panoramic imaging

Question 1

what is a panoramic image?

Answer 1

• shows a wide view of the upper and lower jaws

Question 2

what is panoramic imaging?

Answer 2

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

Question 3

purpose and use of panoramic imaging

Answer 3

• 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

Question 4

fundamentals of panoramic imaging

Answer 4

• 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

Question 5

what is tomography?

Answer 5

• radiographic technique that allows the imaging of one layer or section of the body while blurring images from structures in other planes

Question 6

what is the rotation center?

Answer 6

• 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

Question 7

what is the focal trough?

Answer 7

• can be defined as a 3D curved zone in which structures are clearly demonstrated on a panoramic radiograph

Question 8

what equipment is needed for panoramic imaging?

Answer 8

• panoramic x-ray units
• film
• intensifying screens
• cassette

Question 9

what are the 3 components of the panoramic x-ray tubehead found in all different types?

Answer 9

• x-ray tubehead
• head positioner
• exposure controls

Question 10

what is the X-ray tubehead?

Answer 10

• similar to an intraoral x-ray tubehead

Question 11

what is the collimator?

Answer 11

• 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

Question 12

what is the head positioner?

Answer 12

• 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

Question 13

what are exposure controls?

Answer 13

• 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

Question 14

what type of film is used in panoramic imaging?

Answer 14

• 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

Question 15

what are intensifying screens?

Answer 15

• calcium tungstate (emit blue light)

- rare earth (emit green light, require less x-ray exposure than calcium tungstate screens)

Question 16

what is the cassette?

Answer 16

• 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

Question 17

step-by-step procedures

Answer 17

• equipment preparation
• patient preparation
• patient positioning

Question 18

how do we prepare the panoramic x-ray equipment?

Answer 18

• 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

Question 19

patient preparation

Answer 19

• 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

Question 20

patient positioning

Answer 20

• 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

Question 21

common errors in panoramic imaging

Answer 21

• patient preparation errors (ghost images, lead apron artifact)
• patient positioning errors

Question 22

what are ghost images?

Answer 22

• 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

Question 23

what is the problem and solution with ghost images?

Answer 23

• 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

Question 24

what is the problem and solution with a lead apron artifact?

Answer 24

• 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

Question 25

common patient positioning errors:

Answer 25

• 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

Question 26

positioning of the lips and tongue

Answer 26

• 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

Question 27

problem and solution of positioning of the Frankfort plane upward

Answer 27

• 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

Question 28

problem and solution of positioning of the Frankfort plane downward

Answer 28

• 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

Question 29

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

Answer 29

• 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

Question 30

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

Answer 30

• 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

Question 31

problem and solution of positioning of the midsagittal plane

Answer 31

• 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

Question 32

problem and solution of positioning of the spine

Answer 32

• 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

Question 33

advantages of panoramic radiography

Answer 33

• field size
• simplicity
• patient cooperation
• minimal exposure

Question 34

disadvantages of panoramic radiography

Answer 34

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