The effect of tin prefiltration on extremity cone-beam CT imaging with a twin robotic X-ray system

Radiography (Lond). 2022 May;28(2):433-439. doi: 10.1016/j.radi.2021.10.009. Epub 2021 Oct 27.

Abstract

Introduction: While tin prefiltration is established in various CT applications, its value in extremity cone-beam CT relative to optimized spectra has not been thoroughly assessed thus far. This study aims to investigate the effect of tin filters in extremity cone-beam CT with a twin-robotic X-ray system.

Methods: Wrist, elbow and ankle joints of two cadaveric specimens were examined in a laboratory setup with different combinations of prefiltration (copper, tin), tube voltage and current-time product. Image quality was assessed subjectively by five radiologists with Fleiss' kappa being computed to measure interrater agreement. To provide a semiquantitative criterion for image quality, contrast-to-noise ratios (CNR) were compared for standardized regions of interest. Volume CT dose indices were calculated for a 16 cm polymethylmethacrylate phantom.

Results: Radiation dose ranged from 17.4 mGy in the clinical standard protocol without tin filter to as low as 0.7 mGy with tin prefiltration. Image quality ratings and CNR for tin-filtered scans with 100 kV were lower than for 80 kV studies with copper prefiltration despite higher dose (11.2 and 5.6 vs. 4.5 mGy; p < 0.001). No difference was ascertained between 100 kV scans with tin filtration and 60 kV copper-filtered scans with 75% dose reduction (subjective: p = 0.101; CNR: p = 0.706). Fleiss' kappa of 0.597 (95% confidence interval 0.567-0.626; p < 0.001) indicated moderate interrater agreement.

Conclusion: Considerable dose reduction is feasible with tin prefiltration, however, the twin-robotic X-ray system's low-dose potential for extremity 3D imaging is maximized with a dedicated low-kilovolt scan protocol in situations without extensive beam-hardening artifacts.

Implications for practice: Low-kilovolt imaging with copper prefiltration provides a superior trade-off between dose reduction and image quality compared to tin-filtered cone-beam CT scan protocols with higher tube voltage.

Keywords: Cone-beam computed tomography; Extremities; Filtration; Prefiltration; Radiation dosage; Tin.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cone-Beam Computed Tomography / methods
  • Copper
  • Extremities
  • Humans
  • Radiation Dosage
  • Robotic Surgical Procedures*
  • Tin*
  • X-Rays

Substances

  • Tin
  • Copper