Transcript Chain of Survival and EMSC

Chapter 2
The X-ray Beam
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
1
X-ray production requires three
things
Lots of electrons
Give electrons kinetic energy
Convert electron kinetic energy into
electromagnetic energy (x-rays)
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
2
X-ray machine
X-ray machine is an electrical / mechanical
device which converts energy from one form
into another
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
3
X-ray Production

The production of x-rays requires a rapidly
moving stream of electrons that are suddenly
decelerated or stopped.


The negative electrode (cathode) is heated, and
electrons are emitted (thermionic emission).
The electrons are attracted to the anode, move
rapidly towards the positive electrode, and are
stopped or decelerated.
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
4
tube housing
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
5
X-ray Tube Housing



Metal or glass
envelope
Negatively charged
electrode
Positively charged
electrode
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
6
Cathode

Filament



Source of electrons
• Filament current
• Thermionic emission
Coiled tungsten wire
• Large and small
Focusing cup
• Space charge effect
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
7
Anode

Rotating anode



Requires a stator and
rotor to rotate
Tungsten metal
• High melting point
• Efficient x-ray
production
Target
• Decelerates and
stops electrons
• Energy converted to
heat and x-rays
• Bremsstrahlung and
characteristic
interactions
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
8
Target Interactions

Bremsstrahlung interactions



Characteristic interactions




Braking or slowing down radiation
85% of x-ray beam
Projectile electron energy at least 69.5 keV
Inner shell electron ionized
15% of x-ray beam
X-ray properties the same
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
9
Target Interactions (cont.)
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
10
X-ray Exposure
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
11
X-ray Exposure (cont.)
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
12
X-ray Emission Spectrum
The range and intensity of x-rays emitted changes with
different exposure technique settings on the control
panel.
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
13
X-ray Beam Quantity and Quality





Quantity: number of x-ray photons in primary
beam
Quality: penetrating power of x-ray beam
Kilovoltage
Milliamperage
Exposure time
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
14
Kilovoltage

Creates potential difference



Determines the speed of the electrons in tube current
Greater speed results in greater quantity and quality of
primary beam
Increasing electron speed will increase x-ray beam
penetrability
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
15
Milliamperage

Unit to measure tube current or number of electrons
flowing per unit time


mA directly proportional to quantity of x-rays produced
Double the mA will double the number of x-ray photons
produced
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
16
Milliamperage and Time

Exposure time determines the length of time
x-rays are produced.

Increasing time will increase the total number of xrays produced.
• Exposure time and x-ray quantity are directly
proportional.
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
17
Milliamperage and Time (cont.)

Milliamperage × time = mAs




200 mA × 0.25 s = 50 mAs
400 mA × 0.25 s = 100 mAs
200 mA × 0.50 s = 100 mAs
Changing the mA or time will change the
quantity of x-rays produced.
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
18
Three things to have usable
x-rays
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
19
X-rays must come from as close
to a point source as possible
X-rays must travel in straight
lines
X-rays must create contrast
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
20
Why can’t x-rays come from a
point source??????
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
21
Line Focus Principle

Relationship between
actual and effective focal
spot

Actual focal spot: area on
anode target exposed to
tube current electrons
 Effective focal spot: focal
spot size as measured
directly under anode target
 The smaller the anode
angle the smaller the
effective focal spot size
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
22
Anode Heel Effect



X-rays are more intense
on the cathode side of
the x-ray tube.
The intensity of the xrays decrease toward the
anode.
Place the thicker
anatomic area under the
cathode end for more
even exposure to the
image receptor.
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
23
filtration
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
24
Heat Units


During x-ray production, most of the electron kinetic
energy is converted to heat and can damage the x-ray
tube.
Heat units (HU) = mA × time × kVp × generator factor
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
25
Extending X-ray Tube Life






If applicable, warm up tube.
Avoid excessive heat generation.
Do not hold down rotor button without making
exposure.
Use lower mA and longer exposure time.
Don’t move tube while energized.
Recognize unusual noises, and report.
Copyright © 2013, 2009, 2004, 2000 by Mosby, an imprint of Elsevier Inc.
26