2D mode ultrasound imaging from the zone of apposition for the measurement of diaphragm thickness. The diaphragm is located beneath the intercostal muscles and we can distinguish three layers: a hypo-echogenic thick layer (diaphragm muscle) surrounded by two hyper-echogenic lines (pleural layer and peritoneal layer). Here is a reduced diaphragm thickness (1.3 mm) in a patient with Duchenne muscular dystrophy.