Cross-Modality Registration of 2D Super-Resolution Ultrasound to 3D Micro-CT

For the purpose of super-resolution ultrasound validation, this study presents a parameter-free projection method for micro-CT volumes that weights the co-registered volume by the simulated ultrasound energy field. The hypothesis is that this ultrasound-field-weighted CT maximum intensity projection (MIP) is indistinguishable from an equidistant MIP over the slab spanning ±2 standard deviations (the 95% energy support), and is comparable to a contrast-free super-resolution ultrasound image. The ultrasound energy field is used to compute the thickness for an equidistant CT MIP that renders the greatest structural similarity index (SSIM) to the weighted CT image. In rat kidney data, the weighted CT projection achieved a peak SSIM of 97.2% against the 0.45mm equidistant MIP, and a projection distance of 0.72mm corresponds to 95% energy support in the ultrasound field. These results demonstrate that ultrasound-field-weighted CT MIPs yield images quantitatively equivalent to both equidistant MIPs and contrast-free super-resolution ultrasound, providing an improved framework for rigorous super-resolution validation.