Ultrasound Beamforming and Image jjd/RSNA_ Concepts â‍ BEAMFORMING ... In adaptive beamforming ... Ultrasound Beamforming and Image Formation

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  • Ultrasound Beamforming and Image Formation

    Ultrasound Beamforming and

    Image Formation

    Jeremy J. Dahl

    Duke University Page 1

  • Ultrasound Beamforming and Image Formation

    Overview

    Ultrasound Concepts

    Beamforming

    Image Formation

    Absorption and TGC

    Advanced Beamforming Techniques

    Synthetic Receive Aperture

    Parallel Beamforming

    Spatial Compounding

    Adaptive Beamforming

    Duke University Page 2

  • Ultrasound Beamforming and Image Formation

    Ultrasonic Imaging

    Use acoustic (pressure) waves to form images

    Frequency range: 1-20 MHz

    Tomographic view: imaging plane is orthogonal to the surface

    Pulse-echo imaging

    Duke University Page 3

  • Ultrasound Beamforming and Image Formation

    Ultrasound System

    Transducer

    Scan Conversion and Display

    Signal Processing

    Beamformer

    IQ Computation Magnitude Calculation Compression Filtering Flow Processing Image Mode Processing

    Summation Geometric Focal Delays A/D Conversion TGC

    Duke University Page 4

  • Ultrasound Beamforming and Image Formation

    Coordinate System

    Elevation (y)

    Azimuthal (x)

    Axial (z)

    TransducerElements

    Duke University Page 5

  • Ultrasound Beamforming and Image Formation

    Ultrasound Concepts

    BEAMFORMING

    Image Formation

    Absorption and TGC

    Advanced Beamforming Techniques

    Synthetic Receive Aperture

    Parallel Beamforming

    Spatial Compounding

    Adaptive Beamforming

    Duke University Page 6

  • Ultrasound Beamforming and Image Formation

    Transmit Beamforming

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    System TimeDelays Scattering Medium

    Duke University Page 7

  • Ultrasound Beamforming and Image Formation

    Receive Beamforming

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    ScatteringMedium

    AlignmentSignal

    Summed RF Data(RF Line out)

    DelaysSystem Time

    Duke University Page 8

  • Ultrasound Beamforming and Image Formation

    PhasedLinear

    Beams

    Transducer Array

    Duke University Page 9

  • Ultrasound Beamforming and Image Formation

    Duke University Page 10

  • Ultrasound Beamforming and Image Formation

    Fixed Focus Beamforming

    Azimuthal Span (mm)

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    Duke University Page 11

  • Ultrasound Beamforming and Image Formation

    Fixed Focus Beamforming

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    Duke University Page 12

  • Ultrasound Beamforming and Image Formation

    Dynamic-Receive Beamforming

    System Time Delays

    Propagation Direction

    Transducer

    Duke University Page 13

  • Ultrasound Beamforming and Image Formation

    Dynamic-Receive Beamforming

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    Duke University Page 14

  • Ultrasound Beamforming and Image Formation

    Dynamic-Receive Beamforming

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    Duke University Page 15

  • Ultrasound Beamforming and Image Formation

    Aperture Growth and Apodization

    Dep

    th

    ApodizationWeight:

    ApertureGrowth:

    Time: t t t1 2 3

    0

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    Unused TransducerElements

    Duke University Page 16

  • Ultrasound Beamforming and Image Formation

    Aperture Growth and Apodization

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    Duke University Page 17

  • Ultrasound Beamforming and Image Formation

    Aperture Growth and Apodization

    (mm)

