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.”

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.

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.)

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.

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.

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.

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.

Using CT to Search for Urinary Tract Stones

CT to search for urinary tract stone is a very commonly performed procedure because both negative and positive results may have significant impact on subsequent patient care. Often the patients are younger since stones can occur at any age.

This article presents very encouraging news about significantly lowering the dose of a CT for urinary stones by using statistical iterative reconstruction – yet with acceptable image quality and no loss of diagnostic power.

This report adds to a rapidly growing body of data about both statistical iterative reconstruction and model based iterative reconstruction for various types of CT exams.  This body of data almost uniformly reports substantial patient radiation dose reduction in the 30% to 60% range with equal or even better image quality.

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.

New Algorithm Provides Lower Radiation Dose, Better Image Quality

At the recent International Society for Computed Tomography (ISCT) meeting in San Francisco, studies were presented showing that CT scanning with a new algorithm, called model-based iterative reconstruction (MBIR), could offer better image quality and lower radiation dose than scanning with an adaptive statistical iterative reconstruction (ASIR).

According to AuntMinnie.com, “researchers claim that MBIR outperforms previous efforts to maximize the utility of low-dose CT exams, with researchers reporting excellent image quality and enhanced lesion conspicuity.”

University of Washington is one of the international sites for the multi-center trial of MBIR. My colleague, Paul Kinahan, was one of the two scientists who reported on MBIR images at the ISCT meeting.

We are very impressed with the technique here – it may someday result in a further huge dose reduction for CT. At this point it is in early stages of development and assessment of its clinical impact has not yet begun. But it looks very promising!