Caroline Majoral

The use of combined single photon emission computed tomography and X-ray computed tomography to assess the fate of inhaled aerosol

BACKGROUND Gamma camera imaging is widely used to assess pulmonary aerosol deposition. Conventional planar imaging provides limited information on its regional distribution. In this study, single photon emission computed tomography (SPECT) was used to describe deposition in three dimensions (3D) and combined with X-ray computed tomography (CT) to relate this to lung anatomy. Its performance was compared to planar imaging. METHODS Ten SPECT/CT studies were performed on five healthy subjects following carefully controlled inhalation of radioaerosol from a nebulizer, using a variety of inhalation regimes. The 3D spatial distribution was assessed using a central-to-peripheral ratio (C/P) normalized to lung volume and for the right lung was compared to planar C/P analysis. The deposition by airway generation was calculated for each lung and the conducting airways deposition fraction compared to 24-h clearance. RESULTS The 3D normalized C/P ratio correlated more closely with 24-h clearance than the 2D ratio for the right lung [coefficient of variation (COV), 9% compared to 15% p < 0.05]. Analysis of regional distribution was possible for both lungs in 3D but not in 2D due to overlap of the stomach on the left lung. The mean conducting airways deposition fraction from SPECT for both lungs was not significantly different from 24-h clearance (COV 18%). Both spatial and generational measures of central deposition were significantly higher for the left than for the right lung. CONCLUSIONS Combined SPECT/CT enabled improved analysis of aerosol deposition from gamma camera imaging compared to planar imaging. 3D radionuclide imaging combined with anatomical information from CT and computer analysis is a useful approach for applications requiring regional information on deposition.

Using Helium-Oxygen to Improve Regional Deposition of Inhaled Particles: Mechanical Principles

BACKGROUND Helium-oxygen has been used for decades as a respiratory therapy conjointly with aerosols. It has also been shown under some conditions to be a means to provide more peripheral, deeper, particle deposition for inhalation therapies. Furthermore, we can also consider deposition along parallel paths that are quite different, especially in a heterogeneous pathological lung. It is in this context that it is hypothesized that helium-oxygen can improve regional deposition, leading to more homogeneous deposition by increasing deposition in ventilation-deficient lung regions. METHODS Analytical models of inertial impaction, sedimentation, and diffusion are examined to illustrate the importance of gas property values on deposition distribution through both fluid mechanics- and particle mechanics-based mechanisms. Also considered are in vitro results from a bench model for a heterogeneously obstructed lung. In vivo results from three-dimensional (3D) imaging techniques provide visual examples of changes in particle deposition patterns in asthmatics that are further analyzed using computational fluid dynamics (CFD). RESULTS AND CONCLUSIONS Based on analytical modeling, it is shown that deeper particle deposition is expected when breathing helium-oxygen, as compared with breathing air. A bench model has shown that more homogeneous ventilation distribution is possible breathing helium-oxygen in the presence of heterogeneous obstructions representative of central airway obstructions. 3D imaging of asthmatics has confirmed that aerosol delivery with a helium-oxygen carrier gas results in deeper and more homogeneous deposition distributions. CFD results are consistent with the in vivo imaging and suggest that the mechanics of gas particle interaction are the source of the differences seen in deposition patterns. However, intersubject variability in response to breathing helium-oxygen is expected, and an example of a nonresponder is shown where regional deposition is not significantly changed.

Controlled, Parametric, Individualized, 2D, and 3D Imaging Measurements of Aerosol Deposition in the Respiratory Tract of Healthy Human Subjects: Preliminary Comparisons with Simulations

Preliminary comparisons of simulation results from existing extrathoracic (ET) models and a lung deposition model with individualized, two-dimensional and three-dimensional (3D) imaging measurements of aerosol deposition in the respiratory tract of healthy human subjects have been presented. In general, the ET models did not correspond well with each individuals experimental data. However, there is rather good agreement between simulated and experimental results for regional lung deposition comparable to those previously found in the literature. Comparisons of generational distributions are relatively poor. These preliminary results suggest not only the need for further developments in deposition modeling, but also the need for better methods for analyzing experimentally determined 3D deposition distributions for comparison to simulated results. Copyright 2013 American Association for Aerosol Research

A technique for determination of lung outline and regional lung air volume distribution from computed tomography.

BACKGROUND Determination of the lung outline and regional lung air volume is of value in analysis of three-dimensional (3D) distribution of aerosol deposition from radionuclide imaging. This study describes a technique for using computed tomography (CT) scans for this purpose. METHODS Low-resolution CT scans of the thorax were obtained during tidal breathing in 11 healthy control male subjects on two occasions. The 3D outline of the lung was determined by image processing using minimal user interaction. A 3D map of air volume was derived and total lung air volume calculated. The regional distribution of air volume from center to periphery of the lung was analyzed using a radial transform and the outer-to-inner ratio of air volume determined. RESULTS The average total air volume in the lung was 1,900±126 mL (1 SEM), which is in general agreement with the expected value for adult male subjects in the supine position. The fractional air volume concentration increased from the center toward the periphery of the lung. Outer-to-inner (O/I) ratios were higher for the left lung [11.5±1.8 (1 SD)] than for the right [10.1±0.8 (1 SD)] (p<0.001). When normalized for the region sizes, these ratios were 1.37±0.16 and 1.20±0.04, respectively. The coefficient of variation of repeated measurement of the normalized O/I ratio was 5.9%. CONCLUSIONS A technique for outlining the lungs from CT images and obtaining an image of the distribution of air volume is described. The normal range of various parameters describing the regional distribution of air volume is presented, together with a measure of intrasubject repeatability. This technique and data will be of value in analyzing 3D radionuclide images of aerosol deposition.