LAUSR

HighlightsWe study the effect of non‐stationary noise and spatially variant bias in CT images for different doses, reconstruction techniques, and devices.We derive a functional relation between the spatially variant noise and the bias observed.A robust methodology to estimate the spatially variant noise is derived.An autocalibration scheme is proposed to remove the bias due to the spatially‐variant noise and the systematic bias of different reconstruction techniques.The validation of the proposed methodology shows the effectiveness in the reduction of systematic bias and spatially variant bias in phantoms and clinical images. Graphical abstract Figure. No Caption available. Abstract Computed tomography (CT) is a widely used imaging modality for screening and diagnosis. However, the deleterious effects of radiation exposure inherent in CT imaging require the development of image reconstruction methods which can reduce exposure levels. The development of iterative reconstruction techniques is now enabling the acquisition of low‐dose CT images whose quality is comparable to that of CT images acquired with much higher radiation dosages. However, the characterization and calibration of the CT signal due to changes in dosage and reconstruction approaches is crucial to provide clinically relevant data. Although CT scanners are calibrated as part of the imaging workflow, the calibration is limited to select global reference values and does not consider other inherent factors of the acquisition that depend on the subject scanned (e.g. photon starvation, partial volume effect, beam hardening) and result in a non‐stationary noise response. In this work, we analyze the effect of reconstruction biases caused by non‐stationary noise and propose an autocalibration methodology to compensate it. Our contributions are: 1) the derivation of a functional relationship between observed bias and non‐stationary noise, 2) a robust and accurate method to estimate the local variance, 3) an autocalibration methodology that does not necessarily rely on a calibration phantom, attenuates the bias caused by noise and removes the systematic bias observed in devices from different vendors. The validation of the proposed methodology was performed with a physical phantom and clinical CT scans acquired with different configurations (kernels, doses, algorithms including iterative reconstruction). The results confirmed the suitability of the proposed methods for removing the intra‐device and inter‐device reconstruction biases.