Ultrasound

A-scans

• Stand for amplitude scan

• One transducer held at one angle to skin

• Pulse partly reflected and partly transmitted at boundary between two tissues.

• Transducer receives reflected pulse

• Allows a 1D, cross-sectional image to be seen

• Scan results shown as peaks on a voltage against time graph on an oscilloscope screen

• Peaks may decrease with time as reflected pulse will have less energy due to energy losses within the body and because energy from original pulse is transmitted through the boundary.

• Time taken is the time for the pulse to travel to the boundary and be reflected, so distance must be halved after being calculated.

• Example of use is for finding tissue depths in the eyes or determining the thickness of bone.

B-scans

• Stand for brightness scan

• Transducer at different angles to the skin/multiple transducers used

• Transducer moved over patient’s skin.

• Reflected ultrasound pulses from between boundaries are received by the transducer

• Each reflected pulse received forms a bright spot on computer screen

• Each dot corresponds to the boundary between two tissues.

• Dot brightness is proportional to the intensity of the reflected ultrasound pulse.

• Repeated pulses allow computer to form image

• Image formed is 2D and a section through the patient.

• Effectively multiple A scans (do not write this in the exam, just to help understand it!)

• Example of use is for imaging unborn child.