Abstract
ObjectivesTo compare ultra-low-dose CT (ULD-CT) of the osseous pelvis with tin filtration to standard clinical CT (CT), and to assess the quality of computed virtual pelvic radiographs (VRs).MethodsCT protocols were optimized in a phantom and three pelvic cadavers. Thirty prospectively included patients received both standard CT (automated tube voltage selection and current modulation) and tin-filtered ULD-CT of the pelvis (Sn140kV/50mAs). VRs of ULD-CT data were computed using an adapted cone beam–based projection algorithm and were compared to digital radiographs (DRs) of the pelvis. CT and DR dose parameters and quantitative and qualitative measures (1 = worst, 4 = best) were compared. CT and ULD-CT were assessed for osseous pathologies.ResultsDose reduction of ULD-CT was 84% compared to CT, with a median effective dose of 0.38 mSv (quartile 1–3: 0.37–0.4 mSv) versus 2.31 mSv (1.82–3.58 mSv; p < .001), respectively. Mean dose of DR was 0.37 mSv (± 0.14 mSv). The median signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of bone were significantly higher for CT (64.3 and 21.5, respectively) compared to ULD-CT (50.4 and 18.8; p ≤ .01), while ULD-CT was significantly more dose efficient (figure of merit (FOM) 927.6) than CT (FOM 167.6; p < .001). Both CT and ULD-CT were of good image quality with excellent depiction of anatomy, with a median score of 4 (4–4) for both methods (p = .1). Agreement was perfect between both methods regarding the prevalence of assessed osseous pathologies (p > .99). VRs were successfully calculated and were equivalent to DRs.ConclusionTin-filtered ULD-CT of the pelvis at a dose equivalent to standard radiographs is adequate for assessing bone anatomy and osseous pathologies and had a markedly superior dose efficiency than standard CT.Key Points• Ultra-low-dose pelvic CT with tin filtration (0.38 mSv) can be performed at a dose of digital radiographs (0.37 mSv), with a dose reduction of 84% compared to standard CT (2.31 mSv).• Tin-filtered ultra-low-dose CT had lower SNR and CNR and higher image noise than standard CT, but showed clear depiction of anatomy and accurate detection of osseous pathologies.• Virtual pelvic radiographs were successfully calculated from ultra-low-dose CT data and were equivalent to digital radiographs.
Highlights
The radiation dose of a standard CT of the osseous pelvis is many times higher compared to pelvic radiographs [1] and carries a higher risk of developing cancer, especially in young adults [2]
Tin-filtered ultra-low-dose CT (ULD-CT) of the pelvis at a dose equivalent to standard radiographs is adequate for assessing bone anatomy and osseous pathologies and had a markedly superior dose efficiency than standard CT
Ultra-low-dose pelvic CT with tin filtration (0.38 mSv) can be performed at a dose of digital radiographs (0.37 mSv), with a dose reduction of 84% compared to standard CT (2.31 mSv)
Summary
The radiation dose of a standard CT of the osseous pelvis is many times higher compared to pelvic radiographs [1] and carries a higher risk of developing cancer, especially in young adults [2]. In several patients, an additional CT scan of the pelvis is performed to exclude fractures or as part of preoperative planning as it provides detailed cross-sectional anatomic information While techniques such as automatic tube voltage, tube current modulation, and iterative image reconstruction have resulted in a reduced radiation dose, CT still results in much higher radiation exposure for the patient than radiographs. Low-energy photons that contribute little to image quality of high-contrast structures such as bone but expose the patient to higher radiation are filtered out. This results in hardening of the X-ray spectrum with more penetrable photons and reduction of radiation dose [5, 6]. CT studies of the thorax [7,8,9] and abdomen [10] showed promising results with remarkable reduction of radiation dose by using this technique without compromise in image quality
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