A computationally efficient method for dimensionality reduction in multi-channel spectral CT

Objective Multi-channel spectral CT technology holds the promise of measuring incoming X-rays across various energy spectrums, significantly enhancing iodine imaging performance. Nonetheless, it necessitates the reduction of data dimensions, such as condensing multiple energy bins, to ensure processing times remain within clinically acceptable limits and to maintain compatibility with traditional two-dimensional material decomposition methodologies. This study presents an optimization strategy designed to efficiently integrate multi-channel spectral CT data, aiming to minimize the anticipated noise in the iodine domain across different system parameters influencing channel content. Approach The Cramer-Rao lower bound of variance (CRLB) was used to estimate the iodine domain noise for four two-input weighting schemes including kVp-switching compared to a four-input material decomposition noise estimate. Two of the four weighting schemes were optimized to contain weights that minimized the expected CRLB noise. A model of rapid kVp-switching x-ray tube and dual-layer detector were used to simulate acquisitions of a hybrid, combined technology multi-channel spectral CT system. The impact of the duty cycle ratio, or proportion of high kVp to low kVp, and the phantom size ranging from adult to pediatric were investigated. Main Results The two-input weighting schemes with varying amounts of each spectral channel, optimized for low iodine noise, showed consistent low estimated noise performance within 0.27% difference to the ideal, four-input material decomposition results for all tested duty cycles in a standard adult-sized 300 mm water phantom. These schemes were always superior to kVp-switching regardless of duty cycle or phantom size. In the pediatric (150 mm) and large adult (400 mm) phantom cases, the two-input weighted schemes were within 1% difference to the ideal four-input noise estimator results on average, across all tested duty cycles. Significance Advanced dimensionality reduction techniques, such as those presented in this work, that merge multi-channel spectral CT data illustrate a potential in improvement the accuracy of iodine contrast material measurement, while filling clinical specifications. This study also indicates the significant role that hybird spectral CT technologies could play in elevating the reliability of quantitative CT. ### Competing Interest Statement PN has received a hardware grant from Philips Healthcare. PN receives research grant funding from Philips Healthcare. AP, KB, and RM are employees of Philips Healthcare. HD and TK are employees of Philips Innovative Technologies. The other authors have no relevant conflicts of interest to disclose. ### Funding Statement We acknowledge support through the National Institutes of Health (R01EB030494). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors