scintillator photomultiplier tube (PMT). The STXM images of the whole mounted platelets were collected in an area of 8 µm × 8 µm with 150 × 150 pixels. Energy calibration at the carbon K-edge was performed using the 3p Rydberg peak at 294.96 eV of gaseous CO2 flushed into the STXM chamber. To obtain the carbon K-edge and calcium L2,3-edge XANES spectra, stack images of the platelets were collected in the energy range of 280.0 to 320.0 eV and 340.0 eV to 360.0 eV. The energy positions of the calcium L3-edge and L2-edge main peaks were calibrated to 349.2 eV and 352.5 eV. aXis2000 software [29] (version 11-Oct-2019) was used to calculate the optical density (OD), carbon and calcium distribution maps, and principal component analysis (PCA). The PCA was performed using two methods: Euclidean distance similarity and angle-based similarity.