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!
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.
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.
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 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.
This is an interesting addition to the sophistication of systematic lowering of kVp during CT coronary angiography. Of course, such sophistication strongly supports 30% dose reduction without compromising diagnostic power.
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.
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.
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.
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 still true that the best way to maximize value and impact on disease while minimizing cost and radiation dose is to do only appropriate exams and not do inappropriate exams. But how to decide what is appropriate? Many of the standard criteria – such as those published by the ACR – are as evidence based as the current peer-reviewed literature evidence will support. But sometimes there may not be scientific evidence available for a hard clinical question – particularly if a randomized trial might be very expensive and take a long time. Under those circumstances, expert opinion is often a pretty good alternative.
Expert opinion can be incorporated into computerized decision support programs but also into daily practice. Indeed, every radiologist is on their own an expert in imaging and its appropriate use – which is valuable if they use this local expertise to guide choice of exams through being a consultant.
Your practice should make radiologist consultation easy to access … and widely known as a valuable service.
See this article.
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.
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.
This article goes straight to the heart of the challenge of tailoring care to each individual patient. Such a tailoring challenge bumps up against algorithmic appropriateness analyses, particularly those which are computerized for decision support. Generalized appropriateness may not ideally apply to individual patients and their unique situations.
How we balance these challenges is to be worked out – to fail at this challenge would be to compromise care, both overall and individually. The coming 5 years will be very interesting for this balance.
A University of Washington study featured in the August issue of JAMA Pediatrics claims that 4 million annual pediatric CT scans of the head, spine, abdomen and pelvis are predicted to cause nearly 5,000 future cancers, according to HealthImaging.com. However, the study goes on to state that the risk can be mitigated by CT dose reduction and appropriate imaging initiatives which have the potential to prevent more than half of the projected radiation-related cancers. Practices like eliminating unnecessary scans and targeting high-dose scans are called out in the study.
I believe that the best way to reduce radiation dose from CT in children is to not do studies which are inappropriate or which have a very low chance of producing impactful diagnostic information. The next best way to reduce dose is to pay close attention to all the tricks of technique: accurate patient centering in the gantry, use of radiation shields, use of 80 or 100 kVp, minimizing Z axis scan length, etc. Then newer technology will greatly further reduce dose – automated tube current modulation, iterative reconstruction – especially fully model-based iterative reconstruction. Together these can reduce radiation dose by 70-80 percent. Scanning in kids above 6-8 mSv should be a thing of the past and sub-1.0 mSv scans should be common.
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.
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!
I came across an article from the Journal of the American College of Radiology on a number of recommendations for optimizing patient dose level in chest CT scans, the third most commonly performed CT exam in the country.
As the article points out, the lungs are an ideal organ for low dose radiation CT scans. Some of the recommendations offered include:
- Doctors should ensure that patients understand all instructions fully, including when to hold their breath and how much movement is permitted.
- Automated exposure control (AEC) techniques should be used as often as possible to assist with breathing in children and adults.
- Iterative reconstruction techniques reduce radiation dose exposure substantially and should be performed as often as possible.
- Centering patients in the gantry isocenter avoids excessive scan length dose. Additionally, CT scans should only be performed on the area of indication.
- Reading thicker sections ensures CT scan radiation risk reduction, while allowing fine details to be examined in nosier, thicker sections. This procedure should be utilized by imaging professionals.
- All CT scans should be done for a clinical and justifiable reason.
The tips and pointers in this article are all good tools for lowering patient radiation dose in chest CT. We have found that the use of iterative reconstruction is a big help – lowering dose by as much as 40%. Now that model based iterative reconstruction has recently become available in the USA (GE’s version is called VEO), we can look for dose reductions of more like 80%!
The following is an interview I conducted with Dr. Lee Mitsumori, Assistant Professor of Radiology at the University of Washington.
Dr. Shuman: Please give us a brief overview of your work involving weight-based selection of CT parameters.
