Xray and mammo Flashcards

Question

COMPTON "BAD GUY" What is? 3 actors when its done

Answer 1

HIGH ENERGY incoming xray hits an outer shell e, knocks it out, loses some energy and heads off in new direction IONIZED atom - bad Free electron - bad, 2ary interactions scattered photon bad - fogs image

Answer 2

DOESNT depend on Z of the atom **DOES depend on density of material** DOMINANT contributor to **scatter/fog** **MAJOR SOURCE OF OCCUPATIONAL EXPOSURE**

Answer 3

LOWER ENERGY RELATIVE to COMPTON incoming xray gives all **energy to inner shell e** **ALL OR NOTHING, incomin xray is TOTALLY ABSORBED** **--\> characteristic xray or Auger (auger dominates in soft tissue, lower Z)**

Answer 4

need energy higher than inner shell binding peak energy for PE is around this binding energy **Xrays with more energy pass through** **INVERSE to THRID POWER** **HIGHER Z makes PE more likely** **ALSO INVERSE TO THIRD POWER**

Answer 5

**HIGHER Z = greater chance of PE = more xray absorption**

Answer 6

**DIRECTLY PROPORTIONAL TO Z cubed** **INVERSELY PROPORTIONAL TO ENERGY CUBED**

Answer 7

**spike in attenuation corresponding to the K shell binding energy** **Lower energy are easily attenuated (no contrast)** **Higher pass through everything (no contrast)**

Answer 8

K edge of barium = 37 keV, iodine = 33 keV Select kVp of 65-90 average energy around these (1/3 - 1/2 kVp)

Answer 9

**NO GRID** **lower kVp ~ 65** (kids are small, don't need much to penetrate) (adult cxr kVp = 120-140) same or just less mAs

Answer 10

Effective Z in tissue X ray beam quality (energy) Tissue density

Answer 11

Above = COMPTON Below = PE

Answer 12

photon starvation

Answer 13

Not a good answer. raw data is still crap

Answer 14

smaller field/collimation decrease photons, increase noise therefore mAs usually increased with collimation (in this situation book says answer is collimation decreases noise)

Answer 15

**Collimation** - less field less scatter Thickness of body part Energy of beam (Compton dominates \>26kVp in soft tissue, 35kVp in bone)

Answer 16

height to distance between

Answer 17

increases dose (abc) mAs with grid/mAs without **(usually 2-3)**

Answer 18

too many photons blocked --\> quantum mottle grid not aligned/positioned correctly.

Answer 19

both increase exposure but kVp going up will increase Compton scatter potentially more noise. mAs better answer for decreasing noise

Answer 20

Increase in noise with increased SDD, described by inverse square law

Answer 21

noise includes scatter mottle = photon starvation

Answer 22

line pairs per mm spatial frequency = spatial resolution unsharpness means loss of spatial res

Answer 23

Motion (decrease exposure time) System unsharpness = limiting factor of detector Geometric unsharpness

Answer 24

Film = size of the grain of photographic chemical CR = size of laser used to read the phosphor plate DR = size of individual thermoluminescent transistor

Answer 25

focal spot - smaller = less blur SOD - further = less blur ODD - closer = less blur mag --\> blur

Answer 26

SOD + ODD ------------------------------ SOD

Answer 27

ability to maintain contrast as a function of spatial resolution curve with MTF on Y and spatial res on X As spatial res increases, MTF, ability to maintain contrast, decreases

Answer 28

**spatial resolution = half of nyquist frequency** How little you can sample something and still be able to tell what it is... Harder and harder to keep up signal when looking at smaller and smaller line pairs (harder and harder to have contrast when looking at smaller things)

Answer 29

estimate of required exposure level necessary to create an optimal image "prediction of dose" ideally = 1.0 (all radiation energy absorbed and converted to image) at any spatial resolution **Better the DQE, the less radiation needed to maintain spatial resolution** **high DQE, low dose**

Answer 30

- Is a measurement of **EFFICIENCY** - **Directly proportional to MTF** - Inversely proportional to SNR - **Better at LOW SPATIAL RES** - Usually **better, around 0.45 for DR, CR or film 0.25** **HIGH DQE = HIGH DOSE LOW DQE = LOW DOSE** **MORE JUICE PER SQUARE INCH to see fine details**

Answer 31

probably only advantage of film, made of a continuous thing, no pixels, **small advantage in spatial res**

Answer 32

**Grid and collimation**

Answer 33

Pixel depth = determined by number of bits number of shades of gray available for imaging more bits = more contrast resolution

Answer 34

narrower window = more contrast ## Footnote **Level determines BRIGHTNESS**

Answer 35

**Plain film** primary factor for contrast is **kVp** **Digital systems** primary factor for contrast is **LUT**

Answer 36

histogram of known input intensities and corresponding grayscale allows rescaling for adjustment to present optimal image (underexposed scaled darker, overexposed scaled lighter) Means less important to adjust kVp when using digital **MEANS WIDER DYNAMIC RANGE IN DIGITAL SYSTEMS**

Answer 37

FIlm, brightness means how many xrays are blocked bones block a lot, they're bright **Digital imaging, brightness = level** **level up to see lung**

Answer 38

narrow in film easy to under or overexpose **Digital** **larger dynamic range and linear response to exposure**

Answer 39

with digital can underexpose a little and fix later kVp less important, can go up by 15% and cut mA in half to decrease dose

Answer 40

distance from center of one pixel to another

Answer 41

Better spatial res = higher pixel density (pixels per unit area) lower pixel pitch

Answer 42

ionization chamber BETWEEN PATIENT AND RECEPTOR charge produced in chamber, calibrated to know how much charge to terminate an exam based on body part

