As radiologists learn to live with a little noise in exchange for a smaller radiation dose, vendors aim to tackle both.
Radiation dose has received a lot of bad press of late, in part because of some egregious incidents resulting in severe patient harm. But among pediatric radiologists, radiation dose has been a concern for some time, and many facilities have already begun to implement dose reduction measures. As recent incidences have shown, there is always room for improvement, whether a facility has still to implement a program or has had one in place for some time.
With the media attention, one would think it unlikely to find institutions without a dose reduction program, but that is not the case. “As a big tertiary referral center, we get CT scans from outside facilities requesting second opinions. And every once in a while, we’ll get a CT from a small community hospital, where they’re still using adult radiation doses on a little child and you can tell they haven’t implemented a lot of the strategies that most large and medium institutions have implemented,” said Daniel Podberesky, MD, chief of thoracoabdominal imaging in the department of radiology at Cincinnati Children’s Hospital Medical Center.
In some instances, the lack of effort is due to a lack of resources; in others, it’s a lack of education. Often, starting a program is intimidating. “You’ve got to start somewhere. You can’t just throw your hands up and say these things are all too complicated or too expensive. A lot of [dose reduction tools and techniques] cost nothing—they just require some education. Once you start, you’ll find many of these things aren’t as hard as you thought and really don’t have any poor effect on the image quality,” Podberesky said.
Image quality is a concern; lower doses in CT exams tend to produce noisier images. “It gets to be a question of people learning to live with images that are of less aesthetic quality but of acceptable diagnostic quality,” said Beverley Newman, MD, associate professor of radiology with Lucile Packard Children’s Hospital at Stanford in Palo Alto, Calif.
Newman recently coauthored a study that explored this question and found quite a bit of room to moderate dose according to patient size without impacting the diagnostic usefulness of the image. These weight-based protocols, particularly when automated, provide an excellent way to begin reducing dose but are certainly not the only way.
Podberesky likes to consider how he will limit exposure starting with the outside of the patient and working toward the inside of the machine. The first consideration is whether CT is the most appropriate choice for the patient. “If the diagnosis is something that’s amenable to using a different modality, let’s say ultrasound or MRI, then that would obviously be the first step in limiting radiation exposure to zero,” Podberesky said.
Comer Children’s at The University of Chicago uses these opportunities to educate ordering physicians on when CT is appropriate and to educate radiologists on modification of exams to limit radiation exposure. “We try to choose the best CT exam, whether we move the area to be scanned, use different parameters, or change our plan based on the patient’s condition,” said Kate Feinstein, MD, section chief of pediatric radiology at Comer Children’s, and a professor of radiology and surgery at the Pritzker School of Medicine, University of Chicago Medical Center.
If CT is appropriate, shielding is a first step in protecting the patient from radiation exposure. “We try to limit exposure by shielding those body parts that are more radiosensitive,” Podberesky says, citing breasts in young girls, the lens of the eye, and the thyroid gland as examples.
Patient size, rather than age, has been found to be key to successful dose moderation1,2 and many institutions have already implemented weight-based protocols. Equipment manufacturers have helped this effort by developing tools to automate the algorithms. The results can be dramatic.
Newman and Kim2 compared the effect of lowered dose and exposure parameters on image noise and subjective image quality in pediatric chest scans and found significant impact, such that the numbers indicate a past trend toward too-high dose. “If you use too high a dose with CT, the only thing that happens is your images get smoother and smoother and prettier and prettier. There’s no penalty to high dose in terms of image quality,” Newman said.
As a result, exposure has crept up, leaving room to “very considerably reduce dose.” For instance, in patients weighing less than 15 kg (33 pounds), volume CT dose index, dose?length product, and effective dose were reduced by 73%, 75%, and 73%, respectively.2
Noise increased by 55%, but the images remained diagnostically acceptable.2 “If you look at the percentages, they are sort of scary—50% more noise. But for all of our images, even those that were more noisy, I think the highest average noise index was about 13 or 14. So they were well within the range of what has been described as acceptable noise levels, a noise index of less than 20 half field units,” Newman said.
