ABSTRACT
PURPOSE: To determine whether new pulmonary lesions will develop in COVID-19 patients with negative initial chest CT findings and to investigate their CT features and outcome during treatment. PATIENTS AND METHODS: Data were collected retrospectively from 29 patients who had tested positive for COVID-19 by reverse-transcription polymerase chain reaction testing but negative by initial chest CT from January 22 to February 17, 2020. Clinical manifestations, laboratory indicators, and follow-up CT data were evaluated. RESULTS: Among 317 confirmed COVID-19 patients, 29 (9.1%) (mean ± SD, 38.5 ± 20.5 years; 12 women) with negative initial chest CT findings were evaluated. New pulmonary lesions developed in 10 (34.5%) patients on follow-up CT. Mean time from onset of new lesions to initial CT was 5.8 ± 3.0 days (range: 2-12 days). New lesions (mean involved lobes and segments: 2.5 ± 1.6 [range: 1-5] and 4.5 ± 4.5 [range: 1-13]) were mainly spherical/patchy ground-glass opacities frequently located in the left lower lobe (9, 90.0%). Among the 10 patients, lesions in 6 (60.0%) indicated progression after occurrence, and those in 10 (100.0%) indicated significant absorption on latest CT. When new lesions developed, 6 (60.0%) patients developed new symptoms or had aggravated symptoms and 3 (30.0%) had decreased lymphocyte count. Patients with worsening symptoms had higher involvement of lung segments (mean: 6.5 ± 5.0, range: 1-13) than asymptomatic patients (mean: 1.5 ± 0.6, range: 1-2) (P = 0.057). CONCLUSION: In COVID-19 patients with negative initial chest CT findings, new pulmonary lesions may develop during treatment. Repeat CT is necessary for monitoring the disease, especially when patients have worsening symptoms or laboratory indicators.
ABSTRACT
Cloud cover hinders the effective use of vegetation indices from optical satellite-acquired imagery in cloudy agricultural production areas, such as Guangdong, a subtropical province in southern China which supports two-season rice production. The number of cloud-free observations for the earth-orbiting optical satellite sensors must be determined to verify how much their observations are affected by clouds. This study determines the quantified wide-ranging impact of clouds on optical satellite observations by mapping the annual total observations (ATOs), annual cloud-free observations (ACFOs), monthly cloud-free observations (MCFOs) maps, and acquisition probability (AP) of ACFOs for the Sentinel 2 (2017–2019) and Landsat 8 (2014–2019) for all the paddy rice fields in Guangdong province (APRFG), China. The ATOs of Landsat 8 showed relatively stable observations compared to the Sentinel 2, and the per-field ACFOs of Sentinel 2 and Landsat 8 were unevenly distributed. The MCFOs varied on a monthly basis, but in general, the MCFOs were greater between August and December than between January and July. Additionally, the AP of usable ACFOs with 52.1% (Landsat 8) and 47.7% (Sentinel 2) indicated that these two satellite sensors provided markedly restricted observation capability for rice in the study area. Our findings are particularly important and useful in the tropics and subtropics, and the analysis has described cloud cover frequency and pervasiveness throughout different portions of the rice growing season, providing insight into how rice monitoring activities by using Sentinel 2 and Landsat 8 imagery in Guangdong would be impacted by cloud cover. [ABSTRACT FROM AUTHOR] Copyright of Remote Sensing is the property of MDPI and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)