The implementation of automatic-exposure controlled (AEC) x-ray equipment made it necessary to develop a method to simulate the radiographic attenuation properties of a real patient. The goal was to develop a phantom which would be suitable for use in a large-scale, nationwide field survey program as well as for routine quality-assurance procedures in an individual facility.
The phantoms, in essence artificial models, have been designed to invoke a response by the AEC system that is similar to that for average-sized patients subjected to a wide range of practical x-ray conditions. The Luc-Al phantoms are primarily composed of clear acrylic, polymethyl methacrylate (PMMA), and aluminum. This two-component object is designed to match accurately the narrow-beam attenuation of the tissue thickness being simulated with good accuracy for all energies in the diagnostic range.
These phantoms were created to be economical, easily transportable, and most importantly to produce consistent and clinically representative results. The attenuation phantom is relatively lightweight, made of readily available and inexpensive materials, rugged, not detector or position dependent, and accurate in simulating the primary and scatter transmission through the lung field regions of an anthropomorphic phantom for any diagnostic x-ray spectrum.
There are now six phantoms within the NEXT family. The first phantoms to be developed by CDRH were the adult chest and the adult Abdomen-LS spine phantoms.
Adult Posterior-Anterior (PA) Chest
(NEXT Surveys of 1984, 1986, 1994, and 2001)
The adult chest phantom approximates a 5'8" adult weighing approximately 165 lbs with an anterior-posterior (AP) thickness of about 23 cm (actual phantom chest AP thickness is 22.5 cm). The measurement is listed as 23 cm for comparison with prior surveys. The anatomical region the phantom simulates is the lung field and therefore contains an air gap within the center. The phantom is composed of polymethyl-methacrylate (PMMA).
Adult Abdomen-Lumbosacral (LS) Spine
(NEXT Surveys of 1987, 1989, 1995, and 2002)
The abdomen/LS phantom approximates a 5'8" adult weighing approximately 165 lbs with an anterior-posterior (AP) thickness of 23 cm (actual phantom AP thickness is 21.5 cm). The measurement of the phantom lists as 23 cm for the sake of comparison with prior surveys. The phantom is a composed of polymethyl-methacrylate (PMMA), is dense throughout, and contains a raised axial section that emulates the spine.
Dental (NEXT Surveys of 1993 and 1999)
The dental phantom is composed of Plexiglas, with image quality objects placed within for evaluating high contrast resolution (copper meshes) and low contrast sensitivity (holes). Embedded within the phantom is a human tooth to describe in a realistic manner the attenuation characteristics of the phantom.
Computed Tomography (CT) Head
(NEXT Surveys of 1990 and 2000)
CT head phantom
The CT head phantom is a right circular cylinder made of polymethyl-methacrylate (PMMA). It is approximately 15.7 centimeters in length, and 16.0 centimeters in diameter. There are five holes extending through the length of the phantom, with each hole open at one end and closed off by a phantom face plate at the opposite end. Each hole has a diameter of 1.27 centimeter and is parallel to the cylindrical axis of rotation. The central axis of one of these holes coincides with the phantom axis of rotation, and those of the remaining four holes are equally spaced on a 14-cm-diameter circle centered on the cylindrical axis of rotation. Each hole can accommodate either a PMMA rod used to align the phantom within the CT gantry or else an ionization chamber used for measurements of air kerma.
Adult Fluoroscopy (NEXT Surveys of 1991, 1996, and 2003)
The fluoroscopic phantom approximates a 5'8" adult weighing approximately 165 lbs with a posterior-anterior (PA) thickness of 23 cm. The anatomical region the phantom simulates is the upper gastrointestinal (GI) tract.
Pediatric PA Chest (NEXT Survey of 1998)
The NEXT pediatric phantom is representative of a 15 month, 24 pound infant.
The phantom is composed of Plexiglas, aluminum, air gaps, and is equipped with a spine-heart shadow insert. This insert was included in order to reflect, as reasonably possible, the orientation of the heart and spine during examinations. The phantom can accommodate surveys of either PA or AP projections.