Different methods of assigning ROI in 2D gamma camera scintigraphy

The 2D gamma camera scintigraphy is an important and established technique used to evaluate the deposited dose in the lung of radiolabeled, inhaled aerosols. For further quantification of this aerosol deposition within the whole respiratory tract, scintigraphic images are divided into regions of interest (ROIs).

The basis for a good determination of the ROIs is a reproducible identification of the lung boundaries. Different approaches to determine pulmonary regions of interest and quantify aerosol deposition will lead to different results, and this effect might be even higher in severe patients. Five different methods to define ROIs of the intrathoracic and the extrathoracic regions were compared, in order to quantify the influence of ROI assignment on deposition results in healthy subjects, COPD patients, asthmatic patients and CF patients.

The evaluation of five ROI assessment methods showed a maximum deviation[1] of the intrapulmonary deposition of up to 26 % (mean = 15 %) and of the extrapulmonary deposition of up to 47 % (mean = 28 %). These observations confirm the need for a standardized approach to define ROIs of the intrathoracic and the extrathoracic regions. A classification of ROI determination methods based on different pathologies might be an appropriate way of standardization.

[1] The maximum deviation is calculated relative to the mean value of the depositions results of all five ROI assignment methods. Please note the mean value is an arithmetic mean and does not reflect an optimal deposition.