The Flat Panel Source (FPS)
The Flat Panel Source
Our Flat-Panel X-ray Source (FPS) is made up of an array of cold cathode field emitters, sealed into a unit together with a power supply. The field emitters each generate a conelet of X-rays. Because the array would otherwise produce a large number of overlapping X-rays, a proprietary system allows for each X-ray emission to be addressed and individually controlled which avoids the common problem of high voltage switching.
The Flat-Panel array emits X-rays covering many different angles allowing depth information to be derived through tomosynthesis. A reduced standoff distance (for instance, 50cm instead of 170cm for chest imaging) is used for an FPS-based solution, reducing power requirements and thermal challenges compared to conventional tube-based X-ray sources. A further benefit of the array is the production beam focal spots which are well below the typical millimetre range and allows for enhanced resolution.
Differences in beam geometry and standoff –distance between a conventional X-ray tube, including linear arrays and a Flat Panel Source
Digital tomosynthesis (DT), where a conventional X-ray tube is moved through a range of angles to derive 3D data, has been shown to give better diagnostic information than 2D X-ray.
However, the limited depth resolution of DT (due to the acquisition covering only a circa 40-degree angle instead of 360 degrees as in a CT exam) may lead to difficulties in localising some structures as well as to artefacts. Given that the acquisition time on commercially available systems ranges from five to twelve seconds, breathing induced motion artefacts, and consequently blurred images are another concern with chest DT. Holding their breath for up to twelve seconds can be very difficult for many patients and the resulting artefacts are often impossible to correct - even with sophisticated reconstruction algorithms. None of the existing DT systems are mobile, therefore cannot be used for point-of-care diagnostics. They are also too large and expensive to be deployed in primary care or out of a hospital setting.
Adaptix’s FPS uses a rectangular array of emitters instead of a just a line. It has the potential to enable lower-cost, smaller footprint, higher performance DT devices that are compact enough to be employed at the patient’s bedside. The FPS is composed of an array of cold cathode field emitters that can produce X-ray energies in a range relevant for medical imaging: 20-120 keV. The array generates a large number of overlapping X-ray conelets, and a raster system allows for each X-ray emitter to be fired individually or in clusters. Control of the emission process is achieved through electromagnets, avoiding the common problem of high-voltage switching. The use of an FPS for tomosynthesis enables the source to be much closer to the patient than standard CXR stand-off distances.
This innovative approach is complemented by application of novel image reconstruction techniques producing a slice-by-slice reconstruction which enables extremely quick partial analysis and adjustment of slice thickness over regions of interest. The approach uses backprojection together with a ramp-filter, and is substantially less memory intensive than techniques that must reconstruct the volume as a whole. In addition, noise and artifact reduction techniques and the ability to reconstruct slices in super-resolution improve the reconstruction quality, whilst computational optimisation ensures that the method is fast.