Lecture 3

Question 1

bremsstrahlung radiation

Answer 1

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

Question 2

what is the intensity of the bremsstahlung determined by

Answer 2

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

Question 3

what happens with higher z

Answer 3

more efficient material- like tungsten or mollubenium or rhodium

Question 4

what is a characteristic x-ray production

Answer 4

it is discrete energy levels

Question 5

what is an electron cascade

Answer 5

fills the vacancy of the inner shells of electrons

Question 6

when does emission of characteristic Xray happen

Answer 6

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

Question 7

what is the electron source

Answer 7

cathode

Question 8

what is the target

Answer 8

anode

Question 9

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

Answer 9

generator

Question 10

what are the components of an X-ray tube

Answer 10

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

Question 11

cathode assembly

Answer 11

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

Question 12

what is a tungsten filament

Answer 12

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

Question 13

what do the electrons accelerate towards

Answer 13

anode

Question 14

what does the focus cup do

Answer 14

it compresses the electron stream

Question 15

what is dual focus

Answer 15

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

Question 16

why is there not a point focal spot

Answer 16

it is impossible plus tube current limits

Question 17

what is the max tube current dependent on

Answer 17

kV

Question 18

what is the max focal spot size dependent on

Answer 18

KV and mA

Question 19

why is tungsten good for X-ray tubes

Answer 19

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

Question 20

xray production is inefficient why

Answer 20

lots of heat and little X-ray production

Question 21

what does heat do to the tube

Answer 21

it limits the tuber perforamtice

Question 22

radiative energy loss/ total energy loss=

Answer 22

EkZ/820000

Question 23

what is the X-ray tube envelope made of

Answer 23

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

Question 24

what is the tube rotor/stator

Answer 24

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

Question 25

xray tube housing

Answer 25

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

Question 26

what is the X-ray generator

Answer 26

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

Question 27

rectification

Answer 27

tube only works one way

Question 28

generator power

Answer 28

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

Question 29

what is the generator power benchmarked for

Answer 29

.1 sec exposure

Question 30

what is the max power of a generator

Answer 30

instanteanous limit or FS

Question 31

what is tube heating

Answer 31

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

Question 32

what is the formula for energy

Answer 32

energy= potential x current x time

Question 33

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

Answer 33

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

Question 34

how do you calculate the effective focal spot length

Answer 34

sin (theta) times the true FS length

Question 35

what happens with a large anode angle and small filament lenth

Answer 35

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

Question 36

what happens with a large anode angle and long filatment

Answer 36

large coverage and large focal spot with good power loading

Question 37

small anode angle and long filament lenth

Answer 37

small field overage small effective focal spot but good power loading

Question 38

explain the heel effect

Answer 38

there is lower X-ray intensity under the anode

Question 39

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

Answer 39

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

Question 40

what is quality in terms of X-ray spectrum

Answer 40

describes the shape of the spectrum energy and canc be HVL

Question 41

what is the probability of bremmstralung

Answer 41

2xpixr

Question 42

what happens with the bremmstralung further from nucelus

Answer 42

higher probability and lower energy

Question 43

who came up with xrays

Answer 43

roentgen

Question 44

what is the inverse square law

Answer 44

exposure is proportional to (1/distance)squared

Question 45

what is X-ray quantity proportional to

Answer 45

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

Question 46

what does X-ray quality change with

Answer 46

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

Question 47

what creates a characteristic xray

Answer 47

it is the holes in the electron orbits

Question 48

what creates a characteristic xray

Answer 48

it is the holes in the electron orbits

Question 49

high Z emits more electrons because

Answer 49

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