Feasibility study of ultra-low-dose dedicated maxillofacial computed tomography using filter-based spectral shaping in patients with craniofacial trauma: assessment of image quality and radiation dose.

Background: In the setting of multiple trauma, radiation exposure is considered a relevant issue because patients may require repeated imaging to evaluate injuries in different body parts. Recently, spectral shaping of the X-ray beam has been shown to be beneficial in reducing radiation exposure. We investigated the clinical feasibility of a tin-filtered 100 kV protocol for the diagnostic use, compared to routine dedicated maxillofacial CT at 120 kVp in patients with craniofacial trauma; we assessed the image quality, radiation dose, and interobserver agreement.

Methods: We retrospectively evaluated 100 consecutive patients who underwent dedicated maxillofacial CT for craniofacial trauma. Fifty patients were examined with a tin-filtered 100 kV protocol performed using a third-generation dual source CT. The other 50 patients were examined with a standard protocol on a different scanner. Two readers independently evaluated image quality subjectively and objectively, and the interobserver agreement was also assessed. CT dose index volume (CTDI) and dose-length product (DLP) were recorded to compare radiation exposure. A quality-control phantom was also scanned to prospectively assess the impact of tin filtration.

Results: All CT scans showed diagnostic image quality for evaluating craniofacial fractures. The tin-filtered 100 kV protocol showed sufficient-to-good image quality for diagnostic use; however, overall image quality and anatomic delineation from the tin-filtered 100 kV protocol were significantly lower than from the standard protocol. Interobserver agreement was moderate to almost perfect (k=0.56-0.85). Image noises in the air, eye globe, and retrobulbar fat were comparable between the two protocols (P>0.05), whereas both signal-to-noise ratio and contrast-to-noise ratio in the eye globe and retrobulbar fat showed a significant difference (P<0.05). The tin-filtered 100 kV protocol showed a significant reduction in radiation dose compared to the standard protocol: CTDI, 3.33 30.5 mGy (P<0.001); and DLP, 70.70 669.43 mGy*cm (P<0.001). The phantom study also demonstrated a lower radiation dose for the tin-filter 100 kV protocol compared to the standard protocol.

Conclusions: Dedicated maxillofacial CT using spectral shaping with tin filtration can allow a significant reduction in radiation dose while maintaining sufficient diagnostic image quality, when compared to the standard protocol.