Our experience at UW Medicine Radiology mirrors that of the authors in this article. DECT image quality is very much better with the current reconstruction software. It now rivals SECT in image quality and is the same in radiation dose. But tissue characterization is better and iodine contrast is much brighter – you may need much less injected contrast (up to 70% less).
This interesting article documents both the degree of CT dose reduction from model-based iterative reconstruction and improvement in image quality when looking at lung parenchyma detail.
This study further validates that model-based iterative reconstruction can decrease CT exam dose by 50-80% without compromising diagnostic power. There now is a substantial accumulation of published reports of this type in multiple body areas and organs. The same is becoming true for blended types of adaptive statistical plus model based (minus the optical components) iterative reconstruction (such as ASIR-V).
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!
The authors raise this question from a patient-centered approach: “What would patients choose if given the option to drink or not drink oral contrast material, and why? Some patients might prefer a risk-averse approach and prioritize diagnostic accuracy, whereas other patients might prefer a comfort-based approach and prioritize examination comfort. Asking patients how they value these trade-offs can inform an optimal imaging strategy.”
Modern oral contrast (diluted Omnipaque) is tasteless and odorless. Most patients think they are drinking water. But, it significantly increases diagnostic accuracy, particularly in cases involving GI questions.
These authors concluded, “If oral contrast material has any diagnostic benefit, most outpatients (89%) would rather drink it than accept any risk for missing an important finding.”
This excellent research from UCSF documents that education about best CT dose practices has a significant impact. The authors state, “The project strategy was to collectively define metrics, assess radiation doses, and move toward dose standardization. This article presents the results of our efforts using a combination of facility-level audit and collaborative efforts to share best practices.”
In this article, the authors discuss how awareness of dose and risks of medical imaging by patients can facilitate shared decision making and reduce unnecessary radiation exposure.
Kalpana M. Kanal, Ph.D., a medical physicist, professor and section chief in diagnostic physics in the Department of Radiology at the University of Washington School of Medicine, Seattle, and colleagues examined actual patient data from the American College of Radiology (ACR) CT Dose Index Registry to develop size-based DRLs that enable healthcare facilities to compare their patient doses with national benchmarks and more effectively optimize CT protocols for the wide range of patient sizes they examine.
The use of DRLs have shown to reduce overall dose and the range of doses observed in clinical practice.
Dr. Kanal’s research is published here in Radiology.
This landmark work is very helpful in benchmarking CT dose levels. It will be widely cited, I predict. Congratulations, Kalpana!
Kalpana M. Kanal, Ph.D.
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.”
This article highlights the wide variation in CT patient radiation dose between similar institutions for similar exams. Recent analysis of ACR dose registry data also suggests there is wide variation amongst different regions of the country.
Such variations suggest that attention to the details of CT technique and technology can produce CT exams at much lower dose – presumably without compromising diagnostic power.
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.
Study concludes that ultralow-dose CT may substitute for standard-dose CT in some COPD patients
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 provides another neat bit of knowledge to consider when looking for lowest dose – though this is multi-factorial.
“Rate of backboard use during CT examinations of the chest–abdomen–pelvis performed in the ED from 1 January 2010 to 31 December 2012 (n=1532). Note the dramatic drop in backboard use in 2011 after multidisciplinary implementation of a policy for prompt removal of patients from backboards using primary clinical survey rather than waiting for a CT examination.”
Guest blog by Kalpana M. Kanal, PhD, Director of Diagnostic Physics Section and Professor in the Department of Radiology at University of Washington
In a recent article published online1, the authors state in their introduction that radiation dose risk is cumulative and an increasing number of patients are undergoing multiple follow-up procedures at regular intervals. Is cumulative dose of concern in patients who have repeated scans? The jury is still out on this question. There is support for tracking cumulative dose2 as well as thought that cumulative dose should not be given any importance when making decisions about individual patients3, 4.
Radiation risk is based on the linear no-threshold model which states that all radiation exposure carries some risk but these need to be weighed against the benefits of the radiation exposure. This linear relationship implies that irrespective of which CT scan a patient is receiving, the absolute risk is the same. There is no increase in sensitivity from the increasing dose received from repeated CT scans, only an accumulation of probability. The linear no-threshold model would break down and not make any sense if there was an increase in sensitivity from repeated scans.
Consider the analogy of driving to work every day which has a risk of a fatal automobile accident associated with it. We do not keep track of the number of times we have driven in the past and its influence on whether we drive tomorrow or not. Similarly, as far as medical decisions are concerned, cumulative dose should not play a factor in deciding if a CT scan should be ordered or not. The benefit of getting the CT may far outweigh the risks. Also, individual risks are hard to quantify as all our risk models are based on large population data.
