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Ultrasound Physics--Chapter 14 & 15
Pulsed Echo Instrumentation/Displays and Image Processing
46
Physics
Professional
02/28/2021
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Term

 

 

 

 

 

An ultrasound system has 2 major functions:

 Definition

 

 

 

 

  1. 1. The preparation and transmission of electrical signals to the transducer, which creates a sound beam. 

  1. 2. The reception of electrical signals from the transducer, with subsequent processing into clinically meaningful images and sounds. 
Term

 

 

 

 

 

maintains and organizes the proper timing and interaction of the system’s components. 

 Definition

 

 

 

 

 

 

Master Synchronizer
Term

 

 

 

 

 

creates and controls the electrical signals sent to the transducer that generate sound pulses.  

 Definition

 

 

 

 

 

Pulser and Beam Former

 
Term

 

 

 

 

 

determines the amplitude, pulse prepetition period, and pulse prepetition frequency.  

 Definition

 

 

 

 

 

 

The pulser
Term

 

 

 

 

What is Coded excitation 

 Definition

 

 

  • Traditional imaging uses a very short pulse to create images. 

  • Coded excitation is a sophisticated method of improving image quality. 

  • It was developed within the context of bioeffects. 

  • It creates very long sound pulses containing a wide range of frequencies. It keeps peak intensity below the FDA’s limit. 

  • Takes place in the pulser for deeper penetration. 

  • Improves signal-to-noise ratio. 

  • Improves spatial and contrast resolution. 
Term

 

 

 

 

 

determines the firing delay patterns for phased array systems. 

 Definition

 

 

 

 

 

The beam former
Term

 

 

 

 

 

protects the delicate receiver components from the powerful signals that are created for pulse transmission. Also directs the electrical signals from the transducer to the appropriate electronic and processing components within the ultrasound system. 

 Definition

 

 

 

 

 

Switch
Term

 

 

 

 

 

What is a transducer and what does it do?

 Definition

 

 

 

 

 

During transmission, the transducer transforms electrical energy into acoustic energy. During reception, it converts the returning acoustic energy into electrical energy.  
Term

 

 

 

 

Single PZT element in the transducer, the electronics in the beam former/pulser, and the wire that connects them. The number of elements in an array transducer that can be excited simultaneously is determined by the number of channels in the ultrasound system. Most systems have between 32 – 256 channels. 

 Definition

 

 

 

 

 

Channel
Term

 

 

 

 

 

transforms the electrical signals from the transducer (produced by the reflected sound) into a form suitable for display. 

 Definition

 

 

 

 

 

Receiver
Term

 

 

 

 

 

What is the order of receiver operations?

 Definition

 

 

1. Amplification

2. Compensation

3. Compression

4. Demodulation

5. Reject
Term

 

 

 

 

 

Amplification (receiver gain) 

 Definition

 

 

 

 

  • Each electronic signal returning from the transducer is made larger. 

  • Adjustable? Yes 

  • Image effect? Entire image gets brighter or darker. 
Term

 

 

 

 

 

Compensation (time gain compensation, depth gain compensation, swept gain) 

 Definition

 

 

 

 

  • Correcting for attenuation. 

  • Adjustable? Yes 

  • Image effect? Image will be uniformly bright from top to bottom. 
Term

 

 

 

 

 

Compression (log compression or dynamic range) 

 Definition

 

 

  • Performed twice: 

  1. Keeps the electrical signals level within the accuracy range of the system’s electronics. 

  1. Keeps and image’s grey-scale content within the range of detection by the human eye. 

  • Adjustable? Yes 

  • Image effect? Changes grey-scale mapping. 
Term

 

 

 

 

 

Demodulation or Detection 

 Definition

 

 

 

  • Two-part process: 

  1. Rectification—converts all negative voltages into positive voltages. 

  1. Smoothing or Enveloping—places a smooth line around the “bumps” and evens them out. 

  • Adjustable? No 

  • Image effect? None. 
Term

 

 

 

 

Rejection (threshold, negative, filter, or suppression) 

 Definition

 

 

 

Allows the sonographer to control whether low-level gray-scale information within the data will appear on the displayed image. 

  • Adjustable? Yes 

  • Image effect? Weak echoes are present or eliminated from the image. 
Term

 

 

 

 

 

translates the information (image data) from the spoke format into the video format to store (write) or display (read). 

