Physics

Question 1

Cathode is also called the?

Answer 1

Filament

Question 2

Anode is also called?

Answer 2

Target

Question 3

The cathode is what charge?

Answer 3

Negative

Question 4

The anode is what charge?

Answer 4

Positive.

Question 5

What is the purpose of the oil in an x-ray tube?

Answer 5

Electric shielding X-ray attenuation/protection Transmission of heat

Question 6

What percentage of the kinetic energy of the electrons colliding into the target gets converted to x-rays?

Answer 6

1%

Question 7

What are the three main ways to cool an x-ray tube?

Answer 7

Brute force - add more material to the anode Material approach - Add rhenium to the focal track. Add graphite or molybdenum to the anode disk for more heat capacity. Use liquid metal vacuum bearings for faster rotation of the anode. Add circular grooves in the anode. Add more rows to reduce scan duration (indirect) Paradigm Shift - new technologies (example dual-source)

Question 8

How many collimators does a CT have?

Answer 8

Two: Tube collimator and detector collimator

Question 9

What defines the slice thickness in a single slice CT?

Answer 9

Tube collimator

Question 10

What does a filtration do?

Answer 10

Filters out low-energy x-rays that contribute to patient dose and scatter

Question 11

What are filters normally made from?

Answer 11

Aluminium ~3mm

Question 12

What is the advantage of a bow-tie filter?

Answer 12

Allows a lot of x-rays to pass through the center of the patient and less to pass through the thinner margins of the patient.

Question 13

What type of detectors are used in CT?

Answer 13

Scintillation detectors

Question 14

What material is used in a scintillation detector?

Answer 14

Crystals - cesium iodide or cadmium tungstate

Question 15

What is another name for the third generation gantry?

Answer 15

Rotate/rotate - meaning the both the x-ray tube and detectors rotate

Question 16

When was CT invented?

Answer 16

1972

Question 17

Why was fourth generation CT created?

Answer 17

To get rid of the ring artifact

Question 18

What is the fourth generation CT?

Answer 18

Stationary detectors at 360 degree - very high cost

Question 19

What is the collimator pitch in a single slice system?

Answer 19

Ratio between the table movement per 360 degrees of rotation to collimator width (single slice CT)

Question 20

What is the detector pitch?

Answer 20

Ratio between the table movement per 360 degrees of rotation to detector width (single slice CT)

Question 21

What is the collimator pitch in a multi slice system?

Answer 21

Ratio of the detector pitch to the number of detector rows

Question 22

What does the pitch influence?

Answer 22

Dose Scan time Image quiality

Question 23

What is interpolation?

Answer 23

Reconstructing the CT image and filling in the blanks in helical scanning

Question 24

What do collimators determine in single slice vs multislice CT?

Answer 24

Single slice = detector width Multi slice = number of slices

Question 25

What is the table made out of to reduce artifacts?

Answer 25

Carbon fiber

Question 26

What is the scan field of view?

Answer 26

The area where there is complete overlap of the wedges of exposed area

Question 27

What is display field of view?

Answer 27

It is the area of the SFOV where the image is reconstructed. This determines pixel size.

Question 28

Slice thickness is proportional to the what?

Answer 28

The magnitude of the volume averaging

Question 29

Slice thickeness is inversely proportional to what?

Answer 29

The magnitude of noise

Question 30

Structures with wide inherent object contrast (bone, lung) should be viewed with what type of window?

Answer 30

Wide window... this suppresses noise. Therefore small slices are used for orthopedics because they can handle the noise

Question 31

Structures with narrow inherent contrast (brain, liver, spinal cord) show be viewed in?

Answer 31

A narrow window which enhances noise. Therefore 3-5mm slices are good cause they decrease noise and in crease signal

Question 32

What is this artifact? How does the nyquist theory play into it?

Answer 32

Aliasiing.. specifically ray aliaising. Nyquist theory states that you must have at least two samplings per wave length.

Question 33

How is aliasing created?

Answer 33

Insufficient data sampling leading to data ambiguity

Question 34

What are the two types of aliasing?

Answer 34

Ray View

Question 35

How to remedy aliasing?

Answer 35

Avoid high frequency/dense objects Quarter detector offset (where the center of the beam is offset by 1/4 of a detector) Dynamic focal spot (focal spot wobbles back and forth between two positions) Reduce rotation time

Question 36

What artifact is this?

Answer 36

Motion Slice mismatch Blurring Ghosting Streaks

Question 37

How do you correct for motion?

Answer 37

Underscanning - only collect datat from part of the tube revolution Overscanning - The tube rotates 400 degrees and

Question 38

What artifact is this?

Answer 38

Photon starvation

Question 39

What is photon starvation/streaking?

Answer 39

When you go through a highly dense area and it starves the beam of the appropriate amount of photons. Basically blocks the beam.

Question 40

What is this artifact?

Answer 40

Beam hardening

Question 41

What is this artifact?

Answer 41

Beam hardening

Question 42

What is this artifact?

Answer 42

Beam Hardening

Question 43

How does beam hardening happen?

Answer 43

You block the low energy and therefore there is increased average beam energy. This causes streaking because your beam passes through structures without being attenuated and therefore makes it look like a less dense structure than it is.

Question 44

What is this artifact?

Answer 44

Volume averaging

Question 45

What is this artifact?

Answer 45

Ring artifact

Question 46

What is this artifact?

Answer 46

Ring artifact

Question 47

How does the ring artifact happen?

Answer 47

Miscalibration of a detector or detector fails

Question 48

What is this artifact?

Answer 48

Stair step

Question 49

What is this artifact?

Answer 49

Metal artifact