The use of spectral CT with electron density imaging is showing promise to improve the assessment of lung lesion severity in patents with early-stage COVID-19. According to Beatrice Daoud and colleagues at Antony's Private Hospital in France, "we report the first retrospective data from the spectral chest CT findings of patients with reverse transcription-polymerase chain reaction (RT-PCR)-confirmed COVID-19 (i.e., patients with positive RT-PCR test results)."
Since March 17, 2020, every patient who has had CT performed at the authors' institution for either suspected or RT-PCR-confirmed COVID-19 has undergone dual-layer detector-based spectral CT (IQon Spectral CT, Philips Healthcare). In order to evaluate spectral imaging, specifically electron density imaging, two thoracic radiologists reviewed the cases of four patients who each underwent two chest CT scans for confirmed COVID-19.
In all four patients, their pulmonary lesions (45 ground-glass opacities, overall) were more conspicuous on electron density images than on initial conventional CT images and were clearly confirmed on follow-up conventional CT images. Additionally, lesion extent was analyzed using semiquantitative reporting scale denoting surface area involvement for each lobe, was easier to ascertain on electron density images. With Daoud and colleagues' results indicating electron density imaging improves early assessment of the extent of ground-glass opacities that could be missed by conventional CT, electron density showed the most promising results by enhancing the contrast of ground-glass opacities compared with the normal lung.
"We reviewed conventional chest CT images obtained with a parenchyma kernel and standard lung window setting, as is usually the case in everyday radiology practice," Daoud et al. explained, adding that they analyzed these images with conventional images using a soft mediastinum kernel and standard lung window setting, conventional images obtained using a soft mediastinum kernel and narrow lung window setting, virtual low-monoenergy images, virtual high-monoenergy images, and electron density images.
"Our results suggest that the better ground-glass opacity visualization obtained using electron density imaging may be chiefly related to the increased visual noise in the image with soft kernel reconstruction and narrow lung window setting compared with electron density imaging, for which narrowing the window does not impair image quality," concluded the authors.