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Clinical Applications and Protocols of Single Photon Emission Computed Tomography
Published in Bhagwat D. Ahluwalia, Tomographic Methods in Nuclear Medicine: Physical Principles, Instruments, and Clinical Applications, 2020
Tomographic radionuclide imaging began in 1963 with the pioneering work of Kuhl and Edwards1 performing section-scanning of the brain. After Kuhl’s MARK III and MARK IV multidetector brain scanners, considerable time elapsed before commercial tomographic systems became available.2 Finally, the Cleon 710 transaxial brain scanner and the Cleon 711 transaxial whole-body scanner were released. With the advent of a general-purpose SPECT system developed by Larsson,3 tomographic imaging began to employ a rotating large-field-of-view scintillation camera. All major manufacturers now offer single- or dual-headed rotating tomographic systems that can be interfaced to any standard nuclear medicine computer.
Chemical Dosimetry
Published in Gad Shani, Radiation Dosimetry, 2017
The NMR experiments were carried out using a 1.5-T Signa whole-body scanner. The longitudinal relaxation rates were determined using seven single-slice images of the same spatial location acquired with different repetition times by saturation recovery analysis. Typical repetition times were 100, 300, 600, 1000, 1500, 3000, and 6000 ms. Single-slice images were obtained in lieu of multi-slice images to avoid any out-of-plane saturation effects. R1 was calculated using a three-parameter fit of the equation below, using the standard region-of-interest software provided with the system:
Positron Emission Tomography
Published in George C. Kagadis, Nancy L. Ford, Dimitrios N. Karnabatidis, George K. Loudos, Handbook of Small Animal Imaging, 2018
From consideration of Equations 8.1 and 8.2, it can be shown that for 511 keV photons, scatter through smaller angles (<45°) is favored. The photoelectric effect, in which the photon is completely absorbed, has an almost negligible probability of occurrence at this energy in tissue (Figure 8.3). In PET, the Compton interaction can give rise to two possible outcomes. First, the scattered photon can be detected by the scanner in coincidence with its partner annihilation photon, and the event is accepted and assigned to an incorrect LOR (Figure 8.4). This erroneous event is classified as a scattered coincidence. The LOR to which the event was assigned no longer passes through the location of the positron–electron annihilation; as a result of the scattering, the opportunity to measure a true coincidence is lost and in its place a scattered coincidence is recorded. Even though such events do not contribute to an overall count loss, they carry wrong information and must be subtracted or otherwise accounted for during data processing. In the second case, no coincidence event is recorded, either because the scattered photon was not detected (e.g., the new trajectory did not intersect the detectors) or because the scattered (and hence lower-than-511-keV-energy) photon was detected but failed to satisfy the constraints of the scanner’s energy window settings (typically 450–650 keV). Both cases lead to a reduction in the true (“good”) signal, which is termed attenuation. The magnitude of scatter and attenuation depends on the size and density of the object being imaged and on the geometry of the scanner. Increasing the solid angle subtended by the scanner, and/or increasing the width of the energy window, leads to a higher chance that a scattered photon will form a scattered coincidence. It is thus understandable why the scatter fraction (SF), typically defined as the ratio between the number of scattered events (S) and total true coincidence events (T), S/T, can be quite high in small animal imaging. Although the animal body may be small, the detectors cover a large solid angle. The SF can be as high as 30% in some scanners when imaging rats (Goertzen et al. 2012). This is comparable to the SF obtained in human brain PET imaging when using a whole body scanner (Olivier et al. 2005). A minor but interesting subtle point is the fact the detector thickness can also influence the SF. Since the scattered photons have a lower energy than the unscattered 511 keV photon, they require less detector material to interact: thinner detectors will thus preferentially detect scattered events compared to thicker detectors.
