x-ray imaging SI units Flashcards
What is a dimension?
A dimension is a property that can be measured such as length [L], time [T], or mass [M]. Dimensions are fundamental physical properties that can be measured.
What is a unit?
A unit is a way to assign a number or measurement to that dimension. Units provide agreed systems of measurement
Give an example of a dimension?
Length is a dimension, but it is measured in units of meters (m) in the metric system. The length could also be measured using another agreed system such as the Imperial System, in which case the units would be feet (ft).
What is the main system of units today?
The main system of units in use today:
The International System of Units
Referred to as SI Units from Le Systeme International d’Unites
SI Base Units
Quantity Name Symbol Dimension Symbol
Length- Meter-m-L
Mass-Kilogram-kg-M
Time-Second-s-T
Electric current-Ampere-a-I
Temperature-Kelvin-k-θ
Amount of substance-Mole-mol-N
Luminous intensity-Candela-cd-J
SI Base & Derived Units Example (velocity/force)
Velocity is defined by the simple equation:
v=d/t
Where d is the distance and t is the time. In SI base units:
distance is expressed in units of metres (m)
time is expressed in units of time (s)
So, the derived units of velocity are m/s. The dimensions of velocity are therefore [L] [T]-1
Force is defined by Newton’s Second Law by the simple equation:
F=ma
Where m is the mass and a is the acceleration. In SI base units:
mass is expressed in units of kilograms (kg)
acceleration is expressed in derived units of m/s2
So, the derived units of force are kg-m/s2 which is given a special unit name called a newton
The dimensions of force are therefore [M] [L] [T]-2
SI units used in radiography
Quantity/ SI Unit/ Symbol/ Application
Energy
joule
J
Production of X-rays
Power
watt
W
Output of X-ray generator
Electric current
ampere
A
Quantity of electrons flowing in a electrical circuit
Electrical potential
volt
V
Accelerating force acting on electrons in an X-ray tube
Resistance
ohm
W
Quantity limiting the flow of electrons in an electric circuitGray
gray
Gy
Amount of absorbed radiation doseSievert
sievert
Sv
Biological effect of ionizing radiation
Common prefixes
Name/ Symbol/ Base 10/ English Descriptive Word/ Example Usage
giga
G
10’9
billion
GB – gigabyte, unit of memory storage
mega
M
10’6
million
MHz – megahertz, unit of frequency
kilo
k
10’3
thousand
kV – electrical potential across X-ray tube
centi
c
10’-2
hundredth
cm – centimetres, unit of mesurement
milli
M
10’-3
thousandth
mA – milliamp, unit of electric current
micro
µ
10’-6
millionth
mGy – microgray, unit of absorbed dose
nano
n
10’-9
billionth
nF – nanofarad, unit of capacitance
femto
f
10’-15
quadrillionth
fm – femtometre, unit of distance
Simple Formulae Example: Equation of motion: v=u+at
v is the final speed in metres/second (m/s)
u is the initial speed in metres/second (m/s)
a is the acceleration in metres/second (m/s2)
To calculate the final speed of an object with initial speed 5 m/s moving with an acceleration of 2 m/s2 for 3 seconds substitute these values into the formula v=u+at=5+2×3=11 m/s
Simple Formulae Transposition Example
v is the subject of the formula above, but suppose we want a formula where t is the subject.
The basic strategy is to get t on its own by moving terms to the other side of the equals sign.
The general rule that we apply in doing this is “What ever operation is applied to one side of the equation then this must be applied to the other side of the equation”
Subtract u
v-u=u+at-u
v-u=at
Divide by a
(v-u)/a=at/a
Swap sides
t=(v-u)/a
Make u the subject: v^2=u^2+2as
Subtract 2as
v^2-2as=u^2+2as-2as
v^2-2as=u^2
Square root each side and swap sides
u=√(v^2-2as)
Linear Relationships: equation
y=mx+b
Here, m represents the gradient of the line and b represents the y-axis intercept
exponential relationships: equation
y= kb’x
Mass, volume & Density
density=mass/volume
If a material has a mass 3.2 g and a volume of 0.4 cm3 its density is given by:
density=mass/volume= 3.2 g/0.4cm^3 =8 g/cm^3
What is thermal energy?
Thermal energy transfer is the movement of heat energy from one substance to another.
Heat energy always moves from objects with high temperature to objects with low.
What is heat energy?
A form of energy which flows from a hotter region to a cooler region.
Unit of measure:
Measured in Joule (J)
Property:
Flows from a hot area to a cold.
What is Temperature?
The degree of hotness and coldness of a body.
