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!
This recent article from Radiology reports the use of an 80% reduced dose CT protocol for assessing moderate to high risk patients for ureteral stones in an ED environment.
Reduced dose CT was correct for stone versus no stone in 100% of 108 patients. Dose reduction was achieved by lowering both the mAs and the kVp and adding iterative reconstruction.
Using model-based iterative reconstruction, CT colonography can be a very low radiation dose method of screening. This article applauds the United States Preventive Services Task Force (USPSTF) approval, cited as a “big win for patients.”
This article illustrates how iterative reconstruction can be used to markedly lower CT radiation dose without significant impact on diagnostic content in CT exams.
For patients with Crohn’s disease who likely will have multiple CT exams over time, lowering dose is especially important.
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.
As this article demonstrates, iterative reconstruction is a very powerful way to reduce dose without impacting diagnostic ability. Key points of the authors include, “To reduce patient and operator radiation dose involves optimization of medical imaging equipment and best control of the equipment by the operator. … The results of our study confirm in a large patient number reflecting the routine clinical setting that the image noise reduction technology allows a significant reduction in radiation dose. … The substantially lower radiation dosage achieved in a routine clinical setting with the image noise reduction technique, provide further evidence of the substantial impact of the new technology. They indicate potential reduction in radiation dosage in invasive and interventional cardiology with more diffusion of newer radiation technology in clinical practice.”
All iterative reconstruction techniques powerfully reduce CT radiation dose in the 40-80% range – without compromising diagnostic power. And they all continue to be refined and to evolve, as this article illustrates. While the “look” of CT images may change from the noise removal, the diagnostic power is not compromised despite the substantial dose reduction. As radiologists, working with change is our future. The old days of nothing but filtered back projection are in our history but not in our future.
This article illustrates how much good diagnostic information can be obtained using very low CT radiation doses when screening for lung nodules.
In the screening environment, doing no harm is especially important since so many patients are screened. But detection rates cannot suffer.
Here is encouragement that we can meet both goals with very low dose CT combined with iterative reconstruction.
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.)
Paying attention to limiting Z axis coverage yields big dose saving dividends! See this article for results of this study designed to assess the safety and efficacy of radiation dose reduction in hospitals lacking iterative reconstruction.
This comprehensive article demonstrates the importance of CT dose monitoring and utilizing strategies to achieve ALARA (as low as reasonably achievable) doses while maintaining image quality for optimal clinical diagnosis. The authors also describe how the use of technology can improve the radiation dose efficiency of CT scanners.
This article highlights that it is possible to achieve much lower radiation dose CT scans for commonly employed types of CT studies – the CT for urinary tract stones is one of the most common.
While not done everywhere, attention to detail can produce remarkable reductions in patient radiation without compromising diagnostic power.
Use of a lower kVp will actually make stones a bit brighter.
Careful attention to patient centering in the gantry can make a difference of up to 40% in dose.
And the use of iterative reconstruction techniques is now widely accepted to not compromise detection, yet with marked dose reduction – whether it be statistical iterative reconstruction, model based iterative reconstruction, or some blend of the two.
Radiologists and technologists both need to understand the importance of these tricks and the physics behind each.
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 illustrates that Radiologists’ perceptions of image quality and content change as they become accustomed – over time – to the different noise pattern of the various types of iterative reconstruction.
In fact, no spatial resolution or low contrast resolution is lost with iterative reconstruction techniques – and diagnostic power is maintained.
Our work here at UW Medicine agrees with this report.
And it is important to know this because iterative reconstruction can result in 30%-60% dose reduction for all types of CT, without loss of diagnostic power.
This is a major advance as American healthcare evolves from reactive to preventive.
But a key to success in this lung cancer screening program is keeping the radiation dose of each exam as low as possible – certainly well below one mSv. Ideally, a low dose approach would involve model based or some other form of iterative reconstruction. All the other techniques to minimize dose should be employed together. Fortunately, this is an application where very low kVp will work well (70-100).
Next – and possibly even more impactful: coverage for screening CT colonography.
