Crystals are layer and packed closely.Low frequency like curved-linear array probe but with smaller footprint and flat surface.Chose small if you need to get into small area, i.e eyeball, ultrasound-guided central line insertion. Available in large and small footprint.Does not allow deep penetration into the body, approximately reliable at 6-8 cm depth.Great axial resolution therefore is the one usually used looking at small objects close to the surface.Generate a pie, wedge-shape field of view with a quarter-circle cut out of the top part.Has large footprint therefore hard to fit into small areas and hard to make a full contact of the entire probe head with the skin.Low frequency, 2-5 MHz, allow deep penetration into the body.There are three types which are commonly used convex- or curved-linear, flat-linear and phased. Array is the way crystals are arranged in the probe head.Usually used for looking at deep objects. Sector format has pie-wedge shape field of view.Usually used for looking at objects close to the surface. Linear format has rectangular field of view.Format is the field of view produced by the probe which appear on the screen.High frequency probe is good for look at small objects near the surface.Low frequency probe is good for looking deep into the body cavity (better penetration).Frequency is directly related to axial resolution (the ability to distinguish between two objects at different depth).Frequency is inversely related to penetration.Different types of probes have different range of frequency.D: Doppler "Colour" and "Pulse Wave" functions.Free fluid in hepatorenal or splenorenal pouch.The greater the different in echogenicity the easier it is to identify structures.Apply generous amount of gel to create better acoustic contact. Gas or air between the probe and the body can cause problem.Appear as grey, "snow storm" appearance, which provide no information.Subcutaneous emphysema and pathologic gas-forming process in structure can also be the case.Also it can be useful serving as landmark, i.e.spine. No waves traverse beyond bone therefore no energy after that.Bone reflects back almost 100% of the ultrasound waves.Fluid filled bladder has the same function as well. Can function as "acoustic window", which allow deeper penetration into the body.Free fluid (internal haemorrhage or ascites) has no membrane and has irregular shapes. In normal location fluid is contained and surrounded by echogenic membrane.Blood filled structures: heart or blood vessels.No resistance therefore no echo and no energy. If the probe is not at right angle to surface of interest scatter (deflection) of ultrasound waves occurs, especially when scanning aorta.On the other hand the less it reflects, the darker the image. The more a substance reflect energy back towards the probe the brighter the image appears on screen.Not at all though bone (high resistance).
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |