equipment test 1: x-ray tube + circuit

omg u got this

Cathode

negative side of the x-ray tube where electrons are emitted from the filament

Anode

positive side of the x-ray tube that receives electrons and upon interaction creates x-ray photons

Tube housing

made of metal/lead + immersed in oil (dissipates heat/insulates against electrical shock), role is to enclose + support x-ray tube by preventing radiation leakage to 1mGya/hr bc x-rays are isotropic meaning they spread in all directions

Glass envelope

made of pyrex glass layers because of its ability to withstand heat, maintains vacuum in tube, provides supports and electrical insulation for better x-ray production/longevity for tube

What components are on the cathode side ?

focusing cup + filament

Stator

made of electromagnets spaces around the neck of the tube, is stationary and just OUTSIDE GLASS ENVELOPE role is to induce rotation of the rotor by energizing in opposing pairs in sequence

Rotor

made of copper bars/soft iron around molybdenum shaft; INSIDE THE GLASS TUBE rotates the anode

Bearings

supports rotating anode disks allowing for smooth spins at high speeds

Focusing cup

made of nickel/molybdenum; holds released electrons around filament wires in tiny cloud = space charge until exposure switch engaged; when kVp applied during exposure = electrons focusing into narrow beam; directed from cathode to anode to area of focal track

What components are on the anode side?

the anode, rotor, stator, bearings

Filament

coil made of tungsten (atomic number 74) steel that heats up and creates electrons through thermionic emission

Details on the electron current in x-ray tube ?

flows in one direction, from the cathode to the anode

2 Forms of Energy X-ray tube makes?

x-ray = 1%; heat 99%

kVp (technique factor)

stands for kilovoltage peak; is the amount of voltage (potential) selected for x-ray tube; controls penetrability of the beam + beams energy, primarily controls beam QUALITY (1kilovolt = 1000 volts)

mAs (technique factor)

stands for milliamperage seconds calculated as mA (milliamps 1000 amps) x seconds; amount of current supplied to x-ray tube (by heating filament); control number of x-ray photons produced, controls beam intensity/primarily beam QUANTITY

X-ray photon production needs (4)

1. Source of free electrons = free electrons generated on cathode side by the tungsten filament through thermionic emission (controlled by the mAs: current supplied to x-ray tube)

2. Acceleration of electrons = free electrons move in one direction from the cathode to the anode side by voltage/potential (kVp), forces electrons across tube giving them kinetic energy; higher the kVp, more energy accelerated electrons have (like pre-workout/redbull)

3. Focusing of electrons = focusing cup focuses electrons into beam to hit anode (focusing cup made of nickel/molybdenum)

4. Deceleration of electrons = electrons decelerate once hitting the anode to convert kinetic energy into x-ray photons (anode made of tungsten metal)

Thermionic emission

process where electrons are released from the tungsten filament once heating it which gives the electrons energy to break free from it (when heated, electrons from tungsten atoms orbits spin faster moving farther away from nucleus leading to electrons in outer orbits to be flung out of the atom making free electrons)

Other terms for “free electrons” (2)

electron cloud, space charge

Increasing mA leads to what effects?

increases filament current increasing tube current increasing x-ray photons

Filament Sizes (2)

most machines are dual filament meaning one large and one small filament in the focusing cup; determined by size of focal spot)

Focal spot size (2)

specific area where electrons collide on the anode

1. Small focal spot size: small filament/small mA, can only handle small amount of heat; creates smaller EFFECTIVE FOCAL SPOT + more aligned beam = higher detail

2. Large focal spot size: large filament/large mA, handle large amount of heat; larger EFFECTIVE FOCAL SPOT + less aligned beam

Types of Anodes (2)

1. Stationary: unable to sustain high heat, used for small structures (dentistry)

2. Rotating: rotor/stator turns anode to prevent cracking/pitting from high heat amount, used for larger exposures (basically everything but dental)

How Exposure Made (from Rad Tech Input) (3)

1. Rotor button pressed = press exposure button halfway to activate rotor allowing for rotor to accelerate w/ designated rpm (revolutions/rotations per min); an electromagnetic induction motor (stator component) used to turn anode + creates magnetic field

2. kVp = only then is voltage/potential kVp applied to tube

3. Press exposure button all the way = listen to audible tone, then exposure fully made

Anode heel effect (all details)

refers to lower beam intensity on the anode side, higher intensity towards cathode end since the anode surface is at an angle meaning more x-ray photons absorbed on anode side

1. Focal Spot size relationship = small focal spot:smaller anode heel; larger focal spot:larger anode heel (direct relationship)

2. Anode Angle Degree relationship = smaller angle:larger anode heel; larger anode angle:smaller anode heel (indirect relationship) (thinner the heel, the more the pain!)

