Development and validation of a quantitative method for estimation of the urate burden in patients with gouty arthritis using dual-energy computed tomography

Current Techniques in the Imaging of Gout

Gout is a common inflammatory arthritis with well-described imaging characteristics. Radiography depicts erosive change and in advanced cases, tophus deposition near joints and in association with tendons or bursae. Computed tomography demonstrates the same features but may also use dual-energy or photon-counting techniques that allow for tissue composition analysis and the specific identification of monosodium urate deposition. Magnetic resonance imaging (MRI) is useful in identifying tophi and the damage associated with gout, such as bone erosion and cartilage loss in advanced cases. MRI also helps differentiate gout from other types of inflammatory arthritis, infection, or tumor that may have a similar clinical presentation. Ultrasound is widely used in the diagnosis of gout and also useful in procedural guidance of joint aspiration or soft tissue biopsy.

Material decomposition approaches for monosodium urate (MSU) quantification in gouty arthritis: a (bio)phantom study

BACKGROUND

Dual-energy computed tomography (DECT) is a noninvasive diagnostic tool for gouty arthritis. This study aimed to compare two postprocessing techniques for monosodium urate (MSU) detection: conventional two-material decomposition and material map-based decomposition.

METHODS

A raster phantom and an ex vivo biophantom, embedded with four different MSU concentrations, were scanned in two high-end CT scanners. Scanner 1 used the conventional postprocessing method while scanner 2 employed the material map approach. Volumetric analysis was performed to determine MSU detection, and image quality parameters, such as signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR), were computed.

RESULTS

The material map-based method demonstrated superior MSU detection. Specifically, scanner 2 yielded total MSU volumes of 5.29 ± 0.28 mL and 4.52 ± 0.29 mL (mean ± standard deviation) in the raster and biophantom, respectively, versus 2.35 ± 0.23 mL and 1.15 ± 0.17 mL for scanner 1. Radiation dose correlated positively with detection for the conventional scanner, while there was no such correlation for the material map-based decomposition method in the biophantom. Despite its higher detection rate, material map-based decomposition was inferior in terms of SNR, CNR, and artifacts.

CONCLUSION

While material map-based decomposition resulted in superior MSU detection, it is limited by challenges such as increased artifacts. Our findings highlight the potential of this method for gout diagnosis while underscoring the need for further research to enhance its clinical reliability.

RELEVANCE STATEMENT

Advanced postprocessing such as material-map-based two-material decomposition might improve the sensitivity for gouty arthritis in clinical practice, thus, allowing for lower radiation doses or better sensitivity for gouty tophi.

KEY POINTS

Dual-energy CT showed limited sensitivity for tophi with low MSU concentrations. Materiel-map-based decomposition increased sensitivity compared to conventional two-material decomposition. The advantages of material-map-based decomposition outweigh lower image quality and increased artifact load.

Computed tomography-current status and future directions for arthritis imaging

Applications of computed tomography (CT) in arthritis imaging have rapidly expanded in recent years due to ongoing technical developments. Dual-energy CT (DECT) has become indispensable in clinical practice, particularly for diagnosing gouty arthritis and assessing bony structural changes. Technological innovations such as low-dose CT and state-of-the-art reconstruction algorithms reduce radiation exposure while maintaining image quality and short acquisition times. This review explores the growing role of CT in arthritis imaging. Recent innovations have extended DECT's utility beyond gout diagnosis to the detection of inflammatory changes in various arthritic conditions. Postprocessing techniques such as the generation of subtraction images and iodine maps provide valuable insights into tissue perfusion and inflammatory activity, crucial for arthritis management. DECT can distinguish calcium from uric acid crystals, facilitating the differential diagnosis of various crystal arthropathies in a variety of clinical settings. This ability is particularly valuable in distinguishing between different clinical conditions in patients with inflammatory joint changes within a single imaging examination. Moreover, the advent of four-dimensional CT promises a better assessment of dynamic joint instabilities and ligament injuries, especially in the wrist. Overall, DECT offers a comprehensive approach to arthritis imaging, from the detection of structural changes to the assessment of active inflammation in joints and tendons. Continuous advances in CT technology, including photon-counting CT, hold promise for further improving diagnostic accuracy and expanding the role of CT in arthritis imaging and therapy monitoring.

Virtual noncontrast images reveal gouty tophi in contrast-enhanced dual-energy CT: a phantom study

BACKGROUND

Dual-energy computed tomography (DECT) is useful for detecting gouty tophi. While iodinated contrast media (ICM) might enhance the detection of monosodium urate crystals (MSU), higher iodine concentrations hamper their detection. Calculating virtual noncontrast (VNC) images might improve the detection of enhancing tophi. The aim of this study was to evaluate MSU detection with VNC images from DECT acquisitions in phantoms, compared against the results with standard DECT reconstructions.

