4 The diagnostic tests
4.1 The EOS 2D/3D imaging system is a biplane system that uses slot-scanning technology to produce images of comparable or better quality with less irradiation than standard imaging techniques as well as 3D images of osseous structures. The EOS system allows imaging in an upright weight-bearing (or seated or squatting) position, and can image the full length of the body (up to 175 cm), removing the need for 'stitching' of multiple images. The system takes approximately 20 seconds for an adult full-body scan and 4–6 seconds to scan just the spine, depending on the patient's height. As for all spine radiographs, the patient is asked to remain still, with their arms folded at 45°, and to hold their breath during the scan.
4.2 The EOS system takes PA and lateral images simultaneously, using a c-shaped imaging device. The digital image is available immediately on a 2D workstation. A 3D image can be reconstructed on the separate sterEOS workstation using the PA and lateral images and a statistical 3D spine model, generated from data from multiple patients. The reconstruction of a 3D image takes 5–10 minutes for each part of the skeleton (for example, the spine or femur). The EOS system takes up a similar amount of space and uses a similar amount of power as other computed or digital X-ray suites.
4.3 The acquisition cost of the EOS system in the UK is approximately £400,000, with a current annual maintenance cost of approximately £32,000. The maintenance contract covers all parts except X-ray tubes, which require replacement every 3–5 years at a cost of approximately £25,000 (including fitting). In addition to the cost of purchasing and maintaining the equipment, there may be some building costs if existing rooms complying with radiation legislation requirements are not available. The EOS system requires the same room planning and shielding as a general X-ray room and the same radiation protection protocols apply. The EOS system is not currently in general use in the NHS, although it has been used in research settings.
4.4 Currently available imaging technologies that can be used in an upright weight-bearing position include X-ray film, computed radiography and digital radiography, although X-ray film has been replaced by computed radiography and digital radiography in standard UK practice. X-ray film, computed radiography and digital radiography can only take images from one angle at a time; simultaneous PA and lateral images, and 3D reconstruction are not possible. When a full-body image is required, these conventional X-ray imaging technologies need adjustment for distortion or stitching of multiple images.
4.5 The acquisition cost of a computed radiography system is approximately £95,000, with an annual maintenance cost of approximately £10,000. Cassettes for computed radiography need replacing every 3–5 years at a cost of £150–200. The acquisition cost of a digital radiography system is between approximately £105,000 and £230,000, with an annual maintenance cost of approximately £18,000. Upgrading software to improve the functionality and performance of digital radiography costs approximately £2000 and was assumed to occur every 4 years.