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
 |  14.09.2020


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.

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.

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.

Examination Protocol

ScannerSOMATOM Force
Scan areaThorax
Scan modeTurbo Flash mode
Scan length331.6 mm
Scan directionCaudo-cranial
Scan time0.46 s
Tube voltageSn100 kV
Effective mAs96 mAs
Dose modulationCARE Dose4D
CTDIvol0.34 mGy
12.5 mGy cm
Effective dose0.18 mSv
Rotation time0.25 s
Slice collimation2 x 96 x 0.6 mm
Slice width
1 mm
Reconstruction increment0.7 mm
Reconstruction kernelBr40/Br54 (ADMIRE 3)


[1] Ho Yuen Frank Wong, et al. Frequency and Distribution of Chest Radiographic Findings in COVID-19 Positive Patients. Radiology. Published Online: Mar 27, 2020.

[2] Yicheng Fang, et al. Sensitivity of Chest CT for COVID-19: Comparison to RT-PCR. Radiology. Published Online: Feb 19, 2020.

[3] AAPM Report No. 96: The Measurement, Reporting, and Management of Radiation Dose in CT-Report of AAPM Task Group 23 of the Diagnostic Imaging Council CT Committee.

The outcomes by Siemens Healthineers customers described herein are based on results that were achieved in the customer’s unique setting. Since there is no “typical” hospital and many variables exist (e.g., hospital size, case mix, level of IT adoption) there can be no guarantee that other customers will achieve the same results.