The Use of Combined Single Photon Emission Computed Tomography and X-ray Computed Tomography to Assess the Fate of Inhaled Aerosol

Abstract

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.

Controlled, Parametric, Individualized, 2D and 3D Imaging Measurements of Aerosol Deposition in the Respiratory Tract of Healthy Human Volunteers:In VivoData Analysis

“…Deposition by airway generation was calculated using a conceptual (3) The bronchial airways deposition fraction, BADF, defined by generations 2 to 8 was also calculated.…”

“…Note that though the two methods of presenting the data are essentially equivalent, the resulting statistics in the form of correlation coefficients are different, if just slightly. We will use C/P ratio for the remainder of this paper to be consistent with our previous papers 2,3 .…”

“…The inherent difficulty of assigning spatial deposition data to anatomical regions has been addressed by Fleming and his colleagues 3 by overlaying a morphological model in order to assign the deposition to the lung generations. , using the 3D-SPECT images that permit the exclusion of counts in the stomach and more precise attenuation correction.…”

Bridging the Gap Between Science and Clinical Efficacy: Physiology, Imaging, and Modeling of Aerosols in the Lung

“…This is complicated by the relatively poor resolution of the images (0.6-1.5 cm) and the complex structure of the lung airway, with nearly all of the airways being much smaller than the image resolution. Methods have been described for correcting for the limited image resolution and for transforming the spatial distribution to an anatomical distribution by airway generation, (115,136) but most work to date has relied on simplified models of the lung airway. Nevertheless, 3D models combined with CT do provide a wealth of data on aerosol deposition related to anatomy, which would benefit from improved analysis techniques.…”

Pulmonary radioaerosol mucociliary clearance in primary ciliary dyskinesia

“…Planar gamma camera images were taken at time 0, 1, 2, 4 and 24 h on a dual-head GE Infinia gamma camera (GE Systems, Milwaukee, WI, USA). A single-photon emission computed tomography/computed tomography scan and krypton-81 ventilation images were also obtained to characterise the initial distribution, allow attenuation correction and define the lung outline to assist interpretation of clearance data [12]. Geometric mean image data were interpreted after applying attenuation correction.…”