Ch. 1 & 2 - Image Production

Front 1

X-ray Tube

Back 1

-aka: insert
-device that creates the x-ray beam
-enclosed w/n a lead-lined metal
housing
-layer of oil lies btwn tube and
housing to serve as an electrical
insulator and heat dissipater
-referred to as either dual-filament
or tubes or dual-focus tubes

Front 2

Collimator Box

Back 2

-attached to under-surface of
horizontally positioned tube and
housing
-defines size of beam to area being
irradiated
-contains a set of lead
plates/shutters that block
unnecessary portion of beam
-positioned w/n it is a light bulb
whose light is reflected by a mirror
toward the pt, illuminating the area
to be irradiated

Front 3

X-ray Beam

Back 3

-only useful part is projected toward pt
-passes through thin glass window in
bottom of tube, then through an
opening in housing (called housing
port), and then through collimator box

Front 4

Electromagnetic Induction

Back 4

-an electric current, running through
the stator, that produces a magnetic
field that turns the metal rotor

Front 5

Anode and Cathode

Back 5

-contained w/n a vacuum envelope
-connected by an electrical circuit,
called the x-ray circuit, which is
responsible for their operation

Front 6

Stator

Back 6

-surrounds glass envelope and rotor
-not physically connected to anode
-responsible for turning rotor and
attached stem and disk at a high
speed during x-ray exposure
through electromagnetic induction

Front 7

Metal Disk

Back 7

-comprises anode
-referred to as disk or target
-attached to metal stem and a rotor,
which serves as a housing for
bearings

Front 8

Cathode

Back 8

-negative charge
-usually contains 2 coiled tungsten
filaments supported w/n a focusing
cup

Front 9

Anode

Back 9

-positive charge
-consists of a metal disk and stator
-usually rotating type, which allows
better heat distribution over the
face of the disk when the disk is
bombarded by electrons during an
exposure

Front 10

Cathode Filaments

Back 10

-1 small and 1 large
-connected to branch of x-ray circuit
called filament circuit that is solely
responsible for producing intense
heat w/n them
-only 1 is heated during exposure
-heated to liberate electrons
(thermionic emission)
-made of tungsten b/c high melting
point allows filament to be heated
repeatedly w/o rapid evaporation of
the metal

Front 11

Degree of Filament Heating

Back 11

-controlled by mA setting
-as temperature increases, rate of
emission increases
-heat causes some electrons to
leave the wire surface and "hover"
in space next to filament (b/c
electrons reside mostly on outside
of filament wire)
-these electrons remain as an
"electron cloud" (aka: space
charge) as long as filament is
heated

Front 12

Focusing Cup of Cathode

Back 12

-has a negative charge
-repels and contains electrons in a
small space so they can be
accurately focused on the anode disk

Front 13

Focal Spot

Back 13

-area on which the electrons bombard
the anode disk
-electrons that strike it are
absorbed and converted to thermal
energy and x-rays
-very inefficient process
-produces more than 99% heat
and less than 1% x-rays

Front 14

Anode Disk

Back 14

-composed of either solid tungsten or
of a layer of tungsten-rhenium alloy
overlaid on molybdenum or graphite
-periphery is beveled to allow
x-rays produced w/n the disk
material to be minimally impeded
as they travel toward the pt and it
promotes recorded detail
-known as the line-focus principle
-bearings in rotor attached to disk
allow disk to rotate freely and
smoothly during boost-and-hold
step and during exposure

Front 15

External Electrical Circuit

Back 15

-connected w/ x-ray machine
-provides voltage to tube
-measured in kV
-high voltage causes electrons of
heated filament to jump quickly to
anode disk

Front 16

Tube Current

Back 16

-flow of electrons from cathode to
anode
-measured in mA

Front 17

Speed at which Electrons Move from Cathode to Anode

Back 17

-depends on kV setting
-higher the kV from external circuit,
faster electrons travel
-energy of x-rays produced w/n
disk depends on speed (kinetic
energy) of electrons

Front 18

Selecting kV Setting

Back 18

-according to thickness, density, and
atomic number of anatomical part
being radiographed
-higher kV used to produce higher
energy x-rays that are able to
penetrate anatomical parts either
thicker, more dense, or have
higher atomic numbers and vice
versa