It is very important that we do not misuse the patient history information about previous scans to influence our medical decision today. Educating the physicians and the public on this is paramount to avoid such misuse.
- Roobottom CA and Loader R. Virtual Special Issue Radiation dose reduction in CT: dose optimisation gains both increasing importance and complexity! Clinical Radiology, 2016; 71(5): 438–441.
- Sodickson A, Baeyens PF, Andriole KP, et al. Recurrent CT, cumulative radiation exposure, and associated radiation-induced cancer risks from CT of adults. Radiology 2009; 251: 175-84.
- Durrand DJ, Dixon RL, Morin RL. Utilization Strategies for Cumulative Dose Estimates: A Review and Rational Assessment. Journal of the American College or Radiology 2012; 9: 480-485.
- Eisenberg JD, Benjamin Harvey HD, Moore DA et al. Falling Prey to the Sunk Cost Bias: A Potential Harm of Patient Radiation Dose Histories. Radiology: 2012; 263(3): 626-628.
To quote the American Association of Physicists in Medicine:
- The risk from medical diagnostic radiation in doses below 50 mSv as a single dose or 100 mSv as a cumulative dose is too small to be measured and may be non-existent.
This article illustrates two key points:
- CT information is particularly impactful in the ER environment where they need correct diagnoses quickly in order to initiate therapy and triage patients safely from crowded facilities.
- Dual energy CT provides incremental diagnostic information in the ER setting but without any incremental radiation dose – so using it routinely for certain indications may be effective.
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.
Guest blog by Kalpana M. Kanal, PhD, Director of Diagnostic Physics Section and Associate Professor in the Department of Radiology at University of Washington
At the AHRA conference in Las Vegas recently, Dr. Pizzutiello, a medical physicist, discussed the complexity of CT radiation management and monitoring in diagnostic imaging. With the growing use of CT exams being performed and radiation dose in CT being a hot topic in the radiology community, it is imperative to monitor radiation dose from the CT exams as well as observe trends over time. Regulations now require that CT dose has to be documented and available on demand, CT protocols be revisited on an annual basis and incidents with high dose CT exams be reviewed. Several states around the US have CT regulations or are in the process of regulation implementation. It is a monumental task to monitor and manage dose, especially for large hospitals.
There are several dose management software products available that can help in managing the dose. Dose management is, however, a team effort and it is not possible to do this effectively without a team of radiologists, technologists, and medical physicists participating in this important task.
At our institution, we have been managing dose using a commercial product, Dose Watch (General Electric Healthcare) and also have a radiation safety committee within the department to review dose trends and make intelligent decisions based on our dose data. We have also been participating in the ACR CT Dose Index Registry since its inception and review our trends and benchmark values to our peer institutions. This is definitely a good idea if one is unaware of dose trends at their institution and how it compares to others around the nation.
Dose monitoring is complex but a necessary patient safety tool and, if well planned, can be accomplished and maintained with the help of dedicated professionals who understand the importance of the task.
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 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.
Seattle King5 TV’s Jean Enerson reported recently on UW Medical Center’s installation of the GE Revolution CT scanner.
The new technology of the Revolution features the following:
- Much longer and wider detector
- (16 cm vs. 4 cm)
- Much faster rotation speed and scanning
- (0.28 seconds – 70 G’s centrifugal force)
- Much better radiation dose lowering technology
- ASIR-V, auto kVp, density modulated auto mA
16 cm wide-detector array: Whole organ scanning on one 0.2 second rotation
Currently, the Revolution CT scanner is being used at UW Medicine for scans of the heart, blood vessels, and organs that involve more than one pass and the evaluation of transplanted organs. In the future, we intend to expand further into:
- All aortograms
- coronaries, perfusion, congen., ablation
- All misc. vascular studies
- Renal arteries, HA, runoffs, carotids, COW, grafts/stents, venograms
- Non-Dual-Energy multi-pass exams
- Liver, pancreas, IVP
- Perfusion (brain, transplants, tumor)
- Workhorse (CAP, KUB, brain, spine)
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.
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.
Here’s a neat trick for dose reduction in appendicitis CT cases – which often are done in young patients.
It falls into the general category of only scanning as much Z-axis length as is needed to address a given indication – and no more.
