3D, 3T MRA demonstrates clinical value for PAD

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A non-contrast time-resolved MR imaging technique promises to help interventional cardiologists treat peripheral vascular disease.

According to the U.S. Centers for Disease Control and Prevention (CDC), almost 21 million Americans have diabetes, the vast majority of which have type 2, associated with a sedentary lifestyle and poor diet. This cohort represents about 7 percent of the population and more than one-quarter are unaware of their disease state.

In 2006, the director of the CDC’s diabetes program, Frank Victor, MD, stated that “diabetes is a leading cause of adult blindness, lower-limb amputation, kidney disease, and nerve damage.” Given the size of the diabetes patient population in the United States, the utilization of non-invasive diagnostic imaging for peripheral artery disease (PAD) diagnosis is gaining clinical importance.

  
Maximum intensity projections of time-resolved 3D MR angiography after background subtraction in 64-year-old man with peripheral arterial disease, Fontaine stage IIb, show markedly delayed contrast inflow. Venous system is not enhanced yet. Image and caption by permission of the American Roentgen Ray Society.  
   

Although intraarterial digital subtraction angiography (DSA) has been the traditional imaging procedure for PAD, and it is a relatively safe procedure, complications have been reported, including hemorrhage, dissection or arterial embolism. In addition, the required use of iodinated contrast material in the procedure may further impair the renal function in patients with diabetic nephropathy.

“In contrast, MR angiography (MRA) is noninvasive and avoids the use of iodinated contrast material and exposure to ionizing radiation,” wrote the authors of a multi-institution study published in this month’s American Journal of Roentgenology. “Contrast-enhanced MRA has evolved to be a safe, fast, reproducible, and reliable imaging technique.”
  
A research team from the department of radiology at University Hospital of the Saarland in Homburg/Saar, Germany, and the department of vascular surgery at Aachen University in Aachen, Germany, conducted a prospective clinical study of the potential of 3-T 3D MRA for foot imaging in patients with PAD.

“We evaluated the potential of sub-millimeter in-plane spatial resolution contrast-enhanced, time-resolved 3D MRA at a high magnetic field strength of 3T for preoperative evaluation of the pedal vasculature in patients with diabetes, PAD, or both,” they wrote.

A cohort of 21 patients was enrolled in the trial and their imaging was performed on a Philips Healthcare Achieva 3T MR system. The researchers collected 24 time-resolved (3.9 seconds) 3D MRA exams of the foot (two patients were examined before and after bypass surgery and one patient had both feet imaged).

The MRA images were acquired in a sagittal plane using a 3D gradient-echo T1-weighted sequence with the foot in a cylindrically shaped 8-element phased-array radiofrequency coil manufactured by MRI Devices.

A paramagnetic contrast agent, MultiHance by Bracco, was administered via the Spectris Solaris EP MR Injection System by Medrad through a peripheral catheter. Images were transferred to a dedicated workstation, the Philips’ ViewForum, for review via the institution’s Sectra PACS.

“Two radiologists read the images in consensus regarding good image quality with sharply delineated pedal vessels, differentiation between arteries and veins, presence of arteriovenous shunting with early venous drainage, and pronounced soft-tissue enhancement,” the authors wrote.

The team reported that 3D MRA was successfully performed in the entire cohort and images of good diagnostic quality were obtained from all exams.

“Our results show that the arteries and the potential vessel to be used for bypassing could be clearly separated from the veins due to the temporal resolution given by our approach—even in patients who suffered from diabetic foot syndrome with arteriovenous shunting,” they wrote.

The researchers observed that the vascular surgeons planning to conduct pedal bypass surgery need to have diagnostic images that reliably discriminate arteries from veins. They noted that their time-resolved 3D protocol allowed for the evaluation of anterior and posterior circulations and the patency of the pedal arch in every patient.

“The key information needed before vascular surgery, which includes patency of the pedal arch, documentation of the presence and degree