Dual-Energy Computed Tomography for Detection and Characterization of Monosodium Urate, Calcium Pyrophosphate, and Hydroxyapatite: A Phantom Study on Diagnostic Performance

The role of renal dual-energy computed tomography in exploring the gouty kidney: the RENODECT study

OBJECTIVE

The objective of this study was to explore the ability of dual-energy computed tomography (DECT) to detect monosodium urate (MSU) crystal deposits in the kidneys and renal artery walls, and uric acid urolithiasis, in patients with gout and chronic kidney disease (CKD).

METHODS

Patients with gout and with stage 2-4 CKD were prospectively included in this cross-sectional study. Patients underwent renal, knee and feet DECT scans. Renal DECT scans were read for MSU-coded lesions in the kidneys, renal artery walls, and urinary tract using different post-processing settings. Characteristics of patients with and without DECT-positive lesions were compared, and the DECT parameters of these lesions were measured.

RESULTS

A total of 27/31 patients with had renal DECT scans and were included in the analysis (23/27 men, mean (standard deviation) 73 (9) years old, mean eGFR 45.3 mL/min/1.73 m2 (21.0), volumes of MSU in the knees and feet ranging from 0.11 to 475.0 cm3). None of the patients exhibited deposition of MSU crystals in the kidneys. One case of calyceal calculi and one case of ureterolithiasis were observed, wrongly coded as MSU in default post-processing settings for gout but identified as uric acid in the "kidney stone" settings. Five patients had MSU-coded plaques in the renal arteries, which had DECT parameters consistent with early calcified plaques rather than MSU, and had no association with volumes of peripheral MSU deposition.

CONCLUSION

DECT is unable to detect genuine monosodium urate crystal deposits in kidneys and renal artery walls, and but can characterize chronic asymptomatic urolithiasis.

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.

Advanced imaging techniques in crystal arthritis

Gout and calcium pyrophosphate deposition (CPPD) disease are the most common causes of crystal arthritis. Identifying the pathogenic crystal deposition is the cornerstone of the diagnosis, but also prognosis and monitoring of the diseases. Conventional radiography has been for decades the only imaging technique used, with its very restricted sensitivity in both diseases. Advanced techniques, namely ultrasound and dual-energy computed tomography (DECT), are being increasingly used in the diagnosis and management of gout and CPPD diseases, and their role is now well recognized in classification criteria and in recommendations for the diagnosis and management. In gout, ultrasound elementary lesions of monosodium urate deposition are well defined and have been shown to be sensitive to change and can be monitored, while direct quantification of these deposits can be performed with DECT. In CPPD disease, the definition of elementary lesions and their scoring has been well established for ultrasound, while the proof of concept that DECT can help discriminate calcium pyrophosphate crystal deposits among other calcium-containing structures has been shown. The aim of this narrative review is to provide an overview of the use of advanced imaging techniques in crystal-induced arthropathies.

Are gout patients with negative dual-energy computed tomography for monosodium urate crystal deposition easy to treat?

OBJECTIVES

To determine the clinical associations and predictive value of two thresholds of negative dual-energy CT (DECT) for MSU crystal deposition in gout patients initiating urate-lowering therapy (ULT) and identify which threshold is more clinically relevant.

METHODS

Patients from the CRYSTALILLE cohort with a diagnosis of gout naïve to ULT with baseline DECT scans of the knees and feet were selected. Two thresholds of positivity for DECT detection of MSU crystal deposition were considered (<0.01 cm3 and <0.1 cm3). Baseline characteristics and the prediction of key outcomes after ULT initiation, including reaching serum urate (SU) levels <6.0 and 5.0 mg/dl and occurrence of flares at 6, 12 and 24 months, associated with both thresholds of negative DECTs were compared with those of patients having positive DECT scans.

RESULTS

A total of 211 patients, median age 66.2 years [interquartile range (IQR) 57-75.8], with a median symptom duration of 3 years (IQR 0-7.8) were included. A total of 38/211 (18%) and 90/211 (43%) had negative DECT scans for the 0.01 and 0.1 cm3 thresholds, respectively. Factors associated with negative DECT scans were younger age, shorter symptom duration and an absence of cardiovascular disease for both volume thresholds. A total of 9/39 (23.1%), 3/26 (11.5%) and 1/18 (5.6%) patients with <0.1 cm3 MSU crystals had flares at 6, 12 and 24 months, respectively, compared with 18/45 (40.0%), 9/36 (25.0%) and 2/18 (11.1%) patients with ≥0.1 cm3 (P > 0.05). Overall, 95 patients (68.3%) reached SU levels <6.0 mg/dl and 68 (48.9%) reached levels <5.0 mg/dl, without any difference between positive and negative DECTs, with ULT dosages that tended to be lower in patients with negative DECTs.