3. SID = decrease distance:increase heel; increase distance:decreases heel

not always a bad thing, can use to advantage like putting a thicker area of the body on the cathode side ex/proximal femur thicker, distal thinner so put thigh under cathode end w/ thinner distal end of femur under anode side

Line Focus Principle (all details w/ actual/effective focal spot)

relationship between actual focal spot on anode surface and effective focal spot

1. Actual Focal spot = where electrons interact w/ anode (the target) (LARGER)

2. Effective Focal spot = beam that exits tube to interact w/ patients (SMALLER)

3. Anode Angle/Line Focus Principle relationship = smaller anode angle/decrease:smaller focal spot/decrease effective focal spot; larger anode angle/increase:larger effective focal spot/increase effective focal spot (direct relationship)

Off Focus Radiation

extrafocal/off-focus rad made from rebounding electrons, refers to emission of x-ray photons that originate outside of anode focal spot

Atom Review!

nucleus in center; electron shells:

1. k-shell = inner shell 2 electrons

2. l-shell = second shell, 8 electrons

3. m-shell = third shell

4. o-shell = outer shell

Bremsstrahlung interaction

one of the 2 interactions at the anode where the electrons strike it; braking radiation, incident electron comes close to the, braking around the nucleus and bends around it in another direction, produces x-rays of all energies; 90% of all x-ray production (100% below 70 kVp) (moves like a boomerang)

Characteristic interaction

one of the 2 interactions at the anode where the electrons strike it; incident electron collides w/ k-shell electron knocking it out of place causing other shell’s electrons to go to fill its place = cascade effect

(k-shell binding energy of tungsten 69.5 kev so 69.5 kVp needed at least, round to 70)

X-ray beam + Radiation (3)

1. Primary beam = x-rays made by x-ray tube that strikes pt; either bremsstrahlung/characteristic or both

2. Remnant/exit radiation = remaining beam after leaving/exiting pt, made of primary/secondary radiation

3. Scatter radiation = type of secondary rad that happens when beam intercept object scattering x-rays

X-ray properties (11)

1. travels in straight lines (photons represented by wavy lines tho)

2. highly penetrating invisible rays

3. electrically neutral no charge !

4. no mass

5. wide range of wavelength (heterogenous)

6. travels at speed of light 186,000 miles/sec (3×10³ m/s)

7. capable of ionizing matter

8. cannot be focused by lens

9. effects digital images

10. causes crystals to fluoresce (glow)

11. produces secondary + scatter radX-ray

Frequency (x-ray beam)

number of times per second the electric + magnetic fields generate themselves (amount of wavelengths a second)

1. Higher energy of x-ray = higher frequency (direct relationship)

2. Higher kVp = higher energy so higher frequency (direct relationship)

3. Unit of frequency = hertz hz, cycles per sec

Wavelength (x-ray)

distance x-ray travels during one regeneration of electric and magnetic fields, distance between 2 successive peaks the tops of the waves

1. Higher kVp = short wavelength (almost like zigzags)

2. Low kVp = longer wavelength (less energy, camels humps)

3. Unit of Wavelength x-ray = angstrom (10th billionth of a meter)

A. Relationship with Frequency = increase frequency, wavelength decrease; decrease frequency, increase wavelength (inverse)

X-ray imaging system function

provide controlled flow of electrons intense enough to made x-ray beam appropriate for imaging

X-ray circuit/sides (2-3)

1. Primary side = low voltage: control panel; includes the operating console, autotransformer (kVp selection), rheostat (mA selection), time selection, kVp meter

2. Secondary side = high voltage: generator; step transformer, step down transformer, rectifier

Sometimes circuit is split into 3 circuits and not just two sides

1. Primary circuit = autotransformer (kVp selector), kVp meter, first part of the step up transformer

2. Secondary circuit = second part of step up transformer, rectifier

3. Filament Circuit = includes the rheostat + step down transformer

Operating Console (5)

1. controls for selecting technique (kVp, mA, seconds)

2. means to indicate when x-rays being made

3. light and audible tone required

4. exposure fixed on fixed unit, 6ft away on mobile unit connected by wire + is handheld to comply w/ ALARA (as low are reasonably achievable)

5. Low voltage (techs will only touch low volt control panel)

Electrical supply (3 components in the primary circuit)

