CT (Beam) Collimation & Data Acquisition

Question 1

SSCT uses two types of collimation: Pre-patient and post-patient. What is PRE-patient collimation?

Answer 1

pre-patient: a mechanical device at the tube aperture; this limits the beam to slice width

Question 2

SSCT uses two types of collimation: Pre-patient and post-patient. What is POST-patient collimation?

Answer 2

post-patient: after the patient (duh) but before the detectors, this form of collimation limits the scatter reaching the IRs

Question 3

T/F: MSCT uses the same two types of collimation, but the big difference is when collimated, MSCT changes which detector rows will be active during acquisition.

Answer 3

true

Question 4

For MSCT, what is a Uniform Matrix-Array?

Answer 4

a detector array running longitudinally. each detector element is the same dimensions

Question 5

For MSCT, what is an Adaptive-Array?

Answer 5

a detector array in which DELs are smaller in towards the center and get incrementally wider toward the periphery

Question 6

For MSCT, what is a Hybrid-Array?

Answer 6

a detector array in which the center DELs are small and the outside DELs are large

Question 7

Define binning.

Answer 7

electronic combination of signal from adjacent detectors to form a reconstructed slice that is thicker than the individual detector width

Question 8

What type of scanning offers the most detail and best spacial resolution?
A. Helical B. Axial

Answer 8

B. Axial

Question 9

What part of the machine is responsible for converting the electronic signal to a digital one?

Answer 9

Analog-to-digital converter (ADC)

Question 10

Describe data channels.

Answer 10

data channels control the number of slices the system can acquire with each gantry rotation. The more data channels a system has, the thinner and more numerous slices it can produce with each rotation

Question 11

A MSCT system has 16 data channels, 64 detectors, each 1.25 mm thick. If all of the detectors are used at 1.25 mm thickness, what would be the slices thickness per gantry rotation?

Answer 11

64 x 1.25 = 80;
80 / 16 = 5;
=5 mm thick

Question 12

A decrease in slice thickness will cause a(n) __________ in number of gantry rotations. This would cause a(n) _______ in patient radiation dose.

Answer 12

increase; increase

Question 13

An increase in slice thickness will cause a(n) _______ in spacial resolution.

Answer 13

decrease

Question 14

During a scan, each sample of ray sum measurements made by the data acquisition system (DAS) is called a _______.

Answer 14

view

Question 15

A decrease in aperture size (an increase in primary beam collimation) causes a(n) _______ in noise level.

Answer 15

increase

Question 16

An increase in slice thickness will cause a(n) ______ in noise.

Answer 16

decrease