The environmental density artifact: a beam-hardening effect in computed tomography

Area of Science:

• Medical Imaging Physics
• Radiological Sciences

Background:

• Computed tomography (CT) imaging relies on accurate attenuation measurements.
• Beam hardening is a known phenomenon in CT, causing energy-dependent X-ray attenuation.
• Environmental density artifacts can affect CT number accuracy, particularly in heterogeneous regions.

Purpose of the Study:

• To quantify the environmental density artifact in computed tomography.
• To investigate the impact of varying attenuation coefficients on central CT numbers.
• To assess the potential diagnostic implications of this artifact during contrast-enhanced CT.

Main Methods:

• Concentric cylindrical phantoms were utilized for measurements.
• The outer cylinder contained solutions with different attenuation coefficients (iodinated contrast medium, isopropyl alcohol).
• The central cylinder was filled with water to measure CT number changes.

Main Results:

• A measurable change in the CT number of the central water cylinder was observed.
• When the outer cylinder's CT number increased by approximately 100 HU, the central water cylinder's CT number increased by about 5 HU.
• This indicates a direct relationship between the surrounding material's attenuation and the central region's measured density.

Conclusions:

• The environmental density artifact, stemming from beam hardening, demonstrably alters CT numbers.
• This artifact can introduce inaccuracies in CT imaging, especially when contrast enhancement is used.
• Clinicians should be aware of this artifact to avoid potential misdiagnosis in contrast-enhanced CT examinations.