In the 50 years since the first computed tomographic images in the United States were captured by EMI-made scanners at the Mayo Clinic in Rochester, Minnesota, computed tomography (CT) imaging has become an invaluable diagnostic tool. Its persistent evolution spans devices built around xenon gas detectors, to those made with solid-state detectors, to those capable of spiral and multi-slice CT, and eventually, to those capable of spectral imaging: a technology that allows physicians to determine what’s going on in the body at levels that were only theoretical in the previous half-century.
Matthew Fuld, Ph.D., director of photon-counting CT at Siemens Healthineers North America of Malvern, Pennsylvania, described the fundamental value of CT as lying both in its ability to capture exceptionally high-quality images, and at rapid speeds. Optimization of these features has always been tied to the corollary optimization of dose sufficient to achieve these images while limiting exposure of the patient’s body to as little ionizing radiation as possible. Spectral imaging compares data sets collected from different X-ray spectra, to better visualize tissue differences and enhance clinical diagnostic decision-making. In the NAEOTOM Alpha, the first photon-counting CT scanner to achieve FDA clearance, Siemens Healthineers has achieved what Fuld calls “a huge leap” in technology.
The NAEOTOM Alpha photon-counting CT unifies the imaging functions of spatial resolution, speed of image acquisition, and dual-energy, or spectral, capabilities in a single technology platform that also limits the amount of ionizing radiation to which a patient is exposed throughout a study. The clinical value of such functionality in inpatient, outpatient, and research spaces is already being demonstrated across a number of environments, Fuld said, with 175 publications dedicated to the NAEOTOM Alpha in the fewer than two years of its operation. What makes the scanner so distinct from others in the field is its construction, which measures X-rays individually, as electrical signals on the order of 8 nanoseconds, rather than as light, he said.
“The idea is one that the physics community has worked on for many years,” Fuld said. “The challenge with clinical imaging is that we use a large number of X-rays to generate an image. The proof of concept of measuring an individual X-ray was always done with a very low amount of X-rays that would never be sufficient or fast enough to capture a clinical image. With the NAEOTOM Alpha, we’ve been able to get just shy of 45 line-pairs per centimeter, which offers tremendous detail in bone structure, coronary arteries, the tiny vasculature in the brain and the liver; anywhere in the body, you can see detail you never thought possible. Because we’ve eliminated light, we are measuring each X-ray on its own.”
By differentiating the energy of an individual X-ray from background noise, a photon-counting CT scanner can create better quality images; by comparing the electrons to one or more energy thresholds, it can present dual-energy information, Fuld said.
“Whether that’s separating iodine and calcium to reduce the blooming artifact in a coronary artery, or to calculate iodine uptake in a pancreatic tumor, the inherent spectral sensitivity of the detector allows us to do spectral imaging on every scan, no matter how it’s operated,” he said. “It has the speed of dual-source, it’s lower radiation dose, and it’s giving spectral information at the same time.”
The power of photon counting technology has already been demonstrated in the cases of patients with spontaneous intercranial hypertension, in which leaking cerebrospinal fluid causes debilitating painful headaches. Traditional methodologies for finding the sources of those leaks in Type II CSF don’t work anywhere near as well as those based around photon counting do, Fuld said.
“It’s changing care for patients,” he said.
The bottom line is that photon-counting CT simply “makes everything better,” he said, by offering a clearer look at the inner workings of the body through precise, structural measurements taken at full speed. It’s particularly useful in pediatric applications, cardiac cases, lung diseases, and differentiating patients who need interventional procedures from those who need diagnostics.
“It gives us considerably more insight into things we never would have thought before,” Fuld said. “In the past, what we believed to be certain clinical presentations, when we scan them with photon counting, what was once blotchy or blurry is now crisp, with strong details, and it allows us to change the characterization of these patients. My personal opinion is that this will lead to better treatment in the future.”