Front 19

Energy Levels/Shells

Back 19

-shell closest to nucleus is innermost
-named moving away from nucleus as
K-Q shells
-determine max # of electrons
allowed in any given shell at 1 time
using formula: 2n^2, where n
stands for the number of the shell

Front 20

Binding Energy

Back 20

-electrostatic attraction felt by the
electrons for the protons in the
nucleus, despite the fact that they
reside in various shells outside the
nucleus
-innermost shell is lowest energy
level of atom, but has highest
binding energy
-outermost shell is highest energy
level of atom, but has lowest
binding energy

Front 21

Bremsstrahlung Radiation

Back 21

-means "breaking radiation"
-when an exposure is made, electrons
from cathode travel at approx
93,000mps toward anode disk
-attraction to positively charged
nuclei cause electrons to slow
down and veer toward attracting
nuclei
-sudden deceleration causes
release of kinetic energy in form of
x-radiation
-electrons passing closest to nuclei
veer at sharper angles and release
more kinetic energy
-electrons passing closest to nuclei
produce higher energy x-rays
-predominant type of x-radiation
produced in diagnostic x-ray
energy range

Front 22

Characteristic Radiation

Back 22

-produces characteristic x-ray of
which energy is equal to difference
between energy of the 2 shells
-projectile electrons randomly
strike inner-shell electrons of
target atoms
-collisions result in ejection of
orbiting electrons
-when an electron is bumped out
of its shell, an electron from a
higher shell moves down and fills
the space left by the ejected
electron
-successive exchanges occur, and
characteristic x-rays are produced,
until no higher energy level exists
to provide an electron
-space left by outermost shell is
left open, leaving once neutral
atom positively ionized

Front 23

Scattered Radiation

Back 23

-results when primary x-rays interact
w/ atoms of irradiated tissues
-needlessly increases exposure of
pt and personnel
-places undesirable fog (called
supplemental density) over image

Front 24

Compton Scatter

Back 24

-predominant type contributing to film
fog and personnel exposure
-primary x-ray interacts w/ an atom of
irradiated tissue
-x-ray collides w/ outer-shell
electron, ejecting it from its orbit,
and causing ionization
-ejected electron can attach to a
nearby atom, causing it to become
negatively ionized
-ejected electron called Compton or
Recoil electron
-primary x-ray loses energy during
collision and changes direction
-this photon is now considered a
Scattered Photon b/c it changed
direction
-if scattered photon has sufficient
energy after its interaction, it may
exit pt and either expose
personnel or fog film
-especially true when using high
kV
-scattered photon and ejected
electron traveling through tissue
may interact w/ neighboring atoms
in the tissue and cause more
ionization

Front 25

Photoelectric Interaction

Back 25

-responsible for contrast on
radiographic image
-causes some primary x-rays to be
completely absorbed in pt's body
-occurs when an x-ray photon w/
energy equal to or slightly greater
than the binding energy of an
inner-shell electron collides w/ that
electron
-energy of primary x-ray is
completely absorbed by and
stored in the atom, causing it to
be in an excited state, and the
x-ray no longer exists
-atom responds by ejecting
inner-shell electron, now called
photoelectron
-electron from any higher energy
level then fills the hole
-amount of energy equal to the
difference in the binding energies
of the 2 shells involved in the
exchange is then given off in the
form of a secondary x-ray

Front 26

Classical Interaction

Back 26

-produces scattered radiation
-doesn't cause ionization
-called Classical Scattering
(aka:coherent, unmodified,
Rayleigh, and Thompson scatter)
-very low-energy x-ray (x-rays w/
energy below the energy range of
those used in diagnostic
radiography) is absorbed after
colliding w/ an atom, causing
excitation of the atom
-excited atom returns to unexcited
state by emitting another x-ray
(classical-scatter x-ray), one that
has the same energy as the
incoming (primary) x-ray but one
that travels in a different direction
-don't have sufficient energy to exit
the body, so not a concern for
personnel exposure or for fogged
film
-unable to exit the pt's body b/c
they're absorbed when they collide
w/ either tightly bound electrons or
atomic nuclei of nearby atoms

