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Digital Cardiovascular X-ray Systems

25 January, 2011 | X-ray

Digital Cardiovascular X-ray Systems

Cardiovascular X-ray equipment is used to produce dynamic images of the patient’s heart and blood vessels. Historically, these systems used an image intensifier, attached to a video camera, to display the images. Modern systems use flat panel detectors, which are substantially lighter than image intensifiers, allowing faster C-arm rotations, therefore reducing examination times.

With current digital X-ray imaging equipment, the image is produced by a digital detector, much in the same way as a digital photo camera produces pictures. A flat panel detector converts the X-rays, which pass through the patient into an electrical signal, which is then processed by a computer to produce an image. Cardiovascular systems typically have smaller detector sizes than general purpose X-ray systems.

One of the major advantages of this type of equipment and procedure is that treatment can also be carried out at the same time. Blocked vessels can be opened by inflating a balloon catheter and a stent can be placed to keep the vessel open, if required.

The demand for high quality in cardiovascular imaging is due to many factors, such as the requirement to visualize and grade subtle lesions or anatomical structures and follow the route of small catheters within a beating heart. However, it is always important to minimize the radiation dose to patients and staff during any X-ray examination. In cardiac imaging, this is of particular concern due to potentially long examinations and risk of skin erythema.

Flat panel detectors offer several advantages with respect to image quality: lack of geometric distortion, no veiling glare, uniform response across the field-of-view and better noise-reduction algorithms. It is also substantiated that image quality of image intensifier systems degrades over time, necessitating increased input doses.
It has been shown that using flat panel detector systems reduces the mean number of stents used. This may be due to the improved image quality which leads to more accurate assessment of lesion size and better stent replacement.

Cardiovascular systems are used to acquire several different views of the patient’s heart and coronary vessels during a procedure. Typically, this is done by acquiring a run of images from a particular projection, then moving the X-ray system and acquiring another run from a different projection. However, with rotational angiography, a number of different views can be acquired during a single run. The X-ray system moves during the exposure and therefore covers different views. With appropriate start and finish points for the sequence, vessels which would normally require two or more runs to visualize fully can be imaged in a single run, reducing the on-table time and the quantity of contrast agent required.

This type of rotation permits the system to acquire sufficient data to reconstruct 3D images of the coronary tree. It appears that 3D techniques allow easier visualization of vessels and heart.

Also, it has been shown that 3D angiography gives a lower patient radiation dose and uses less contrast agent than a standard series of five to six views to obtain the same clinical information. 3D angiography is also faster, offering the potential to improve workflow.

The cardiovascular X-ray system consists of several parts: The X-ray tube and flat panel detector are mounted on a movable C-arm with adjustable positioning to allow different views of the patient and positioning at different distances. In addition to the C-arm, a moveable patient couch is present. Both the C-arm and the couch are controllable from tableside controls. Display monitors both in the room and in the shielded control room allow the cardiologist, radiographer and other observers to view the images.

Cardiovascular procedures present a substantial risk of producing effects such as skin erythema. Therefore, the entrance surface dose which is delivered to the patient is the most relevant parameter to measure and compare.