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7/30/2019 Radio Last Lec

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Dr. Louie Hammad

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Extra-Oral Radiographs

*Panoramic Radiography

-Panoramic radiograph is an extra-oral radiograph. Its also called(Orthopantomograms). that is used to examine the upper and lower

jaws on a single film.

-When taking a panoramic radiograph the patient may stand up or sit

down depending on the type of machine. The head, chin & the occlusal

plane must be in correct position.

PANORAMIC X-RAY MACHINE


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Dr. Louie Hammad

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-The source of radiation always moves

behind the patient and the film in front of

the patient.

-Panoramic radiograph is called 2Dmodality however it is highly used, it

shows the mandible, maxillary sinuses

&TMJ all in 1 radiograph.

-Nowadays we have other 3D modalities

(like cone beam CT) & we use these

modalities to generate panoramic

radiograph. (We can also generate

panoramic radiograph from 3D images.)We also have normal panoramic

radiographs.

-I am sure many of you took a panoramic radiograph when you went to

your dentist to check your dental status, old teeth, and sinuses. It is also

the 1st step to see abnormalities in TMJ & is commonly used to see the

status & position of 3rd molars.

-Radiation dose is equal to 4-5 times more than intra-oral films which are

not a lot.

-Around 50 landmarks can be seen in the radiograph. Doctor said weshould search about them.

-Panoramic radiograph can also show us pathology, but its resolution is

not as good as intraoral radiograph so we cant depend on panorama to

show us caries or periodontal problems.

-Most common anatomy landmarks are in this pic.


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Dr. Louie Hammad

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Dr. Louie Hammad

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-We are expected to memorize all of them Why? To differentiate thenormal from abnormal anatomy.

*Now we are going to talk about soft tissues that can be seen on the

panoramic radiograph

1-tongue

2-soft palate

3-ear lobe

-soft tissues appear radiopaque in comparison with air.

*We have 3 air spaces:

1- Between the tongue and palate. Its called (palatoglossus /

glossopalatine air space)

2- Between the nose and pharynx. Its called (nasopharygeal air space)

3 Between the oral cavity and pharynx. Its called (glossopharyngeal /

oropharyngeal air)


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Dr. Louie Hammad

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*In extra- oral radiography the tube head and the film is connected to

each other within the same x-ray machine, while in intra- oral

radiography the film is not a part of the x-ray machine. As a result, in

extra-oral radiography when the tube head rotates, automatically the film

will rotate. Since the two jaws are going to be radio graphed from left to

right, then it is a must that the tube head and the image receptors (film)

will rotate all around the skull.

-Now the area closest to cassette will be exposed by x-ray photons and

printed on a defined part of the film, afterwards the tube head will rotate

and at same time the cassette is rotating in the opposite direction,

eventually exposing another part to x-ray photons and printing it on

another defined area on the film.This is the principle of

tomography

**EXPLANATION OF TOMOGRAPHY TECHNIQUE:

-we have a tube head, cassette carrier, and an axis of rotation. Now the

cassette and the tube head will rotate around the axis of rotation so the

patient must be positioned in the center.

-The tube head and the cassette carrier will rotate in the same direction

(NOT the cassette or the film), while the film and the cassette will

move in the opposite direction. In the cassette itself there is a little

window or slit that exposes the film, and this little part of the film is

going to be exposed by the x-ray photons...This technique is called

Tomography.


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Dr. Louie Hammad

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-where the x-ray photons can reach the film, there is a continuous

movement of the film, thus each part of the film will be accommodated

for anatomical structure, and once this anatomical structure exposed this

part of the film will be covered by metal shield, as a result it will be cut asslices (1st slice, 2nd slice, 3rd sliceetc), then at the end we will get

sectional images as a one section (one image).


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Dr. Louie Hammad

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*Tomography:

-Tomography means sections, panoramic will not be taken as a single

shot the machine rotates at least 180 degrees & then forms the image.

*Tomography: it is a radiographic technique that allows the imaging of

one layer or section of the body while blurring images for structures inother planes.

***ROTATION CENTERS

-In panoramic radiograph the film or cassette carrier and X-ray tube head

are connected and rotate simultaneously around a patient during

exposure.

-The pivotal point or axis around which the cassette carrier and X-ray

tube head rotate is termed a rotation center.

-Some panoramic machines have 2 or 3 rotational points depending on

the manufacturer.

-The function of rotation centers is to facilitate getting the real dimension

of the jaws and to get a clear final image.

-In order to improve the image quality of the skull radiogram in the

panorama film we should increase the number of rotation centers, so in

order to make the image quality comparable to the intra-oral films .we

should increase the number of rotation centers as much as possible

*Note: the number of rotation centers starts from two so we will have:

1. Double-center rotation2. Triple-center rotation

3. Moving or sliding center rotation


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Dr. Louie Hammad

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Double-Center rotation

*Let suppose that the x-ray photon will enter the right cheek , it will

continue to left cheek and it will go to the film through the window offilm(through the slit on the cassette)..The x-ray photon passes from the

right side to the left side so which of them will be on the final

image???

-Its the part that is closer...That means once the photon travels from right

side to the left side...The final image will be forthe left side.

-And the rotation will be continued...molars left side, premolars left side,

left laterals and left centrals.

