DICOM (Digital Imaging and Communications in Medicine)
DICOM is the international standard that defines how medical images and their associated patient and study metadata are formatted, stored, and transmitted between imaging equipment and software.
A DICOM file is not just a picture. Each image carries an embedded header holding patient identifiers, accession number, study and series descriptions, modality, acquisition parameters, and the referring clinician. This is why a CT study pulled from an archive still knows which patient and which order it belongs to, and why a mismatch between the header and the hospital's patient record causes studies to land against the wrong chart.
In practice a hospital encounters DICOM at three points: the modality itself (CT, MRI, ultrasound, digital X-ray), the archive that stores studies, and the viewer radiologists read on. Vendors advertise DICOM conformance statements — the document that lists exactly which DICOM services and transfer syntaxes a device supports. When an integration between a modality and an archive fails, the conformance statements of both ends are the first thing to compare.