Fully automated microvessel counting and hot spot selection by image processing of whole tumour sections in invasive breast cancer

Background-ManuaI counting of microvessels is subjective and may lead to un acceptable interobserver variability, which may explain conflicting results . Aim-To develop and test an automated method for microvessel counting and objective selection of the hot spot, based on image processing of whole sec tions, and to compare this with manual selection of a hot spot and counting of microvessels. Methods-Microvessels were stained by CD31 immunohistochemistry in 10 cases of invasive breast cancer. The number of microvessels was counted manually in a subjectively selected hot spot, and also in the same complete tumour s ections by interactive and automated image processing methods. An algorithm identified the hot spots from microvessel maps of the whole tumour section . Results-No significant difference in manual microvessel counts was found be tween two observers within the same hot spot, and counts were significantly correlated. However, when the hot spot was reselected, significantly diffe rent results were found between repeated counts by the same observer. Count ing all microvessels manually within the entire tumour section resulted in significantly different hot spots than manual counts in selected hot spots by the same observer. Within the entire tumour section no significant diffe rences were found between the hat spots of the manual and automated methods using an automated microscope. The hot spot was found using an eight conne ctive path search algorithm, was located at or near the border of the tumou r, and (depending on the size of the hot spot) did not always contain the f ield with the largest number of microvessels. Conclusions-The automated counting of microvessels is preferable to the man ual method because of the reduction in measurement time when the complete t umour is scanned, the greater accuracy and objectivity of hot spot selectio n, and the possibility of visual inspection and relocation of each measurem ent field afterwards.