Chapter 15 Flashcards
Images composed of only 2 shdes: black and white
Bistable
_ presents multiple levels of brightness (white, light gray, medium gray, etc.)
Gray scale
In gray scale, the numerous levels allows the system to _
assign different gray shades to different echo amplitudes and differentiate biologic tissues of different reflectivity.
Two user controls on video monitors can
alter characteristics of displayed images
- Contrast
2. Brightness
Determines the range of brilliancies within the displayed image.
Contrast
Bistable images (only black and white) are _ contrast
High
Determines the brilliance of the displayed image
Brightness
Functions of scan convertors
Store digital image information to later display it.
Change format of data; translate data
Scan converters _ and then later _
Store information
Display it
Storage of information is called
Writing
Image data is _ for display on the monitor.
“read” from the scan converter
scan convertors used to be _, now they use _
Analog
Digital technology
scan converters:
Ultrasound information is obtained from the body from
multiple scan lines (spokes)
Monitors display video information as
Horizontal lines
Scan converter translates the information from _ format into the _ format
“Spoke”
Video
Data stored in the scan converter can be altered between
the writing process and the reading process.
_ numbers are real world numbers
found in our everyday lives
Analog
Numbers with unlimited and continuous range of values
Analog
_ numbers are associated with computer devices and have discrete values
Digital
_ scan converter:
Funnel-shaped vacuum tube with an electron gun
located within its smaller end.
Analog
Analog Scan Converter:
_ containing the image information are shot out of the electron gun
Electrons
Analog Scan Converter:
The larger end of the tube contains
a dielectric matrix or silicon wafer.
Analog scan converter:
The electrons strike the _ and are _
Matrix
Stored
Analog scan converter:
The matrix is divided into _
Millions of tiny storage elements
Analog scan converter:
The stored electrons are _
Read to retrieve the image info
Analog Scan Converter has _ spatial resolution
Excellent
Limitations of analog scan converteers
Image fade – stored charges on the silicon wafer dissipate
over time
Image flicker – caused by switching between read and wrote modes
Instability – picture quality depends on many different factors
Deterioration – image degrades as the device ages
_ scan converters use computer technology to convert images into numbers (_)
Digital
Digitizing
Digital scan converter:
Image is stored in _ as _
Computer memory
Series of zeroes and ones
Digital scan converters:
The numerical representation of the image is _ and then _
Processed
then retranslated into an image displayed on a monitor.
Advantages of digital scan converters:
Uniformity – consistent gray scale quality throughout the image Stability – does not fade or drift Durability Speed Accuracy
Two important elements of digital scan converters
- Pixel
2. bit
Smallest building block of a digital picture
Pixel
At any instant in time, the entire pixel is _
A single shade of gray
number of pixel elements per inch
Pixel density
Low pixel density: _ pixels per inch _ pixels _ detailed image _ spatial resolution
Few
Larger
Less
Lower
High pixel density: _ pixels per inch _ pixels _ detailed image _ spatial resolution
Many
Smaller
More
Higher
Smallest amount of computer memory
Bit
A bit is _, has a value of _
Bistable
Either 0 or 1
a group of bits; simply a series of zeroes and ones.
Binary number
group of eight bits of computer memory
Byte
Two bytes (16) bits
Word
Each pixel’s shade of gray is determined by _
the cluster of bits assigned to it.
Fewer bits per pixel:
_ shades of gray
_ contrast resolution
Fewer
Degraded
More bits per pixel:
_ shades of gray
_ contrast resolution
More
Improved
To determine the number of gray shades that can be represented by a cluster of bits, _
multiply the number 2 by itself the same number of times there are bits: 2^n
Number of bits:5
Number of shades: _
32
digital information is _ susceptible to noise contamination
Less
Information is taken from the transducer in _ form. It is then changed into _ form for _. It then must be _ for display.
Analog
Digital
Computer storage
Analog
Step 1. electrical signals created by the transducer during reception are converted from _ to _ form by the _
Analog
Digital
Analog to digital converter
Step 2:
The digital information is stored in the _. Any processing of the reflected signals before storage is called _
scan converter’s computer memory
Preprocessing
Step 3:
The image information (digital form) is processed by the _. Any processing after storage in the digital scan converter is called
US systems computer
Postprocessing
Step 4:
Digital signals are translated _ to be displayed on the analog display devices by a
back into analog form
digital-to- analog (D-to-A) converter.
Step 5:
The signal is now in _ form and can be displayed on the analog display.
Analog
Modern flat-panels are _ display devices
Digital
cases of digital display devices, step _ is unnecessary.
4
the manipulation of image data before
storage in the scan converter.
Preprocessing
Preprocessing is controlled by _
Sonographer
_ alters image data forever and cannot be reversed or undone
Preprocessing
manipulation of image data after storage in the scan converter
Postprocessing
Postprocessing is controlled by
Sonographer
Pre or postprocessing:
Changes can be reversed
Alterations to a frozen image
Postprocessing
Functions of Image Processor:
◼ Preprocessing ◼ Persistance ◼ 3-D acquisition ◼ Storing imaging frames ◼ Cine loop ◼ Post processing ◼ Grayscale ◼ 3-D presentation ◼ D-A conversion
Enlarging a portion of the image to fill the entire screen
Magnification/zoom
Selected part of image is called
Region of interest (ROI)
Two types of magnification
Read
Write
_ magnification occurs after the image data is stored in the scan converter
Read
Read magnification: 3 steps:
- US System scans the anatomy
- Image is converted from analog to digital form and stored in the scan converter
- Sonographer identifies the ROI and the system reads and displays only the original data that pertains to that area. The ROI is not rescanned.
