One of the most powerful examples of this is PET or Positron Emission Tomography imaging. In one of the few applications outside of fundamental research of antimatter, PET imaging uses positrons, otherwise known as anti-electrons to provide precise, localized data. The "evil twin" of regular matter, these antiparticles are almost identical to their everyday counterparts. However they do possess opposite charges (hence the name "posi"-trons), and when they meet their regular matter counterparts, they annihilate each other in a blinding flash of energy (these antimatter annihilations between positron-electron pairs are perfect representations of Einstein's famous Mass-Energy equivalence equation discussed on the Fusion section of this site). When this annihilation happens, two gamma rays are produced, each photon possessing an energy of 511 keV (the rest mass of an electron) speeding out at almost 180 degrees from each other. By using precisely placed gamma detectors, timing electronics, and a computer algorithm, it is possible to resolve the origin of these coinciding photons to a very precisely location in multiple dimensions.
So now that we a very precise camera, what can we do with it? One of the most common uses of PET imaging today is for the imaging of cancer using a tracer known as FDG or Fluorodeoxyglucose. FDG is a glucose analog that contains an attached Fluorine atom (in this case positron emitting Fluorine-18, with a 110 minute half-life). Glucose is in high demand in rapidly dividing cancer cells, so when FDG is injected into the bloodstream of a cancer patient, it localizes or "tags" these areas which can then be imaged via a PET scanner. This technique is one of the best ways to see cancer by allowing the doctor to see the distribution of biologically relevant molecules known as "biomarkers" as opposed to just simply getting an image of the tissue that is present.
While FDG-PET is the most broadly adopted PET technique by far, many other biomarkers can be produced and many high resolution procedures are in various stages of deployment. PET allows functional imaging of the brain to look for degenerative diseases and research mental illness, and PET tracers can allow for a much more detailed investigation of the heart including blood flow measurements. Fluorine-18 is not the only positron emitting isotope that can be used either, its broad adoption is primarily due to its comparatively longer half-life meaning a hospital does not have to have a production center on site to utilize it (other isotopes include Carbon-11 with a 20 minute half-life, 10 minute Nitrogen-13, and 2 minute Oxygen-15). With these shorter lived isotopes, the committed dose to a patient could be significantly reduced, changing the risk-reward benefit of radiation dose from many PET procedures.
PET has not spread as widely as it's usefulness primarily due to the financial and logistical problems associated with these short lived isotopes that are required. Longer lived Technetium-99m (from its 66 hour parent Molybdenum-99) has found broad adoption in medicine, however 99mTc's single photon emission (along recent global supply chain events) has limited its applicability.