A Phantom for CT Gout Identification: Fabrication and Longevity
Abstract
Purpose
To develop a phantom for evaluating CT gout identification and determine phantom longevity.
Methods
Different human tissue mimics were tested - Tendon: lamb & beef tendon, & polyurethane, & rawhide; Tissue: gelatin, agar, & polyacrylic; Gout: Uric Acid Sodium Salt (UASS) & Uric Acid. Materials were evaluated based on ease to work with, HU on 110keV images, and material decomposition concentrations. A final phantom was fabricated based on the best materials for each tissue. Tissue dimensions were similar to a human lower leg and included mimics of gout and pseudogout (Calcium Pyrophosphate) with concentrations of 10%-50%, tendon, bone, and 50% gout cubes with side length of 2-10mm. Phantom measurements were made between Day 1 and Day 78. The HU at 110keV & concentrations in Gout Decomposition images were measured. Additionally, gout overlay images were evaluated on a 5-point Likert scale (0-no gout to 4 - > 80%). Tendon, bone, and tissue were evaluated on a 5-point Likert scale (0-no false positive to 4 - > 80%). Agar dimensions were measured to estimate shrinkage from drying.
Results
Agar was the preferred tissue material due to its more solid structure and other characteristics. HU was similar to soft tissues 17±13HU for agar, 43±14HU for gelatin, & 4±27HU for polyacrylic. Uric Acid was preferred due to cost and advantageous physical characteristics. Lamb tendon was preferred due to its 107±14HU. Beef tendon was too dense (144±13HU) and rawhide was too variable (119±31HU). Longevity was between 78 days (last imaging) and 93 days (fungal growth). The phantom shrank < 1mm. No consistent and clinically meaningful HU, concentration, or Likert rating changes over time were noted among inserts.
Conclusion
A phantom suitable for evaluating CT gout identification was developed. Phantom longevity makes it useful for evaluation and quality tasks.