The last several years have seen the advent of the final digital component to cardiac angiography. For more than 10 years, several X-ray equipment companies have been attempting to replace the image intensifier with a more digital component. Now, all four major companies (General Electric (GE), Phillips, Siemens and Toshiba) are either marketing or on the verge of marketing a flat-panel device in the US.
The flat-panel technology is a major digital advance, resulting in both improved image quality and lower X-ray dose. It is the purpose of this article to examine this new technology and narrate the clinical experience at North Shore University Hospital (“the hospital”) in New York. The hospital’s digital flatpanel use currently encompasses nearly three years and over 10,000 cases, resulting in a busy institution, performing over 13,000 procedures per annum, including 3,500 coronary interventions in five catheterisation laboratories. The hospital currently has three digital flat-panel laboratories and expects to replace the final two image-intensifier systems during 2003.
Image-intensifier systems were developed to improve picture quality from the original X-ray phosphors. As such, they typically require between seven and nine steps from the X-ray hitting the cesium iodide phosphor to the production of the final digital image (see Figure 1). Each step can be associated with image noise production and no individual step can be 100% efficient. Therefore, the final image, although better than the original method, is associated with significant noise and can never be ideal.
This description applies to the technology utilised by GE, Phillips and Siemens. Toshiba, on the other hand, presented their technology as a work in progress at the American College of Cardiology (ACC) in March 2003. With their panels, selenium, which does not produce light but translates the X-ray directly to an electrical signal, is used instead of cesium iodide. There is no phosphor. Compared with all of the other vendors, it remains to be seen if this translates to a better image.
The hospital’s clinical experience with the GE flatpanel system has been extensive, starting in September 2000 with one flat panel – the Innova 2000™, which, at the time, was GE’s third clinical site in the world. Initially, the improvement in image quality was not apparent and there was no improvement in spatial resolution, as is measured by line pairs. As the flat panel is not lens-based, the images are square and not round. To angiographers not accustomed to working with a square image this might be unpleasantly different. Most images viewed in life, however, are rectangular and not round.
Television, cinema and computer screens and windows in buildings all generate a rectangular image, whereas circular images are generally lens-based. These include microscopes, telescopes and image intensifiers. Other non-lens-based circular images are distinctly unusual and include ship portholes.
To gain a better idea of the resulting flat-panel images, the hospital began comparing images of the same patient taken in its own image-intensifier rooms and in the flat-panel room. Several improvements became obvious. The lens-based image intensifier had a smaller ‘sweet spot’ – the central area in the image where the optimum image was present – and, since the flat panel was, in essence, composed of independent pixels, the image was better over a larger area of the field.