Kevin P. Nott

Quantitative magnetic resonance imaging of fresh and frozen-thawed trout.

Magnetic resonance imaging (MRI) has been used to visualise the major organs and muscular-skeletal frame-work of fresh rainbow trout (Salmo gairdneri) in two dimensions, and to identify the spatial distribution of lipid- and collagen-rich tissues. Quantitative MRI provides the MR parameters (T1, T2, M0, T1sat, Msat/M0, and the Magnetisation Transfer (MT) rate) for the tissue water; variations in those parameters enable distinction to be made between a freshly killed trout and one which has been frozen-thawed. The effects of freezing method, repeat freeze-thawing, and storage time on the MR parameters are discussed.

Advances in temperature validation of foods

Abstract Whereas the major purpose of cooking is to increase the palatability of food, the heating of many foods is essential to kill bacteria thereby increasing the foodstuffs safety and storage life. In practice, pasteurization and other sterilization processes require stringent assurance that all parts of the food product have been heated above a certain temperature for a defined period of time; unfortunately this often means that parts of the product have been overheated, resulting in loss of product quality. As a consequence much research has been carried out to optimize the quality and safety of many heating processes. As the complexity of heating methods increase, so too does the need for more innovative measurement techniques to monitor the efficiency of heating, particularly since some measurement methods may interfere with the heating process itself. Hence, despite the ever-increasing sophistication of models for heat transfer and the increasing power of computers to deal with them, there continues to be a need to validate models by in situ measurement, ideally with capability for on-line process control. At present in situ temperature monitoring still remains a challenge. Ideally the temperature measurement technique should be easily incorporated into the process without disturbing it; be non-contact because of the need for stringent sterile conditions; and have good spatial- and temporal-resolution: those requirements suggest use of some kind of tomographic technique 1 , 2 . Fortunately, several such technologies have been developed for medical applications and this review outlines previous work in this area and more recent developments of magnetic resonance imaging (MRI) temperature mapping [3] . Particular emphasis is devoted to temperature measurement in new processing methods (such as microwave sterilization) since that topic has not been adequately covered elsewhere.

Combination of NMR and MRI quantitation of moisture and structure changes for convection cooking of fresh chicken meat

This study demonstrates that a combination of bulk NMR and magnetic resonance imaging measurements of the T(2)-values of water protons can be used to determine the heat-induced changes in the structure and moisture content of fresh chicken meat which had been cooked in a convection oven at 200°C for a range of times. The gravimetric moisture content was also determined for both the raw and cooked meat. Multi-exponential fitting of the bulk NMR T(2) relaxation time data demonstrated three distinct water populations T(21) (39-43ms), T(22) (82-99ms) and T(23) (2-3ms) for raw meat which changed to 18-31ms (T(21)), 61-208ms (T(22)) and 3-7ms (T(23)) after the meat had been cooked. The T(1) and T(2) values obtained by MRI for cooked meat decreased progressively with increased heating time. There are highly significant correlations between the T(2) values from MRI and the T(21) values from bulk NMR measurements of cooked meat (r=0.986; p<0.01), and also between the normalised M(0) values from MRI and the gravimetric moisture content (r=0.953; p<0.01).

Measurement of textural changes of food by MRI relaxometry

This article summarises the current status of, and future prospects for, the use of magnetic resonance imaging (MRI) to evaluate the texture of a range of foods, and changes therein which accompany pathogen infection, natural ageing, damage, ripening and processing. The basic concept is that the magnetic resonance parameters of water are sufficiently sensitive to the texture of the food matrix, that magnetic resonance images of the spatial distribution of those parameters are effectively maps of the structural status of the foodstuff. This is illustrated in the context of the effects of pathogen infection in cucumbers, internal necrosis of melons, bruising in peaches, ripening of pineapples, and the effect of freeze-thawing on meat and fish.

[20] Study of biofilm within a packed-bed reactor by theee-dimensional magnetic resonance imaging

Publisher Summary This chapter describes the 3D MRI technique used to acquire images. MRI technique discussed in this article has great potential for studies not only of biofilms immobilized onto supports, but also of the overall functioning of bioreactors. MRI can also be used to monitor systems over a period of time. This technique is sensitive to motion and to temperature and it can be used to measure quantitatively in three dimensions dynamic changes, such as flow, diffusion, and mass- and heat-transfer. Besides the obvious importance of such experimental data in their own right, such data have unique potential for validation of the computer software used to model bioreactor processes. The chapter also provides an overview of the underlying principles of MRI and of some of the limitations of the technique with respect to imaging of biofilms. Other applications of MRI that are relevant to the study of bioreactors are described.

MRI phase mapping of temperature distributions induced in food by microwave heating.

A range of temperature-sensitive MRI parameters of water (T2, T1, diffusion coefficient, and chemical shift) were evaluated to map in three dimensions the non-uniform temperature distributions induced by microwave heating in both model and real food systems. Phase mapping was found to be the most robust method, and evaluations of possible experimental errors were based on semi-quantitative studies of homogeneous and heterogeneous systems. The MRI protocol provides complementary phase and magnitude data, which are related to the sample temperature and structural heterogeneity, respectively. Used together, they relate the temperature changes to the differential thermal properties of the various components within a heterogeneous sample. The potential applications of this technique to microwave and other forms of heating is discussed.

Visualisation of metal deposition in biofilm reactors by three-dimensional magnetic resonance imaging (MRI)

Three-dimensional magnetic resonance imaging (MRI) was used to visualise polyurethane foam-immobilised Citrobacter after challenging with La3+ and/or Cu2+ in citrate buffer supplemented with glycerol 2-phosphate. Extensive phosphatase-mediated bioaccumulation of LaPO4 was observed but no evidence for deposition of Cu3(PO4)2 was obtained by X-ray diffraction and proton-induced X-ray emission analyses. Image analysis showed that La3+/Cu2+ is a good model system to study the function of this biofilm reactor non-invasively by MRI.

Magnetic resonance imaging for industrial process tomography

Magnetic resonance imaging (MRI) is a noninvasive method for quantitating in three dimensions the spatial distribution of water and/or hydrocarbons in an optically opaque environment. This article uses three applications to illustrate how that unique ability of MRI can provide insight to aspects of process engineering. The first involves mapping temperature distribution due to microwave and/or conventional heating. The second demonstrates how MRI can be used to measure the flow of fluids through complex geometries, including a screw thread extruder and a porous medium. The third, measurement of solid-liquid separation, is illustrated by studies of two different types of filters. Although no background to the theory is provided, substantial practical details are given about the design of MRI-compatible processing equipment.

Efficient magnetic resonance imaging methods for automated quantitation of magnetic resonance parameters from multiple samples

Magnetic resonance imaging methods have been developed which simultaneously measure the bulk magnetic resonance parameters of many samples contained in stacks of multi‐well sample plates using either a 2.35 T, 31 cm or a 2 T, 100 cm horizontal bore magnet each with a quadrature ‘birdcage’ resonator. Computerized automatic edge detection software detects the position of each well within the first spin‐echo image which can then determine the mean magnetic resonance parameters of the sample in each well. An example is given of the automated quantitation of T1, T2 and M0 values for 2% (w/v) agar gel in four plates each with 30 wells per plate (120 samples in total). It was found that the maximum number of samples that can be analysed is limited by the homogeneity of the probe B1 field and the B0 field of the magnet. The applicability of this technology for future applications is discussed.