MUSC researchers test practical applications of new CT technology developed by Siemens Healthineers

Computed tomography scanning – generally known as a CT scan or CAT scan – revolutionized medicine when it was introduced 50 years ago in October 1971. Suddenly, doctors could see images of organs and tissue inside the body in a way that just wasn’t possible with conventional X-rays – and still isn’t even today.

Over the years, as the technology improved, CT scans have enabled doctors to peer inside vital organs and vessels like the heart, brain and arteries.

Now, CT scanning is making another leap forward, and researchers at the Medical University of South Carolina have a hand in the process.

Siemens Healthineers will officially unveil its NAEOTOM Alpha photon-counting CT system during a virtual event on Nov. 18, but MUSC researchers and technicians have been working with the new device since July as part of a hallmark project in the MUSC-Siemens strategic value partnership. MUSC has a decades-long relationship with Siemens Healthineers, which was further solidified in 2018 when the two entities announced a strategic partnership aimed at transforming the way that health care is delivered.

 

Until now, the photon-counting CT system has been used solely for research, but with the Food and Drug Administration’s recent clearance of the new technology, it will soon be available for patient care as well.

“These are exciting times for MUSC. It’s another first,” said U. Joseph Schoepf, M.D., director of the Division of Cardiovascular Imaging and assistant dean for clinical research in the College of Medicine at MUSC.

This isn’t simply an update to existing technology, according to Siemens Healthineers. It’s a new way of detecting the photons that make up X-rays.

Traditional CT scanners use X-rays, but instead of scanning the body from one side, the scanner circles around the patient’s body, sending X-rays through as it moves. Computer algorithms assemble the results into images, allowing radiologists to see “slices” of the body, much like the slices of a loaf of bread.

However, the X-rays are registered and form an image only if they are of a certain strength and exceed a certain level.

The photon-counting CT uses a new kind of detector that enables it to register, or “count,” every photon, resulting in an image that displays the full spectrum of photons, Schoepf said.

Jim O’Doherty, Ph.D., a research scientist and R&D collaborations manager with Siemens Healthineers who is stationed full time at MUSC, explained that each X-ray has its own energy.

“On the old scanner, we had no idea what the energy was. On this new photon-counting CT, we can now detect the energy of the X-rays, which means we can make better images at each specific energy,” he said.

 

Better images mean doctors and patients have better information to make critical decisions with.

Radiologists can see how tissue is composed, Schoepf said. And, because the scanner doesn’t waste radiation on X-rays that can’t be read, less radiation is required.

Schoepf and his group have been scanning patients in a study, comparing the images they get with the photon-counting CT to a regular CT, to test whether the theory behind the photon-counting CT holds up in a real-world setting. So far, they’ve scanned about 70 patients, out of a goal of 130 patients.

 

Tilman Emrich, M.D., director of photon counting CT research at MUSC, said they've been able to demonstrate the theoretical advantages, including sharper images, less radiation used on the patient and an improvement upon some of the limitations of existing CT scanners.

One of those drawbacks – Schoepf called it the Achilles’ heel of CT – is imaging of coronary artery calcium.

“Calcium looks much larger in a CT image than it is in real life,” he said.

That means CT images are more likely to indicate a stenosis, or narrowing of the artery. Whenever the CT scan indicates a possible stenosis, the patient is sent to the cath lab for additional tests, which requires a tube inserted in the groin, the use of contrast media and more radiation – not to mention additional anxiety and expense for the patient.

“The better spatial resolution allows us to better read through that calcium, which means we send fewer patients to the cath lab unnecessarily,” Schoepf said.

The reverse is true as well – the photon-counting CT can pick up irregularities that a regular CT could not. Because Schoepf’s group was using the photon-counting CT as part of the trial, they did not provide less than the existing standard of care for any trial volunteer. They could, however, provide additional care – for example, in one patient in which the photon-counting CT showed a myocardial perfusion defect that wasn’t visible on the traditional CT. The patient was given a referral for additional MRI tests.

As part of the study, information flows back and forth between Siemens Healthineers and MUSC to continually improve the scanner. Anonymized data from MUSC allows the engineering team to improve the reconstruction algorithm.

“We want them to be able, if they're post-processing scans, to make sure that they're happy with the results,” O’Doherty said. “We want to be sure that what the software is doing is actually scientifically correct – but also medically correct. So a lot of it is to-and-fro between our developers in Germany and the clinical team here; that's essentially my link.”

The MUSC team is excited by what they’ve seen so far.

“We are impressed by the image quality and sharpness that we see, but we know it will go a step further,” Emrich said.

 

 

The expectation is that this scanner can improve imaging of the heart, which Akos Varga-Szemes, M.D., Ph.D., director of cardiovascular imaging research at MUSC, described as the most difficult organ to image because it is always moving. It takes more time to generate data as resolution is increased, he said, making ultra-high resolution scans of the heart a technical challenge.

Emrich explained further.

“If you want to image a hand, you can say, ‘Don't move your hand.’ If you want to image the lung, you can say, ‘Don’t move and stop your breathing for a second’ and then we rush over it. But for the heart, it’s constantly moving,” he said.

Schoepf said the researchers are also investigating whether the traditional two-scan protocol can be consolidated into a single scan, further reducing radiation exposure. Heart CT scans usually involve one scan to capture calcification and a second scan with contrast dye injected to highlight blood vessels; the photon-counting CT could potentially capture all of this information during a single scan.

While the MUSC team is focusing on cardiac imaging, Siemens Healthineers is working with other institutions around the world that are focused on brain, chest and cancer scanning. Schoepf expects the scanner to improve images for a variety of conditions, such as interstitial lung disease; procedures, like tumor imaging before and after cancer treatment; and areas of the body, including the inner ear.