physics ch 4 (Part 2)

a 4-bit memory is a ____________ memory.

16-shade

Transparent views allow _____________ imaging of the anatomy as with plain film radiographs.

"see-through"

The common display is a _________________ that presents an image in horizontal lines from top to bottom.

flat-panel display

A 4-bit memory has __________________- assigned to each pixel, that is, four layers of memory.

four binary digits

The result of panoramic imaging is a larger field of view allowing presentation of _____________.

large organs and regions of anatomy on one image.

Interpolation assigns a brightness value to a missed _____ based on an average of brightnesses of adjacent pixels

pixel

Three-dimensional images can be acquired at rates of up to __________________ and thus are considered "live" or real-time presentations.

30 volumes per second

[PERSISTENCE] ______ levels of persistence are appropriate for slower-moving structures

Higher

Panoramic imaging provides

a way to produce an image that has a wider field of view than what is available on an individual frame from a transducer.

Three-dimensional imaging (volume imaging) is accomplished by

acquiring many parallel two-dimensional (2D-slice imaging) scans and then processing this 3D volume of echo information in appropriate ways for presentation on 2D displays.

[PANORAMIC IMAGING] During the addition of new echoes, as the transducer is moved, it is important to properly locate the new echoes relative to the existing image. This is accomplished by correlating locations of echoes common to _______________ (i.e., the overlap) so that the new information on the new frame is located properly

adjacent frames

Preprocessing includes functions that are performed _________.

as part of scan conversion.

Image improvement can be accomplished by ___________.

filling in missing pixels.

The 2D image plane is divided like a checkerboard into squares called __________________, in a rectangular matrix, for example, 1024 × 768 or 512 × 384.

pixels (picture elements)

Panoramic imaging expands the image beyond the _____________.

normal limits of the field of view of the transducer.

The pixels _________________________ (786,432 and 196,608 in the previous examples), so they are tiny and not normally noticed unless magnified sufficiently.

number several thousands

Surface renderings are popular in ___________________.

obstetric imaging

Three-dimensional echo data are acquired by

obtaining many parallel two-dimensional sections of echo information from the imaged anatomy yielding (B) a three-dimensional fetal surface-rendered image.

[Scan conversion] A pulse emitted in an ___________________ will result in a series of echoes that must be located in various rows and columns

off-vertical direction

To image gray scale (several shades of gray or brightness, in addition to black and white), storage of _______________________ in each memory location is necessary. This requires the memory to have more than one matrix.

one of several possible numbers

elastography is the imaging version of _______.

palpation

Panoramic imaging is achieved by manually sliding the transducer in a direction ______________, thus extending the scan plane. At the same time, the old echo information from previous frames is _________, while the new echoes are added to the image in the direction in which the scan plane is moving.

parallel to the scan plane retained

As part of the scan conversion process (scan-line information going into the image memory), various processing functions may be performed on the image. This is called __________________ because it occurs before the echo data are stored in the image memory.

preprocessing

The same tumor shown in elastography mode:

red- colors signifying soft tissues blue- colors signifying hard tissue

[PERSISTENCE] Noise, primarily speckle, is ________ because it is a random process.

reduced

[PERSISTENCE] When several frames containing random content are averaged, the random content is ________.

reduced.

The _________________ properly locates each series of echoes corresponding to each scan line for each pulse emitted from the transducer, filling up the memory with echo information.

scan converter

[PIXEL INTERPOLATION] A common situation where this occurs is in ___________ in which scan lines have increasing separation with distance from the transducer and intervening pixels are left out

sector scans

[PERSISTENCE] ____________ improves dynamic range and contrast resolution.

