Our experience at UW Medicine Radiology mirrors that of the authors in this article. DECT image quality is very much better with the current reconstruction software. It now rivals SECT in image quality and is the same in radiation dose. But tissue characterization is better and iodine contrast is much brighter – you may need much less injected contrast (up to 70% less).
This interesting article documents both the degree of CT dose reduction from model-based iterative reconstruction and improvement in image quality when looking at lung parenchyma detail.
This study 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.”
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.
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.
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.”
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.
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.
Here’s a neat trick for dose reduction in appendicitis CT cases – which often are done in young patients.
It falls into the general category of only scanning as much Z-axis length as is needed to address a given indication – and no more.
Guest blog by Kalpana M. Kanal, PhD, Director of Diagnostic Physics Section and Associate Professor in the Department of Radiology at University of Washington
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.
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.