Dr. Mitsumori: We have been investigating the use of body-size-dependent CT scan parameters to optimize the radiation dose of each scan. Several imaging parameters can be modified at the time of the CT that can alter the amount of radiation of the scan (tube current, tube potential, scan range, scan phases, image reconstruction techniques). The challenge is to adjust each so that the final set of patient images are of diagnostic image quality and were obtained with the lowest possible radiation dose. The risk is that incorrect settings or too aggressive dose reduction can create a scan that is of poor image quality that does not allow a correct interpretation. Current work at University of Washington Medical Center involves studies comparing different CT image reconstruction techniques (adaptive iterative reconstruction, model based iterative reconstruction) that can significantly reduce CT image noise and how these can be best implemented in patient CT exams.
Dr. Shuman: Why is weight an important concern regarding CT? How does weight affect CT?
Dr. Mitsumori: A patient’s body size, as reflected by weight, affects two important feature of a CT scan. The first is the amount of photons needed to generate an interpretable CT image. A CT is a projection technique, where an x-ray source emits photons that then pass through the subject before being recorded by a detector on the other side of the patient. Larger patients need more photons with higher energy than smaller patients to create images that can be correctly interpreted. If the CT parameters are not correctly set and only a small number of photons are recorded by the detector, the images created are noisy. If an image is too noisy, the interpreting physician may not be able to see if a problem or disease process is present. Unfortunately, the more photons used the higher the radiation exposure of the CT exam. While large patients are at risk for having noisy images, small patients can have scans done with parameters selected for an average sized patient, in which case too many photons are used than what would be needed to create diagnostic images. Thus, the importance of matching the radiation dose (number and energy of photons emitted) with the patient’s body size to prevent non-interpretable studies in larger patients, and avoid excessive radiation dose in the smaller patient.
The second feature of a CT scan where patient size is important is in the amount of iodinated contrast needed for the scan. Iodinated CT contrast is injected intravenously during the scan and improves the depiction of the different organs and vascular structures in the body. With CT imaging, the use of contrast greatly improves the radiologist’s ability to differentiate diseased (tumors, infection, inflammation) from normal tissues. Similar to radiation dose, the amount of contrast needed to enhance the organs is dependent upon patient body size. Small patients will have smaller organs, less blood volume, and be shorter than larger patients. Thus the amount of CT contrast needed may not be the same for every patient.
Dr. Shuman: What are the risks involved when a hospital or imaging center does NOT take a patient’s weight into account?
Dr. Mitsumori: The risks for scanning with fixed CT parameters are that when compared to an average sized patient, the large patient may have scans with noisy CT images that could lead to interpretation errors, or a non-diagnostic scan in which the scan may need to be repeated or an alternative imaging test performed. For the smaller patient, the risk would be that more radiation is used than what is needed to generate adequate, diagnostic images.
Similar risks occur with CT contrast administration. If a fixed amount of contrast is used for every scan that is based on an “average” patient size, then large patients may not receive enough contrast to adequately enhance the internal organs rendering the scan potentially non-diagnostic, and the small patients are given more than the amount of contrast needed to obtain an adequate scan.
Dr. Shuman: When discussing CT exams with their doctors, are there questions a patient should ask regarding their weight? In other words, what would make an “informed patient” as it relates to weight and CT?
Dr. Mitsumori: An informed patient would want to ask if their CT scans will be performed with “patient tailored” or “patient specific” protocols that use the amount of radiation and iodinated contrast that best match the patient’s body size.
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.
A New York Times op-ed about nuclear radiation exposure, called “Unsafe at Any Dose,” got me thinking about CT scan radiation exposure – and the ongoing debate regarding CT scan risks.
Many activities and endeavors in human life have associated risk. Driving a car is risky; people die. And the more miles you drive, the greater the risk. But that does not mean we don’t use cars. Rather, we minimize risk by driving carefully, using seatbelts, etc. And we go ahead and drive in order to capture the benefits.
So it is with medical radiation… and nuclear energy. But an important note: even with Dr. Caldicott’s pessimistic predictions and numbers, if you look at human deaths associated with kilowatt hours of electrical generation, coal powered electricity is the worst. Oil is next, and nuclear is at the vary bottom of the list (i.e., it has historically caused the fewest deaths).
