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Robust fat suppression and shorter exams in pediatric imaging

Best Practice
Chung, Taylor, M.D. Children’s Hospital & Research Center Oakland • USA

MR imaging of pediatric patients can be challenging, as they are prone to movement and difficulties holding their breath. Clinicians at Children’s Hospital & Research Center Oakland (CHRCO, Oakland, California, USA), have started using 2-point mDIXON TSE as it addresses challenges related to fat suppression imaging. They obtain robust and homogeneous fat suppression in various parts of the body with different types of weighting (T1, T2, proton density) by using mDIXON TSE, as it can shorten total examination time.

 

 Taylor Chung, MD <br>
Taylor Chung, MD

mDIXON TSE for obtaining images with and without fat suppression in a single scan

“In MRI, fat suppression is used to help increase the conspicuity of pathology and distinguish the high signal intensity of fatty tissue from pathology,” says Taylor Chung, MD, pediatric radiologist at CHRCO. “I have been very interested in applying the Dixon method of separating water and fat clinically for many years because of its robustness, but scan times of the early 3-point Dixon techniques were too long for routine clinical use. Philips has developed the faster 2-point mDIXON method with TSE, which is very advantageous.”

 

Dr. Chung has begun to add mDIXON TSE to clinical exams, mainly MSK, of pediatric patients performed on Achieva 3.0T. “This allows us to directly compare mDIXON TSE to conventional TSE with fat suppression (SPIR and SPAIR). After systematically looking for any differences, we intend to switch to using just mDIXON TSE.”

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Shorter exam times

“The mDIXON TSE sequence gives us – in a single acquisition – the water-only image, the fat-only image, and the ‘full image’ (water-andfat image, both in-phase and opposed-phase). The water-only image is equivalent to a fat-suppressed image,” says Dr. Chung. “The advantage of getting the water-only image and the in-phase full image in the same acquisition is that it cuts down on the time of the entire exam. This is very helpful, as some of our pediatric patients can’t hold still for very long. Because it’s only one scan, we also avoid the problem of a patient moving in between scans with and without fat suppression, so there’s no spatial misregistration.”

 

“For instance, in a knee exam, we would normally include TSE PDweighted scans with and without fat suppression, which are two separate scans. When we change to just one mDIXON TSE PD-weighted scan, we’ll get the advantage of a shorter exam time as this is only one scan. So, the real time saving is not in the mDIXON TSE sequence itself, but in the shorter overall exam time. In fact, the mDIXON TSE is a longer scan – however, we can take advantage of the fact that the 2-point mDIXON method has increased SNR and we use a combination of decreasing NSA and/or adding SENSE to reduce the scan time. The scan time of an mDIXON TSE sequence can be made comparable to a conventional proton density TSE sequence with fat suppression, depending upon how much image noise you want to tolerate. We are still optimizing parameters to see whether we can reduce scan times and still be satisfied with the resulting image.”

Robust fat suppression

“With conventional sequences, it can be difficult to obtain good fat suppression, for instance, when imaging soft tissue masses along the side of the body, at the head and neck and shoulder areas, around the ankles, or imaging around the orbits and the sinuses,” says Dr. Chung. “mDIXON TSE helps tremendously in these challenging areas. It is a very robust sequence, since it is not sensitive to magnetic field (B0) homogeneity. This robustness allows us to maintain good quality and performance, even in areas with significant perturbation of the B0 field. We find that we can rely on mDIXON TSE to give us excellent homogeneous ‘fat suppression’ in the water-only images.”

 

“The mDIXON TSE advantage applies to T1 and T2 weighting, which is quite important,” continues Dr. Chung. “If we have problems with the traditional fat suppression in T2-weighted images, we can compromise and utilize a different type of fat suppression like inversion recovery. But in traditional T1-weighted imaging with fat suppression, there is no other choice, especially after giving contrast. When the fat suppression is not good in the post-contrast T1-weighted scan, then we’re in trouble. That’s why a robust fat suppression like mDIXON TSE is a great method there.”

Diagnostic confidence, benefit for patients

“If we can avoid troublesome inhomogeneous fat suppression artifacts versus real pathology, there is no need to add another sequence in another imaging plane or to find a different way to suppress fat; therefore we would be able to shorten the exam time. The shorter overall examination time achieved with mDIXON TSE, together with robust fat suppression, is a great benefit,” says Dr. Chung.

 

“Even before we start the MR examination, we know we’re going to get the information; there’s no choice between doing one scan or another. We don’t need to run extra sequences to get what we need. It has a huge impact on our pediatric patients, when we can say, ‘just hold on for five minutes and we’ll be done’ instead of 10 or 15 minutes. And it also means we can potentially decrease the sedation time for some patients.”

Advantages combine into a great solution

“The most significant benefit of the mDIXON TSE method is the robust fat and water separation. It consistently provides high quality effective fat suppression with the water-only image because the method is not sensitive to magnetic B0 field inhomogeneity,” says Dr. Chung. “The Dixon method for clinical MR examination has been around for over 20 years, but it always took too long. Philips developed the 2-point mDIXON method and now we have shorter overall scan times and at the same time have high quality fat suppressed images. We have started using mDIXON TSE in MSK, but I think it has the potential to be used much broader; it gives the most robust fat suppression we can get.”

 

Taylor Chung, MD, is a clinical pediatric radiologist. He serves as the Associate Director in the department of Diagnostic Imaging at Children’s Hospital & Research Center Oakland in Northern California, USA. His interests are in pediatric body and cardiovascular MR.



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Sep 5, 2014

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Best Practice
Achieva 3.0T
Fat suppression, Knee, mDIXON, mDIXON TSE, Musculoskeletal, Neck, Pediatric, Wrist
 

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