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Radiography > panoramic imaging > Flashcards

panoramic imaging Flashcards

1
Q

what is a panoramic image?

A
  • shows a wide view of the upper and lower jaws
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2
Q

what is panoramic imaging?

A
  • used to examine the upper and lower jaws on a single projection
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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
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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
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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
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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
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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
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8
Q

what equipment is needed for panoramic imaging?

A
  • panoramic x-ray units
  • film
  • intensifying screens
  • cassette
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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
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10
Q

what is the X-ray tubehead?

A
  • similar to an intraoral x-ray tubehead
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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
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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
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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
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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
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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)

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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
Q

common patient positioning errors:

A
  • 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
Q

positioning of the lips and tongue

A
  • 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
Q

problem and solution of positioning of the Frankfort plane upward

A
  • 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
Q

problem and solution of positioning of the Frankfort plane downward

A
  • 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
Q

problem and solution of positioning of the teeth - anterior to the focal trough

A
  • 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
Q

problem and solution of positioning of the teeth - posterior to the focal trough

A
  • 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
Q

problem and solution of positioning of the midsagittal plane

A
  • 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
Q

problem and solution of positioning of the spine

A
  • 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
Q

advantages of panoramic radiography

A
  • field size
  • simplicity
  • patient cooperation
  • minimal exposure
34
Q

disadvantages of panoramic radiography

A
  • image quality
  • focal trough limitations
  • distortion
  • equipment cost

Radiography (25 decks)

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