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

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.

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.

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.

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.