Quantitative analysis of inhomogeneity in ventilation SPET

Abstract

The aim of this study was to evaluate a method for quantification of inhomogeneity in ventilation single-photon emission tomography (SPET). Nine emphysematous patients, nine life-long non-smokers and nine smokers were included in the study. The SPET investigation was performed after 50 MBq (99m)Tc-Technegas had been inhaled by each subject in the supine position. A single-head gamma camera, equipped with a general-purpose parallel-hole collimator using 64 projections (20 s each) over 360 degrees, was used. Data were acquired in 128x128 matrices. Attenuation correction was applied based upon computed tomography (CT) density maps. Lung regions of interest were delineated manually on CT images and then positioned on SPET images. Several attenuation-corrected transaxial SPET slices (thickness 1 cm, spacing 3.5 cm) were reconstructed. Each SPET slice was divided into several 2x2x1 cm(3) elements. Inhomogeneity was assessed by the coefficient of variation (CV) of the pixel counts within these elements (micro-level) and the CV of the total counts of the elements (macro-level). Micro-level CVs in non-smokers varied between 1% and 41%, whereas they were dispersed over a wide range (1%-600%) in emphysematous patients. In seven smokers, the frequency distribution of micro-level CVs was within the normal range, whereas in the other two smokers the values were between the normal range and the range in emphysematous patients. The pooled mean values of micro-level CVs and macro-level CVs in each subject clearly separated the patients from the others. Parametric images of micro-level CV indicated the localisation and severity of ventilation inhomogeneity. We conclude that the present method enables quantification and localisation of regional inhomogeneity in ventilation SPET images.

Physiological imaging of the lung: single-photon-emission computed tomography (SPECT)

“…Several recent SPECT studies have evaluated objective estimates of ventilation heterogeneity in normal and diseased lung (57,97). For example, Xu et al (97) showed that intraand interregional ventilation heterogeneity discriminated between normal and emphysematous lungs.…”

“…For example, Xu et al (97) showed that intraand interregional ventilation heterogeneity discriminated between normal and emphysematous lungs.…”

Quantification and optimisation of lung ventilation SPECT images

“…My work towards this objective can be divided into the following specific aims  Evaluation of reconstruction methods for subjective visual evaluation of lung SPECT images.  Improving the methodology introduced by Xu (Xu et al, 2001a) of extracting CV values out of a lung ventilation SPECT image.  Evaluating the ability of the CV T -method to differentiate between uniform and heterogeneous ventilation distributions using a anthropomorphic phantom.…”

“…Xu presented in 2001 (Xu et al, 2001a), regional heterogeneity measurements determined by calculating the coefficient of variation (CV) in small ele-ments of the lung. Heterogeneity maps and frequency curves were generated based on the CV values from ventilation SPECT images of nine emphysematous patients, nine healthy smokers and nine healthy non-smokers.…”

Application of texture analysis to ventilation SPECT/CT data

“…Ventilation scans, however, have been adapted for studies of ventilation in airways disease (King et al, 1997and 1998, 4 Downie et al, 2007. SPECT imaging offers the potential to characterise the topographical distribution of ventilation so that inhomogeneity can be quantified at the regional level (Xu et al, 2001, Venegas et al, 2005. Combining imaging information with the pulmonary function measures of inhomogeneity will provide important information about the ventilatory abnormalities in asthma and COPD (Tgavalekos et al, 2007, Berend et al, 2008.…”