Guest blog by Kalpana M. Kanal, PhD, Director of Diagnostic Physics Section and Associate Professor in the Department of Radiology at University of Washington
In a recent article, radiation dose was dramatically reduced when technical changes combined with radiation safety initiatives were implemented for adult and pediatric patients undergoing procedures in a cardiac catheterization lab. The air kerma was compared between the first year and the final year of the study. Radiation safety initiatives such as formation of a safety committee, dose reporting and fellow training were implemented into the practice along with technical changes such as reduced dose rates and removal of grid for smaller patients. Considering all procedures, the air kerma decreased by 61% which was significant. For pediatric patients in age range 10-17, the air kerma decreased by 74% which is important as these patients are at higher risk than adults.
This study is important as the patients undergoing cardiac catheterization procedures typically receive high doses and are also potentially repeat patients. This study demonstrated that increased provider awareness combined with radiation safety initiatives, education and technical changes does have an impact on reducing radiation dose.
Standardizing dose description parameters and metrics is an ongoing and very active area in ACR and nationwide. This will be a big help to comparing metrics between institutions and over time. The SSDE (Size Specific Dose Estimate) is a good step in that direction.
But this article also points out the large impact of exam appropriateness on dose. It is an impressive fact that a profound way to lower population dose is to avoid doing inappropriate exams. Tools such as the ACR Appropriateness Criteria or Computerized Decision Support at the point of order entry can empower appropriateness review. And every radiologist needs to increase their awareness of exam appropriateness in daily work.
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.
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.
It is often said that radiation from diagnostic imaging is not an important issue in cancer patients.
But this report suggests otherwise – as expressed by oncologists.
Many patients with cancer are young and/or are being treated for cure. Many have long life expectancies despite having cancer.
And the basic principal of “Do no harm” plus that of ALARA still apply – as much to cancer patients as to any other patient with a serious disease.
So we should be striving for maximal diagnostic information from minimal radiation dose with CT and other modalities in cancer patients, too.
“Don’t Skip the CTA” that’s the word going out to patients with advanced renal failure based on findings of researchers in Baltimore. In a study presented at June’s International Society for Computed Tomography (ISCT), Dr. Barry Daly demonstrated how CTA using moderate doses of IV contrast negatively affects only a small percentage of patients and provides valuable information that outweighs the chance of adverse effects.
However, because lower dose is better for patients, especially that small portion at risk with normal doses, Daly and his team also did a study of low-kVp, low-contrast-dose CTA in chronic renal failure patients. This technique is possible due to the advances in CT technology that have allowed radiologists the ability to get more out of smaller amounts of iodine.
While the low kVp techniques enabled much lower doses of iodinated contrast and resulted in images that looked great, the dual-energy CT technique may have accomplished this effect even better!
With dual-energy, you get the best of both worlds. You get the benefit of lower kVp effect (kEv in GE units), plus the ability to look at images which are equivalent to 100 or 120 kVp from the same CT raw data. Essentially, you still achieve substantial iodine dose reduction, but also get very dense HU enhancements in vessels and organs.
The bottom line is this: CTA isn’t something that patients with advanced renal failure should think about skipping. There is a too big a risk for going into surgery without one. The key is finding the safest technique to reduce the dosage level of iodinated contrast while getting the best images. Dual-energy CT may be the best solution out there.
The American College of Radiology’s (ACR) Dose Index Registry pilot project has already amassed a number of studies, according to a presentation given at RSNA 2011. The program strives to accurately track CT radiation dose in order to establish national benchmarks, allowing practices to monitor radiation dose exposure and compare patterns. Although only launched in June 2011, the Dose Index Registry is already up and running and any medical imaging facility can now register for the program.
The University of Washington was the second institution to sign up for the ACR Dose Index Registry. Using a DoseWatch product, we will get real time information on every CT scan and every patient scanned, including the dose each machine puts out in general, and dosage each patient is exposed to per scan and over time. This information then gets forwarded to the central registry maintained by the ACR for monitoring and for comparison purposes.
This should be a very powerful monitoring program and a big boost to safety. We are glad to take part in the program and look forward to the insights that being part of the Dose Index Registry can provide!
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.
GE recently announced the introduction of a breakthrough low- dose imaging reconstruction technology in Canada. This CT image reconstruction technology, called Veo, is the first Model- based Iterative Reconstruction (MBIR) technique. The technology is a response to radiologists’ demand for a technique that maximizes CT image clarity and quality while optimizing the dosage level for patients’ safety.
MBIR is indeed a radical breakthrough in the drive toward lower dose CTs. While very computationally intensive, this technique allows marked reduction in patient dose from CT (by up to 80% or greater), yet also provides some improvement in spatial resolution without compromising contrast resolution. How could all that be possible – seemingly defying the laws of physics? The answer is in the much faster computational speeds of the modern computer chip.
The University of Washington will be part of the group assessing the degree to which MBIR, commercially known as Veo, outperforms more traditional CT reconstruction techniques.