Try this
brightThings = grayImage > yourThresholdValue; % Creates a binary (logical) image.
imshow(brightThings);
props = regionprops(brightThings, 'All') % Measure a bunch of things about each bright blob.
Obviously, change variable names if you have to, to match what names you already have.
If you're just beginning image processing you really need to step through my Image Segmentation Tutorial in my File Exchange : http://www.mathworks.com/matlabcentral/fileexchange/?term=authorid%3A31862&sort=downloads_desc.
