Comparison of SPECT Aerosol Deposition Data with Twenty-Four-Hour Clearance Measurements

Abstract

Three-dimensional (3D) radionuclide imaging provides detailed information on the distribution of inhaled aerosol material within the body. Analysis of the data can provide estimates of the deposition per airway generation. Information on regional distribution of deposited aerosol can also be obtained from 24-hour clearance measurements. In this study, a nebulizer was used to deliver a radiolabeled aerosol to nine human subjects. Single photon emission computed tomography (SPECT) has been used to assess the distribution of aerosol deposition per airway generation. The deposition pattern was also estimated using measurements of the aerosol remaining in the lung 24 h after inhalation. The error in the SPECT value was assessed by simulation and that in the 24-h clearance value by repeat analysis. The mean fraction of lung deposition in the conducting airway (CADF) from SPECT was 0.21. The corresponding 24-h clearance value was 0.23. These values were not significantly different. There was a weak but non-significant correlation between the SPECT and 24-h measurements (r = 0.49). The standard error of the difference was 0.11. The corresponding errors on the SPECT and 24-h clearance measurements were 0.04 and 0.05, respectively. There was no systematic difference between the values of conducting airways deposition obtained from 24-h measurements and SPECT. However, there were random differences on individual subjects, which were larger than the estimated measurement errors.

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

“…This provides encouraging evidence for the validity of the generational parameters derived from SPECT-CT imaging. The correlation is improved compared to the previous study, (21) which might be explained for a number of reasons.…”

“…(20) However, this is at variance with modeling estimates, which tend to predict a much higher exhaled fraction particularly for particles of around 2 mm diameter. (21) The use of helium as the carrier gas in the one subject studied generally gave similar deposition results compared to air. However, there was relatively higher penetration of aerosol to the lung periphery and more exhaled compared to the two subjects given the same aerosol inhalation regime with air.…”

“…(15) This finding agrees with a previous comparison of SPECT derived airway deposition measurements and 24-h clearance. (21) When the Weibel definition of the conducting airways is used to calculate the deposition fraction (wdf), the systematic difference with 24 h clearance is much lower (Fig. 6b).…”

Application of Magnetic Particle Imaging to Pulmonary Imaging Using Nebulized Magnetic Nanoparticles

“…Techniques using radioisotopes such as technetium-99m are widely used to measure mucociliary clearance [16]. The observation time in these studies, however, is limited by the short half-life of the radioisotopes.…”

Computational and bioengineered lungs as alternatives to whole animal, isolated organ, and cell-based lung models

“…However, since this technique projects a 3D organ such as lungs in planar images and estimates particles deposition on the basis of (2D) images, it lacks 3D resolution and overestimates particle deposition in overlapping airways. Hence attenuation for the radioactivity in the chest wall is required to be corrected for accurate estimation (114).Recent advances in the field of nuclear imaging have made possible much accurate measurement of deposited radiolabeled particles in human lungs (12,41,44,50,51,93,107,118). SPECT and PET (positron emission tomography) are now used to create tomographic 3D lung structure by utilizing the information gathered by revolving detector cameras around the subject.…”