Difference between revisions of "NEIRetinalRegistration"

Revision as of 12:05, 27 August 2012

This topic is a stub. The HTML help for NEI Build MP Maps algorithm can be found here [1]

Screening for low macular pigment (MP) and monitoring supplementation requires robust methods to estimate the optical density of the MP. The method includes the measurements of MP that are performed by analysis of autofluorescence (AF) images and building the MP maps.

The technique, which is implemented in the MIPAV "NEI Build MP maps" plug in, uses AF images with two excitation wavelengths (yellow and blue) to calculate the MP optical density distributions over a central eight fifteen degrees diameter area radius centered on the fovea (in this plugin defined to be the center of mass of macular pigment optical density within the selected VOI, in typical cases of centro-symmetric pigment distributions, this corresponds to the maximum value of pigment that is anatomically typically at the center of the fovea (TBD). Background

The algorithm takes as an input two groups of retinal images acquired at two different excitation wavelengths, and creates MP maps that show the distribution of macular pigment over the retina. The input images are obtained with a standard Fundus camera for retinal photography, equipped with an autofluorescence modality. Images are captured using different wavelength filters - yellow and blue (defined in Appendix I, TBD) and have a fixed black background. It is important for the user to know the weighted average of the normalized macular pigment absorption coefficient in the excitation.

Typical values for NEI filter sets are provided in Table ## (see Appendix I, TBD).1 Outline of the method

1 The plug in takes two directories of retinal images - one with "yellow" images and another one with "blue" images. 1 The images from these directories are then converted to 32-bit. 1 Images are, then, registered to a common reference image. Registration employs the assumption that in all images pixels are in the same physical location on the retina. Therefore, it is possible to measure the amount of macular pigment in the fovea over time, comparing the pigment's absorption over time and how vitamins and other supplements quantitatively affect the retina, in addition to monitoring correlations between macular pigment levels and other microscopic changes in disease state and other local quantities such as lipofuscin levels and drusen. 1 The MP maps are, then, built for registered images using the user defined values for maximum and minimum intensity and relative extinction coefficients. 1 The MP map average and standard deviation images are also created. 1 All output images are converted back to 16-bit. 1 The method also provides the user with the opportunity to analyze the MP map using the user defined VOI(s).

Registration