All transducers have an orientation marker which represents the side of the probe from which elements are ‘fired’ first in any given frame to form the image. This marker is usually both palpable and visible and is a dot or raised line at one the end of the probe.
· There will also be a visible mark on the ultrasound screen which correlates with the marker on the transducer (assuming probe orientation is correct).
· The convention for abdominal scanning is that the orientation mark corresponds to the left-hand side of the screen when scanning in a long (sagittal plane) axis i.e., towards the cranial aspect of the patient (be aware that in cardiac scanning this is reversed). So, when scanning in a long axis and holding the probe the correct way, anything to the left of the ultrasound image on screen will be more cranially positioned than anything on the right-hand side of the image as the probe moves.
· To scan in a short axis (transverse plane), it is essential that the transducer is rotated correctly, anti-clockwise through 90 degrees – meaning that the orientation marker is turned towards you, the operator. Never turn the probe in a clockwise direction. Aside from the risk of incorrect orientation to the patient, you will find this more uncomfortable and can cause damage to your wrist and arm.
· Imagine the patient in dorsal recumbency to appreciate the correct probe orientation convention more easily for the transverse or short axis plane. With the probe placed on the patient’s midline in a transverse or short axis section with the orientation marker towards the operator, the left-hand side of the image/screen should correspond to the right side of the patient (i.e., region closest to the operator) and the right side of the screen/image represents structures sited to the left of the patient (away from the operator). With our patient in the right lateral recumbency position we place the probe on the ventral aspect of the patient’s abdomen in a short axis plane, the left-hand side of the screen will still correspond to the right side of the patient, but this time the patient’s right side is in close contact with the tabletop. Try practicing this so that you become more confident with your orientation!
· The convention in the transverse plane is that the left-hand side of the image/screen now corresponds to the aspect of the patient situated to the right (i.e., closest to the operator) and the right side of the screen/image represents structures sited further to the left (away from the operator).
· Holding the transducer, the wrong way round will at best, lead to confusion when scanning a structure but at worst could lead to potential harm for example when performing an interventional ultrasound guided procedure. Before starting a scan, always check (either visually or by feeling for the raised marker) you are holding the transducer correctly.
· Practice moving the probe in a long and short axis section on a patient or pet to see the impact incorrect probe orientation has on the screen as the probe is moved!