By Dr. Amit Gupta
Dual-energy spectral CT delivers more data for precise interpretations and more confident diagnoses, so you can improve patient care.
Ultimately, radiologists are trying to solve a “puzzle” of figuring out what’s the root cause of the ailment for patients and the best way to treat it. To do that, they need to acquire the best images or pictures of what’s happening inside the patient. With spectral CT, low and high X-ray energies are registered separately on an image, so radiologists can see more on that image than they would from a standard, single-energy CT scan.
Essentially, spectral CT provides radiologists with more data and more insight. This enables greater clarity for radiologists to find things that aren’t visible on an ordinary scan – things that they may not even have been looking for, but that might be significant in helping to determine the patient’s diagnosis. Better insight and visibility means more confident diagnoses and, in many cases, it means definitive diagnoses, eliminating the guesswork in image reading. As radiologists, that is our goal: to overcome imaging obstacles so that we can improve diagnostic confidence, treatment efficiency and streamline workflows to positively impact patient care and healthcare overall. Spectral CT helps us do that more quickly and more accurately than ever before.
Why are two energies better than one?
To understand the benefits of dual-energy spectral CT in enabling a confident diagnosis, you must first understand the more technical difference between single-energy and dual-energy. Standard or single-energy CT depends on the mass density of a material, so materials having different elemental compositions are represented by identical pixel values on a CT image because the attenuation coefficient is not unique for any given material. Some diagnoses can be challenging with standard CT since there is no distinction between materials such as calcium or iodinated contrast.
With dual-energy spectral CT, an additional attenuation measurement is obtained with a second X-ray spectrum, allowing the differentiation of multiple materials. Spectral CT’s unique two-layer detector provides an upper layer that captures the low energy photons, and the lower layer that captures the high-energy photons. This enables low- and high-energy photons to be registered separately, which provides a completely new set of images and unprecedented levels of insight.
How does spectral benefit patients?
The biggest benefit for patients with spectral CT is that we can make more confident diagnoses using low-contrast tools to get the same information, or even better information, at a low radiation dose. Additionally, radiologists can sometimes miss something on an image due to patient movement or the patient’s circulation being too fast or too slow during the exam. With spectral CT, the radiologists can go back retrospectively to the low energy images (e.g., 40keV) without having to rescan the patient. This also leads to less harmful effects from an additional dose of potentially nephrotoxic intravenous contrast and, ultimately, a faster turnaround on diagnosis, so we can improve patient care.
For example, one important application of dual-energy technology is the amplification of contrast enhancement. In our hospital, if a patient with a diseased heart valve is undergoing a Transcatheter Aortic Valve Implantation (TAVI), a planning CT scan is required. Instead of injecting 150 or 200 mL of contrast with standard CT, we can use our Philips IQon Spectral CT to do a scan of the chest, abdomen and pelvis in 50 mL, because the 40keV spectral images enable us to improve contrast and create the 3D volume-rendered reconstruction of the vessels. The automatic vessel segmentation of IQon Spectral CT software works better than any routine raw data you would get from a standard CT scanner. Using the algorithms that we have specifically in Philips IQon Spectral CT and the 40keV image, we get the contrast boost but not at the expense of increased image noise. The biggest application of spectral CT is in 40keV images because it gives you high image quality without a noise penalty.
How can I best use spectral?
When talking with my peers about spectral CT, some are hesitant because of the cost or the sheer volume of images produced with spectral versus standard CT. It may seem overwhelming to figure out where to start with the immense amount of data spectral provides. However, it can be broken down in a pragmatic way. When using spectral CT, I recommend to my colleagues that they only need to look at four images: a conventional CT image, a virtual non-contrast image, a 40keV image, and an iodine density image. I have found that the clinical relevance of these four images is routine in approximately 95 percent of patient cases. Each of these images provides different information:
• Conventional CT image – is similar to the image as that from a standard CT scanner, which radiologists are comfortable with and have been trained to use. This can serve as starting point for image interpretation.
• Virtual non-contrast (VNC) image – through identification and removal of iodine (intravenous contrast), VNCs are recreated, which obviated the need for an additional true non-contrast CT scan and reduces radiation exposure for patients. It is also helpful in the evaluation of incidental findings, and is available retrospectively for every scan.
• Low-energy virtual monoenergetic image (40keV image) – provides high-contrast, high-quality images with minimal artifacts as compared to higher-contrast scans. This results in reducing intravenous contrast dose and enhances disease characterization, as described in the above example.
• Iodine density image – shows distribution of iodine in the scanned object or part of the body, which is helpful for the assessment of issues such as organ perfusion, or hemodynamic relevance of vessel occlusion.
How does spectral CT benefit healthcare?
When radiologists can make a definitive diagnosis for patients, it not only benefits the patient but the hospital as well because it ties into value-based care. By obtaining the right diagnosis the first time, we can avoid the need to send them to get extra imaging exams such as an MR, or be sent to other parts of the hospital for tests. When hospitals adopt advanced technology, it enables higher-quality images, simplifies insight and data gathering, and offers more comfort and safety for patients. Additionally, in comparison to other commercially available dual-energy CT approaches, spectral CT requires no planning prior to the scan and therefore beautifully integrates with existing workflow. Patients and providers will both reap the benefits of diagnostic confidence: faster time to treatment, reduced costs, and an enhanced patient experience.
As a practicing radiologist, my main objective is to make more precise diagnoses and find ways to make it easier to fulfill my role in improving patient care as quickly and efficiently as possible. With spectral CT, we are given additional data, beautiful images and advanced imaging options that help us improve our interpretations and ability to make more assertive interpretations. Spectral CT provides me with the information I need to help me solve problems in a way that is patient-centric, and that will help shape the future of imaging and healthcare.
About the author: Dr. Amit Gupta is a board-certified radiologist with nine years of specialty experience and has been associated with University Hospitals Cleveland Medical Center and Case Western Reserve University for the last four years; currently serving as an assistant professor of radiology in the cardiothoracic division. He is a big proponent of newer imaging techniques, modalities and software for image interpretation, including Spectral Detector CT. He also teaches medical students and residents, and has been a joint author on several research papers in peer reviewed journals pertaining to diagnostic imaging in healthcare.