Lecture 3 Flashcards
Digitizing a signal from a radiographic unit means assigning a _______ ______ to each ______ ______?
Digital radiography uses ______ to convert incident x-rays into a digital image.
numerical value; signal point
detectors
Digital image begins as a(n) ______ signal.
analog
What is the smallest element in the digital image?
Pixel
Which is directly proportional to the spatial resolution?
A. Bit depth
B. Pixel Size
C. Matrix size
B. Pixel Size
What does bit depth illustrate?
What does bit depth affect?
Bit depth illustrates the number of shades of grey in the digital imaging system.
Bit depth affects contrast resolution
What two factors contribute to the formation of the digital image?
Spatial location & Gray level of the pixels in the matrix
A) T or F. Changing the size of the matrix will affect pixel size.
b) T or F. Changing the FOV affects the size of the matrix.
C) T or F. A change in the matrix or FOV will affect the size of the pixels
a) T
b) F
c) T
What is exposure index?
Exposure index refers to the amt of exposure received by the image receptor.
Define air kerma and give the unit of measurement.
When an IR is exposed, can the air kerma be determined?
Air kerma is a measurement of radiation energy absorbed in a unit of air. Jkg^-1 or Gray.
Yes
What is kSTD? What is it’s purpose? How is it derived?
Standard radiation exposure.
Ensures the equipment is functioning properly.
Derived by making exposures with additional filtration to simulate patient tissue
- What is kIND?
- What does it determine?
Indicated Equivalent Air Kerma, it is a measurement of incident radiation on the IR for a particular exposure.
Determines if the IR is over or underexposed.
What is kTGT?
Targeted Equivalent Air kerma, set of values set by the system manufacturer or system user to represent optimal exposures for specific anatomy.
1.What is the Deviation Index (DI)?
2. What does it determine?
3. Evaluate a DI of 0.0, +ve DI & -ve DI.
4. To increase the DI, we increase/decrease technique by?
1.Difference between the actual exposure (kIND) and the target exposure (kTGT)
- Determines if an image needs to be repeated.
- DI of 0.0 deems a perfect image, +ve DI means over exposed image, -ve DI means under exposed image.
- Increase = 25%, Decrease = 20&
What is the Modulation Transfer Function? It is the ratio of ______ to ______ .
Ability of a system to record variable spatial frequencies
object; image
- What is “noise”?
- Differentiate between anatomic noise & radiographic noise.
- What is Signal to Noise Ratio?
- A higher SNR results in _____ noise and _____ exposure to patient.
- Noise is defined as anything that interferes with the formation of an image.
- Anatomic noise - superimposition of body parts; Radiographic noise - equipment noise, quantum noise
- How much noise can be tolerated in an image.
- less; increase/higher
