COVID-19 pneumonia – Chest X-ray or CT?

V.S. Lajarin, MD; C.G.Y. Verrastro, MD; A.S. Albuquerque, MD; P. Bertolazzi, BS*; G. Meirelles, MD
Radiology Department, Fleury S.A., Paraíso, Sao Paulo, SP, Brazil
* Siemens Healthineers, Brazil
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A 46-year-old female patient, suffering from coughing and dyspnea for the past two weeks, presented herself for a checkup. She had no fever and no history of smoking or previous pulmonary diseases. A chest CT examination was requested, based on a clinical suspicion of COVID-19 pneumonia.

CT images revealed multiple groundglass opacities (GGO) and sparse foci of consolidation in the posterior segment of both lower lobes. The extension of pulmonary involvement was, visually measured, less than 25%. Such findings, although nonspecific, were consistent with viral pneumonia. Subsequently, the patient underwent RT-PCR testing, which resulted positive for SARS-CoV-2.

CT imaging plays an important role in the evaluation of COVID-19 pneumonia at an early stage when RT-PCR tests may be negative or unavailable – a common scenario especially in developing countries. Typical findings on a chest CT are GGO, consolidation, “crazy-paving”, airways abnormalities and the reversed halo sign. These findings vary according to the stages of the infection. Chest X-ray abnormalities mirror those of CT, demonstrating bilateral peripheral consolidation, although less dense opacities such as ground glass may be very difficult to detect. Recent studies on COVID-19 reported a sensitivity of 69% for chest X-rays [1] and 98% for CTs.[2] CT is also applied to assess potential complications, such as viral and bacterial co-infections, pulmonary embolism or other conditions. Considering that these patients may have dyspnea, that some are young and that some may need repeated examinations as follow-ups, a quick and low-dose CT scan protocol is preferred. In this case, a so-called “Turbo Flash mode” is applied, providing ultra-fast scanning and an ultra-low radiation dose. The scanning is performed and completed in 0.46 s. This is enabled by a high pitch spiral scanning with a maximum table movement speed of 737 mm/s. A total effective dose of 0.18 mSv is achieved, which is within the dose range of a standard chest X-ray.[3] This significant dose reduction is mainly enabled by an advanced tin filter technology, which optimizes the X-ray spectra, minimizes beam-hardening artifacts and optimizes image quality by improving the air/tissue contrast. Standard dose reduction techniques, such as CARE Dose4D™ (automatic controlled tube current modulation) and ADMIRE (advanced modeled iterative reconstruction) also contribute to dose optimization.

As seen in this case, chest CT scanning, using Turbo Flash mode, has clear advantages over a chest X-ray – similar radiation dose, faster speed and higher sensitivity – to evaluate COVID-19 pneumonia, even at an early stage when chest X-ray is more prone to false negative results.

Axial image, coronal and sagittal MPR images show multiple mild patchy areas of GGO with sparse foci of consolidation in the posterior segment of both lower lobes.
Courtesy of Fleury S.A., Paraíso, Sao Paulo, SP, Brazil

Fig. 1: Axial image (Fig. 1a), coronal (Fig. 1b) and sagittal (Fig. 1c, left lung) MPR images show multiple mild patchy areas of GGO (arrows) with sparse foci of consolidation in the posterior segment of both lower lobes.

Fig. 2: Axial (Fig. 2a), coronal (Fig. 2b) and sagittal (Fig. 2c, left lung) views of VRT images demonstrate the corresponding areas in three dimensions.

Simulation of an anterior-posterior and a lateral chest X-ray, using CT images, suggest difficult or impossible visualization of the GGO due to overlapping with the heart or spine and mild density change.
Courtesy of Fleury S.A., Paraíso, Sao Paulo, SP, Brazil

Fig. 3: Simulation of an anterior-posterior (AP, Fig. 3a) and a lateral (L, Fig. 3b) chest X-ray, using CT images (MPR Thick reconstruction), suggest difficult or impossible visualization of the GGO due to overlapping with the heart or spine and mild density change.

Scanner

Scan area

Thorax

Scan mode

Turbo Flash mode

Scan length

331.6 mm

Scan direction

Caudo-cranial

Scan time

0.46 s

Tube voltage

Sn100 kV

Effective mAs

96 mAs

Dose modulation

CARE Dose4D

CTDIvol

0.34 mGy

DLP

12.5 mGy cm

Effective dose

0.18 mSv

Rotation time

0.25 s

Pitch

2.9

Slice collimation

2 x 96 x 0.6 mm

Slice width

1 mm

Reconstruction increment

0.7 mm

Reconstruction kernel

Br40/Br54 (ADMIRE 3)