METHODS

A grid-like and a biophantom with 25 suspensions containing different concentrations of ICM (0 to 2%) and MSU (0 to 50%) were scanned with sequential single-source DECT using an ascending order of tube current time product at 80 kVp (16.5-220 mAs) and 135 kVp (2.75-19.25 mAs). VNC images were equivalently reconstructed at 80 and 135 kVp. Two-material decomposition analysis for MSU detection was applied for the VNC and conventional CT images. MSU detection and attenuation values were compared in both modalities.

RESULTS

For 0, 0.25, 0.5, 1, and 2% ICM, the average detection indices (DIs) for all MSU concentrations (35-50%) with VNC postprocessing were respectively 25.2, 36.6, 30.9, 38.9, and 45.8% for the grid phantom scans and 11.7, 9.4, 5.5, 24.0, and 25.0% for the porcine phantom scans. In the conventional CT image group, the average DIs were respectively 35.4, 54.3, 45.4, 1.0, and 0.0% for the grid phantom and 19.4, 17.9, 3.0, 0.0, and 0.0% for the porcine phantom scans.

CONCLUSIONS

VNC effectively reduces the suppression of information caused by high concentrations of ICM, thereby improving the detection of MSU.

RELEVANCE STATEMENT

Contrast-enhanced DECT alone may suffice for diagnosing gout without a native acquisition.

KEY POINTS

• Highly concentrated contrast media hinders monosodium urate crystal detection in CT imaging • Virtual noncontrast imaging redetects monosodium urate crystals in high-iodinated contrast media concentrations. • Contrast-enhanced DECT alone may suffice for diagnosing gout without a native acquisition.

Advanced Imaging of Gout and Other Inflammatory Diseases Around the Knee

The knee is one of the most commonly affected joints in the course of inflammatory arthropathies, such as crystal-induced and autoimmune inflammatory arthritis. The latter group includes systemic connective tissue diseases and spondyloarthropathies. The different pathogenesis of these entities results in their varied radiologic images. Some lead quickly to joint destruction, others only after many years, and in the remaining, destruction will not be a distinguishing radiologic feature.Radiography, ultrasonography, and magnetic resonance imaging have traditionally been the primary modalities in the diagnosis of noninflammatory and inflammatory arthropathies. In the case of crystallopathies, dual-energy computed tomography has been introduced. Hybrid techniques also offer new diagnostic opportunities. In this article, we discuss the pathologic findings and imaging correlations for crystallopathies and inflammatory diseases of the knee, with an emphasis on recent advances in their imaging diagnosis.

Influence of contrast medium on tophus detection using dual-energy CT: phantom study and clinical illustration

BACKGROUND

To investigate the influence of iodinated contrast medium (ICM) on detection of monosodium urate (MSU) with dual-energy computed tomography (DECT) in two types of phantoms and demonstrate an example patient for clinical illustration.

METHODS

Approval is by the institutional review board, and written informed consent was obtained. A grid-like and a biophantom with 25 suspensions containing different concentrations of ICM (0 to 2%) and MSU (0 to 50%) were prepared and scanned with sequential single-source DECT using established methodology. Ascending orders of tube currents were applied at 80 kVp (16.5 to 220.0 mAs) and 135 kVp (2.75 to 19.25 mAs). Volume and mass measurements were performed using clinical gout software (dual-energy decomposition analysis). Numbers of true-positive and false-positive MSU detections were recorded and compared for different ICM concentrations. We demonstrate a patient with gouty arthritis for clinical illustration.

RESULTS

Effects of ICM on MSU detection varied with the amount of iodine. Lower ICM concentrations (0.25 and 0.50%) improved detection of small uric acid concentrations of 35 to 45% in comparison to scans without ICM. However, high ICM concentrations (1 and 2%) almost completely precluded MSU detection for all MSU concentrations investigated. In a patient with gouty arthritis, tophi in the wrist were only detected after intravenous ICM administration.

CONCLUSIONS

Exploring multimodal DECT for arthritis imaging, enhancement of ICM influences tophus detection. It can help in visualizing previously undetected MSU depositions but, with too strong enhancement, also obscure tophi.

RELEVANCE STATEMENT

Use of iodinated contrast media in dual-energy CT might help in visualizing previously undetected uric acid depositions but, with too strong enhancement, obscure gouty tophi.

KEY POINTS

• Iodine significantly influences the uric acid crystal detection in systematic phantom studies. • Lower iodine concentrations improved detection of low and medium uric acid concentrations. • High concentrations of iodine hampered detection of all uric acid concentrations.

Uric Acid Expression in Carotid Atherosclerotic Plaque and Serum Uric Acid Are Associated With Cerebrovascular Events

BACKGROUND

Uric acid (UA) concentration within carotid plaque and its association with cerebrovascular events have not been detected or quantified. Systemically, serum UA is a marker of inflammation and risk factor for atherosclerosis. However, its association with carotid plaque instability and stroke pathogenesis remains unclear. In patients undergoing carotid endarterectomy, we aimed to determine whether UA is present differentially in symptomatic versus asymptomatic carotid plaques and whether serum UA is associated with cerebrovascular symptoms (stroke, transient ischemic attack, or amaurosis fugax).