Makes one stop and think, doesn’t it?
Here on this blog I often talk about the importance of patient education and awareness, as it relates to CT scans, radiation dose and cancer risks. Informed patients are smart patients! To that end, I wanted to share with you an interesting resource I recently came across: a “radiation risk calculator” sponsored by the American Society of Radiologic Technologists.
According to the site, the purpose of this (free) tool is to “calculate your dose and estimate cancer risk from studies including CT scans, x-rays, nuclear scans and interventional procedures.” I think this is good for patients, if combined with counseling about the meaning of the numbers.
I always say: the more info, the better – as long as it is understood appropriately. Remember too, that a 1 in 2000 risk of causing cancer means a 1999 in 2000 risk of not causing cancer…
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!
Unfortunately, ct scan radiation overexposure continues to be a problem in hospitals and imaging facilities across the country. However, the question of regulation of dose from ct scanners is a complex issue. Many say that the best pathway to regulation is through the existing American College of Radiology mechanisms – such as certification of CT sites and subspecialty certification of both radiologists and CT technologists. This may expand to include requirements for regular monitoring of dose from typical exams and reporting the results of such monitoring to a central ACR registry.
Others advocate a role for the FDA, though that government agency may turn to a group of experts, such as the ACR or the Society of Computed Body Tomography. A national registry of individual patients which records dose from each CT exam for each patient, and cumulative dose for each patient, would also be a best practice – Europe does this now in the EU.
Finally, we need many and repeated courses, texts, electronic educational media, and monographs focused on the topic of how to consistently achieve CT scans at much lower dose than a few years ago. This education should be widely available and ongoing.
Our recent UW Symposium on Low Dose CT was a repeat from six months ago, and was equally well attended.
Check out this KING 5 news story where I discuss the recent discovery of trace radiation in milk being sold in Washington, due to the Japanese nuclear power plant leaks. As I mention in the interview, there’s no cause for concern, given the amount of radiation being detected. It’s a tiny fraction of the dose you’d be exposed to during a CT scan, for example.
Watch (and read) the interview here.
A new study published in the March issue of the Journal of the American College of Radiology shows that the use of virtual colonoscopies at U.S. hospitals is increasing – even though the procedure is not covered by Medicare.
A neat feat of virtual colonoscopy is how the radiation dose associated with the exam has dropped considerably since it was introduced. Newer reconstruction techniques on newer CT scanners have made this possible.
While it is still true that Medicare will not pay for any type of screening (except mammography), some commercial insurance companies have realized the value of screening for colon cancer, particularly in high-risk patients. Screen CT colonography does well when compared to other tests for detecting colon tumors and polyps. And patient acceptance is higher because it is quick and less uncomfortable.
…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.
One of the most common complaints of patients in the ER is abdominal pain, and as a recent article at TIME.com details, diagnosis is rarely straightforward. It is important to understand that the ER is different from other places where healthcare is provided. ER physicians see a broad spectrum of disease – from the insignificant to the life-threatening. There are great time constraints in the ER, as well, and follow-up care is hard to arrange (and may be unreliable) so there is pressure for a definitive diagnosis in a single encounter.
Physicians considering the CT scan to assist with diagnosis for abdominal pain or other illness and injuries should consider three questions:
1. Is CT the right test to do for this patient?
Many ER physicians are good at a answering this question, but it is also helpful to remember that the best expert on appropriate use is one phone call away: the radiologist. Having the patient’s EMR handy is important, too, in reporting how many CT scans this patient may have had historically, since this is a data-point in choosing whether or not to do CT. A national registry of individual patient cumulative radiation dose is coming to the U.S., similar to the one that now exists in the EEU, but it is not here yet.
2. If CT is the right test, what kind of CT?
With contrast or without? Oral contrast or not? Positive oral contrast or negative? One pass or three? Arterial or portal venous phase? Abdomen only or abdomen plus pelvis? Again, the radiologist is a valuable consultant for getting the most information about the patient’s condition at the least radiation cost.
