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Spring 2023 > Recorded Detail > Flashcards

Recorded Detail Flashcards

1
Q

March 13 = physics exam

A
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2
Q

Recorded detail

A

detail definition or sharpness in film/screen radiography
Known as spatial resolution in DR
The sharpness of structure lines in a radiograph

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3
Q

4 factors affecting recorded detail

A

Geometric
motion
IR
Object

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4
Q

Geometric factors

A

Focal spot size
SID
OID
Heel effect
Deal with the arrangement in space of xray beam, part being radiographed, and IR

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5
Q

Motion factors

A

X-ray source
IR
Patient

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6
Q

IR factors

A

Film speed
Intesifying screen
Quantum mottle

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7
Q

Object factors

A

Size
shape

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8
Q

Focal spot size

A

Smaller focal spot size, the greater the recorded detail and vice versa
Small focal spot range: 0.3mm to 1.0mm
Large focal spot range: 1.0mm-2.5mm

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9
Q

2 ways to describe focal spot size

A

Actual focal spot size - the actail area being bombarded by electrons
Effective, apparent, projected, or nominal focal spot - the way the actual area appears from the perspective of the IR

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10
Q

Line focus prinicle

A

effective focal spot will always appear smaller than the actual focal spot
Relationship between the actual and effective focal spot size is governed by this

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11
Q

Size of affected focal soot is affected by 2 factors

A
  1. Size of actual focal spot - smaller the actual, smaller the effective
    Size of actual focal spot is governed by size of filament in cathode
  2. Anode angle - smaller the anode angle, smaller the effective focal spot size
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12
Q

Dual focused xray tube

A

Required to give radiographer a choice of either a small or large focal spot,

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13
Q

Advantages + disadvantages of focal spot size

A

Small - better detail
use at less than 50 mAs
Lower heat capacity
Reduces tube life
Large- Detail not as sharp
use at any mAs
Higher heat capacity
Increases tube life

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14
Q

Effect of focal spot size on recorded detail

A

Umbra (shadow) – the distinctly
sharp area of a shadow or region
of complete shadow.
This will be the true image of the
object being radiographed.
Penumbra - the imperfect, unsharp shadow surrounding the
umbra.
It can also be referred to as
unsharpness, edge gradient or
geometric unsharpness.

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15
Q

Penumbra

A

As focal spot size increases, so does the size of the penumbra
Recorded detail decreases

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16
Q

Focal spot blooming

A

Over time or with increase in mA used, size of the focal spot can increase from its stated nominal value

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17
Q

Focal spot size evaluation

A

to determine if focal spot blooming has occured

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18
Q

Focal spot size testing can be performed by one of three devices

A

Pinhole camera - tiny hole of a specified shape is cut into a plate of metal allloy
Focal spot test tool - series of slits is radiographed, corresponding chart is used
Star or slit resolution patterns - chart if various shapes and/or lines that can
estimate focal spot size.

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19
Q

Effect of SID

A

Short SID’s will decrease recorded detail because the penumbra size increases
Long SID’s will increase recorded detail because penumbra is smaller
SID and recorded detail have a direct relationship

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20
Q

Effect of OID

A

Larger OID will cause larger penumbra before reaching IR, thereby reducing recorded detail
Shorter OID will increase recorded detail
Inverse relationship for OID and recorded detail

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21
Q

Calculating average penumbra size

A

penumbra = EFS x OID/SOD
SOD = SID-OID

22
Q

Anode heel effect

A

The penumbra is always
larger on the cathode side of
the x-ray field due to the
heel effect.
Therefore, recorded detail is
slightly better toward the
anode side

23
Q

Motion factors

A

Motion of patient, xray source, IR during exposure can cause motion blur
Motion blurs destroys recorded detail

24
Q

Patient motion

A

Common cause of motion blur
Minimized by:
Suspend respiration
Communicate clear instructions
Utilize short exposure times
Immobilize when necessary

25
Q

IR factors

A

Film speed - faster speed, decreased recorded detail
Intensifying screen - Faster speed will decrease recorded detail
- Crystal size/shape: smaller size or columnar shape will increase recorded detail
-Active layer: thinner layers increase recorded detail
-Film/screen contact: bad contact reduces recorded detail
Quantum mottle - causes blotchy appearance which reduces recorded detail

