Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

EXAM QS & A Practice > CT > Flashcards

CT Flashcards

1
Q

Why CT

A

CT resolves issues associated with projection radiography: superimposition of structures and limited ability to distinguish structures with low contrast resolution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What does LCD mean?

A

Ability to identify and differentiate objects with similar level of radiographic density , attenuation coefficient and level of grey form its homogeneous background

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Briefly outline the CT overall process?

A
  1. CT scanner has an x-ray tube within a gantry that rotates 360 degrees around a patient
    2- A fan shaped beam ‘slices’ through the anatomical area being scanned
    3- An array of digital detectors opposite the x-ray source capture the attenuated beam
    4- Images are processed and can be viewed in multiple planes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What characteristics should a CT detector have?

A
  • small in size for better spatial resolution and capability of combining multiple detectors to form a detector array
  • high detection efficiency and high sensitivity to capture a dynamic range of x-ray intensities
  • A fast response with negligible afterglow
  • higher stability to function under the high speeds of the rotating gantry
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What does ‘dynamic range’ mean? (what other module does this come under too)

A

The range of x-ray intensities that a detector can accurately capture and covert into usable signals. wide dynamic range allows both the capture of both low and high intensities (comes under digital image processing)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What features does a CT x-ray tube have and what implication do they have?

A
  • larger and thicker anode to absorb and dissipate large amounts of heat
  • modified cathode assembly to produce a smaller focal spot , allowing a more focused x-ray beam for sharper images
  • metal envelope and ceramic insulators providing stability under high heat and prevent overheating
  • flying focal spot to allow precise control of the focal position on the anode to enhance image sharpness

All in all the features allow continuous exposure times at higher KV and mA required for CT scanning

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

A CT detector is designed for better spatial resolution. What does spatial resolution mean/ refer to?

A

The detectors ability to differentiate between small structures that are close together. higher spatial resolution allows the detection of fine details like minor hairline fracture

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is slip ring technology, how does it work and what did it enable us to do?

A

Slip ring technology is a electromechanical device that allows the the transfer of power and electrical signals between the stationary and rotaing components of a CT scanner.

The electromechanical brushes press and slide against rotating circular conductors with grooves enabling energy transfer and continuous gantry rotation without the need for cables.

This innovation has allowed:
- Helical Scanning
- FasterScanning
- Better image quality

Ensures fast, seamless, and uninterrupted imaging.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What does attenuation mean and its relation to x-ray imaging, and examples?

A

Attenuation is a measure of how easily a material can be penetrated by an x-ray beam . We use the term and value attenuation co-effiecient to qunatify and describe how much the of the beam is absorbed or scattered per unit thickness. Denser tissues (like bone) attenuate more X-rays than less dense tissues (like air or fat).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How are images produced in CT?

A
  1. The gantry rotates around the patient
  2. The x-ray beam goes through the patient and out and recieved by the detector
    3- The detector captures x-ray transmission through 360 degrees around the body, forming what is known as ray sum
    4 - An attenuation profile is created by gathering ray sums from the volumes of material. These co-efficients are converted into Hounsfield Units and displayed as shades of grey in the final image through image reconstructions algorithms like BP and FBP
    ___________________
    5- Back projection is used to construct the image - resulting in a blurred image representation
    6- Filtered Back Projection is used to sharpen edges and subtract out extra smearing using the sharpening filter.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is back projection and how is it used? and what can be done additionally to improve diagnostic value?

A

Back projection is used to construct the image - which is an algorithm that works out the attenuation calculations in reverse based on the angle they were originally acquired and smeared back into the image, creating a blurry representation that then goes through filtered back projection to sharpen edges and reduce blurring created by standard back projection using a sharpening filter to get a better diagnostic image.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is filtered back projection and what is it used for?

A

Filtered back projection is an algorithm used to sharpen edges and reduce blurring created by standard back projection using a sharpening filter.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How is the CT image displayed?

A

The grey-scale image produced and diplayed is that of a square matrix -a grid of rows and columns. Each square in the grid represents a pixels, each of which represents a voxel - the small volume of the patients tissue.

Each voxel has a hounsfield unit (CT number based on the x-ray attenuation of that section).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Whats an image matrix?

A

A grid of rows and columns used to form a digital image.
Each square in the grid represents a pixel.
The matrix size (e.g., 512 × 512) determines the resolution of the image; larger matrices provide finer detail.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are Hounsfield Units and what is their significance?

A

A linear scale of grey scale values (densities) based on tissue density and measured attenuation coeffiecients.

Water is assigned a HU of 0, while air is -1000 HU and dense structures like bone range up to +1000

Significance:

  • Tissue Differentiation
  • Pathology Identification:
  • Quantitative Analysis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Explain tissue differentiation as a significance of HU?

