Ultrasound physics

# Ultrasound physics - Term Definition What is the bandwidth...

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Term: What is the bandwidth of an acoustic impulse? Definition: Bandwidth represents the range of frequencies that are present within an acoustic impulse. Although each transducer has a primary frequency, such as 3.25 MHz or 5MHz , the pulse that is produced by the transducer does not consist of only a single frequency but consist of sound with a range of frequencys. Term: What effect does the backing material have on the bandwidth? Definition: Because acoustic pulses from imaging systems are a very short ( in order to improve axial resolution ) they have a wide bandwidth . It is the backing or damping material that is responsible for keeping the pulse short. Term: Since high frequency sound beams provide enhanced longitudinal and lateral resolution , why isn't ultrasound with a frequency of 100 MHz used in diagnostic imaging? Definition: Higher the frequency , the greater the degree of attenuation. ( attenuation is the decline of intensity in a sound beam as it travels through a medium.) With use of 100-MHz transducer , the energy of the sound beam would rapidly dissipate as it traveled through the body.

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Term: The location of the focus of an ultrasound beam the focus yields the best lateral resolution . What two factors have an effect on the length of the near zone ( or the depth of the focus? Definition: 1. The diameter of the transducer active element. 2. The frequency of the ultrasound wave. The greater the diameter of the PZT crystal the longer the near zone and the deeper the focus. Likewise the higher the frequency of the sound wave the longer the near zone and the deeper the focus. Term: Which of the following ultrasound transducers will have the shortest near zone ( or the shallowest focus) ? Definition: D . 3mm active element diameter, 7 mm active element thickness and 2 MHz frequency. ( the transducer with the smallest diameter and the lowest will have the shortest near one length( the deepest focus). Term: What is focusing ? Definition: Is any process that narrows the diameter of an ultrasound beam, thereby improving the lateral resolution. Term: Why is focusing important in diagnostic imaging? Definition: It improves your image quality. Lateral resolution is determined by the diameter of a sound beam.
Term: Name 3 methods that may be used to focus an ultrasound beam. Definition: 1. Use of an acoustic lens ( external focusing) . 2. Use of a curved active element ( internal focusing) . 3. Electronic focusing ( phased array ) . Note : phased array means adjustable focus or multi- focus. Term: How does focusing affect the depth of the focus ( also known as the near zone length)? Definition: As the degree of focusing increases , the depth at which the focus is located becomes shallower. A strongly focused transducer will have a shallower focal depth than an otherwise identical transducer that is weakly focused.

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