Ch. 5: Direct Conversion

Question 1

What material is commonly used for direct conversion detectors?

Answer 1

Amorphous selenium (a-Se).

Question 2

What happens in direct conversion?

Answer 2

X-ray photons are directly converted into an electrical signal.

Question 3

What is the thickness of the selenium layer for radiography and mammography?

Answer 3

500 µm for radiography and 200–250 µm for mammography.

Question 4

What are the small elements of a TFT array called?

Answer 4

Pixels or detector elements (dels).

Question 5

What component isolates each pixel element?

Answer 5

A field-effect transistor (FET) or silicon TFT.

Question 6

How fast can over 1 million pixels be read and converted into a digital image?

Answer 6

In less than one second.

Question 7

What do the integrated circuits along the detector edges control?

Answer 7

Line scanning, amplification, and analog-to-digital conversion.