Assessment of temporal resolution and detectability of moving objects in CT: A task-based image quality study.

The metrics used for assessing image quality in computed tomography (CT) do not integrate the influence of temporal resolution. A shortcoming in the assessment of image quality for imaging protocols where motion blur can therefore occur. We developed a method to calculate the temporal resolution of standard CT protocols and introduced a specific spatiotemporal formulation of the non-prewhitening with eye filter (NPWE) model observer to assess the detectability of moving objects as a function of their speed. We scanned a cubic water phantom with a plexiglass cylindrical insert (120 HU) using a large panel of acquisition parameters (rotation times, pitch factors and collimation widths) on two systems (GE Revolution Apex and Siemens SOMATOM Force) to determine the in-plane task-based transfer functions (TTF) and noise power spectra (NPS). The phantom set in a uniform rectilinear motion in the transverse plane allowed the temporal modulation transfer function (MTF) calculation. The temporal MTF appropriately compared the temporal resolution of the various acquisition protocols. The longitudinal TTF was measured using a thin tungsten wire. The detectability index showed the advantage of applying high rotation speed, wide collimations and high pitch for object detection in the presence of motion. No counterpart to the increase in these three parameters was found in the in-plane and longitudinal image quality.

Pulmonary embolism in patients with COVID-19: Time to change the paradigm of computed tomography.

OBJECTIVE: To raise awareness for possible benefits of examining known COVID-19 patients presenting sudden clinical worsening with CT pulmonary angiography instead of standard non-contrast chest CT.

Site and Rate of Occlusive Disease in Cervicocerebral Arteries: A CT Angiography Study of 2209 Patients with Acute Ischemic Stroke.

BACKGROUND AND PURPOSE: CTA can rapidly and accurately detect and localize occlusive disease in patients with ischemic stroke. We have used CTA to assess arterial stenosis and occlusion in an ischemic stroke population arriving at a tertiary stroke center within 24 hours of symptom onset in order to obtain a comprehensive picture of occlusive disease pattern, and to determine the proportion of eligible candidates for endovascular treatment. MATERIALS AND METHODS: Data from consecutive patients with acute ischemic stroke admitted to a single center between 2003 and 2012, collected in the Acute Stroke Registry and Analysis of Lausanne data base, were retrospectively analyzed. Patients with a diagnostic CTA within 24 hours of symptom onset were selected. Relevant extra- and intracranial pathology, defined as stenosis of ≥50% and occlusions, were registered and classified into 21 prespecified segments. RESULTS: Of the 2209 included patients (42.1% women; median age, 72 years), 1075 (48.7%) had pathology in and 308 (13.9%) had pathology outside the ischemic territory. In the 50,807 arterial segments available for revision, 1851 (3.6%) abnormal segments were in the ischemic (symptomatic) territory and another 408 (0.8%) were outside it (asymptomatic). In the 1211 patients with ischemic stroke imaged within 6 hours of symptom onset, 40.7% had symptomatic large, proximal occlusions potentially amenable to endovascular therapy. CONCLUSIONS: CTA in patients with acute ischemic stroke shows large individual variations of occlusion sites and degrees. Approximately half of such patients have no visible occlusive disease, and 40% imaged within 6 hours show large, proximal segment occlusions amenable to endovascular therapy. These findings show the importance of early noninvasive imaging of extra- and intracranial arteries for identifying occlusive disease, planning recanalization strategies, and designing interventional trials.