Since many patients who get CT enterography have repeated exams (inflammatory bowel disease, etc.), Model Based Iterative Reconstrucion has primarily been used to markedly reduce radiation dose while maintaining acceptable image quality.
However, this might be another application – especially if the patient will have only one such exam.
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.
Patients with Crohn’s disease often are young and often have their disease activity assessed repeatedly with CT – though MR is used more frequently now as well.
So – they are good candidates for reducing radiation dose by means of iterative reconstruction.
This paper demonstrates that considerable reduction of dose can be achieved without damaging image quality.
There are some who say that iterative reconstruction should be reserved only for younger patients and not used on older cancer patients who already have serious disease.
But many patients with malignancies are younger or are being treated for cure.
This article suggests that an iterative reconstruction technique (such as model-based iterative reconstruction, MBIR) which can reduce patient radiation dose by 50% may have salubrious utility in patients with lymphomas – who often are younger, who get multiple CT scans, and who are being treated for cure.
This may apply to other malignancies as well.
At the 2014 ISCT-sponsored MDCT meeting in San Francisco – dose reduction was a key theme during all four days.
Iterative reconstruction was a common theme of an overall dose reduction program. While adaptive statistical iterative reconstruction (ASIR) now has been well-shown to reduce average doses by up to 40% without impact on image quality, the hot topic was model-based iterative reconstruction (MBIR) in its various forms.
Consensus is now developing around MBIR being capable of 50-70% dose reductions incremental to adaptive statistical iterations. While image appearance may be somewhat different from that of filtered back projection, it is now pretty clear that such different appearance does not compromise diagnostic power. Indeed, with experience, some radiologists have developed a preference for the image appearance of MBIR.
This direction of combining a higher noise index (NI) to get lower dose images and then correcting for the resultant noise by using an increased percent of iterative reconstruction (ASIR) is exactly the way to go when striving towards “as low as reasonably achievable” (ALARA) – in my opinion.
At UWMC, we have for a couple of years now gone even further – we use NI in the 30-36 range and routine 70 percent ASIR as a standard for all our CT imaging except high resolution lung (which is NI 25 and ASIR 30%). According to the ACR CT Dose Registry, we are in the bottom 10% of their data base for CT dose….. but the images are very good.
Check out this article to learn more.
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.
At the recent International Society for Computed Tomography (ISCT) annual meeting, held in San Francisco, Dr. Eliot Siegel, from the University of Maryland, discussed an evolving technique for CT dose-reduction. This application does not focus on simulated image noise as a measure of image quality, but instead, works to more accurately depict that noise in low-dose CT scans. In other words, this technique aims to optimize dose based on what the radiologist needs to see.
According to the presentation, the future of low- dose optimization will rely on a combination of the visual perception system and sophisticated mathematical models designed to minimize the dose for every imaging exam without impairing the quality of the image to the radiologist. In fact, the current methods for low-dose optimization are already on the way out as awareness for radiation dose continues to evolve.
Dr. Siegel’s analysis of noise in the new world of iterative reconstruction is very sophisticated and thoughtful. Concepts of pink and white noise plus just-noticeable differences really are cutting edge. These ideas will clearly advance our understanding of how to get a world of fully automated dose minimization.
Dr. Siegel and his team of researches, as usual, are thinking profoundly and in very innovative ways. These concepts certainly raise great hope for a much more systematic future combined with much more sophisticated math to make patient doses even lower than we had previously dreamed! It will be an exciting next three years for dose reduction techniques and technology!
At a recent Society for Pediatric Radiology (SPR) meeting in San Francisco, one presentation addressed low-dose CT’s “bright future, but troubled present.” Texas Children’s Hospital’s Dr. R. Paul Guillerman touched on the many uncertainties and challenges involved in low-dose radiation optimization, citing that these goals are so complex that they may nearly be impossible.
But, let’s take another look at this. Yes—dose reduction is complex and full of potential traps leading to poor technique or image quality. However, that is not a reason to avoid implementing a dose reduction (technique optimization) program at your institution!
So, how do you lead your institution down a road towards dose reduction? First, start with Google. Read what you can find on the topic. Then, go to meetings, talks, and presentations given by experts with considerable experience in the endeavor. Finally, start at your own institution.