3. How can the CT scan be done with the lowest possible radiation dose?
Finally, once the kind of CT exam is decided, how can it be done with the lowest possible radiation dose without compromising the diagnostic value of the scan. A well-informed radiologist can reduce the radiation dose per scan by up to 60 percent. For example, CT of the urinary tract with contrast now can be achieved in a single pass. Careful attention to CT imaging parameters can radically lower dose (low kVp, modulated mA, etc.). Limiting the length of the scan on the patient and careful centering of the patient by the tech can greatly reduce dose. In addition, newer scanners combine better detectors with more complex reconstruction algorithms to substantially lower dose and CT scan radiation risks.
One of the most exciting – and talked about – sessions at RSNA was called “Radiation Dose: Can It Be Too Low?” The expert panel had a healthy debate on radiation dose and risk, and finally reached an agreement that CT scans should be limited to “justified and optimized studies.” (HealthImaging.com has a good recap of the panel’s discussion.)
The debate about risk can go on, but when practicing medicine (radiology) with real patients, the obligation is to both minimize risk AND maximize benefit.
So the challenge for radiologists is to lower dose as much as possible without compromising the amazing diagnostic power of CT. How to accomplish this is both science and art. But we have discovered at UW that with a combination of low dose technique and low dose CT technology, you can take out up to 40 percent of the radiation dose to the patient (compared to 3 years ago) without having any negative impact on diagnosis. So that number certainly is achievable at most sites.
Could we go even further in dose reduction?
A new method of extracting and archiving patient CT dose information has been developed, according to a recent article in Science Daily. Called RADIANCE, this new system should help with compliance with the American College of Radiology’s reporting guidelines and build greater awareness of radiation dose to patients.
Tessa S. Cook, M.D., lead author of the study that lead to RADIANCE, says that extracted radiation dose information “can be used to perform a variety of analyses aimed at quality assurance and patient safety. The automated extraction ‘pipeline’ for radiation dose information allows us to be more cognizant of radiation dose to our patients, thus resulting in improved patient care and management.”
It is clear that we are headed toward the recording of radiation dose from each CT scan in the patient’s medical record. Initially, this will be in the PACS archive, then in the radiology information system (RIS) on the way to being in each radiology CT report. Eventually, the dose will reside in each patient’s electronic medical record (EMR) and a cumulative record as well – just as they do in Europe today in the EEU.
RADIANCE is a big step in that direction.
In the days that followed last month’s Low Dose CT Symposium, I had time to reflect on how wonderful it was that the event drew an unprecedented number of attendees. The interest in the symposium was evident by how far some attendees traveled to get there. I was also struck by the segments of the industry that were represented in the audience: technologists, radiologists, technicians and administrators were all there. It made me think about each segment’s relationship to one another, and their ability to impact change in the industry.
When driving toward much lower radiation dose in CT, it’s good to remember that a team effort is needed. Technologists must be educated on all the tricks and skills needed and must fully understand why dose reduction is important. They can help radiologists be more conscious of dose exactly when radiologists are urging technologists to pay close attention. Both techs and radiologists can use their knowledge to help educate administrators about the importance of investing in low dose CT. Everyone can help educate referring clinicians about thinking of dose when they order, both for an individual study and cumulative dose (over time) in individual patients. And it is the whole chain of providers who monitor appropriateness of studies at each and every level.
I’ve got two events coming up I’d like to share…
The first, on November 4, is the Grand Rounds conference at Overlake Hospital. The conference will focus on radiation exposure and its potential risks with regard to patients receiving multiple imaging studies/multiple radiation doses. Should be interesting!
The second, on November 6, is the Washington State Radiological Society (WSRS) annual meeting. It’s at the World Trade Center in Seattle, and it’s scheduled for 4:00 p.m. Click here for more information about this meeting. If you’d like to attend, you can find the registration form available for download here.
November’s off to a busy start!
A new piece of legislation was announced recently that radiologists all over the country are talking about: California Governor Arnold Schwarzenegger has signed a medical radiation bill into law. It’s the first state law in the United States aimed at “protecting patients from excessive radiation exposure received during CT scans and radiation therapy procedures,” as reported by Aunt Minnie.
