9/24: Sensor Placement & Beam Positioning Problems Flashcards
What are 3 things that sensor placement and beam positioning problems can be related to?
- Image receptor
- shadow casting principles
- human error
What are examples of image receptors?
Film
Phosphor storage plate (PSP)
Charge coupling device (CCD)
Complementary Metal oxide semiconductor (CMOS)
What are examples of shadow casting principles?
Beam angulation
receptor placement
What are types of miscellaneous technique problems?
- Phalangioma
- Movement
- Sensor placement
- beam angulation - horizontal
- beam angulation - vertical
- PID/BID alignment
- Sensor wire superimposition
What is the cause of a phalangioma?
Patient’s finger positioned in front of the sensor
What is the cause of a movement problem?
Patient or x-ray tube head moves during exposure
How are movement problems detected?
- sensor not where we put it
- blurring of image
- looks grainy
- don’t have sharp outlines
What patients do movement problems occur in?
Children because can’t sit still
Sensor placement is _________ critical with solid-state sensors?
MORE
Why is sensor placement more critical with solid state?
Smaller active image capture area so there is less room for error
What should the receptor parallel in a maxillary premolar PA?
- parallels buccal and lingual planes of premolars
- long axis of premolars
What does the anterior edge of a maxillary premolar PA include?
distal 1/2 canine, the premolars, and some molars
What is the horizontal angle of a maxillary premolar PA?
Directed through distal of canine/premolar, premolar/premolar and the 2nd premolar/molar contacts
What does the receptor parallel in a maxillary molar PA?
- buccal and lingual planes of molars
- long axis of molars
What does the anterior edge of the receptor include in a maxillary molar PA?
Distal 1/2 of 2nd premolar and as much of the molar as possible
Where is the horizontal angle directed for a maxillary molar PA?
Distal of 2nd premolar/1st molar and the intermolar contacts
What does the receptor parallel in a premolar bitewing?
- Buccal and lingual planes of premolars
- long axis of premolars
What does the anterior edge of a premolar BW include?
Mesial 1/2 of canine, the premolars, and some molars
Where is the horizontal angle directed in a premolar BW?
Through distal of canine/premolar, premolars and the 2nd premolar/1st molar contacts
Where is the cotton roll placed to keep the sensor in the right place?
Between biteblock and opposing teeth; NOT between biteblock and imaged teeth
Should you place the cotton roll on the arch you are imaging?
NO! Placed on the opposing arch
What are 2 indications of incorrect placement?
- Absence of apical structures
- Dropped sensor corner
What is the cause of absence of apical structures?
Sensor not positioned over the apical area in the mouth
What are reasons for absence of apical structures in terms of inside the mouth?
Bite block not against occlusal/incisal edge; OR patient not biting down
What is tipping?
Dropped film corner
What is the cause of tipping?
Sensor not placed parallel with the occlusal/incisal surface of teeth
With what angulation are overlapped contacts reduced?
Correct horizontal angulation
When setting a horizontal angle, where should the central ray be directed?
Between the interproximal contacts of interest
Where should the central ray project in relation to the sensor?
Perpendicular
What is the cause of incorrect horizontal angulation?
Central ray is not projected perpendicular to sensor
Mesial to distal or distal to mesial?
Mesial to distal
KNOW HOW TO CHANGE ANGULATION TO DIRECT AND WHERE BEAM WAS COMING FROM
Mesial to distal or distal to mesial?
Distal to mesial
KNOW HOW TO CHANGE ANGULATION TO DIRECT AND WHERE BEAM WAS COMING FROM
Mesial to distal or distal to mesial?
Mesial to distal
KNOW HOW TO CHANGE ANGULATION TO DIRECT AND WHERE BEAM WAS COMING FROM
Mesial to distal
KNOW HOW TO CHANGE ANGULATION TO DIRECT AND WHERE BEAM WAS COMING FROM
What can vertical beam angulation problems result in?
- foreshortened image
- elongated images
What is the cause of foreshortened image?
Excessive vertical angulation
Where is the beam located to cause foreshortened image?
Perpendicular to the sensor
Foreshortened image
What occurs in foreshortened images that have a smaller active area?
Parts of image are missed
Foreshortened images
Foreshortened images
- crown is more than 1/3 the size of the tooth
When is foreshortening encouraged?
With a smaller active image capture area AND long roots
- because otherwise we wont capture apices
What is the cause of elongated images?
Insufficient vertical angulation
Where is the beam located to create an elongated image?
Perpendicular to the tooth/teeth
Elongated
because cusps are separating and stretching out
elongation
What are indications of BID/PID alignment problems?
Cone cuts
- with/without sensor holder
What is the cause of cone cuts with sensor holder?
PID not properly aligned with the sensor holding device from
- incorrect SCP assembly
- poor alignment of PID with XCP
Cone cut
No cone cutting here because its a bite block
What are the causes of cone cuts without sensor holder (XCP)?
PID not directed at center of film
U thought cone cut?
NOPE!
This is a thyroid collar.
- can tell by reverse curvature and thread holes on the bottom right
Sensor wire
What are examples of exposure problems?
- Overexposed
- Under exposed
- No exposure (don’t press button at all)
- Wire superimposition
- post exposure
What exposure problems are less dramatic and why?
Overexposed and underexposed because with software it can correct discrepencies
Overexposed
What are causes of overexposed images?
Excessive exposure to x-radiation from excess time, kVp, mA, or any combination
What is the main cause of overexposed/underexposed images at SOD?
TIME because we can’t adjust kVp or mA
Underexposed
What is the cause of underexposure?
Insufficient exposure time, kVp, mA, or any combo
What is excessive tube-receptor distance related to?
Inverse square law
- further away you move = less intense photo which can’t be fixed with software
Post exposure image processeing
What are post exposure image processing problems due to?
Faulty program software image settings: Calibration files
How does ‘gain’ fix faulty images?
Adjusts the bright tones and brings more information into the highlights of the image
How does ‘gamma correction’ fix faulty images?
Adjusts the midtones of an image by adjusting each pixel value in an image
- usually performed automatically on a PC monitor, but precision is adjustable
What is the cause of patient preparation problems?
Failure to remove a non-fixed item from patient that may be i path of the primary xray beam
What are examples of patient preparation problems
Gum, candy, piercings, eyeglass frames
Eyeglass frame
RPD left
Gum or candy
Not removing jewelery risks ____________
masking disease
What is the cause of sensor bending?
Sensor is bending toward source because of impingement against palate
What is the cause of sensor creasing?
Damage to storage phosphors so there is no signal to the area with damaged pixels
Sensor creasing
Creases are _____________
permanent
What is the cause of double exposure?
PSP is accidentally exposed twice
What is double exposure not possible with?
Contemporary CMOS capture software because of poor unstable fit in bite block
Double exposure
What is the cause of reversed placement?
Sensor is placed back to front in sensor holder
Reversed placement
