Panoramic radiography Flashcards
what is the grayscale dependent on
absorption
how does an x ray generate
- operator is responsible for X-ray
- the x ray source
- image receptor
- detect what passes to the patient to form a image receptor
what are the principles of radiography
- tomography
- tube and image receptor both move
- generates an in focus slice of anatomy
- structures outside the slices are blurred
- image big area of patient - in focus slice produced
- the still image is blurred out due to relative movemtn
- area within gantry thats pre determined and which bits of anatomy is demonstrated int each radiograph
what is the panoramic technique
- the dynamic movement of the panoramic machine creates a curved in -focus slice, the ‘focal tough’
the patient is positioned so that the anatomy of interest (their dentition) coincides with the focal trough - the image is generated as the tube head and image receptor move around the paitient
horseshoe shaped
multiple exposures through patient due to the gantry that rotates around
describe panoramic technique II
- the structure which are outside the focal trough are blurred and not seen clearly
- however , they re still present in the image and potentially visible as a ghost image
- the image is produced at an degree upward incline
what are ghost images
- generated by anything between the centre of rotation and x ray source
- compared tot eh object which generates them, ghosts images are
- larger (due to beam divergence)
-higher (due to upward angle of beam) - on the opposite side of the image
-Blurred (more vertically than horizontally)
describe the differences between ghost images and real images
Ghost image
- out of focus
- higher
- bigger
- produced when the object to image receptor distance is long
real image
- in focus
-produced when the object to image receptor distance is short
what can allow ghost images
earrings
tongue studds
anything else situated between the x ray source and centre of rotation
what is done when there is a ghost image
- normal anomy in the region of interest is also imaged twice
- once when the receptor is close tot eh side of interest- generates real image
- second time when the receptor is on the opposite side of the patient - generates a ghost
- best anatomical example is the opposite angle of the mandible
Describe the positioning errors
- If the area of interest ( the dentiosn) does not math. the position of focal trough, some or all of the structures will be out of focus
- the focal tough is in a predetermined position, the panoramic machine has no idea where the patient actually is
- it is therefore important that the operator positions the patient correctly.
describe the common positioning errors
- chin down
-chin up - too far forward
- too far back
- off - centre (rotational)
advantages of panoramic radiography
- shows the entire dentition on one image
- time efficient
- radiation dose may be lower than full mouth series of periapicals
-well tolerated by patients - can be used even when patient can’t fully open mouth or has pronounced gag reflex
what are the disadvanategsa of panoramic radiographs
- only structures in the focal trough are in focus
- oevralppign teeth in some areas
- technique sensitive
- superimposition of soft tissue and air shadows can cause misinterpretation
- image is a distorted and magnified version of the object
-resolution of detail not as good as intra-oral techniques - long exposure-susceptible to movement
what are the indications to panoramic radiography
- bony lesion not completely demonstrated on intra orals
-grossly neglected dentition prior to GA - for the assessment of wisdom teeth prior to planned surgical intervention
-as part of an orthodontic assessment
-in hospital - for assessment of mandibular fractures - assessment of periodontal support
