Introduction of Ultra-High-Field MR Imaging in Infants: Preparations and Feasibility

Abstract

Background and purpose: Cerebral MR imaging in infants is usually performed with a field strength of up to 3T. In adults, a growing number of studies have shown added diagnostic value of 7T MR imaging. 7T MR imaging might be of additional value in infants with unexplained seizures, for example. The aim of this study was to investigate the feasibility of 7T MR imaging in infants. We provide information about the safety preparations and show the first MR images of infants at 7T.

Materials and methods: Specific absorption rate levels during 7T were simulated in Sim4life using infant and adult models. A newly developed acoustic hood was used to guarantee hearing protection. Acoustic noise damping of this hood was measured and compared with the 3T Nordell hood and no hood. In this prospective pilot study, clinically stable infants, between term-equivalent age and the corrected age of 3 months, underwent 7T MR imaging immediately after their standard 3T MR imaging. The 7T scan protocols were developed and optimized while scanning this cohort.

Results: Global and peak specific absorption rate levels in the infant model in the centered position and 50-mm feet direction did not exceed the levels in the adult model. Hearing protection was guaranteed with the new hood. Twelve infants were scanned. No MR imaging-related adverse events occurred. It was feasible to obtain good-quality imaging at 7T for MRA, MRV, SWI, single-shot T2WI, and MR spectroscopy. T1WI had lower quality at 7T.

Conclusions: 7T MR imaging is feasible in infants, and good-quality scans could be obtained.

Fig 1.

Different positions of the infant model in the radiofrequency coil. On the left, the adult head and torso are shown. They are used as a reference.

Fig 2.

Setup for measuring acoustic noise at the MR imaging table in the presence of the hood. This test setup consisted of a dummy bore with dimensions similar to those of the 7T MR system with a 10-mm plastic plate of polyoxymethylene to create an MR imaging table. The speakers producing the sound are positioned at 28-cm distance around the dummy bore to mimic the sound produced by the MR imaging scanner.

Fig 3.

Local SAR levels in adult head (left) and Charlie in the different coil positions. Shifts of an infant in the x and y directions are unlikely because of limited space; therefore, the results are not included in the figure. The SAR values when infant Charlie is positioned 50 mm in the x or y direction are comparable with those in the +50-mm FH position.

Fig 4.

Examples of images of different patients at 3T (upper row) versus 7T MR imaging (lower row). A and G , MRV at 3T and 7T, respectively, of a preterm infant at term-equivalent age. B and H, An SWI at, respectively, 3T and 7T of a preterm infant at term-equivalent age. C and I, The 6-week follow-up single-shot T2-weighted image of a term-born infant with a perinatal stroke. The arrows indicate perivascular spaces that were better visualized at 3T compared with 7T. D and J, A 3-month follow-up MRA at 3T and 7T of a term-born infant with an occipital stroke. E and K, T1WI (MPRAGE) of a preterm-born infant at term-equivalent age. F and L, An MR spectroscopy spectrum at 3T and 7T of a preterm infant at term-equivalent age, both with a comparable ROI in the left basal ganglia/thalami region.