C-arm flat detector balances image quality, radiation dose

Siemens wants to help physicians tired of the same old angiography images. The company's Axiom Artis dTA C-arm is equipped with flat-panel detector technology and an optional ultrasound system. Its 12 x 16-inch detector offers high image quality at minimal radiation dose, key issues when performing interventions. The ultrasound option offers convenience for medical teams trying to minimize use of x-rays. The choice of a ceiling or floor mount adds to the versatility.

Dr. Daniel Croteau, chief of vascular and interventional radiology at Henry Ford Hospital in Detroit, uses the Artis dTA in a wide range of vascular and nonvascular procedures, particularly complex liver, pelvic, and uterine embolizations. The design provides access to patients from all sides, as the gantry pivots out of the physician's way.

"That's very important to us because we're doing interventions that require all types of patient access," he said.

Software onboard the Artis dTA tracks the patient automatically, ensuring detector and collimator alignment, according to Siemens product manager Thomas Treusdell.

"No matter where the gantry is pivoted, it will always be square on the patient," he said.

The software-driven controls are the same as those built into the company's Multistar angio product line. The difference is that the Multistar was based on image intensifiers (II), while Artis dTA is built around a flat panel.

Flat detectors are the future of angiography, Treusdell said. They allow higher dynamic range and decreased image noise. At Henry Ford, the one built into the Artis dTA is the means for balancing image quality and radiation dose.

"We try to work with as low a radiation dose to the operator and patient as we can, and we are still getting very good image quality," Croteau said.

The flat panel enables high-contrast imaging that visualizes fine structures in great detail, according to Siemens. The true potential of the machine has yet to be realized.

"The software has not yet caught up to what the flat detector can do," Croteau said.

Using the Artis dTA detector, medical physicists at Henry Ford have visualized tiny wires on phantoms that could not be detected using conventional angio systems. That level of resolution is not possible clinically, however. Croteau pins the blame on inadequate software.

"It's taking a little time to get the software rewritten from II-based systems to those with flat panels, but it will get there," he said.

Another shortcoming is 3D reconstruction. It's possible on the Artis dTA, but reconstructions are too slow to make them clinically feasible for routine use.

"My impression is we'll see that capability on the next software upgrade," Croteau said.

Rotational angiography is made possible by arcing the Artis dTA C-arm across the patient. Croteau usually takes three images at different angles: an anterior-posterior, a 30 degrees right anterior oblique, and a 30 degrees left anterior oblique.

"You can get a lot of pictures in between, but I don't think they add much to the diagnostic capability of the exam," he said.

Every now and then, however, rotational angio and 3D reconstructions are worthwhile. A volumetric reconstruction of the biliary tree may be helpful when planning a complex intervention, he said. It might also come in handy as an anatomical model for referring physicians.

The Artis dTA can be equipped with an integrated ultrasound solution. Sonograms appear on the same monitors that display the x-ray angiograms, a transition accomplished with a tableside button click. Treusdell warns that the ultrasound option is not for everybody.

"It's for somebody who uses ultrasound on a regular basis, day in and day out," he said. "This allows them to get the ultrasound unit integrated (with the angio system) and out of the way."

The company is selling the Atis dTA primarily to large medical centers that specialize in interventional procedures. Much of the demand for this system, which lists for about $2 million, is coming from users of Siemens' earlier generation angio product, the Multistar, according to the company.