The Hottest Connected Pixels (HCP) method has been used to outline the locus coeruleus/subcoeruleus in T1 weighted MRI images [2]. Another potential application is the extraction of the image derive input function. The HCP method finds a specified number of connected pixels with maximal average.
With the bounding VOI selected, start the Hottest Connected Pixels (HCP) tool. Besides the Number of connected pixels, the appearing dialog window includes two definitions related to neighborhood and connectivity.
With Direct mode enabled, only immediate neighbors defined by the Connectivity setting are compared, whereas in Bridged mode neighbors of the immediate neighbours are also involved. The Connectivty options are illustrated below.
References
1.https://en.wikipedia.org/wiki/Pixel_connectivity
2.Lorenzo DG, Longo-Dos Santos C., Ewenczyk C., Leu-Semenescu S., Gallea C., Quattrocchi G.,Pita Lobo P., Poupon C.,Benali H., Arnulf I., Vidailhet M., Lehericy S.: The coeruleus/subcoeruleus complex in rapid eye movement sleep behaviour disorders in Parkinson’s disease. Brain 2013, 136:2120–2129. DOI.