According to the same article, the bill “requires that radiation dose be recorded on the scanned image and in a patient’s health records, and that radiation overdoses be reported to patients, treating physicians, and the state Department of Public Health (DPH).”
Both the goals of this law are very commendable and worthwhile. Putting the dose of each exam into the medical record is done in Europe now and should begin in the U.S. This will require some commitment from radiation device manufacturers and from the DICOM standard, but is quite doable.
And disclosing errors, of any type in any part of healthcare, is just part of good practice.
Last year a New York Times investigation uncovered more than 200 radiation overdose cases at Cedars-Sinai Medical Center. According to a New York Times follow-up published on July 31 this year, 200 additional cases were revealed at other hospitals leading to more than 400 cases nationwide. The radiation overdose delivered to patients in these overdose cases was between 4 to 13 times higher than a typical dose for the performed scans. These overdoses led patients to experience hair loss, headaches, confusion, and may increase their long-term risk of cancer and possible eye and brain damage. The patients had received CT brain perfusion exams, which help to identify strokes through a number of blood flow images.
Why did these overdoses happen? This could be due to equipment malfunction, the need for “prettier” clinical images (requiring high radiation dose), or a serious lack of operator knowledge in setting up the CT imaging protocols for this type of exam. CT brain perfusion is a high-dose exam but can be performed safely if the technologists, physicists and radiologists work diligently together to ensure that the CT imaging protocols are set up optimally to follow the As Low As Reasonably Achievable (ALARA) principle. The dose delivered by this exam should also be monitored on a regular basis to ensure it remains at minimal levels and no equipment malfunction or dose creep has occurred. Physicians should also be aware of the potential side effects, as discussed above, which can be triggered by such high-dose exams.
Following 2009’s overdose discoveries, the FDA launched a collaborative Initiative to Reduce Unnecessary Radiation Exposure from Medical Imaging, to promote the safe use of medical imaging devices, support informed clinical decision making, increase patient awareness, and optimize patient exposure to radiation.
At the recent American Association of Physicists in Medicine (AAPM) annual meeting, the patient safety symposium focused on these overdose cases and the AAPM CT dose summit’s recent efforts to ensure CT scan parameter optimization and patient safety. The AAPM also produces reports on quality and safety in medical imaging and radiotherapy, along with letter-writing and policy campaigns targeted at the government and public.
Researchers at Mayo Clinic are also investigating the use of new image-processing algorithms to reduce the dose for CT perfusion exams up to 95 percent and maintain the same image quality as a high-dose perfusion exam.
If appropriate steps are taken to ensure patient safety and dose optimization, the benefits from a CT brain perfusion scan far outweigh the risks associated with it.
A recent editorial in the Journal of the American Medical Association took the position that the best course of action to address the issues of CT overutilization, quality control and training would be government regulation, according to an article on HealthImaging.
In the original editorial, authors David J. Brenner, PhD and Hedvig Hricak, MD reported that “the radiation dose in America has doubled over the past 30 years, and medical imaging contributes half of the dose to the U.S. population,” as stated in HealthImaging. They argue that only through national legislation will we be able to ensure lower CT radiation dose and an improvement in overall safety to patients undergoing CT exams.
Actually, there are very good resources available now for deciding appropriateness and supporting referring physicians, such as the American College of Radiology’s (ACR) appropriateness criteria or commercially available, evidenced-based decision support programs which are built into electronic order entry systems.
Rather than have the FDA develop a new agency, perhaps wider and better application of these existing resources and regulation through societies of experts (like the ACR and the Radiological Society of North America) might be impactful.
Despite the attention being given to the cumulative CT scan radiation effect and the buzz surrounding risks of repeat CT scans, one leading expert is disputing the theory.
As reported in Diagnostic Imaging, Richard Morin, Ph.D, chair of the American College of Radiology’s safety committee says, “There is no radiation biology to demonstrate CTs are additive in any way.”
Morin uses a driving analogy that relates probability of an accident to the number of miles logged by a driver, but notes that there is not a certain mile threshold, like 200 miles, that would trigger an accident.
