The Value of Oral Contrast from the patient’s point of view

Oral Contrast

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.”

Optimizing CT Radiation Doses Across Institutions Leads to Dose Reductions

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.”

 

Patients’ awareness of radiation dose and risks associated with medical imaging

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.

Revolution CT Scanner at UW Medical Center Department of Radiology

 

New National Dose Levels Established for Common CT Exams

Dr. Kanal’s Research Establishes New National Dose Levels for Common CT Exams

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.

Adopting Best Practices for CT Radiation Dose Monitoring

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.”

CT technique and technology

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.

Ureteral Stones: Reduced-Dose CT Protocol in the Emergency Department

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.

CT colonography

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.”

CT dose reduction in assessment of active Crohn’s disease

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.

Decreasing radiation dose in CT for COPD patients

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.

Reducing dose via iterative reconstruction technology

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.”

Novel iterative reconstruction method for reducing CT dose

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.

The effect of trauma backboards on CT radiation dose

This article provides another neat bit of knowledge to consider when looking for lowest dose – though this is multi-factorial.

[Excerpt below]Backboard use in ED Figure 6

“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.”

Should cumulative radiation dose be tracked?

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.

References:

  1. 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.
  2. 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.
  3. 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.
  4. 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.

Low-dose Radiation

Low-dose Radiation Not Harmful

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.
UW Medicine Physicists

UW Medicine Physicists

The value of CT imaging in clinical decision making

This article illustrates two key points:

  1. 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.
  2. 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.
CT Scanner at UW Medicine

CT Scanner at UW Medicine

Detection of pulmonary nodules with low-dose CT and iterative reconstruction

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.

Low-dose CT enterography

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.)

Reducing dose for CT pulmonary angiography

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.

Gentle and wise use of CT radiation dose

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.

Radiation Dose Management in CT: Is it easy to accomplish?

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.

The importance of dose alerts

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.

 

Low dose techniques for urinary stone detection

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.

CT Colonography: Reducing the Radiation Dose

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.

Low dose CT Revolution scanner

Seattle King5 TV’s Jean Enerson reported recently on UW Medical Center’s installation of the GE Revolution CT scanner.

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:

    • TAVR
    • All aortograms
    • Cardiac
      • 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)

 

Low radiation dose without compromise of image quality

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.

Annual screening for lung cancer low-dose CT

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.

Radiation protection shielding

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.

Reducing radiation dose in diagnostic CT of the abdomen

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.

Lowering radiation dose without affecting diagnostic confidence

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

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

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

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

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

Achieving appropriate radiation dose for coronary CT angiography

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.

Reducing radiation dose for CT enterography

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.

A thoughtwise approach to CT iterative reconstruction

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.

Low-dose CT technique in diagnosing Crohn’s disease

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.

Lowering medical radiation dose with CT and other modalities in cancer patients

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.

The Challenge of Tailoring Care to Individual Patients

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.

The Truth about CT Exposure: 1980 to 2012

recent article published in CA: A Cancer Journal for Clinicians states that education of referring physicians, more assertive radiologists, and an increased use of healthcare IT are the keys to reducing patient exposure to radiation.

While these assertions may be true, the article also touched on rising radiation exposure due, primarily, to CT scans. Since the early 1980s, the estimated per capita dose from medical radiation in the US has increased significantly. But this isn’t the whole story…

While it is true that medical radiation from CT has increased markedly since 1980, so has the benefit to health from CT. We no longer do “exploratory surgery” for example, in order to sort out complex diagnostic imaging challenges. The false negative rate from Appendix surgery has plummeted. And cancer diagnosis rates overall are declining while cancer cure rates have gone up substantially, particularly in the last 5 years.

Meanwhile, the radiation dose per CT scan has gone down dramatically as the principles of low-dose CT continue to be better understood and implemented. Scans that used to require 25 mSv of radiation are now being done for 20% of that amount. While negative effects from low dose radiation have never bee proven (below 50 mSv), we still strive to keep our doses as low as possible.

So the issue is not radiation cost, but cost/benefit ratio. Driving a car is dangerous too, but we accept the cost/benefit ration. For CT that ratio is much better!

