4 ms·

So many things. "It takes doctors around 20 mins to do the same" is patently false. I would say a full review and dictation of a chest CT by a trained radiolog

So many things. "It takes doctors around 20 mins to do the same" is patently false. I would say a full review and dictation of a chest CT by a trained radiologist takes... 10 minutes? 20 if really complicated (metastatic cancer). But for the radiologist to decide whether or not there were findings compatible with COVID-19 (i.e. what this algorithm is performing) would probably take seconds. In fact, you could probably train almost any adult (and probably most children!) to distinguish between "possibly COVID" and "no COVID" lung CTs very quickly. However, as pointed out elsewhere, the presence of these findings (such as what we call "ground glass opacities" -- which is just a fancy/weird way to describe areas that are slightly less transparent than normal lung but not quite opaque) is not specific at all. They can be caused by COVID-19 or any number of other viral or fungal lung infections, as well as by reactions to drugs, hemorrhage or edema in the lungs, and so on. A positive CT would almost certainly require a confirmatory COVID-19 test. A negative CT scan in a patient with symptoms... would still demand a COVID-19 test, because findings in the lungs often lag behind the infection. So CT doesn't change your decision-making in the screening process. And they are time-consuming, costly, and harmful (they use radiation!). Their utility in caring for COVID-19 patients is probably to assess severity of disease, monitor response, and to rule out additional pathologies in the lungs. (Not to say AI couldn't help with those!)

_bxg1 7y ago
It also doesn't sound like it even lowers the bar for getting a diagnosis, even with all these caveats. You'd still need a CT scan, in a world where many can't even get a respirator. I'd be more interested in a model that tries to give a preliminary diagnosis (positive or negative) based on data a patient already has with them or can get at home. An image of their throat, audio of their cough, maybe a time sequence of thermometer readings. If we could self-diagnose (or at least rule out some cases) using a smartphone, that would truly change the game.
jcampbell1 7y ago
> And they are time-consuming, costly, and harmful (they use radiation!) To put things in perspective, I got a CT in China, and the imaging took less than 5 minutes, and cost $35 (just the machine, not reading). The radiation is less than the increased radiation than taking a flight to China. While your perspective is probably accurate for the US, if you step back and think, it is no more complicated than getting grade school photos.
- projektfu 7y ago
  By my math, a chest CT is about 10x the dose from a flight. However, there is no “safe” level of ionizing radiation. There is only acceptable and unacceptable risk.
  - klipt 7y ago
    Right, one CT scan increases your lifetime risk of cancer 0.1%: https://www.scientificamerican.com/article/how-much-ct-scans-increase-risk-cancer/ https://www.scientificamerican.com/article/how-much-ct-scans... Which isn't much for one person, but if you're CT scanning thousands of people, on average that's an extra case of cancer per thousand scanned. The PCR test is probably more accurate and in the US, maybe even cheaper? Although it probably does have higher latency.
  - jcampbell1 7y ago
    A lung CT can be done at about 1/5th the radiation dose of a chest CT. The future will decide if we took the correct risk with extremely limited testing in the early stages. In my experience, “not my job” , “too much risk”, and “need more data to make a decision“ is the default attitude in the medical profession. People choose that career because it is safe, and very few doctors have military experience these days. That being said, people adjust to a new reality very quickly.
    - projektfu 7y ago
      By the time pneumonia has occurred it’s too late for screening. This isn’t replacing rtPCR for people who are coughing.
- roywiggins 7y ago
  Keeping everyone safe and antiseptic while you move a possibly COVID patient in and out of a CT scan will make the whole thing way more complicated and slow.
zaroth 7y ago
