Positioning Terminology

Overview

This chapter is the dictionary every other Procedures chapter assumes, and Procedures is the largest domain on the ARRT exam: 66 of 200 scored questions to 28 February 2027, and 72 from 1 March 2027. The core distinction: projection describes the path of the central ray, position describes what the patient is doing, and view is not a correct positioning term in the United States. These terms follow standard definitions the ARRT has published, so an answer can describe the right picture and still use the wrong word.

The anatomy is numeric. The adult skeleton has 206 bones, 80 axial and 126 appendicular, with the patellae counted as the only sesamoids inside the total. Joints classify structurally as fibrous, cartilaginous or synovial, and the seven synovial movement types run from plane to ball and socket, with exceptions such as the sacroiliac joint, which is synovial yet only slightly movable.

Projection names read entrance to exit: posteroanterior, mediolateral, dorsoplantar, submentovertical. Body obliques such as RAO and LPO are positions named by the aspect closest to the receptor, an axial projection means a central ray angle of 10 degrees or more, and a decubitus always uses a horizontal beam because it exists to show air-fluid levels and free air.

Then come the working rules. Body habitus splits the population sthenic 50 percent, hyposthenic 35, asthenic 10, hypersthenic 5, and the hypersthenic chest takes a landscape receptor. SID is 40 inches minimum for most skeletal work and 72 inches for chest. Every image needs two markers, patient identification with date and an anatomic side marker exposed in the beam, and a missing side marker means a repeat, never a digital annotation.