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Medical Imaging

MSc by Research in Medical Imaging (Coventry University), W. E. Crofts, 1998

in collaboration with Walsgrave Hospitals, Coventry, and Guy's Hospital London

An Analytical Technique to Improve the Diagnosis of Scaphoid Bone Injury

 The brief for this project was to investigate possible means of applying an image processing technique to the problem of adding structural information regarding carpal bone location to the functional radionuclide image of a patient’s hand with suspected scaphoid bone lesion. The compact structure of bones in the carpus makes accurate location of a radionuclide ‘hotspot’ difficult.Current practice in analysing such a radionuclide image appears to fall into only two categories. One category - probably the most prevalent - is to simply make an experienced guess at the exact location of the radiotracer ‘hotspot’. A second category - in use at Guy’s Hospital, London - involves the use of image processing but not without some reasonable overhead in time and cost. The developmental stage of this project produced a number of algorithms in MATLAB which were capable of orientating, scaling, translating, and registering an edge-detected image of the patient’s x-ray onto the corresponding radionuclide image of the patient’s hand. This could be achieved with or without the use of fiducial markers, and the edge-detected image was over-lapped onto the radionuclide image via a pixel replacement algorithm which allowed the merged images to be displayed using a ‘hot’ (red/yellow) colourmap to highlight the high intensity areas of the radionuclide image whilst the edge-detected lines remained a bright white colour for maximum clarity. A method of fitting a ‘wire diagram’ of the carpal bone outlines to a radionuclide image was also developed as an extension of the same algorithms, and displayed in the same way. All of the above methods had varying levels of alignment error, but all were considered successful as they were within the bounds of acceptable error defined by the purpose for which the algorithms were designed.

 

 

   

The position of the scaphoid bone (A) can be seen to be immediately below the base of the thumb. It is the prominent bone that protudes when the hand is pronated backwards, and hence is commonly damaged when a person falls forwards and puts out their hands to break the fall.

 

Note that the centre of fiducial marker 1 on the edge-detected x-ray image (small white circle indicated by green arrow) appears to be in the centre of the high-intensity area (brighter red area) which indicates the position of fiducial marker 1 on the radio nuclide image, i.e. the images are registered.

Location of the bone damaged area is indicated by the very high-intensity (yellow) concentration of radio-tracer. Its registration to the structural information now indicates that this is most likely to be abrasion between the scaphoid and hamate bone, rather than a direct fracture of the scaphoid bone.