Comparison of X-ray CT and MRI of watercore disorder of different apple cultivars

• We obtained 3D image stacks of watercore affected apples using X-ray CT and MRI.
• X-ray CT and MRI images were matched pixel-by-pixel.
• The contrast of MRI images was significantly higher than that of X-ray CT images.
• Watercore classification rates of 79–89% were achieved for MRI and X-ray CT.
• High-resolution X-ray CT images revealed 3D microstructure of affected tissue.

Watercore is an internal disorder that appears as water-soaked, glassy regions near the core in apples. Fast and non-destructive solutions for sensing watercore would be readily accepted in the postharvest industry. X-ray CT and MRI were compared as potential imaging technologies for detecting this particular disorder. After matching the 3D datasets of X-ray CT and MRI, the images that were obtained on identical fruit were compared quantitatively. Both MRI and CT were able to detect watercore, however the contrast in MRI images was superior. High-resolution micro-CT images showed the microstructural changes in watercore fruit: the intercellular spaces of the affected apple tissue are filled with water. This explained the higher density that is detected here by the X-rays and the higher water content in the MRI. Mean and variance of the frequency distribution of MRI and X-ray CT intensity appeared to be a parameter that allows the identification of healthy apples from affected fruit. Automatic image processing based on thresholding the images resulted in comparable watercore classification accuracy of up to 89% for X-ray CT and 79% for MRI data, despite the better contrast in the MRI images.