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Imaging > Lecture 3 > Flashcards

Lecture 3 Flashcards

1
Q

bremsstrahlung radiation

A

incoming charged particle slows down as it interacts with the nucleus. Collisional energy loss is through heat and radiative energy loss forms the Xray

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2
Q

what is the intensity of the bremsstahlung determined by

A

target z. radiative energy loss/ total energy loss= EkZ/820000. Where EK is the kinetic energy

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3
Q

what happens with higher z

A

more efficient material- like tungsten or mollubenium or rhodium

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4
Q

what is a characteristic x-ray production

A

it is discrete energy levels

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5
Q

what is an electron cascade

A

fills the vacancy of the inner shells of electrons

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6
Q

when does emission of characteristic Xray happen

A

only happens when the incoming electron has kinetic energy that exceeds the binding energy of an orbital electron. They can also come from electron transitions as holes fill but for image formation purposes, the K characteristic X-rays because the others have energies too low for imaging

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7
Q

what is the electron source

A

cathode

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8
Q

what is the target

A

anode

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9
Q

what is the device to energize the electron to gain kinetic energy

A

generator

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10
Q

what are the components of an X-ray tube

A

cathode, anode, gnerator, envelope, rotator/stator, housing

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11
Q

cathode assembly

A

filament current heats a wire and thermionic emission of electrons. The filament current is 10mV and current goes up to 7000

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12
Q

what is a tungsten filament

A

helical wire coil, 5-20mmlong with 2-5 mm width

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13
Q

what do the electrons accelerate towards

A

anode

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14
Q

what does the focus cup do

A

it compresses the electron stream

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15
Q

what is dual focus

A

a second shorter filament is present and it can be selected during the exam

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16
Q

why is there not a point focal spot

A

it is impossible plus tube current limits

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17
Q

what is the max tube current dependent on

A

kV

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18
Q

what is the max focal spot size dependent on

A

KV and mA

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19
Q

why is tungsten good for X-ray tubes

A

relatively high bremmastralung output and high melting point alloyed with things to make it even higher

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20
Q

xray production is inefficient why

A

lots of heat and little X-ray production

21
Q

what does heat do to the tube

A

it limits the tuber perforamtice

22
Q

radiative energy loss/ total energy loss=

A

EkZ/820000

23
Q

what is the X-ray tube envelope made of

A

glass or metal and air molecules would impede flow, so it is vacuumed and it cannot have air because it will oxidize. Envelope has a window or small region of glass so beam can go through

24
Q

what is the tube rotor/stator

A

mechanism that allows the anode to rotate, it uses an induction motor. The anode is connected to rotor within envelope. Stator consists of cold of wire outside envelope. AC in stator induces rotation of rotor/anode within the tube

25
Q

xray tube housing

A

provides strucutural support, insulation, and shielfing, there is an old bath around the envelope the carry away heat. Lead within the housing shields external environment from leakage radiation

26
Q

what is the X-ray generator

A

it provides the power necessary for X-ray production, provides adjustable low voltage to heat tube filament and provides an electron source. Transforms low voltage AC to adjustable high voltage which is used to accelerate electrons. operator then an select X-ray energy quantitiy, and exposure time

27
Q

rectification

A

tube only works one way

28
Q

generator power

A

power (kW)= V(Kv)xI(A)

29
Q

what is the generator power benchmarked for

A

.1 sec exposure

30
Q

what is the max power of a generator

A

instanteanous limit or FS

31
Q

what is tube heating

A

99% is converted to heat so heat unit is peak potentialxtubecurrent x time

32
Q

what is the formula for energy

A

energy= potential x current x time

33
Q

how do we balance heat and cooling in the X-ray tube

A

FS, anode, bearings, and tube housing have thermal limits and repeated exposures can damage the tube, and this must balance against energy input, and cooling proportional to the Temp to the fourth. The hotter the tube, the faster it cools

34
Q

how do you calculate the effective focal spot length

A

sin (theta) times the true FS length

35
Q

what happens with a large anode angle and small filament lenth

A

large field overage, but small effective focal spot- poor power loading

36
Q

what happens with a large anode angle and long filatment

A

large coverage and large focal spot with good power loading

37
Q

small anode angle and long filament lenth

A

small field overage small effective focal spot but good power loading

38
Q

explain the heel effect

A

there is lower X-ray intensity under the anode

39
Q

in terms of the X-ray spectrum, what is quntitiy

A

the number of X-rays or fluency. it is proportional to the area under the spectrum.

40
Q

what is quality in terms of X-ray spectrum

A

describes the shape of the spectrum energy and canc be HVL

41
Q

what is the probability of bremmstralung

A

2xpixr

42
Q

what happens with the bremmstralung further from nucelus

A

higher probability and lower energy

43
Q

who came up with xrays

A

roentgen

44
Q

what is the inverse square law

A

exposure is proportional to (1/distance)squared

45
Q

what is X-ray quantity proportional to

A

Zx KV2 x mA x time/distance2, so it decreases with increased filtration. and it increases with decreased voltage ripple.

46
Q

what does X-ray quality change with

A

z, kVP (maximum energy_ filtration with increased percent of X-rays with increased filtration, waveform (increased percent of high energy rats decreased ripple

47
Q

what creates a characteristic xray

A

it is the holes in the electron orbits

48
Q

what creates a characteristic xray

A

it is the holes in the electron orbits

49
Q

high Z emits more electrons because

A

they have so many electrons that it is hard to hold onto them

Imaging (19 decks)

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