Project Outline

i. The holder must be designed to accommodate as wide a range of egg size as possible. This is necessary since both during the building of the holder and more importantly during its subsequent use for imaging a wide range of egg sizes will be used. During building it is anticipated that egg fragility will lead to many breakages and so many different eggs will be used for the production of the mould; for imaging it is only natural that researchers using the holder will want to image a large number of samples. It should be noted that there is a general lack of UK or EU regulation concerning the standardisation of egg size and so it will not be possible to follow a strict guideline concerning size during egg selection. The British Egg Industry Council [2] provides only four broad categories of egg size (small, medium, large, extra large) based on the mass of the eggs.

ii. The sources and detectors that are to be attached to the mould must be rigidly fixed in position and the fixed spatial coordinates of all sources and detectors must be determined prior to any imaging. This is necessary because it forms an essential requirement for the subsequent image reconstruction using the temporal optical absorption and scattering algorithm (TOAST).

iii. Provisions must be made in the design so that each detector can be optically isolated from direct illumination by sources in neighbouring detectors as well as from all external sources of light.

The outer shell of the egg holder will be constructed in two equal halves, an upper and a lower half, from low-temperature thermoplastic. The lower half will be mounted on rods that in turn will be mounted on a flat horizontal rectangular or square base. Elevating the lower half of the holder on rods will make the holder more stable (in the absence of any support the holder will roll around on any surface it is placed) and provide access to its entire surface area. This will facilitate the placement of sources/detectors over the entire surface. The two halves will come together and attach in such a way so that irrespective of the containing egg the spatial coordinates of the sources/detectors will remain fixed. Small sockets mounted onto the thermoplastic shell at predetermined positions will be used to attach source/detector connectors. The inner surface of the holder will be lined with soft NIR-absorbing foam of thickness to be determined. The foam will serve a dual purpose: On the one hand, since it is compressible it will provide the necessary padding to accommodate a wide range of egg sizes while the spatial coordinates of the sources/detectors remain fixed. On the other, its NIR absorbing properties will ensure that detectors are optically isolated. Holes will be made in the foam through which the connectors will be radially translated bringing the sources/detectors up to the egg surface.

For purposes of carrying out this stage of the investigation as well as the next, eggs must be carefully selected so as to be of high quality. In accordance with EU legislation, there are three quality classes for eggs: Class A, Class B and Class C. Classification takes into account the quality of the cuticle, shell, albumen and yolk, the air space within the egg, the development of a germ cell and smell. The criteria to be met by all of the aforementioned constituents of the egg for the various classification are outlined in the “Egg quality guide” of the Department for Environment, Food and Rural Affairs (DEFRA) [3]. In general, all eggs sold in supermarkets are Class A eggs. Despite this, prior to imaging eggs should, if possible, undergo some form of candling (even if it involves simply using a strong flashlight) to ensure that there has not been any damage from when they underwent candling prior to marketing.

Various methods will be considered to determine the spatial coordinates of the sources/detectors required for image reconstruction. One possibility would involve a more or less random positioning of the sources/detectors and the subsequent use of a 3D digitising arm preferably while the egg is within the holder but if not possible then either before or after (since as mentioned previously, theoretically, the design of the holder will be such that the presence or not of an egg will not affect the spatial coordinates of the sources/detectors). Another possibility would involve a more orderly positioning of the sources and detectors as well as more careful construction. The maximum number of source/detector rings and the maximum number of sources/detectors that could be placed on each ring would be estimated. The sources/detectors on each ring would then be placed at equal angular separation as shown in figure 1 below.

This will enable more accurate determination of the spatial coordinates of the sources/detectors.

An appropriate preliminary validation measurement will be the imaging of an egg prior to and after cooking. The imaging system used will be one developed at University College London (UCL) known as MONSTIR (multi-channel opto-electronic near-infrared system for time-resolved image reconstruction). Image reconstruction will be performed using an algorithm known as TOAST (temporal optical absorption and scattering tomography) also developed at UCL.

Using information obtained either from the general literature or from a research group involved in using magnetic resonance imaging (MRI) to monitor the development of chick embryos, the correct type and amount of dye necessary to simulate various conditions of stress will be injected into the egg. It is predicted that injection of the dye can be achieved using a hypodermic needle inserted through the tiny pores that permeate the shell and allow gases to move between the contents of the egg and the surroundings.

MONSTIR and the TOAST algorithm will then be used to determine the changes in optical properties resulting from this injection.

Based on the outcome of the previous three stages the usefulness of eggs as a test-bed for optical imaging will be determined and suggestions will be made for future development and research.