Recently, the novel photon-counting computed tomography (CT) technology has been shown to be able to detect and quantify anemia in patients with oncologic diseases. How does anemia detection in cancer patients using photon-counting CT work? This article gives a short overview on what the major new findings of these recent studies published in Radiology and European Journal of Radiology are.
In a Nutshell: How Does it Work?
In brief, virtual non-contrast series need to be reconstructed using photon-counting CT datasets. On these series, the attenuation of blood needs to be measured. If this measurement is low, it may indicate anemia. Using gender-specific cut-offs, this value can then be used to quantify anemia.
The following process diagram gives a very condensed overview:
How Can Anemia be Detected on Non-Contrast CT Scans?
On CT images, the blood has a specific density or attenuation. As a radiologist, I can identify anemia, when specific signs are present. For example, the non-anemic blood has a density very similar to the heart muscle. Therefore, the radiologist cannot distinguish between the myocardium and the blood of within the heart in non-contrast scans. However, if we see the myocardium (heart muscle) appearing whiter (denser) than the blood on non-contrast scans, this can hint to a present anemia. For example, see this case on radiopaedia.
How Can Anemia be Detected on Contrast-Enhanced CT Scans?
Most patients will receive contrast-enhanced CT scans. This is especially true for patients with oncologic diseases. These staging CT scans often require intravenous contrast agents. This prevents radiologists to being able to distinguish between the blood- and heart muscle-density.
However, there are ways to calculate non-contrast data out of contrast-enhanced CT scans. This technique called material differentiation has been enabled by dual-energy CT and it has been shown to be able to detect anemia on these dual-energy scans. Using this technique the contrast of the applied iodinated contrast material can be subtracted to obtain images that look like no contrast has been administered. These reconstructions are called virtual non-contrast (VNC) reconstrucions and they have various application areas.
What Does This Mean for the Individual Patient?
Anemia detection and quantification is routinely NOT being done by acquiring CT scans. It is done by testing the blood (complete blood count; CBC). However, especially patients with malignant diseases are somewhat special. Both the underlying disease and the treatment can cause anemia or worsen existing anemia.
Naturally, these patients are also regularly checked using blood tests. However, there may be patients that dont have a current blood test. If they get a CT scan and the radiologist obtains evidence for potential or worsening anemia, this may be an important information. Therefore, the possibility of detection and quantification of anemia can be very benefitial in the diagnostic workup of patients with oncologic diseases.
Why wasn’t this Potential for Anemia Detection Found Out Earlier?
As briefly stated above, this can only be done on true or virtual non-contrast series. Traditionally, patients with malignant diseases are scanned with i.v. contrast. Therefore, this cannot be measured on these scans.
Recently, CT systems with photon-counting detectors were made available in clinical routine. This novel technology allows for generation of virtual non-contrast (VNC) series in every scan. This is because these detectors have something called “spectral sensitivity”. Ultimately, this technical novelty allows to routinely look at these VNC series and (among multiple other application areas) to detect anemia on contrast-enhanced scans.
I personally find this topic very fascinating. Not only the possibility to detect anemia but to use technology to answer questions and help patients in ways that were not possible before. That is one of the pros of being a radiologist.
References for Anemia Detection on Photon-Counting CT Scans
- Decker, J. A., Huber, A., Senel, F., Bette, S., Braun, F., Risch, F., … & Schwarz, F. (2022). Anemia detection by hemoglobin quantification on contrast-enhanced photon-counting CT data sets. Radiology, 305(3), 650-652.
- Decker, J. A., Huber, A., Senel, F., Risch, F., Bette, S., Braun, F., … & Schwarz, F. (2023). Anemia Detection and Quantification in Contrast-Enhanced CT scans on a novel Photon-Counting Detector CT: A Prospective Proof-of-Concept Study. European Journal of Radiology, 110967.
- Zopfs, D., Rinneburger, M., Pinto dos Santos, D., Reimer, R. P., Laukamp, K. R., Maintz, D., … & Große Hokamp, N. (2021). Evaluating anemia using contrast-enhanced spectral detector CT of the chest in a large cohort of 522 patients. European Radiology, 31, 4350-4357.
