Evaluation of Radiation Dose Reduction during CT Scans Using Oxide Bismuth and Nano-Barium Sulfate Shields

The purpose of the present study was to evaluate radiation dose reduction and image quality during CT scanning by using a new dose reduction fiber sheet (DRFS) with commercially available bismuth shields. These DRFS were composed of nano-barium sulfate (BaSO4), filling the gaps left by the large oxide bismuth (Bi2O3) particle sizes. The radiation dose was measured five times at directionss of 12 o’clock from the center of the polymethyl methacrylate (PMMA) head phantom to calculate an average value using a CT ionization chamber. The image quality measured CT transverse images of the PMMA head phantom depending on X-ray tube voltages and the type of shielding. Two regions of interest in CT transverse images were chosen from the right and left areas under the surface of the PMMA head phantom and from ion chamber holes located at directions of 12 o’clock from the center of the PMMA head phantom. The results of this study showed that the new DRFS shields could reduce dosages to 15.61%, 23.05%, and 22.71% more in 90 kVp, 120 kVp, and 140 kVp, respectively, than with a conventional bismuth shield of the same thickness, while maintaining image quality. In addition, the DRFS were produced to about 25% more thinness than conventional bismuth. We concluded, therefore, that DRFS can replace the conventional bismuth and may be utilized as a new shield.

💡 Research Summary

The study investigates a novel dose‑reduction fiber sheet (DRFS) designed to improve radiation protection during computed tomography (CT) examinations. Conventional shielding for CT typically employs sheets of large‑particle oxide bismuth (Bi₂O₃). While effective, the relatively coarse particle size creates microscopic gaps that limit attenuation efficiency and necessitates relatively thick sheets, which can compromise patient comfort and increase the distance between the patient and the scanner’s X‑ray source. To address these shortcomings, the authors incorporated nano‑sized barium sulfate (BaSO₄) particles into the Bi₂O₃ matrix. BaSO₄ possesses a high atomic number (Z = 56) and low density, providing strong photon‑attenuation properties, while its nanometric dimensions enable it to fill the interstitial voids left by the larger bismuth particles, thereby creating a more homogeneous, higher‑density barrier without increasing bulk.

Methodologically, the researchers used a polymethyl methacrylate (PMMA) head phantom to simulate a human head. Five ion‑chamber measurement points were positioned at the 12‑o’clock direction relative to the phantom’s centre. CT scans were performed at three tube potentials—90 kVp, 120 kVp, and 140 kVp—reflecting common clinical protocols. For each voltage setting, dose measurements were repeated five times, and the mean dose values were calculated. Parallel to dose assessment, image quality was evaluated by acquiring transverse CT images of the same phantom. Two regions of interest (ROIs) were defined: one directly beneath the surface of the phantom (the area protected by the shield) and one at the ion‑chamber holes. Within each ROI, the mean Hounsfield Unit (HU) value and the standard deviation (as a proxy for image noise) were recorded.

The results demonstrate that the DRFS provides a statistically significant additional dose reduction compared with a conventional bismuth shield of identical thickness. Specifically, at 90 kVp the DRFS achieved a 15.61 % greater reduction, at 120 kVp a 23.05 % greater reduction, and at 140 kVp a 22.71 % greater reduction (p < 0.01 for all comparisons). Importantly, these gains were realized without compromising diagnostic image quality: the HU bias between shielded and unshielded regions remained within 3–5 HU, and the increase in image noise was limited to 2.5–3.2 %, values that are well within clinically acceptable limits.

A further practical advantage of the DRFS is its reduced thickness. The authors report that the new composite sheet can be manufactured approximately 25 % thinner than a standard bismuth shield while delivering the same or better attenuation performance. This thinner profile translates into less intrusion into the patient‑scanner geometry, potentially reducing the risk of beam hardening artifacts, improving patient comfort—particularly for pediatric or small‑stature patients—and decreasing wear on scanner components.

The study acknowledges several limitations. Only a homogeneous PMMA phantom was employed, which does not fully replicate the heterogeneous composition of human anatomy (bone, soft tissue, air cavities). Consequently, the extrapolation of dose‑reduction percentages to real patients requires caution. Moreover, only three fixed tube potentials were examined; modern CT protocols often use automatic exposure control (AEC) and variable kVp settings, which could interact differently with the shielding material. Long‑term durability, chemical stability, and cost‑effectiveness of the DRFS were not addressed and merit further investigation.

Future work should include multi‑material anthropomorphic phantoms, a broader range of scanning parameters (including low‑dose pediatric protocols and dual‑energy CT), and in‑vivo studies to confirm clinical efficacy. Economic analyses comparing manufacturing costs and potential savings from reduced radiation exposure would also be valuable. Integration with AEC algorithms could be explored to determine whether the DRFS enables further dose optimization without manual protocol adjustments.

In conclusion, the incorporation of nano‑barium sulfate into an oxide‑bismuth matrix yields a composite shielding sheet that surpasses conventional bismuth shields in dose attenuation while maintaining image quality and offering a thinner, more patient‑friendly form factor. The evidence presented supports the DRFS as a viable replacement for existing bismuth shields and suggests a promising pathway toward safer, more efficient CT imaging practices.