Emphysema quantification using chest CT: influence of radiation dose reduction and reconstruction technique

Area of Science:

• Radiology
• Pulmonary Medicine
• Medical Imaging

Background:

• Computed tomography (CT) emphysema quantification is influenced by radiation dose and reconstruction techniques.
• Filtered back projection (FBP) overestimates emphysema at low doses due to noise.
• Iterative reconstruction (IR) can underestimate emphysema at low doses due to noise reduction.

Purpose of the Study:

• To assess the impact of dose reduction and iterative reconstruction (hybrid IR and model-based IR) on CT emphysema quantification.
• To determine optimal thresholds for accurate emphysema measurement under varying dose and reconstruction conditions.

Main Methods:

• 22 patients underwent inspiratory chest CT at standard and reduced radiation doses (45%, 60%, 75%).
• Acquisitions were reconstructed using FBP, hybrid IR, and model-based IR.
• Emphysema quantified using 15th percentile and percentage of voxels below -950 HU; various thresholds were tested.

Main Results:

• Dose reduction significantly overestimated emphysema; HIR and MIR underestimated it.
• Adjusting HU thresholds (lower for FBP, higher for IR) yielded comparable results to reference.
• The 15th percentile method showed similar performance to the HU threshold method.

Conclusions:

• CT emphysema quantification is sensitive to radiation dose and IR techniques.
• Adapting commonly used thresholds is a viable strategy to address these variations.
• This study highlights the need for individualized threshold adjustments in clinical practice.