Lindsay Machan reviews the use of a dynamic collimation system to reduce radiation exposure to the operator, staff and patient during fluoroscopy and cine. He spoke about this topic at the 2014 Transcatheter Cardiovascular Therapeutics (TCT) meeting (13–17 September, Washington, USA).
Image-guided procedures have become both more numerous and more complex. Radiation exposure to the patient, operator and staff can be substantial, especially in long, difficult cases. At the same time, there is increasing concern that the traditionally held concepts of “safe thresholds” for radiation exposure are not accurate. As with all biological processes, there appear to be significant individual variations in susceptibility to chronic exposure. Thus the average endovascular proceduralist and associated staff have a greater lifetime radiation exposure than in the past, while each individual has an unknown susceptibility for chronic radiation damage. Also, studies are now demonstrating that radiation damage, such as radiation-induced cataracts, is more common in physicians and ancillary staff than had previously been recognised. With this in mind, it is important that all interventionalists think of radiation in the same way as iodinated contrast—use the lowest dose possible to achieve the desired result, but no more. It is prudent to employ as best as one can the standard methods for restricting radiation dose (avoiding magnification, use of passive shielding, etc). Additive to these well-described manoeuvres, innovative modifications to the imaging chain to further lower the dose are in development. The ideal dose reduction method should reduce radiation to the patient, operator and staff, not change the operator’s procedural methods nor impair access to the patient, and should preserve image quality; activation and deactivation should be easy and intuitive.
One such invention is a dynamic collimation system (Ikomed Technologies), which can potentially reduce the radiation exposure of a procedure up to five-fold without image degradation. It consists of a rapidly moving lead shutter (which works in addition to the existing manual collimation system), placed between the X-ray source and the patient, and image-blending software. During fluoroscopic procedures, even with excellent coning, the physician is typically focused on a small portion of the image, usually where there is movement of a device. The remainder of the screen image provides context. The system allows three different methods of achieving different radiation doses to different parts of the image, with the highest in the region of interest. Two of the three result in a “normal” fluoroscopic image. In manual mode a “normal” fluoro pulse rate (eg. 15 fps) is chosen by the operator for the predetermined area of active interest. At a slower rate (eg. once per second), the cones open to the full area chosen by the operator and then return to the more rapid tighter coning. All acquired images are blended in real time, thus the projected image looks like normal fluoroscopy. The reduction in radiation dose depends on the size and frame rate of the active coning area, which is chosen by the physician. The second method works in the same manner but the area of active coning is altered in position and size by automated software which tracks catheter movement or contrast injection. The final mode provides an image of lower signal to noise outside the region of interest.
Ideally all possible methods would be utilised to reduce the total amount of radiation generated in addition to optimal protective shielding to reduce scatter, as the effects are additive. This device and others which lower the radiation output of the fluoroscopic unit have the added benefit of lowering the dose to the patient. There are procedures, particularly with non-traditional or multiple points of vascular access where rigid adherence to best practices of radiation safety are not possible, particularly with certain room geometries. Therefore, innovations such as a dynamic collimation system help to offset those situations. In my opinion, particularly in light of the concerning data regarding the effects of chronic radiation exposure, every possible dose reduction strategy should be applied simultaneously to ensure endovascular medicine remains a progressive and safe specialty.
Lindsay Machan is from the Department of Radiology, University of British Columbia, Vancouver, Canada