Pulse
Over-Exposed
Karen Blumberg, M.D., medical director of radiology at Children’s Hospitals and Clinics of Minnesota, has seen the rise and fall of CT usage during her 25-year career. When she first started practicing, CT was used infrequently—Children’s might do a handful of scans a day. But usage went “up, up, up,” she says, until 2007. That’s the year the Alliance for Radiation Safety in Pediatric Imaging, a coalition of concerned providers from around the country, launched a campaign to raise awareness about radiation exposure in children.
Concern had been growing since 2001, when seminal articles about radiation overdoses from CT appeared in the American Journal of Roentgenology. Before those articles were published, adults and children received almost the same radiation doses. Radiologists became concerned about the potential effects on children, whose tissues are more radiosensitive and who were effectively getting larger doses given their size.
At Children’s, the radiology department began to reduce exposure. “We found that for certain CT scans, we could lower the dose and still obtain excellent pictures,” Blumberg says. “And we found that we could lower the dose beyond that and still get diagnostically satisfactory pictures.” By the time the Image Gently campaign began, Children’s had already cut the amount of radiation pediatric patients received from CT in half. She estimates they have since reduced those amounts by another quarter to a third.
Image Gently encourages providers to scan only the area required, reduce tube output (they provide a number of protocols for this), perform single-phase studies, and shield the breasts of girls undergoing chest CT. In addition, it encourages doctors to consider alternatives. “We’re thinking twice before we do a CT and sometimes substituting other exams, namely ultrasound and MR,” Blumberg explains. Ultrasound is now used to assess for appendicitis, for example.
In addition to training her staff, Blumberg says she is also sharing the Image Gently messages with the medical students and residents who do rotations at Children’s. “Most physicians have never had any education on radiation safety,” she says.— Carmen Peota
Showing Stiffness
A technology developed by Mayo Clinic researchers is proving useful in identifying a spectrum of liver diseases. Magnetic resonance elastography (MRE) uses low-frequency acoustic waves to explore the mechanical properties of the liver. The miniscule motions are imaged using an MRI technique that shows liver elasticity or stiffness. The noninvasive procedure takes seconds to conduct and could spare patients from needle biopsy.
In a study of 113 patients, Mayo hepatologist Jayant Talwaker, M.D., M.P.H., and his team found elastography to be highly effective in detecting moderate-to-severe hepatic fibrosis. They also found it detected cirrhosis with 88 percent accuracy and nonalcoholic fatty liver disease without significant inflammation or fibrosis with 97 percent accuracy. They presented their findings at the annual gathering of the American Association for the Study of Liver Disease last fall.
Mind Readings
Clifford Jack, M.D., is optimistic that one day we will be able to predict not only if but when someone will develop Alzheimer’s disease. A professor of radiology at Mayo Clinic, Jack became interested in Alzheimer’s disease during the 1980s while studying how magnetic resonance imaging (MRI) could be used to localize seizure foci in order to better plan surgery for patients with epilepsy. “One of the developments of that work was a way to measure the volume of certain parts of the brain, specifically the hippocampus, which is important in epilepsy and also happens to be one of the, if not the first, areas of the brain to be affected by Alzheimer’s disease,” he says.
Jack has since been working with Ron Petersen, M.D., Ph.D., a behavioral neurologist at Mayo, to find ways to use diagnostic imaging technology to diagnose Alzheimer’s disease.
Their team has been testing whether modalities such as structural MRI, MR spectroscopy and diffusion imaging, and 11C-Pittsburgh Compound B (PIB), a positron emission technology-based imaging method, can be used to identify the underlying cause of cognitive impairment and predict who will eventually become demented.
In 2008, they along with Val Lowe, M.D., published results of a study in Brain that used both 11C-PIB, which identifies the amyloid plaques that are seen early in Alzheimer’s disease, and anatomic MR, which detects the brain shrinkage that happens later in the disease, to monitor changes in the brain. They looked at 20 patients who were cognitively normal, 17 with mild dementia, and eight with probable Alzheimer’s disease. They found that the two imaging modalities provided independent information that sheds light on the underlying mechanisms of Alzheimer’s disease.
In another study, researchers led by radiologist Kejal Kantarci, M.D., used a combination of imaging techniques to study 126 individuals with mild cognitive impairment. The participants received both MRI and MR spectroscopy scans annually from 1998 to 2005. Kantarci’s analysis showed that an abnormal MRI indicated a 41 percent chance that an individual would progress to Alzheimer’s disease within three years. An abnormal MRI and MR spectroscopy indicated a 56 percent likelihood. And positive results of both tests plus evidence of stroke on MRI upped the likelihood to 85 percent.
Jack says prediction is important. By the time a person is cognitively impaired enough to be classified as having Alzheimer’s disease, they’ve incurred considerable brain damage and are unlikely to be helped by treatment. “In order to have an impact on the disease, people need to be treated when they’re still cognitively normal or have mild symptoms,” he says.—Kim Kiser
Guidelines Reopen Debate
Last month, the U.S. Preventive Services Task Force (USPSTF) reignited debate about mammography by changing its recommendations for when women should start routine screenings. The new recommendations, published in the November 17 issue of the Annals of Internal Medicine, advise biennial screening mammography for women starting at age 50 years, up from 40. In addition, they advise against teaching women to do self-breast exams. Among those issuing statements opposing the USPSTF conclusions was the American Cancer Society, whose chief medical officer Otis Brawley, M.D., said in a published statement that although mammography has limitations, “the limitations do not change the fact that breast cancer screening using mammography starting at age 40 saves lives.”
The American Society of Breast Surgeons came down against the recommendations as well, saying in a statement: “We believe there is sufficient data to support annual mammography screening for women age 40 and older.”
In Minnesota, Mayo Clinic and Fairview Southdale Hospital were among providers rejecting the new task force recommendations. And in Washington, Health and Human Services Secretary Kathleen Sebelius stated that federal insurance programs would continue to cover routine mammograms for women starting at age 40.