Modern helical CT scanners offer tremendous acquisition speed and rarely require significant, if any, sedation to obtain technically adequate images. However,
Table 2. Features of basic MRI sequences
T1-weighted images (WI)
CSF (water) is dark and fat is bright
CSF is bright
Proton density (PD)-WI
CSF is intermediate to bright
Fluid attenuated inversion recovery (FLAIR)
T2*-WI ("T2-star" or gradient recalled echo; GRE); uses small RF pulse
Diffusion-weighted imaging (DWI)
Predominantly T2-weighted images with dark CSF due to special nulling of signal from water by an "inversion pulse."
Like T2-W1, but particularly sensitive to blood products and other causes of inhomogeneous local magnetic fields, which appear markedly hypointense.
Acute ischemic injury (i.e., cytotoxic edema) is bright and remains so up approximately 7-10 days.
the longer imaging times required by MRI often necessitate sedation of pediatric patients to reduce motion artifact (see Table 6). While we offer several suggested protocols for the sedation of children during MRI studies, these must be discussed in advance with pediatricians and/or pediatric anesthesiologists at the reader's institution to ensure safe implementation. Additionally, MRI-compatible equipment must be available to enable proper monitoring of the heart rate, respiratory rate, blood pressure and oxygen saturation of sedated children.
Infants should be kept NPO for 4 hours prior to the study, and older children should be placed NPO for 6 hours before imaging. Sleep deprivation also improves the quality of sedation, and can be achieved by keeping children awake the evening before the procedure, and preventing napping during the day of the study. Children should also be placed in a quiet and dark environment shortly following administration of sedation.
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