Detection and Characterization of Monosodium Urate and Calcium Hydroxyapatite Crystals Using Spectral Photon-Counting Radiography: A Proof-of-Concept Study

A novel parameter derived from post-processing procedure of dual energy CT for identification of gout

ROI analysis is frequently used for obtaining acid content on rapid-kV-switching dual energy CT (DECT), providing inadequate accuracy. A new parameter derived from post-processing procedure, maximum lower limit with stain visible (MLLSV), was used by us to diagnose gout. 30 gout patients and 20 healthy volunteers were analyzed by using MLLSV. MLLSV was defined as the maximum lower limit of display window allowing only one stained site visible. Radiologists were asked to continuously increase the lower limit of display window of uric acid to decrease number of stained sites until the last stained site disappeared. MLLSV obtained by this way was compared between gout patients and volunteers. Receiver operating characteristic (ROC) curve was used to determine the performance. MLLSV of gout patients was significantly higher than that of volunteers (1373.3 ± 23.0 mg/cm³ vs. 1315.4 ± 20.7 mg/cm³, p = 0.000). The area under ROC curve of MLLSV was 0.993 in identifying gout. When using the optimal cutoff of 1342 mg/cm³, the sensitivity and specificity of MLLSV in identification of gout were 96.7% and 95% respectively. MLLSV derived from post-processing procedure of DECT is useful in discriminating gout patients from healthy people.

The diagnostic value of conventional radiography and musculoskeletal ultrasonography in calcium pyrophosphate deposition disease: a systematic literature review and meta-analysis

OBJECTIVE

To examine and compare the accuracy of conventional radiography (CR) and musculoskeletal ultrasonography (US) in the diagnosis of calcium pyrophosphate (CPP) crystals deposition disease (CPPD).

DESIGN

A systematic search of electronic databases (PubMed, Embase, and Cochrane), conference abstracts and reference lists was undertaken. Studies which evaluated the accuracy of CR and/or US in the diagnosis of CPPD, using synovial fluid analysis (SFA), histology or classification criteria as reference tests were included. Subgroup analyses by anatomic site and by reference test were performed.

RESULTS

Twenty-six studies were included. Using SFA/histology as reference test, CR and US showed an excellent (CR AUC = 0.889, 95%CI = 0.811-0.967) and an outstanding (US AUC = 0.954, 95%CI = 0.907-1.0) diagnostic accuracy (p < 0.01), respectively. Furthermore, US showed a higher sensitivity (0.85, 95%CI = 0.79-0.90 vs 0.47, 95%CI = 0.40-0.55) and only a little lower specificity (0.87, 95%CI = 0.83-0.91 vs 0.95, 95%CI = 0.92-0.97) than CR. A considerable heterogeneity between the studies was found, with adopted reference test being the main source of heterogeneity. In fact, subgroup analysis showed a significant change in the diagnostic accuracy of CR, but not of US, using Ryan and McCarty criteria or SFA/histology as reference test (CR: AUC = 0.956, 95%CI = 0.925-1.0 vs AUC = 0.889, 95%CI = 0.828-0.950, respectively, p < 0.01) (US: AUC = 0.922, 95%CI = 0.842-1.0 vs AUC = 0.957, 95%CI = 0.865-1.0, respectively, p = 0.08) CONCLUSIONS: Although US is more sensitive and a little less specific than CR for identifying CPP crystals, both these two techniques showed a great diagnostic accuracy and should be regarded as complementary to each other in the diagnostic work-up of patients with CPPD.

Differentiation of Crystals Associated With Arthropathies by Spectral Photon-Counting Radiography: A Proof-of-Concept Study

OBJECTIVES

The aims of this study were to test whether spectral photon-counting radiography (SPCR) is able to identify and distinguish different crystals associated with arthropathies in vitro and to validate findings in a gouty human third toe ex vivo.

MATERIALS AND METHODS

Industry-standard calibration rods of calcium pyrophosphate, calcium hydroxyapatite (HA), and monosodium urate (MSU) were scanned with SPCR in an experimental setup. Each material was available at 3 different concentrations, and a dedicated photon-counting detector was used for SPCR, whereas validation scans were obtained on a clinical dual-energy computed tomography (DECT) scanner. Regions of interest were placed on SPCR images and consecutive DECT images to measure x-ray attenuation characteristics, including effective atomic numbers (Zeff). Statistical tests were performed for differentiation of Zeff between concentrations, materials, and imaging modalities. In addition, a third toe from a patient with chronic gouty arthritis was scanned with SPCR and DECT for differentiation of MSU from HA.

RESULTS

In both SPCR and DECT, significant differences in attenuation and Zeff values were found for different concentrations among (P < 0.001) and between different materials (P < 0.001). Overall, quantitative measurements of Zeff did not differ significantly between SPCR- and DECT-derived measurements (P = 0.054-0.412). In the human cadaver toe, gouty bone erosions were visible on standard grayscale radiographic images; however, spectral image decomposition revealed the nature and extent of MSU deposits and was able to separate it from bone HA by Zeff.

CONCLUSIONS

Identification and differentiation of different crystals related to arthropathies are possible with SPCR at comparable diagnostic accuracy to DECT. Further research is needed to assess diagnostic accuracy and clinical usability in vivo.