This study illustrates how iterative reconstruction techniques can be used to lower the radiation dose when using CT to search for urinary tract stones – without compromising accuracy significantly.
Its time has come!
This study illustrates how iterative reconstruction techniques can be used to lower the radiation dose when using CT to search for urinary tract stones – without compromising accuracy significantly.
Its time has come!
In this article, the research conducted by University of Washington Radiology Fellow Dr. Achille Mileto and colleagues highlight the importance of dose monitoring, but also the challenges: “Successful efforts to reduce overall radiation doses may actually direct attention away from other critical pieces of information that have so far been underappreciated, namely the widespread variability in global radiation dose values across clinical operation volumes.” … “These data may provide a foundation for the future development of best-practice guidelines for patient-specific radiation dose monitoring.”
Dr. Achille Mileto from the University of Washington
“We are kind of obsessed with radiation dose reduction, but I think we should keep in our minds the concept of radiation dose optimization, which means trying to adjust the dose to the specific clinical task,” Mileto said. “With technology we are reducing the dose, but we are increasing the room for variability. This is great if you are consistently reducing the dose, but we really want to understand what’s going on in terms of variability. So I think the main lesson is to try to develop best-practice guidelines for patient-specific radiation dose monitoring. I think basically the scenario in the near-term future will be to create some kind of shared library for radiation doses.”
There are at least three different generations of iterative reconstruction, all of which enable substantial CT dose reductions without compromise of diagnostic power. While earlier versions of IR yielded 30% dose reductions, those with model-based IR or some blend thereof can result in 50-80% patient radiation dose reductions – with even better spatial and low contrast resolution. Access the full article on this study.
This article pretty well confirms what many have felt: model-based iterative reconstruction (MBIR) lowers radiation dose by 70-80% compared to adaptive statistical iterative reconstruction (ASIR), without loss of diagnostic power/information. While the images do indeed look different because there is much less noise and because of a slightly different pattern in the remaining noise, all the findings are there. Further, the anatomy and the findings are displayed as well or better.
So, in a young patient (under age 45) – especially if they are likely to be getting multiple exams – use of model-based iterative reconstruction is well worth the longer reconstruction time.
(To read more about CT enterography, Radiologyinfo.org is a great resource for patients.)
At UW Medicine, we use a dose alert system built into DoseWatch (GE Healthcare) as well as in the individual CT scanners. While this is a good safety mechanism to prevent accidents and notice high dose exams, it’s not the whole answer. As this article points out, “… in practice, CT technique and therefore patient dose depends very much on patient size.”
Size specific dose exposure (SSDE) is a better measure which we will be hearing more about in the near future.
This interesting paper talks about the use of iterative reconstruction to help lower the radiation dose of screening CT colonography.
Of course, as with all screening exams, the first order of priorities is to do no harm – hence the motivation to keep the radiation dose especially low.
The challenge is to lower dose without compromising diagnostic power.
For about the past two years, here at UW Medicine (Seattle) we have been using Model Based Iterative Reconstruction (VEO, GE Healthcare) for all our CT colonography exams. As recommended in this article, we also keep the kVp low – 80 or 100, which also helps to reduce the dose.
The result is a very low dose exam, but with excellent image quality and low image noise. This helps to make great coronal/sagittal reconstructions plus very nice 3D fly-through on the post-processing workstation.
This article outlines the substantial reduction in radiation exposure to body parts which are shielded during a CT scan but not included in the field of imaging.
That is a very good practice.
More controversial is another practice: shielding sensitive body parts which ARE included in the field of imaging, specifically breasts, thyroid and gonads.
For some types of scanners this works well, while for other types less well.
With our scanners (GE) IF shielding to the sensitive body part is applied after the scout views are obtained, and IF the shield is separated from the body by placing towels or a blanket to elevate the shield off the body by 2-3 cm – then this works well. Any artifacts or other issues with image quality are minimal or out of the area of interest and the dose to the shielded body part does drop measurably.
Further, such shielding sends a strong message to patients and to our own staff about our concern for their safety.
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.
This very wise philosophy for implementing iterative dose reduction in any CT program was well presented at the recent MDCT meeting of the ISCT in San Francisco in June. A key component is to have regular and measurable ways for radiologists to regularly grade or score image quality as dose is ramped down slowly with increasing amounts of iterative reconstruction. With Model Based Iterative Reconstruction (MBIR), it may be possible to drop dose up to 60% compared to otherwise low dose adaptive statistical iterative reconstruction methods (ASIR) – but not in one jump. It takes time to get accustomed to the slightly different look of images with iterative reconstruction.
At least a month’s worth of experience should accrue before passing judgment on image quality. It is also important to guard against anecdotal cases used to render judgments, so experience over time is important. But with a methodical approach, a lot of progress can be achieved in overall dose reduction.
The ultimate goal is to have a fully informed and well educated patient – this will result in best personalized healthcare and outcomes.
