sensor problems Flashcards
sensor placement and beam positioning problems related to
image receptor:
a. film
b. PSP (phosphor storage plate)
c. charged coupling device (CCD)
d. complementary metal oxide semiconductor (CMOS)
sensor placement and beam positioning problems related to
shadow casting principles
a. beam angulation
c. receptor placement
sensor placement and beam positioning problems related to
human element
a. clinician
b. patient
c. a and b
3 sensor placement and beam positioning problems
- miscellanous technique problems
- exposure problems
- patient preparation problems
miscellaneous technique problems
- phalangioma
- movement
- sensor placement
- beam angulation -horizontal
- beam angulation - vertical
- PID/BID alignment
- sensor wire placement
- sensor bending [just PSP and film!]
- sensor creasing
- double exposure
- reversed placement [just PSP and film!]
pt finger positioned in front of sensor
phalangioma
patient or x-ray tube head moves during exposure
movement
sensor palcement is MORE critical with
solid state sensors
with sensors, there is a ____active image capture area
smaller
maxillary premolar PA requirements
- Receptor parallels B and L planes of premolars
- Receptor parallels long axis of
premolars - Anterior edge of receptor includes
distal ½ of canine, the premolars
and some of molars - Horizontal angle directed through
distal of canine/premolar,
premolar/premolar and the 2nd
premolar/ molar contacts
maxillary molar PA requirements
Receptor parallels B and Li
planes of molars
* Receptor parallels long axis
of molars
* Anterior edge of receptor
includes distal ½ of 2nd
premolar and as much of the
molars as possible
* Horizontal angle directed
through distal of 2nd
premolar/1st molar and the
intermolar contacts
premolar bitewing requirements
Receptor parallels B and Li
planes of premolars
* Receptor parallels long axis of
premolars
* Anterior edge of receptor
includes mesial ½ of canine, the
premolars and some of molars
* Horizontal angle directed
through distal of
canine/premolar, premolars
and the 2nd premolar/ 1st molar
contacts
cotton roll placement:
between biteblock and opposing teeth; NOT between biteblock and imaged teeth
two examples of incorrect placement
- absence of apical structures
- dropped sensor corner
cause of absence of apical structures
-sensor not positioned over apical area in mouth
-bite block not against occlusal/incisal edge
OR patient not biting down
cause of “tipping” aka dropped film corner
sensor not placed parallel with the occlusal / incisal surface of teeth
incorrect horizontal angulation
beam angulation horizontal
-dont want overlapping: want to see interproximals
(anterior and posterior bitewing placements)
with horizontal angle, the central ray should be directed between
interproximal contacts of interest
and
projected perpendicular to sensor
incorrect horizontal angulation caused by
central ray is not projected perpendicular to sensor
(looking at fence straight on, between the wood pickets are open)
mesial to distal
(looking at the fence from right to left, the spaces get narrower the farther left one looks
distal to mesial
move (m/d) to (m/d)
move mesial to distal
KNOW
two examples of beam angulation vertical
- foreshortened images
- elongated images
(distortion)
cause of foreshortened images
(shortening the image)
1. excessive vertical angulation
2. beam is perpendicular to the sensor
3. with smaller active area, parts of image are missed
the sensor placement is MORE critical with solid-state sensors, BUT with a smaller active image capture area AND long roots=
foreshortening is encouraged!
cause of elongated images
- insufficient vertical angulation
- beam is perpendicular to the tooth
point up: foreshorterning
pointing down: elongation
???? idk he said this in lecture
BID/PID alignment problems
cone cuts:
1. with sensor holder
2. without sensor holder
PID alignment problems with cone cuts with sensor holder cause
-PID not properly aligned with the sensor holding device from:
1. incorrect XCP assembly
2. poor alignment of PID with XCP
PID alignment problems with cone cuts without sensor holder (XCP) cause
PID not directed at center of film
II: exposure problems:
- overexposed
- underexposed
- no exposure
- sensor wire superimposition
- post exposure
what exposure problems are less dramatic because post-exposure image processing by the software immediately corrects large exposure
- overexposed
- underexposed
overexposed =
HIGH density image
a. increased time
b. increased mA
c. increased kV
all contribute to being too dark
causes excessive exposure to x-radiation from excess time, kVp, mA, or any combo of these
overexposed images
cause insufficient exposure time, kVP, mA, or any combo of these
-in SoF radiology, ____is the main cause
underexposed image
TIME
underexposed:
- insufficient
-time
-mA
-kVp
excessive tube-receptor distance; released to INVERSE SQAURE LAW
excessive tube-receptor distance; released to INVERSE SQAURE LAW
underexposed
faulty program software image setting: calibration files
exposure problems: post exposure image processing
faulty program software image settings: + gain, gamma, -gam
gain:
adjusts bright tones and brings more information into the highlights of an image
gamma correction:
adjusts midtones of an image by adjusting each pixel value in an image.
usually performed automatically on a PC monitor, but the precision is adjustable
failure to remove a non-fixed item from patient that may be in path of the primary xray beam
patient preparation problem
patient preparation problem examples
eyeglasses
frame
RPD left in mouth
gum or candy
piercing
what happens if dont remove jewelry
risks masking disease
