Digital angiography systems allow for faster acquisition, sharper image quality and less x-ray exposure to the patient and staff. It is good news all around.
The increasing use of minimally-invasive surgical techniques performed with guidewires and catheters under fluoroscopic guidance has brought with it a renewed focus on radiation exposure. Vendors have designed cutting-edge technologies and software for fluoroscopy machines that help reduce dose. Hospitals and staff have instituted protocols to ensure that certain thresholds of fluoro time or dose are not breeched. And many facilities are working toward having patient dose exposure automatically uploaded to an EMR.
Health Imaging & IT spoke with a number of practitioners to see how they are implementing the latest dose-reduction technologies in their interventional suites.
Nuts and bolts
All modern fluoroscopy systems have sophisticated collimators and filters that help reduce radiation exposure. Collimators limit the beam, while filters raise its quality. In older models, as the image intensifier was moved away from the patient’s body, the amount of x-ray beams delivered to the body was the same. Even though the image was less sharp, the patient was still receiving the same high dose of radiation. Today’s models correct for that problem.
“Now, as you raise the image intensifier, the collimators automatically kick in and you are not irradiating the entire field of view,” says Linwood Williams, RT(R), unit director of the cath lab at Carilion Clinic in Roanoke, Va. Carilion has six cath labs, which are equipped with five fluoro units from Siemens Healthcare.
Copper filters, another tool to help reduce exposure, remove low-energy photons that do not thoroughly penetrate the body and, consequently, do not contribute to image quality. These low-energy x-ray beams also have a tendency to “scatter,” thereby hitting the cath lab staff as well.
Pulsed, rather than continuous, fluoroscopy is a standard dose reduction technique today, which cuts the radiation dose exposure by half. Each pulse can be calibrated to a certain dose (milli-Roentgen per minute, or mR/m). At the push of a button, the interventionalist can drop the dose by as much as one-half or as little as one-fourth. Frame rates also can be adjusted to save on radiation exposure. Coronary artery interventions generally need the finest image detail (25 to 30 frames per second), while some procedures, includ-ing many pediatric procedures, will be effective with a lower frame rate (from 1 to 15 frames/s). Variations in between include a lower frame rate with a higher calibrated mR/m or vice versa.
“You need to look at angiography procedures as fluid. At some point, you may need very little fine detail, but when you’re pushing out micro-coils for embolizing arteriovenous malformations, it’s critical to go up to a higher level,” says John Racadio, MD, division chief for interventional radiology at Cincinnati Children’s Hospital Medical Center in Ohio. Racadio makes use of three fluoro systems from Philips Healthcare.
The Q/A system at Cincinnati Children’s has what the technologists refer to as a “speeding ticket.” If a patient receives a skin dose greater than or equal to 2 Grays (Gy) or a cumulative dose greater than or equal to 3 Gy, a form (the “ticket”) must be completed that calls for a follow-up clinical exam in three weeks to look for signs such as temporary hair loss or skin problems.
“These types of symptoms manifest themselves at 3 gray,” Racadio says.
For now, the patient dose, which appears onscreen during the procedure, is recorded as part of the dictation, but the hospital is in the process of installing a new system (Epic) with the capability of automatically uploading patient dose data to the EMR.
At the Richard M. Ross Heart Hospital at the Ohio State Medical Center in Columbus, Ohio, radiation dose is recorded in the GE Healthcare Mac-Lab hemodynamic information system. Every 30 minutes, the staff takes a time out to check radiation exposure or contrast media dose amount, according to Linda Paxton, director of cardiovascular services. They then determine whether it’s safe to continue with the procedure, which depends on the patient’s weight and comorbidities, or whether the