So as far as radiation dose from individual CT exams is concerned, it is good for patients to know what they received – but it is not enough. Patients also need to be educated about the meaning and risk of their radiation dose.
Educating patients about extremely low risk is difficult – as would be true about any very low risk. But, it should be coupled with educating patients about the potential health and healthcare benefits from their CT exam.
This is because what they really need to know is their risk/benefit ratio – from each CT exam. An educated patient who understands their risk/benefit ratio from CT will be a truly informed healthcare consumer.
Who should educate patients about risk and benefit? All of us – all providers. The primary care physician, the subspecialist, the radiologist, the CT technologist, the radiology nurse, PA’s and LPN’s – everyone who contacts the patient can help advance this education and this understanding.
MDCT 2014 speakers weighed in on this subject at the ISCT Symposium in early June.
CT to search for urinary tract stone is a very commonly performed procedure because both negative and positive results may have significant impact on subsequent patient care. Often the patients are younger since stones can occur at any age.
This article presents very encouraging news about significantly lowering the dose of a CT for urinary stones by using statistical iterative reconstruction – yet with acceptable image quality and no loss of diagnostic power.
This report adds to a rapidly growing body of data about both statistical iterative reconstruction and model based iterative reconstruction for various types of CT exams. This body of data almost uniformly reports substantial patient radiation dose reduction in the 30% to 60% range with equal or even better image quality.
A 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.
A few weeks ago, the New York Times featured an article, “Medical Radiation Soars, With Risks Often Overlooked.” The article brought up some valid points about radiation, but also requires readers to take a step back when processing some of the information given.
Yes, as the article ascertains, radiation has its indisputable medical advantages, in addition to its potential medical downsides. The amount of medical imaging, including CT scans, has significantly increased over the last few decades, as more life-saving procedures are discovered and as technology develops. As a result, some patients are subjected to higher levels of radiation, which, according to this article, is “believed to account or 1.5 percent of cancers” in the United States.
The piece goes on to say that “the cancer-causing effects of radiation are cumulative” and that doctors and hospitals fail to track the amount of radiation patients have already been exposed to when ordering a new exam. While it is critical to practice “As Low As Reasonably Achievable” (ALARA) for every protocol and to closely scrutinize every exam request for appropriateness, there is absolutely no evidence that risk from well spaced CT exams is cumulative. Therefore, canceling an otherwise appropriate exam because of cumulative dose may not be in the patient’s best interests. For all CT exams a risk/benefit evaluation should be made by a well informed radiologist. For the existence of multiple prior exams alone to change the risk/ benefit ratio would be extremely rare.
Additionally, the claim that “no one” keeps track of how much radiation patients have been exposed to is inaccurate. A number of institutions, including UW, are a part of the American College of Radiology’s Dose Index Registry, a program striving to accurately track CT radiation dose in order to establish benchmarks, monitor patient radiation dose exposure, and compare patterns. More recently, a pediatric dose registry was introduced to perform similar functions, but for a younger demographic.
Both doctors and patients should be as informed as possible when it comes to radiation. Understanding the risk/ benefit ratio is an important part of this—and no appropriate medical imaging exam should be cancelled if it will benefit the patient, especially if its radiation level is ALARA.
A new study presented at the American Roentgen Ray Society (AARS) meeting brought attention to another key point in radiation dose reduction. Currently, a majority of the focus on cutting CT scan radiation is centered on dosage levels, but it is also important to monitor cumulative dosage in patients receiving multiple scans. While government and industry are increasingly focused on single CT scan dosage reduction (which is great news!), there is a lesser concern for decreasing the overall number of CT scans for patients.
The research tracked the amount of repeated CT exams performed on patients in order to calculate cumulative radiation dosage. Some of the results are shocking. The study identified a group of patients from the test population undergoing more than 20 medical imaging exams in one year, and as a result, being exposed to high cumulative dosage—more than 300 mSv per annum! In fact, one patient received 70 different scans in one year!
This is, of course, something we are working to mitigate continuously. Europe (EEU) has been tracking the cumulative dose of its citizens for about 10 years—by law! This is certainly a good thing for patients and in the U.S, we are beginning efforts towards this direction. Several products are now available that serve as a repository for dose from devises and particular protocols, to keep track for individual patients (including cumulative).
We recently purchased such a product (DoseWatch, GE Healthcare) which will be integrated with our RIS and connected to every radiation emitting device in our medical center. This product will pick up cases of unusually high cumulative dose in patients, but also identify protocols which have high dose or devices which are emitting high dose. We are looking forward to implementing DoseWatch a few months from now.
Be sure to check back regularly as we document our experience with the product.
That there are strong associations between smoking and emphysema and smoking and lung cancer is well established. Therefore, it’s of little surprise that a report from Lung Cancer finds emphysema that is visible to radiologists from CT scans is correlated with an increased risk of lung cancer.