Unit of measure:
Kelvin (K) and Celsius (degrees C)
Property:
Increases when heated
Decreases when cooled
Thermal energy equation
∆T=E/km
∆T temperature change (°C)
E energy (J)
m mass (kg)
k specific heat (J/kg°C)
- Which one of the following is NOT an SI base unit?
a. second
b. metre
c. ampere
d. kilogram
e. ounce
ounce
- Which one of the pairs of units & dimensions match?
a. kilogram & [T]
b. second & [L]
c. ampere & [T]
d. kilogram & [M]
e. kelvin & [M]
kilogram & [M]
- Which one of the pairs of units have the same dimension
a. second & metre
b. kilogram & second
c. ampere & candela
d. kilogram & foot
e. second & hour
second & hour
- Which one of the following gives the correct dimensions for speed
a. [L] -1 [T]
b. [L] [T]-1
c. [M] [T]
d. [M] -1 [T]
e. [L] [M]
[L] [T]-1
- Which one of the following is a derived SI unit
a. kilogram
b. second
c. volt
d. metre
e. mole
volt
- An electrical current of 0.5 A is equal to which one of the following
a. 5 mA
b. 50 mA
c. 500 mA
d. 5000 mA
e. 50, 000 mA
c. 500 mA
- A voltage of 75 kV is equal to which one of the following
a. 7.5 V
b. 750 V
c. 7500 V
d. 75, 000 V
e. 750, 000 V
75, 000 V
- A voltage of 500 V is equal to which one of the following
a. 50 kV
b. 5 kV
c. 0.5 kV
d. 0.05 kV
e. 0.005 kV
0.5 kV
- An electrical resistor has a value of 1 MΩ which is equal to
a. 1 × 10’9 Ω
b. 1 × 10’6 Ω
c. 1 × 10’3 Ω
d. 1 × 10’2 Ω
e. 1 × 10’12 Ω
1 × 10’6 Ω
- An entrance surface dose of 1 mGy is equal to which one of the following
a. 10 µGy
b. 100 µGy
c. 1000 µGy
d. 10,000 µGy
e. 10,00 µGy
1000 µGy
- An entrance surface dose of 500 µGy is equal to which one of the following. (1 mGy= 1000 µGy)
a. 0.05 mGy
b. 0.5 mGy
c. 5 mGy
d. 50 mGy
e. 5000 mGy
0.5 mGy
- An electrical current of 0.0016 A can be expressed in standard form by which one of the following
a. 1.6 × 103 A
b. 1.6 × 10-3 A
c. 16 × 104 A
d. 0.16 × 10-2 A
e. 160 × 10-6 A
1.6 × 10-3 A
- An entrance surface dose is measured as 2.3 × 10-3 Gy. Which one of the following expresses this measurement correctly?
a. 2.3 Gy
b. 23 Gy
c. 23 mGy
d. 2.3 mGy
e. 230 mGy
d. 2.3 mGy
- An X-ray tube current is displayed as 52 mA. Which one of the following expresses this measurement correctly in standard form?
a. 52 x 10’-3 A
b. 5.2 x 10’-3 A
c. 52 x 10’-4 A
d. 5.2 x 10’-6 A
e. 5200 x 10’-6 A
52 x 10’-3 A
The power dissipated by a resistor is given by the equation P=I^2 R, where P is the power expressed in units of watts, I is the current expressed in units of amps, and R is the resistance expressed in units of ohms. If the formula is rearranged to make I the subject, then which one of the following formulae is correct:
I=(R/P)^2
I=(P/R)^2
I=√(P/R)
I=(PR)^2
I=(PR)^(1/2)
I=√(P/R)
If the intensity of an X-ray beam at a distance of d1 from the X-ray source is defined as I_1, then the intensity I_2 at some other distance d_2 from the X-ray source can be calculated using the formula for the inverse square law
I_2=I_1 (d_1/d_2 )^2
If this formula was rearranged to make d_2 the subject which of the following formulae is correct
d2=d1 √I2/I1
d2=d1 √I1/I2
d2=I1 √d1/I2
d2=I2 (I1/d1 )^2
d2=d1 (I1/I2 )^2
d2=d1 √I1/I2
- Before melting, most metals in solid form tend to _______ when heated. Select the correct answer.
a. Contract
b. Expand
c. Evaporate
d. Dissolve
e. Sublimate
b. Expand
- Which one of the following gives the correct volume for a cube measuring 0.5 cm × 0.5 cm × 0.5 cm.
a. 0.125 cm2
b. 0.25 cm3
c. 0.125 cm3
d. 1.25 cm3
e. 0.125 cm-3
0.125 cm3
- Which one of the following gives the correct dimensions for mass density
a. [L] -1 [T]
b. [M] [L]-3
c. [L] [M]2
d. [M] [L]-2
e. [T] [M]
[M] [L]-3
- A substance has a mass of 100 g and a volume of 50 cm3. Select the correct density from the following
a. 2 g/cm2
b. 0.5 g/cm3
c. 2 g/cm3
d. 5000 g/cm3
e. 20 g/cm2
2 g/cm3
- A large bath of water and a teacup full of water are heated. The initial temperature of the water in each vessel is 20°C and the final temperature of the water is 70°C. Which one of the following statements is true
a. The water in the bath feels hotter than the water in the teacup when you place your hand in each vessel.
b. The water in the bath stored the same thermal energy than the water in the teacup and therefore the temperature is the same.
c. The water in the bath absorbed less thermal energy to achieve the same temperature as the water in the teacup.
d. The water in the teacup absorbed more thermal energy to achieve the same temperature.
e. The water in the bath stored more thermal energy than the water in the teacup.
The water in the bath stored more thermal energy than the water in the teacup.
- You burn your hand on a metal pan handle which was heating food on a gas stove. What was likely to be the primary heat transfer mechanism responsible for the handle heating up.
a. Convection.
b. Conduction.
c. Radiation.
d. Electrical induction
e. Electrical conduction
b. Conduction.
