Author: Michalis Aristophanous, Laura I. Cervino, Maria F. Chan, Puneeth Iyengar, Hsiang-Chi Kuo, Nancy Y Lee, Xiang Li, Seng Boh Gary Lim, Usman Mahmood, Jean M. Moran, Jason Ocana 👨🔬
Affiliation: Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, Department of Medical Physics, Memorial Sloan Kettering Cancer Center 🌍
Purpose: To determine the limits of iodine concentration detection (LOD) and quantification (LOQ) in dual-energy computed tomography using a 3D printed phantom while considering different background, target sizes and DECT protocols.
Methods: Seven iodine solutions (0.25 to 20 mg/mL) were tested in a 3D printed phantom with vessel diameters of 15, 10, 5, and 2 mm, using fat and liver as background materials. The phantom underwent five scans with two protocols across three scanners, including two scanners with Sn filters and one without, utilizing various kVp combinations. Virtual monochromatic images (VMI) and iodine maps were created, and the average iodine signal from the plugs was recorded. The limit of blank (LOB) was set as the upper limit of the 95% confidence interval for water and background materials. The limit of detection for iodine maps (LODI) and VMI (LODV) was defined as the lowest concentration with a 95% probability of exceeding the LOB. The limit of quantification (LOQ) for iodine maps was the lowest concentration with a coefficient of variation below 20%. Spearman correlation analysis assessed factors influencing LODV.
Results: The LODV ranged from 0.0-0.23 mg/mL in a fatty background and 0.4-3.9 mg/mL in a hepatic background, except for VMI at 120 keV or higher. LODI varied from 0.17-1.1 mg/mL for filtered scanners and from 0.74-1.82 mg/mL for unfiltered one. The LOQ was 0.5-1 mg/mL for vessels ≥10 mm and 0.5-5 mg/mL for vessels ≤5 mm. Spearman analysis ranked the factors affecting LODV as: background, VMI energy, protocol, scanner, and vessel size.
Conclusion:
For vessels >5 mm, a VMI setting of 40 keV can detect iodine concentrations as low as 0.6 mg/mL in liver tissue. Iodine mapping quantifies concentrations from 0.5 to 1.0 mg/mL in scanners with a filter for improved energy separation. LOD and LOQ decreased with smaller target sizes.