A Comparative Analysis of Single-Energy CT and Dual-Energy CT in Detecting Crystal Deposits in Gout and Calcium Crystal Deposition Diseases
Mouad Khorsi (1), Jérôme Damet (1,2), Lucia Gallego Manzano (1), Pascal Monnin (1), Anaïs Viry (1), Fabio Becce (3)
Affiliation(s):
1. Institute of Radiation Physics (IRA), Lausanne University Hospital (CHUV) and University of Lausanne (UNIL), Lausanne, Switzerland
2. University of Otago, Christchurch, New Zealand
3. Department of Diagnostic and Interventional Radiology, Lausanne University Hospital (CHUV) and University of Lausanne (UNIL), Lausanne, Switzerland
Purpose: CT imaging is playing an increasingly important role in the diagnosis and classification (ACR/EULAR criteria) of patients with gout and calcium pyrophosphate deposition diseases. Here, we aimed to compare the diagnostic performance of conventional CT (single-energy CT, SECT) and dual-energy CT (DECT) for the detection of monosodium urate (MSU), calcium pyrophosphate (CPP) and hydroxyapatite (HA) crystal deposition using phantoms and task-based image quality metrics.
Methods: We used two dedicated CT phantoms: the first containing synthetic crystals of increasing concentration (MSU: 200-600 mg/ml; CPP and HA: 50-200 mg/ml) suspended in a background mimicking soft tissue. The second assessed noise and spatial resolution. Phantoms were scanned successively using SECT (100 kVp) and DECT (80/140 kVp) at two dose levels: 7 mGy and 14 mGy. For DECT, virtual monoenergetic images (VMIs) at 40 keV were reconstructed. Noise and spatial resolution were integrated into a mathematical model observer (MO) to assess detectability of 2-, 1-, and 0.5-mm diameter crystal deposits. The area under the curve (AUC) served as a figure of merit with an AUC≥90% denoting an excellent diagnostic performance.
Results: (Table 1)
Detectability increased with increasing radiation dose and increasing crystal concentration and diameter. For 1-mm diameter crystal deposits, SECT showed AUC values of 75% (MSU), 88% (CPP), and 89% (HA) at the highest crystal concentrations, while DECT (40 keV VMIs) identified all three crystals with an AUC of 1. For the highest HA concentration, SECT AUC values gradually decreased from 1 to 0.89 to 0.53 as the crystal deposit diameter decreased from 2 to 1 to 0.5 mm, respectively. In comparison, DECT provided corresponding AUCs of 100%, 100%, and 75%. DECT detects all 1-mm crystals regardless of their concentrations, outperforming SECT at 7 mGy. In contrast, SECT, even with a doubled dose (14 mGy), only identifies high-concentration CPP and HA crystals, failing in detecting MSU and low-concentration calcium crystals.
Conclusion: Despite higher image noise, DECT outperforms SECT, especially at low-keV VMIs, for the detection of small MSU and calcium crystal deposits.
Clinical relevance: DECT provides enhanced crystal detectability and presents a potential for reducing radiation dose compared to SECT in diagnosing gout and calcium crystal deposition diseases, especially in clinical scenarios (e.g. early disease stages) with low-concentration deposits.