A

Tissue Differentiation: HU values allow radiologists to distinguish between different tissue types based on their density (e.g., fat, muscle, bone).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Explain Pathology Identification as a significance of HU?

A

Pathology Identification: Helps detect abnormalities such as tumours, haemorrhages, and cysts by comparing their density to normal tissues.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What do we mean by windowing and how do we do this?

A

A process used to adjust the CT image greyscale and enhance the visibility of certain structures by manipulating the CT numbers

To do this we can manipulate the window width ( the range of CT numbers that an image contains) affecting contrast and window length (the midpoint of the range of the CT numbers displayed) affecting brightness

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What does narrow window width result in?

A

Enhanced contrast

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What’s the main difference between axial and helical scanning?

A

Axial -
1- the gantry stops and rotates to acquire data from a single slice

2- x-rays switched off

3- patient moves to the next slice

4- Rotates to acquire data from the next slice

Helical - involves continuous gantry rotation with a simultaneously moving table, resulting in a continuous spiral scanning pattern

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

List the advantages of helical scanning in comparison to axial scanning?

A

FLIP-M”
• Faster speed
• Longer continuous scanning (avoiding respiratory mis-registrations)
• Increased pitch control (to reduce scan time/radiation dose while covering the same volume)
• Provides overlapping slices (better reconstruction and revealing smaller lesions)
• More effective use of contrast agents

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is pitch?

A

Pitch is the ratio of speed of the table per gantry rotation in relation to the beam width

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Impact of pitch greater than 1?

A

Pitch is greater than 1:
- table travels more than the beam width , so there are gaps
- lower radiation does
- quicker scan
- low SNR because of fewer projections obtained so lower image quality

24
Q

Impact of pitch less than 1?

A

Pitch is less than 1:
- table moves less than the beam width so there is overlap
- better z-axis resolution
- higher patient dose

25
Q

Impact of pitch = 1

A

pitch is 1:
- ideal
- the table is travelling the exact width of the beam,

26
Q

What is interpolation and why is this necessary in helical scanning?

A

Interpolation is a mathematical process used to estimate unknown data points between measured values.

This is necessary because helical scanning results in overlapping or gaps in the data points

This ensures we get complete data correction and image accuracy of the scanned anatomy even with continuous motion

27
Q

What is the difference between acquired and reconstructed slice thickness?

A

Acquired slice thickness - is the thickness of each slice set in the scan parameters

Reconstructed slice thickness - is the thickness of each slice determined by the reconstruction parameters

28
Q

What is the implication of having thinner slices?

A
  • increased spatial resolution
  • increased noise (due to photon starvation)
  • reduced partial volume artefacts
29
Q

What is the implication of having thicker slices?

A
  • reduce noise
  • increase contrast resolution
  • lower spatial resolution
  • increased partial volume artefacts
30
Q

What is MDCT and what are its advantages?

A
  • A CT system with multiple detector rows that captures multiple slices simultaneously during each gantry rotation.

Advantages:
- Faster Scanning
- Ideal for trauma, emergency imaging, and paediatric patients.
- Thinner Slices
Allows for higher spatial resolution and detailed imaging of small structures.
- Larger Coverage in a single scan (e.g., whole-body imaging).
- Improved 3D and Multiplanar Reconstructions:
- Reduced Motion Artefacts
- Optimised Contrast Timing:
Speed enables imaging during specific contrast phases, such as arterial or venous​

31
Q

What are the types of MDCT detectors?

A
  • uniform
  • non uniform
  • hybrid
32
Q

When talking about MDCT pitch - whats the most important factor to consider?

A

TOTAL THICKNESS OF ALL SIMULTANEOUSLY ACQUIRED SLICES

  • pitch is the ratio of the table movement per gantry rotation to the total width of the X-ray beam.
33
Q

Impact of MDCT pitch greater than 1?

A
  • Table moves faster than the beam width.
  • Effect: Faster scans, lower radiation dose, but potential for gaps in data leading to reduced image axial z-resolution
  • Ideal for trauma or emergency imaging where speed is critical to cover large volume
34
Q

Impact of MDCT pitch lower than 1?

A
  • Table moves slower than the beam width.
  • Effect: Overlapping slices improve image axial z- resolution but increase radiation dose.
  • Best for detailed scans, such as cardiac or vascular imaging​
35
Q

What is a main issue related to cone beam acquistion?

A

Off-Centre Structures: Misplacement of lesions or structures causes artefacts.

36
Q

What are 2 main cone beam interpolation types?

A

1- Tilted Reconstruction: Produces non-axial images that are subsequently processed using filtered back projection at an angle to the axial plane, resulting in standard axial images

2- Feldkamp Algorithm - uses 3-dimensional back projection

37
Q

What are the characteristics of a good quality CT image?

A
  • good low contrast detectability
  • low noise
  • good high spatial resolution
  • artifact free
38
Q

What is noise and how does it affect image contrast in CT?

