Photon-counting detectors may enable a new clinical modality for diagnosing and monitoring crystal-related arthropathies (CRAs)

A 10-minute read

The diagnosis and continuous treatment of crystal-related arthropathies (CRAs) rely heavily on efficient clinical modalities. In pursuit of a simpler and safer way to identify the causes of these diseases, Dr. Florian Huber and PD Dr. Roman Guggenberger from the Radiology Department of the University Hospital Zurich (USZ), along with colleagues, partnered up with DECTRIS physicists Dr. Thomas Thüring and Dr. Spyridon Gkoumas. In their recent publication summarized below, they present a proof of concept lab radiography setup using a photon-counting detector. Their results reveal substantial potential for performing material decomposition in clinical applications.

CRAs belong to the broad spectrum of long-term joint diseases, and while their symptoms usually manifest as remarkable pain and swelling, their origin is microscopic. Accumulated in and around joints, tiny crystals of monosodium urate, calcium pyrophosphate, and/or calcium hydroxyapatite can cause a variety of CRAs. In order to diagnose the right form of the disease, it is crucial to identify the causative compound(s) and monitor the severity of its/their accumulation. 

Although current clinical techniques can provide sufficient data for accurate diagnosis and monitoring, they do have some shortcomings. Increasingly, medical professionals and scientists are looking into novel modalities that would fulfill four core requirements of an efficient diagnostic method: specific in its identification of crystals, sensitive to a low presence of crystals, safe for the patient, and simple for the physicians to use.

The gold standard for identifying these crystals is light microscopy, a technique that is based on examining the crystals’ morphology; however, obtaining a sample for analysis requires an invasive and painful procedure. Non-invasive diagnostic options include ultrasound, plain radiography, and dual-energy computed tomography (DE-CT), but the first two are not crystal-specific and thus provide limited diagnostic information. DE-CT, on the other hand, yields 3D information and allows for differentiation of crystals even if they are surrounded by soft tissue, but it also may impose relatively high radiation dose on the patient. Inconclusive plain radiography imaging usually leads to a DE-CT patient examination which often comes back with negative results. This workflow inefficiency exposes both the patient and the hospital to unnecessary additional radiation and costs, respectively.

A new approach to diagnosing CRAs

A new approach to the conventional plain radiography approach is to use at photon-counting detector and enhance the obtained diagnostic information. The detector’s thresholds are used to differentiate energies, and thus to perform material decomposition based on the materials’ effective atomic number. This may lead to future upgrades of conventional radiographhic imaging systems setup allows for material-specific identification of CRA crystals at low radiation doses.  

The researchers’ proof of concept was obtained by first testing a series of standardized clinical samples in vitro, and then testing an ex vivo sample. In both cases, the SPCR approach yielded diagnostic accuracy that is comparable to that of DE-CT, indicating that SPCR could be a promising technique: it allows for simple operational procedures and widespread use for any material decomposition that is currently performed via DE-CT. More details on the technique, its application in CRA diagnosis, and future research plans can be found in a recently published paper by Huber et al. (2020).