Scintigraphy (from Latin scintilla, "spark"), also known as a gamma scan, is a diagnostic test in nuclear medicine, where radioisotopes attached to drugs that travel to a specific organ or tissue (radiopharmaceuticals) are taken internally and the emitted gamma radiation is captured by external detectors (gamma cameras) to form two-dimensional images in a similar process to the capture of x-ray images. In contrast, SPECT and positron emission tomography (PET) form 3-dimensional images, and are therefore classified as separate techniques to scintigraphy, although they also use gamma cameras to detect internal radiation. Scintigraphy is unlike a diagnostic X-ray where external radiation is passed through the body to form an image. Scintillography is an imaging method of nuclear events provoked by collisions or charged current interactions among nuclear particles or ionizing radiation and atoms which result in a brief, localised pulse of electromagnetic radiation, usually in the visible light range (Cherenkov radiation). This pulse (scintillation) is usually detected and amplified by a photomultiplier or charged coupled device elements, and its resulting electrical waveform is processed by computers to provide two- and three-dimensional images of a subject or region of interest. Another extensive use of scintillography is in medical imaging techniques which use gamma ray detectors called gamma cameras.