 Definition

 

 

 

 

 

Scan Converter
Term

  • Originally made gray-scale display possible. 

  • Divides picture into a 1000 x 1000 matrix with an electrical storage element. 

  • Electrons from the CRT gun strike these elements and the “charge” is stored. 

  • Stored changes later read to retrieve information. 

  • Advantage: excellent spatial resolution, matrix grid provides superb image detail. 

  • Disadvantages: 4 shortcomings made analog scan converter obsolete. 

  • Image fade—charges on silicon wafer dissipate. 

  • Image flicker—constant switching between read and write modes. 

  • Drift—inconsistent pictures from day to day. 

  • Deterioration—tube ages and images degrade. 

 Definition

 

 

 

 

 

Analog Scan Converter: real world 
Term

  • Uses computer technology to convert images into numbers, a process called digitalizing. 

  • The image is stored in computer memory as a series of zeros and ones. 

  • The numbers can be processed and then retranslated for display as an image on a monitor. 

  • Advantages: 

  • Uniformity--consistent gray-scale quality throughout the image. 

  • Stability—does not fade or drift. 

  • Durability—not affected by age or heavy use. 

  • Speed—nearly-instant processing. 

  • Accuracy—error-free 

 Definition

 

 

 

 

 

Digital Scan Converter: computer world 
Term

 

 

 

 

 Electrical signal from the transducer is analog. But a digital scan converter can only process computer information. So, the analog signal must be converted into digital form for input into the scan converter. This is done by A to D Converter (to store). 

 Definition

 

 

 

 

 

Analog-to-Digital Conversion:
Term

 

 

 

 

Information in the scan converter is digital, but the televisions are analog, so the signal must be reconverted to analog to form prior to display on the TV. Accomplished by the D to A Converter (to display). 

 Definition

 

 

 

 

 

Digital-to-Analog Conversion
Term

  • The image can be manipulated in between the “storing” and the “displaying” of the data. Once preprocessing occurs, the data is alerted forever Preprocessing cannot be reversed or “undone.” 

  • TGC 

  • Log compression 

  • Write magnification: Improves anatomic detail by enlarging a chosen portion of an image (region of interest) to fill the entire screen. 

  • Acquires new data 

  • Identical pixel size 

  • More pixels than the original ROI 

  • Improved spatial resolution 

  • Possible improved temporal resolution 

 Definition

 

 

 

 

 

 

Image Processing
Term

 

 

 

  •  Improves anatomic detail by enlarging a chosen portion of an image (region of interest) to fill the entire screen. 

  • Acquires new data 

  • Identical pixel size 

  • More pixels than the original ROI 

  • Improved spatial resolution 

  • Possible improved temporal resolution 

 Definition

 

 

 

 

 

Write magnification
Term

  • Combining frames from different time to form an image. 

  • An image processing technique that continues to display information from older images. 

  • The displayed image contains “history” from earlier images. 

  • A smoother image will reduce noise, higher signal-to-noise ratio and improved image quality is produced. 

  • Reduces temporal resolution. 

  • It is most effective with slow moving structures. 

 Definition

 

 

 

 

 

Temporal compounding or persistence →frame averaging/compounding 
Term

  • Combining frames from different angle to form an image. 

  • Is a method of using sonographic information from several different imaging angles to produce a single image. The more frames in the compound acquisition sequence, the better the compound image quality, it reduces speckle and minimized shadowing artifacts. 

  • Limitations of the technique; reduce frame rates and reduce temporal resolution. 

 Definition

 

 

 

 

 

 

Spatial compounding 
Term

 

 

 

  • Increases the contrast at a boundary to make an image appear sharper; most useful to emphasize different tissues. 

  • Ideally suited to distinguish interfaces between structures with different gray-scale characteristics. 

  • The top of the image is without edge enhancement; the bottom half has edge enhancement. 

 Definition

 

 

 

 

Edge enhancement 
Term

  • It is preprocessing. 

  • Improves image detail (spatial resolution) by filling in the missing data, especially for deeper parts of the sector shaped image. 

  • Example: The edges of a circular structure will be better defined. 

  • Images with a low line density are most improved with fill-in interpolation. 

  • Images with a low line density generally have a high frame rate (good temporal resolution). 

 Definition

 

 

 

 

 

Fill-in interpolation 
Term

  • manipulating the data after it has been stored in the scan converter memory but prior to display. Increases versatility of the display process. This can be undone. 

  • Done on a freeze frame. 

