Digital Ch 2 Carter

Question 1

Kinetic energy released per unit mass; measures (in joules) radiation energy that is absorbed in a unit of air.

Answer 1

air kerma

Question 2

A device or system that captures or measures a continuously changing signal.

An ________ signal wave is recorded or used in its original form.

Answer 2

Analog

Question 3

A digital image is separated into ________, with discrete (whole numbers only) values.

The process of associating the ________ with discrete values defines maximum contrast resolution.

Answer 3

Pixel

Question 4

The ____ of the pixel is directly related to the amount of spatial resolution or detail in the image

Answer 4

Pixel Size

More pixels = greater spatial resolution
Less pixels = less spatial resolution

Question 5

number of bits within a pixel

2(16) = 65,536

Each pixel has a gray level

Determines the image contrast resolution

Answer 5

Pixel Bit Depth

Question 6

Columns and rows

Images are digitized by spatial location and intensity (gray level)

512 x 512 = 262,144

Answer 6

Matrix

Question 7

X-ray field

Key point - a change in the x-ray field will not change the matrix size

Answer 7

Field of view

Question 8

Exposure Indicator

Answer 8

Amount of exposure received by IR (not patient)

CR System - Exposure Index (EI)
DR System - Deviated Index (DI)

Question 9

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).

Answer 9

Air Kerma

Question 10

K(std)

Answer 10

standard exposure typical of an imaging receptor system

Additional filtration is used to simulate patient tissue

Question 11

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.

Answer 11

K(ind)

Indicated equivalent air kerma

Question 12

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 :)

Answer 12

K(tgt)

Target equivalent air kerma

Question 13

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….

Answer 13

Deviated Index

Question 14

Describe the variances that could cause pixel values to be off…

Answer 14

• 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

Question 15

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

Answer 15

Brightness

Question 16

ability of the digital system to display subtle changes in the shade of gray

Answer 16

Contrast resolution

Question 17

Does kVp matter in digital imaging?

Explain why?

Answer 17

Certainly does…an image needs kVp to penetrate tissues AND provide enough gray tones for signal separation…

Question 18

ability of the imaging system to demonstrate small details of an object

Answer 18

Spatial resolution

Question 19

How is spatial resolution determined?

Provide the values for DR system

Answer 19

Line pairs/mm

2.5 lp/mm - DR
10 /l/mm - CR

Question 20

ability of a system to record available spatial frequencies

Answer 20

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

Question 21

anything that interferes with the formation of the image

Answer 21

Noise

Two kinds: anatomic = superimposition of body structures
Radiographic = equipment & quantum

Question 22

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

Answer 22

SNR = signal-to-noise-ratio

Higher signal = better image, low noise

Question 23

range of exposure diagnostic image values the image detector is able to produce

Answer 23

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

Question 24

measurement of the percentage of x-rays that is absorbed when they hit the detector

Answer 24

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 :)

Question 25

Instagram is just Twitter for people who go outside.

Answer 25

Hahahahaha!

Question 26

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.

Answer 26

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.

Question 27

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.

Answer 27

• 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%

1. decrease the kVp by 15% = 88 - 13 = 75
   OR
2. 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)