CONCLUSION

The 0.1 cm3 threshold was better correlated with clinical presentation and evolution than the 0.01 cm3 threshold. Gout patients with negative DECTs exhibit milder disease and a lower comorbidity burden. They do not exhibit particularly easy-to-treat hyperuricaemia but they may have a lower risk of flares.

Imaging and management of calcium pyrophosphate deposition disease

The radiological manifestations of calcium pyrophosphate deposition (CPPD) revolve around two main axes: the asymptomatic form and CPPD disease. The latter is a consequence of an immune response to calcium phosphate crystals. Chondrocalcinosis is broadly considered the radiographic manifestation of CPPD regardless of whether it is asymptomatic or associated with inflammatory arthritis. CPPD is associated with osteoarthritis although the direction of such association is still unclear. Apart from the detection of CPP crystals in synovial fluid, imaging (mainly conventional radiography and increasingly ultrasound) plays a central role in the diagnosis of CPPD disease. Recently, CT has been added as a diagnostic tool, especially in deep anatomic locations such as crowned dens. To date, no treatment is effective in dissolving CPP crystals. For now, the focus of current treatment strategies remains inflammation control. Our aim is to review the epidemiology, pathogenesis, and clinical and imaging manifestations of asymptomatic and symptomatic CPPD. We will also discuss recent consensus definitions and classifications of CPPD disease.

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.

CT in musculoskeletal imaging: still helpful and for what?

Computed tomography (CT) is a common modality employed for musculoskeletal imaging. Conventional CT techniques are useful for the assessment of trauma in detection, characterization and surgical planning of complex fractures. CT arthrography can depict internal derangement lesions and impact medical decision making of orthopedic providers. In oncology, CT can have a role in the characterization of bone tumors and may elucidate soft tissue mineralization patterns. Several advances in CT technology have led to a variety of acquisition techniques with distinct clinical applications. These include four-dimensional CT, which allows examination of joints during motion; cone-beam CT, which allows examination during physiological weight-bearing conditions; dual-energy CT, which allows material decomposition useful in musculoskeletal deposition disorders (e.g., gout) and bone marrow edema detection; and photon-counting CT, which provides increased spatial resolution, decreased radiation, and material decomposition compared to standard multi-detector CT systems due to its ability to directly translate X-ray photon energies into electrical signals. Advanced acquisition techniques provide higher spatial resolution scans capable of enhanced bony microarchitecture and bone mineral density assessment. Together, these CT acquisition techniques will continue to play a substantial role in the practices of orthopedics, rheumatology, metabolic bone, oncology, and interventional radiology.

Review: The Role of Dual-Energy Computed Tomography in Detecting Monosodium Urate Deposits in Vascular Tissues

PURPOSE OF REVIEW

To highlight novel findings in the detection of monosodium urate deposits in vessels using dual energy computed tomography, and to discuss the potential clinical implications for gout and hyperuricemia patients.

RECENT FINDINGS

Gout is an independent risk factor for cardiovascular disease. However, classical risk calculators do not take into account these hazards, and parameters to identify patients at risk are lacking. Monosodium urate measured by dual energy computed tomography is a well-established technology for the detection and quantification of monosodium urate deposits in peripheral joints and tendons. Recent findings also suggest its applicability to identify vascular urate deposits. Dual energy computed tomography is a promising tool for detection of cardiovascular monosodium urate deposits in gout patients, to better delineate individuals at increased risk for cardiovascular disease.

Monosodium urate crystal depletion and bone erosion remodeling during pegloticase treatment in patients with uncontrolled gout: Exploratory dual-energy computed tomography findings from MIRROR RCT

OBJECTIVE

Monosodium-urate (MSU) crystal deposits can be visualized and quantified with dual-energy CT (DECT). Pegloticase lowers serum urate (SU) in uncontrolled gout patients, with methotrexate (MTX) co-therapy recommended to increase SU-lowering response rate and decrease infusion reaction risk. The literature on serial DECT-imaging during pegloticase+MTX co-therapy is sparse, with only 2 prior cases of rapid MSU deposition depletion with subsequent bone-erosion remodeling reported from a small open-label trial. Here, we report DECT findings during pegloticase treatment in a larger number of patients from a randomized controlled trial to confirm bone-erosion remodeling that follows MSU depletion with pegloticase. The influence of length-of-therapy is also explored.

METHODS

Patients received pegloticase (8mg every 2weeks)+MTX (15mg/week orally) or pegloticase+placebo (PBO) during the MIRROR RCT trial. A subset underwent DECT-imaging on Day1 (first pegloticase infusion) and at Weeks 14, 24, and 52. Patients with paired baseline-Week 52 images were included. Imaged regions with baseline MSU-crystal volume (VMSU)<0.5cm3 were excluded to minimize artifact contributions. VMSU and bone-erosion remodeling were assessed.

