Reid's base line is used for an unambiguous definition of the orientation of the

human skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominen ...

conventional radiography Projectional radiography, also known as conventional radiography, is a form of radiography and medical imaging that produces two-dimensional images by X-ray radiation. The image acquisition is generally performed by radiographers, and the images ...

computer tomography A computed tomography scan (CT scan), formerly called computed axial tomography scan (CAT scan), is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or ...

(CT), and

magnetic resonance imaging Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to generate pictures of the anatomy and the physiological processes inside the body. MRI scanners use strong magnetic fields, magnetic field gradients, and ...

(MRI) studies. It is defined as a line drawn from the inferior margin of the orbit (''Orbitale'' point) to the auricular point (center of the orifice of the external acoustic meatus, ''Auriculare'' point) and extending backward to the center of the occipital bone. Reid's base line is used as the zero plane in computed tomography. Paediatric base line is an anatomic line that maintains a fixed relation to facial bones throughout the period of growth. In 1962, the World Federation of

Radiology Radiology ( ) is the medical specialty that uses medical imaging to diagnose diseases and guide treatment within the bodies of humans and other animals. It began with radiography (which is why its name has a root referring to radiation), but tod ...

defined it as the line between the

infraorbital margin The infraorbital margin is the lower margin of the eye socket. Structure It consists of the zygomatic bone and the maxilla, on which it separates the anterior Standard anatomical terms of location are used to describe unambiguously the anatom ...

and the upper margin of the

external auditory meatus The ear canal (external acoustic meatus, external auditory meatus, EAM) is a pathway running from the outer ear to the middle ear. The adult human ear canal extends from the auricle to the eardrum and is about in length and in diameter. Str ...

. It originally derived from

Robert William Reid Robert William Reid (1851–1939) was a Scottish anatomist whose 1884 paper "Observations on the relation of the principal fissures and convolutions of the cerebrum to the outer surface of the scalp" introduced what would become known as Reid's bas ...

's 1884 paper "Observations on the relation of the principal fissures and convolutions of the cerebrum to the outer surface of the scalp".The Lancet, 1884, 2, 539. With the head upright, it is typically tilted about 7 degrees nose up with respect to the horizontal plane.

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* Radiology {{med-imaging-stub

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