Distribution of anesthesia-induced atelectasis in magnetic resonance images (MRI) and lung sonographic images (LUS). To facilitate comparisons between LUS and MRI, the lungs were divided into 12 segments, an anterior (A), lateral (L), and posterior (P) segment for both lungs which were further subdivided into cranial and caudal subsegments. The numbers within each one of the lung segments represent its respective percentage (mean value of two radiologists) of the total amount of atelectasis found.