RESULTS

Eight patients (6 MTX, 2 PBO) were included. Included patients had received 52weeks (5 MTX), 42weeks (1 PBO), and 6weeks (1 MTX, 1 PBO) of pegloticase therapy. Patients who prematurely discontinued pegloticase maintained SU<6mg/dL on allopurinol (n=2)/febuxostat (n=1). At Week 52, VMSU had markedly decreased in both the pegloticase+MTX and pegloticase+PBO treatment groups, with faster depletion during pegloticase therapy. Bone-erosion remodeling was observed in 29/42 (69%) evaluated erosions: 29 (69%) size decrease, 4 (9.5%) recortication, 3 (7.1%) new bone formation.

CONCLUSION

Rapid VMSU depletion during pegloticase therapy was observed with concomitant bone remodeling within 1year. Following pegloticase discontinuation, VMSU reduction slowed or stopped even when SU was maintained<6mg/dL with oral ULT.

CLINICAL TRIAL REGISTRATION

NCT03994731.

A Narrative Review of Chondrocalcinosis: Clinical Presentation, Diagnosis, and Therapies

Calcium pyrophosphate deposition disease is categorized into radiographic chondrocalcinosis, acute calcium pyrophosphate arthritis, chronic calcium pyrophosphate arthritis, and osteoarthritis with calcium pyrophosphate deposition. These entities collectively are characterized by the deposition of calcium into joints, which then may cause localized and systemic inflammation, resulting in pain and swelling in the affected joints. Patients with the ANKH gene are more susceptible to the development of CPP arthritis as are those with primary hyperparathyroidism, hypomagnesemia, and hemochromatosis. Radiographic chondrocalcinosis is asymptomatic. Acute calcium pyrophosphate arthritis results in self-limited periods of joint pain and swelling in the affected joint. Along with localized inflammation, there may also be systemic inflammation characterized by fever and elevated inflammatory markers. Chronic calcium pyrophosphate arthritis results in periods of quiescence interrupted by flares that are identical to acute periods of disease. Osteoarthritis associated calcium pyrophosphate arthritis presents with chronic pain well described in osteoarthritis with periods of acute flares. In 2023, a joint effort by the American College of Rheumatology and the European League Against Rheumatism developed guidelines meant to aid in the recognition of calcium pyrophosphate deposition diseases. The diagnosis is made if there is proof of either crowned dens syndrome or synovial fluid analysis demonstrating calcium pyrophosphate crystals or when more than 56 points are summed utilizing the criteria described in the guidelines. Radiographic chondrocalcinosis requires no therapy. Acute calcium pyrophosphate arthritis is treated with the goal of aborting the flare. Treatment options include nonsteroidal anti-inflammatory drugs (NSAIDs), colchicine, oral corticosteroids, parenteral corticosteroids, intraarticular corticosteroids, IL-1 inhibitors, or parenteral adrenocorticotropic hormone (ACTH). The goal in treatment for chronic calcium pyrophosphate arthritis is the suppression of acute flares. The drugs used for acute flare treatment may be given as maintenance therapy with the additional options of methotrexate and hydroxychloroquine.

Dual energy computed tomography cannot effectively differentiate between calcium pyrophosphate and basic calcium phosphate diseases in the clinical setting

Background

Recent reports suggested that dual-energy CT (DECT) may help discriminate between different types of calcium phosphate crystals in vivo, which would have important implications for the characterization of crystal deposition occurring in osteoarthritis.

Purpose

Our aim was to test the hypothesis that DECT can effectively differentiate basic calcium phosphate (BCP) from calcium pyrophosphate (CPP) deposition diseases.

Methods

Discarded tissue after total knee replacement specimens in a 71 year-old patient with knee osteoarthritis and chondrocalcinosis was scanned using DECT at standard clinical parameters. Specimens were then examined on light microscopy which revealed CPP deposition in 4 specimens (medial femoral condyle, lateral tibial plateau and both menisci) without BCP deposition. Regions of interest were placed on post-processed CT images using Rho/Z maps (Syngo.via, Siemens Healthineers, VB10B) in different areas of CPP deposition, trabecular bone BCP (T-BCP) and subchondral bone plate BCP (C-BCP).

Results

Dual Energy Index (DEI) of CPP was 0.12 (SD ​= ​0.02) for reader 1 and 0.09 (SD ​= ​0.03) for reader 2, The effective atomic number (Zeff) of CPP was 10.83 (SD ​= ​0.44) for reader 1 and 10.11 (SD ​= ​0.66) for reader 2. Nearly all DECT parameters of CPP were higher than those of T-BCP, lower than those of C-BCP, and largely overlapping with Aggregate-BCP (aggregate of T-BCP and C-BCP).

