DI

Question 1

the amount of current is corrected by

Answer 1

mA

Question 2

the potential difference between the cathode and anode is adjusted with

Answer 2

• 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.

Question 3

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

Answer 3

small focal spot>>shapper/more detailed image

Question 4

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

Answer 4

the smaller the angle,the smaller the effective focal spot

Question 5

the type of xray interaction where all photons are completely absorbed

Answer 5

• photoelectric effect (PE)
• no scattered radiations is produced

Question 6

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

Answer 6

• 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⁾

Question 7

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

Answer 7

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

Question 8

explain how the campton scattering cause x-ray scattering

Answer 8

• 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

Question 9

which image generation is independent of the atomic number

Answer 9

campton scattering

Question 10

the blackening of the film in analog radiography depends on

Answer 10

• 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

Question 11

what are the factors that increases scatter

Answer 11

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

Question 12

what are ways to prevent scatter

Answer 12

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

Question 13

what is the grid ratio

Answer 13

height of lead stripes to width of the spaces between them

Question 14

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

Answer 14

grid factor

Question 15

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

Answer 15

magnification

Question 16

what is the advantages of magnification

Answer 16

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

Question 17

what are the disadvantages of magnification

Answer 17

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

increased FFD needs more output

• exacebate motion blur

Question 18

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

Answer 18

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

Question 19

how are the shades of grey in high contrast

Answer 19

few shades of grey

Question 20

how are shades of grey in low contrast radiograph

Answer 20

• many shades of grey (wide lattitude)

Question 21

image contrast depends on

Answer 21

• thickness
• physical density
• atomic #
• x ray beam energy

Question 22

explain how the indirect flat panel detector system works

Answer 22

• 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

Question 23

discuss how the direct flat panel detector system works

Answer 23

• 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.

Question 24

discuss how the charged couple system(CCD) works

Answer 24

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

Question 25

roentgen signs

Answer 25

* use to describe any structure visible on the radiograph * Location * –Number * – Size * – Shape * – Margination * – Opacity

Question 26

define frequency

Answer 26

number of times a wave is repeated per second

Question 27

define wavelength and write down the equation

Answer 27

* waveleng is the distance travelled by a wavesound in one sec. * * wavelength=/velocity /frequency

Question 28

explain the relationship of wavelength and frequency at a constant velocity

Answer 28

* 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 *

Question 29

define amplitude

Answer 29

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

Question 30

discuss the impedence of a tissue

Answer 30

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

Question 31

a black, no signal/echo ultrasound image

Answer 31

anechoic

Question 32

dark grey ultrasound image

Answer 32

hypochoic image

Question 33

medium grey ultrasound image

Answer 33

echogenic

Question 34

white ultrasound image

Answer 34

hyperechoic image

Question 35

define Acoustic.impedance (Z)of a tissue

Answer 35

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 *