Embodiments of the present invention disclose improved micro-pore catalyst structures containing catalytic material comprised of mixed oxides of vanadium and phosphorus and using such improved micro-pore catalyst structures for the production of maleic anhydride. An initial phase response \u03c6 corresponding to A is generated. The task is solved in that a gradient layer is applied by arc wire spraying upon a surface, wherein during the spray application at least one of the process parameters current strength or voltage of the arc or gas pressure of the carrier gas is varied. The section of the tissue either at the surface or within the tissue is scanned and the reflectance image is produced with enhanced visualization of the cellular or nuclear structure thereof thereby enabling determination of the extent of the tumor in the section.