Lowering radiation dose without affecting diagnostic confidence

Guest blog by Kalpana M. Kanal, PhD, Director of Diagnostic Physics Section and Associate Professor in the Department of Radiology at University of Washington

How low can we go in radiation dose without affecting diagnostic confidence for detection of low-contrast liver lesions?

In a recent article we published, we studied the impact of incremental increases in CT image noise on detection of low-contrast hypodense liver lesions. Clinical CT liver exams were obtained on a 64-slice CT scanner using automatic tube current modulation at a routine clinical noise index 15.   An artificial image noise addition tool was used to increase the noise level in clinical liver CT images to simulate 75% (NI 17.4), 50% (NI 21.2), and 25% patient radiation dose (NI 29.7) scanning relative to the original images (NI 15.0; 100% dose).  The images were reviewed by radiologists of varying experience who subjectively scored lesion detectability on all the images, original and simulated.

We concluded that there is little loss of detection sensitivity for low-contrast liver lesion detectability of CT exams scanned with a NI at least up to 21.2 compared to a NI of 15, a patient radiation dose reduction of 50%. No significant degradation was observed when reader performance was evaluated as a function of lesion size (>10 mm) and contrast (>60 HU) at 90% sensitivity.  When lesion size dropped to <10 mm or contrast was <60 HU, sensitivity did drop to 85%.

This study had some limitations, the most important of which was that this study was a simulation and not a true study of CT scanning at lower radiation dose compared to high dose scanning which would have involved scanning patients multiple times. Nevertheless, this study was important as it demonstrated that dose could be reduced by 50% without affecting diagnostic confidence for detecting low-contrast liver lesions.

Lung Cancer Screening in High Risk Patients

For the question of whether lung cancer screening in high risk patients causes more good than harm, check out this article.

I’m pretty convinced the data shows that in a research study high risk population where the scans are read by highly skilled experts closely following the rules, lives are saved by CT screening and the cost is reasonable for each QUALY.

Further, the interpretation of these chest CT screening exams is fairly straightforward for experienced and trained radiologists. That suggests that when CT screening is extended beyond research to broader community practice, results should also be good.

Studies Offer Hope for Future CT Protocol Comparisons

recent study featured in the Journal of Computer Assisted Tomography touches on the perennial issue for radiology researchers studying and evaluating the effectiveness of different low-dose protocols. The topic brings the need for accurate CT dose reporting to the forefront, as researchers use different techniques to compare dose levels without relying on unnecessary CT scans in the same patient.

At the Mayo Clinic, researchers have used iterative reconstruction to acquire half-dose virtual colonoscopy exams to compare with full-dose exams. Previously, radiological researchers have relied on phantom studies to approximate dose differences among different protocols, or on patient division, in which patient groups (that are similar but never match precisely) undergo different scan protocols to approximate dose differences.

The issue, however, is that radiation dose and image quality must be compared in every patient, not just groups, because discrepancies in patient shape, cardiac output, lesion pathology, and other factors are highly individualized. The study continues, “matched-cohort research studies can’t evaluate the impact of noise reduction on reader performance for identifying findings, and even back-to-back full- and half-dose studies cannot control for the effect of phase enhancement on lesion conspicuity.”

Both of these points are valid. But, there is hope in the form of positive scientific studies on the way. Research from the University of Washington will soon be published in the American Journal of Roentgenology involving patients with cirrhosis and hypervascular liver tumors. This research offers valuable information for the future of low-dose CT reconstructed with multiple techniques from the same data set when comparing lesion detection.

Additionally, research involving the challenge of scanning the same patient twice with two different dose levels is ongoing. The Institutional Research Board has approved this study at a number of institutions, which analyzes patients who are scanned with ASIR and then full-iterative techniques. Stay tuned for full data available next year.

While these challenges do indeed exist, these ongoing studies offer hope for the effectiveness of low-dose protocols and understanding which protocols work most effectively.

Radiology on the Horizon: Can a Pill Prevent Cancer?

In July’s Radiology, a new study was featured that suggests that a new pill can prevent DNA damage that might lead to cancer. Researchers analyzed DNA double strand breaks (a precursor lesion to cancer) before and after X-raying human blood that had been mixed with the pill, a compound of antioxidants and glutathione-elevating agents.

At this point, the most common way to prevent radiation damage, which can damage the DNA, is lowering the radiation dose level and exposure timeshielding, and staying away from radioactive sources. However, further research may prove that this pill could be an additional way to prevent radiation damage. According to this study, there was a 58 percent reduction in double strand breaks from subjects who ingested the compound one hour prior to imaging.

The idea is in its first stages so it remains experimental and esoteric, but my esteemed colleague, James Brink, MD, from Yale has done an analysis of the research. He says:

“The study was very exciting from a methodological standpoint. I was impressed with the methods by which the authors were able to assess the formation of double strand breaks in response to low doses of ionizing radiation using the fluorescent tagging technique.