Speckle reduction

The reason is that the memory element assigned to each pixel is an electronic device that is_________, like an on-off switch and so can operate only in _____________ corresponding to one or zero. This would allow only ____________(black-and-white) imaging.

binary (bi meaning "two") two conditions bistable

Computer memories and processors use ____________ in carrying out their functions because they contain electronic components that operate in only two states, representing the numbers 0 and 1.

binary numbers

Contrast resolution depends on the number of____ per pixel in the image memory.

bits

A number that corresponds to the echo strength received from the location within the anatomy corresponding to that memory position is stored in ____________________________.

each of the pixel locations in the memory

Holding and displaying one frame out of the sequence is known as _________ .

freeze-frame

Postprocessing is image processing performed on __________ retrieved from the memory.

image data

After echo data are preprocessed and scan-converted into image form, the image frames are stored in the _______________.

image memory.

The_____________ converts scan-line data into images, processes the images before storing them in the image memory, processes them as they come out of the memory, converts them from digital form to analog form, and sends them on to the display.

image processor

The ________ divides the image into pixels, such as a matrix of 512 × 384.

memory

rapid-sequence presentation is called __________, and the entire process is called _________.

real-time display, real-time sonography.

Common ways of presenting the 3D echo data include

surface renderings, 2D slices through the 3D volume, and transparent views.

A 3D volume of echo data can be displayed in several ways, including _______________________.

2D slices, surface renderings, and transparent views.

spatial compounding (TERM)

Averaging of frames that view the anatomy from different angles.

persistence (TERM)

Averaging sequential frames together.

[PERSISTENCE] _____ levels of persistence, or none at all, are appropriate for following rapidly moving structures.

Lower

B color is a form of postprocessing that _________ contrast resolution by assigning colors, rather than gray shades, to different echo strengths.

improves

Spatial compounding

is the averaging of frames that view the anatomy from different angles.

Using a computer-monitor scan format, digital scan converters provide means for displaying the acquired information in a ____________.

linear or sector ultrasound scan-line format.

Functions of the Image Processor

• Scan conversion • Preprocessing • Persistence • Panoramic imaging • Spatial compounding • Three-dimensional acquisition • Storing image frames • Cine loop • Postprocessing • Gray scale • Color scale • Three-dimensional presentation • Digital-to-analog conversion

The scan converter is accomplished in a _______________, yielding one scan or frame of image information.

fraction of a second

[PERSISTENCE] _____________, in effect, reduces frame rate because averaged frames are no longer independent.

frame averaging

Persistence reduces noise and smoothes the image by ____________.

frame averaging.

Averaging sequential frames spatially, up to nine typically, improves the quality of the image in several ways:

•As in persistence (which is temporal averaging), speckle is reduced. •Clutter caused by artifacts is reduced. •Smooth (specular) surfaces are presented more completely because they are interrogated at more than one angle, increasing the probability that close to 90-degree incidence is achieved (which is necessary to receive echoes from them). •Structures previously hidden beneath highly attenuating objects can be visualized.

the procedure for entering the echo information required for display of the 2D cross-sectional image into a digital memory is as follows:

•The beam is scanned through the patient in such a way that it "cuts," like a knife, through the tissue cross-section. •Echoes received from all points on this cross-section are converted to numbers that are stored at corresponding pixel locations in the digital memory. •All the information necessary for displaying this cross-sectional image now is stored in the memory. •The information then can be taken out of the memory and presented on a 2D display and in such a way that the numbers coming out of the memory are displayed with corresponding pixel brightnesses on the face of the display

It is commonly shown as a color overlay on top of the gray-scale image and has been used clinically for

cancer detection, for characterization of small parts (breast, thyroid, and prostate), for assessing the viability of the myocardium, and for monitoring therapies that alter tissue composition, such as ablation procedures.

"________________" can be thought of as being layered back to back.

checkerboards

Most instruments store the last several frames acquired before freezing. This is called _______________.

cine loop, cine review, or image review feature.