26
Q

Quantum mottle

A

Speckled appearance caused by insufficient xray photons covering IR

27
Q

Object factors - size

A

Thinner objects allow for a smaller penumbra than thicker objects
Recorded detail is better with thinner object

28
Q

Object factors - shape

A

Objects similar in shape to xray beam (cone-shaped) have smaller penumbra size than any other shape
Results in better spatial resolution

29
Q

Related terms

A

Visibility and resolution - not the same thing as recorded detail but are related

30
Q

Visibility of detail

A

How well the radiographic image can be seen and affect mainly by optical density and contrast

31
Q

Modulation transfer function

A

can be used to measure visibility of detail
Numbers from 0 to 1 obtained using fourier analysis
The closer to 1.0, better spatial resolution

32
Q

DR image quality characteristics

A

MTF measures visibility of detail, which is clarity of the image
DR systems should deliver a MTF of 30% at 2 lp/mm and 60% at 60% at 1 lp/mm

33
Q

Resolution

A

Ability of an imaging system to deliver recorded detail, visibility of detail, and events happening in time
3 types of resloution:
Contrast
Temporal
spatial

34
Q

Contrast resolution

A

Ability of imaging system to distinguish structures that are similar in size or density as separate entities
Also known as low contrast resolution
Affected by contrast sensitivity of IR

35
Q

Evaluation of contrast resolution

A

Use a scoring system from a phantom image

36
Q

Contrast resolution and visibility of detail

A

Image of contrast resolution test tool can be used to create a contrast detail-curve
Further the curve is toward y-axis, better contrast resolution and visibility of detail

37
Q

Contrast detail curve

A

Smaller the object to be observed, the more contrast in the image you need in order to see it
MRI has the best contrast resolution

38
Q

Temporal resolution

A

Ability of an imaging system to show events that are happening close together in time as being separate events
Applicable to real-time modalities such as fluoro, CT, MR angiography, MRI
Affected by framte rate of acquisition and display rate

39
Q

Frame rate

A

the number of frames/second or Hertz (Hz)
The faster the frame rate, the better the temporal resolution,
but the greater the patient dose.

40
Q

Spatial resolution

A

The ability of an imaging system to create
separate images of closely spaced objects. Also known as High Contrast Resolution.
Is equivalent to recorded detail in DR

41
Q

Spatial frequency

A

requires an image of a resolution pattern that creates a series of black and white lines
Frequency of 5 lp/mm means that each black and white line is only 0.1 mm wide

42
Q

Point spread function

A

Can also be used to measure spatial resolution
A narrower peak on the
graph indicates better
spatial resolution

43
Q

Line spread function

A

Creates a similar graph to Point Spread Function
but requires a slit camera instead of a pinhole
camera.
The slit camera has an aperture that is 10 μm
wide.

44
Q

Edge spread function

A

Can also be used to measure spatial resolution
Closer the graph is to the center
line, the better the spatial resolution

45
Q

Distortion

A

A misrepresentation of the true size, shape, or
spatial relationship of the part in the
radiographic image.
3 types of distortion:
Size - msirepresentation of true size. SID, OID, SOD
shape - Misrepresentation of true object shape. Elongation, foreshortening
spatial - Misrepresentation of true spatial relationship between objects in image

46
Q

Size distortion or magnification

A

Misrepresentation of true size of the object in the radiographic image
Factors are:
SID
OID
SOD

47
Q

Effect of SID on magnification

A

As SID increases, the amount of magnification decreases due to less beam divergence
Shorter SID will cause more magnification

48
Q

Effect of OID on magnification

A

As OID increases, so does amount of magnification
A decrease in OID will cause less magnification

49
Q

Magnification calulations

A

Amount of Size Distortion
* Image size/object size = SID/SOD
Magnification Factor – tells how many times bigger image is
than object
* Use either half of the above equation
Percent Magnification – tells what percent bigger is image
than object
* = (image size – object size)/object size x 100

50
Q

Cieszynski’s Law of Isometry

A

Can be used to determine foreshortening of objects that are not parallel to IR
Cr angle should be 1/2 of the angle between the part and IR to minimize shape distortion

51
Q

Spatial distortion

A

taking 3-dimensional object and capturing it in a 2-dimensional image
Can be corrected by taking 2 separate images at 90 degrees from each other

Spring 2023 (81 decks)

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