Chapter 29 Creating the Digital Image

Film based radiography required a subject contrast difference of at least 10 percent between tissues, but the contrast enhancing capability of digital imaging can resolve structures with a subject contrast as low as ___ percent.

1

For a pixel size of 0.3 mm, what is the associated spacial frequency in line pairs per millimeter?

1.6 LP/mm

At least ___ pixels are required to record a line pair from a resolution template

2

To enable the enhanced contrast resolution an processing features of CT, MRI, CR, and DR, most digital imaging systems have their dynamic ranges set at _____________, _______________,or _______________.

2^8= 256 2^10=1024 2^12=4048

The human eye can only discern approximately ___ different levels of brightness.

32

What is the spacial frequency for an I are with 0.1 mm pixels

5

When pixel size is reduced to 0.1 mm, actual special resolution is about ___-___ LP/mm

6-8 (as of 1990 it is about 6-8 but prior to 1990 it was about 5)

If the pixels are 6 bits deep, they each have a range of ____ gray levels to choose from.

64

List the typical equivalent matrix sizes for the following medical imaging modalities: nuclear medicine=__________pixels sonography=_______pixels MRI and CT=________pixels DR and CR=________pixels

64x64 128x128 512x512 1024x1024

What are the three different general ways that post processing parameters can be modified?

By re-processing the image under a different procedural algorithm windowing by applying special features

To speed up transmission and allow the electronics in a display monitor to process them electrically, signals flowing out of the computer to the display monitor must pass through a __________-to-____________ converter.

Digital-to- analog

Why may the actual dynamic range set for image reconstruction be less than the bit depth of the computer system?

The human eye is only capable of discerning approximately 32 different levels of brightness therefore we do not need to see the full bit depth. plus by selecting a smaller range of pixel values the processing time can be accelerated.

Adjustments to the original image can be made in at least three different ways: 1. by re-processing the image under a different procedural __________ 2. by __________ 3. by applying special features

algorithm windowing

For each type of radiographic procedure, digital radiographic systems have the ideal dynamic range and average gray level settings for the anatomy pre-programmed into the system. Radiographers re really refer to these protocols as procedural _____________.

algorithms

The rounding up or down of measure pixel values to the nearest available digital number the computer can process is the function of the ____________-to-_____________ ________________.

analog -to- digital converter

To assign a single gray level to a pixel in the final image, within each voxels, the attenuation coefficients for various tissues must be ______________.

averaged

For radiographic images, the numerical value stored for each cell represents the ______________ ___________ assigned to that location.

brightness (or density)

For CR? the aperture is ________in shape, and the samplings overlap each other, because of the circular laser beam in the CR reader.

circular

The ratio or percentage of the original xray beam intensity absorbed by a particular tissue area within the patient is the tissues attenuation _______________.

coefficient

In DR, the number of available pixels is the number of detector elements embedded in the imaging plate, so _____________ of the xray beam is analogous to the scanning function.

collimation

Since DR uses hardware dexels, _____________ of the xray beam becomes analogous to the scanning function in digitizing an image.

collimation

Digital radiographic imaging became feasible when the exponential increase in the power of _______________ brought contrast enhancement capabilities up to an overwhelming level.

computers

Digital imaging systems were adopted when the power of computer reached a point where increases in ____________ resolution far outweighed the loss of __________ resolution.

contrast spacial

Display stations, as well as workstations, should always be in an area where ambient lighting can ____________.

controlled

Changing the window level from 80 to 300 causes the image to become __________.

darker

Increasing the window level makes the overall image _________, but the number of steps in the gray scale remains equal.

darker

The maximum range of pixel values a computer, monitor, or other hardware device can store is expressed as the "bit ________" of the pixels.

depth

For a particular physical area, the matrix size of an image (by pixel count) is __________ proportional to the spacial resolution or sharpness of the image.

directly

A computer terminal that is limited to image display and has no ability to permanently manipulate or change the image is called a ________ ___________.

display station

What type of image viewing station is likely to be placed in an emergency room?

display terminal

Increasing the brightness brings the level number

down

Increasing the contrast brings the window number

down

To speed up processing time, the system software selects a smaller range of pixel values from the bit depth which will be made available to build up images, referred to as the systems ___________ _________.

