C-arm technology brings soft- tissue resolution to angio suite

The catheter sliced through the weakened wall of an intracranial blood vessel, a not-uncommon complication during the treatment of shallow aneurysms. Interventionalists at Methodist Hospital in Houston quickly documented the result: ventricles swelling with blood from the hemorrhage. Neurosurgeons relieved the pressure with a ventriculostomy that shunted the blood from the ventricles, allowing the interventionalists to finish treating the aneurysm and stop the bleeding.

In the past, these interventionalists would have moved the patient to CT to assess the situation. This time, they turned to DynaCT, an enhancement for C-arm angiography systems that brings soft-tissue imaging into the angio suite.

"If we had taken this patient to CT, it could have been the same outcome," said Dr. Charles Strother, an interventional neuroradiologist at Methodist. "But DynaCT sure saved time. And time is very important in such a case."

DynaCT supports neurologic interventions, providing information helpful in assessing, treating, and monitoring patients with stroke or tumor. The introduction of coils and stents to these vascular weak spots is sometimes accompanied by bleeding. When this happens, blood pressure, pulse, or respiration rate can change. Anomalies may appear in the images, such as the shift of a vessel to a different location or the accumulation of dye, suggesting a rupture.

CT provides a definitive answer, but moving a patient to the scanner is not only difficult but dangerous. Patients undergoing neurointerventions are very sick, Strother said. And they are intubated, often with more than one line.

"It is an onerous thing to move a patient in that condition," he said. "Now, if there is any hint that something has gone wrong, we do a DynaCT."

Siemens calls the technique angiographic CT (ACT), because physicians can obtain CT-like images without using a CT scanner, eliminating the need to transfer patients out of the angio suite. ACT acquires about 300 images during a 10-second spin of the C-arm.

A volumetric image is reconstructed on Siemens' Leonardo workstation. Tissue differentiation in the range of 10 HU visualizes abnormalities such as tumors and hemorrhaging.

"Before this was available, we were able to do highly detailed imaging of the vascular system, but we were blind to the soft tissue that surrounded the vessel," Strother said.

The new capability is shipping as an option on Siemens' Axiom Artis dBA, dFA, and dTA systems. Each vascular imaging system uses a flat detector. The dBA is a biplane system optimized for neurointerventional work. The dFA and dTA systems are single-plane units, one floor-mounted (dFA), the other ceiling-mounted (dTA).

DynaCT is available to the installed base as an upgrade, using software and an enhanced Leonardo workstation. Only about a dozen installed sites could make use of this upgrade, however, because of DynaCT's requirement for a flat detector. But about 90% of new Axiom Artis vascular systems are shipping with flat panels, and about one in five of these will go out the door with DynaCT installed, according to Thomas Treusdell, Siemens product manager for interventional radiology. This translates to about 35 to 40 systems per year.

"The actual number will depend on how well the word spreads about DynaCT and its benefits, as well as what interventional radiologists do in the future," Treusdell said.

Interventionalists at Methodist in Houston are still learning how and when to put this new capability to best use. Staff at the hospital, one of four sites in the U.S. with DynaCT, use it when they suspect a problem in the patient's brain. They have also started using the technique as a routine part of their procedures, obtaining baseline assessments of ventricles in the brain and examining blood vessels for calcium deposits.

"It is a little early to be dogmatic about how it is going to be used and what is going to bring the greatest value, but I think it adds tremendously to making the angio suite a much more robust environment," Strother said.