By Rosemary Marchese (Physiotherapist – Schroth, SEAS)
Monitoring of scoliosis can often involve regular X-Rays. This has led to some patient concern about radiation exposure. In more modern times we have had the opportunity to use the EOS system, which produces X-ray images at a loser dose. So what do you need to know?
How does EOS differ from X-Ray?
The EOS machine uses a particle detector (multi wire chamber) invented in 1969 by Georges Charpak, for which he won the 1992 Nobel prize in physics. As the X-Ray particles pass through the chamber, they will ionise gas atoms and set free a charge, which the amplifier collects. This information is then converted into a digital image. It simultaneously captures a side image (lateral or sagittal view) and a frontal image. Basically the end result is that we get a 3D reconstruction of the spine. X-Ray does not give us that in one image.
X-Ray is useful for diagnosis of bony problems and anomolies in the spine. However it is only accurate at the centre of the beam being pointed at the person, therefore it does not make it as accurate to measure leg lengths. EOS is very useful for measuring leg lengths as well as monitoring scoliosis. A significant leg length discrepency is often an issue requiring addressing in scoliosis.
The standard EOS imaging system has been shown to moderately reduce the total radiation exposure to skeletally immature scoliosis patients. It is also worth noting that posteranterior films, as opposed to anteroposterior films, significantly reduces the radiation exposure to breast and thyroid.
It should be noted however, despite EOS being promoted as low dose, that X-Rays can in fact also be set to lower dose radiation settings. We should also remember that we are constantly exposed to background radiation in our lives. For example, an overseas flight from Sydney to Europe, does expose us to more radiation than if we had not travelled!
Advantages of an EOS
The advantages of an EOS include:
- lower dose radiation than X-Ray
- Simultaneous frontal and lateral X-Ray capture
- Accurate leg length assessment
- 3D computer simulate reconstruction (although this is not as accurate as a CT scan, because you cannot see the architecture of the bone or the actual 3D deformity as well as a CT scan).
Disadvantages of an EOS
The disadvantages of an EOS include:
- Long time for the scan means that patients may move and cause artefacts on the scan
- There can be some issues with positioning consistently and appropriately
- It is not accurate for diagnosis of pathology
- There is still some radiation
- It cannot be used in a supine (lying down) view
- It is very expensive to run.
The expense is an issue in many locations. In fact, one study has shown that although it does produce lower radiation, that is not enough to justify the cost in some locations. Whether or not using EOS over X-Ray leads to better outcomes has not been clarified. However many patients opt for this scan due to the lower radiation dose.