Pg 33- Flashcards
What is bremsstrahlung radiation
Interaction of incoming electron with target nucleus, electron passes close to nucleus and changes direction which causes loss of energy which is converted into xray
Makes up 85% of xray beam
What is characteristic radiation
A incoming electron interacting with a target electron, the electron collides with the K shell target electron knocking it outta orbit. To replace the K shell electron the outer shell electron moves down.
What are the two types of filtration with tube complex
Inherent and added
Filtration attenuates (reduces)
Beam intensity
Soft rays _______ the skin entrance and organ dose to patient
Increase, hence why they are filtered out. Normally measured in aluminum (AI) thickness
What is half value layer (HVL)
The amount of material needed to reduce beam intensity by 1/2. its used for filtration recommendations and regulations.
What is inherent filtration
From the oil and glass window, is equivalent to 1/2 mm of AI thickness. Manufacturers add 1-2 mm of AI to the housing port
How much filtration is required for 70-100 kV
2.5 mm
HVL for up to 125 kV is 3mm of AI most machines are this.
Most machines are rated a _____ kV
125 but usually dont use above 100 for spine, sometimes for chest
What limits the beam to the desired port or film size
Collimation,
Collimation helps reduce
Secondary exposure to patient and operator, also improves film quality by reducing the secondary rays
Where is a collimator fitted
On front of the tube housing
Collimators have ____ shutters and can be
4, adjusted to desired size, shutters are made of lead
2 adjustment knobs on collimator that both work
Independently
When smaller than film size there will be
Collimation cut off
If collimation is too tight the film will be
Over colliimated. To large then its under collimator
Cut off will be ______ or ______ due to primary beam absorption
White, light
Often the area of cut off is gray or dark due to secondary exposure from the patient but not
As dense as the primary exposure . Also can happen from off focus radiation (rays exiting anode other than the target)
Cut off occurs when
Collimating to part size instead of film size
Cut off will be equal if CR and film are
Centered
The center of a beam after collimation through the glass window is shown by cross hair formed by
Horizontal and vertical lines, postition the tube vertically and patient horizontally
Collimator accuracy is require to be within ____ of the distance between focal spot and film
2%
What are the 3 basic types of collimation
Manual- all adjustments made by operator
Semiautomatic
Automatic- semi and full automatic ar POSITIVE BEAM LIMITATION devices (PBL)
PG. 39 about cross hairs on patient look at it super easy
Yep!!!
What is selective/ compensating filtration
Improves film quality, compensates for patients varied thickness
Selective filtration can
Lessen intensity to the thinner parts of the body, should be placed between the tube and patient to reduce exposure
What are portal filters
Are placed on the front of the beam limiting device, usually made of aluminum or copper.
Selective filters are ________ with spinal radiography
Necessary, used during full spine films and most A-P and lateral thoracic films
Selective filters can be used on feet to filter
Toes
A line can be seen between filtered and unfiltered part unless
The filter was tapered
Wedge filters taper
Thus no line of demarcation between the filtered and unfiltered area called wedge filter system
What is the most common filter used in chiropractic
Nolan filter system
What is a underpart filter
Refers to reducing the beam intensity after it passes through the patient thus adding unneeded exposure, mostly in the form of SPLIT SCREENS, often used for full spine films
Plating and arcing of the tube damage it which
Wears down the ball bearings causing slower rotation and anode surface melting
To help prevent tube failure
Limit the time you hold the rotor button to prevent increased thermionic emission. Excessive exposures may cause anode pitting of tube if not cooled sufficiently before another exposure
What are heat units (HU)
Calculates by mA x time x kV. Tube rating and tube cooling charts included
What is recommended if tube hasn’t been used for a number of hours before a large exposure
Warm up, this prevents thermal shock to the anode which can cause your anode to crack or more likely the anode stem to crack and break off
If you need to increase the mAs do it either with the
MA STATION OR TIME
A lower mA setting will ______ tube stress
Lessen
Generators normally require
220 volts and 100 amps, some new units run on 100 volts called sorted energy units which operate with a battery.
HOWEVER 220 is more commonly used
What do transformers do
Change incoming current
Whats a high voltage transformer
Converts volts to kilovolts 1000 volts= 1 kV and kV are needed for xray
_________ kV are most commonly used for offices
40-125
A high voltage transformer is also called a
Step up transformer or high voltage circuit
A filament circuit converts arms to
Milliamps (mA) 1/1000th of an amp is 1 milliamp
50-300 mA is usually used but can be higher (often 600)
The filament circuit is also called
Filament transformer or low voltage circuit or step down transformer
Rectifiers change current from
AC to DC
Alternating current (AC) electrons move
Forward and backward, this would send electrons to the cathode and destroy it
Direct current (DC) is needed for the tube bc
It travels in one direction from cathode to anode
What is rectification
Changes the AC to DC and is done by the recitifiers. They are diodes. Eliminates the lower (-) pulse of the cycle protecting the filaments. The result is HALF WAVE RECTIFICATION
What is full wave rectification
Changes the - to a + allowing 2 + pulses, more efficient than 1/2 wave rectification
What is kilovolt peak (kVp)
The desired kV
The kV builds up from 0 to the peak and then
Descends back to 0
All of the kV below the peak make up some of the exposure which this variable is called
Ripple, the less ripple the better
Single phase generators have
1 line source and has maximum ripple
A 3 phase generator has three separate intertwined incoming lines, which allows
More peaks and less dips. Results= less ripple
Maintains kV, its more efficient but not practical due to to expense
High frequency generator have
Virtually no ripple allowing more accurate and predictable output. Even less ripple than 3 phase
Benefits of high frequency generators
Produces greater photon energy, has fewer soft rays, gives patient less exposure, is affordable
The longer the time, the more electrons bombard the anode which
Increases the number of X-rays
How long is exposure time
1/120th of a second to a couple seconds.shortest time is preferred to reduced the chance of patient motion
What are the types of timers
Synchronous, electronic, mAs, automatic exposure control
Which timers are most accurate and versatile
Electronic, wider in use
MAs timer combine mA and seconds in
1 control (popular), they are calculated using the lowest time and safest mA
Automatic exposure control (AEC) has
Photocells in front of a film
The 4 primary factors for controlling X-ray exposure are
Kilovoltage peak (kVp)
Milliamperage (mA)
Length of time of exposure
Distance of the tube from the receptor
Photons striking the film is inversely proportional to the square of the distance
Inverse square law
