panoramic imaging Flashcards
1
Q
what is a panoramic image?
A
- shows a wide view of the upper and lower jaws
2
Q
what is panoramic imaging?
A
- used to examine the upper and lower jaws on a single projection
3
Q
purpose and use of panoramic imaging
A
- an overall image of the maxilla and mandible
- often used to supplement bite-wing and selected periapical images
- images seen on a panoramic projection are not as defined or sharp as the images seen on intraoral projections
4
Q
fundamentals of panoramic imaging
A
- in panoramic imaging, the receptor and x-ray tubehead move around the patient
- the X-ray tube rotates around the patient’s head in one direction while the receptor rotates in the opposite direction
- the patient may stand in a stationary position
- the movement of the receptor and the tubehead produces an image through the process known as tomography
5
Q
what is tomography?
A
- radiographic technique that allows the imaging of one layer or section of the body while blurring images from structures in other planes
6
Q
what is the rotation center?
A
- the pivotal point, r axis, around which the cassette carrier and x-ray tubehead rotate
- there are 3 basic rotation centres depending on the manufacturer: double-centre rotation, triple-centre rotation, moving centre rotation
7
Q
what is the focal trough?
A
- can be defined as a 3D curved zone in which structures are clearly demonstrated on a panoramic radiograph
8
Q
what equipment is needed for panoramic imaging?
A
- panoramic x-ray units
- film
- intensifying screens
- cassette
9
Q
what are the 3 components of the panoramic x-ray tubehead found in all different types?
A
- x-ray tubehead
- head positioner
- exposure controls
10
Q
what is the X-ray tubehead?
A
- similar to an intraoral x-ray tubehead
11
Q
what is the collimator?
A
- differs from the collimator used in the intraoral x-ray tubehead
- the collimator used in the panoramic x-ray machine is a lead place with an opening in the shape of a narrow vertical slit
- the x-ray beam emerges from the panoramic tubehead through the collimator as a narrow band
- it passes through the patient and exposes the receptor through another vertical slit in the cassette carrier
- the vertical angulation is fixed so that the x-ray beam is directed slightly upward
12
Q
what is the head positioner?
A
- a chin rest, notched bite block, forehead rest, and lateral head supports or guides
- used to align the patient’s teeth as accurately as possible
13
Q
what are exposure controls?
A
- suggested exposure factors for milliamperage and kilovoltage are provided by the manufacturer and can be varies to accommodate patients of different sizes
- exposure time is fixed
14
Q
what type of film is used in panoramic imaging?
A
- screen film (unless it is digital)
- it is sensitive to the light from an intensifying screen
- it is placed between two intensifying screens in a cassette holder
15
Q
what are intensifying screens?
A
- calcium tungstate (emit blue light)
- rare earth (emit green light, require less x-ray exposure than calcium tungstate screens)
16
Q
what is the cassette?
A
- a device used to hold the extraoral film and intensifying screens
- may be rigid or flexible, curved or straight
- must be light-tight
- must be marked to orient the finished image
17
Q
step-by-step procedures
A
- equipment preparation
- patient preparation
- patient positioning
18
Q
how do we prepare the panoramic x-ray equipment?
A
- load the panoramic cassette in the darkroom under safelight conditions
- cover the bite-block with a disposable plastic coverslip or sterilize between patients
- set the exposure factors
19
Q
patient preparation
A
- explain the radiographic procedures
- place a lead aprons without a thyroid collar on the patient and secure it (a double sided lead apron is recommended)
- remove all objects from the head and neck area that may interfere with the procedure
20
Q
patient positioning
A
- instruct the patient to sit or stand ‘as tall as possible’
- instruct the patient to bite on the plastic bite-block
- position the midsagittal plane perpendicular to the floor
- position the Frankfort plane parallel with the floor
- instruct the patient to position the tongue on the roof of the mouth and keep the tongue in that position during exposure of the receptor
- instruct the patient to close the lips around the bite-block
- instruct the patient to remain still while the machine is rotating during exposure
- expose the receptor and proceed with receptor processing
21
Q
common errors in panoramic imaging
A
- patient preparation errors (ghost images, lead apron artifact)
- patient positioning errors
22
Q
what are ghost images?
A
- a radiographic artifact seen on a panoramic image that is produced when a radio dense object is penetrated twice by the x-ray beam
- it is found on the opposite side of the receptor
- it appears indistinct, larger and higher than its actual counterpart
23
Q
what is the problem and solution with ghost images?
A
- problem: if all metallic or radio dense object are not removed before exposure, a ghost image results that obscures diagnostic information
- solution: the dental radiographer must instruct the patient to remove all radio dense objects in the head and neck region prior to positioning the patient
24
Q
what is the problem and solution with a lead apron artifact?
A
- problem: a radiopaque cone shaped artifact that obscures diagnostic information results if the lead apron is incorrectly placed, or if a lead apron with a thyroid collar is used
- solution: the dental radiographer must always use a lead apron without a thyroid collar when exposing a panoramic projection
25
common patient positioning errors:
- positioning of the lips and tongue
- positioning of the Frankfort Plane - upward
- positioning of the Frankfort Plane - downward
- positioning of the teeth - anterior to the focal trough
- positioning of the teeth - posterior to the focal trough
- positioning of the midsagittal plane
- positioning of the spine
26
positioning of the lips and tongue
- problem: if the patient's lips are not closed on the bite-block during the exposure of a panoramic projection, a dark radiolucent shadow results that obscures the anterior teeth
- if the tongue is not in contact with the palate during exposure of a panoramic projection, a dark radiolucent shadow results that obscures the apices of the maxillary teeth
- solution: instruct the patient to close lips around the bite-block and swallow and raise the tongue up to the palate during the exposure of the receptor
27
problem and solution of positioning of the Frankfort plane upward
- problem: if the patient's chin is positioned too high a 'reverse smile line' is apparent on the image
- solution: position the patient so the Frankfurt plane is parallel with the floor
28
problem and solution of positioning of the Frankfort plane downward
- problem: the patient's chin is positioned too low or is tipped down or 'exaggerated smile line' is apparent on the image
- solution: position the patient so that the Frankfort plane is parallel with the floor
29
problem and solution of positioning of the teeth - anterior to the focal trough
- problem: the patient's teeth are positioned too far forward on the bite-block or anterior to the focal trough, the anterior teeth appear 'skinny' and out of focus
- solution: position the patient so that the anterior teeth are placed in an end-to-end position in the groove on the bite-block
30
problem and solution of positioning of the teeth - posterior to the focal trough
- problem: the patient's teeth are positioned too far back on the bite-block or posterior to the focal trough, the anterior teeth appear 'fat' and out of focus
- solution: position the patient so that the anterior teeth are placed in an end-to-end position in the groove on the bite-block
31
problem and solution of positioning of the midsagittal plane
- problem: if the patient's head is not entered the ramps and posterior teeth appear unequally magnified on the panoramic radiograph
- the side farthest from the receptor appears magnified
- solution: position the patient's head so that the midsagittal plane is perpendicular to the floor while the midline is entered on the bite-block
32
problem and solution of positioning of the spine
- problem: if the patient is not standing or sitting with a straight spine, the cervical spine appears as a radiopacity in the centre of the receptor and obscures diagnostic information
- solution: instruct the patient to stand or sit 'as tall as possible' with a straight back
33
advantages of panoramic radiography
- field size
- simplicity
- patient cooperation
- minimal exposure
34
disadvantages of panoramic radiography
- image quality
- focal trough limitations
- distortion
- equipment cost
