# Synchrotron X-ray Radiation (SXR) in Medical Imaging: Current Status and Future Prospects
## 3 Synchrotron X-ray Radiation in Medical Imaging
### Coronary Angiography  
One of the approaches of synchrotron radiation in the field of cardiovascular studies is SR microangiography, which is suggested to be used as a substitute for conventional angiography. SR microangiography performs high contrast imaging of microvessels in milliseconds with an enhanced image resolution and clarity compared to conventional angiography. The two approaches that vary in using SR angiography include (1) K-Edge subtraction angiography (KES) and (2) single energy temporal subtraction angiography. These two approaches vary in the case of imaging area and the way of achieving optimization of the vessel image contrast. In KES, an iodine contrast agent is used in the blood which absorbs X-rays, and an image is produced subtracting the low energy image from the high energy image created from just below and above the K-Edge energy, respectively, using narrowly separated line detectors. In the second approach of single energy temporal subtraction, images are produced using single energy of SXR just above the K-Edge. An image without contrast is first subtracted, which helps to emphasize the contrast agent contained in blood vessels. Though it is well developed, complications and mortality (0.1-0.2%) are still there. Injection of the contrast agent into a peripheral vein could help in avoiding risks associated with arterial catheterization. However, the contrast gets diluted through the heart and lung before reaching the coronary arteries. The coronary arteries of rats were visualized with a big focal spot X-ray tube that delivered enough flux and exposure periods of 100 milliseconds with a finely tuned X-ray of 33.2 keV using a monochromator which is just above the iodine K Edge energy for maximum contrast. The absorbed X-rays in the pick-up tube's photoconductive layer are transformed immediately into electron-hole pairs, resulting in a video signal. The detector has two zoom imaging modes: (1) fields of view of \(7.0\times 7.0\) mm and \(4.5\times 4.5\) mm, with \(1024\times 1024\) pixels and pixel sizes of \(7.0\) um and \(4.5\) um, respectively; (2) the principal mode, with an input field of \(9.5\times 9.5\) mm and pixel size of \(9.5\) um. A total of 22 images are captured at a rate of 30 frames per second in a digital image acquisition system with a 10-bit resolution, \(1024\times 1024\)-pixel format with 30 frames per second [4]. Figure 3: Synchrotron X-ray nanoscopic images of the hair samples. In this figure, the three rows show projection (**upper**), axial (**middle**) and 3D rendering (**lower**) images, respectively. The medulla of a healthy hair, and the distribution of discontinuous or complete medulla loss in a cancer hair are shown in the columns from the right to left, respectively (reprinted with permission from [13]). On the other hand, an SXR-based coronary angiography with intravenous injection and the KES method can provide details that can be suitable for diagnosing coronary disease. The advantage of SXR microangiography is the ability to study the microcirculation of small animals within their physical milieu as it can visualize the coronary and pulmonary microvessels within the intact chest wall of the animals. This approach was not possible before with conventional X-ray systems. Figure 4 shows SXR-based microangiography [9]. Another application of SXR in coronary angiography is transvenous angiography. In this method, chronography of iodine is used in which K-edge of iodine is enclosed by two monochromatic X-ray beams. The final image is produced by the logarithmic subtraction of the images created by the beams. The advantages of this method are that the signals arising from attenuation of iodine are enhanced and the signals arising from attenuation of soft tissue and bone are suppressed. The X-ray dose used during SXR angiography is comparatively less than conventional angiography and requires significantly less patient exposure. It is assumed that with additional experience, fewer frames will be needed to be recorded during transvenous angiography [39].