Double-bowtie filter design for pediatric spectral CT imaging: A fan beam simulation study

Despite concerns about radiation dose in pediatric patients, computed tomography (CT) remains a first-line imaging modality for children. Spectral CT provides additional diagnostic information that benefits pediatric imaging. However, most existing spectral CT systems are primarily optimized for adult patients.

To develop and evaluate a novel double bowtie filter integrating a K-edge material layer with a conventional Teflon filter for CT. The proposed design aims to enhance spectral signal-to-noise ratio (SNR) and spectral separation within the projection domain while maintaining radiation dose levels suitable for pediatric imaging.

A simulation framework was developed and used to model a rapid kVp-switching CT system operating at 70/110 kVp with realistic tube power and geometric constraints. Pediatric phantoms of three sizes (100-200 mm anterior-posterior width) were used to evaluate performance. Five accessible and safe filter materials-gadolinium (Gd), holmium (Ho), erbium (Er), silver (Ag), and tin (Sn)-were tested in combination with a Teflon bowtie. System performance was quantified using virtual monoenergetic image (VMI) SNR at 40 and 70 keV, and the area under the monoenergetic SNR curve (AUMC) as a comprehensive spectral image quality metric. Dose consistency was ensured using a traditional Teflon bowtie as the reference.

The Teflon + Gd configuration achieved the highest performance, improving mean AUMC over all fan angles by 53.6% on average and up to 56% for the largest phantom. VMI SNR increased by approximately 46% at 40 keV and 42% at 70 keV.

The double-bowtie concept substantially enhances spectral performance. The Teflon + Gd design provides a manufacturable, pediatric-optimized solution adaptable to kVp-switching and other spectral CT architectures, offering improved diagnostic quality at low dose levels.