1068 Kulinowski, Dorożyński, Młynarczyk and Węglarz Fig. 1 MR image of HPMC-based controlled release quetiapine fumarate tablet at 2:45 h (A), image intensity histogram (B), binary images (C1: - dry glassy core; C2: swollen glassy matrix; C3: gel). original image and feature stack. This segmentation approach is sensitive not only for intensity of particular pixels but also patterns of local intensity changes (texture) in the pixel’s vicinity. This segmentation approach was applied to each image in the stack separately. Segmented binary images of bulk fluid after some minor manual correction were used as masks for removing bulk fluid from original images. After removal of bulk fluid, a gaussian blur filter (with standard deviation of the distribution, σ = 3 pixels) was applied to reduce small local intensity changes, preserving the image edges better than a similarly sized mean filter. Next, the threshold levels were assessed: the region of interest (ROI) containing two regions were selected manually—for example: dry glassy core and swollen glassy regions—and one of the global segmentation methods/algorithms was used. The procedure was per- formed for several images in the stack where the adjacent regions had reasonable areas and mean threshold level was calculated. Dry glassy-swollen glassy modes threshold was estimated with Iterative Self-Organizing Data Analysis Techniques (ISOdata) algorithm. The threshold was set at 0.16 level (0.16± 0.003 as assessed for nine images from the stack). While the swollen glassy mode is relatively narrow, the gel mode is usually broad and consequently has lower amplitude; in this case, a triangle method was used. The threshold was set to 0.43 (0.43±0.036 as assessed for fourteen images from the stack). All images in the stack were thresholded using the same two threshold levels—one separating glassy dry core and swollen glassy part of the matrix, the second separating swollen glassy and gel. The result was three series of binary images reflecting the evolution of segmented regions, i.e. dry glassy core, swollen glassy and gel regions. Finally, the areas of the regions were calculated. Consequently, the evolution profiles of the areas of the three selected regions were obtained. Two additional profiles were calculated: the total swelling profile, which reflects changes of the total cross- section area of the system, and the glassy core profile, which reflects changes of the total area of polymer in glassy state. Fig. 1 shows an example of image segmentation for image recorded at 2:45 h. It was selected as an illustrative example because at this time point all three regions coexist and have comparable sizes. Fig. 1A1 represents MR image in grayscale. Fig. 1A2 shows region of interest (ROI) containing hydrated matrix Fig. 2 An example of MR images of the quetiapine fumarate tablet during the hydration inside USP Apparatus 4 (TR/TE=19/625 ms).