dose reduction mechanisms Flashcards
Goals for Oral and Maxillofacial
Radiology
- Reduce radiation exposure
- Maintain a high degree of diagnostic
efficiency
juggling act of oral radiology
●reduce a patient’s radiation exposure
●maintain a high degree of diagnostic efficiency
Dose Reduction Mechanisms
X-ray Tube Head
Patient Protection
Operator Safety
Et cetera
ALARA:
As Low As Reasonably Achievable
Guiding Principle ofRadiation Protection
Since the probability or severity of biological damage increases as the radiation dose increases, it is desirable to avoid receiving even the smallest dose of radiation unnecessarily.
ALADA:
As Low As Diagnostically Acceptable
Guiding Principle of Radiation Protection
* ALADA lowers exposure to patients
* ALADA lowers exposure of all office personnel
mandated dose reduction mechanisms of tube head
- Filtration
- Collimation
purpose of the filter
removal of low E (large wavelenght) photons
* Selectively removes a greater proportion of low keV x-ray photons
* Increases mean energy of the beam
based on? Al filtration needed?
Mandated Minimum Total Filtration
for X-ray Tubes
majority of machines in the 50-70/ 1.5mm range
tube head collumination
mandated on tube side
can be circular or rectangular
* Maximum 2.75” diameter
* (Rectangular preferred)
optional dose reduction mechanisms xray tube options
- Rectangular collimator
- High kV generator/ transformer
- Constant potential (DC) fully rectified
- Increased focal length
rectangular collimination
decreases beam size to size of receptor= decrease in dose
no compromise to diagmostic info if done correctly (alignment)
must learn to have precise placement of both source and receptor
area exposed and beam size
directly related
what can help with rectangular collimnator alignment
ring assemblies like in clinic (XDR?)
can depend on?
_________ dose is reflective
of the specific technique
effective dose is reflective of the specific technique
can depend on receptor and collination
higher kV and dose
will actually reduce the dose, may be due to increased filtration measures (distance and actual filter)
higher kV units are?
larger and heavier
constant potential of xray tube and dose
reduced dosage with constant production of xrays (no intermittment periods of low E production= less low E photons)
increased focal length (distance) and dosage
based on TRD, TOD, BID
due to the inverse square law
although increasing the distance means that exposure must be increased as well, overall will usually decrease dosage
Increased of Long BID Benefits
- 27% less head volume
- reduced effective dose
- sharper image (smaller pneumbra)
how can the xray tube be modified to increase focal length and increase sharpness?
recessed tube, away from the window
also helps to increase image sharpness
practice options to decrease dosage
- Film speed
- Lead (Pb) thyroid collar
- Film-holding devices with beam alignment capability
- Time-temperature quality control processing
film speed and dosage
decreased with solid state sensors
CCD with lowest dosage (most sensitive)
film has much higher doses but better resolution (negligable)
lead apron and thyroid collar
usually only a concern with larger beams/ very little beam exposure in these areas with rec collimination
helps to protect the pt
should pt hold receptors?
Avoid holding the receptor, would increase dose (hand exposed)
can also cause receptor to move and decrease image quality
