Nuclear medicine is radiology turned inside out, imaging what organs do
An X-ray shines radiation through you from outside. Nuclear medicine does the reverse: a small radioactive tracer goes into the body, and cameras catch the radiation it gives off. The pictures are blurry on anatomy but sharp on function, revealing a fracture, a busy tumour or a sluggish kidney by how tissue behaves.
The core trick is the tracer, a radioactive atom bolted to a molecule the body handles in a predictable way. Technetium-99m attached to methylene-diphosphonate, for instance, heads for bone. Where bone is working harder, as at a healing fracture, the tracer piles up and shows as a hot spot; some diseases instead push tracer away, leaving a cold spot. Tracers can be swallowed, inhaled or injected, and many have been designed for particular organs and processes.
Two workhorse scanners dominate. The gamma camera, often named the Anger camera after its inventor Hal Anger, records flat images, and rotating it around the patient produces SPECT, a stack of slices forming a 3D map. PET relies on isotopes that emit positrons; each one meets an electron almost immediately and the pair annihilate into two gamma rays flying off nearly back to back, which lets detectors pinpoint the source. Among the most common studies are FDG glucose scans for cancer, heart perfusion scans for coronary disease and bone scans.
Because resolution and anatomical detail are weak, hybrid machines now overlay function on structure. PET/CT is the most widespread, SPECT/CT increasingly common, and PET/MRI has begun to appear. The fused picture can supply information that would otherwise require an invasive procedure or surgery.
Radiation safety follows a principle called ALARP, as low as reasonably practicable, which replaced the older ALARA wording to stress what is reasonable. An exam must first offer a clear benefit, and images should be no sharper than a confident diagnosis needs, since extra dose only buys prettier pictures. Doses therefore vary widely, from below annual background radiation to well above an abdominal CT. The specialty also treats disease, using short-range emitters against overactive thyroid glands, thyroid cancer, some lymphomas and non-melanoma skin cancers, usually as outpatient procedures.
Source: Nuclear medicine