Effect of axonal fiber architecture on mechanical heterogeneity of the white matter—a statistical micromechanical model
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2022
Hesam Hoursan, Farzam Farahmand, Mohammad Taghi Ahmadian
The MR images were obtained from a 25-year-old male volunteer. Images were acquired using a Toshiba's Vantage Elan 1.5-Tesla whole body scanner with a 32-channel head coil. In order to extract the anatomical information of the brain structure, an Magnetization Prepared Rapid Gradient Echo (MPRAGE) sequence (TR/TE = 6700/5.5 ms, 1 mm in plane resolution, 1 mm slice thickness, 256 × 256 mm FOV, 176 slices) was applied. Diffusion weighted images (DWI) were acquired using the single shot echo planer imaging (EPI) pulse sequence (b-value = 1000 smm–2. The total acquisition time was approximately 15 min. The FSL software (Jenkinson et al. 2012) was used to extract the brain tissue from the head. Thresholding and segmentation techniques were used to separate white matter, grey matter, and cerebrospinal fluid. Freesurfer (Reuter et al. 2012) was used to verify the segmentation results (Figure 1). The DTI data was registered onto the T1 image and extracted using SPM12 software package in MATLAB in the form of 4D tensors. Explore DTI was used to perform tractography in three regions including the brain stem, corpus callosum, and corona radiata (Leemans et al. 2009) (Figure 2). Following the tractography, the DTI information from the voxels of the brain stem, corpus callosum, and corona radiata were extracted by using a semi-automatic brain atlas (Mazziotta et al. 2001).
Proton magnetic resonance spectroscopic analysis of changes in brain metabolites following electroconvulsive therapy in patients with major depressive disorder
Published in International Journal of Psychiatry in Clinical Practice, 2020
Şakir Tosun, Mesude Tosun, Gür Akansel, Aziz Mehmet Gökbakan, Hatice Ünver, Ümit Tural
The patients participating in the study were given 1H-MRS twice before the first ECT and after the 6th ECT. 1H-MRS scan was taken once for the control group. 1H-MRS scanning was performed with the Philips 3 Tesla Achieva/Intera Release 2.6.1 12.6 series whole body scanner MR device (Philips Medical Systems, Eindhoven, The Netherlands). Patients were asked not to move during the scan and practitioner technicians were observed the patients during the procedure. The imaging process took about 20 min for each case. T2 weighted spin echo (Time to Repetition: TR: 3000, Time to Echo: TE: 80 ms, slice thickness: 5 mm) was performed on the axial, coronal and sagittal planes of the subjects. T1 weighted spin echo on the sagittal plane (Time to Repetition: 20, Time to Echo: 2.1 ms, slice thickness: 2 mm) were applied with 8-channel head coils. Single voxel long TE point resolved surface coil spectroscopy (PRESS) spectra was acquired using automated single-volume 1H-MRS software for water and oil suppression. Taking the Talairach coordinate system as reference, an 8 cm3 voxel (2 × 2×2 cm) was placed in midline ACC. The voxel of ACC was chosen anterior part to genu of corpus callosum. The inferior line of the voxel was aligned with line from anterior commissure to posterior commissure (Figure 1). NAA peak at 2.02, Cho peak at 3.22 and Cr peak at 3.03 ppm were measured.
Development of a three-dimensional body shape model of young children for child restraint design
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2018
Monica L. H. Jones, Sheila M. Ebert, Matthew P. Reed, Kathleen D. Klinich
A comprehensive description of the human subject testing can be found in Kim et al. (2015). Briefly, traditional manual anthropometric measures were gathered from each child to characterize the overall body size and shape using techniques similar to those used by Snyder et al. (1977). The locations of body landmarks were measured using a three-dimensional coordinate measuring machine (FARO Technologies) and measurement methods derived from those used in previous studies for both adults and children (Reed et al. 1999, 2005, 2006). Body shape and surface contours were recorded in a range of seated postures using a VITUS XXL whole-body laser scanner and a specially constructed seating fixture as shown in Figure 2. A hand-held infrared scanner was used to record contours in body areas shadowed from the whole-body scanner, such as the lap. The locations of surface landmarks on the participants were recorded via skin targets stamped on the skin prior to scanning and manually extracted from surface scan data using a custom script in Meshlab software (meshlab.org).