FAQ – HRCT in COVID-19

Dr. Nishikant Lokhande
Consultant Radiologist
Orange City Hospital & Research Institute

Q:  What is HRCT chest?
ANS: HRCT is the short form of High Resolution Computed Tomography, which is a method of examination with a modern CT scan machine which enables a volume HRCT scan covering whole lung tissue. High resolution refers, the thin sections of lung i.e. thickness upto 0.5mm.

Q:   Is it harmful?
ANS: No. Although CT scan uses X-Rays for imaging, modern CT scan machine uses vary less radiation to scan your lungs, so, there is no consistent evidence that there is any health risk.

Q:   How is it helpful in Covid-19 infection?
ANS: Covid-19 infection has wide spectrum of symptoms viz. fever, headache, cough, loose motions, body pains, loss of taste & smell, etc., These infections are predominantly involving the lungs & cause multiple patches of pneumonia. HRCT is very helpful in detecting these pneumonias in vary initial stage, if present.

In the symptomatic patient with negative RT-PCR test for Covid-19, HRCT chest can be investigation of choice to see lung involvement. It can be very well categorized with CO-RADS classification

CO-RADS CLASSIFICATION

Chances of COVID

CT Finding

CO-RADS 1

No

Normal or Non-infectious abnormalities.

CO-RADS 2

Low

Abnormalities consistent with infections other than COVID-19.

CO-RADS 3

Intermediate

Unclear whether COVID – 19 is present.

CO-RADS 4

High

Abnormalities suspicious for COVID-19.

CO-RADS 5

Very High

Typical Covid-19.

CO-RADS 6

PCR+

HRCT chest is helpful in staging the disease process which ranges from normal appearing lung to early, advanced, severe stages & also stage of healing / dissipation.

 

Q:   Can it give information about severity of the infection?
ANS: Yes.
The HRCT scan is also helpful in assessing severity of the disease process.
CT severity score can be calculated from the percentage of involvement of each lobe of bilateral lungs. It is very useful in evaluating the disease progression. nced, severe stages & also stage of healing / dissipation.

  • Affected lung in percentage per lobe – max.25 points.
    0% = 0 point;
    <5% = 1 point;
    5-25%= 2points;
    25-50% = 3 Points;
    50-75%=4 points
    75-100%= 5 points.

CT SEVERITY SCORE

Lung Segments

Points (out of 5)

Right Upper Lobe
Right Middle Lobe
Right Lower Lobe
Left Upper Lobe
Left Lower Lobe

Apart from this, it can detect other lung diseases as well.

CT severity score:  1 to 8 considered as mild disease.
                                      9 to 15 considered as moderate disease.
                                      16 to 25 considered as severe disease.

MILD

MODERATE

SEVERE

Q:   Does it need to get follow up HRCT scan done?
ANS: Depending on your clinical condition, your treating doctor will decided about the follow up HRCT scan.
It will be helpful in evaluating the lung opacities, weather it is increasing /progressing to more severe form or decreasing, with or without residual scarring of lungs.

POST-COVID-19 FIBROSIS

Q:   Can HRCT chest provide information about other pathologies than COVID-19?
ANS: Yes. Along with COVID-19, HRCT chest can provide information about many associated complication caused by COVID-19, like pulmonary thromboembolism (HRCT chest with contrast / pulmonary angiography), pulmonary infarcts, underlying interstitial lung disease, COPD and to the some extend cardiac abnormalities. HRCT chest can be also helpful in accessing the disease process than COVID-19, like other pulmonary infections, COPD, asthma & interstitial lung disease.

To sum-up HRCT chest is great diagnostic tool for evaluation of the lung involvement in the COVID-19 infection as well as other respiratory conditions.