I think everything that you've said is completely true. However, I'll add that it matters a lot more if you otherwise don't have testing capacity available, or if your test has a large false negative rate. China relied heavily on CT-based diagnosis to backstop a lack of available and reliable testing. Another issue is that modern sanitation standards don't really enable using a CT to diagnose an infectious disease. The equipment is far too slow and expensive to truly sanitize, you would have to be willing to just PPE the patient and hope that works out. Again, perhaps better than skipping any diagnostic testing altogether if you don't have any alternative, but certainly not a first-line choice, and ethically questionable if you risk exposing uninfected people.
- haldujai 7y ago
  Actually you just need to have them wear a mask and wipe down the equipment with standard hospital grade wipes. We know now that COVID-19 is not airborne and is spread by droplets only so this would be routine precautions, unlike TB which we scan routinely and is an airborne pathogen. The problem with CT is we know that the test is completely normal in 50% of patients from day 0-2, and 10-15% of patients up to day 5, and roughly 7-10% of patients up to day 10. These numbers are probably an under representation given how few people with the illness get CT imaging. Additionally as has been stated the findings are considered only somewhat specific, we believe that specificity will decrease as more and more people will eventually get scanned and prove our findings thus far to be false. That is why we (in radiology) currently recommend against the routine use of CT in screening or diagnosis of COVID-19 related illness as a negative test does not mean anything and a positive test is usually noncontributory (clinical diagnosis of COVID-19 infection already made). Additionally, this will rarely affect clinical management. The only potential argument being made is the small subset of people who have viral pneumonia and may theoretically avoid being asked to self-quarantine however I highly doubt in the present climate any infectious patient with a cough will be allowed/think it wise to roam the streets. China has also removed CT from their sixth edition diagnostic manual for this disease as an aside. Source is from STR/ACR, there is a good video below: https://veritastv.org/programs/covid-19 https://veritastv.org/programs/covid-19
  - 7y ago
throwGuardian 7y ago
The article fails to ask the obvious next question: if this can potentially apply to much cheaper and instantaneous tests, maybe something ultrasound based? I'm not an expert on medical imagining, so can someone comment on ultrasounds' usefulness here?
- doctoring 7y ago
  Ultrasound has a ton of untapped utility and is a fantastic medical imaging modality. Like you said, the equipment is cheap and portable (can be pocket sized, even!). It’s near instantaneous, allowing you to image in real time. You can even measure blood flow velocity and see other physiology. (I could go on!) But its great advantage over x-ray and CT, which is that it doesn’t use ionizing radiation, is also its greatest weakness. Ultrasound uses sound waves, of course, which unfortunately simply cannot travel very far in the body, and (critically) do not travel well across certain interfaces. One such interface is with air. Sound waves travel through your chest wall fine but on arriving at the lung... they just sort of fizzle out. Very little sound continues, and even less comes back to the transducer as meaningful signal. So ultrasound is unfortunately very poor at seeing lung tissue. (It can show us some secondary findings of pulmonary disease in the lungs, such as fluid collecting in the thoracic cavity [a pleural effusion], but that’s yet another non-specific finding.)
  - haldujai 7y ago
    Not entirely true. Ultrasound actually has pretty good sensitivity for pneumonia (88%) and even higher if you look at the “difficult” cases requiring CT in the Cochrane review I link to below. While the fundamentals of what you say are correct, consolidation by definition is the build up of fluid which is very well depicted by ultrasound. For a predominately peripheral airspace disease like COVID-19 ultrasound should theoretically be very sensitive. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5279077/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5279077/
    - doctoring 7y ago
      I wasn’t aware lung US was at this point — I’ll have to read more!

