Normal variance in emphysema index measurements in 64 multidetector-row computed tomography

Area of Science:

• Radiology
• Pulmonary Medicine
• Medical Imaging

Background:

• Emphysema index (EI) is a key metric for assessing emphysema severity.
• Understanding the normal variance of EI is crucial for accurate longitudinal monitoring.
• Multidetector-row computed tomography (MDCT) is widely used for lung imaging.

Purpose of the Study:

• To determine the normal variance of emphysema index (EI) measured by 64-MDCT.
• To establish acceptable thresholds for EI changes in clinically stable patients over short intervals.

Main Methods:

• A longitudinal study analyzed 475 chest MDCT scans to select 50 stable patients with two scans within three months.
• CT densitovolumetry was employed to calculate EI at -950 Hounsfield units (EI-950) and -970 Hounsfield units (EI-970).
• Variations in total lung volume (TLV), mean lung density (MLD), and EI were assessed between baseline and follow-up scans.

Main Results:

• Observed mean differences between baseline and follow-up scans were: TLV (149 ml), EI-950 (0.02%), EI-970 (0.04%), and MLD (15 HU).
• The 95% confidence intervals for EI variations were 0.89% for EI-950 and 0.23% for EI-970.
• Strong correlations were found between TLV and EI measurements (r=0.79 to 0.85).

Conclusions:

• Differences below 0.89% for EI-950 and 0.23% for EI-970 are considered within the normal variance for stable patients over three months.
• These findings provide a basis for interpreting serial EI measurements in emphysema monitoring.
• The study validates the reliability of MDCT-based EI measurements in stable individuals.