Reconstruction-Independent Resolution Limits in Preclinical Cone-Beam Micro-CT: A Closed-Form Analysis

Abstract

Spatial resolution in preclinical cone-beam micro-CT is bounded by two reconstruction-independent limits, a photon-noise limit from the projection-domain signal-known-exactly, background-known-exactly (SKE/BKE) ideal observer with the Rose criterion, and an angular-sampling limit from the Crowther criterion. The photon-noise bound is a property of the input data and applies to any reconstruction algorithm. The angular-sampling bound applies to classical analytic and iterative reconstructions (FDK, FBP, SIRT) that do not inject signal priors. We derive both limits in closed form for a circular feature in a uniform background, including an off-axis fan-beam extension, and combine them into a spatially varying effective resolution map. The combined limit yields a closed-form scan-design optimum. The maximum worst-case spatial frequency scales as the cube root of the total photon budget per detector pixel (per-view flux times number of views), and an analytic rule sets how to split that budget between flux and views. We illustrate the framework on a representative preclinical micro-CT scanner, with parametric sweeps over flux and projection count that show how each acquisition parameter reshapes the resolution map. An accompanying open-source web calculator implements these bounds for arbitrary scanner geometries.