Mitigating X-Ray Focal Spot Induced Blurring in Small Animal Cone Beam CT Resolution Via Deconvolution
X Hu*, Y Zhong, Y Huang, C Shen, X Jia, University of Texas Southwestern Medical Center, Dallas, TX
Presentations
TH-E-201-4 (Thursday, 7/14/2022) 1:00 PM - 2:00 PM [Eastern Time (GMT-4)]
Room 201
Purpose: Image resolution of cone beam computerized tomography (CBCT) for preclinical small animal radiation studies is of particular importance for visualizing fine animal anatomical structures. One major cause limiting spatial resolution is the relatively large size of the x-ray focal spot. In this work, we proposed a simple method to measure x-ray focal spot intensity map and a CBCT image domain deblurring model to mitigate the effect of focal spot-induced image blurring.
Methods: We measured an x-ray projection image of a tungsten ball bearing using the flat panel detector of the CBCT platform. We built a blurring model of the projection image relating the blurring kernel to the spot intensity map. We then solved the spot intensity map based on this model. Using the measured spot intensity map, we derived an approximate model to represent CBCT image domain blurring for images reconstructed by the filtered backprojection algorithm. Based on this model, we computed image domain blurring kernel and improved the CBCT image resolution by deconvolving the CBCT image.
Results: We successfully measured the x-ray focal spot intensity map. The spot size characterized by full width at half maximum was about 0.75x0.55 mm² at 40 kVp. We computed image domain convolution kernels caused by the x-ray focal spot. Experimental studies on a CT calibration insert phantom and a plastinated mouse phantom demonstrated improved spatial resolution after image domain deconvolution, as indicated by visually improved resolution of fine structures. Quantitatively, modulation transfer function at 50% was improved from 1.05 to 1.25 mm⁻¹ for in-plane direction and 0.71 to 0.87 mm⁻¹ for cross-plane direction.
Conclusion: The proposed method is practical and effective to mitigate blurring caused by a finite x-ray focal spot size and improve CBCT image resolution.
Funding Support, Disclosures, and Conflict of Interest: This study was supported in part by grants from National Institutes of Health (R37CA214639, R01CA227289).
Keywords
X Rays, Spatial Resolution, Deconvolution
Taxonomy
IM/TH- Cone Beam CT: Development (New Technology and Techniques)
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