Ultrasound Beam Profile and Focusing

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the purpose of receive focus in an array transducer?

To 'listen' in a particular direction with a listening focus at a particular depth.

How do modern scanners employ receive focus?

Automatically in the background.

What is the definition of aperture in the context of ultrasound?

The surface area of the crystal(s) or element(s) used to generate and receive the sound beam.

How can the aperture of an array be changed?

By electronic control. Signup and view all the answers

What is the ultrasound beam axis?

The center of the main beam, with two lateral and axial limits. Signup and view all the answers

What are secondary off-axis low energy beams known as?

Side lobes and/or grating lobes. Signup and view all the answers

What is the difference between a single-crystal transducer and an array transducer in terms of aperture?

A single-crystal transducer has a fixed aperture equal to the transducer diameter, while an array transducer can change its aperture electronically. Signup and view all the answers

What is the shape of the sound beam?

Three-dimensional (3D), having two lateral and axial limits. Signup and view all the answers

What is the process of reducing beam width in a focused ultrasound beam?

Focusing Signup and view all the answers

What is mechanical focusing, and how is it achieved?

Mechanical focusing is reducing beam width by using an external lens or shaping the crystal. Signup and view all the answers

What is the difference between internal and external focusing?

Internal focusing is used for frequencies 5 MHz and lower, while external focusing is used for higher frequencies. Signup and view all the answers

What is electronic focusing, and how is it performed?

Electronic focusing is achieved by applying small time delays to the firing group of crystal elements in an array transducer. Signup and view all the answers

What is the advantage of electronic focusing?

The operator can change the depth at which the beam is focused. Signup and view all the answers

What is transmit focusing, and how is it achieved?

Transmit focusing is applied during the transmission of the ultrasound pulse by applying short timing delays to the center elements group. Signup and view all the answers

What is the relationship between the timing delay and the depth of focus in transmit focusing?

Increasing the delay causes the pulse to be focused at a shallower depth, and conversely, decreasing the delay causes the pulse to be focused at a deeper depth. Signup and view all the answers

What is the difference between transmit focusing and receive focusing?

Transmit focusing is applied during the transmission of the ultrasound pulse, while receive focusing is applied during the reception of the echo signal. Signup and view all the answers

What is the primary characteristic of an unfocused ultrasound beam?

The sound beam produced by an unfocused transducer has a natural beam profile and is not mechanically or electronically focused to obtain a narrower beam width. Signup and view all the answers

What are the two distinct regions of an unfocused sound beam?

The two regions are the near field (NF) and the far field (FF). Signup and view all the answers

What is the distance from the transducer face to the transition point called?

"One near field length" Signup and view all the answers

What is the natural focus of an unfocused transducer?

The transition point. Signup and view all the answers

What is the purpose of dynamic aperture in ultrasound imaging?

Not mentioned in the provided text, but in general, dynamic aperture is used to adjust the beam width and focus during ultrasound imaging. Signup and view all the answers

What is the ultrasound beam axis?

Not mentioned in the provided text, but in general, the ultrasound beam axis is the direction of the ultrasound beam. Signup and view all the answers

What is the characteristic of the near field region of an unfocused ultrasound beam?

Beam convergence and a natural focus. Signup and view all the answers

What is the characteristic of the far field region of an unfocused ultrasound beam?

Not mentioned in the provided text, but in general, the far field region is characterized by a diverging beam profile. Signup and view all the answers

Study Notes

Electronic Focusing

When an array transducer receives echoes, the electrical outputs of the elements can be timed to "listen" in a particular direction with a listening focus at a particular depth.
Most modern scanners employ receive focus automatically in the background.

Dynamic Aperture

Aperture refers to the surface area of the crystal(s) or element(s) used to generate and receive the sound beam.
For arrays, the aperture relates to the group of elements pulsed collectively to generate the sound beam.
A single-crystal, fixed-focus transducer aperture is equal to the transducer diameter.
The aperture of an array can be changed electronically.

Ultrasound Beam Axis

The sound beam axis is 3D, having two lateral and axial limits.
The center of the main beam is known as the beam axis.
In addition to the primary or main beam (lobe), all ultrasound transducers also generate secondary off-axis low-energy beams known as side lobes and/or grating lobes.

Focusing

Focusing is the mechanical and/or electronic process of reducing beam width.
There are two main types of focusing: mechanical and electronic.

Mechanical Focusing

Focusing a transducer with an external lens or shaping the crystal is referred to as mechanical focusing.
There are two types of mechanical focusing: external focusing and internal focusing.
External focusing is inserting an acoustic lens in front of the crystal or by using a system of lens and mirrors.
Internal focusing is shaping or curving the crystal.
Internal focusing is generally used for frequencies 5 MHz and lower, while external focusing is usually applied for higher frequencies.

Electronic Focusing

Electronic focusing is more complex than mechanical focusing.
It is performed by applying small time delays in a specific way to the firing group of crystal elements in an array transducer.
Only array transducers can be focused electronically.
The advantage of electronic focusing is that the operator can change the depth at which the beam is focused.

Transmit Focusing

Transmit focusing is applied during the transmission of the ultrasound pulse.
Short timing delays are applied to the center elements group, causing the pulse to be focused at a certain depth.
Increasing this delay will cause the pulse to be focused at a shallower depth, and conversely.