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Quantification in Emission Tomography
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
Brian F. Hutton, Kjell Erlandsson, Kris Thielemans
Inter-reconstruction correction: In motion-compensated image reconstruction (MCIR), the deformation is directly incorporated into the iterative reconstruction process. A separate system model that includes the warping is used for each motion state, and a single image is directly reconstructed from all the motion states. As all data are used, this approach does not suffer from the bias problem of RRA, while it has similar computational requirements. However, RRA images can have a less noisy visual appearance due to averaging effects from the interpolation used for the resampling [68, 69].
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
Most commercial scanners allow the user to choose between filtered back projection (FBP) and iterative reconstruction methods. Furthermore, if the iterative reconstruction method is chosen, the “strength” can be set by the user. Iterative reconstruction methods have the potential to reduce the dose for a given image quality or to reduce the image noise for a given level of radiation exposure [30]. Although iterative reconstruction techniques increase the image quality when measured quantitatively, the images may appear smoother or glossier, which is disturbing to radiologists familiar with the texture known from FBP-reconstructed images. Consequently, vendors and scientists have embarked upon new ways of generating something that looks like a high-dose FBP image from low-dose images, and one promising path is to use deep-learning algorithms to up-convert low-dose images to high dose quality without changing the noise-texture of the images. One such commercially available deep-learning approach was recently presented. It is called True Fidelity and is developed by GE Healthcare. Their Deep Learning Image Reconstruction (DLIR) features a deep neural network that has been trained on high-quality FBP data sets in order to learn how to differentiate noise from signals, and thus to suppress noise without impacting anatomical and pathological structures [31].
Computed Tomography Imaging in Radiotherapy
Published in W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald, Handbook of Radiotherapy Physics, 2021
The measured attenuation along each ray path through the patient is representative of the sum of the attenuation coefficients of all voxels along the path. At each tube angle, the transmission profile along one detector row is back-projected uniformly onto the image area at the corresponding angle. The combination of back-projections for a full 360° rotation allows the reconstruction of a 2D image representing a transverse slice of the patient, where each pixel is attributed a specific attenuation coefficient. However, the resulting image would be blurred if the profiles were not filtered before back-projecting them onto the image space. This is achieved by applying a reconstruction kernel called a filter or convolution filter or algorithm. Such filtered back-projection is the standard reconstruction technique used in CT. Another reconstruction technique called iterative reconstruction will be discussed in Section 32.4.2.3.
Long axial field-of-view PET/CT devices: are we ready for the technological revolution?
Published in Expert Review of Medical Devices, 2022
Luca Filippi, Antonia Dimitrakopoulou-Strauss, Laura Evangelista, Orazio Schillaci
In last decades hybrid imaging, combining molecular and anatomical data in a unique, synergistic approach, has thoroughly changed the face of medical diagnostics [1,2]. In particular, positron emission computed tomography (PET/CT) has established itself as an essential tool in many oncological and non-oncological scenarios [3], providing the opportunity of investigating in vivo physio-pathological processes at a cellular and molecular level [4,5]. Notably, in recent years some technological improvements have been introduced in PET imaging, such as novel iterative reconstruction algorithms, or time-of-flight (TOF) PET/CT scanners operating in fully-3D mode [6]. Most importantly, the silicon photomultiplier (SiPM)-based detectors have been implemented instead of the ‘old-fashioned’ photomultiplier tubes (PMTs) [7,8], giving rise to the so-called digital PET/CT (dPET/CT). With respect to the PMT-equipped PET/CT, namely analogue PET/CT (aPET/CT), dPET/CT is characterized by higher sensitivity, spatial and temporal resolution, with a significantly greater detection rate of pathological lesions, also employing fast protocols [9–15].
Making computed tomography safer for patients with Crohn’s disease
Published in Scandinavian Journal of Gastroenterology, 2022
John O’Grady, Brian W. Carey, Richard G. Kavanagh, Aislinn O’Connell, Owen J. O’Connor, Elizabeth Kenny-Walsh, Syed A. Zulquernain, Michael M. Maher, Fergus Shanahan
Imaging modalities that do not require radiation with similar sensitivity and specificity to CT [3], such as MRI and ultrasound, have an important and expanding clinical role. However, current increased availability, accessibility, and reduced cost of CT compared with MRI suggest an ongoing essential diagnostic role for CT in Crohn’s disease. Furthermore, MRE performed following diagnostic CT may offer little additional information [21]. CT in the acute setting where disease complications are suspected is also preferred over MRI. Reduced radiation exposure from CT imaging, without compromising image quality, is, therefore, worth pursuing. Iterative reconstruction (IR), as used in this study, enables re-construction of CT images acquired with reduced radiation dose as an alternative to traditional re-construction techniques, such as filtered back projection (FBP) [22]. This technique has been applied to abdominal imaging [15,23], and previously effective in the investigation of patients with Crohn’s disease [7–9].
Use of coronary artery calcium and coronary tomography angiography in the evaluation of ischemic heart disease
Published in Hospital Practice, 2022
Abdullah Zoheb Azhar, Devesh Rai, Dhrubajyoti Bandyopadhyay, Wojciech Rzechorzek, Tauseef Akhtar, Wilbert S. Aronow, Pragya Ranjan
The CAC is calculated noninvasively using multi-detector non-contrast CT. It is the measurement of calcified plaque burden in epicardial coronary vessels. Studies have shown an association between coronary calcium and obstructive coronary artery disease[13]. Coronary artery calcium was defined as a lesion greater than 130 Hounsfield units on CT with an area greater than three adjacent pixels (at least 1 mm2)[14]. The product of the calcified plaque area and the maximal calcium lesion density determines Agatston’s original calcium score (from 1 to 4 based on Hounsfield units)[3]. The CAC score has been divided into standardized categories, with 0 indicating no calcified plaque, 1 to 10 minimal plaque, 11 to 100 mild plaque, 101 to 400 moderate plaque, and ≥400 severe plaque. Current guidelines suggest that a CAC score can help improve cardiovascular risk assessment in asymptomatic persons and play a role in preventative management[15]. Modern coronary calcium scans may be completed in 10 to 15 minutes of total room time at roughly 1 mSv of radiation. The sole requirement is the need to hold one’s breath for 3 to 5 seconds. Newer techniques, such as iterative reconstruction, have substantially reduced the radiation burden as well[16]. Consistent and progressive relationship between coronary artery calcification and ACS has been shown in population-based cohorts such as HNR (Heinz Nixdorf Recall [Risk Factors, Evaluation of Coronary Calcium and Lifestyle]), Rotterdam and MESA (Multi-Ethnic