The enhanced resolution of the system and the capability of giving a very detailed image of the anatomy provides many opportunities for new research projects within this area.
Musculoskeletal Imaging Using Photon-Counting Computed Tomography
Musculoskeletal imaging is an important part of the clinical diagnosis of diseases or structural damage in bones, joints, ligaments and tendons. This flagship is an umbrella project of several different research projects all involved in the new photon counting detector computed tomography (PCD-CT), which is especially well suited for musculoskeletal imaging.
The flagship project
Medical physicist Erik Tesselaar is principal investigator of the musculoskeletal imaging project using computed tomography (CT) and above all photon counting detector computed tomography (PCD-CT).
- The availability of the new PCD-CT at CMIV has created a massive interest to start new research projects, and many of the projects are still in a very early phase, Erik says. We know that the new system has a better performance than current CT scanners, but what we do not know how much better it is, and in which areas it adds the most value.
For musculoskeletal imaging there are two major advantages of PCD-CT. The first is the increased spatial resolution, which makes it possible to visualize smaller structures, and especially the microstructure on the inside of the bones called the trabecular bone, which is the porous and spongy bone tissue.
The second is the possibility to separate different photon energies. The ability of the detector to analyze the absorption of different photon energies in the body provides much more information about different materials in the body.
- Separating different materials in bone structures is very useful when looking at small fractures that cannot be distinguished on plain radiographs, Erik explains. With PCD-CT you can not only see smaller fractures, due to the better resolution of the images, but it is actually possible to see ‘bone bruising’, which is the buildup of blood and fluid in and around the injured bone. We expect that the PCD-CT may offer a good alternative to magnetic resonance imaging in the diagnosis of these small fractures.
One of the sub-projects is specifically looking into osseointegration, which is the functional connection between bone and a load-bearing implant e.g., in orthopedic hip replacements. If a patient needs to replace the hip with an implant, it is important that the interface between the bone and the implant is stable. When the osseointegration fails the hip implant becomes loose and this can cause a lot of pain. It is hard to diagnose this condition, and we think that PCD-CT may offer a better way to evaluate the osseointegration.
For complicated fractures near joints more advanced imaging techniques are required and CT is the most used modality both for preoperative as well as postoperative planning to verify the result.
After surgery of a knee or an ankle there are often screws or plates attached to the bone and the metal causes artifacts making it hard to see the healing process. By using the PCD-CT the metal artifacts can be substantially reduced.
Yet another project is looking at osteoporosis, a disorder that results in fragile bones that easily break. Elderly people are sometimes screened for osteoporosis with Dual-energy X-ray absorptiometry, (DXA) by looking at the amount of bone mineral. The microstructure of the bone, the trabecular bone is very important when looking for the risk of future fractures. In this project the DXA measurements are compared with the images obtained with different CT scanners: dual energy CT, cone bean CT (CBCT) and the new PCD-CT.
The research group at the photon counting computed tomography. Photo credit Emma Busk Winquist
In the last project Erik himself is involved. In this project the visualization of small bone structures in the wrist is compared between PCD-CT and the best conventional CT that we currently have in Linköping, the Siemens Somatom Force.
- We scanned wrist specimens on both systems and asked five radiologists to evaluate the image quality by looking at the visualization of the bones, the trabecular bones, the nutritional channels in the bones and the amount of noise. It was very clear both in terms of spatial resolution and contrast-to-noise ration that the PCD-CT was better for this imaging task, Erik explains.
The next step will be to study patients with traumatic wrist injuries. At Vrinnevi Hospital in Norrköping, all patients with a suspected fracture of the wrist are examined by using CBCT, which is a small CT scanner available in the emergency department. In the CBCT, fractures can be more accurately diagnosed since the resolution is much better than regular radiographs, but very small fractures in some of the bones of the wrist may still be missed due to the limited image quality. In this new study, we work together with the orthopedic surgeons in Norrköping. They will ask all patients examined in the CBCT to be examined in the PCD-CT at CMIV as well. We expect that with PCD-CT, we will see the same fractures much better and that we will detect fractures in other wrist bones that are not visible on the CBCT images.
- With this new technology we also hope that we will be able to track subtle signs of healing so that hand surgeons easier can decide on when the fracture is sufficiently healed so that the cast may be removed.
This new PCD-CT will have a direct impact on patient care, eventually leading to improved quality of life, Erik concludes.
