Lubrication of chocolate during oral processing

The structure of chocolate is drastically transformed during oral processing from a composite solid to an oil/water fluid emulsion. Using two commercial dark chocolates varying in cocoa solids content, this study develops a method to identify the factors that govern lubrication in molten chocolate and saliva's contribution to lubrication following oral processing. In addition to chocolate and its individual components, simulated boluses (molten chocolate and phosphate buffered saline), in vitro boluses (molten chocolate and whole human saliva) and ex vivo boluses (chocolate expectorated after chewing till the point of swallow) were tested. The results reveal that the lubrication of molten chocolate is strongly influenced by the presence of solid sugar particles and cocoa solids. The entrainment of particles into the contact zone between the interacting surfaces reduces friction such that the maximum friction coefficient measured for chocolate boluses is much lower than those for single-phase Newtonian fluids. The addition of whole human saliva or a substitute aqueous phase (PBS) to molten chocolate dissolves sugar and decreases the viscosity of molten chocolate so that thinner films are achieved. However, saliva is more lubricating than PBS, which results in lower friction coefficients for chocolate-saliva mixtures when compared to chocolate-PBS mixtures. A comparison of ex vivo and in vitro boluses also suggests that the quantity of saliva added and uniformity of mixing during oral processing affect bolus structure, which leads to differences in measured friction. It is hypothesized that inhomogeneous mixing in the mouth introduces large air bubbles and regions of non-emulsified fat into the ex vivo boluses, which enhance wetting and lubrication.

Direct use of CT scans for hyperthermia treatment planning

In the field of deep regional hyperthermia cancer therapy, the BSD-2000 Hyperthermia System is one of the most widely used devices. Because of the complexity of the treatment process, computer modeling has long been viewed as a desirable means of planning patient treatments. Patient-specific, three-dimensional computer modeling for treatment planning in the BSD-2000 has been in clinical use at this institution for two years. Two of the persistent problems have been the large amount of time needed to create the patient model from a computed tomography (CT) scan (one and a half days), and the lack of a way to view the large amounts of data that comprise the output of a treatment plan, i.e., the specific absorption rate (SAR) at 20,000 to 30,000 cells. Here we present a method that obtains the dielectric properties needed for hyperthermia treatment planning directly from the CT image with minimum operator interaction, a process which takes about a half day and is more accurate. Comparison is made with the previous method of drawing contours around the different tissue types. We further describe a method which displays the output as iso-SAR contours directly over the CT scan of the patient.

Creation of three-dimensional patient models for hyperthermia treatment planning

The finite difference time domain (FDTD) method has been used to simulate hyperthermia treatment using the Sigma-60 applicator of the BSD-2000 Hyperthermia System. In order to use this simulation capability in treatment planning, a detailed anatomical representation of the patient must be created. This paper describes a system developed to create such models from the CT scans of the patients and then display the results of the simulation. About a day and a half is required to create a patient model.

The effect of insertion depth on the theoretical SAR patterns of 915 MHz dipole antenna arrays for hyperthermia

Interstitial microwave antenna array hyperthermia (IMAAH) is presently used clinically in the treatment of cancer. This paper presents the theoretical specific absorption rate (SAR) patterns of 915 MHz microwave antenna arrays for varying insertion depths. The antennas were oriented in a 2 x 2 cm square array. Insertion depth, defined as distance from skin to antenna tip, ranged from 5.9 to 17.6 cm. Two different antenna configurations were considered. In the first the antenna had a distal section a quarter-wavelength long (resonant case), while the second had a distal section approximately 13% longer than a quarter-wavelength (non-resonant case). SAR patterns were calculated from theoretical expressions, and displayed as lines of constant SAR normalized to the maximum SAR value in the array. The results show that regions of concentrated power deposition or 'hotspots' occurred in the centre of the array and moved in a complex but predictable fashion as insertion depth was varied. For insertion depths shorter than a resonant half-wavelength, there occurred one hotspot distal to the antenna junctions. As insertion depth was increased beyond a resonant half-wavelength, the hotspot moved proximal to the antenna junctions and eventually split in two. For depths very much longer than a resonant half-wavelength a hotspot centred about the antenna junction dominated the SAR pattern. For the resonant case the maximum SAR was often along the central axis of the array, while for the non-resonant case the maximum SAR was at the antennas with a local maximum on the central axis.