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PET Systems
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
A detector in PET is a device formed by the combination of scintillator, light conversion unit, and electronics. An ideal detector in PET should have the following properties: high stopping power for 511 keV, good energy resolution, good timing resolution, and good spatial resolution. Furthermore, the cost should be acceptable. The scintillators are discussed in the Section 18.2. The conversion of the output light into the electrical signal can be done by different devices (Photomultiplier tube, Position-sensitive Photomultiplier tubes, Avalanche Photodiode, Silicon Photomultiplier). As it is the most cost-effective way to achieve quite good performance, the previous generation of human PET systems are using Photomultiplier tubes (PMT) for this conversion step. These are characterized by a high-gain, low-noise, and fast response. The other devices are used in small-animal PET systems or research prototypes to achieve better spatial resolution, count-rate capability, or because they can operate in an environment with high magnetic fields (MRI scanners). The focus in this part is on the use of PMTs for determining the position, energy, and time.
Laser Beam Management Detectors
Published in Chunlei Guo, Subhash Chandra Singh, Handbook of Laser Technology and Applications, 2021
Alexander O. Goushcha, Bernd Tabbert
For the beam tracking, positioning and some other applications requiring ultra-low light-intensity detection with a relatively high-frequency bandwidth, the APDs operating in a single-photon counting mode (Geiger mode) promise undisputable advantages (see Chapter 9 for description of the Geiger mode of APD operation). A relatively novel type of avalanche photodetector with Geiger mode operation, known as silicon photomultiplier (SiPM) or multi-pixel photon counter, was developed by several groups, see, e.g. Buzhan et al. (2003). SiPM is an array of microcell APDs operating in the Geiger mode. A typical SiPM may contain several hundreds to thousands of microcells coupled to a common signal output terminal. The size of each microcell is usually ten to hundred square microns. The number of microcells defines the photon-counting dynamic range of SiPM. In each microcell, an arriving photon can trigger an avalanche flow of carriers, leaving the surrounding cells untriggered and ready to record other arriving photons. The output signal of the SiPM is the analogue sum of all individual cell signals. As long as the number of instantly impinging photons is less than approximately half the total number of microcells, it can be assumed that a given microcell will be hit by one photon at a time only. Under this condition, the sensor output will depend linearly on the input light flux.
Radiation Measurements and Spectroscopy
Published in Douglas S. McGregor, J. Kenneth Shultis, Radiation Detection, 2020
Douglas S. McGregor, J. Kenneth Shultis
The primary disadvantages of scintillator spectrometers are (1) that a photon detector such as a PMT must be incorporated into the device and (2) that the energy resolution is inferior to that of a semiconductor spectrometer. Historically, scintillation crystals were coupled to PMTs so that the spectrometers were fragile and bulky. A special μ-metal is also needed to shield the PMT from magnetic fields. Modest success was realized with the coupling of scintillators to semiconductor photodiodes, yet the energy resolution was inferior to that obtainable with a PMT. The introduction of the silicon photomultiplier (SiPM) has greatly reduced the problem of fragility of PMTs and their bulkiness while nearly preserving the energy resolution achieved with PMTs. Scintillator spectrometers of many varieties coupled to SiPMs are now commercially available as rugged and compact devices unaffected by magnetic fields and provide nearly the same energy resolution as their PMT-coupled counterparts. Regardless of these new benefits, the spectroscopic performance of scintillators remains inferior to semiconductor spectrometers, especially to that of high-purity Ge and Si spectrometers (see Fig. 20.25).
Adenosine triphosphate (ATP) bioluminescence-based strategies for monitoring atmospheric bioaerosols
Published in Journal of the Air & Waste Management Association, 2022
Yueqi Zhang, Bing Liu, Zhaoyang Tong
A novel biosensor extracts ATP from bacterial cells through a microfluidic channel and using an aerosol condensation system to quantitatively determines ATP in bioaerosols. Santangelo et al. (2018) reports the design, fabrication and testing of 3D printing microfluidic chips coupled with silicon photomultiplier tubes (SiPMs) for high sensitivity real-time ATP detection. The 3D microfluidic chip reduces the consumption of reactants, facilitates the delivery of solutions close to SiPM, and improves the detection efficiency. The LOD of ATP detected by their system is 8 nm, the analysis dynamic range is between 15 nm and 1 μ m, the stability error is 3%, and the repeatability error is less than 20%. And (Zhang et al. 2017) proposed a new biochemical system prototype, which uses nano probes related to ATP technology to count E. coli colonies. Its novelty lies in that magnetic nanoparticle beads are modified with specific antibodies and used as probes to capture and enrich Escherichia coli through the specific connection between antigen and antibody. Within 20 minutes, the detectable concentration of bacteria ranged from 102 CFU/ml to 108 CFU/ml. Under the best test conditions, LOD is only 3.0 × 102 CFU/mL. Independent experimental data show that the maximum fluctuation of signal-to-noise ratio of the prototype is less than 6.98%, which has good reliability and repeatability.
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].
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].