Systems for Lung Volume Standardization during Static and Dynamic MDCT-based Quantitative Assessment of Pulmonary Structure and Function

Abstract

Rationale and Objectives Multidetector-row Computed Tomography (MDCT) has emerged as a tool for quantitative assessment of parenchymal destruction, air trapping (density metrics) and airway remodeling (metrics relating airway wall and lumen geometry) in chronic obstructive pulmonary disease (COPD) and asthma. Critical to the accuracy and interpretability of these MDCT-derived metrics is the assurance that the lungs are scanned during a breath-hold at a standardized volume. Materials and Methods A computer monitored turbine-based flow meter system was developed to control patient breath-holds and facilitate static imaging at fixed percentages of the vital capacity. Due to calibration challenges with gas density changes during multi-breath xenon-CT an alternative system was required. The design incorporated dual rolling seal pistons. Both systems were tested in a laboratory environment and human subject trials. Results The turbine-based system successfully controlled lung volumes in 32/37 subjects, having a linear relationship for CT measured air volume between repeated scans: for all scans, the mean and confidence interval of the differences (scan1-scan2) was −9 ml (−169, 151); for TLC alone 6 ml (−164, 177); for FRC alone, −23 ml (−172, 126). The dual-piston system successfully controlled lung volume in 31/41 subjects. Study failures related largely to subject non-compliance with verbal instruction and gas leaks around the mouthpiece. Conclusion We demonstrate the successful use of a turbine-based system for static lung volume control and demonstrate its inadequacies for dynamic xenon-CT studies. Implementation of a dual-rolling seal spirometer has been shown to adequately control lung volume for multi-breath wash-in xenon-CT studies. These systems coupled with proper patient coaching provide the tools for the use of CT to quantitate regional lung structure and function. The wash-in xenon-CT method for assessing regional lung function, while not necessarily practical for routine clinical studies, provides for a dynamic protocol against which newly emerging single breath, dual-energy xenon-CT measures can be validated.

Biomechanical CT metrics are associated with patient outcomes in COPD

“…One of the limitations of our study is that the CT scans were not spirometrically controlled 30 31. As varying respiratory effort can affect the reproducibility of image-registration metrics, participants were coached to maximum inhalation and end expiration.…”

Repeatability and Sample Size Assessment Associated with Computed Tomography-Based Lung Density Metrics

“…Multi-detector row CT (MDCT) scanners, Siemens Sensation 64 or Siemens Definition Flash 128 (110mAs, 120kV, pitch = 1, slice thickness = 0.72mm, slice spacing = 0.5mm and reconstructed voxel size ~0.62mm), were used for all subjects and scanners settings were calibrated on the day of the study. Subjects performed volume-controlled breath holds, using a previously established method for volume standardization(11). Briefly, a flow-based pneumo-tachometer coupled with a computer-based monitoring system was used to monitor and occlude airflow flow during designated breath-holds.…”

Progress in Imaging COPD, 2004 - 2014

“…34 However, the change between 100% and 90% of vital capacity is relatively slight. While several studies have used spirometers to standardize inspired lung volume, 35,36 such systems are not widely available, and the strong physiologic correlations obtained without lung volume control suggest that it may not be necessary. In the absence of a spirometer, careful coaching of the patient by the technologist is important to achieve total lung capacity.…”