I would suggest trying one variable at a time. Implement a weight based (or cross-sectional area based) kVp selection program. Then, embark on understanding how to use weight (or BMI) based selection of Noise Index for automated tube current modulation. Don’t forget to check out the easy stuff – like patient centering, use of bismuth shields, and limiting Z axis. Realize that even your contrast injection protocols – volume, rate, blending – might benefit from a weight based approach. Decide how to implement iterative reconstruction, varied by body region.
With these steps you are set to embark on a continual journey. Get started… today!
RSNA (Radiological Society of North America) is the largest annual trade show in the world, with about 55,000 people in attendance for the 6 day event in Chicago, Illinois. The expo includes a large number of presentations and courses on science and modern radiology.
RSNA 2011’s two main themes were lower radiation dose in diagnostic radiology imaging (especially CT) and new technology. For lower dose, there was much material on tailoring a CT scan exactly to an individual patient – based on their body size, their cardiac output, their disease process, or the type of diagnostic challenge. Additionally, a lot about new iterative reconstructions in CT – both statistical and model based, was presented. Either method lowers dose a lot, but model based results in lowered radiation exposure by up to 80%.
New technology presentations and courses covered a range of topics including dual energy CT for better tissue characterization, and the combination of imaging modalities in one platform – like SPECT/CT, or PET/MR. These combined modalities may provide a better combination of disease identification plus precise localization.
In all, RSNA 2011 offered great insights and interesting presentations. Did you attend? Share your thoughts below!
I am often asked what, exactly, iterative reconstruction is – and why it is so important. I thought it would be a good idea to discuss what I do and what my work means for the University of Washington Medical Center and our patients.
A brief overview of iterative reconstruction
Iterative reconstruction to us means potentially significant radiation dose reduction to our patients, but the look of the CT image itself needs some getting used to. When we first got the option on our scanners, we wanted to make sure that our radiologists would be comfortable with the images produced.
So, based on our protocols at the time, we reconstructed them with varying percentages of iterative reconstruction and noise indexes, and had our radiologists evaluate the images and decide what they found to be the most similar in noise and image quality to our standard at the time.
They used a double-blind method to evaluate the images, and based on what they decided, for noise index and iterative reconstruction percentage we were able to reduce radiation dose to our patients by 40-60 percent.
The evolution of iterative reconstruction at UW
We are constantly striving for improvement in image quality and dose reduction – both of which lead to better patient care. So we look again at our existing protocols and evaluate how we can combine certain series or opt for higher noise indexes in order to reduce dose. We also introduce different percentages of the iterative reconstruction and display these for our radiologists to further evaluate.
What UW is doing that others aren’t
Our radiologists are always willing to go out of their comfort zone in order to reduce dose. I say this again because of their willingness to take the time to look at images that traditionally would not be pleasing to their eyes, but may be more than adequate for answering the questions that the ordering physicians need.
And, again, a prime example of that is the different percentages of iterative reconstructions that they’ve seen and continue to look at, in order to properly evaluate the balance of dose vs. image quality – and always striving to improve both.
Why this work is important for patients
We always put patients first. To do this, we need to make sure that we give the right amount of radiation dose. With the modern machines we have, it is far too easy to give too much dose to produce the prettiest of images, but easy is not safe. To use these modern machines properly and responsibly takes a lot of extra work to accurately and safely fine tune each protocol for each patient’s needs. Our patients deserve all of that extra effort and more.
I recently came across this video from RSNA. About halfway in, they ask the question, “What is the biggest advancement in CT technology this year?”
I would agree with Dr. Siegel that iterative reconstruction has stimulated thinking and conversation among radiologists about how to substantially lower CT dose without compromising the benefits of CT. Based on our 18 months of experience, we know the reduction is at least 40 percent with the current version of iterative reconstruction. And we suspect much greater reductions are coming. Some of the issues centers around radiologists’ “preferences” for how a CT images looks. But preferences can change, even dramatically, when driven by the hope of much lower patient dose.
What do you think – what do you view as the biggest advancement in CT?