Conclusion

Differentiation of different types of calcium crystals using DECT is not feasible in a clinical setting.

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.

Imaging Features of Calcium Pyrophosphate Deposition Disease: Consensus Definitions From an International Multidisciplinary Working Group

OBJECTIVE

To develop definitions for imaging features being considered as potential classification criteria for calcium pyrophosphate deposition (CPPD) disease, additional to clinical and laboratory criteria, and to compile example images of CPPD on different imaging modalities.

METHODS

The American College of Rheumatology and European Alliance of Associations for Rheumatology CPPD classification criteria Imaging Advisory Group (IAG) and Steering Committee drafted definitions of imaging features that are characteristic of CPPD on conventional radiography (CR), conventional computed tomography (CT), dual-energy CT (DECT), and magnetic resonance imaging (MRI). An anonymous expert survey was undertaken by a 35-member Combined Expert Committee, including all IAG members. The IAG and 5 external musculoskeletal radiologists with expertise in CPPD convened virtually to further refine item definitions and voted on example images illustrating CR, CT, and DECT item definitions, with ≥90% agreement required to deem them acceptable.

RESULTS

The Combined Expert Committee survey indicated consensus on all CR definitions. The IAG and external radiologists reached consensus on CT and DECT item definitions, which specify that calcium pyrophosphate deposits appear less dense than cortical bone. The group developed an MRI definition and acknowledged limitations of this modality for CPPD. Ten example images for CPPD were voted acceptable (4 CR, 4 CT, and 2 DECT), and 3 images of basic calcium phosphate deposition were voted acceptable to serve as contrast against imaging features of CPPD.

CONCLUSION

An international group of rheumatologists and musculoskeletal radiologists defined imaging features characteristic of CPPD on CR, CT, and DECT and assembled a set of example images as a reference for future clinical research studies.

Chondrocalcinosis: Advances in Diagnostic Imaging

PURPOSE OF REVIEW

Calcium pyrophosphate deposition disease (CPPD) arises from calcium pyrophosphate deposition throughout the body, leading to different clinical syndromes that may be diagnosed using various imaging modalities. The purpose of this review is to highlight recent updates in the imaging of CPPD.

RECENT FINDINGS

Conventional radiography remains the initial test when imaging CPPD; but musculoskeletal ultrasound and conventional computed tomography (CT) may also assist in diagnosing and characterizing CPP deposits, with increased sensitivity. Dual-energy CT is also being used to differentiate CPP crystals from other crystal deposition diseases. CPP discitis has been diagnosed with MRI, but MRI has lower sensitivity and specificity than the aforementioned imaging studies in CPPD diagnosis. Assorted imaging modalities are increasingly used to diagnose CPPD involving atypical joints, avoiding invasive procedures. Each modality has its advantages and disadvantages. Future imaging may be able to provide more utility than what is currently available.

Identification and characterization of peripheral vascular color-coded DECT lesions in gout and non-gout patients: The VASCURATE study

OBJECTIVE

To characterize peripheral vascular plaques color-coded as monosodium urate (MSU) deposition by dual-energy computed tomography (DECT) and assess their association with the overall soft-tissue MSU crystal burden.

METHODS

Patients with suspected crystal arthropathies were prospectively included in the CRYSTALILLE inception cohort to undergo baseline knees and ankles/feet DECT scans; treatment-naive gout patients initiating treat-to-target urate-lowering therapy (ULT) underwent repeated DECT scans with concomitant serum urate level measurements at 6 and 12 months. We determined the prevalence of DECT-based vascular MSU-coded plaques in knee arteries, and assessed their association with the overall DECT volumes of soft-tissue MSU crystal deposition and coexistence of arterial calcifications. DECT attenuation parameters of vascular MSU-coded plaques were compared with dense calcified plaques, control vessels, control soft tissues, and tophi.

RESULTS

We investigated 126 gout patients and 26 controls; 17 ULT-naive gout patients were included in the follow-up study. The prevalence of DECT-based vascular MSU-coded plaques was comparable in gout patients (24.6%) and controls (23.1%; p=0.87). Vascular MSU-coded plaques were strongly associated with coexisting arterial calcifications (p<0.001), but not with soft-tissue MSU deposition. Characterization of vascular MSU-coded plaques revealed specific differences in DECT parameters compared with control vessels, control soft tissues, and tophi. During follow-up, vascular MSU-coded plaques remained stable despite effective ULT (p=0.64), which decreased both serum urate levels and soft-tissue MSU volumes (p<0.001).

CONCLUSION

Our findings suggest that DECT-based MSU-coded plaques in peripheral arteries are strongly associated with calcifications and may not reflect genuine MSU crystal deposition. Such findings should therefore not be a primary target when managing gout patients.