Minimizing exposure dose
Minimizing radiation exposure during fluorography is an important goal. In particular, when a time-consuming procedure is conducted in a left anterior oblique (LAO) caudal view (LAO 40°, caudal 30°; the so-called spider view), there is an increased risk of excessive X-ray exposure. For example, one patient who was treated at our institution developed severe radiodermatitis that required skin grafting. To avoid such adverse events in the future, the actual exposure dose was measured in each of our four catheterization laboratories, under the same conditions.
A 20-cm acrylic plate was placed at the examination position, and measurements were obtained while the fluorography and radiography programs were run on the four different systems, using the same parameters as in routine clinical practice. The dose measurements obtained for Alphenix were equal to or lower than those obtained from the other three systems. Compared to the Infinix system we had used previously, Alphenix showed dose reductions of approximately 60% and 50% in fluorography and radiography, respectively. This is truly a remarkable improvement. When the thickness of the acrylic plate was increased to simulate a larger patient, the dose during image acquisition was increased by a factor of three to seven in all the systems, but Alphenix was found to have the lowest dose.
Alphenix also provides a tool known as the Dose Tracking System (DTS), which measures and displays the patient estimated peak skin dose in real-time. This function makes it easy for the operator to identify ‘hot spots’ and take appropriate measures to avoid them as much as possible.
Furthermore, while DTS improves awareness of high-exposure areas where the radiation dose should be reduced, another function known as SPOT ROI has also been found to be effective in routine clinical practice.
Various functions that allow the operator to collimate the region of interest (ROI) within the overall field of view are available in the systems produced by other companies, but these functions tend to be rather difficult to use because the area outside the ROI is displayed in black.
The SPOT ROI function in Alphenix, on the other hand, continues to show the surrounding anatomy. It is like covering the image with a thin cellophane film with an opening that matches the area of the ROI (Figure 2).
Using this function, the image quality within the ROI is maintained at the usual level, and surrounding areas can also be observed to some degree. This means that the operator can perform procedures at a lower radiation dose while still being able to observe changes that may occur quickly. In fact, the measurement results showed that Spot ROI can reduce the dose in surrounding areas by 65-85%. It is also easy to operate the ROI, which minimizes the burden on the operator and makes it possible to perform less-invasive therapeutic procedures.
The speed of C-arm movement is another critical factor during cardiac imaging, in which images must be acquired from various angles. The four systems produced by different companies were compared in terms of the time needed to move the C-arm to specified positions during a set of routine examination procedures. Alphenix was found to be the fastest, at one minute 40 seconds, resulting in more efficient operation. The time needed for the systems produced by the other companies was two minutes or more. One of the reasons for the higher speed of Alphenix is that its flexible wide arm opening minimizes interference (Figure 3).