Adjusted subpixel method enables optimisation of bronchial measurements in high-resolution CT

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The purpose of this paper is to present a new technique of high-resolution computed tomography (HRCT) bronchial measurement, which was worked out in our centre and is based on a mathematically adjusted subpixel method (ASM). This study used a bronchial tree model comprising two polyvinyl chloride/rubber pipes with various densities placed in a larger plastic object. External and internal diameters of both pipes corresponded to the sizes of structures that are usually evaluated in HRCT scans (i.e. the bronchus with accompanying blood vessel). The model was subjected to repeated HRCT measurements of the external and internal diameters of model pipes using a subpixel technique and ASM. Significant differences were observed between mean values of external and internal diameters of model pipes determined by means of subpixel method or ASM, with the latter being the ones that resembled real diameters of the model pipes more closely. Mean external diameters of the larger and smaller model pipes determined by ASM differed from the real diameters by 0.23% and 0.57%, respectively. The internal diameter of the larger pipe was on average 25.96% larger, whereas the internal diameter of the smaller pipe was 48.05% smaller than the real diameter. The technique of non-linear prediction of HRCT bronchial measurements described in this paper raises attractive prospects in its clinical application owing to potential improvements in the objectivity and reproducibility of bronchial wall measurements.