1. An imaging system for a plethysmograph, the system comprising: one or more imaging devices, wherein each of said one or more imaging devices is operatively configured to capture one or more images of a subject inside the plethysmograph as the subject breathes one or more gases contained within the plethysmograph and operable to provide an output signal including information regarding said one or more images, said one or more imaging devices including at least two imaging devices positioned orthogonal to each other with respect to the subject; a contrast assistance element positioned so as to be opposite at least one of said one or more imaging devices; and an imaging processor in communication with said one or more imaging devices and operatively configured to estimate a change in volume of said subject from said information.