_bxg1 7y ago

It also doesn't sound like it even lowers the bar for getting a diagnosis, even with all these caveats. You'd still need a CT scan, in a world where many can't even get a respirator. I'd be more interested in a model that tries to give a preliminary diagnosis (positive or negative) based on data a patient already has with them or can get at home. An image of their throat, audio of their cough, maybe a time sequence of thermometer readings. If we could self-diagnose (or at least rule out some cases) using a smartphone, that would truly change the game.

jcampbell1 7y ago

> And they are time-consuming, costly, and harmful (they use radiation!) To put things in perspective, I got a CT in China, and the imaging took less than 5 minutes, and cost $35 (just the machine, not reading). The radiation is less than the increased radiation than taking a flight to China. While your perspective is probably accurate for the US, if you step back and think, it is no more complicated than getting grade school photos.

projektfu 7y ago
By my math, a chest CT is about 10x the dose from a flight. However, there is no “safe” level of ionizing radiation. There is only acceptable and unacceptable risk.
- klipt 7y ago
  Right, one CT scan increases your lifetime risk of cancer 0.1%: https://www.scientificamerican.com/article/how-much-ct-scans-increase-risk-cancer/ https://www.scientificamerican.com/article/how-much-ct-scans... Which isn't much for one person, but if you're CT scanning thousands of people, on average that's an extra case of cancer per thousand scanned. The PCR test is probably more accurate and in the US, maybe even cheaper? Although it probably does have higher latency.
- jcampbell1 7y ago
  A lung CT can be done at about 1/5th the radiation dose of a chest CT. The future will decide if we took the correct risk with extremely limited testing in the early stages. In my experience, “not my job” , “too much risk”, and “need more data to make a decision“ is the default attitude in the medical profession. People choose that career because it is safe, and very few doctors have military experience these days. That being said, people adjust to a new reality very quickly.
  - projektfu 7y ago
    By the time pneumonia has occurred it’s too late for screening. This isn’t replacing rtPCR for people who are coughing.
roywiggins 7y ago
Keeping everyone safe and antiseptic while you move a possibly COVID patient in and out of a CT scan will make the whole thing way more complicated and slow.

zaroth 7y ago

I think everything that you've said is completely true. However, I'll add that it matters a lot more if you otherwise don't have testing capacity available, or if your test has a large false negative rate. China relied heavily on CT-based diagnosis to backstop a lack of available and reliable testing. Another issue is that modern sanitation standards don't really enable using a CT to diagnose an infectious disease. The equipment is far too slow and expensive to truly sanitize, you would have to be willing to just PPE the patient and hope that works out. Again, perhaps better than skipping any diagnostic testing altogether if you don't have any alternative, but certainly not a first-line choice, and ethically questionable if you risk exposing uninfected people.

haldujai 7y ago
Actually you just need to have them wear a mask and wipe down the equipment with standard hospital grade wipes. We know now that COVID-19 is not airborne and is spread by droplets only so this would be routine precautions, unlike TB which we scan routinely and is an airborne pathogen. The problem with CT is we know that the test is completely normal in 50% of patients from day 0-2, and 10-15% of patients up to day 5, and roughly 7-10% of patients up to day 10. These numbers are probably an under representation given how few people with the illness get CT imaging. Additionally as has been stated the findings are considered only somewhat specific, we believe that specificity will decrease as more and more people will eventually get scanned and prove our findings thus far to be false. That is why we (in radiology) currently recommend against the routine use of CT in screening or diagnosis of COVID-19 related illness as a negative test does not mean anything and a positive test is usually noncontributory (clinical diagnosis of COVID-19 infection already made). Additionally, this will rarely affect clinical management. The only potential argument being made is the small subset of people who have viral pneumonia and may theoretically avoid being asked to self-quarantine however I highly doubt in the present climate any infectious patient with a cough will be allowed/think it wise to roam the streets. China has also removed CT from their sixth edition diagnostic manual for this disease as an aside. Source is from STR/ACR, there is a good video below: https://veritastv.org/programs/covid-19 https://veritastv.org/programs/covid-19
- 7y ago

throwGuardian 7y ago

The article fails to ask the obvious next question: if this can potentially apply to much cheaper and instantaneous tests, maybe something ultrasound based? I'm not an expert on medical imagining, so can someone comment on ultrasounds' usefulness here?

doctoring 7y ago
Ultrasound has a ton of untapped utility and is a fantastic medical imaging modality. Like you said, the equipment is cheap and portable (can be pocket sized, even!). It’s near instantaneous, allowing you to image in real time. You can even measure blood flow velocity and see other physiology. (I could go on!) But its great advantage over x-ray and CT, which is that it doesn’t use ionizing radiation, is also its greatest weakness. Ultrasound uses sound waves, of course, which unfortunately simply cannot travel very far in the body, and (critically) do not travel well across certain interfaces. One such interface is with air. Sound waves travel through your chest wall fine but on arriving at the lung... they just sort of fizzle out. Very little sound continues, and even less comes back to the transducer as meaningful signal. So ultrasound is unfortunately very poor at seeing lung tissue. (It can show us some secondary findings of pulmonary disease in the lungs, such as fluid collecting in the thoracic cavity [a pleural effusion], but that’s yet another non-specific finding.)
- haldujai 7y ago
  Not entirely true. Ultrasound actually has pretty good sensitivity for pneumonia (88%) and even higher if you look at the “difficult” cases requiring CT in the Cochrane review I link to below. While the fundamentals of what you say are correct, consolidation by definition is the build up of fluid which is very well depicted by ultrasound. For a predominately peripheral airspace disease like COVID-19 ultrasound should theoretically be very sensitive. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5279077/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5279077/
  - doctoring 7y ago
    I wasn’t aware lung US was at this point — I’ll have to read more!