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Activity Quantification from Planar Images
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
where denotes the linear attenuation coefficient for the imaging radionuclide. Often the entire patient is scanned with the transmission source, thus yielding a whole-body attenuation-correction map . As an alternative to a 57Co flood source image, an X-ray scout may be used, which is otherwise acquired for positioning purposes before CT scans [19, 20]. The energy scaling (Eq. 25.15) then needs to be made with respect to the average energy of the X-ray spectrum. Figure 25.5 shows both kinds of attenuation maps. Note that the X-ray scout has the advantages of being considerably less noisy, includes less scatter, and is faster to acquire.
Special Considerations in Pediatric Nuclear Medicine
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
Sofie Lindskov Hansen, Søren Holm, Liselotte Højgaard, Lise Borgwardt
In order to correct for both overestimation and underestimation of the activity due to attenuation, a map of the linear attenuation coefficients, µ, is required. Computed Tomography images represent tissue attenuation and can thus provide the information needed to correct for attenuation. Attenuation correction becomes increasingly important with the size of the attenuating object. For this reason, attenuation correction plays a smaller role in younger children than it does in adults. This is also visible when comparing sub-figures (a) and (b) with sub-figures (c) and (d) in Figure 17.4. However, as is visible from 17.4 (c) and (d), attenuation correction does play a significant role in depicting the distribution of activity accurately throughout the body.
Application of dual energy x-ray absorptiometry
Published in R. C. Richard Davison, Paul M. Smith, James Hopker, Michael J. Price, Florentina Hettinga, Garry Tew, Lindsay Bottoms, Sport and Exercise Physiology Testing Guidelines: Volume I – Sport Testing, 2022
DXA uses two x-ray beams of different energies that are diversely attenuated by bone and soft tissue. The x-ray source (which in most models of DXA is usually below the scanner table) generates the x-ray beams containing photons, which are transmitted through electromagnetic energy. As the photons pass through the body, there is differential attenuation depending on the density of the tissues. The level of attenuation also depends on the energy of the photons and the tissue thickness. The measurement of bone is based on the assumption that the body is made up of two compartments: bone and soft tissue. Bone has a higher density than soft tissue, and therefore the photon energies are attenuated less. In order to image either tissue, the two energy beams are subtracted from one to another, to either subtract the soft tissue and image the bone or subtract the bone and image the soft tissue. In distinguishing what is lean and what is fat tissue, the bone is subtracted and the ratio of the two photon energies is linearly related to the proportion of fat in the soft tissue (Laskey, 1996). The resulting outcomes are bone mineral, lean tissue mass and fat mass.
Dual-zone material assignment method for correcting partial volume effects in image-based bone models
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
Brendan Inglis, Daniel Grumbles, Hannah L. Dailey
Partial volume effects (PVEs) are a known byproduct of medical imaging and image-based finite element analysis (FEA). Partial volume effects first arise at the image-acquisition stage. In computed tomography (CT) imaging, when tissues of widely different absorption are captured within the same CT voxel, they produce an effective local X-ray attenuation (Hounsfield Unit [HU]) that is proportional to the weighted average value for the tissues within the volume (Keyak et al. 1990; Merz et al. 1996; Cattaneo et al. 2001; Taddei et al. 2004). These partial volume effects appear as image “blur” at tissue boundaries, such as between mineralized and non-mineralized tissue (Falcinelli et al. 2016) and when resolving thin features in cortical bone (Pakdel et al. 2012). The blur creates a halo effect that thickens the apparent cortical geometry (Rittweger et al. 2004). These effects can be mitigated by acquiring images with smaller voxels, but they are inevitable. Image-acquisition PVEs can be mitigated through image deblurring using a deconvolution filter by estimating the point spread function of the acquired image, computing its inverse, and convolving the acquired image with that inverse (Pakdel et al. 2014; 2016).
Clinical Utility of 18F-FDG PET/CT in the Work-up of Children with Uveitis
Published in Ocular Immunology and Inflammation, 2023
M. Bazewicz, D. Makhoul, L. Goffin, J. El Mouden, L. Judice M. Relvas, L. Caspers, D. Draganova, L. Postelmans, C. Garcia, F. Willermain
18F-FDG PET/ ULD CT were performed using a PET-CT Discovery 690 (GE Medical Systems, Milwaukee, Wisconsin, USA). Prior to 18F-FDG injections, patients fasted for at least 6 hours. Blood glucose level was systematically measured before injection, and the patient was not injected if glucose was greater than 150 mg/dL. Strict intravenous injection of FDG following EANM pediatrics recommendations28 was adjusted for age and weight. Time-of-flight acquisition was performed with the patient lying in supine position, at least from the midthigh to the cranial vertex. No oral and no iodine-based contrast medium was administered. Typically the CT portion of the hybrid PET/CT was a low/ultra low dose CT using helical 64-row scan with the following parameters: 80 kVp, 5 mAs, and a pitch of 1.529:. The PET element was operated in 3-dimensional mode, for 1.5 minutes per bed position and overlap of 23.4%. Attenuation correction was based on the CT data. PET reconstruction parameters were as follows: slice thickness 3.27 mm, pixel size 2.73 mm, matrix size 192 × 192. PET images were reconstructed with the built-in GE Healthcare Advance software, using the ordered subset expectation maximization algorithm with 2 iterations and 18 subsets, and were postfiltered with a 6.4-mm full-width at half-maximum Gaussian function.
Digital PET/CT with 18F-FACBC in early castration-resistant prostate cancer: our preliminary results
Published in Expert Review of Medical Devices, 2022
Luca Filippi, Oreste Bagni, Orazio Schillaci
All the patients underwent PET/CT with 18F-FACBC according to present imaging guidelines [15]. All patients fasted for at least 4 hours before PET/CT scan and were asked to avoid any significant physical exercise 24 hours prior to the scan. Whole body PET/CT scan was performed, from the skull base to the proximal thigh, starting at 3–5 minutes after the intravenous (i.v.) injection of 370 MBq of 18F-FACBC. PET/CT scans were performed with a digital Biograph Vision PET/CT system (Siemens Healthcare; Erlangen, Germany). A CT scan from proximal thigh to skull base was performed with slice thickness of 1.0 mm, pitch factor 1, bone, and soft tissue reconstruction kernels and maximum of 120 keV and 90 mAs by applying CARE kV and CARE Dose. After CT scanning, a whole-body PET (proximal thigh to skull base) was acquired at 3–5 min post tracer administration in 3D (matrix: 440 × 440) with a zoom factor of 1.0. Digital PET was acquired on a Siemens Biograph Vision 450 with an axial FOV of 197 mm using continuous-bed motion (FlowMotion®) with a bed speed of 0.9 mm/s (equivalent to approximately 2 min/bed position). Reconstruction was conducted with a TrueX + TOF algorithm and Gauss-filtered to a transaxial resolution of 2 mm at FWHM (full width at half maximum). Attenuation correction was performed using the low-dose non-enhanced computed tomography data.