Although many researches have obtained promising results with Magnetic Resonance Imaging  (MRI) techniques for fruit and vegetable internal quality assessment, many problems remain to be solved for a commercial use of such techniques. Moreover, in these researches, high cost equipment has been employed. MRI based on low magnetic field equipment can be an adequate alternative because of its low costs. In this work MRI techniques with a low magnetic field (0,18T) were used, and new algorithms for image analysis were developed and tested for the automatic detection of different internal damages of peaches and oranges that currently are only detected with conventional, destructive techniques.

Different MRI sequences were evaluated by means of six quality criteria established in this work, which allowed to select the best  one to obtain internal images of the fruits. Two spin echo sequences, one weighed in T1, and the other in T2 allowed to obtain high quality MRI images in the equatorial and longitudinal planes, both in peaches and oranges, that were used to visualize several types of internal defects.

In peaches, the developed algorithms detected 98% of fruits affected by a Alternaria sp. fungus, with 21,1% false detection of healthy fruit. 71% of fruit presenting Medfly punctures were detected, with 42% false assignment of healthy fruit. Algorithms detected up to 98% fruit presenting chilling injuries due to storage during 32 days at 5ºC, from day 22, two days before than conventional, destructive methods.

In oranges, the developed algorithms detected damages caused by fungi in more than 80% of affected fruits, with 20 % false detection of healthy fruit. The automatic and anticipated fungal disease detection was carried out 2-7 days before fruit presented external symptoms. Algorithms for detecting freezing injuries in oranges presented the best detection rates, with 94% damage detection and 8% of false detections.

Considering all the contributions of this research, at the end, a proposal of a MRI automatic system for the internal quality inspection of fruit, for a low magnetic field equipment is presented.


KEY WORDS: magnetic resonance imaging, MRI, image analysis, internal quality of fruit, damages, peach, oranges.