I’m respectful of the challenges, but without a clear-cut identifiable clinical benefit, we only have a laboratory benefit. While many lab studies on the biochemistry of antioxidants have been encouraging, some clinical studies have not shown antioxidants to be beneficial to subjects. That’s why we’d want to be cautious about jumping the gun.”

Though additional research must be done to assess the widespread benefits of the use of this compound prior to imaging, its potential benefits could be great for radiation damage reduction.

Study Offers Promising Benefits for Iterative Reconstruction

At UW, we are outspoken for our support of adaptive statistical iterative reconstruction (ASIR).  As a big proponent of the method, I find this write-up from Radiology to be a landmark article, and the research it highlights, very impressive work.

A team of researchers recently confirmed that iterative reconstruction allows significant CT radiation dose reductions for patients undergoing urolithiasis imaging, without unintended decreased image quality or diagnostic confidence.

Urolithiasis is a common condition, with high likelihood (estimated at 75 percent) of recurrence amongst individuals diagnosed. Therefore, imaging scans are a regularity for those patients with the disease. It is important to treat these patients with the lowest radiation dose possible, as to alleviate fear of potentially excessive radiation.

For the 25 patients involved in the study, image quality was significantly boosted by adding iterative reconstruction, while dose was reduced by about 85 percent, thanks to the ultra-low dose. While previous studies report substantial degradations in imaging quality, 80 percent of the images acquired in this study had suboptimal image quality.

This study is just further evidence of the promising benefit of ASIR. I firmly believe that every imaging site with access to the protocol should use it regularly as to lower dose by 80 percent in frequently performed exams.

To learn more about iterative reconstruction, please click here!

New Data on Lung Cancer Screening Shows Low Dose CT Saves Lives

Earlier this year, I wrote a blog entry about the news surrounding an important study involving CT and lung cancer screening. Now, the same study is making big headlines again as stronger (final) findings have been released. According to CNN, the study found that “low-dose CT screening reduces the number of lung cancer deaths in high risk smokers by 20 percent.”

Here’s another interesting fact coming out of the latest data: In high-risk populations, lung cancer CT screening can save a life for every 300 people screened. That’s more potential lives saved than mammography, colonography and prostate cancer screening COMBINED!

The only hitch: lung cancer CT screening is not covered by most insurance. However, many hospitals and imaging centers are offering this service at attractive rates for those who are willing to pay themselves.

Study by Dr. Kanal, UW Researchers Featured in JACR

Recent findings from blog contributor Dr. Kalpana Kanal and her team of University of Washington researchers have been published in the April issue of the Journal of the American College of Radiology!

The purpose of the study was to examine the variation in pediatric trauma head CT imaging protocols in Washington State – including the use (or not) of low radiation dose CT. Based on their findings, the team is now working on a campaign to adopt CT dose reduction protocols throughout the state. For more information on the study, click here.

Great work by Kalpana and her team!

High Dose CT Preferred Method…

…for dead people.

Check out this interesting story, “Radiology Helps Unwrap Mummy Mystery,” about a radiology lab helping out a university museum with some mummy research. They were hoping that, through the use of CT scans, they’d learn some valuable information about the mummy and the person he once was.

What caught my eye was this quote: “Radiation protection is very important in living humans…but this concern was completely inapplicable to this situation. So we were able to do two things: we were able to use a much higher radiation dose and also use much thinner slices than we would typically use on living patients to examine them.”

Amusing, isn’t it? Dead people are willing to pay the price for images that look too good: high radiation.

Important Studies on CT Scans and Lung Cancer Make Headlines, Generate Debate

In the last few months I’ve read several stories concerning research about CT screenings for lung cancer.

In mid-November, there was a story making the rounds among the major news outlets about a study that found that CT lung scans can reduce the risk of lung cancer death among former and current heavy smokers. During the excitement of this study, a New York Times piece was published that expressed concern that the study’s findings could easily be taken out of context – and perhaps incite unnecessary fear, as well as drive demand for unnecessary scans.

I’d like to point out the importance of this study: it showed a 20 percent reduction in mortality in patients at very high-risk who were screened with low dose CT compared to patients who were not. Several things to keep in mind about this study – first, it was a study of patients with 30 or more pack-years of smoking history. Second, the technique was a quick and a low dose CT. And third, the costs of false positive findings and their workup have not yet been analyzed.

Now, another study is gaining traction that provides even more support for the findings of the November study. While this data suggests that screening can lower lung cancer mortality substantially in high-risk individuals, what we don’t yet know is the cost of a QUALY – a quality adjusted life-year. Calculating that cost involves knowing how much society had to expend paying for CT exams and the costs of false-positive results in order to capture a saved life-year in an at-risk person. Generally, if you can save a QUALY for $50,000 or less, it’s worth doing. If more, it’s a debate.

Just some things I’ve been thinking about as more and more news agencies report on these findings. I’m interested in learning what you think – what’s your opinion on these studies? Was the New York Times piece correct in its cautionary tone? Or could these findings, in fact, be as revolutionary as some reporters (and researchers) want us to believe?