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
