![]() ![]() Based on this, DXA produces the so-called R-value, which is the ratio between the attenuation coefficients at the two energy levels. Also, the density of material has to be taken in account, as high-density tissues (such as bone) attenuate the X-ray beam more than low-density tissues (such as soft tissues) ( 4). ![]() Thus, the X-ray beam with lower energy will be more attenuated by tissues, with fewer photons passing through. First, the principle of X-ray attenuation relies on the fact that the higher the photon energy, the lowest the attenuation. ![]() Basically, radiation energies emitted by DXA machines are variably attenuated based on both density and thickness of anatomical structures and tissues, as well as the intensity of emitted energy. The physical principle beyond DXA is that of X-ray transmission and attenuation thorough human body at two different energy levels ( 3). Whenever available, we will provide possible cut-off diagnostic values for each of these LM and FM indices, according to current literature and guidelines. The possible use of adipose indices will be considered, such as the fat mass index (FMI) or the android/gynoid ratio, as well as lipodystrophy indices and the evaluation of visceral adipose tissue (VAT). We will also cover the current clinical practical application of whole body DXA values, with particular emphasis on the use of LM indices in the diagnostic workup of reduced muscle mass, sarcopenia and osteosarcopenic obesity according to the most recent guidelines. In this review we will explain the technical working principles of body composition with DXA, together with the possible limitations and pitfalls that should be avoided in daily routine to produce high-quality DXA examinations. In addition, fat mass (FM) and lean mass (LM) values by DXA shows very good accuracy compared to that of computed tomography and magnetic resonance imaging. The advantages of DXA over other imaging techniques are the very low radiation dose, its accuracy and simplicity of use. Dual-energy X-ray absorptiometry (DXA) in nowadays considered one of the most versatile imaging techniques for the evaluation of metabolic bone disorders such as osteoporosis, sarcopenia and obesity. ![]()
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