As the technological components of next-generation CT scanners continue to improve alongside new data transmission and computing capacities, Fuld believes that patients and imaging technicians alike will continue to benefit from the automation of technology that can compensate for the variability of one study to the next, and save a lot of time along the way. Manufacturers like Siemens Healthineers will continue to focus on providing greater clinical value with less operational expense, the better to optimize the process.
“If I’m talking to a clinician who would operate this equipment, they don’t want complexity, they want simplicity,” he said; “make the user experience high-level. The technologist doesn’t have to make manual choices; it will make them automatically in the background. They’re helping that patient off the table, making sure their experience is good, and on to the next one, with the throughput that hospitals need.”
“We have a wide variety of clinical questions, and the more capable the technology becomes, the more different questions we can ask, and the context of where you ask them expands,” Fuld said. “If you have the right level of clinical capabilities, we can achieve high clinical value. Technology is giving us amazing clinical insight. How well we can take this information and use it collectively to take care of patients?”
Chief among the critical functions of advanced CT technology is the potential expansion of clinical screening, particularly for lung cancers and heart disease. Olivia Egan, director of CT product marketing at Siemens Healthineers North America described how dramatically lung cancer survivability rates climb with early detection, and how expanded eligibility in concert with more sensitive imaging equipment can save higher orders of lives.
“If you catch lung cancer early, it’s 70 to 90 percent survivable,” Egan noted; “it’s less than 20 percent if you don’t. In the U.S., although there’s been lung cancer screening established since 2013, only six percent of all those eligible are actually being screened.”
In November 2021, the Centers for Medicare and Medicaid Services (CMS) released a final ruling on the Medicare Outpatient Prospective Payment System (OPPS), expanding nationwide eligibility criteria for lung cancer screening to cover 14.5 million Americans (up from 8 million in 2013), and increasing reimbursement rates for hospital outpatient lung cancer screening by around 37 percent (up to around $111 from $80).
Despite this expanded eligibility and higher reimbursement rate, Egan said additional efforts are required to reach the at-risk patients who would benefit most from early detection of lung cancer.
In North America, Siemens Healthineers expanded its CT scanning portfolio to include a dedicated mobile CT solution for lung cancer screening. This mobile CT configuration incorporates the SOMATOM go. Up CT scanner, which uses tin filter technology that is unique to Siemens Healthineers. The tin filter cuts out lower photon energies to reduce dose and optimize image quality, and has direct benefits in lung imaging, resulting in ultra-low-dose CT lung cancer screening examinations. This mobile, self-contained vehicle can support community outreach programs dedicated to connecting with people in rural and farther-flung areas of the country by taking lung cancer screening directly to them.
In Chattanooga, Tennessee, Rob Headrick, chief of thoracic surgery at CHI Memorial Rees Skillern Cancer Institute, worked to develop a rural outreach lung cancer low-dose screening project, outfitting a Winnebago shell with a 16-slice refurbished CT scanner as his prototype. The data Headrick was able to gather from that outreach in Spring City, Tennessee, a rural hamlet with a population of 2,400 people, literally changed the fabric of the community.
“One death in a community like that doesn’t go unnoticed,” Headrick said. “The pessimism of lung cancer hangs over you. After five years, we have screened half the eligible people in that community with a dozen lung cancer patients alive and walking around. Now the people in that community sign themselves up.”
For Headrick’s team, the program was successful not necessarily because it was revolutionary, but more so because it paired advanced health care technologies like AI-powered computing, wireless data transmission, and HIPAA-compliant text messaging to rapidly acquire images, communicate results of studies, and share same-day results with practitioners who can develop care plans and treatments for those who need them. The benefit of that early-stage detection is quite literally the difference between life and death, Headrick said.
“The people who need it most are in rural communities,” he said. “They’ll still come to Nashville, Knoxville, or Chattanooga for health care, but when it’s too late. The key to lung screening is high volume, and how quickly you can manage the process. What started as a local solution for our geographical barriers to health care is now becoming a national solution.”
