Non-unique water and contrast agent solutions in dual-energy CT

TL;DR

This study investigates the occurrence of non-unique solutions in dual-energy CT when imaging objects with water and contrast agents, revealing conditions that lead to multiple solutions and potential inaccuracies in material mapping.

Contribution

The paper identifies conditions under which dual-energy CT solutions become non-unique, using Jacobian analysis and simulations for practical contrast agent and water thickness ranges.

Findings

Non-unique solutions occur with iodine and gadolinium contrast agents.

Vanishing Jacobian determinants indicate potential multiple solutions.

Significant discrepancies can arise between true and recovered material maps.

Abstract

The goal of this work is to study occurrences of non-unique solutions in dual-energy CT (DECT) for objects containing water and a contrast agent. Previous studies of the Jacobian of nonlinear systems identified that a vanishing Jacobian determinant indicates the existence of multiple solutions to the system. Vanishing Jacobian determinants are identified for DECT setups by simulating intensity data for practical thickness ranges of water and contrast agent. Once existence is identified, non-unique solutions are found by simulating scan data and finding intensity contours with that intersect multiple times. With this process non-unique solutions are found for DECT setups scanning iodine and gadolinium, including setups using tube potentials in practical ranges. Non-unique solutions demonstrate a large range of differences and can result in significant discrepancies between recovered and true material mapping.