Contour diagrams reveal the structure of the eyeball, allowing the surgeon to determine where the corrections should be made. Doctors use the concepts of flux , vector fields , and optimization to understand the circulatory system. Optimizing the veins' capacity provides the doctors with an approximation of the amount of blood that should be flowing through unobstructed veins. Together with the information provided from a blood pressure test, doctors are able to determine whether the veins are obstructed. A Thallium Radionucleotide scan allows doctors to see where the flow of blood has been readily diminished.
Density is another multivariable calculus concept used by doctors.
Recent medical breakthroughs involve a connection between tissue density and breast cancer. Researchers are now reviewing women's mammograms to determine whether a difference in breast density correlates to a higher risk of developing cancer. Ecologists, specifically entomologists, use population density to determine the levels of pests in certain agricultural areas. Dense populations of certain pests determine whether or not an active pesticide management regimen should take place or if other alternatives can elevate the problem.