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CT boards > CT Principles part 1 > Flashcards

CT Principles part 1 Flashcards

1
Q

Name the steps that the xrays go through from generation to what is seen at the console

A

Xrays are produced by the tube, emitted, filtered, and collimated. Then xray penetration occurs (through the patient), passes through post patient collimators, striking detectors. The computer system then converts that to a digital signal that the computer processes.

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2
Q

What is the relationship between the number of bits of the ADC and it’s accuracy?

A

Direct - the more bits the higher the accuracy

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3
Q

What is the term that describes the reduction in intensity of the x-ray beam as it passes through the patient by either absorption or scatter?

A

Attenuation

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4
Q

When discussing Beam Quality - how do homogeneous and heterogeneous differ?

A

A homogeneous beam is composed of photons with the same amount of energy while a heterogeneous beam possesses varying energies

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5
Q

Name a term that describes a quantitative measurement of attenuation per cm of an absorber (ie. bone or soft tissue)

A

Linear Attenuation Coefficient

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6
Q

What two main factors affect the Linear Attenuation Coefficient?

A

The energy of the beam and the atomic number of the absorber

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7
Q

What is another name for ‘CT numbers’?

A

Hounsfield Units

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8
Q

What is the HU of water?

A

zero

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9
Q

What is the HU of average bone?

A

1000

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10
Q

What is the HU of fresh blood?

A

20-50

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11
Q

What is the HU of Air?

A

-1000

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12
Q

What is the HU of fat?

A

-100

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13
Q

What is meant by “beam hardening”

A

This is when low energy, long wavelength photos are absorbed as the xray beam passes through an object (such as a filter or the patient) leaving the remaining beam with a higher average energy or penetrating power.

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14
Q

A single measurement of the x-ray attenuation along a path between the source and a detector is know as:

A

a ray or single ray

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15
Q

What is a view?

A

A collection of rays from one viewing angle

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16
Q

What is the equation for determining the total number of data samples?

A

Data samples = # of detectors x # of samples at each detector

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17
Q

What is the formula to calculate volume coverage aka Z axis coverage?

A

pitch x collimation x scan time / gantry rotation time.

18
Q

The reduction in intensity of the x-ray beam as it passes through the patient by either absorption or scatter of photons from the beam is termed:

A

Attenuation

19
Q

A quantitative measurement of attenuation per cm of an absorber for example bone or soft tissue is called:

A

Linear attenuation coefficient

20
Q

The absorption of low energy, long wavelength x-ray photons within the anatomical structure with higher energy photons continuing through the body with an increasing mean beam energy or penetrating power is referred to as:

A

Beam Hardening

21
Q

The movement of the tube & detectors with x-ray transmission is termed:

A

scanning

22
Q

As a result of the scanning process, a single measurement of the x-ray attenuation along a path between the source and detector is termed:

A

ray

23
Q

A view generates a ______ which is an electric signal relative to the amount of attenuation that has occurred as the x-ray is transmitted through the patient.

A

Profile

24
Q

The number of detectors multiplied by the number of samples at each detector result in the:

A

Data Sample Total

25
Q

What year was helical (spiral) scanning introduced? [think Taylor Swift]

A

1989

26
Q

Gaps between slices, inter scan delay, variability of contrast media enhancement, inconsistent respiration or motion, and inaccurate 3D or reformations are all limitations of what kind of scanning?

A

Axial or step-and-shoot

27
Q

What is the term for the geometric corrections that take place to convert the fan beam information to parallel beam information?

A

interpolation

28
Q

What are three types of interpolation that are used in CT?

A
  1. Fan beam to parallel beam interpolation 2. helical to single slice interpolation 3. helical to multislice interpolation
29
Q

Increasing pitch ______ coverage

A

increases

30
Q

Increasing pitch ______ overall scan time

A

reduces

31
Q

Increasing pitch ______ patient dose

A

reduces

32
Q

Increasing pitch ______ resolution in the slice (Z) direction.

A

reduces

33
Q

What is the definition of pitch in a single slice helical scan

A

PITCH = TABLE TRAVEL PER GANTRY ROTATION DIVIDED BY BEAM COLLIMATION

34
Q

What is the definition of pitch in a multislice helical scan?

A

Pitch - table travel per gantry rotation divided by the number of channels times the detector size

35
Q

How is pitch calculated differently in single slice CT vs MDCT?

A

Single slice is divided by the beam collimation where in MDCT you must divide by the (number of channels x detector size)

36
Q

How do you calculate Z axis coverage?

A

pitch x section thickness x total scan time

37
Q

What could be one negative consequence of reducing you scan time by increasing pitch?

A

You might miss small lesions or fractures.

38
Q

Gapless examination of Anatomy, rapid volume scanning, reduced exam time, reduced motion artifacts, reconstruction of arbitrary slices, no mis-registration due to respiration level changes, less contrast required, uniform contrast enhancement, better multiplanar and 3D images, allows CT fluoro, CT angio, CT endoscopy, 3DCT ARE ALL ADVANTAGES OF WHAT KIND OF SCANNING (helical or axial)?

A

Helical

39
Q

After x-rays are emitted from the CT x-ray tube, they pass through a ______ to shape the energy of the beam.

A

Beam filter

40
Q

Slice thickness is impaced by (a. collimator system b. beam filter system c. DAC d. ADC)

A

a. collimator system

41
Q

After the x-ray beam passes through the patient it is directed through the ______.

A

detector collimator

42
Q

The x-ray beam is picked up by the _____ device that measures the amount of attenuation that occurs.

A

detector

CT boards (20 decks)

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