Analyzing the pear bruised volume after static loading by Magnetic Resonance Imaging (MRI)

“Dar Gazi” variety of Pear fruit is very sensitive to bruising from mechanical impact and compression. At this study Pear (Pyrus communis L.) fruits were loaded in a perpendicular direction to their longitudinal axis. Samples were placed between two solid steel plates and loaded at a constant deformation rate of 0.167 mm/s under five different levels of compressive forces of 40, 50, 60, 70 and 80 N (Loading-Unloading tests), and then kept in cold storage. Propagation of internal bruised volume of fruits was determined by the nondestructive method of Magnetic Resonance Imaging and image processing techniques at different time intervals after loading. This study was carried out based on T2 type images (based on spin-spin relaxation times) with specifications of Spin-Echo (SE) pulse sequence, echo time (TE): 102 ms, repetition time (TR): 4930 ms, slice thickness: 3 mm, slice-to-slice distance (slice gap): 0.3 mm (center to center), Matrix Size (MS): 288*448, Field of View (FOV): 289*450 mm2, pixel resolution: 1.003*1.003 mm and Number of Acquisition (NA) of 2. The time intervals between imaging were specified based on the expansion of observed bruised volume on the prior Images. Image processing was performed by ImageJ 1.48 software. To calculate the bruised volume of the pears, a three-dimensional image was modeled for each pear using 3D Viewer plugin. The results indicated the bruised volume expanded linearly against the increase of the applied force, but it expanded non-linearly by time. Indeed, it increased logarithmically for 26 days from loading and then its expansion almost stopped. The effect of force and time, both separately and simultaneously were significant on bruised volume. Also, it was concluded that the optimum time for consumption of the product and appearing the least damage is 12 days after loading/unloading or external impact during harvesting and storage.