Real‐time respiratory phase matching between 2D fluoroscopic images and 3D CT images for precise percutaneous lung biopsy

Purpose A 3D CT image is used along with real‐time 2D fluoroscopic images in the state‐of‐the‐art cone‐beam CT system to guide percutaneous lung biopsy ( PLB ). To improve the guiding accuracy by compensating for respiratory motion, we propose an algorithm for real‐time matching of 2D fluoroscopic images to multiple 3D CT images of different respiratory phases that is robust to the small movement and deformation due to cardiac motion. Methods Based on the transformations obtained from nonrigid registration between two 3D CT images acquired at expiratory and inspiratory phases, we first generate sequential 3D CT images (or a 4D CT image) and the corresponding 2D digitally reconstructed radiographs ( DRR s) of vessels. We then determine 3D CT images corresponding to each real‐time 2D fluoroscopic image, by matching the 2D fluoroscopic image to a 2D DRR . Results Quantitative evaluations performed with 20 clinical datasets show that registration errors of anatomical features between a 2D fluoroscopic image and its matched 2D DRR are less than 3 mm on average. Registration errors of a target lesion are determined to be roughly 3 mm on average for 10 datasets. Conclusions We propose a real‐time matching algorithm to compensate for respiratory motion between a 2D fluoroscopic image and 3D CT images of the lung, regardless of cardiac motion, based on a newly improved matching measure. The proposed algorithm can improve the accuracy of a guiding system for the PLB by providing 3D images precisely registered to 2D fluoroscopic images in real‐time, without time‐consuming respiratory‐gated or cardiac‐gated CT images.