Answer 43

QUANTITY of radiation reaching receptor, NO effect on kVp

Answer 44

number of bits determining number of shades of gray that can be displayed on a monitor 2 to the X number of bits = number of gray shades

Answer 45

CR - storage phosphor (computer think laser), type of indirect DR - Flat panel detectors direct or indirect

Answer 46

**INDIRECT = SCINTILLATORS** **XRAYS --\> LIGHT --\> CHARGE** **DIRECT = photoconductors** **XRAYS --\> CHARGE**

Answer 47

electons in phosphor interact with xrays, change to metastable state (in 'conduction band') storage phosphor holds 'LATENT IMAGE' CASSETTE then docking station, readout **"photostimulable luminescense"**

Answer 48

laser **red light laser liberates trapped electrons, return to their shells and release energy as BLUE-GREEN LIGHT** blue green light signal directed to a photodetector which then converts it to an electronic signal signal digitized and divided into a matrix

Answer 49

what most people mean when they say "digital detector" faster than CR or film INDIRECT or DIRECT

Answer 50

**INDIRECT THINK SCINTILLATOR** **INDIRECT THINK LIGHT inbetween XRAYS and CHARGE** Xray activates Cesium Iodide light emitted, converted by a photodiode into a charge Charge captured and transmitted by **Thin-Film-Transistor (TFT)** to the workstation

Answer 51

LOSS of spatial res phosphors **WORSE WITH GREATER THICKNESS OF CRYSTAL**

Answer 52

CR = INDIRECT = PHOSPHOR DR INDIRECT = CS scintillator (and photodiode, TFT)

Answer 53

PHOTOCONDUCTOR NO LIGHT IN BETWEEN XRAY --\> CHARGE AMORPHOUS SELENIUM

Answer 54

DIRECT THINK SELENIUM charge applied across selenium, same direction as x rays Xrays absorbed by selenium, electrons released, travel to surface of selenium and neutralize some of applied charge NO LAT DISPERSION charges are drawn to charge storage capacitor connected to TFT pattern of charges scanned and converted to a digital signal

Answer 55

Area of detector sensitive to Xrays (in relation to entire detector area) HIGHER = more EFFICIENT DR - electric field shaping allows near 100% fill factor CR WORSE

Answer 56

**DR better fill factor** = more efficient = **HIGHER DQE**

Answer 57

SMALLER LASER BETTER THICKER PHOSPHOR WORSE HIGHER SAMPLING FREQ = SMALLER PIXEL PITCH = BETTER

Answer 58

avoid lateral dispersion

Answer 59

CR Centralized (Cassettes have to be brought somewhere) DR Decentralized. image acquired, adjusted and transferred to PACS by the tech, in the room

Answer 60

16-23 keV therefore set kVp to 25-30 keV

Answer 61

molybdenum or rhodium (vs tungsten)

Answer 62

goal = creating a mono-energetic beam moly used, 20keV k edge, energies lower than 15 and higher than 20 filtered out

Answer 63

similar, slightly stronger spectrum than moly

Answer 64

Rh/Rh for denser breasts (higher energy) Mo/Rh intermediate

Answer 65

.1 and .3 mm in mammo general .6 and 1.2 smaller spot gets hotter, have to lower mA **mA 50 for 0.1 and 100 for 0.3** **lower mA means longer exposure**

Answer 66

cathode side = chest wall **ANGLING TUBE UP TO ABOUT 20 degrees**

Answer 67

Anode angle + tube angle

Answer 68

General uses PYREX Mammo uses Beryllium PYREX attenuates energies used in mammo

Answer 69

Less scatter = lower kVp can be used lower kVp and less scatter = improved contrast Thinner = less mAs, less dose no motion Closer to Bucky = less mag less motion and mag = better spatial resolution

Answer 70

low kVp and compression already lower scatter, so lower grid ratio used usually 4-5 standard xray 6-16

Answer 71

distance to source cut in half --\> double mag

Answer 72

NO GRID NECESSARY increased object to detector distance means scatter scatters further away from detector

Answer 73

**smaller focal** spot used to improve spatial res **mA decreased** so not to melt anode **exposure time increased,** compensation for boob to detector distance

Answer 74

Digital - 1.6 mGy analog - 1.8 mGy

Answer 75

electronic fluctuations **within the detector element** effect **proportional to temp of detector** **coolers**

Answer 76

imaging a large piece of acrylic improve image quality calibrate digital detectors

Answer 77

residual from prior exposure lead is not allowed on flat panel digital systems

Answer 78

square or a streak

Answer 79

proportion of people who have a positive study and actually have breast cancer PPV think **all we care about is positive tests** **positive test, has cancer** **------------------------------------------** **positive test with cancer + positive test, no cancer**

Answer 80

ANYTHING other than continued screening (BR0, BR3, BR4, BR5) ## Footnote **4.4% cancer within 1 year**

Answer 81

Cases where biopsy was recommended (BR4 or 5) ## Footnote **25.4% dx cancer within 1 year**

Answer 82

Results of biopsy, PBR pos biopsy rate 31%

Answer 83

SEMI annually

Answer 84

Semi annually

Answer 85

SEMI annually

Answer 86

3 years ## Footnote **MQSA = FDA**

Answer 87

**240 during a 6 month period in last 2 years** 3 months of formal training 60 documented hours of mammo education

Answer 88

**4.2 cm** of compressed breast that is **50/50 adipose and glandular**

Answer 89

**UNDER 300 millirads** **3 mGy** ONLY FOR PHANTOM MEASURED WITH A GRID WITHOUT GRID = 1mGy

Answer 90

Moiré type artifact can be seen in computed radiography (CR) systems if grids with low grid frequencies are used that are oriented parallel to the plate readers scan lines.

Xray and mammo Flashcards

(127 cards)