DXA: state of the art. Machine used
DXA densitometers have undergone remarkable technological improvements both in the process of x-ray emission and x-ray absorption.
These facts have allowed a shorter scan time, increased diagnostic accuracy (accuracy of density measurements) and a reduction of the dose to the patient.
In first generation DXA densitometers the x-ray beam is extremely thin (pencil beam), as it is obtained by means of a narrow collimation.
Given the dot-like morphology of the beam, the scans of the x- ray source are characterized by repeated passages separated by few millimeters over different positions of the longitudinal axis of the patient.
The detection system is usually represented by a phosphor crystal.
A further generation of densitometers (second generation machines) is represented by the use of a fan beam rather than pencil beam technology.
Fan beam machines employ wider beams that permit more rapid scanning and a spatial resolution of 0,5-0,7 mm. There have also been employed new detection devices made of arrays of solid detectors.
Obviously, such improvements have significantly shortened the scanning times, that are less than one minute for the spine and around five minutes for a “total body” study. Newer machines have now the capacity to perform lateral scanning. This is permitted by a C-arm structure on which the x-ray tube is mounted and that can be rotated along 90°. Lateral scanning increases measurement accuracy avoiding the superimposition of vertebral posterior elements, marginal osteophites, vascular calcifications that may artificially increase bone density in the postero-anterior measurements of the lumbar spine.
Lateral images of vertebral bodies have a good definition, are obtained with the patient in a supine position avoiding the artefacts that are commonly found when the patient lies on his/her flank and may be very useful for vertebral morphometric evaluation using a specific software. Need medication you can’t afford? Buy generic cialis mastercard
These statements are acceptable only in case of patient with a straight spine; when scoliosis or kiphosis is present the examination becomes difficult to perform and less reliable, as supine position does not permit enough compensation for the curvatures.
Moreover, updated machines are now supplied with specific softwares for the evaluation of periprothesic bone (hip, knee) and for distal and ultradistal radius.
