Iterative Reconstruction in Dose Reduction of A Head CT Examination and Corresponding Acquisition Parameter Selection

Purpose To investigate the potential of iterative reconstruction in radiation dose reduction during head computed tomography (CT) examinations and to evaluate the relationship between the parameters milliampere second (mAs), kilovoltage (kV), and iterative reconstruction strength using a live ovine (sheep) model. Methods A sheep was scanned on a SOMATOM Force (Siemens Healthineers) CT scanner at 12 mAs and 3 kV. Images were reconstructed with filtered back projection (FBP) and the Advanced Modeled Iterative Reconstruction (ADMIRE; Siemens Healthineers) strengths 1 to 5. Images with 216 combinations of varying doses, kVs, and reconstructions were rated by 2 neuroradiologists for low-contrast detectability (ie, gray-white matter differentiation) and image texture. Results Using only gray-white matter differentiation, maximum dose reduction was 75% at 100 kV with ADMIRE-3, and using only image texture, maximum dose reduction was 75% at 120 kV (and 140 kV) with ADMIRE-5. When these 2 metrics were combined, maximum dose reduction was 50% at 120 kV with ADMIRE-3. Other kV levels and higher iterative reconstruction strengths did not offer superior results. Discussion Although artificial intelligence algorithms are certainly gaining momentum, iterative reconstruction technology likely will remain more accessible to most hospitals and imaging centers. Dose reduction with preservation of image quality (ie, gray-white differentiation and image texture) can be achieved when complemented by appropriate iterative reconstruction strength. However, the effect of iterative reconstruction strength on gray-white differentiation and image texture does not necessarily converge on the same pattern. Conclusion Maximum dose reduction was 50% at 120 kV with ADMIRE-3, which confirms the potential for dose reduction with appropriately chosen iterative reconstruction strength and reveals a preference for 120 kV, as well as a limit to dose reduction by further increasing iterative reconstruction strength. A better understanding of dose-voltage-reconstruction relationships in iterative reconstruction might allow for greater dose reductions than current practices allow.