November 4/Werribee, Australia/Journal of Technology & Science -- According to a study from Werribee, Australia, "In microwave processing a number of microwave specific factors cause non-uniform heating patterns with hot and cold spots. Hence, the quality and safety of food products can be compromised."
"Capabilities for creating three-dimensional temperature maps are therefore essential for control, optimization and validation of microwave heating processes. This paper will discuss the advantages and shortcomings of different techniques for measuring temperatures in electromagnetic fields. The unique possibilities of applying non-invasive magnetic resonance imaging (MRI) for temperature mapping are demonstrated by experiments. In particular, in-situ measurements with three-dimensional isotropic resolution of 1mm and a reasonable temporal resolution of 13 s are presented and compared with infrared thermography and fiberoptic thermometry. Numerical simulations are employed to assess the extent of two kinds of systematic errors involved in the MRI experiment. Industrial relevance: The presented approach for measuring temperatures volumetrically in-situ during a microwave heating process allows for the determination of three-dimensional temperature distributions; hence hot and cold spots in the products can be detected. Although the experiments in this study have been conducted in a high-resolution MRI tomograph with a small sample diameter, the same approach works in larger scale medical tomographs with bores up to 1m diameter, making it also relevant for industrial scale applications. The costs of an MRI tomograph are still high; however, having premium products where quality would be adversely affected by overheating and safety compromised by under-processing, the application of such technology would be of great benefit for the food industry.