Module 2

Question 1

Who discovered X-rays in 1895?

Answer 1

Wilhelm Rontgen

Question 2

Who is Wilhem Rontgen?

Answer 2

Discovered Xrays on 8th november 1895 and in 1896 the first xray was taken in the UK at the Glasgow Royal infirmary.
In 1896 medical xray diagnosis began.

Question 3

When was the first dental xray taken and who by?

Answer 3

The first dental xray was taken by otto walkhoff a german dentist in january 1896 less than two weeks after wilhem roentgen announced discovery of xrays and it used a 25 minute exposure.

Question 4

RADIOGRAPHY -

Answer 4

uses xrays to produce images of areas inside objects

Question 5

RADIOLOGY -

Answer 5

uses images to diagnose and treat disease

Question 6

Electromagnetic spectrum -

Answer 6

• Electromagnetic Radiation is made up from both electric and magnetic fields
• Waves are energy and momentum from one point to another known as wave packet called a photon
• One photon is equivelent to one quantum of energy
• Photons have no mass and travel at the speed of light, they behave as both a wave and a particale
• there are millions of photons of diffrent energies which move at 90 degrees to each other.
• if the frequency is doubled then the energy of the photon is doubled.
• energy of photons is measured in electrons volts (eV)
• electromagnetic waves travel through a vacuum without changing speed
• vibrations transfer energy from one place to another without matter being transferred
• electromanetic raidation travels through empty space and the electic and magnetic fields vibrate as they travel
• all electromagnetic radiation act in this way.

Question 7

Frequency -

Answer 7

• Number of repetitions in a given time period
• Greek letters nu, v
• more repetitions = higher frequency = shorter wave length
• measured hertz ‘Hz’
• measured from one point to another
• Greek letter lambda (λ)

Question 8

EMR waves -

Answer 8

• energy and momentum
• electric and magnetic
• travel at 90 degrees to each other
• wave packets - photo/quantum
• no mass
• measured in electron volts (eV)
• travel through a vacuum
• the shorter the wavelength the more dangerous they are
• any waves shorter than visible light can cause cancer
• gamma rays are the shortest, then Xrays!

Question 9

Natural background radiation

Answer 9

Radioactive substances can be found around us, in the ground, granite releases randon a decay product of uranium, the air, building materials and food as well as cosmic rays from space. it is estimated that an individuals dose from background radiation will be approximatley 2.7mSv per year.

Question 10

How many xrays are approx. taken in the uk per year?

Answer 10

In the uk approximately 20-25 million dental xrays are taken a year and it is estimated that the overall risk in the UK us apporximatley 10 fatal malignancies per year therfore we must keep all exposures As Low As Reasonable Practicable -ALARP

Question 11

What xray equipment is in the dental surgery?

Answer 11

• tube head
• positioning arm
• control panel
  
  • wall mounted
  • part of chair
  • on wheels
  • hand held

Question 12

Equipment and requirements

Answer 12

• Safe and robust
• accurae and simple to operate
• capable of generating Xrays for film and digital
• small
• easy to position, move and store
• stable and balanced once positioned

Question 13

what are the components of the tubehead?

Answer 13

• the outer casing is made of lead - this must be checked regurlarly to ensure no cracks or damage
• xray tube is in a glass envelope which is filled with oil to remove the heat
• step up transofrmer - increases the voltage from 240v to 60-90kv
• step down transformer - decreases the 240v to 7-10v required to heat the filament
• aluminum filtration - removes harmful low energy x-rays (soft xrays less than 30kv)
• focal spot

Question 14

production of x-rays

Answer 14

• glass tube which is where the x-rays are produced
• found at the back of the tubehead surrounded by lead which absorbs any excess x-rays which are travelling in all directions, it also creates a vacuum

Question 15

Cathode

Answer 15

• a tungsten filament centred in a focusing cup
• electrons are produced by the filament and are focused at the target on the anode(the xrays are produced at the anode)
• the focusing cup has a negative charge - the same as the electrons - this helps direct the electrons to the target

Question 16

focusing cup

Answer 16

aims the stream of electrons to the focal spot on the target

Question 17

thermionic emmisions

Answer 17

• when the exposure button is pressed the electricity flows from the filament in the cathode - the filament gets hot
• electrons are released which surround the filament
• the hotter the filament gets the greater number of electrons are realeased

Question 18

Anode

Answer 18

• comprised of a tungsten target on a copper base
• when the electron from the filament hit the target they generate the xrays and heat the copper ase removes the heat so as it dosen’t get too hot.

Question 19

High voltage (kilovoltage, kV)

Answer 19

connected between the anode and the cathode to accelerate the electrons from the negative filament to the positive target Kvp or kilovoltage peak

Question 20

A current (milliamperage, mA)

Answer 20

flows from the cathode to the anode - measurment of the quantity of electrons being accelerated

Question 21

spacer cone or beam indicating device (BID)

Answer 21

direction the beam and sets the ideal distance from the focal spot on the target to the skin (FSD)
200mm for kV over 60
100mm for kV below 60
pointed types must no longer be used

Question 22

focal spot size and the principle of line focus

Answer 22

source of the xrays should be a single area to reduce blurring of the image causing the penumbra effect but the heat produced at the target by the bombarding electrons needs to be distributed over as large an area as possible.
these two opposite rquirements are satisfied by using an angled target and the principle of line focus

Question 23

collimator

Answer 23

a metal disc with a hole in the middle found by the window in the lead casing. it limits and shapes the beam and shapes to the same size as an intra oral film.
the maximum size of the collimator should be 40 x 50 mm
the rectangular collimator overlap the dimensions of a standard ISO size 2 film by 2mm

Question 24

Aluminium filtration

Answer 24

is found between the collimator and the spacer cone

removes non diagnostic low energy (soft) xrays which are easily absorbed by the patient and therefore is more damaging

Question 25

control panel

Answer 25

mains on/off switch with a warning light
timer - electronic impulse or clockwork
exposure time selector - numerical or anatomical
must have an exposure warning light and audible signal
- film speed selector
- patient size selector
- mains voltage compensator
- kilovoltage selector
- milliamperage switch
- exposure adjustment for digital imaging

Question 26

alternating current

Answer 26

• 240V current is an alternating current - half is negative and half is positive
• the positive half is only needed for the productions of xrays
• therefore the stepped up high voltage applied across the xray tube needs to be rectified to eliminate the negative half of the cycle
• this means that the equipment is only working at is peak output and the top of each cycle = kV peak or kVp

Question 27

Direct current

Answer 27

• used by modern xray equipment
• keeps the kilovoltage at the kVpeak throughout the exposure
• the xray production per unit of time is more efficient, there are more high energy useful photons produced and less low energy harmful photons produced
• enables a shorter exposure time

Question 28

Factors affecting the intesity and quality of the beam

Answer 28

Intensity is the number of xray photons in the beam
Quality is the energy carried by the photons
- size of the tube voltage - kV
- size of the tube current - mA
- distance from the target - d
- time = length of exposure (t)
- filtration
- target material
- tube voltage waveform
- xrays travel in straight lines and they obey the inverse square law - intensity = I/d² - they decrease as you get further away from the beam
- xrays are referred to as ionising radiation
- energy carried can be attenuated by matter
- xrays can affect film emulsion to produce a visual image and can cause certain salts to fluoresce