Photon-Counting Detector CT Revolutionizes Neuroradiology

First approved by the U.S. Food and Drug Administration for clinical use in 2021, PCD-CT scanners work by converting X-ray photons directly into an electronic signal. This gives it advantages over energy integrating detector CT (EID-CT) scanners that follow a two-step process with a scintillator to convert X-rays to light and a detector to convert that light into a signal. PCD-CT scanners can achieve a slice thickness of 0.2 millimeters, compared with 0.6 millimeters for EID systems. 

“That’s a three-fold increase in how thin you can scan, and that directly impacts sensitivity and specificity for imaging disease processes,” said presenter Felix Emanuel Diehn, MD, from the Mayo Clinic in Rochester, MN, home of the first PCD-CT in the United States. “It’s truly a major step forward in CT imaging.”

Dr. Diehn and his Mayo colleagues have been using PCD-CT’s imaging power to zero in on some of the small, delicate structures of the head and neck—structures like the temporal bone. The temporal bone contains the middle and inner portions of the ear, where the smallest bones in the human body are located. 

“We try to do every single temporal bone CT on photon counting because it’s clearly superior to EID,” Dr. Diehn said. “With the ultra-high spatial resolution, we can better see not just the normal minute anatomy, but also disease processes that can affect this anatomy.” 

PCD-CT also brings benefits to neurovascular imaging. Its higher spatial resolution helps better visualize aneurysms and distinguish them from normal anatomic outpouchings called infundibula. 

“If you can tell a patient that they have an infundibulum rather than an aneurysm and they don’t need further head CTAs or MRAs to follow this lesion, that’s a big win in terms of health care expenses and the patient’s emotional expense of having to worry every year that their aneurysm has gotten bigger,” Dr. Diehn said. 

In CT myelography procedures, PCD-CT is much more sensitive than EID-CT at finding cerebrospinal fluid (CSF) venous fistulae. Its faster scanning power is useful when looking for CSF leaks.

“The really quick scanning affords us ultra-high temporal resolution in addition to the ultra-high spatial resolution,” Dr. Diehn. “That’s important because these CSF leaks are sometimes transient, and the timing of acquisition really matters.” 

Other PCD-CT benefits include the ability to scan at 30% to 50% lower radiation doses while achieving image quality like that of EID-CT. Scan protocols can also be tweaked to have lower noise in the image. PCD-CT’s ability to provide spectral data helps optimize contrast-enhanced imaging.

As it gets more use in the clinic, PCD-CT’s benefits to patients become more apparent, Dr. Diehn said. “We have some data and case examples where PCD-CT found lesions that the other modalities couldn’t, and now we’re able to offer treatment to those patients.”

Access the education exhibit, “Clinical Applications of Photon-Counting Detector CT in Neuroradiology,” (NREE-70) on demand at RSNA.org/MeetingCentral