Radiologists, therefore, must learn to accept grainy images but need not compromise diagnosis. The study specifically examined whether “we could see the things we needed to see, and for the most part, they were rated as either satisfactory or good,” Newman said. The increase in noise was considered an acceptable trade-off for the significantly decreased dose.
Inside the Machine
Other parameters can also be modified to produce a significant reduction in dose pending anatomy. “There are certain exams where you don’t really care how noisy the image is, so we can answer a question using extremely low-dose radiation,” Feinstein says, citing pectus excavatum as an example.
In this same exam, Feinstein’s team will also restrict the scan to the depressed part of the sternum to limit exposed tissue, a technique also employed at Cincinnati Children’s. Proper training for technologists and new technology advance this effort.
Comer Children’s will soon install the Brilliance iCT 256-slice scanner from Philips Healthcare, Andover, Mass, that will inherently limit overscanning. “The opportunity for performing more sophisticated exams and decreasing dose on our routine type of exams is amazing,” Feinstein said.
In addition to the special collimator that reduces overscanning, Feinstein expects to be able to reduce dose using the system’s lower kV parameters, special beam filters, modified beam shapes, iterative reconstruction, and faster scan times. “If we can accomplish a scan in 10 seconds where we used to need 20 seconds, then the likelihood of motion will decrease,” Feinstein said.
Limiting the number of scans is another method by which pediatric radiologists reduce dose. Very rarely are multiseries taken in children today. “Instead of scanning the patient three times, now we just go through once,” Feinstein said.
Tips and Tools
Each child will require a different dose reduction approach depending on their unique circumstances. “We’re always using every tool we can think of on every [eligible] patient to lower dose as much as possible without compromising the image,” said Podberesky.
The toolbox from which to choose is constantly growing as vendors continue to attack the problem from different angles. “All the vendors now, not only CT vendors, are trying to develop new, ingenious ways of maintaining image quality while lowering dose, and they all have great ideas,” Podberesky said.
Many focus on behind-the-scenes techniques to remove noise. Examples include: GE Healthcare, Waukesha, Wis—Adaptive Statistical Iterative Reconstruction (ASIR), which uses up to 40% less dose with no loss of image quality and improves low contrast detectability up to 30%; Philips iDose, a new dose reconstruction technique enabling 20 times faster reconstruction than current hardware with up to 80% less dose, while the company’s DoseAware tracks x-ray exposure of patients and staff; Sapheneia Global, LLC, Barrington, Ill—aftermarket product, Clarity CT solution, that enables a 20% to 80% reduction in dose, depending on anatomy; and Toshiba America Medical Systems Inc, Tustin, Calif—Aquilion One 320 detector row volume scanner, which features SUREExposure Pediatric software with size-, age-, and anatomy-based protocols and a Pediatric Kit with tools to teach breath-hold techniques, child-size accessories, colorful designs, and a small, child-friendly replica of the machine.
If a health care institution has the financial resources to buy equipment, Podberesky thinks technology provides valuable solutions to dose reduction, but if resources are scant, smaller steps can be taken. When the team at Cincinnati Children’s does see the occasional child image captured with an adult dose, it will send a courtesy letter pointing the smaller facility to specific articles in the literature to help them get under way. “You just have to start somewhere,” said Podberesky.
Renee Diiulio is a contributing writer for Axis Imaging News.
- Kleinman PL, Strauss KJ, Zurakowski D, et al. Patient size measured on CT images as a function of age at a tertiary care children’s hospital. Am J Roentgenol. 2010;194:1611-1619
- Kim J, Newman B. Evaluation of a radiation dose reduction strategy for pediatric chest CT. Am J Roentgenol. 2010;194:1188-1193.