Radiologist study warns about extra-cardiac CT findings; cardiologist responds
Researchers from the department of radiology at the Medical University of South Carolina in Charleston found that using a limited field of view with cardiac CT misses a large percentage of pulmonary nodules. UCLA cardiologist Matthew Budoff, MD, however, says the current evidence suggests it is “better to keep the field of view small, rather than find a lot of nodules, especially in a population at low risk for lung cancer.”

In a retrospective study appearing in the September issue of the American Journal of Roentgenology, Meredith Northam, MD, and colleagues at MUSC reviewed the records of 1,764 patients who underwent CCT studies over a three-year period.

“Cardiac CT was performed for calcium scoring in 463 cases, coronary CT angiography (CTA) in 737 cases, evaluation for pulmonary venous stenosis after radiofrequency ablation in 341 cases, and evaluation of a coronary artery bypass graft (CABG) in 223 cases,” the authors wrote.

A 58-year-old man with indeterminate nodule considered suspicious for lung cancer partially visualized at edge of limited field of view. A, Full-field-of-view axial CT scan (3-mm slice thickness, lung window) obtained in evaluation of pulmonary venous stenosis shows 1.8-cm mixed-density nodule (arrow) in left lower lobe. B, Limited-field-of-view axial CT scan (1-mm slice thickness, lung window) at same level as A shows partially visible nodule (arrow). Image and caption by permission of the American Roentgen Ray Society.  
All studies were performed using a 64-slice CT scanner, either a Siemens Medical Solutions’ Somatom Definition or Somatom Sensation 64 cardiac system. In all cases, limited field-of-view (FOV) images, encompassing the heart and 1 cm from the farthest anterior, posterior and lateral extents of the cardiac chamber, were reconstructed from the full FOV data set.

The scientists then reviewed both FOV data sets to determine the percentage of pulmonary nodules that would be missed with viewing only limited FOV images.

They found that pulmonary nodules, including 15 larger than 1 cm, were found in 11.5 percent of the reviewed cases. Of those with nodules less than 1 cm, 15.5 percent were seen in limited FOV, 2.7 percent were partially visible and 81.8 percent were excluded from view. In the subgroup with nodules larger than 1 cm, 26.7 percent were visible in limited FOV, 6.7 percent were partially visible and 66.7 percent were excluded from view.

“Because FOV can be adjusted with relative ease and without the consequence of increased radiation exposure, it seems reasonable to require full FOV for cardiac CT interpretation,” the authors wrote.

Budoff said that expanding the FOV by using a larger bow-tie filter will afford more radiation to the patient. “On a current Lightspeed VCT (GE Healthcare), a medium bowtie filter for a CCTA affords 13.4 mSv of radiation, while a small bowtie filter—which would still allow reconstructions of the heart to 25 cm, but not a full field of view—reduces this to 8 mSv in the same patient, same protocol,” he said.

The dilemma in CCT study evaluation is what specialist interprets the results of their exam—a radiologist or cardiologist.

The American College of Radiology guidelines for CCT require that interpreters also meet its guidelines for interpreting diagnostic CT scans and must assess and document important extra-cardiac findings in a diagnostic report. The American College of Cardiology makes no implicit or explicit competence requirement for evaluation of extra-cardiac structures.

In an accompanying commentary, Patrick M. Colletti, MD, of the department of imaging science at the University of Southern California in Los Angeles, noted that the moral implications of reviewing the full FOV CCT data set are clear.

“Once an examination is performed, the noblest approach is to view and evaluate all
available data, to apply appropriate judgment and to proceed in the best interest of the patient and society,” he stated.

Buddoff, director of the Harbor-UCLA LA BioMed CT Reading Center, told Cardiovascular Business News that the issue related to overreading cardiac CT scans raised by Colletti in the recent commentary is misdirected.

“The question is not whether we can find millions of lung nodules, but rather should we. There is no proven benefit, and may be proven harm, to identifying these incidental nodules on cardiac CT.” (1)

He stated that given the rapid growth of cardiac CT, and since almost all of the nodules are benign, the subsequent costs, radiation exposure and possible morbidity and mortality of the ensuing workup most likely does more harm than good.  

The U.S. mortality rate for a lobectomy is between 2.8 and 3.8 percent, according to Budoff. “Since at least some, if not most, of these lobectomies are done in patients found to have benign findings, we may be killing patients to tell them we should not have looked in the first place,” he said.

He cited Stephen J. Swenson, MD, of the Mayo Clinic in Rochester, Minn., who helped to validate the currently held practice that routine chest x-rays in smokers cause more harm than good “and thus are not recommended.”

Swenson et al subsequently published a study showing no benefit to those who underwent lung CT. “As their fiduciary, you should tell your patients in no uncertain terms that there is no proven benefit and that there are serious risks involved that could even outweigh benefits (if indeed there are any),” the authors wrote (Mayo Clin Proc 2003;78:1187-1188).

“Keep in mind, the intent of these studies is to look for heart disease,” Budoff said. “Over 99 percent of such nodules found on screening CT are benign, and finding the remaining 1 percent that are not benign has not been shown to benefit the patient (2) – based on current available evidence, which may change once the results from the National Lung Screening Trial are published.”  

Budoff raised the issue of subsequent serial CT scans of the chest and other exams such as PET/CT and the specter of increased radiation, as well as an increase in cost to the patient, insurance companies and society in general. “Can we afford to screen every person who undergoes CT screening for heart disease for lung cancer?” he asked.

James G. Ravenel, MD, senior author of the current study and vice chair of radiology education at MUSC, told Cardiovascular Business News that future research could look for better ways to determine which pulmonary nodules need intensive follow-up, potentially identifying nodules with low pre-test probability of cancer, and to determine the most cost-effective approach to management of these small nodules.

For now, though, Budoff said, “Let’s let the science lead us in this endeavor, and currently, the science points us down a road that indicates less imaging may be better for the patient.”

1. Budoff MJ, Gopal A. Incidental findings on cardiac computed tomography. Should we look?, J Cardiovasc CT 2007;1:97-105.

2. Swensen SJ; Jett JR; Sloan JA; et al. Screening for lung cancer with low-dose spiral computed tomography. Am J Respir Crit Care Med 2002 Feb 15;165(4):508-13.