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.

Airflow modeling of steady inspiration in two realistic proximal airway trees reconstructed from human thoracic tomodensitometric images.

Detailed description of the flow field in human airways is highly important to better understand human breathing and provide a patient's customized diagnosis. An integrated numerical simulation platform is presently proposed in order to incorporate medical images into a numerical software to calculate flow field and to analyze it in terms of fluid dynamics. The platform was set up to compute steady inspiratory airflow in realistic human airways reconstructed from tomodensitometric medical images at resting breathing conditions. This morpho-functional simulation platform has been tested retrospectively with two CT-scanned patient airway morphological models: (i) a normal airway model (subject A) with no evidence of morphological alteration and (ii) a highly altered airway model (subject B) exhibiting a severe stenosis in the right main bronchus. First, various morphological aspects proper to each airway model are provided to show the performance and interest of the reconstruction method. Second, we describe the three-dimensional flow patterns associated to the global morphological features, which are mainly shared by the present realistic models and previous idealistic airway models. Finally, the flow characteristics associated to local morphological features specific to realistic airway models are discussed. The results demonstrate that the morpho-functional simulation platform is able to capture the main features of airway velocity patterns but also more specific airflow patterns which are related to customized patient morphological features such as laminar vortex formation. The present results suggest that the proposed airway functional imaging platform is adequate to provide most of functional information related to airflow and enable a patient to patient diagnosis.