Abstract
Introduction: Premature babies in Neonatal Intensive Care Units (NICUs) are among the most fragile patients treated today. They are very sensitive to light, sound, temperature and physical disturbances. For these babies even subtle environmental changes and/or injuries can have life-long consequences. While NICU babies have many medical conditions that could be diagnosed with modern imaging techniques, in reality babies are rarely sent out of the NICU for advanced imaging exams such as Magnetic Resonance Imaging (MRI). This is because the risk of moving a premature baby typically outweighs the medical benefits of the exam.
Methods: To overcome the challenges of imaging premature babies we have created a new type of MR scanner that is small enough to be placed directly in the NICU. This 1.5 Tesla MR scanner has a footprint of only a few square feet, and was created by converting a small-bore magnet designed for imaging adult knees (Optima™ 430s, GE Healthcare) into one suitable for whole-body imaging of premature babies. A new patient handling system and new RF coils were made to address the special needs of infants. We also outfitted the new scanner with the same high-performance control electronics found on conventional large-bore MR systems to ensure that there are no compromises in image quality. The system supports 16-channel multi-coil arrays, a full complement of MRI protocols, and advanced pulse sequences found in most imaging centers.Results: The NICU MRI scanner at CCHMC was successfully tested in a pilot study of 15 babies. The scanner met all expectations, and provided MR images that matched or exceeded that possible with a conventional large-bore system. On average, the imaging protocols were found to be 11 dBA quieter than a conventional system, and with hearing protection, all babies were exposed to less than 64 dBA acoustic noise during scanning (i.e. equivalent to a normal conversation). More significant was the reduction in time needed to move the baby from its crib, to the scanner, and back. Because the NICU scanner is co-located with the babies, and because the scanner is customized for infants, the average transport time (bed to scanner and back) was less than 30 minutes. This is a dramatic improvement over the current practice of moving babies between departments, which is often a multi-hour ordeal. Clinical use of the scanner has begun and to date we have scanned approximately 450 babies. In general, images obtained with the new scanner have equal or better image quality to that obtained using identical protocols on conventional large-bore scanners.
Discussion: The small size of the new NICU scanner offers advantages over large-bore systems. For example, the new NICU systems employ a gradient subsystem that is twice as fast (slew rate = 300 mT/m/ms), and twice as strong (gradient amplitude = 70 mT/m) as that found in a conventional adult-sized MR system. This increase in gradient performance is key to pushing the NICU systems’ imaging capability. Because the gradient coils are smaller, however, they also provide a substantial reduction in acoustic noise. When combined with other noise reduction strategies, we believe that scanning neonates without hearing protection may be possible.
The new NICU MRI scanner provides an opportunity to revisit almost everything that is known about MRI. We expect that MR’s new-found accessibility to neonates will open up new clinical horizons. We also expect that the capabilities of the new scanner will take MRI into realms that are not possible with large-bore MR systems. No longer will the premature baby’s small size put him/her at a disadvantage when it comes to MR, but instead it will enable MR imaging beyond that possible in an adult scanner.
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