Ultrasound and MRI Measurement of Quadriceps Femoris Muscle in Critically Ill Children

In sedated critically ill children, quadriceps femoris thickness and cross sectional area will be measured with thigh bedside ultrasound, performed by two trained operators consecutively. These two measurements will also be made at the exact same location on a magnetic resonance imaging transverse view of the thigh, to allow comparing them to ultrasound measurements.