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Essential Inquiries: Dose, Benefit, and Risk in Medical Imaging
Published in Lawrence T. Dauer, Bae P. Chu, Pat B. Zanzonico, Dose, Benefit, and Risk in Medical Imaging, 2018
Pat B. Zanzonico, Bae P. Chu, Lawrence T. Dauer
Developed in the late 1950s by Hal Anger, the gamma camera, also known as the scintillation or Anger camera, has long been the predominant imaging device for SPECT and single photon (gamma-and X-ray) imaging in general. Almost all gamma-camera scintillation crystals are composed of thallium-doped sodium iodide (NaI[Tl]), with thicknesses of the order of 1 cm; such a crystal stops ~approximately 95% of the 140-kev gamma rays emitted by technetium-99m, the most commonly used non-PET radionuclide. The gamma camera collimator, comprised of a lead plate with holes (apertures) through which radiation must pass to reach the crystal, “directionalizes” the incoming radiation where any radiation traveling at an oblique angle to the axes of the apertures will strike the inter-aperture lead walls (septa) instead of the crystal, thereby allowing only radiation traveling parallel, or nearly parallel, to the aperture axes to reach the crystal and contribute counts to the resulting image. So-called parallel-hole collimators, in which the apertures and septa are parallel to one another, are used almost exclusively. Once the incident radiation passes through the collimator aperture, it strikes and may produce a scintillation (or light “flash”) within the crystal. The resulting light signal is distributed among a two-dimensional array of photomultiplier tubes (PMTs) backing the crystal; a PMT is essentially a vacuum tube that converts the light signal to an electronic signal, which is then amplified by virtue of an ~1000 approximately V high voltage. The light intensity reaching each PMT varies inversely with the distance between the scintillation and the respective PMT: the farther the PMT is from the scintillation, the less light it receives and the smaller its output pulse. This inverse relationship is the basis of the Anger position logic circuitry for determining the precise position of a scintillation within the crystal. In older gamma cameras, the x- and y-coordinates were calculated by analog circuitry, that is, using matrices of resistors. In the current system, this is done by digitizing the output signal from each PMT and using digital electronics. For SPECT, the gamma camera assembly actually rotates around the subject to acquire projection images, each typically taking 20 to 30 seconds. Because of the total length of time (20–30 min) thus required for such a study, dynamic SPECT imaging remains largely impractical. However, gamma camera collimators are interchangeable and one may choose to use parallel-hole collimation for either dynamic or static planar imaging.
Dose rate distribution measuring method using personal dosimeters and localization devices
Published in Journal of Nuclear Science and Technology, 2022
Daisuke Shinma, Yukihiro Murata, Yuichiro Ueno, Akihito Yamaguchi, Masahiro Tomizawa, Toshiya Yamano, Junichi Kitamura
There are various conventional methods to measure radiation distribution, with examples listed in Table 1. A gamma camera [1] has a planar array of radiation detectors and a pinhole shutter to measure radiation distribution similarly to an optical camera picture. As the gamma camera can only measure the strength of a radiation source, it cannot measure spatial dose rate. For area monitors, they are installed in multiple places in a nuclear power plant to measure the representative ambient dose rate of the installation area. This means that they cannot measure the detailed radiation distribution of a single area. However, in one example from previous research, small-sized portable radiation devices [2] have been proposed that operate using batteries. When the devices are installed densely in an area of concern, the collected data includes detailed radiation distribution information. However, in such an installation, the devices are considered obstacles that prevent workers from moving around smoothly.
Correlation Method of 3-D Detection of Distant Sources of Gamma Radiation and Neutrinos by Intensity Interferometry
Published in Nuclear Technology, 2023
V. I. Vysotskii, V. D. Rusov, T. N. Zelentsova, M. V. Vysotskyy, V. P. Smolyar
In this method, the radioisotope is administered to the patient and the escaping gamma rays are incident upon a moving (rotating around the patient) gamma camera, which computes and processes the image. The total scan time is about TR ≈ 15 to 20 min (or more). The typical activity of 99mTc preparation for a single injection is about Q0 ≈ 108 Bk. The typical example of computed isotope tomography (spatial distribution of the 99mTc isotope during such a diagnostics) is presented in numerous works (e.g., Ref. 20). The method based on the intensity correlation should show a similar tomography, but in a significantly shorter time, which is very important for the health of patients.
Nuclear Medicine in Oncology
Published in Computer Methods in Biomechanics and Biomedical Engineering: Imaging & Visualization, 2018
Carla Oliveira, Rui Parafita, Ana Canudo, Joana Correia Castanheira, Durval C. Costa
There are two major types of equipment for imaging, gamma cameras and Positron Emission Tomography (PET) cameras. The gamma camera is a device used to detect single photon emissions and consists of one or more ‘camera heads/detectors’ mounted on a gantry with the ability to acquire static images, whole body scan images and SPECT (Single Photon Emission Computed Tomography) images. The latter, SPECT, is a tomographic capability of the gamma cameras enabling 3D representation of the radioactive signal within the body.