dynamic range

The file size of medical images can be a problem when thousands of images are stored. The formula to determine the file size of an image is:

file size= matrix size x bit depth

What is the formula for the computer file size required for a medical image?

file size= matrix size x bit depth

The window width controls the length of _______ _________ in the image.

gray scale

For each anatomical procedure, what two image qualities are pre-set within the procedural algorithms?

gray scale average gray level (brightness)

For a given physical area, the size of the image matrix, by pixel count, is ____________ proportional to pixel size, and __________ proportional to spacial resolution.

inversely directly

Increasing the window width ___________ the gray scale, but does not alter the average brightness.

lengthens

The adjusted overall brightness or average brightness of the image is referred to as the window ________.

level

For a particular image pixel, the higher the attenuation coefficient for xray in the corresponding voxels, the ___________ the gray level that will be assigned to the pixel by the imaging system.

lighter

Workstations should be located in an area where ambient _____________ is subdued.

lighting

The greater the dynamic range, the __________ the gray scale in the image.

longer

All digital images, whether photographic, radiographic, or fluoroscopic, consist of a _________ of numeric values that can be stored in a computer

matrix

The longer the gray scale, the _______ details can be represented in an image.

more

Changing the field of view, or the physical size of the matrix, may affect spacial resolution, but only if these changes alter the ______ size.

pixel

For radiographic images, each _______ in the image represents a voxels within the patient.

pixel

Ultimately, what really matters for spacial resolution is ______ size.

pixel

Each square cell within a digital images is called a ________, which is an acronym for ___________ _____________.

pixel picture element

The set dynamic range for an i aging system must be much greater than the capability of the human eye in order to allow for ________-______________ of the image.

post-processing

Another factor in determining an approximate dynamic range is that the range chosen must be wide enough to allow post-____________ of the image.

processing

Windowing provides more flexibility and accuracy than simply re-_______________ the image under a different procedural algorithm.

processing

The final step in digitizing an image is to assign to each pixel a discrete numerical value from a pre-designated gray scale which the computer can process. This process is called ___________.

quantizing

Workstations used for diagnosis by radiologists consist of two high ______________ display monitors and peripherals.

resolution

For CR, the scanning aperture is ______ in shape.

round

These attenuation coefficients must then be ____________ out by the ARC to discrete values from the computers dynamic range and stored as gray levels.

rounded

The initial measurement of pixel values within an image field is called ______________.

sampling

The second step for digitizing an analog image is to measure the intensity of light or radiation from each designated pixel area. This is called __________.

sampling

The first step to digitizing any analog image is to divide the image up into a matrix of pixel cells by a process called ________.

scanning

Digital images could only achieve the resolution of analog images by reducing pixels to the size of a single ________ __________ _________

silver bromide crystal

By comparison, _____-speed film systems were once able to achieve a spacial resolution of about 10-12 LP/mm

slow

The trade off for the Digital image is that extremely ________ details with slight separation between them cannot be resolved

small

For a given physical area, the larger the image matrix, the __________ the pixels, and the ___________ the special resolution of the image.

smaller greater

Overall resolution of an image is dependent upon both _________ resolution and contrast

spacial

For DR, the sampling aperture is _______ in shape and the samplings are adjacent to each other, since they are determined by the detector elements.

square

For CR and DR, the saamp,ed voxels within the patient take on the shape of ________ ________.

square tubes

Although each voxels from a CT scan is in the shape of a cube, the voxels from a CR or DR scan take on the shape of square _______ that extend all the way from the front to the back of the patient.

tubes

The brightness of a pixel in the displayed electronic image is a function of the electronic ____________ applied to that segment of the monitor screen.

voltage

When an image is brought up on a display monitor screen, the brightness of each pixel in the image is controlled by the amount of electrical __________ applied to it, which depends on the gray level number stored for that pixel.

voltage

To determine the attenuation coefficient for a tissues, data are acquired from three-dimensional vo,fumes of tissue within the patient called ________, which is an acronym for __________ ______________.

voxels volume elements

The user friendly "contrast" adjustment is exactly inverse to window _______.

width

_______________ refers to adjusting the brightness and contrast of the image displayed at the monitor screen with controls on the console as the image is being viewed.

windowing

A fully equipped computer terminal that can be used to manipulate image quality and permanently save changes made to the image in the PACS system is called a __________________.

workstation