Image memories used in sonographic instruments are _________; that is, they are computer memories that store numbers (digits) as digital cameras do.

digital

The scan converter formats _______ into__________ for image processing, storage, and display.

echo data image form

Examples of preprocessing include

edge enhancement (a function that sharpens boundaries to make them more detectable and measurements more precise), pixel interpolation, persistence, panoramic imaging, spatial compounding, and three-dimensional (3D) acquisition.

_______________ subjecting tissues to a small push (by the sonographer using a push on the transducer or a high-amplitude ultrasound pulse) and then tracking the movement of tissues, it is possible to estimate and depict tissue stiffness since soft tissues will move more than hard ones.

elastography

The more pixels there are, the ______ is the spatial detail in the stored image.

finer

In a _____________________, there are four checkerboards back to back so that each pixel has 4 bits (binary digits) associated with it.

four-binary-digit memory

scan converter process is repeated several times per second to produce a rapid sequence of _______.

frames stored in the memory and presented on the display.

The advantage of the 2D slice presentation is that it is possible to present _______________ that are impossible to obtain with conventional 2D scanning.

image-plane orientations

____________ determines the depth to be displayed and thus the depth range covered by the image memory in the scan conversion process.

Image depth control

The multiple 2D frames are obtained by

(1) manual scanning of the transducer, with position-sensing devices keeping track of scan-plane location and orientation; (2) automated mechanically scanned transducers; or (3) electronic scanning with 2D element-array transducers.

Binary numbers use only the digits _____. Each column of a binary number represents double the column to its right.

0 and 1 double

In the binary numbering system, this allows numbers from ________ to be stored (a 16-shade system).

0 to 15

real-time display (TERM)

A display that, with a sufficient frame rate, appears to image moving structures or a changing scan plane continuously.

frame (TERM)

A single image produced by one complete scan of the sound beam.

scan converter (TERM)

An electronic device that reformats echo data into an image form for image processing, storage, and display.

panoramic imaging (TERM)

An expansion of the field of view beyond the normal limits of a transducer scan plane.

_________________ is the ability of a gray-scale display to distinguish between echoes of slightly different intensities.

Contrast resolution

_________________ is accomplished by adding new information to one end of an image, spatially correlating the overlapping old echoes to properly locate the new ones.

Panoramic imaging

____________ is the averaging of sequential frames for providing a smoother image appearance and for reduction of noise

Persistence

pixel (TERM)

Picture element; the unit into which imaging information is divided for storage and display in a digital instrument.

[PERSISTENCE] Operator control permits _________________________ from zero up to some maximum.

averaging of a selectable number of sequential frames

_________ is signal and image processing done as echo data are stored in the memory.

Preprocessing

preprocessing (TERM)

Signal and image processing accomplished before storage in the memory.

_________________ is a technique in which scan lines are directed in multiple directions by phasing so that structures are interrogated more than once by the ultrasound beam

Spatial compounding

the memory elements are ___________, digital memories use the binary numbering system to store echo information in the ___________.

binary image memory.

If the digital memory were composed of a single-layer matrix checkerboard, each pixel location could store only one of two numbers: __________________.

a zero or a one.

Three-dimensional images are acquired by

assembling several 2D scans into a 3D volume of echo information in the image memory.

Storing each image in the memory as the sound beam is scanned through the anatomy permits display of a __________ out of the rapid sequence of several frames acquired each second in real-time sonographic instruments.

single image (frame)

Postprocessing determines how echo data ___________________ will appear on the display.

stored in the memory

[Scan conversion] a pulse emitted from the transducer ____________ into the body will result in a series of echoes that are located in appropriate memory locations straight down a column in memory at various depths, that is, various row locations

straight down

Information about the direction of each scan line and the location of echoes in depth down each scan line is used to determine __________.

the proper location in the memory (and thus on the display) for each echo.

The current tendency is to call this 4D imaging, where the fourth dimension is________. Although this term sounds fashionable for marketing purposes, it is inconsistent with previous terminology; that is, real-time 2D imaging is not called 3D.

time.