By Hana Ohama Slevin and Akira Oikawa
Healthcare professionals are finding that computed tomography (CT) images are useful in determining the seriousness of the new coronavirus infection. CT scans may be used to make an early diagnosis of suspected or mild cases of the infection. CT scans have assisted in determining the risk of the patient’s condition becoming serious or needing hospitalization. Expansion of PCR tests is a most urgent issue in Japan, but the effective use of CT scans is needed as well.
Shigeru Omi, vice chair of the government’s expert panel on coronavirus measures, explained in a May 4 press conference that “the number of PCR tests conducted in Japan is small, but the number of CT’s are high compared with other countries. There has been little oversight of serious cases that led to pneumonia.” Omi suggests that CT scans play an important role in pinpointing serious cases and crafting a response to them.
A PCR test detects a virus’s genetic material. A CT scan uses X-rays to examine the lungs or other parts of the body. A CT scan does not detect the virus itself, and thus cannot definitively determine whether a patient is infected. If the patient has pneumonia, a CT scan will determine its severity and characteristics. While the number of PCR tests is lagging, many medical facilities are using the CT scan [for diagnosis of the coronavirus].
A paper by the Japan Radiological Society states that a CT scan does not replace a PCR test. The paper says it is “permissible” to use a CT scan can as a measure to determine whether a patient should be hospitalized. In case of patients with severe symptoms, the paper recommends a CT scan as a method of “triage” to determine which patients should be given priority in treatment.
A CT scan is useful in determining severity, something that cannot be determined by a PCR test. The Self-Defense Forces Central Hospital, which admitted patients from the Diamond Princess cruise ship, reported that a CT scan found lung abnormalities in about half of the asymptomatic and mild patients. The condition of one-third of such patients later worsened.
St. Marianna University School of Medicine Hospital uses the CT scan to predict whether some patients’ conditions will become serious. The observation of a “shadow” in the CT scan of the lungs several days after the development of fever is taken as an indication that the patient is at high risk of aggravation.
Japan lags behind in the number of PCR tests. According to the government’s experts panel, the number of tests per 100,000 people is 187, far lower than the figure of several thousands in other major countries.
Japan has one of the world’s highest number of CT scanners. According to the Organisation for Economic Co-operation and Development (OECD), Japan has about 112 CT scanners per 1 million people. This figure is much higher than in the U.S. and Europe, where it is less than 50 per 1 million people. It is much easier to get a CT scan in Japan than elsewhere.
There are issues associated with CT scans. Special attention is required to prevent infection in the scanning room. Careful disinfection is indispensable. Many people who are not coronavirus patients also need to take a CT scan. If the number of infections increase, facilities may not be capable of handling many patients. The Japan Radiological Society emphasizes that it “does not recommend a CT scan for all patients with the coronavirus infection.” (Partially abridged)