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Single Photon Emission Computed Tomography (SPECT) and SPECT/CT Hybrid Imaging
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
Michael Ljungberg, Kjell Erlandsson
Prior to SPECT/CT, most manufactures offered transmission imaging using either scanning-line sources, scanning-point sources, a single static line source or multiple static line sources. These systems were used to generate maps of linear attenuation coefficients for attenuation compensation [7], although the poor resolution and image quality prohibited more diverse applications. The need for faster and better attenuation maps, as well as anatomical localization capability, led to the development of SPECT/CT.
Brachytherapy Clinical Introduction
Published in W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald, Handbook of Radiotherapy Physics, 2021
Intraluminal brachytherapy delivers brachytherapy typically through a single line source using an afterloading catheter placed within the lumen of a tubular structure such as the oesophagus, bronchus, rectum or biliary tract. Usually, the catheter is passed through the tumour-bearing region under direct vision or with radiological guidance and verification. Using a single line source with equal dwell times results in a cigar-shaped distribution with dose fall-off at each end, which should be taken into account when defining the CTV; the dose prescription is conventionally at 1 cm from the central axis of the source. Clearly, this means that the use of this technique is limited to those tumours that can be encompassed by a 2 cm diameter cylinder of high dose. There are also issues in relation to eccentric positioning of the catheter within the lumen, and various devices using balloon catheters or umbrella catheters have been devised to enable centring of the line source within the lumen.
The external radiation hazard
Published in Alan Martin, Sam Harbison, Karen Beach, Peter Cole, An Introduction to Radiation Protection, 2018
Alan Martin, Sam Harbison, Karen Beach, Peter Cole
Note that at distances that are short in comparison to the length L of the source, the dose rate from the line source at point P reduces approximately as 1/r (and not 1/r2 as it was from a single point source). This indicates the ‘cylindrical geometry’ of a line source (as opposed to the ‘spherical geometry’ of a point source). The dose rate reduces with distance away from a line source; however, it does not drop off as quickly with distance as it does from a point source. Thus, although increasing the distance from a line source is still a valid radiation protection measure, it is not as effective as it is for a point source.
Experimental validation of acoustic and thermal modeling in heterogeneous phantoms using the hybrid angular spectrum method
Published in International Journal of Hyperthermia, 2021
Megan Hansen, Douglas Christensen, Allison Payne
Acoustic and thermal property characterization was performed on each gelatin and canola-oil component of the phantoms using techniques that have been previously described [25]. In particular, through-transmission testing was employed to measure the speed of sound and attenuation of the materials using the W-Type phantoms [28]. The density was calculated by dividing phantom mass by calculated cylinder volume. After through-transmission testing with the W-Type phantoms, a commercially available device (KD2 Pro Thermal Properties Analyzer, Decagon Devices, Pullman, WA) pierced the ends of the phantoms for transient-line-source measurements of thermal diffusivity. This device has two 30-mm-long probes spaced 6 mm apart, with one probe being used for heating and the other for temperature measurements. Thermal measurements were not possible in the canola oil with this tool and therefore previously published values were used [29]. The measurement uncertainty of each technique was determined based on the variability of the experimental data or the manufacturer's reported precision.
Enhancing perioperative landmark detection during sacroiliac joint fusion in patients suffering from low back pain
Published in Computer Assisted Surgery, 2021
Bas Schippers, Edsko Hekman, Sven van Helden, Martijn Boomsma, Jochen van Osch, Robert Nijveldt
Although visually valid DRRs were obtained, one intrinsic factor within the proposed approach might have decreased DRR accuracy. The DRR algorithm does not incorporate the magnification factor that is present in the obtained fluoroscopy images correctly as it simulates a line source instead of a point source. Although not clearly visible, this factor intrinsically reduced the similarity between the fluoroscopy and DRR images. Implementing a point source, which was not available in this study, could potentially resolve this issue. Additional discrepancies between fluoroscopy and DRRs could be caused by different patient position during data acquisition, as the CT scan was obtained in supine position while the perioperative fluoroscopy images were acquired in prone position. Obtaining CT scans and fluoroscopy imaging in identical positions could resolve this limitation. Despite the increased bone visualization on the DRRs, thresholding introduced considerable visible discrepancies between the fluoroscopy and DRRs on soft tissue and image contrast. It is expected that these discrepancies hindered the implementation of an automatic intensity-based and feature/landmark-based registration algorithm as a high degree of mutual information is lacking [18].
Thermal diffusivity and perfusion constants from in vivo MR-guided focussed ultrasound treatments: a feasibility study
Published in International Journal of Hyperthermia, 2018
Christopher R. Dillon, Viola Rieke, Pejman Ghanouni, Allison Payne
Immediately following the MRgFUS experiment, the rabbits were euthanised and, in two of the three animals, invasive measurements of thermal diffusivity in the back muscle were made with a commercial thermal property analyser (KD2 Pro, Decagon Devices, Pullman, WA). The property analyser induces a 1–3 °C temperature rise in the tissue over 2 min via a thin-needle that applies uniform power along its 30 mm length. A second needle spaced 6 mm away measures transient temperature changes in the tissue. Fitting the transient temperature data with the analytical temperature solution for an infinite line source with constant power per unit length [35] yields the thermal diffusivity of the tissue. The manufacturer reported accuracy of this device is ±10% for thermal diffusivity between 0.1 and 1.0 mm2 s−1. In total, nine measurements were made at unique locations within the back muscle.