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Clinical Perspectives of Spectral Photon-Counting CT
Published in Katsuyuki Taguchi, Ira Blevis, Krzysztof Iniewski, Spectral, Photon Counting Computed Tomography, 2020
Salim Si-Mohamed, Loic Boussel, Philippe Douek
Conventional and Dual-energy CT with dual-source and detector assembly with their superior quality for imaging coronary arteries and functional cardiac imaging capability is increasingly used as a noninvasive imaging investigation. They have been proposed to detect myocardial perfusion defects, including following acute or chronic infarction (38). However, studies using CT data are susceptible to beam-hardening artefacts that may mimic perfusion defect. Furthermore, CT, as MRI, allows a visualization of the perfusion defect but not a real quantification of the perfusion. This quantification can be performed with PET but again with a poor accessibility and a high cost. Finally, the radiation dose in perfusion CT is currently too high for a clinical application of CT perfusion.Similarly, studies in animals and humans indicate that myocardial perfusion studies performed with CT accurately detect myocardial ischemia and infarcts compared with single photon emission computed tomography (SPECT), but includes a rather high-radiation exposure. Furthermore, the detection of myocardial late enhancement has been demonstrated with conventional CT (39). However, because of the poor contrast between normal and abnormal myocardium in late enhancement studies with conventional CT limits its clinical use and its potential in determining precisely the different components of reperfusion myocardial lesions.
Iterative Reconstruction Methods in X-ray CT
Published in Paolo Russo, Handbook of X-ray Imaging, 2017
Geert Van Eyndhoven, Jan Sijbers
The most well-known application of dynamic CT can probably be found in medical CT (see also Section III, Chapter 41, for 4D CT diagnostic imaging). The motion of the heart and/or lungs cause tissue to deform during the imaging process, making the tomography problem a dynamic one (Nehmeh and Erdi 2008). In gated CT, projections are sorted into several phase bins, and a reconstruction is generated separately for every separate phase bin. The sorting is typically performed with an external breathing or electrocardiogram (ECG) signal (Low et al. 2003; Vedam et al. 2003; Nieman 2014a). In order to improve reconstruction quality, the correlation of reconstructions at adjacent phases can be exploited by temporal regularization (Jia et al. 2010; Gao et al. 2011). Approaches without gating typically incorporate motion models into the reconstruction algorithm (Rit et al. 2009; Van Eyndhoven et al. 2012; Van Nieuwenhove et al. 2017). Another medical dynamic CT application is perfusion CT, where a contrast bolus is injected into the patient's blood stream and the local concentration changes in an organ of interest (brain, lung, liver, etc.) are monitored (Miles and Griffiths 2003). The same type of dynamic problems are naturally also encountered in small animal imaging (Schambach et al. 2010).
Central nervous system
Published in David A Lisle, Imaging for Students, 2012
Perfusion-weighted imaging can also be used to calculate the relative blood supply of a particular volume of brain. For PWI, the brain is rapidly scanned following injection of a bolus of contrast material (gadolinium). As for perfusion CT, the data obtained may be represented in a number of ways including maps of regional cerebral blood flow, cerebral blood volume and mean transit time. In general, the perfusion defects identified with PWI are larger than the diffusion abnormalities shown on DWI; the difference between these areas represents the ischaemic penumbra. MRI using DWI and PWI is therefore able to diagnose hyperacute infarction and identify the ischaemic penumbra.
Computer-aided detection and characterization of stroke lesion – a short review on the current state-of-the art methods
Published in The Imaging Science Journal, 2018
Shervin et al. presented a study to identify the ‘at-risk’ penumbral tissue destined to infarct in acute stroke patients with large vessel occlusion. Absolute and relative MTT-CTP maps with suitable thresholds could optimally differentiate the penumbra from benign oligaemia in acute stroke patients [24]. Kawiorski et al. conducted a validation study to correlate the clinical and radiological aspects to identify the potentially salvageable tissues through perfusion CT. It was reported that perfusion CT provides better indicators to identify viability of tissues and it could predict the degree of progress after reperfusion therapy [25]. Kheradmand et al. presented a study to compare the prediction value of perfusion CT for ischaemic stroke. The reported results present that the MTT overestimates the ischaemic penumbra. Also, the time to peak (TTP) parameter with proper threshold serves as a good predictor of infarct in acute stroke [26]. Bivard et al. [27] presented a study to identify PCT thresholds for ischaemic core and salvageable penumbra in acute stroke patients. The TTP parameter with an increase in value of 5 s was able to define the penumbra in a better way when compared to CBF values. Table 8 presents an overview on the surveyed methods of advanced imaging modalities of stroke.