  • Black/white inversion 

  • Read magnification: Improves anatomic detail by enlarging a chosen portion of an image (region of interest) to fill the entire screen.  

  • Uses old data 

  • Larger pixel size 

  • Same number of pixels as the original ROI 

  • Unchanged spatial resolution 

  • Unchanged temporal resolution 

 Definition

 

 

 

 

 

 

Postprocessing
Term

  • The theory that tissues will deform differently following the application of force. 

  • Stiffness data and ultrasound reflections are combined into elastogram images. 

  • It can be combined with anatomical images and Doppler to add to the diagnostic value of the exam. 

 Definition

 

 

 

 

 

Elastography 
Term

 

 

 

 

presents processed data.   

  • Essential link between ultrasound system and medical staff. 

  • The display maybe a flat screen monitor, a transparency, a spectral plot, or a variety of other formats. 

 Definition

 

 

 

 

 

Display
Term

 

 

 

  • an electron beam emitted from the gun flies through a time varying magnetic field. The electrons are swept across the face of the screen and strike the phosphor coating on the screen. The phosphor glows and turns electrons into light. 

  • Interlaced display: 525 horizontal closely spaced lines. The odd lines are written by the electron beam, then the remaining even lives are written. 

  • Progressive scan display: an alternative format presents all the lines in sequence. 

 Definition

 

 

 

 

 

CRT (Cathode-Ray Tube)
Term

 

 

 

 

smallest element of a digital picture. If we divided a picture into a grid, each square is a pixel. 

 Definition

 

 

 

 

Pixel (picture element)
Term

 

 

 

 

the number of picture elements per square inch. The more pixels per square inch, the greater the details in the image. The detail is called, “spatial,” or “details resolution.” 

 Definition

 

 

 

 

 

 

Pixel density 
Term

 

 

 Few pixel/inch 

Larger pixels 

Less detailed image 

Lower spatial resolution 

 Definition

 

 

 

 

Low Pixel Density
Term

 

 

Many pixels/inch

Smaller pixels

More detailed image

Higher spatial

resolution 

 Definition

 

 

 

 

 

 

High Pixel Density 
Term

 

 

 

 

 

Bistable

 Definition

 

 

 

 

 

 

black and white (high contrast)
Term

 

 

 

 

 

Gray-scale

 Definition

 

 

 

  •  multiple levels of brightness. 

  • Different shades of gray are assigned to different echo amplitudes to facilitate differentiation the various biological tissue. 
Term

 

 

 

 

 

Contrast: Determines the range of brilliancies within the displayed image. Brightness: Determines the brilliance of the displayed image. 

 Definition

 

 

 

 

 

Display controls
Term

 

 

 

 

 

Determines the range of brilliancies within the displayed image. 

 Definition

 

 

 

 

 

Contrast
Term

 

 

 

 

 

Determines the brilliance of the displayed image.

 Definition

 

 

 

 

 

Brightness:
Term

 

 

 

 

 

controlled by compression.

 Definition

 

 

 

 

 

Contrast Resolution
Term

 

 

 

 

archives the ultrasound studies Typical storage devices (or media) include computer hard drives, CD, DVD, videotape, magneto-optical discs, paper printouts, photographs, and USB flash drives.  

 Definition

 

 

 

 

 

Storage
Term

 

 

 

 

 

Storage of an image is called 

 Definition

 

 

 

 

 

 

“writing.”
Term

 

 

 

 

 

Computer memory is called,

 Definition

 

 

 

 

 

“random access memory,” or RAM 
Term

 

 

 

 

binary digit, the smallest amount of digital storage.  

  • Bistable, has a value of either zero or one.  

  • Binary number 

 

  • A group of “bit” is assigned to each pixel to store the gray-scale color assigned to that pixel. 

  • The more bits per pixel, the more shades of gray, and the better is the contrast resolution. 

  • The ability of the machine to recognize different shades of gray. 

  • More bits →more shades of gray →better contrast resolution. 

  • Less bits →less shades of gray →bad contrast resolution. 

 Definition

 

 

 

 

 

 

Bit
Term

 

 

 

 

 

How to calculate the number of gray shades 

 Definition

 

 

 

 

 

  • Find how many bits are assigned to each pixel. 

  • Multiply the number 2 by the power of how many bits. 

  • Example: 3 bits/pixel 

  • 23 = 2 x 2 x 2 = 8 
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