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

 

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 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.

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.

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.

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.

Optimizing Radiation Dose

Standardizing dose description parameters and metrics is an ongoing and very active area in ACR and nationwide. This will be a big help to comparing metrics between institutions and over time. The SSDE (Size Specific Dose Estimate) is a good step in that direction.

But this article also points out the large impact of exam appropriateness on dose. It is an impressive fact that a profound way to lower population dose is to avoid doing inappropriate exams. Tools such as the ACR Appropriateness Criteria or Computerized Decision Support at the point of order entry can empower appropriateness review. And every radiologist needs to increase their awareness of exam appropriateness in daily work.

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.

CT radiation dose reduction by iterative reconstruction in lymphoma staging

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.

Educating patients about radiation dose

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.

Significant radiation dose reduction without sacrificing image quality

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.

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.

Striving towards ALARA

This direction of combining a higher noise index (NI) to get lower dose images and then correcting for the resultant noise by using an increased percent of iterative reconstruction (ASIR) is exactly the way to go when striving towards “as low as reasonably achievable” (ALARA) – in my opinion.

At UWMC, we have for a couple of years now gone even further – we use NI in the 30-36 range and routine 70 percent ASIR as a standard for all our CT imaging except high resolution lung (which is NI 25 and ASIR 30%). According to the ACR CT Dose Registry, we are in the bottom 10% of their data base for CT dose….. but the images are very good.

Check out this article to learn more.

CT Scans and Children–Consider the Risk/ Benefit Ratio

A new pediatric imaging study has been making headlines, but it’s important for patients to keep in mind both the risks and benefits of CT scans when evaluating the research. The study, published this week in Lancet, a British medical journal, claims that CT scans expose children to cancer causing radiation.

According to the researchers, for every 10,000 CT scans performed on children under the age of 10, one additional child will get a brain tumor and another child will get leukemia within 10 years of the initial scan. The research claims that these cancers would not have otherwise been expected regardless of medical imaging exams.

However, this article documents an extremely small risk. In fact, this figure is less than what we have been assuming historically prior to any evidence. But, the article also cautions that any decision on whether or not to scan should involve a risk/ benefit ratio consideration. The study does not change our assessment of risk in that ratio. Thus, the potential benefit from CT remains the critical determinant on whether to perform a scan.

As always, the ACR appropriateness guidelines help with that assessment. That also is the role of trained Board Certified radiologists—to know and advise about when CT scanning creates a risk/ benefit ratio strongly in a patient’s favor.

Remember parents, discussing the risks of CT with your health care provider should certainly be done, but be sure to get the full set of facts before refusing care that may save and extend a child’s life.

Obesity and CT Scan Radiation—Technology Helps to Cut Exposure

Most medical equipment is not designed for obese patient optimization, including diagnostic imaging modalities. Due to this, overweight and obese individuals are subject to higher levels of radiation during routine CT scans and X-rays.

A recent study, published in the Journal of Physics in Medicine and Biology, calculated exactly how much additional radiation overweight patients are exposed to from CT scans. According to the research, obese men and women receive 62 percent and 59 percent more radiation during CT scans than normal weight individuals. However, new technology can help control that percentage.

Phantoms, realistic 3-D computer models of overweight and obese men and women, can now be used to determine the risk of radiation scans on different body types.  The use of various sized phantoms to study CT dose distribution within the human body is a very scientific approach when considering the effects of CT. This technology will be able to accurately tell radiologists how much radiation patients receive from different devices so that they can make the safest and optimal choice for the patient.

Notice, this article highlights the significant increase in radiation dose—especially in obese patients—from increasing kVp to 140. At UW, our technologists use 140 kVP for CT only after having a conversation with a radiologist about each specific case.

Learn more about the use of phantoms for obese patients here.

UW and the ACR Dose Registry

The American College of Radiology’s (ACR) Dose Index Registry pilot project has already amassed a number of studies, according to a presentation given at RSNA 2011. The program strives to accurately track CT radiation dose in order to establish national benchmarks, allowing practices to monitor radiation dose exposure and compare patterns. Although only launched in June 2011, the Dose Index Registry is already up and running and any medical imaging facility can now register for the program.

The University of Washington was the second institution to sign up for the ACR Dose Index Registry. Using a DoseWatch product, we will get real time information on every CT scan and every patient scanned, including the dose each machine puts out in general, and dosage each patient is exposed to per scan and over time. This information then gets forwarded to the central registry maintained by the ACR for monitoring and for comparison purposes.

This should be a very powerful monitoring program and a big boost to safety. We are glad to take part in the program and look forward to the insights that being part of the Dose Index Registry can provide!

Radical Breakthrough in the Drive toward Lower Dose

GE recently announced the introduction of a breakthrough low- dose imaging reconstruction technology in Canada. This CT image reconstruction technology, called Veo, is the first Model- based Iterative Reconstruction (MBIR) technique.  The technology is a response to radiologists’ demand for a technique that maximizes CT image clarity and quality while optimizing the dosage level for patients’ safety.

MBIR is indeed a radical breakthrough in the drive toward lower dose CTs. While very computationally intensive, this technique allows marked reduction in patient dose from CT (by up to 80% or greater), yet also provides some improvement in spatial resolution without compromising contrast resolution. How could all that be possible – seemingly defying the laws of physics? The answer is in the much faster computational speeds of the modern computer chip.

The University of Washington will be part of the group assessing the degree to which MBIR, commercially known as Veo, outperforms more traditional CT reconstruction techniques.

Time Saved Does Not Justify Inaccuracy

A recent article on Time.com discusses situations where physicians may “bend the truth” in order to arrive at quicker results – in this case, the decision to perform an appendectomy.

CT scanning without oral contrast for possible appendicitis gives up several percentage points in accuracy. A radiologist may mistake a non-contrasted terminal ileum for an inflamed appendix. And the earliest sign of appendicitis is called the arrowhead sign, which is contrast in an edematous appendiceal orifice – cannot be detected without the contrast. Many surgeons take comfort from the presence of contrast in the appendix as evidence that portion of the appendix is not obstructed and inflamed.

Sure you can cut corners and save time. The ultimate time-saving corner to cut is to not do a CT and just decide based on physical exam plus lab results. The accuracy of CT without contrast is similar to that approach. But if we do CT in order to get more accurate diagnosis, we need to have the CT do its best job in terms of accuracy… which requires oral contrast.

In my opinion, the time saved by doing CT without oral contrast definitely does not justify the loss in accuracy. Pressure to practice this way comes from well intentioned folks who do not have to interpret CT exams themselves, and stand by the results.