Imaging technique shows success as alternative to MRI in restless children

Scientists have found a viable alternative to conventional MR imaging in pediatric patients who have a hard time keeping still during exams, according to a study published this month in the American Journal of Roentgenology.

Magnetic resonance imaging is a common diagnostic technique in children, since, unlike CT scans, it provides superior soft-tissue contrast and involves no radiation exposure, Ji Eun Park, MD, and colleagues wrote. But MRI still presents a major issue in younger patients—restricted movement.

Magnetization-prepared rapid acquisition gradient echo, or MP-RAGE, is one of the more routinely used sequences for acquisition of T1-weighted 3D datasets of the brain, the authors said. MP-RAGE sequence has the ability to provide high spatial resolution and “excellent” tissue contrast, but the method is especially susceptible to patient motion and flow-related artifacts due to the fact that its k-space acquisition entails conventional cartesian sampling, meaning data are compiled along parallel lines.

Movement during the imaging process, then, can offset the phase encoding scheme that makes MP-RAGE successful.

“Motion artifact is a more important problem for young children, because children often do not have the ability to remain still for the necessary time,” Park et al. wrote.

Changing k-space acquisition can reduce motion artifacts, the paper stated, by switching the acquisition to different sampling strategies. One such strategy is a radial sampling technique called the radial volumetric interpolated breath-hold examination (radial VIBE), which uses varying sampling directions and oversampling of the center of the k-space as an alternative to the traditional cartesian sampling technique.

“To our knowledge, there have been no previous studies in which the radial VIBE sequence has been applied to brain MRI, especially in children,” Park and co-authors said. “The aim of this study was to evaluate the usefulness of the radial VIBE sequence for contrast-enhanced brain MRI of children through comparison with the MP-RAGE sequence.”

The researchers used data from 65 contrast-enhanced brain MRIs for their work, performed with both axial MP-RAGE and radial VIBE sequences. Results were scored based on coefficients of variants of white and gray matter, relative contrast between tissue types, motion, pulsation artifacts, overall image quality and lesion conspicuity.

For children who moved excessively while in the machine, additional qualitative and quantitative subgroup analyses were performed, the authors wrote.

Park and the team found that overall, images obtained with the radial VIBE technique were of higher quality than MP-RAGE images, and scored better in almost all qualitative categories, suggesting a radial fat-suppressed T1-weighted gradient-echo sequence is a viable alternative to conventional cartesian acquisition for contrast-enhanced brain imaging in restless children. In children who could remain still, though, the MP-RAGE technique produced better results.

“Many pediatric patients cannot stay still during MRI examinations, which decreases the image quality of the conventional contrast-enhanced MP-RAGE sequence,” the authors wrote. “We found that the radial VIBE sequence reduces motion-related artifacts in brain imaging.”