Week 1- radiology

x-ray machine

_____ energy is what forms x-rays

electrons

How are x-rays produced ?

when charged electrons are stopped or slowed down by the atoms of a target area

• occurs in the x-ray tube 

Photon 

the x-ray beam is a bundle of energy that travels in a wave 

• shorter the wavelength the greater the energy

Electromagnetic radiation 

transportation of energy through space with no mass 

• travel at a speed of light (radiation) 

Types (ionizing radiation) (6)

1. x-rays (emitted from electrons)

2. Gamma rays (unstable atomic nuclei)

3. radio waves

4. radar

5. microwaves

6. visible light

Velocity of electromagnetic radiation is the production of what? (2)

1. wavelength

2. frequency

Wavelength

the distance between 2 consecutive points of a wave 

• inversely proportional to energy

Frequency

number of cycles of the wave that pass a stationary point per second (cycles per second)

Velocity formula

Velocity (m/sec) = frequency (cycles per second) x wavelength (m)

Excitation

electron is moved to a higher energy level within the atom (non-ionizing)

1. microwaves

2. radar

3. cellphones

Ionization

outer electron is removed from the atom, which now leaves the atom positively charged. 

1. x-rays

2. cosmic rays

3. radioactive material 

what are some substances that will fluoresce after absorbing electromagnetic radiation? (2)

1. calcium tungstate

2. phosphorus

Who discovered x-rays in 1895?

Wilhem conrad roentgen

basic definition of x-rays

negative electrons move from the cathode (negative) to the positive Anode in the x-ray tube causing a collision which generates x-ray radiation and heat

• 1%= radiation, 99% = heat

x-ray tube consists of what?

Consists of cathode and a positive anode, encased in a glass envelope to form a vacuum 

Cathode 

consists of a coiled filament (tungsten) that emits electrons once heated 

Anode

positive target composed of tungsten, with a target base of copper that conducts and draws heat away from the target

Stationary Anode

1. fixed non-movable anode

2. dental xray- portable 

3. angled target at 15-23 degrees (altered focal spot size)

4. unable to withstand large amount of heat

Rotating anode

is shaped like a disc that rotates around the center of the tube

Heel effect

unequal distribution of the x-ray beam intensity emitted from the x-ray tube (variation)

• place thicker tissue on cathode side (ex: head smaller than chest. head to anode side)

Focal spot

the small area of the target anode where electrons collide

• smaller the focal spot the greater the clarity of the x-ray

Penumbra 

halo effect on a radiographic image that is caused by a focal spot larger than a pinpoint (causes blurring) 

Actual focal spot

perpendicular to the anode target in the x-ray tube

How does actual focal spot affect the Heel Effect? (2)

1. small actual focal spot increases the heel effect

2. more x-ray leave the cathode side rather than the anode side, causing a variation of exposure to the x-ray film

Effective focal spot

area that is on the patient or 90 degrees angle from the x-ray tube

Rectification

process of converting an alternating current (AC) to a direct current (DC)

• limits electron flow in one direction from cathode to anode

3 Ways of Rectification

1. half-wave rectification

2. full wave-single phase rectifier 

3. three phase rectified (full waved) - most efficient 

Collimator (conning down)

restrictive device that controls the size of the primary x-ray beam