However, these results were only discovered when the emphysema was read by radiologists— and not by computer interpretation. Researchers point out that radiologists and automated computer software likely detect different types of emphysema- with only doctors appearing to detect the type of emphysema associated with lung cancer. This clearly highlights the “intuition” factor in scan interpretation by experienced radiologists—a factor not yet evident in intelligent computers!
Patients that are found to have emphysema detected by CT scans are already at an increased risk of developing lung cancer and should quit smoking as soon as possible. It is interesting to remember that before cigarette smoking became widespread, both lung cancer and emphysema were exceedingly rare diseases. Those high risk patients should explore the benefits of lung cancer screening and lung cancer screening programs.
For more information on the benefits of lung cancer screening, please see here.
A recent article published in CA: A Cancer Journal for Clinicians states that education of referring physicians, more assertive radiologists, and an increased use of healthcare IT are the keys to reducing patient exposure to radiation.
While these assertions may be true, the article also touched on rising radiation exposure due, primarily, to CT scans. Since the early 1980s, the estimated per capita dose from medical radiation in the US has increased significantly. But this isn’t the whole story…
While it is true that medical radiation from CT has increased markedly since 1980, so has the benefit to health from CT. We no longer do “exploratory surgery” for example, in order to sort out complex diagnostic imaging challenges. The false negative rate from Appendix surgery has plummeted. And cancer diagnosis rates overall are declining while cancer cure rates have gone up substantially, particularly in the last 5 years.
Meanwhile, the radiation dose per CT scan has gone down dramatically as the principles of low-dose CT continue to be better understood and implemented. Scans that used to require 25 mSv of radiation are now being done for 20% of that amount. While negative effects from low dose radiation have never bee proven (below 50 mSv), we still strive to keep our doses as low as possible.
So the issue is not radiation cost, but cost/benefit ratio. Driving a car is dangerous too, but we accept the cost/benefit ration. For CT that ratio is much better!
I was recently asked the question: “How low is low enough for CT?” With the risks of CT scans, the answer is: as low as you can go without significantly compromising diagnostic power.
Sometimes we do very noisy CT exams at extremely low doses, knowing that we may miss a 1 mm ureteral stone. However, we accept that possibility since such a small stone may not be clinically relevant.
Our routine abdominal/ pelvic exam is noisier than most of the CT exams we see referred in – but we deliberately chose to become accustomed to the higher noise levels (even when using iterative reconstruction) in order to minimize CT radiation dose. Thus, our doses are 40 percent lower than those on some of the CT scans we see being administered at many other places. There is no evidence we have compromised diagnostic power with our reduced dosage CT scans.
In today’s world, the 1-3 mSv cardiac CT is commonplace. In the near future, a CT of the abdomen and pelvis (40 cm of Z axis) using 0.6 mSv will soon be commonplace with the arrival of model based iterative reconstruction. With MBIR recently becoming available in the United States we will soon see dose reductions of up to 80 percent!
A recent study published in the Annals of Emergency Medicine on the rapid increase in CT scans being performed in Emergency Rooms (ER) paired with the decline in hospital admission rates between 1996 and 2007, got me thinking. During this time, the number of CT scans being performed increased by 330 percent, while the rate of those admitted following a CT scan decreased from 26 percent in 1996 to 12.1 percent in 2007. Does this mean that more patients are receiving unnecessary radiation exposure? Well… not necessarily.
The article points out a conflict about the use of CT in ER patients. Remember that practicing medicine in an ER is very different from a physician’s office. Patients are more acutely ill and ER congestion can be marked. Plus, time spent in the ER is very expensive.
In our study of patients presented to an ER with low to moderate risk chest pain, we found that a negative triple rule out CT resulted in shortening the stay by over 20 hours and cutting the cost of the ER encounter by 50%. Further, discharging a patient to home if their CT was negative was a safe practice.
Therefore, under the right circumstances, the use of CT in ER patients can be very effective. Our challenge is – through outcomes research – finding those right circumstances.
For more information on emergency medicine at UW, please see here.
It’s a fact of life that all CT scans involve radiation. And certain types of diagnoses and diseases are going to require regular repeated CT scans – resulting in a high cumulative CT radiation dose to the patient over time. But as a recent news story profiled, there is a new technique and technology that can help reduce CT scan radiation exposure by up to 60%.
Researchers at the University of Washington have pushed the frontiers of CT technique by circumventing the noisiness and blurriness of images scanned at very low radiation dose. These noisy images are made sharp and clear by better software reconstruction technology. It’s a bit like what NASA does with high altitude satellite technology. This means that the same diagnostic power is achievable with much less radiation to the patient.
This new approach works for all types of CT scans, but can be especially important for children and certain areas of the body – in particular, the female breast, the gonads and other tissues in the abdomen. These are particularly radiation sensitive, so we want CT scans to be as low in radiation dose as possible without compromising the diagnostic power of the CT scan. Low dose technique combined with low dose technology accomplishes this.
New innovations are continually being made in the field of medical imaging. If you need a CT scan, it’s always OK to ask your doctor if you can get one with a lower dose of radiation.