Principles Week 8

What is the pixel size in millimeters of a 512 matrix with a 30cm field of view? Pixel size = FOV / matrix

0.6mm

Some Advantages of digital imaging over conventional screen/film radiography include: 1. immediate visualization of the image 2. ability to adjust the image post exposure 3. highest spatial resolution possible

1 and 2

What is the pixel size in millimeters of a 256 matrix with a 25 cm field of view? Pixel size = FOV / matrix

1.0mm

Of the following: Which matrix size has the smallest pixels? 128 x 128 256 x 256 512 x 512 1024 x 1024

1024 x 1024

why is DR used more than CR?

7% reimbursement for image taken with CR vs full reimbursement with DR

digital imaging is available in two forms:

Computed radiography (CR) Direct radiography (DR)

Contrast resolution in a digital image:

Is the ability of a system to display a large number of shades of gray Is controlled by the number of pixels and pixel bit depth

A digital matrix is made up of:

a matrix of pixels

Which of the following is a contributor to image noise? 1. Scatter radiation 2. plus density artifacts 3. minus densities artifacts

all of the above

Any unwanted information on an image is the definition for:

artifacts

language used by computers

binary

The number of shades of gray that can be demonstrated in a digital image is affected by:

bit depth

calculated using the formula 2^n; reports the number of grey shades available

bit depth

The amount of luminance of an image or link displayed by a monitor is termed:

brightness

The window level control is used to alter image

brightness

amount of luminance an image displays on a monitor

brightness

If a pixel has a bit depth of 8, this means that the pixel: ( hint--- 2n)

can produce 256 shades of gray

The window width control is used to alter image:

contrast

resolution; the ability of a system to distinguish between and/or display objects that attenuate photons differently

contrast

In general, as image noise increases:

contrast decreases

the higher the pixel number, the ______ the anatomy in that cell

darker

increased image noise = ________ contrast

decreased

increased pixel size = ___________ sharpness

decreased

less attenuation of remnant beam = higher pixel values = __________ brightness

decreased

If pixel pitch is increased, the image will have/display:

decreased spatial resolution

the ability to detect and display a large range of radiographic densities

dynamic range

portion of the collimated field that contains the anatomy and displayed on the monitor

field of view

which exposure type has a narrow range of exposure

film screen

On a PA projection of the wrist, you notice what appears to be a soft tissue mass superimposed over the bony anatomy in the digital DR image. When you inspect the patient, you notice the presence of a large linear scar from a previous injury. The visualization of this scar in the image is primarily due to what characteristic of digital detectors?

high contrast resolution

decreased pixel pitch = ____________ spatial resolution

higher

increased pixel density (pixels per sq. inch) = __________ spatial resolution

higher

The field of view (FOV) best describes:

how much of the patient is imaged in a matrix

If the field of view remains unchanged AND the matrix size increases, then the resulting spatial resolution will be _____ because the pixel size will decrease.

improved

IF the field of view (FOV) increases AND the matrix size is unchanged, then the resulting pixel size MUST ________ and as a result the spatial resolution will decrease.

increase

greater attenuation of remnant beam = lower pixel values = __________ brightness

increased

increased matrix size = _________ sharpness

increased

Which of the following image quality changes is undesirable?

increased image noise

If pixel density is increased, the image will have/display:

increased spatial resolution

Spatial detail (resolution) in a digital imaging system would be improved MOST by:

increasing the number of pixels

Which of the following will allow more line pairs per millimeter to be imaged? using a smaller matrix increasing the number of pixels in the matrix increasing the bit depth using a higher frequency signal

increasing the number of pixels in the matrix

matrix size and pixel size are _________ related

inversely increased matrix=decreased pixel size

what does a narrow range of exposure mean

it's very easy to be over or under exposed

array of cells arranged in columns and rows

matrix

If the window width control is opened wider (a larger range):

more gray shades will be available

image quality constituted of unwanted or useless background information

noise

The H and D curve for digital imaging is linear rather than S-shaped because:

of a wider dynamic range

each cell in a matrix; short for picture element

pixel

the distance from the middle of one pixel to the middle of an adjacent pixel

pixel pitch

if FOV remains constant and the matrix size is increased- pixel size: spatial resolution:

pixel size: decreases spatial resolution: increases

if FOV decreases and matrix size stays constant- pixel size: spatial resolution:

pixel size: decreases spatial resolution: increases

if FOV increases and matrix size stays constant- pixel size: spatial resolution:

pixel size: increases spatial resolution: decreases

if FOV remains constant and the matrix size is decreased- pixel size: spatial resolution:

pixel size: increases spatial resolution: decreases

same matrix with smaller FOV = improved resolution, why?

pixels get smaller

Digital systems have _________ spatial resolution than film, but ____________ contrast resolution

poorer higher

The use of high-resolution monitors: (High resolution means a monitor with a large matrix size)

promotes or improves the visibility of anatomical structures

The anatomical structures that would cause the greatest degree of x-ray photon attenuation and image brightness would be those that are:

radiopaque

If a high degree of quantum mottle is noted on an image, the most appropriate solution to correct this exposure error would be to:

repeat the exposure using a higher mAs

formula to calculate this is 1/2(PS); determines the number of line pairs that can be resolved if the pixel size is known

spatial frequency

true or false: changes in the FOV do not affect the matrix size

true

true or false: the term field of view is synonymous with x-ray field

true

the minimum number of pixels needed to image one line per millimeter

two

postprocessing function that alters image brightness

window level

postprocessing function that alters image contrast or greyscale

window width