Molecular Tagging Velocimetry (MTV) is a molecular based technique which can study the whole field simultaneously. In this method, the photons with the appropriate wavelength excite the molecules of the flow and make these molecules traceable. In fact the excited molecules play the role of seeding particles in the PIV technique. So, MTV as a seedless technique can be categorized as molecular counterpart of PIV. Pulsed lasers are commonly used to label the molecules of the flow field, and similar to PIV technique two consecutive images will be taken during the tracer lifetime. As MTV is a seedless technique, it is a good option when using seeding particles is challenging or undesirable.