Dual- Energy CT: Less Radiation, Higher Image Quality

recent presentation at the 2011 International Society for Computer Topography (ISCT) meeting in San Francisco highlighted the effectiveness of using dual- energy CT for abdominal imaging. This CT- technique has become more promising for uncovering certain pathology that has otherwise been hidden by traditional diagnostic imaging procedures.

Dual- energy CT- by whatever technology – can be configured to employ less radiation than single energy CT. But for some specific applications, it produces more diagnostic and specific information. Dual- energy CT currently may be the best radiology technique for characterizing urinary tract stones to their chemical composition (which determines whether medical, shockwave, or laser therapy will be required), characterizing small renal masses, and characterizing liver masses into cyst versus tumor.

Additionally, dual- energy CT may apply to better detecting minimal liver tumors, lowering the amount of iodine needed for CT angiograms, and creating virtual non- contrast scans. The latter may reduce the overall CT radiation dose of a multi- phase study by 20 to 50 percent!

While dual- energy is still relatively new to the field, it is clear that it is a promising technique for CT dose reduction, while maintaining imaging quality. Further research and testing will be conclusive of the absolute benefits of dual- energy CT.

UW’s Team Approach to Radiation Dosage Reduction

A recent article published in the American Journal of Roentgenology touched on the importance of taking a team wide approach to CT radiation dose reduction. While CT only account for about 15 percent of diagnostic imaging exams, it is responsible for contributing up to 70 percent of radiation dosage to the population, according to this study. Hence, the reason why it’s imperative to have the whole team on board when it comes to reducing CT scan radiation exposure in patients.

Ensuring that CT exams are appropriate is a critical component of overall dose reduction. At UW, we use a computerized Decision Support program, which acts at the point of Computerized Physician Order Entry (CPOE) to check appropriateness. Radiologists also double-check at the time of electronic protocoling.

At the time of the scan, the use of external body shields – including breast shielding – is important. Additionally, patient centering in the gantry is critical and can lower dose by as much as 40% compared to off-center exams. The routine use of iterative reconstruction technique – compared to the older FBP – can further substantially lower dose.

By having low- dose protocols and procedures set in place, we can be sure that we are providing our patients with the safest, most effective imaging procedures!

Abdominal CT Scans: How Low a Dose is Low Enough?

I was recently asked the question: “How low is low enough for CT?” With the risks of CT scans, the answer is: as low as you can go without significantly compromising diagnostic power.

Sometimes we do very noisy CT exams at extremely low doses, knowing that we may miss a 1 mm ureteral stone. However, we accept that possibility since such a small stone may not be clinically relevant.

Our routine abdominal/ pelvic exam is noisier than most of the CT exams we see referred in – but we deliberately chose to become accustomed to the higher noise levels (even when using  iterative reconstruction) in order to minimize CT radiation dose. Thus, our doses are 40 percent lower than those on some of the CT scans we see being administered at many other places. There is no evidence we have compromised diagnostic power with our reduced dosage CT scans.

In today’s world, the 1-3 mSv cardiac CT is commonplace. In the near future, a CT of the abdomen and pelvis (40 cm of Z axis) using 0.6 mSv will soon be commonplace with the arrival of model based iterative reconstruction. With MBIR recently becoming available in the United States we will soon see dose reductions of up to 80 percent!

Frequent CT Scanning Not Linked to Cancer Diagnosis

study published in a recent issue of the Journal of American College of Radiology asserts that CT -induced cancers are more likely to occur amongst rarely scanned young adults, as opposed to frequently scanned patients–the group that many assumed was at the highest risk for radiation induced cancer diagnoses.

It is still true that a definite relationship between cancer induction and less than 100 mSv of radiation has never been proven. This is assumed, for safety’s sake – based on proven relationships with much higher doses of radiation. Remember, a typical CT of the abdomen and pelvis in the modern world is about 6-10 mSv.

The other variable that has never been proven is the assumption that the risk from multiple scans which are widely spaced in time is additive. In fact, we know that the body has tremendous capacity to heal and repair any kind of damage – so any damage from a single event of low dose radiation may be fully repaired before a second event occurs. Hence the effect may not be at all additive.

So… results like those found in this article are not surprising.

Nothing, however, should lessen our vigilance about striving for as low a radiation dose as possible for all medical diagnostic imaging applications. In a world of unknowns (and possibly unknowable’s), that’s just common sense.