Module 04. Hybrid Imaging-Hybrid Imaging (Slides)

Hybrid Imaging (Slides)
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Module 4 of this document focuses on hybrid imaging with PET/CT. The learning objectives of this module include understanding the uses of hybrid imaging for attenuation correction, examining CT-related artifacts and strategies for mitigation, understanding strategies for acquiring CT data for assessing coronary calcium, and maximizing image quality while minimizing radiation dose. <br /><br />Hybrid imaging with PET/CT is important for various reasons, such as high count transmission study for attenuation correction, assessment of coronary calcium, assessment of anatomical structures, CT angiography, equipment sharing with other departments, and combining PET and CT systems. <br /><br />The production of X-rays in a CT scanner involves electrons accelerated in a vacuum tube and stopped in a block of Tungsten, which then emits X-rays (Bremsstrahlung Radiation). The X-ray tube settings include kVp (voltage) and mAs (milliamps), which determine the kinetic energy of electrons and the flux of electrons, respectively. <br /><br />Multi-detector CT systems have advantages over single-detector systems, such as increased scanned volume, shorter scan time, shorter breath-hold, more redundancy, and finer plane-plane resolution. The resolution of a CT system depends on the number of slices, with a higher number of slices leading to a more isotropic point spread function. Temporal resolution is limited by the rotation speed of the scanner. <br /><br />PET/CT combines PET and CT systems, with attenuation correction being very straightforward and accurate in PET due to higher system sensitivity and resolution. Two approaches to attenuation correction in PET include physical origins of attenuation, such as Rayleigh scattering, Compton scattering, and the photoelectric effect. <br /><br />Transmission Computed Tomography (TCT) is used for attenuation correction in PET/CT, with dedicated systems using rotating sources. CT acquisition for attenuation correction in PET involves converting CT numbers to attenuation coefficients. Motion in cardiac PET/CT can cause misregistration, which can lead to false positive results. Strategies to minimize motion artifacts include breath-hold with misregistration compensation. <br /><br />CT quality control is important in PET/CT, with factors such as image quality, image uniformity, image noise, slice thickness, and CT number accuracy being assessed. Radiation dosage in CT can be minimized by adjusting scanner parameters, such as kVp and mAs. Lead shielding is very effective in reducing worker radiation exposure in CT due to the low photon energy beam. <br /><br />Overall, hybrid imaging with PET/CT is a valuable tool for attenuation correction and assessment in nuclear cardiology. Various strategies can be employed to optimize image quality and minimize radiation dose in CT.
Keywords
hybrid imaging
PET/CT
attenuation correction
CT-related artifacts
CT data
coronary calcium
image quality
radiation dose
X-rays
CT scanner