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FUS 3.6 Driving the ultrasound and obtaining clinical images

Ultrasound Probe Movements


Law 1 = you want to be directly above the object of interest at a 90 degree angle to footprint of the probe. Any other angle causes a loss of resolution.


Law 2 = no air between probe and skin. Use lots of gel. Any air will result in scattering of ultrasound waves and loss of image detail.


Law 3 = rest hand on bed or patient in order to control small movements. Very important in facial ultrasound as the structures of the face being imaged are small. Big movements can result in easily losing sight of your target.


[US law diagrams]


Driving the probe:


There are 5 basic movements of the probe:


  1. The alignment (sliding) technique moves the transducer antero-posteriorly and laterally, aligning the area imaged with the target structure. 



  1. Tilting the transducer may place the angle Of the probe to the target closer to 90° and will increase the resolution.



  1. Rotating the transducer will change the axis of the image from transverse to longitudinal.



  1. Vertical pressure technique puts the target structure in place by applying vertical pressure to the transducer. 



Understanding crossectional views acquired in ultrasolography


In an ultrasound image, there are typically two axes, or planes, that provide different perspectives of the area being examined. These axes are the transverse (or axial) plane, and the sagittal (or longitudinal) plane.


[diagram of the axes]


Transverse (axial) plane: This plane is oriented horizontally, cutting across the body (or body part) from side to side. It provides a cross-sectional view, dividing the structure into superior (upper) and inferior (lower) portions. To acquire a transverse view, the ultrasound transducer is placed perpendicular to the long axis of the structure being examined.


[diagram of the temple with blood vessel in transverse]


Sagittal (longitudinal) plane: This plane runs vertically from front to back, dividing the body (or body part) into left and right halves. It provides a view of the structure’s length or depth. To acquire a sagittal view, the ultrasound transducer is placed parallel to the long axis of the structure being examined.


[diagram of the temple with blood vessel in longitudinal]


A significant part of interpreting ultrasound images Involves taking 2D images in the longitudinal and transverse views, and using this information to reconstruct the 3D image in your mind of the underlying anatomy. 


Being able to convert an image from longitudinal to transverse, while rotating the probe and keeping the target and focus, is an important skill to develop when learning how to do ultrasound. This will also help you to better understand the anatomy you are imaging and how the cross-sectional images acquired by ultrasonography come together in order to give you a complete anatomical picture.


I suggest you practice this with the parotid gland which we imaged previously in order to calibrate grain, before going onto the next lesson.