METHODS

Carotid atherosclerotic plaques were collected during carotid endarterectomy. The presence of UA was assessed using Gomori methenamine silver staining as well as anti-UA immunohistochemical staining and its quantity measured using an enzymatic colorimetric assay. Clinical information was obtained through a retrospective review of data.

RESULTS

UA was more commonly detected in symptomatic (n=23) compared with asymptomatic (n=9) carotid plaques by Gomori methenamine silver (20 [86.9%] versus 2 [22.2%]; P=0.001) and anti-UA immunohistochemistry (16 [69.5%] versus 1 [11.1%]; P=0.004). UA concentration was higher in symptomatic rather than asymptomatic plaques (25.1 [9.5] versus 17.9 [3.8] µg/g; P=0.021). Before carotid endarterectomy, serum UA levels were higher in symptomatic (n=341) compared with asymptomatic (n=146) patients (5.9 [interquartile range, 4.6-6.9] mg/dL versus 5.2 [interquartile range, 4.6-6.2] mg/dL; P=0.009).

CONCLUSIONS

The current study supports a potential role of UA as a potential tissue participant and a systemic biomarker in the pathogenesis of carotid atherosclerosis. UA may provide a mechanistic explanation for plaque instability and subsequent ischemic cerebrovascular events.

Factors Associated with Bone Erosion in Patients with Gout: A Dual-Energy Gemstone Spectral Imaging Computed Tomography Study

OBJECTIVE

This study aimed to assess the factors influencing bone erosion in patients with gout using dual-energy gemstone spectral imaging CT.

METHODS

We compared the clinical data, laboratory indices, and tissue urate levels at the monosodium urate (MSU)-bone interface measured by dual-energy gemstone spectral imaging computed tomography of 87 gout patients with (n=41) and without (n=46) bone erosion. Logistic regression analysis was used to investigate the risk factors associated with bone erosion.

RESULTS

In total, 47.1% of patients with gout had bone erosion. The disease duration, serum uric acid, tissue urate levels, and the presence of tophi were significantly higher (p<0.05) in gout patients with bone erosion than in those without bone erosion. Longer disease duration (OR=1.11, 95% CI: 1.00-1.24, p<0.05) and increased tissue urate levels (OR=1.01, 95% CI: 1.00-1.02, p<0.05) were independently associated with bone erosion. Tissue urate levels at the MSU-bone interface were correlated with the presence of tophi (r=0.62, p<0.001), bone erosion (r=0.51, p<0.001), renal calculus (r=0.24, p=0.03), and serum uric acid levels (r=0.23, p=0.03).

CONCLUSION

This study found that longer disease duration and elevated tissue urate concentrations at the MSU-bone interface were associated with bone erosion in patients with gout.

Dual-energy computed tomography: Tube current settings and detection of uric acid tophi

PURPOSE

To derive optimal scanning parameters for single-source dual-energy computed tomography (DECT) in the detection of urate by analyzing influence of tube current ratio (TCR) and total radiation exposure in a phantom.

METHOD

Specimens with different urate concentrations in a realistic porcine bio-phantom were repeatedly imaged with sequential single-source DECT scans at 80 kVp (16.5-220 mA s) and 135 kVp (2.75-19.25 mA s). Detection index (DI - true positive minus false positive urate volume) was calculated for every possible tube current combination. Optimal tube current combinations reaching at least 85 % of the highest measured DI of all combinations without exceeding 150 % of equivalent single-energy radiation dose were identified. TCR, DLP and DI were plotted and compared.

RESULTS

Cubic regression analysis showed a flattening increase in the DI with increasing tube currents. Five out of the 100 tube current combinations analyzed achieved the detection target: the lowest DLP of 53.9 mGy*cm at 19.25/16.5 mAs (135/80 kVp) achieved a DI of 2.07 mL and the highest DI of 2.11 mL at a dose of 65.3 mGy*cm and 8.25/79.75 mAs. The optimal TCR is between two and four, while both, higher and lower ratios decreased DI.

CONCLUSIONS

A minimum tube current of the high-energy scans is needed before an acceptable overall sensitivity is achieved and before increases in low-energy exposure result in more urate detection. High TCRs above 10 are not beneficial while the optimal TCR ranges between two and four, indicating that special care has to be taken in designing a suitable DECT protocol.

Imaging of Joints and Bones in Autoinflammation

Autoinflammatory disorders are commonly characterized by seemingly unprovoked systemic inflammation mainly driven by cells and cytokines of the innate immune system. In many disorders on this spectrum, joint and bone involvement may be observed and imaging of these manifestations can provide essential diagnostic information. This review aimed to provide a comprehensive overview of the imaging characteristics for major diseases and disease groups on the autoinflammatory spectrum, including familial Mediterranean fever (FMF), Behçet disease (BD), crystal deposition diseases (including gout), adult-onset Still's disease (AoSD), and syndromatic synovitis, acne, pustulosis, hyperostosis, and osteitis (SAPHO)/chronic recurrent multifocal osteomyelitis (CRMO). Herein, we discuss common and distinguishing imaging characteristics, phenotypical overlaps with related diseases, and promising fields of future research.