Ground glass (GG) foci are the commonest manifestation of Covid-19 and in subtle cases, may be difficult to diagnose. This difficulty may then turn a positive into a negative scan.
Here are two ways to improve conspicuity of GG areas during interpretation.
1. Minimum Intensity Projection (minIP) images while scrolling on the workstation. I use a 3 mm sliding minIP and it allows quick pick-up of subtle lesions. In this case (top row), while a static image does not capture the impact of minIP while scrolling, we can see that the GG focus in the posterior segment of the right upper lobe (RUL) is better appreciated on the minIP image.
2. Monenergetic low keV imaging (middle row). For those who have dual energy imaging, a lower keV image set picks up GG much better. In this patient with pre-existing UIP-IPF and acute exacerbation due to Covid-19, the GG in the posterior segment of the RUL is much better appreciated on the 40 keV image (regular image is 120 keV), even though the 40 keV image is noisier.
If you do a head-to-head comparison (bottom row), 40 keV is better than minIP, which is better than a regular image.