Dual-energy CT in gout patients: Do all colour-coded lesions actually represent monosodium urate crystals?

Abstract

Background Dual-energy CT (DECT) can acknowledge differences in tissue compositions and can colour-code tissues with specific features including monosodium urate (MSU) crystals. However, when evaluating gout patients, DECT frequently colour-codes material not truly representing MSU crystals and this might lead to misinterpretations. The characteristics of and variations in properties of colour-coded DECT lesions in gout patients have not yet been systematically investigated. The objective of this study was to evaluate the properties and locations of colour-coded DECT lesions in gout patients. Methods DECT of the hands, knees and feet were performed in patients with suspected gout using factory default gout settings, and colour-coded DECT lesions were registered. For each lesion, properties [mean density (mean of Hounsfield Units (HU) at 80 kV and Sn150kV), mean DECT ratio and size] and location were determined. Subgroup analysis was performed post hoc evaluating differences in locations of lesions when divided into definite MSU depositions and possibly other lesions. Results In total, 4033 lesions were registered in 27 patients (23 gout patients, 3918 lesions; 4 non-gout patients, 115 lesions). In gout patients, lesions had a median density of 160.6 HU and median size of 6 voxels, and DECT ratios showed an approximated normal distribution (mean 1.06, SD 0.10), but with a right heavy tail consistent with the presence of smaller amounts of high effective atomic number lesions (e.g. calcium-containing lesions). The most common locations of lesions were 1st metatarsophalangeal (MTP1), knee and midtarsal joints along with quadriceps and patella tendons. Subgroup analyses showed that definite MSU depositions (large volume, low DECT ratio, high density) had a similar distribution pattern, whereas possible calcium-containing material (high DECT ratio) and non-gout MSU-imitating lesions (properties as definite MSU depositions in non-gout patients) were primarily found in some larger joints (knee, midtarsal and talocrural) and tendons (Achilles and quadriceps). MTP1 joints and patella tendons showed only definite MSU depositions. Conclusion Colour-coded DECT lesions in gout patients showed heterogeneity in properties and distribution. MTP1 joints and patella tendons exclusively showed definite MSU depositions. Hence, a sole focus on these regions in the evaluation of gout patients may improve the specificity of DECT scans.

Single photon emission computed tomography/computed tomography imaging of gouty arthritis: A new voice

“…[45] DECT and Spectral CT When combined with image processing software which includes a material decomposition algorithm to colorcode urate, DECT dual energy imaging provides a sensitive method for the detection of tophi. [49,50] Different manufacturers have developed slightly different system and algorithms, i.e., dual-source CT with 80 (100) kVp and 140 kVp tubes (Siemens Medical Solution), [49] dual-layer multidetector scanner with acquisition 120 or 140 kVp (Philips Healthcare) [51] and CT unit with one rapid kVp switching source and new detector based on gemstone scintillator materials (GE Healthcare) [50] and particular range of colors to depict urate crystals at articular or periarticular sites. MSU crystals of < 2 mm can be detected earlier by DECT than by using other imaging methods, and additionally, DECT allows bone erosion to be well depicted.…”

Optimization of dual energy computed tomography post-processing to reduce lower limb artifacts in gout

“…Nevertheless, in the case of minimal deposits, the use of these parameters on DECT may lead to a risk of false negatives for the diagnosis of gout. However, the tophaceous volume alone is probably not sufficient to explain the disappearance of R2 deposits, as the density of the deposits is likely to also play a role (26).…”

Dual-energy computed tomography in crystalline arthritis: knowns and unknowns

“…Several attempts have been made to optimize these default settings but the gold standard of a histopathological examination is still lacking, for obvious ethical reasons, except in cadaver studies [17]. Most DECT artifacts are well known, as they can be misidentified as MSU occurrence (mainly nail beds for feet, skin thickening, tendon reflection zone, bone surfaces), and attempts are made to optimize software settings to avoid these misleading images before assessing total MSU volume [18,19 ▪ ].…”