Researchers weigh utility of guidelines for imaging

November 1, 2005



Radiologists are evaluating imaging guidelines to determine their relevance in the context of technology advances and cultural shifts. The scrutiny is prompted by increased use of CT in general, in the ER, and in children, and attendant concerns about radiation exposure. Evidence of imaging overutilization and the growing number of obese patients are other driving factors.

Developing guidelines and standards in radiology generally requires collaboration among radiologists, clinicians, legal experts, vendors, and physicists. At the RSNA meeting, researchers debated pros and cons of guidelines. One forum tackled standards for imaging pregnant women. Participants noted a surprising lack of literature on the topic.

"Welcome to the third rail of radiology," said Dr. Andrew LeRoy, a professor of radiology at the Mayo Clinic in Minnesota.

Radiation to the conceptus should never go above 100 mGy, and cumulative doses of between 50 and 100 mGy reside in a worrisome gray zone, said Dr. Louis Wagner, a professor of radiological physics at the University of Texas. Less than 50 mGy should be acceptable if the benefit-to-risk ratio is kept high.

Dutch researchers confronted their national guidelines for use of CT in minor head trauma and found sensitivity unacceptably low. Five sets of European and international guidelines, applied in a prospective multicenter trial, also fell short. Sensitivity and specificity of each was evaluated in the context of two outcome measures, which included any neurocranial traumatic finding on CT, followed by any CT finding that led to neurosurgical intervention.

Only the European Federation of Neurological Sciences' guidelines reached a sensitivity of 100% for both guideline outcomes, but at the cost of 0% specificity, according to Dr. Marion Smits and colleagues at Erasmus Medical Center in Rotterdam.

Guidelines created by the Scottish Intercollegiate Guidelines Network and the Neurotraumatology Committee of the World Federation of Neurosurgical Societies each achieved sensitivity in the high 90% range, with less than 10% specificity.

The National Institute for Clinical Excellence (U.K.) criteria posted the best specificity for neurocranial traumatic findings (46.2%) and neurosurgical interventions (43.6%), but they showed relatively low sensitivity (82.1% and 94.1%, respectively), Smits said. The Dutch national guidelines for interventions demonstrated the lowest sensitivity (76%), with 23% specificity.

The growing acceptance by neurosurgeons of preoperative functional MRI to map eloquent brain areas has prompted neuroradiologists to develop standards. They formed the American Society of Functional Neuroradiology in 2004 to help convince vendors to standardize fMRI programs and to make these programs more accessible, said society president Dr. Andrei Holodny. The ASFNR is spearheading efforts to get CPT codes issued for fMR brain scans and to convince the Centers for Medicare and Medicaid Services to reimburse for them.

Separate exhibits addressed the need to codify imaging of obese patients, as current protocols do not address this population, said Dr. Michael Vannier, a professor of radiology at the University of Chicago.

Wide-bore CT scanners, some up to 85 cm, are now available. Some vendors provide high-capacity tables for patients weighing up to 615 pounds. Maximum dose per section is required for very obese patients, which can be achieved by decreasing the rotation time (0.75 to 1 sec/rotation) and increasing the section collimation (32 x 1.25 mm, using 40- and 64-slice scanners) and mAs ( >400).

Dr. Raul N. Uppot and colleagues at Massachusetts General Hospital adopted a multimodality approach. For fluoroscopy, the weight limit for patients is 350 pounds and the girth limit is 45 cm. For closed-bore MRI, they are 350 pounds and 60 cm, respectively. Abdominal CT can accommodate 450 pounds and a girth of 70 cm. For vertical field/open MRI devices, weight and girth limits are 500 pounds and 44.7 cm, respectively.