Deposit Evaluation in Crystal Arthritis by Spectral Photon-Counting Computed Tomography

False color scanning electron micrograph of needle-like crystals of sodium urate collected from a tophus (hard deposit of crystalline uric acid & its salts) from a patient with gout (gouty arthritis). Gout is a disease in which a defect in uric acid metabolism causes an excess of the acid & its salts (sodium urate) to accumulate in the bloodstream and the joints. These collect in the joint capsules causing an acute inflammation, with accompanying swelling, redness & pain. Gout is associated with “excessive living”. Treatment involves the use of drugs & a warning against rich food & alcohol. Magnification: X173 at 35mm size.
SPCCT can detect, differentiate between, and quantify, a variety of deposits present in crystal arthritis.

Multi-energy spectral photon-counting computed tomography (SPCCT) can detect, differentiate between, and quantify, a variety of deposits present in crystal arthritis, according to research published in Arthritis & Rheumatology.

Researchers sought to determine whether multi-energy SPCCT could both detect and differentiate between monosodium urate, calcium pyrophosphate, and hydroxyapatite crystal deposits, in excised specimens.

A finger with subcutaneous gouty tophus and a calcified meniscus, excised during total knee replacement surgery, were obtained. The finger was imaged using plain x-ray, dual-energy CT, and a preclinical multi-energy SPCCT scanner. The meniscus was imaged using plain x-ray and multi-energy SPCCT.

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Plain x-ray of the finger revealed bone erosion and soft tissue changes that were consistent with tophus material; further multi-energy SPCCT imaging identified monosodium urate deposits. SPCCT highlighted the finer details and the higher volume of monosodium urate.

Plain x-ray, conducted preoperatively, showed chondrocalcinosis, confirmed within the meniscus. Multi-energy SPCCT showed “a predominance of [calcium pyrophosphate] deposits” in calcified regions of the meniscus. No significant peaks, indicating the presence of hydroxyapatite crystal deposits, were identified.

The investigators of the study noted that while the differentiation between calcium pyrophosphate and hydroxyapatite deposits was moderate, that of the monosodium urate and the calcium crystals was really good.

They also noted that multi-energy SPCCT had “potential advantages” over dual-energy CT for the detection and characterization of monosodium urate crystal deposits.

“Further work using samples with smaller urate and calcium burden will be needed to determine the diagnostic accuracy and lower detection limit…using the multi-energy SPCCT,” the researchers of the study concluded. “With these initial data, we are now in a position to demonstrate that the image quality we achieved for ex vivo samples can be replicated in living [individuals] with crystal deposition diseases.”


Stamp LK, Anderson NG, Becce F, et al. Clinical utility of multi-energy spectral photon-counting computed tomography in crystal arthritis [published online May 28, 2019]. Arthritis Rheumatol. doi: 10.1002/art.40848