Sonography Principles & Instrumentation Flashcards

What happens to the visual display when a mechanical transducer's PZT crystal is damaged?

Answer: Loss of entire image

A mechanical transducer typically utilizes a single, rotating or oscillating PZT crystal to generate and receive the ultrasound beam. If this sole PZT crystal is damaged, the transducer loses its ability to produce and detect ultrasound waves entirely. Consequently, this results in a complete loss of the entire image on the display.

Many PZT crystals are placed in an arched line with ______ transducers.

Answer: Convex array

Convex array transducers, also known as curvilinear arrays, are characterized by their PZT crystals being arranged in an arched or curved line. This curved configuration allows for a wider field of view in the far field, producing a sector-shaped image. This design is commonly used for abdominal and obstetric imaging.

A sonographer is using an annular array transducer to do an examination. In the near field of the image that is being presented, there is a horizontal band of dropout. Which PZT crystal ring damage does this most likely relate to?

Answer: Innermost ring

Annular array transducers use concentric ring-shaped PZT elements for focusing. Damage to an innermost ring specifically affects the central portion of the ultrasound beam, which corresponds to the near field of the image. This typically manifests as a horizontal band of dropout in the near field, as the central part of the image information is compromised.

The PZT crystal in a linear phased array transducer is divided into 280 distinct active elements. This transducer has how many channels?

Answer: 280

In a phased array transducer, each distinct active PZT element is typically connected to its own independent electronic circuit, known as a channel. These channels allow for individual control of each element's excitation, enabling electronic steering and focusing of the ultrasound beam. Therefore, if a transducer has 280 active elements, it has 280 channels.

Active elements in 3D transducers are arranged in a particular pattern, or _________.

Answer: Checkerboard

Active elements in 3D transducers, also known as matrix arrays, are arranged in a two-dimensional pattern, commonly described as a checkerboard or grid. This arrangement allows for electronic steering and focusing in multiple planes (azimuth and elevation), enabling the acquisition of volumetric data necessary for three-dimensional imaging.

When depth is raised, which of the following happens?

Answer: Frame rate decreases

When imaging depth is increased, the ultrasound pulse must travel a greater distance to and from the deepest reflector. This increases the 'time of flight' for each pulse, which in turn lengthens the pulse repetition period (PRP) and decreases the pulse repetition frequency (PRF). Since frame rate is directly proportional to PRF, an increase in depth ultimately leads to a decrease in the frame rate.

The sonographer increased output power by changing system settings. Which of the subsequent takes place?

Answer: Overall gain increases

When a sonographer increases output power, they are increasing the strength of the electrical voltage applied to the transducer, resulting in stronger ultrasound pulses transmitted into the patient. This directly increases the intensity of the sound waves and the strength of the returning echoes. Consequently, the overall signal amplitude received by the system increases, which can be interpreted as an increase in the effective 'overall gain' of the signal before display, leading to a brighter image.