Motion-Compensation Techniques in Neonatal and Fetal MR Imaging

Abstract

SUMMARY:Fetal and neonatal MR imaging is increasingly used as a complementary diagnostic tool to sonography. MR imaging is an ideal technique for imaging fetuses and neonates because of the absence of ionizing radiation, the superior contrast of soft tissues compared with sonography, the availability of different contrast options, and the increased FOV. Motion in the normally mobile fetus and the unsettled, sleeping, or sedated neonate during a long acquisition will decrease image quality in the form of motion artifacts, hamper image interpretation, and often necessitate a repeat MR imaging to establish a diagnosis. This article reviews current techniques of motion compensation in fetal and neonatal MR imaging, including the following: 1) motion-prevention strategies (such as adequate patient preparation, patient coaching, and sedation, when required), 2) motion-artifacts minimization methods (such as fast imaging protocols, data undersampling, and motion-resistant sequences), and 3) motion-detection/correction schemes (such as navigators and self-navigated sequences, external motion-tracking devices, and postprocessing approaches) and their application in fetal and neonatal brain MR imaging. Additionally some background on the repertoire of motion of the fetal and neonatal patient and the resulting artifacts will be presented, as well as insights into future developments and emerging techniques of motion compensation.ABBREVIATIONS: bFFE ϭ balanced fast-field echo; FLASH ϭ fast low-angle shot; G RO ϭ readout gradient; NSA ϭ number of signal averages; PROPELLER ϭ periodically rotated overlapping parallel lines with enhanced reconstruction; RF ϭ radio-frequency M R imaging is an ideal diagnostic technique for the evaluation of infants and fetuses 1-7 because of the absence of ionizing radiation, the superior contrast of soft tissues compared with sonography, and the availability of different contrast options (T1-weighted, T2-weighted, and diffusion-weighted imaging, Fig 1) to improve characterization of both anatomy and pathology. However MR imaging remains a relatively slow technique, with scanning times for most applications in the order of seconds to minutes, leaving them susceptible to motion artifacts. The normally mobile fetus and the unsettled neonate present a major difficulty because the presence of motion during a long acquisition will decrease image quality in the form of motion artifacts (Fig 2), hamper accurate image interpretation, and often necessitate a repeat MR imaging to establish a diagnosis. This may have major emotional implications for parents and can stress the tight budgets of health care providers.

Wireless Accelerometer for Neonatal MRI Motion Artifact Correction

“…Typical artifacts obtained during neonatal in-plane head rotation, as observed visually during scanning, are shown in Figure 3 [11]. Figure 3.…”

“…Different modes of one-dimensional motion are illustrated in Figure 2 [11]. By choosing either sagittal or coronal image planes, head nodding backwards and forwards or side to side could also be corrected using this method.…”

“…The non-wireless based methods have some advantages but also suffer from increased acquisition time, limited visual access and extended reconstruction times, respectively [1][2][3][4][5][6][7][8][9][10][11]. This feasibility study measured 3D motion in real time using a wireless accelerometer to provide correction data for single angle, in-plane rotations which are common in neonatal imaging and difficult to correct with MR based navigator techniques.…”

Adaptive scan strategies for fetal MRI imaging using slice to volume techniques

“…They have the disadvantage that they cannot fully correct through-plane motion because of the spin history effect [3] and that each step of the algorithms may require several hours to reconstruct the final volume. However, because of a short scan time and their non time critical post processing, they are currently popular for fetal image analysis.…”

“…al. [3] classified motion compensation techniques for fetal and neonatal MRI into prospective and retrospective methods in addition to approaches to minimize motion artifacts by using fast imaging sequences. Prospective methods are usually navigator-based [4] or self-navigated sequences [5].…”