Front 27

Electromagnetic Radiation

Back 27

-tiny bundles of energy (called
photons or quanta) consisting of
varying electric and magnetic
fields traveling through space at
the speed of light (186,000mps)
-electrically neutral and has no
mass
-only difference among
electromagnetic photons is their
energy

Front 28

Intensity

Back 28

-the # of x-ray photons in the beam
-measured in milliroentgen (mR)
-controlled by mAs
-influenced by kV, SID, and filtration

Front 29

kV

Back 29

-determines beam's penetrating ability
-defines beam's average energy

Front 30

Inherent Filtration

Back 30

-filtering done by components of the
x-ray tube assembly
-tube window
-oil surrounding tube
-housing port
-is approx. 0.5-mm aluminum
equivalent in most diagnostic x-ray
tubes

Front 31

Added Filtration

Back 31

-any filtering done by components
lying beyond the housing port
-aluminum plate (either 1- or 2-mm
thick)
-collimator mirror
-plastic cover on opening in the
bottom of the collimator

Front 32

Trough Filter

Back 32

-typically used for chest radiography,
where high-intensity beam is needed
for mediastinal area and low-intensity
beam is needed for lung fields
-thick portions of filter are
positioned to correspond to lung
fields
-thin, central portion left to
correspond w/ mediastinal area

Front 33

Wedge Filter

Back 33

thickest portion positioned to correspond w/ thinnest portion of body part and vice versa

Front 34

Step-Wedge Filter

Back 34

-positioning same as w/ wedge filter
-can be used for abdominal and lower
extremity vascular exams
-for these exams, a long cassette
is used so as to include distal
abdominal aorta to the arteries of
the foot all in one exposure
-thinnest portion is placed over the
abdomen
-thickest portion placed over the foot
-intermediate steps are placed over thigh and lower leg

Front 35

Off-focus Radiation

Back 35

-x-rays produced in areas of anode
other than focal spot
-some high-speed electrons
coming from cathode can strike
focal spot and bounce off
-these electrons can rebound and
strike any other part of the
anode disk and produce
x-radiation
-this radiation is usually stopped
by 1st set of shutters in
collimator box, before it reaches
pt, and is therefore of little
concern

Front 36

Conventional Cassettes

Back 36

-most common type found in medical
imaging departments
-designed to hold 1 or 2 intensifying
screens and a film

Front 37

Intensifying Screen

Back 37

-converts x-ray energy into visible light
energy
-approx. 90-99% of the image is
produced from light exposure
-less than 1-10% of the image is
produced by direct x-ray exposure

Front 38

Cassettes

Back 38

-keep intensifying screens and film in
close contact w/ one another
-protect screens and film from
physical damage
-protect film from being exposed to
external light

Front 39

Frame

Back 39

-made of aluminum, steel, or in some
models, heavy plastic
-gives support to remainder of
cassette components

Front 40

Front Panel

Back 40

-side where x-rays 1st enter cassette
-made of a thin, radiolucent material
that has a low atomic number to
minimize absorption of the x-rays
-common materials: plastic, carbon
fiber, Bakelite, aluminum, and
magnesium

Front 41

Back Panel

Back 41

-commonly made of aluminum,
stainless steel, or plastic
-inside wall is lined w/ lead foil
-allows primary x-rays to exit
from the tube but inhibits the
entry of weaker, scattered
x-rays emanating from objects
behind the cassette
-this scattered radiation is called
backscatter and produces a fog
on the radiographic film

Front 42

Artifact

Back 42

-unwanted, irregular density or mark
seen on a radiograph
-causes: poor processing
conditions, improper film handling,
pt clothing and jewelry, and dirt or
other foreign matter on cassette
screens and film

Front 43

Cassette Labels

Back 43

-screen speed
-size of cassette
-ID # for easy retrieval

Front 44

Characteristics of a Good Cassette

Back 44

-lightweight, durable
-smooth, washable surfaces
-not easily bent
-lightproof
-capable of maintaining good
screen-film contact
-can be opened and closed easily
-smooth, rounded edges and
corners