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Sci‐Fri PM Imaging‐02: Experimental evaluation of Otsu's thresholding technique for air‐volume measurements
Author(s) -
Madani A,
Cunningham I
Publication year - 2006
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2244677
Subject(s) - thresholding , imaging phantom , otsu's method , hounsfield scale , artificial intelligence , computer science , pattern recognition (psychology) , mathematics , materials science , nuclear medicine , computed tomography , image (mathematics) , radiology , medicine
Estimates of lung air volumes are often made in the clinical assessment of respiratory diseases using high‐resolution computed tomography (HRCT). Most algorithms are based on a thresholding of CT Hounsfield unit (HU) values using the “Otsu” method. This algorithm was developed for character recognition tasks in digital image processing chooses an algorithm that separates air from soft tissue by maximizing the ratio of intra‐class to inter‐class variances in voxel HU values. While the Otsu algorithm is widely used, it has not been experimentally validated. We tested the Otsu algorithm in a lung phantom containing solid spheres of known diameter using both HRCT and small‐animal uCT images. We found that air volumes could be determined using HRCT with an inaccuracy of less than 10% when sphere diameters were greater than 3 mm. Spheres of 2 and 1‐mm diameter gave errors of 38% and 75% respectively. It is concluded that thresholding of HRCT using the Otsu method can be accurate in regions containing air spaces larger than 3 mm, but not in regions containing alveoli as they are typically much less than a mm in diameter.