Brainscape's Knowledge GenomeTM

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


See full index

CBA > Rad physics, equipment, apps. > Flashcards

Rad physics, equipment, apps. Flashcards

1
Q

What is a grid? (made of, purpose, when do you use it)

A

A Board made of lead strips with radiolucent material separating the strips. Purpose is to reduce scatter from reaching the IR. Increase contrast & image detail and reduce image degradation.

Use when using more than 70 KVP, and when the patient thickness is more than 10cms.

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

What is grid ratio?

A

height of the strips divided by the width of the interspace material.

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

What is grid frequency?

A

Number of lead strips per centimetre.

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

What is grid factor?

A

What we X the mAs by so that quantity of XR beam is enough to penetrate the grid, IR & pt.

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

What is scatter?

A

Radiation that is formed by the interaction of the primary beam with atoms in the object being imaged. Influenced by pt thickness, kVp, collimation.

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

What type of grids do we have?

What grid ratios do we have.

A

Bucky= focussed grid. Have a specific SID, centered to grid, allows for more transmitted photons to reach the IR. They are oscillating, helps blur out grid lines. Solanoid gives the grid a tug, release and is linked to exposure button.

110cm Grid (109-140cm). Grid ratio is 12 : 1 x 5.

140cm Grid (109-210). Grid ratio is 8 : 1 x 4. (cleans up 85% of scatter).

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

What Is grid cut off?

A

When radiation is absorbed unevenly across film, misuse of a grid.

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

Peripheral grid cut off

A

Absorption of the primary beam due to the divergence of the beam at the periphery of a parallel grid

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

Off focus grid cut off

A

Peripheral grid cut off that occurs because the SID is not within the reccommend focal range. Higher grid ratios have narrower focal ranges.

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

Off level grid cut off

A

decrease in density across the film that occurs when the grid or tube is angled.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Off centre grid cut off

A

Decreased density across the film caused by incorrect centering. The center of the grid must be positioned directly under the x-ray tube target. Correct centering is more important with higher grid ratios.

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

Upside down grid cut off

A

Severe cut off on either side of the central ray and increased density in the middle of the film caused by placing a focused grid in upside down.

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

As grid ratio ___, radiographic density ___.

A

As grid ration increases, radiographic density decreases.

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

Explain the air gap technique.

A

Used instead of a grid as the scatter radiation is attenuated in the air between the patient and the IR before it reaches the IR. Hence, the air is acting as ‘a grid’.
Because of the large OID, detail of the image is lost, therefore SID must be increased from 110cm to 180cm.

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

Explain KVP

A

Quality of the beam penetration, higher the penetration, higher the KVP. Amount of energy of the xray is determined by the voltage applied from cathode to anode.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

mAs

A

Quantity. The amount of xrays reaching the IR (produced), directly related to patient dose. Energy is not changed, just the number. Amount of xrays is determined by the current.

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

Explain the MAS button…

A

Goes up by 25% of original mAs. Must go up 25% to see a noticeable difference.

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

Explain the density step button…

A

Goes up in 1/2 steps (12.5%), this gives you 12.5% more time before the AEC cuts out. Must go up two 1/2 steps to increase time to 25%. 25% change- noticeable difference.

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

Explain the body habitus button…

A

Preprogramed= depends on body type/ pre-set. Goes up in KVP, density step stays the same, but mAs goes up according to the pre set, more dose to patient.

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

What is an AEC?

A

Automated Exposure Controls the length of the exposure. Each examination has a pre set ionisation level that exposes @ right time. When the MRT exposes, air in the chambers is ionised and creates a charge, when the charge is met, the exposure is terminated.

21
Q

Explain safe guard timer…

A

5.29 A device shall be installed which can be set to terminate the exposure after a time no greater than 6 seconds, or after an exposure of no more than 600 mAs, whichever is the lesser.

MidCentral DHB guard timer is set at 2 seconds.

22
Q

Explain Penumbra

A

Image blur= because radiation comes from an area, not a single point. Result from focal spot and geometric unsharpness.

FF, increased SID, decreased OID.

23
Q

What is an EI?

A

Value that relates to exposure. It is an indicator that shows the average amount of photons absorbed by the IR within the collimated field.

24
Q

What is the anode heel effect?

A

The intensity of the x-ray beam being emitted is not uniform, due to the angle of the anode, there is a greater intensity being emitted from the cathode end.
X-rays emitted from the steeper end of the anode must pass through a greater amount of the target material, therefore there is more attenuation of the beam at this end; and hence less intensity.

In practice the thickest part of body should be at the cathode end (this is marked on the tube as ‘+’)
Can be useful for abdomen, DP feet and AP T-spine x-rays.

25
Q

Explain fine/small focal spot…

A

Fine focus: Used for extremities and skull.
Fine focus gives greater detail due to less penumbra as the area targeted on the anode is smaller. However, the mA is limited to 100-200 due to chance of tube heating. This mA limitation means there are long exposure times which may be a problem when imaging children, patients with Parkinson’s and areas that have involuntary motion, i.e. the abdomen, chest.

