Pediatric MRI of the Brain: A Primer

Abstract

1. Kamakshya P. Patra, MD* 2. Jeffrey D. Lancaster, MD* 3. Jeffery Hogg, MD† 4. Jeffrey S. Carpenter, MD† 1. *Department of Pediatrics, Section of Hospital Pediatrics, West Virginia University Children’s Hospital, Morgantown, WV. 2. †Department of Neuroradiology, West Virginia University Health Sciences Center, Morgantown, WV. * Abbreviations: ADHD: : attention-deficit/hyperactivity disorder CSF: : cerebrospinal fluid CT: : computed tomography DWI: : diffusion-weighted magnetic resonance imaging FLAIR: : fluid-attenuated inversion recovery fMRI: : functional magnetic resonance imaging MRI: : magnetic resonance imaging MRV: : magnetic resonance venography NAA: : N -acetylaspartate SDH: : subdural hematoma Because of recent advances in magnetic resonance imaging (MRI) techniques, pediatricians should be aware of the different modalities and their unique advantages and appropriateness in different clinical situations. After completing this article, readers should be able to: 1. Understand the pros and cons of MRI and computed tomography of the brain. 2. Know the basic principles of MRI and its different image modalities. 3. Be aware of the appropriateness of different modalities in specific clinical situations. Magnetic resonance imaging (MRI) is based on the absorption and emission of radiofrequency energy by hydrogen protons whose spin is influenced by changing magnetic fields (0.3 to 1.5 T). Unlike computed tomography (CT), there is no radiation exposure. T1-weighted images cause fat (eg, myelin in white matter) to appear bright and water (eg, cerebrospinal fluid [CSF] or edema) to appear dark on this sequence. The gray-white interfaces of the brain are well depicted on these sequences, especially if with the images are thinly sliced. T2-weighted images cause water (eg, CSF and edema) to appear bright and fat to appear dark. The MRI-based intravenous contrast agents (eg, gadolinium) are frequently used in T1-weighted images (Fig 1A and B) to make serum appear bright. The blood-brain barrier typically serves to limit the passage of many molecules out of the blood vessels. If disease processes break down this barrier (such as infection, tumors, or inflammation), intravenous contrast agents can cross into the brain, causing areas of contrast entry to appear very bright. Figure 1. T1-weighted image at the level of midbrain. A. The cerebrospinal fluid (CSF) appears dark. B. The CSF appears bright. Note the gray and white matter differentiation …