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30th May 2022
A significantly higher proportion of CT chest scans in fully vaccinated patients who experience a breakthrough infection showed no signs of pneumonia during their stay in hospital, according to a study by Korean researchers.
COVID-19 vaccination across the globe has led to a protection against both symptomatic and asymptomatic COVID-19 as well as severe disease, hospitalisation and death. Although a CT chest scan has been described as an indispensable diagnostic tool in COVID-19, no studies have reported on using this imaging modality to examine the features associated with breakthrough infections that are generally less severe.
In the present study, the Korean team compared the imaging features of fully, partially and unvaccinated patients, who were hospitalised because of a COVID-19 infection. The team focused only on patients with a PCR-confirmed positive COVID-19 test result and who underwent at least one CT chest scan during their period of hospitalisation. Partially vaccinated individuals were defined as those for which the infection occurred less than 14 days after their first COVID-19 vaccine. In contrast, fully vaccinated individuals were those who became infected 14 days after their second vaccine dose. Using a retrospective design, the team collected demographic and co-morbidity data for all patients, as well as whether an individual required supplemental oxygen, was admitted to an intensive care unit (ICU) admission or died in hospital. The CT chest scans were obtained either upon admission or within a week of symptom onset and follow-up chest radiographs were obtained every two to three days until discharge. The extent of pneumonia was scored from 0 to 2 (i.e., 0 = no evidence, 1 = 1 – 25% involvement and 2 = > 25% involvement) and the patterns of pneumonia were categorised as either typical, indeterminate, atypical or negative. The researchers used logistic regression to evaluate any associations between clinical factors such as vaccination status and clinical outcomes.
CT chest scan and clinical outcomes
A total of 761 patients with a mean age of 47 years (51% women) were included, of whom, 77% were unvaccinated, 17% partially vaccinated and 6% fully vaccinated. Relevant co-morbidities for the whole cohort included hypertension (22%), diabetes (13%) and cardiovascular disease (5%).
All 761 patients underwent a CT chest scan at admission and 86% had at least one follow-up scan. During the initial scan, 63% of unvaccinated individuals had negative chest radiographs (i.e., a score of 0) whereas 75% of fully vaccinated patients were negative. In 412 patients who underwent a CT chest scan during their stay in hospital, there was no evidence of pneumonia in 59% of those who were fully vaccinated compared to 22% of those who were unvaccinated (p < 0.01).
Fully vaccinated patients were also significantly less likely to need supplemental oxygen (Odds ratio, OR = 0.24, 95% CI 0.09 – 0.64, p = 0.05) compared to unvaccinated patients and to be admitted to an ICU (OR = 0.08, 95% CI 0.09 – 0.78, p = 0.02).
The authors concluded that fully vaccinated individuals who experienced a breakthrough COVID-19 infection had a higher proportion of CT chest scans without signs of pneumonia compared with unvaccinated individuals.
Lee JE et al. Imaging and Clinical Features of COVID-19 Breakthrough Infections: A Multicenter Study Radiology 2022
15th November 2021
Using dark field x-ray, a team from the Department of Physics, Munich School of BioEngineering, Germany, were able to diagnosis emphysema in patients with COPD which to date has not been possible with conventional x-ray methods. Emphysema is caused by the irreversible destruction of alveolar walls, leading to enlargement of distal airspaces. Although this leads to changes in the lung structure, it is not possible to detect the early stages of emphysema with a conventional chest x-ray. As x-rays are subject to other effects such as refraction and ultra small-angle scattering which are not visualised with a conventional X-ray imaging system, in DFX, the contrast is produced by these multiple refractions on microstructures in the object. Hence, the dark-field signal enables visualisation of structural information that is inaccessible with conventional medical x-ray systems and dark field imaging has, for example, enabled the identification of acute lung inflammation in animal models.
With the potential to identify changes at the micro-structural level with dark field x-ray, indicative of emphysema, the German team undertook their study to examine whether this approach could improve the medical lung assessment in patients with COPD. Included patients were those with an initial indication of emphysema as revealed by a CT scan but still absent based on spirometry readings. However, a small number of patients with moderate to severe emphysema were also included. COPD classification was based on the post forced expiratory volume in one second (FEV1) and the forced vital capacity (FVC) as proposed by GOLD classification and patients with a FEV1/FVC value of 0.70 were assessed as having no COPD. Dark field x-rays were performed and visually assessed by five readers.
A total of 77 patients with a mean age of 65.9 years (male) and 63.3 years (female) were recruited with the majority (83%) at GOLD stage 0. Focusing on the first patient examined, the researchers described how the DFX showed that most parts of the lung yielded dark field values comparable with a healthy lung. A group of 42 patients from the cohort underwent diffusion capacity testing and it was found that the dark field signal gave a strong correlation than with either the CT emphysema index or the visual emphysema grading based on the CT-images.
Commenting on their findings, the authors reported that “in direct comparison, dark-field images and visual evaluation of CT images yield consistent findings regarding emphysema diagnosis.” They also added that the visual features seen with the dark field appeared to provide a greater diagnostic value than conventional emphysema charactering parameters. Moreover, while noting that there are currently no commercially available dark field systems available, their study has shown how the system does not require specialist knowledge and that it is operationally comparable to conventional radiography systems.
In their conclusion, they noted how DRX could offer a low radiation alternative to CT in patients with COPD adding that “x-ray dark-field chest imaging could contribute to improving the detection, diagnosis, and thus treatment and care of pulmonary disorders.”
Willer K et al. X-ray dark-field chest imaging for detection and quantification of emphysema in patients with chronic obstructive pulmonary disease: a diagnostic accuracy study. Lancet Digit Health 2021