PRIMOR

PRIMOR reconstructs respiratory-gated computed tomography (CT) images by combining prior-based reconstruction and motion estimation to improve image quality for low-dose or reduced-projection small-animal cardiothoracic studies.

Key Features:

• Prior-Based Reconstruction Enhancement: Extends prior-based reconstruction (PBR) with an additional penalty function that explicitly models respiratory motion to mitigate streak artifacts in low-dose Feldkamp–Davis–Kress (FDK) scenarios.
• Integrated Reconstruction and Motion Estimation: Integrates image reconstruction and respiratory motion estimation into a single algorithmic framework.
• Motion Estimation via Nonrigid Registration: Estimates respiratory motion between gating phases using nonrigid registration based on hierarchical B-splines.
• Prior Image Generation: Generates a prior image by averaging all respiratory gates reconstructed with Feldkamp–Davis–Kress (FDK).
• Performance Evaluation and Metrics: Evaluates performance against traditional PBR using high-dose micro-CT reference reconstructions while varying photon flux and number of projections, reporting Contrast-to-Noise Ratio (CNR), Mean Square Error (MSE), Streak Artifact Indicator (SAI), Solution Error Norm (SEN), and Jaccard Similarity Index.
• Dose and Projection Reduction Capability: Enables reduced radiation dose or fewer projections, with reported two- to three-fold reduction in projections compared to previous PBR approaches.

Scientific Applications:

• Small-Animal Cardiothoracic Imaging: Improves thoracic and cardiac CT image quality in small-animal studies by compensating respiratory motion across gating phases.
• Low-Dose Longitudinal Studies: Facilitates low-dose or reduced-projection imaging protocols to allow more frequent longitudinal imaging while minimizing radiation exposure and preserving data integrity and animal welfare.

Methodology:

Integrates prior-based reconstruction with an additional motion-modeling penalty; generates a prior by averaging all FDK-reconstructed respiratory gates; estimates inter-phase respiratory motion via nonrigid registration using hierarchical B-splines; and evaluates reconstructions against high-dose micro-CT references with simulated changes in photon flux and projection count using CNR, MSE, SAI, SEN, and Jaccard Similarity Index.