Report from SCBT/MR: Two-phase angiography of aneurysm repair reduces dose, maintains integrity

Lifelong follow-up CT imaging of patients who have undergone endovascular stent-graft therapy for abdominal aortic aneurysm can be done without arterial phase imaging, thus allowing a decrease in radiation dose.

Type II endoleaks are seen on only venous phase in follow-up evaluation of patient with a stent-graft for AAA. (Provided by H. Chandarana)

Dr. Hersh Chandarana, a resident at New York University School of Medicine, reported the study at the annual meeting of the Society of Computed Body Tomography and Magnetic Resonance.

Most protocols evaluate postprocedural aortic stents with a three-phase acquisition. Chandarana and colleagues retrospectively evaluated records of 85 patients who underwent 110 exams after AAA repair. They determined that arterial phase imaging was not necessary for routine detection of endoleaks.

"The initial CT angiography done postprocedure should be acquired in a triple phase. Follow-up, however, should be done as a dual acquisition," senior author Dr. Michael Macari told Diagnostic Imaging. "Hopefully, this kind of study will make people realize that more radiation is not always necessary for a number of different applications."

The imaging acquisition protocol called for 150 mL of IV contrast injected at 4 mL/sec. Researchers first evaluated noncontrast and venous phase images to determine if an endoleak was present. They subsequently analyzed the arterial phase images and calculated the effective radiation dose for all phases.

Three type I endoleaks and one type III endoleak were seen on both arterial and venous phase imaging. The combined noncontrast and venous acquisitions revealed 28 type II endoleaks, while 25 of these were seen during the arterial phase. Three type II endoleaks were seen on the venous phase only.

Venous phase imaging showed no endoleaks in 78 exams, and arterial phase imaging failed to demonstrate endoleaks in these patient.

The researchers determined that arterial phase imaging will detect an endoleak missed by the venous phase in no more than 3.5% of all studies. Yet the arterial phase contributed to 36.5% of the effective dose for the exam.

The average effective doses per patient were:

• 8.3 mSv for noncontrast imaging

• 11.6 mSv for arterial phase

• 11.9 mSv for venous acquisitions

Foregoing the arterial phase will result in a 6% reduction in radiation dose, Chandarana said.

Initially, exams were performed on a four-slice scanner. When NYU acquired a 16-slice machine, the studies were performed using automatic dose modulation techniques. This patient population will often receive two to three scans a year, depending on the findings. Multiply that by three CT acquisitions, and you are talking about a lot of radiation, Macari said.

Additionally, vascular surgeons are putting AAA stent-grafts into patients with smaller aneurysms and at younger ages, he said.

NYU is in the process of changing its protocol and eliminating arterial phase imaging in these patients, Macari said.

For more information from the Diagnostic Imaging archives:

AAA screening receives boost from Senate

Aneurysm screening plan falls short of expectations

New generation of stent-grafts curbs migration

Endovascular AAA produces better mortality rates than open surgery