CR-DR MIDTERMS Flashcards
Most people can see objects as small
200 um
is described by the quantity “spatial frequency”.
spatial resolution
dots were not high contrast, the spatial resolution of the eye would require
larger dots.
ability of an imaging system to resolve and render on the image a small high-contrast object.
Spatial Resolution
is a black line on a light background.
line pair.
concept of spatial frequency does not refer to size but to the
line pair.
One line pair consists
line and an interspace of the same width as the line
unit of line pair
lp/mm
*An imaging system with higher spatial frequency has better
spatial resolution.
Bone trabeculae, breast microcalcifications, and contrast-filled vesselsare high-frequency objects; therefore, they are more
difficult to image.
large soft tissues such as the liver, kidneys, and brain have low spatial frequency and therefore
easy to image.
ability of an imaging system to render objects of different sizes onto an image
Modulation transfer function
note
This is just another way of saying that small objects are harder to image.
two bar pattern test tools with spatial frequencies up to
20 lp/mm
is the ability to distinguish many shades of gray from black to white.
Contrast resolution
The principal descriptor for contrast resolution is grayscale,
dynamic range.
is the number of gray shades that an imaging system can reproduce
dynamic range.
The dynamic range of digital imaging systems is identified by the
bit capacity of each pixel.
CT and MRI system dynami range
12-bit dynamic range
DR dynamic range
14
Mammo dynamic range
16
portion of the image-forming x-rays that represents anatomy.
signal
With acceleration to all-digital imaging, we have the opportunity to reduce patient doses by
20% to 50%,
Spatial resolution in screen-film radiography is determined principally by
focal-spot size.
Spatial resolution in digital imaging is determined by
pixel size
type of image such as paintings and printed photographs. Presents various levels of brightness and colors.
Analog image
recorded as multiple numeric values and are divided into an array of small elements that can be processed in many different ways
Digital image
Critical characteristics of digital image:
*Spatial resolution
*Contrast resolution
*Noise
*Dose efficiency
Smallest element in a digital image.
PIXEL
-Contains the smallest divisible component of a digital image (bit).
PIXEL
Directly related to the amount of spatial resolution or detail in the image
Pixel size
Number of bits within a pixel.
Pixel bit depth
Represents the gray level.
Pixel bit depth
-A square arrangement of numbers (pixel values) in columns and rows.
MATRIX
Amount of body part or patient included in the image.
FIELD OF VIEW
- Refers to the amount of exposure received by the IR, not by the patient
EXPOSURE INDICATORS
NOTE
standard exposure typical of that imaging receptor system
Standardized radiation exposure (KSTD)
measurement of the radiation that was incident on the IR for that particular exposure.
Indicated equivalent air kerma (KIND)
set of values, established by either the system manufacturer or the system user,
Target equivalent air kerma value (KTGT)
the difference between the actual exposure (KIND) and the target exposure (KTGT),
Deviation index (DI)
Refers to its appearance on the display monitor of the computer and is a function of the monitor’s ability to emit light through the surface of the display
BRIGHTNESS
BRIGHTNESS IS MEASURED BY
photometer.
Refers to the ability of the digital system to display subtle changes in the shade of gray.
CONTRAST RESOLUTION
Directly related to the bit depth of the pixels in the image
CONTRAST RESOLUTION
Refers to the ability of the imaging system to demonstrate small details on an object
SPATIAL RESOLUTION
PSP pixel size
200μm
Gadolinium AMFPI size -
150μm
Cesium iodide AMFPI size
50μm
To quantify gain or loss of resolution,
Modulation Transfer Function
Ability of a system to record available spatial frequencies
MTF
ratio of the image to the object; thus a perfect system would have an MT OF ____
1% or 100%.
-Anything that interferes with the formation of the image.
NOISE
occurs if body parts are superimposed
Anatomic noise
occurs during the acquisition of the images. Comprises of equipment noise and quantum noise.
Radiographic noise
from noise in the detector elements and non-uniform detector responses.
Equipment noise
Refers to the range of exposure diagnostic image values the image detector is able to produce.
EXPOSURE LATITUDE
How efficiently a system converts the x-ray input signal into a useful output image.
DETECTIVE QUANTUM EFFICIENCY8