1. Incoming power supply = 220 volts of AC (alternating current)

2. Master power switch = single throw double blade switch (big black switch on wall)

3. Fuses (circuit breaker) = protects equipment from excessive current

Line voltage meter

measures incoming line voltage detecting drop/surge, maintains 220 volts to autotransformer, on primary circuit (looks like a clock kinda)

Transformers (3)

transforms volts/amps to whats needed

1. autotransformer = needs AC, works on self induction; kVp selection (NOT PRODUCTION), low voltage on primary circuit/side, determines line voltage sent to step up trans

2. step up transformer = needs AC, mutual induction; high voltage transformer turning volts into kilovolts (1000) since high volt needed to make x-rays

3. step down transformer = needs AC, mutual induction; filament circuit after the rheostat, decreases voltage/increases amperage (milliamperage)

Rheostat

mA selector (NOT mA PRODUCER) in the filament circuit, regulates amperage; aka variable resistor bc determined by mAs which is determined by mass of pt.

Transformer Calculation Dets

1. Autotransformer calc = 2ndary voltage can match primary voltage but not exceed it (equal to or less)

2. Step up calc = 2ndary voltage always exceed primary voltage (more then)

3. Step down = 2ndary voltage always lower then primary voltage (less then)

Exposure timer (4 types)

primary side of highvolt trans = mechanical or electronic device meant to “break” (interrupt, cut off electrical current) the high voltage against the x-ray tube

1. Synchronous = set by tech, old, minimum 1/60s

2. mAs = set by tech, designed to provide highest mA w/ shortest exposure time

3. electronic = set by tech, most accurate to 1ms

4. automatic exposure control (AEC) = automatic, offered in addition to manual timer

Focal spot selector (2 sizes)

in filament, low voltage circuit, selects size of the filament by switching electrical current to larger/smaller filaments;

1. small focal spot range = 0.1 mm - 1.0 mm

2. large focal spot range = 0.3 mm - 2.0 mm

Rectifier

converts alternating current (AC) to direct current (DC) meaning only allowing electrons to flow in one direction since the x-ray tube works on DC only, needs 4 diodes (solid state semiconductor diode)

types of rectification

1. half wave

2. full wave

3. three phase

4. high frequency

Half wave vs. Full wave Rectification

1. Half wave = self rectification, negative phase of electric cycle eliminated with a gap remaining, x-rays are turned off during eliminated (negative) phase, pulsated on/off at 60 pulses per sec which is VERY INEFFICIENT

2. Full wave = four diodes needed in circuit, current redirected during negative half of electric cycle so current will flow in same direction during both +/- halves of cycle; x-ray pulse at 120 per sec resulting in doubling x-ray output compared to half wave

Three phase vs. high frequency rectification

1. Three phase generator (2) = three wires w/ power come into a transformer 3 phase 6 pulse + 3 phase 12 pulse; more efficient then single phase

2. High frequency generator = supply almost constant potential; supply switch on/off rapidly (14 kHz) which can be rectified, more compact then 3 phase supply more commonly used

Voltage Ripple (rectification) + %s

Voltage ripple = amount of fluctuation in voltage of the power to x-ray machine, less ripple the better, as ripple effect decreases:efficiency increases, when voltage ripple less; when tube is energized it says energized

Voltage ripple %s:

1. Single phase = 100%, volt varies from 0 to max

2. 3 phase 6 pulse = 14%, volt never falls below 86% of max

3. 3 phase 12 pulse = 4%, volt never falls below 96% of max

4. High frequency = -1%, volt never falls below 99%

Heat units (4 calcs to memorize)

are a calculation of total heat produced during x-ray exposure; x-ray tubes/tube housing made to absorb certain levels of heat units; most modern equipment prevents overloading tube during a series of exposures allowing tube to cool down before more exposures

Heat unit calcs:

1. Single phase full wave rect = kVp x mA x s x 1

2. 3 phase 6 pulse = kVp x mA x s x 1.35

3. 3 phase 12 pulse = kVp x mA x s x 1.41

4. High frequency = kVp x mA x s x 1.45

Anode Cooling Chart

cooling curve used to estimate cooling time needed between exposures

Tube Warm up Procedure

need to warm up x-ray before starting projections to prevent cracking/damage of anode from switching from cool to very hot quickly; anode warmed up 3-5 exposures

Series Circuit vs. Parallel Circuit

1. Series = components connected end to end to form single path for current form

2. Parallel = multiple paths of energization, like having multiple lanes when one is closed there are other lanes/paths