Digital Ch 2 Carter Flashcards
Kinetic energy released per unit mass; measures (in joules) radiation energy that is absorbed in a unit of air.
air kerma
A device or system that captures or measures a continuously changing signal.
An ________ signal wave is recorded or used in its original form.
Analog
A digital image is separated into ________, with discrete (whole numbers only) values.
The process of associating the ________ with discrete values defines maximum contrast resolution.
Pixel
The ____ of the pixel is directly related to the amount of spatial resolution or detail in the image
Pixel Size
More pixels = greater spatial resolution
Less pixels = less spatial resolution
number of bits within a pixel
2(16) = 65,536
Each pixel has a gray level
Determines the image contrast resolution
Pixel Bit Depth
Columns and rows
Images are digitized by spatial location and intensity (gray level)
512 x 512 = 262,144
Matrix
X-ray field
Key point - a change in the x-ray field will not change the matrix size
Field of view
Exposure Indicator
Amount of exposure received by IR (not patient)
CR System - Exposure Index (EI)
DR System - Deviated Index (DI)
measurement of radiation energy (joules or J) absorbed in a unit of air (kg).
Therefore the quantity kerma is expressed as J/kg or gray (Gy).
Air Kerma
K(std)
standard exposure typical of an imaging receptor system
Additional filtration is used to simulate patient tissue
measurement is derived from reading the pixel values produced by the exposure on an IR
Aids in determining if the patient was under, over or adequate exposed.
K(ind)
Indicated equivalent air kerma
A value set by system manufacturer or the system user, that represents an optimal exposure for each specific body part and view
Determines the values for the “perfect” chest x-ray :)
K(tgt)
Target equivalent air kerma
difference between the actual exposure K(ind)and the target exposure K(tgt)
Let’s the tech know that EXPOSURE REALLY was under, over or adequately exposed….
Deviated Index
Describe the variances that could cause pixel values to be off…
- A prostheses within the image
- Gonadal shielding within the image
- Failure of the system to recognize the collimated border
- An unexpected body part in the image
appearance on the display monitor of the computer.
The amount of light transmitted by the monitor as well as light reflected off the monitor can affect image appearance
Brightness
ability of the digital system to display subtle changes in the shade of gray
Contrast resolution
Does kVp matter in digital imaging?
Explain why?
Certainly does…an image needs kVp to penetrate tissues AND provide enough gray tones for signal separation…
ability of the imaging system to demonstrate small details of an object
Spatial resolution
How is spatial resolution determined?
Provide the values for DR system
Line pairs/mm
2.5 lp/mm - DR
10 /l/mm - CR
ability of a system to record available spatial frequencies
Modulation Transfer Function
MTF is a ratio = 1% = 100%
Larger structures are easier to image - i.e. Liver, spleen, 10 mm lung tumor
Smaller structures more difficult to image - i.e. Calculi, 3 mm lung tumor
anything that interferes with the formation of the image
Noise
Two kinds: anatomic = superimposition of body structures
Radiographic = equipment & quantum
When determining the appropriate exposure techniques to use for a particular body part, it must be decided by the radiologist and technologist how much noise can be tolerated in the image
SNR = signal-to-noise-ratio
Higher signal = better image, low noise
range of exposure diagnostic image values the image detector is able to produce
Latitude
values that are just above background noise and higher and that refer to how much signal amplification is needed…higher the dynamic range of the detector = better images
measurement of the percentage of x-rays that is absorbed when they hit the detector
Detective Quantum Efficiency. (DQE)
DQE of selenium systems is higher than that for PSP, CCD, and CMOS systems
Fill factor = large areas with TFT photodiodes - more radiation detected and better signal acquisition….just saying :)
Instagram is just Twitter for people who go outside.
Hahahahaha!
The exposure index of an AP thoracic was 1350 using the Carestream/Kodak System.. The technical factors were 75 kVP @ 25 mAs on a patient who measured 28 cm cm.
How would you change your technical factors to improve this image? Explain.
Exposure index for Kodak is 1700 - 2100 - value of 2000 is target exposure.
2000 - 1350 = 650 off the target
To increase the value 300 it requires a 50% increase mAs. In this case, the technologist should raise the kVp to 50 mAs.
An AP Abdomen image was obtained using 88 kVp and 32 mAs. The DI was + 2.0. How would adjust the technical factors to achieve a value closer to 0? Explain your answer show the formula(s) you would use.
- 1.0 = underexposure = 20% increase (for each -1.0 value)
+ 1.0 = overexposure = 25% decrease (for each +1.0 value
In this case the technical factor should be decreased 50%
- decrease the kVp by 15% = 88 - 13 = 75
OR - decrease mAs by 50% and use 16 mAs
OR decrease kVp by 7.5% = 6 AND decrease the mAs by 25% 24 ( 80 kVp @ 24 mAs)