26
Q

Explain broad/large focal spot…

A

Broad focus allows for an exposure higher than 200mA to be used without over heating the anode as the heat is dispersed over a larger area. Shorter exposure times can be used because of the higher mA values. This helps when imaging areas of the patient that has involuntary motion such as the abdo and chest to reduce movement unsharpness in the image. However, with broad focus detail is lost due to a larger penumbra.

27
Q

Explain variable/ blended focal spot…

A

Perfect blend of both focal spit sizes & maximum exposure load for examination. Reduces motion blur, improve geometric unsharpness.

28
Q

what is S400?

A

Sensitivity, speed class for all examinations.

  • Oscillating speed for grid, pre set and we do not touch it.
29
Q

How does the DR plates, system work?

A

Direct digital plates (MCDHB)

Uses an amorphous selenium-coated thin-film-transistor (TFT) array to capture and convert X-ray energy directly into digital signals. Under a bias voltage (a voltage given to ensure each image turns out the same) applied across the detector structure, incident X-rays directly generate electron-hole pairs in the selenium layer. These charges are collected by individual storage capacitors associated with each detector element (pixels) and converted immediately into an image on the monitor.

30
Q

mAs Critique points

A
  • There is adequate density over the entire image to visualise all anatomy and pathology, and to see the fine trabecular patterns.
  • There is no sign of quantum mottle.
  • EI is within range.
31
Q

mAs Critique points

A
  • There is adequate density over the entire image to visualise all anatomy and pathology, and to see the fine trabecular patterns.
  • There is no sign of quantum mottle.
  • EI is within range.
32
Q

Explain the inverse square law…

A

Intensity of the radiation beam is inversely proportional to the square of the distance to the source.

New exposure = (New Distance)2
Old exposure = (Old Distance)2

¾ SID = 2 x Intensity = ½ exposure
½ SID = 4 x Intensity = ¼ exposure
¼ SID = 8 x Intensity = 1/8 exposure

33
Q

Tube housing…

A

Protective barrier, aids against leakage, radiation + scatter, cools tube.

34
Q

Put the following into order.

  • AEC
  • Patient
  • Plate
  • Grid
A

Patient -> Grid -> AEC -> Plate

35
Q

What’s Absorbed dose?

A
  • Amount of energy absorbed per unit mass of matter. Applies to any material living or not.
  • Unit: Grays
36
Q

What’s Equivalent dose?

A
  • The ability of different radiations to produce different degrees damage.
  • Related to radiation weighting factors.
  • Unit: Sievert
37
Q

What’s Effective dose?

A

Tissue weighting factors, values given to different tissues dependant on the sensitivity of the stochastic radiation effects.

38
Q

What are Stochastic Effects?

A 
•	Occurs at random and is independent to the size of the dose.
•	There is no threshold.
•	Can cause
o	Leukaemia
o	Cancer
39
Q

What are Non-stochastic Effects?

A

• There is a clear relationship between the exposure dose and effects.
• There is a threshold, below the threshold- no effects, above the threshold- effects will occur.
• Occurs when very large doses are given over a short period of time.
• Can cause
o Hemopoietic syndrome
o Gastrointestinal Syndrome
o Central nervous system effects

40
Q

What are Genetic Effects?

A
  • Seen in the offspring of an individual who received the radiation.
  • Must be encountered preconception.
41
Q

What are Teratogenic Effects?

A

Seen in offspring who was exposed in-utero.

42
Q

What are Somatic Effects?

A

Seen in the individual who was exposed

43
Q

What is an Algorithm?

A

A computer adapted mathematical calculation applied to raw data during image reconstruction to ensure the image appears on the screen as it is expected to look. Each body part has a pre-set characteristic curve and a set density.

44
Q

Collimation

A
  • We collimate to reduce patients’ effective dose and also to enhance image contrast as scatter is reduced due to a smaller area being irradiated.
  • Collimators are made of two sets of adjustable lead shutters.
45
Q

Explain what may cause radiographic distortion..

A 
•	The misrepresentation of an object size or shape on radiographic image.
•	Factors that affect distortion are…
o	SID
o	OID
o	Object-IR alignment
46
Q

What is exposure creep?

A
  • A gradual increase in x-ray exposure over time that results in increased radiation dose to patient.
  • Due to wide exposure latitude of DR.
  • Radiographers aim to have an exposure just above quantum mottle
47
Q

Photographic unsharpness (Up) is a combination of what 3 factors? (Explain each)

A

Us ( screen unsharpness)= unrelated to DR.

Um – movement unsharpness
• Caused by movement of a patient during exposure. The further the movement, or the greater the exposure time, the greater the Um. Um is more obvious if movement is left or right of the tube as compared to towards or away from the tube. Large OID’s increase magnification, making movement more obvious

Ug – geometric unsharpness
Caused by the fact that radiation does not come from a single point, it comes from a predetermined area called the focal spot. Large focal spots cause greater penumbra, so more Ug.

48
Q

What is “noise”?

A
  • Any information on the screen that does not contribute to the diagnostic image.
  • Appears as speckled background and occurs more often when fast-screen and high kVp techniques are used.
  • Noise degrades the image. Can be quantum noise (mottle) due to low photon energy, scatter or electronic or system noise.
  • Electronic/system noises are random effects which degrade the image quality.
  • The noise causes decreased visibility and detail on the image and reduces image contrast.

CBA (6 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions