Ch. 21 - Computed Radiography

Question 1

What is the CR imaging process steps?

Answer 1

1. Latent image production
   a. Reading CR data

b. Analog-to-digital conversion (ADC)

2. Image Processing
   a. pre-processing (histogram and gray scale anaylsis)

b. post processing (frequency and spatial location processing)

3. image display

Question 2

What are characteristics of the photostimulable phosphor imaging plate?

Answer 2

1. Records and transmits image from x-ray beam
2. Inserted into a filmless cassette
3. Transferred to reader assembly for processing
4. PSPs are sensitive to low levels of radiation energy (scatter)

Question 3

Construction of a PSP Plate?

Answer 3

Question 4

what are Common PsP phospors ?

Answer 4

1. Barium fluorohalide bromides (BaFBR:Eu)
2. Barium fluorohalide Iodides
   BaFI:Eu)
3. Europium (Eu)
   - is considered an activator as it maintains the presence of e- holes in the PSP

Question 5

How is latent image formed?

Answer 5

1. Electron pattern stored in active layer of exposed IP “electron traps”
2. Fluorohalides absorb beam through photoelectric
   interactions
3. Fluorohalides trap electrons to create holes at Europium
   sites
4. Latent image is millions of electron holes trapped in an
   energy layer of atom

Important:
Latent image will lose approximately 25% of its energy in 8
hours and CR plates are very sensitive to post-exposure radiation

Question 6

What is the process of photostimulated luminescence (PSL)?

Answer 6

Reading the image plate involves a finely focused red laser beam that frees the trapped e-s, allowing them to return to a lower-energy state, referred to as PSL, which releases blue-purple light photons

Question 7

What is the two steps involved in image processing?

Step 1 only

Answer 7

Pre-processing includes all processing of raw data performed to correct flaws in image acquisition.

a. exposure field recognition
b. histogram analysis
c. *grayscale analysis

(this is where image is compared to pre-set values for the body part being examined)

Question 8

What is the two steps involved in image processing?

Step 2 only

Answer 8

Post processing includes manipulation of data that has been pre-processed

a. Frequency processing
b. Spatial location processing
c. *Edge enhancement (micro-calfication; trabeculae)
d. Image smoothing (suppesses noise)
e. Image stitching (scoliosis; Leg length studies)

Question 9

What are the impact of technical factors on CR image quality?

Answer 9

1. Too much Kvp = comptom scatter
2. Suboptimal mAs =quantum noise
3. CR plate response to radiation is linear and non-limiting