Headrick is now working on what he calls “a traveling show,” aiming to develop a network of bus-mounted CT scanners that could rotate among Veterans Affairs clinics, giving rural community hospitals a modern solution to reach the population they serve. He said that hospitals from Texarkana to southern Georgia to upstate New York are also jumping on board, aiming to improve the poor survivability rates currently associated with lung cancer. More than 20 different hospitals are fundraising towards the goal of a program like the one that debuted in Spring City, Tennessee.
“You’re taking health care to the people who don’t have options, but they’re still lives that matter,” Headrick said. “We can spend an hour driving, scan 45 people in a seven-hour window, drive the bus back, and put it up. This is a more realistic solution than constructing imaging centers in these rural communities.”
“In the state of Tennessee, almost half our population is going to die from a heart attack or lung cancer,” he said. “By scanning somebody who’s high-risk for lung cancer, I can reduce their risk of mortality by 20 to 30 percent. I can do the same for heart disease by adding a calcium score to that scan.”
“What would it do for the state of Tennessee if I cut the mortality rate for both these diseases by 30 percent?” Headrick asked. “That changes our workforce stability; it changes the economics of the state. It saves many lives. You now have the affordability, processing power, and truly can find disease before there’s a problem. I think it will be the future of how we deliver health care in a much more affordable manner.”
Headrick also believes that the future of CT lies in making use of the additional data from studies of the torso. While visualizing the lungs in a three-minute screening, for example, images captured can display information about coronary calcification, heart chambers, visceral fat content, bone density, and core muscle mass; organs like the liver and gall bladder, and more. Without reducing the length of time of that screening, physicians could leverage the low-dose, high-quality images captured “and bring value back to health care,” he said.
“We may have the first screening test that not only reduces mortality from a specific disease, but also offers information on how to improve someone’s quality of life and may be the first screening test that could improve overall longevity,” Headrick said. “That scan is now at a price point, and given the ability to acquire and process the images so quickly, it’s now something you can easily scale up.
“The previous bottleneck was handling all the data present on a CT scan – how much time does it take for the radiologist to measure the aorta, or calculate bone density,” he said. “AI has solved that problem. The national lung cancer screening trial database has also allowed so many people to develop software and test it on this high-risk population dataset. We now have an opportunity to move the hospital closer to the patients; to move the imaging closer to the patients, and bring meaningful health care to those who need it the most.”
Similarly, Dr. Omar Khalique, director of the division of cardiovascular imaging at Saint Francis Hospital and Heart Center Catholic Health in Roslyn, New York, believes that clinicians will only come to gain more and better information faster from advances in CT technology. The modality offers the highest growth potential for cardiac imaging, not only for clarity of images captured, but for the fullness of seeing three-dimensional anatomy for a variety of observers, from imaging experts to cardiologists and researchers.
“With coronary CT, we probably started too early from the technology standpoint,” Khalique said. “We knew what we wanted to look for, but because of the technological limitations, we couldn’t see it then. Imaging of percutaneous valves was first approved in 2011, and now has grown exponentially. Photon-counting CT has superior detectors for spatial resolution. We’re much closer to seeing what we wanted to see 10 years ago.”
Previous cardiac imaging technologies suffered from “blooming,” which makes calcium deposits look larger, and obscures plaques, Khalique said. But because contemporary CT imaging technologies, like the photon-counting NAEOTOM Alpha, allow cardiologists to see more inside of coronary arteries, the requirements for any calcium score cutoffs can be eliminated. Stent imaging is now possible. Patients have the opportunity of non-invasive testing instead of more invasive angiography when they need diagnostic information alone.
“I think the precision of the analysis is just going to keep increasing,” Khalique said. “Photon counting has been the Holy Grail; now that they’ve pushed the envelope, I’m hoping that detectors not only get wider, but offer better resolution. I’m sure others will follow.”
