Select area inside isosurface

Hi everyone,

I’ll try my best to explain my problem... I've a 3-dimensional dataset and I want to select some areas according to the their density. To obtain this I’ve divided my whole data-space in a grid 100x100x100 (that correspond to a matrix) and I’ve counted the number of points that are present in each cell. With this matrix it is easy to evaluate isosurfaces using the function 'isosurface'. What I would like to do now is selecting all the cells contained inside the isosurface I’ve calculated, but I’m not able to do it.. I cannot handle easily the output of the isosurface function...do anyone know how to do it? is there one different function I could use to achieve my goal? Besides, if you have suggestions on how to solve my problem with a completely different approach I would be grateful If you explain it :)

Thanks in advance to anyone answering