Neuroimaging technologies continue to evolve, but there remain three basic methods utilized in the neonatal population – Cranial Ultrasound, Magnetic Resonance Imaging (MRI), and Computed Tomography (CT). These technologies are complex, but a basic understanding of how these technologies work, their benefits, risks, and indications is attainable for every bedside clinician.
So let’s dive in!
Cranial ultrasound remains the most widely used neuroimaging technique for premature babies. An ultrasound technician uses the large anterior fontanel, and to a lesser degree the smaller posterior fontanel as an “acoustic window” into the brain. The mastoid fontanel has become a new standard in cranial ultrasound in the last decade
To obtain images, the tech applies conductive gel to the skin overlying the open fontanels and uses a probe that transmits sounds through the conductive gel and into the brain. These high-frequency sounds bounce back to the probe and a computer uses the sound waves to create an image.
- No radiation
- Images are captured in real-time
- Portable technology
Risks & Limitations
- Only one level of contrast and intensity which limits resolution
- Difficulties seeing small bleeds or infarcts
- Difficulties seeing cerebellum bleeding or infarcts
- Potentially noxious to sick and premature neonates
- May result in hypothermia due to cold gels, open portholes, and raised incubator lids
- Intracranial bleeds
- Germinal matrix hemorrhages and sequelae (IVH, PVL, PHH)
- Detecting masses such as tumors or cysts
- Evaluation of a sacral dimple
Computed Tomography (CT)
- Useful for detecting bleeding and calcifications
Risks & Limitations
- Exposure to radiation
- Requires travel off unit
- Potential for hypothermia
- Trauma such as non-accidental trauma cases
Magnetic Resonance Imaging (MRI)
Different “sequences” can give different clinical information. The most common neonatal sequences are, T1 Weighted and T2 Weighted images for anatomy, and Diffusion Weighted Imaging (DWI) with Apparent Diffusion Coefficient (ADC Maps) for edema, and a newer sequence that has emerging value with small bleeds (micro-bleeds) is Susceptibility Weighted Imaging (SWI). It is also possible to construct 3-D images from the many slices taken which gives you a view of the brain from different angles.
Magnetic Resonance Spectroscopy (MRS)
Functional MRI (fMRI)
Functional MRI scans are similar to MRI. fMRI allows us to create images of metabolic function, blood flow and oxygen use in different areas of the brain or body. Images generated by standard MRI create 3D pictures of anatomical structure, whereas fMRI generates 3D images of metabolic activity within structures. Newer technology combines MRS with functional MRI to create Functional MRS (fMRS).
Benefits of MRI
- No ionizing radiation
- Improved sensitivity for evaluating infarction and white matter changes compared to CT
Risks & Limitations
- Sedation requirements
- Length of study (usually 40 to 60 minutes)
- Off-Unit Transport to MRI Scanner
- Need for MRI compatible equipment (ventilators, IV pumps)
- Priming 10+ feet of tubing if infant on IV fluids or drips
- Focal cerebral injury (such as stroke)
- Neonatal encephalopathy (such as Hypoxic Ischemic Encephalopathy)
- Congenital Malformations
- Etiology of Neonatal Seizures
- Anatomical detail of spine malformations
Dudink, J., Jeanne Steggerda, S., Horsch, S., & eurUS.brain group (2020). State-of-the-art neonatal cerebral ultrasound: technique and reporting. Pediatric research, 87(Suppl 1), 3–12. https://doi.org/10.1038/s41390-020-0776-y
Ibrahim, J., Mir, I. & Chalak, L. (2018) Brain imaging in preterm infants <32 weeks gestation: a clinical review and algorithm for the use of cranial ultrasound and qualitative brain MRI. Pediatr Res 84, 799–806. https://doi.org/10.1038/s41390-018-0194-6
Melbourne L, Chang T, Murnick J, Zaniletti I, Glass P, Massaro AN. (2016) Clinical impact of term-equivalent magnetic resonance imaging in extremely low-birth-weight infants at a regional NICU. J Perinatol. 2016 Nov;36(11):985-989. doi: 10.1038/jp.2016.116. Epub 2016 Jul 28. PMID: 27467565.
New Bedside Technology!
The first Embrace Neonatal MRI scanner in the United States was recently installed at Brigham and Women’s Hospital in Boston. Check out the article HERE.