Dedicated Cone-Beam CT System for Extremity Imaging

TLDR

A prototype cone‑beam CT scanner has been developed for imaging extremities, including weight‑bearing lower limbs, to assess image quality and radiation dose. The study aims to provide an initial assessment of image quality and dose for a cone‑beam CT scanner dedicated to extremity imaging. The prototype was evaluated by measuring dose versus kVp and mAs, assessing contrast resolution via signal‑difference‑to‑noise ratio, determining spatial resolution with a line‑pair phantom, and qualitatively reviewing cadaver images for diagnostic value and artifacts. The scanner achieved optimal SDNR at 80 kVp, provided sufficient contrast for musculoskeletal tissues, resolved >15 lp/cm spatially, produced only minor scatter and beam‑hardening artifacts, and yielded cadaver images with excellent bone and good soft‑tissue detail, demonstrating adequate image quality and low dose (9 mGy) to justify further clinical evaluation.

Abstract

To provide initial assessment of image quality and dose for a cone-beam computed tomographic (CT) scanner dedicated to extremity imaging.A prototype cone-beam CT scanner has been developed for imaging the extremities, including the weight-bearing lower extremities. Initial technical assessment included evaluation of radiation dose measured as a function of kilovolt peak and tube output (in milliampere seconds), contrast resolution assessed in terms of the signal difference-to-noise ratio (SDNR), spatial resolution semiquantitatively assessed by using a line-pair module from a phantom, and qualitative evaluation of cadaver images for potential diagnostic value and image artifacts by an expert CT observer (musculoskeletal radiologist).The dose for a nominal scan protocol (80 kVp, 108 mAs) was 9 mGy (absolute dose measured at the center of a CT dose index phantom). SDNR was maximized with the 80-kVp scan technique, and contrast resolution was sufficient for visualization of muscle, fat, ligaments and/or tendons, cartilage joint space, and bone. Spatial resolution in the axial plane exceeded 15 line pairs per centimeter. Streaks associated with x-ray scatter (in thicker regions of the patient--eg, the knee), beam hardening (about cortical bone--eg, the femoral shaft), and cone-beam artifacts (at joint space surfaces oriented along the scanning plane--eg, the interphalangeal joints) presented a slight impediment to visualization. Cadaver images (elbow, hand, knee, and foot) demonstrated excellent visibility of bone detail and good soft-tissue visibility suitable to a broad spectrum of musculoskeletal indications.A dedicated extremity cone-beam CT scanner capable of imaging upper and lower extremities (including weight-bearing examinations) provides sufficient image quality and favorable dose characteristics to warrant further evaluation for clinical use.