[vtkusers] problem access to specific voxel

[Hossein Nazem]

dear vtk users
hi
how can i access to specific voxel in vtk?
i have a volume from ct image. from dicom header i have "image
position patient", "slice thikness" and "pixel spacing". for example
if  "image position patient"=[-137.699; -310.699; -1222] how can i
reach this point in vtk? (for example change the color of this point)
thanks
hossein