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    Duke University Page 18

  • Ultrasound Beamforming and Image Formation

    Ultrasound Concepts

    Beamforming

    IMAGE FORMATION

    Absorption and TGC

    Advanced Beamforming Techniques

    Synthetic Receive Aperture

    Parallel Beamforming

    Spatial Compounding

    Adaptive Beamforming

    Duke University Page 19

  • Ultrasound Beamforming and Image Formation

    Radio-Frequency (RF) Image

    Duke University Page 20

  • Ultrasound Beamforming and Image Formation

    Envelope Detection

    Envelope

    Signal with Carrier Frequency

    Duke University Page 21

  • Ultrasound Beamforming and Image Formation

    Envelope Detection

    fsin 2 0

    fcos 2 0 +RF Line in

    Q

    Filter

    Filter

    processing filtersTo other post

    andMapping

    ICompression

    2 2

    Duke University Page 22

  • Ultrasound Beamforming and Image Formation

    Duke University Page 23

  • Ultrasound Beamforming and Image Formation

    Compression and Gray Scale Mapping

    The dynamic range of the envelope detected signals is still to large to provide

    useful images. Bright targets can drown out the low signals of important

    structures.

    Compression and gray scale mapping techniques are used to reduce the

    dynamic range.

    0 0.2 0.4 0.6 0.8 10

    0.2

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    Duke University Page 24

  • Ultrasound Beamforming and Image Formation

    Duke University Page 25

  • Ultrasound Beamforming and Image Formation

    Ultrasound Concepts

    Beamforming

    Image Formation

    ABSORPTION AND TGC

    Advanced Beamforming Techniques

    Synthetic Receive Aperture

    Parallel Beamforming

    Spatial Compounding

    Adaptive Beamforming

    Duke University Page 26

  • Ultrasound Beamforming and Image Formation

    Absorption

    Not all of the transmitted ultrasonic energy is reflected. In fact, most of the

    transmitted energy is absorbed by the tissue. The typical rate of absorption

    of ultrasonic energy is 0.5 decibels per centimeter per Megahertz.

    For example, an acoustical pulse at 5 MHz that travels 10 cm into tissue loses

    25 dB of its signal strength (in other words, is about 1/18th of the original

    amplitude).

    Absorption is frequency dependent: The higher the frequency, the greater

    the absorption. Although resolution is better at the higher frequencies, the

    penetration of the ultrasound signal is not as good as the low frequencies.

    Duke University Page 27

  • Ultrasound Beamforming and Image Formation

    5.7 MHz 8.0 MHz 10.0 MHz

    Duke University Page 28

  • Ultrasound Beamforming and Image Formation

    Time-Gain Compensation (TGC)

    Time-gain compensation is used to counteract the effects of absorption. Gain

    is applied to the signal as a function of time (or distance).

    Manufacturers apply pre-determined TGC to the ultrasonic signals, however

    still allow the user some control of the gain with depth.

    Gain can be applied down to reasonable depths depending on the frequency.

    At some point, however, the SNR of the signal is so low that applying any

    TGC only serves to amplify noise.

    Duke University Page 29

  • Ultrasound Beamforming and Image Formation

    Without TGC With TGC

    Duke University Page 30

  • Ultrasound Beamforming and Image Formation

    Advanced Beamforming Techniques

    Synthetic Receive Aperture

    Parallel Beamforming

    Spatial Compounding

    Adaptive Beamforming

    Duke University Page 31

  • Ultrasound Beamforming and Image Formation

    Synthetic Receive Aperture

    Synthetic receive aperture imaging emulates a larger transducer when a sys-

    tems available beamforming channel count is smaller than the number of

    elements in the transducer.

    The beamforming is considered synthetic because multiple transmits are

    used to construct the beam as if it were received on the entire transducer

    at once.

    Duke University Page 32

  • Ultrasound Beamforming and Image Formation

    Second TransmitFirst Transmit

    Transmitting

    Receiving

    Transmitting and Receiving

    Duke University Page 33

  • Ultrasound Beamforming and Image Formation

    Parallel Receive Beamforming

    Parallel receive beamforming, also known as Explososcanning, is a method

    of beamforming that forms multiple receive beams from a single transmit

    event.

    In parallel