I like the driving analogy and used it in my recent post Measuring Risk: Driving vs. CT. Driving is something that most of us can relate to, and therefore the numbers are more meaningful, so I’ve tried to quantify it even further.
Here’s how I like to look at the risk: The risk of dying from a cancer induced from a CT of the abdomen and pelvis in a middle aged male is similar to the risk of dying in a car accident if you drive 36,000 miles – both are about one in 2000.
The debates over cumulative dose theory will continue, and so I feel it’s important to explain the risks in ways people can understand – so that they don’t turn down any life-saving exams out of fear or misunderstandings.
While Dr. Morin explains that there is no way to figure out whether a person developed cancer due to radiation, a carcinogen or chance, he does say “it’s important that the right test is ordered at the right time.” I’ll add that it’s always a good idea to look at lowering the CT dose, too.
And while the effect of cumulative dose from multiple exams is unproven, we really must take the most conservative position when it comes to public health and assume the effect is cumulative.
CT radiation dose has recently been in the limelight, not only in the news media but also for patients undergoing CT exams. Estimating CT dose is complex and further challenged by the different types of CT scanners available in the market today. In a recent study, investigators collected CT radiation dose measurement data from all the multi-detector CT (MDCT) scanners used in the National Lung Screening Trial. Radiation dose in CT is defined as CT Dose Index (CTDI). CTDI represents the average absorbed dose, along the length of the patient’s body from a series of contiguous scans. Normalized CTDI can be used to determine the efficiency of the CT scanner, and finally the dose imparted to patients. Normalized CTDI represents the dose per mAs (tube current x rotation time) where the mAs determines the number of x-ray photons utilized per rotation of the CT scanner.
The results of this study imply that one needs to be aware of the differences in normalized CTDI – not only between manufacturers, but also between models of CT scanners from the same manufacturer (Table 4 of this study).
This study showed that the average normalized CTDI varied greatly (by a factor of 2) across all scanners from different manufacturers. The dose efficiency of the CT scanners improves as the scanners get more complex, with the number of detectors along the length of the patient increasing from four or eight to sixteen and beyond (e.g.: 4- 8- or 16- slice CT scanner). This has an impact on image quality and patient dose because the more efficient the CT scanner, the less the dose to the patient to acquire the desired image quality.
The dose data in this study was collected for 96 MDCT scanners across 33 participating institutions. While the study did not focus on image quality and patient dose, it did examine scanner-specific radiation dose data across all institutions.
A recent article addressing the ongoing debate over the safe use of medical imaging features the opinions of two industry experts on how we should be working to lower radiation doses from CT scans and other imaging exams.
On one side of the debate is Dr. Rebecca Smith-Bindman, who believes that it should be the job of the U.S. Food and Drug Administration to protect patients by regulating radiation from CT scanners. “Radiation doses are higher than they should be and they vary dramatically within and between facilities and that is not acceptable,” she said in the article.
Dr. Bruce Hillman, on the other hand, believes that the problem lies with doctors who order too many scans (which can lead to finding conditions that might have been better left untreated). And, according to the article, he thinks that “heaping more regulation on an industry that has already been squeezed by Medicare cuts may squelch the kind of innovation that produced CT scanners in the first place.”
In my opinion, there are three answers to this storm:
1. We need to make greater efforts to strive for appropriate use of CT. For that we can turn to the best authority available: the American College of Radiology Appropriateness Guidelines. Computerized decision support programs in electronic medical records can help, too.
2. We need to strive for much lower radiation dose per scan. We know that the dose per scan frequently can be reduced by up to 60 percent by the use of better CT techniques (selection of imaging parameters, shielding) and by modern CT technology. Here guidelines from organizations like the Society for Computed Body Tomography (SCBT/MR), an arm of the ACR, can be helpful and can drive education for all levels of healthcare providers.
3. We need to ensure that financial incentives leading to conflict of interest are minimized, so that patients can be comfortable that any CT scans are done only for appropriate diagnostic investigation.
Finally, in all the storm about cost and radiation fear, we need to remember that CT is a very powerful diagnostic tool that provides definitive information which can be used to save lives and select the best therapy quickly. It does far more good than harm — in every institution, every day.