Magnetic Resonance Imaging and Image Analysis for Assessment the longitudinal dimension, and such voids were not observed (5). In the current study, the voids/cracks appear in the planes perpendicular to the longitudinal axis of the system (presumably perpendicularly to the direction of maximum internal tensions). Kazarian et al. (12) applied combined VIS (visible photography) and FTIR with medium flow inside a non- pharmacopeial flow-through cell containing a tablet com- posed of HPMC (K4MRC) and BPP (buflomedil pyridoxal phosphate) (60%). The three observed optical fronts were in agreement with the observations made by Gao and Meury (10). The true penetration front was located at low water concentration scale (<<0.3 w/w) and was attributed to water penetrating through the channels inside the porous tablet with no or partial gelling of HPMC. In terminology introduced by Ju et al. (8), it encircles the dry glassy core. The second front, total gellification front, at approximately 0.6 w/w water content according to the FTIR results, separates the swollen glassy and gel regions. The erosion front appears at very high water concentrations and separates gel and solvent. The data, as presented by Kazarian et al. (12), transformed from front evolution (Fig. 5a) to the system evolution by means of layer thickness, are sketched in Fig. 5b. Our results as presented in Fig. 4 concur with the profiles obtained by Kazarian (12) (Fig. 5b) with the dry glassy–gel interface evolution profile from Fig. 5b corresponding to the swollen glassy region evolution contained in Fig. 4. However, the conditions of the studies by Kazarian et al. (12)—the sample restricted between plates or clamped between ATR crystal and transparent polymer window— and size of the matrix (small tablets of 3 mm diameter) did not fully reflect pharmacopoeial dissolution studies. In spite of 1071 this difference, the FTIR technique still gives unambiguous information concerning water and drug concentrations in particular fronts. The correct identification of particular areas occurring in controlled release matrix systems during wetting allows us to develop an understanding of the mechanism of drug dissolution. It is particularly important when dealing with the original and generic controlled release formulations. This was emphasized in the summary report of the workshop entitled “Challenges and Opportunities in Establishing Scientific and Regulatory Standards for Assuring Therapeutic Equivalence of Modified Release Products” (34). At this workshop, it was concluded that improved prediction of the in vivo performance of modified release products is needed to understand the mechanism underlying the drug release from the dosage form. In the case of generic controlled release dosage forms, modified release mechanisms could not be the same as in the branded product; hence, it is unlikely that one dissolution method might be appropriate or predictive for both formula- tions. From this point of view, in vitro dissolution profile is only one of many elements describing in vivo properties. Structural evolution of the system contains additional information, which reflects mechanisms behind the drug dissolution (4,5). CONCLUSIONS The presented paper describes an image analysis procedure applied to MR images of HPMC-based matrix tablet structure during hydration. The results show the first experimental observation of temporal evolution of HPMC- based matrix systems using MRI techniques integrated with USP Apparatus 4 consistent with the theoretical model presented by Ju et al. (8). Qualitative agreement between Fig. 5 A schematic of the HPMC matrix evolution according to VIS data according to data presented by Kazarian et al. (11). Data were transformed from the front evolution (a) to the system evolution using layer thickness (b).