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Diagnostic imaging > DI > Flashcards

DI Flashcards

1
Q

the amount of current is corrected by

A

mA

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2
Q

the potential difference between the cathode and anode is adjusted with

A
  • the kilovoltage peak KVp)
  • increasing the KVp increses the potential difference between the filament and the target and the electrons are accelerated to higher velocities and have more velocity when striking the target.
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3
Q

discuss the effect of the size of the focal point on the quality of the image

A

small focal spot>>shapper/more detailed image

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4
Q

discuss the effect of the angle of the focal spot on the quality of the image

A

the smaller the angle,the smaller the effective focal spot

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5
Q

the type of xray interaction where all photons are completely absorbed

A
  • photoelectric effect (PE)
  • no scattered radiations is produced
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6
Q

explain the basis for the image production with photoelectric effect (PE)

A
  • probability of the PE is directly proportional to the third power of the atomic # (Z3)–this is the basis for image production
  • because it amplifies the differential absoption of x-rays between tissues ( otherwise there wouldbe no image contrast and all tissues would be of similiar radiographic opacity.)
  • Pe is inversely proportional to the 3rd power of the photon energy (1/E3)
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7
Q

which xray interaction with the patient creates more scattering and exposure to the personnel

A
  • Compton scattering
  • most important film fogging (deteriorating of film quality)
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8
Q

explain how the campton scattering cause x-ray scattering

A
  • incoming xray photon ejects an electron from an outer shell and is deviated and loses some of its energy
  • the ejected electron may cause further ionization or fog the film.
  • cs is independent of the atomic # (Z)
  • CS can increase with increasing photon energy
  • reduces image contrast where it predominates
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9
Q

which image generation is independent of the atomic number

A

campton scattering

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10
Q

the blackening of the film in analog radiography depends on

A
  • the amount of xrays hitting the film
  • the energy of the x-ray, thus the KVp since the high energy x-ray are more likely to penetrate the patient and strike the film
  • it is also related to the focal film distance(FFD).increaseing the FFD, reduces the intensity of the xray beam and vice versa
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11
Q

what are the factors that increases scatter

A
  • mainly the campton scatter
  • increases with the size of patient
  • size of exposed area
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12
Q

what are ways to prevent scatter

A
  • expose as much as needed
  • use a grid for any structure > 10cm
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13
Q

what is the grid ratio

A

height of lead stripes to width of the spaces between them

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14
Q

factor of increase in mAs that is needed to compensate for the absorbed radiation

A

grid factor

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15
Q

the type of artefact which occurs when increasing the distance between the object and film/cassette

A

magnification

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16
Q

what is the advantages of magnification

A
  • improves resolution of small objects
  • enlarged images easy ro interprete
  • air gap eliminates some scatter
17
Q

what are the disadvantages of magnification

A
  • penumbra (blurring at the edges of a a structure on a radiograph) increase

increased FFD needs more output

  • exacebate motion blur
18
Q

unequal magnification of various parts of the patient due to differences in distance to the source

A
  • distortion
  • since our patients are 3 dimension,there will always be some distortion
  • consistent radiographic positioning help recognising/ minimising distortion
19
Q

how are the shades of grey in high contrast

A

few shades of grey

20
Q

how are shades of grey in low contrast radiograph

A
  • many shades of grey (wide lattitude)
21
Q

image contrast depends on

A
  • thickness
  • physical density
  • atomic #
  • x ray beam energy
22
Q

explain how the indirect flat panel detector system works

A
  • light created by an x-ray in an intensifying screen as in analog radiography is an intermidiate step in image formation
  • the screen is in contact with an array of pgotodioets
  • the photodiotes convert the emited light into an elecreical signal
  • readout electronics convert the electronic signal into a file
23
Q

discuss how the direct flat panel detector system works

A
  • the x ray strikes a photoconductor array made from selenium that absorb xray efficiently –>liberated electrons from the se forms a charge which is read and converted into an electronic file by the readout electronics.
24
Q

discuss how the charged couple system(CCD) works

A
  • a light senstitive CCD chip with an intensifying screen to capture the light emited by the screen when hit by xrays
  • not commonly used
25
Q

roentgen signs

A
  • use to describe any structure visible on the radiograph
  • Location
  • –Number
  • – Size
  • – Shape
  • – Margination
  • – Opacity
26
Q

define frequency

A

number of times a wave is repeated per second

27
Q

define wavelength and write down the equation

A
  • waveleng is the distance travelled by a wavesound in one sec.
  • wavelength=/velocity /frequency
28
Q

explain the relationship of wavelength and frequency at a constant velocity

A
  • at a constant velocity(this is the case as sound travel though soft tissue), frequency is inversly related to wavelength
  • thus high frequencies implies short wavelenghth vice versa

*

29
Q

define amplitude

A

amplitude refers to the strenght/intensity of the soundwave and decreased with increasing tissue depth.

30
Q

discuss the impedence of a tissue

A

the aucostic impedance (z) of a tissue is the product of its physical density (p) and sound velocity (V) within.

Z=p*v

the difference in impedence between tissue determines how much sound is reflected and how much is transmitted further into the adjacent tissue

the amplitude of the echo that returns is proportional to the difference in impedence between tissue

31
Q

a black, no signal/echo ultrasound image

A

anechoic

32
Q

dark grey ultrasound image

A

hypochoic image

33
Q

medium grey ultrasound image

A

echogenic

34
Q

white ultrasound image

A

hyperechoic image

35
Q

define Acoustic.impedance (Z)of a tissue

A

is the product of tissues physical density (ρ) and sound velocity (ν) within

  • Z= ρxν
  • The difference of impedance between tissues determines how much sound is reflected and how much is transmited further into the adjacent ti.ssue
  • the differnce in impedencebetween tissues determines how much sound is reflected and howmuch is transmitted further into the adjucent tissue
    *
36
Q
A

Diagnostic imaging (1 decks)

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