A
  • Noise in CT refers to random variations in pixel values that do not represent true anatomical structures.
  • It appears as a grainy or mottled texture in images, obscuring fine details and reducing clarity.
  • Noise is inversely proportional to the number of detected X-ray photons; lower doses increase noise

Effect:
- Reduces Low Contrast Detectability (LCD)

  • Blurring Fine Structures
39
Q

What are the main group heading of scanning parameters and factors that affect noise and how?

A

Several factors that can be grouped under :

  • scanner specifications ad design:
  • Scanning acquisition parameters
  • Patient factors
  • Reconstruction Parameters
40
Q

What are the scanning parameters and factors that affect noise under scanner specifications and design? Are these under our control?

A
  • Efficiency of detectors
  • x- ray beam filteration
  • scanner geometry

not really

41
Q

What are the scanning parameters under scanning acquisition parameters affect noise and how?

A
  • Tube Current (mA):
    Higher mA produces more X-ray photons, reducing noise and improving the signal-to-noise ratio (SNR).
    Trade-off: Increased radiation dose.
  • Tube Voltage (kVp):
    Higher kVp increases photon energy, allowing more photons to penetrate tissues and reach the detectors, reducing noise.
    Trade-off: Reduced contrast resolution.
  • Slice Thickness:
    Thicker slices collect more photons per voxel, reducing noise.
    Trade-off: Decreased spatial resolution.
  • Pitch:
    Higher pitch increases table movement, reducing scan time and photon flux, leading to more noise.
    Lower pitch improves image quality but increases dose.
42
Q

What reconstruction parameters affect noise and how?

A
  • Back projection algorithm
  • Noise filters
43
Q

What patient factors affect noise and how?

A

Patient Size:
Larger patients attenuate more photons, increasing noise. Adjustments in mA or kVp are needed for noise control.

44
Q

What are the 2 types of spatial resolutions?

A
  • Transaxial resolution (axially across the patient)
  • z-axis resolution (along the length of the patient in z-direction)
45
Q

what factors affect transaxial resolution?

A
  • focal spots: smaller focal spots produce sharper images, enhancing spatial resolution.
    Larger cause blurring.
  • detector size (smaller detectors = higher resolution)
  • sampling frequency (the more projections the better the resolution)
  • reconstruction filter (sharp kernels have better resolution than soft kernels)
46
Q

What is z-axis spatial resolution in MDCT and how is this important in relation to image slice thickness?

A
  • Thinner Slices Improve Z-Axis Resolution:

Each slice represents a smaller volume of tissue, reducing partial volume artefacts and enhancing detail.

  • Thicker Slices Reduce Z-Axis Resolution:

Larger tissue volumes are averaged within a slice, potentially obscuring small structures.

47
Q

What is partial volume effect?

A
48
Q

What are CT artefacts ?

A

CT artefacts are distortions or errors in images that do not correspond to the actual anatomy being scanned. They can degrade image quality, obscure important details, and potentially mislead diagnoses.

49
Q

How are CT artefacts classified including examples of each?

A

1: Physics based - beam hardening, partial volume effects

2:Patient based- motion artefacts and metal artefacts

3: Scanner based - Ring artefacts

4:Helical and Multi- slice - windmill artefact and cone beam effect

50
Q

How is radiation dose distributed when scanning in CT?

A
  • In-Plane (x-y Axis):
    Dose is highest at the centre of the scanned region and decreases towards the edges due to beam divergence and filtration.
  • Z-Axis (Patient Length):
    Dose distribution depends on collimation, pitch, and slice overlap.
    Overlapping slices (low pitch) increase dose, while wider collimation (high pitch) spreads dose more evenly but reduces resolution.
51
Q

Is the CT Dose distribution in the x-y plane in our control?

A

No, it depends on:
- filteration
- beam hardening
- scanner geometry
- size of patient

52
Q

Is the CT Dose distribution in the z- plane in our control?

A

yes, it is:
it depends on :
- pitch, area

53
Q

What are the two main dose descriptors in CT and how do they differ?

A
  • Computed Tomography Dose Index (CTDI):
    Measures the average dose within a single slice of tissue in a standard phantom.

-Dose-Length Product (DLP):
Represents the total radiation dose over the length of the scan.

54
Q

What is AEC

A

A system that dynamically adjusts the X-ray tube current based on the patient’s size, shape, and density to optimise image quality while minimising dose.

55
Q

Advantages of AEC?

A
  • dose is optimised
  • image quality is more consistant
  • more constant signal to detectors
  • tube heat capacity conserved
  • artefact reduction
56
Q

What are the latest contemporary developments in CT scanning?

A
  • Photon-Counting CT
  • Dual-Source CT
  • Spectral CT/Dual-Energy CT

EXAM QS & A Practice (9 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions