Dual-energy CT and CT perfusion for improved CT stroke imaging

Abstract

Cardiovascular diseases (CVDs) are the leading causes of death in the world. An estimated 17.9 million people died from a CVD worldwide in 2016. The majority, 85% of deaths, is caused by either a heart attack or a stroke[1]. In the Netherlands, 38199 people died of a CVD in 2018, of which 9176 died of a stroke[2]. Not only does stroke significantly contribute to mortality, it is also a leading cause of disability[3]. Because of the aging population, the number of stroke patients is expected to increase[4]. Strokes can be divided into two groups: 1) ischemic strokes caused by an arterial occlusion, for example by a (temporary) clot, and 2) hemorrhagic strokes caused by a rupture of a vessel[5]. In this thesis we will be focusing on ischemic strokes. Currently, treatment options for ischemic strokes are intravenous administration of tissue plasminogen activator (tPA) for clot dissolution, intra-arterial thrombolysis, and endovascular mechanical clot removal[6]. Therapeutic interventions are most effective when initiated in the early stages after a stroke[7-9]. Guidelines state that intravenous thrombolysis should only be administered to patients within 4.5 hours, and endovascular treatment should only be initiated within 6 hours of ischemic stroke symptom onset[10]. Brain tissue damage may be irreversible, and the loss of brain tissue continues while the arterial occlusion persists. Therefore in stroke care the phrase "time is brain" is often used, meaning that the diagnosis and treatment of a stroke should be as fast as possible. This explains why the preferred imaging modality for acute stroke imaging usually is computed tomography (CT)[11]. CT is fast, relatively cheap and widely available. The acute stroke imaging protocol usually consists of noncontrast CT, CT perfusion and CT angiography scans. CT imaging in stroke Non-contrast CT In stroke imaging, the first acquisition is non-contrast CT (NCCT) of the entire brain. The primary goal of NCCT is to differentiate between ischemic and hemorrhagic strokes. Since blood has a higher attenuation than brain tissue, it appears hyperdense on a CT scan and can therefore be easily detected (Figure 1.1A). In addition to differentiating ischemic from hemorrhagic strokes, NCCT also provides some information on the extent of cerebral ischemia. On NCCT, subtle loss of gray-white matter differentiation and evidence of swelling can be first indications of ischemic stroke[12]. The ischemic area appears hypodense on NCCT (Figure 1.1B). Figure 1.3 | Examples of contrast enhancement curves: A) arterial input function (AIF) and venous output function (VOF), B) gray matter (GM) and white matter (WM). The dashed line shows the partial volume corrected AIF. Figure 1.5 | Illustration of three dual-energy CT techniques. A) Dual-source DECT utilizes two X-ray tubes and two detectors to generate low-and high-energy spectra, B) rapid kV switching utilizes one X-ray tube and detector and switches rapidly between a low and high tube voltage and C) detector-based spectral CT utilizes one X-ray...