Read magnification:
Number of pixels or scan lines in the magnified image is
the same as the original image
Does spatial resolution change with read magnification
No
Read magnification:
Are the pixels larger, smaller, or the same size in the zoomed image
Larger
_ magnification can be used on a frozen image
Read
Is read magnification pre or postprocessing
Postprocessing
_ magnification is applied during data acquisition, before data is stored in the scan converter
Write
Write magnification: 4 steps:
- The US system scans the anatomy and creates an image
- Image is converted from analog to digital and is stored in the scan converter
- Sonographer identifies the ROI. The US system then discards all the existing data in the scan converter
- The US System then rescans only the region of interest and writes new data into the scan converter.
Write magnification: the image used to identify the _ is discarded and _ is acquired
ROI
All new image info
_ magnification:
The number of pixels or scan lines in the ROI image is greater than that in the ROI’s portion of the original image
Write
_ magnification has increased number of pixels which improves _
Write
Spatial resolution for the ROI
Can write magnification be used on a frozen image?
No
Is write magnification pre or postprocessing
Preprocessing
Sophisticated method of improving image quality. Developed within the context of bioeffects due to high intensity levels of short sound pulses
Coded excitation
Coded excitation creates _ sound pulses containing _.
Very long
A wide range of frequencies
Long pulses distribute energy _
Over a broad frequency range
Does coded excitation improve penetration
Yes
Coded excitation occurs in
The pulser
Special mathematical techniques alter the long reflected pulses into a form suitable for high image quality
Coded excitation
The coding of the excitation _ the pulse mathematically and _ resolution
Shortens
Improves
Produces image with a wider field of view
Panoramic imaging
Panoramic imaging is achieved by
sliding transducer parallel to the scan plane
[extending the scan plane]
Panoramic imaging: old information from previous frame are _ and _
Retained
New echoes are added to the image in the same direction the scan plane is moving
Is panoramic imaging pre or postprocessing
Preprocessing
A method of using sonographic information from several different imaging angles to produce a single image
Spatial compounding
_ compounding:
Number of frames and steering angles varies
Spatial
Spatial compounding has _ frames= _ compound image quality
More
Better
Does spatial compounding reduce speckle and shadowing artifact?
Yes
Spatial compounding reduces _
Speckle and shadowing artifacts
Speckle reduction improves
dynamic range and contrast resolution.
_ compounding reduces speckle artifact and noise in ultrasound images
Frequency
All reflected sound pulses contain
a large range of frequencies.
Frequency compounding:
Reflected signal is divided into _ and an image is created from_. Images from the sub-bands are then _
sub-bands of limited frequencies
Each sub-band
combined into a single image.
Frequency compounding: Noise components of the reflections are _ and _
different for each sub-band
Noise is reduced when they are combined
Image processing method that
makes pictures look sharper
Edge enhancement
Edge enhancement: the computer identifies and _
emphasizes sharp edge boundaries in the image
Increases the image contrast in the area immediately around the edge
Edge enhancement
Creates subtle bright and dark highlights on either side of these boundaries to make them appear more defined
Edge enhancement
An image processing technique that continues to display information from older images. A number of previous frames are superimposed on the most current frame.
Temporal compounding
Temporal compounding creates _
smoother image with reduced noise and improved image quality
Temporal compounding aka
persistence, temporal averaging
Temporal compounding: reduction of _
Frame rate/temporal resolution
Temporal compounding is most effective with
Slowly moving structures
With sector shaped images, the scan lines _. This creates _.
Separate at increasing depths.
Gaps between the scan lines
_ method of constructing new simulated data points to fill in the gaps.
Interpolation
Fill in interpolation: the know gray scale level of neighboring pixels are used to _
Predict the missing info
Is fill in interpolation pre or postprocessing
Preprocessing
Fill in interpolation: _ resolution is improved
Spatial
Dynamic technique that produces images from sound reflections in an entirely new way.
Elastography
Elastography is related to _. Tissue will _
the mechanical properties of the tissue
Deform differently following the application of a force
Elastography: _ are obtained and combined with US reflections into images called _
Estimates of tissue stiffness
Elastograms
_ is potential as a complementary tool for the diagnosis of cancer
Elastography
2 [general] methods for performing elastography
Strain elastography and shear weave elastography
Strain elastography:
_ dependent
Measures _
Qualitative or quantitative?
Operator
Tissue strain
Qualitative
Aka transient elastography
Shear wave elastography
Shear wave elastography:
Compressions applied by _
Measures _
Qualitative or quantitative?
Sound pulse
Stiffness
Quantitative
PACS
Picture Archiving and Communications System
Digital ultrasound lab where images and additional medical information are digitized and stored on a computer network
PACS
3 major advantages of PACS
- Virtually instant access to archived studies
- No degradation of data
- “store and forward” telemedicine – can electronically transmit images and reports to remote sites
_ are the primary digital storage devices used in PACS
Computer hard drives
DICOM
Digital Imaging and Computers in Medicine
A set of rules that allows imaging systems to share information on a network
DICOM
If an US system adheres to _, the system can successfully connect to a PACS network
DICOM standards
DICOM guarantees _
that all devices developed in the future will work with PACS as well.
Developed within the context of bioeffects
Coded excitation