And the position of tube head will be in the opposite side, so the image

will reveal right anteriors, premolars, and finally right molars.

-The x-ray photon enters to the center of rotation, and it will give us the

image that related to the opposite side, and it will continue to the anterior

teeth, premolars, and molars.


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Dr. Louie Hammad

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Triple-center

rotation

lateral

rotation

center

anterior

rotation

center

path of

sliding

rotation

center

Moving or sliding center rotation

Here we have one for the right side (posterior)one forleft side (posterior)

and one forthe anteriors both left and right.


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Dr. Louie Hammad

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-The quality when we use sliding or moving center rotation is much better

than when we use 3 centers of rotation or 2 centers of rotation.This is

out of our business, its related to manufacturer of x-ray machine

itselfThats why we have x-ray machine costs 10000 JD and some

might reach up to 40000 JD So increasing in the quality of the film it

will cost more.

*FOCAL TROUGH

-Focal trough: its a three dimensional curved zone in which the

structures are clearly demonstrated on panoramic radiograph.

Three-dimensional curved zone or

image layer in which structures are

reasonably well defined

Focal Trough

minimal visibility*

less sharp

sharpest

* The images of objects with minimal tissue density

are blurred and are not easily seen on film. Dense

objects, such as a bullet fragment, will still be seen.

-Structures out of the focal trough will not appear clear on theradiograph, this is imaginary, and some machines will allow you to


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Dr. Louie Hammad

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choose the shape of the focal trough, so by choosing a narrow focal

trough that suits the patients jaw this is going to give you a clear

radiograph.

-If I increase the width of the focal trough the final panoramic radiographwill not be clear.*EQUIPMENT:

-The doctor started to view images about the machine that we use in our

clinic we have ways to make you see the lines.

-We have 2 lines & there are buttons to

adjust the lines like the midsagittal linewhich has to be perpendicular to thefloor. And Frankfurt line, which is comingfrom the upper border of the external

auditory meatus to the lower border or the

orbital rim, parallel to the floor.

*what you have to do when you have apatient in your clinic and you want to do a

panoramic radiograph??

1. The patient comes to you, you must

make him stand straight as tall as possible.

2. The patient should not slump

or bend since this will result in a shadow in

the middle of the radiograph.

3. The patient bites on the bite block andmake sure the teeth are edge to edge &

tongue is on the palate.

4. The tongue must be on the palate, by

asking the patient to put his tongue on the

palate or ask him to swallow. If it is not onthe palate this will obscure the clearance of

the maxillary teeth.

-The plastic side of the cassette must be

facing the tube head.


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Dr. Louie Hammad

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* What is the difference between panoramic radiograph machine & intra-

oral radiographic machine?

1. itsthe collimator, the collimator in panoramic machine is a verticalnarrow slit it's not rectangular or round like normal intra-oral machines,

the collimator is in the tube head and there is also vertical slits in the

cassette.

2. The vertical angulation of the tube head in not varied. The tube head

is fixed in position so that the x-ray beam is directed slightly upward.

rotation center

filmtubehead angledupward

-Panoramic radiograph is a kind of tomography which deals with section.

You are building sections until the cycle is finished. Sometimes if the

patient is huge the tube head will stop suddenly from rotating (whichprevents some sections to appear in your final image) & other times it

will continue.

-Number of tomography images taken depends on the machine & its type.


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Dr. Louie Hammad

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*HEAD POSITION

-The head position consists of:

1- A chin rest for the patients chin.

2-Notched Bite blockis there for the patient to bite on

3-Forehead rest and lateral head support. Sometimes the shadow of the

head support may appear on the radiograph.

-If you put Frankfurt line parallel with the floorand the patients forehead

on the forehead rest, then you can notice that the occlusal plane is slightlydownward inclined and the beam is slightly come downward.

-You can choose with the controllers of the machine, the control time,

voltage and mille ampere to make the radiograph. However, the machineusually comes with a fixed time.

-The extra oral film must be inside of the cassette. We have several types

of cassettes: green light cassette and blue lights cassettes and it depends

on the type of phosphor used in the extra-oral films.

-Screen spectrum must match the phosphor spectrum of the film. There

are different types of cassettes such as rigid, flexible, curved and

straight depending on the panoramic x-ray unit.

*PURPOSE & USE of OPG

1. We use it to see all the teeth in the both jaws in the same image.

2. To evaluate impacted teeth

3. To evaluate eruption patterns, growth, and Development.

4. Assessing wisdom teeth this is a very important although as I told

you nowadays due to cone-beam computed tomography (CBCT), 3D

imaging is considered the golden standard


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Dr. Louie Hammad

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-In assessing the relationship between the third molar and the canal.

Using panoramic radiography you can sometimes see a shadow of the

canal superimposed on the third molars (due to loss of bone, loss of

cortical bone at that area) but this doesnt happen with CBCT.

5. To examine fractures of the mandible.

6. To Detect Diseases (periodontal diseases if there is loss of bone and

vertical healing), lesions, and conditions of the jaws.

-Its inadequate to use panorama to detect lesions, the much better is

intra-oral radiograph.

7. Assessment of locations of the objects in the jaw and permanent teethimpacted by using panoramaUsually lingually impacted looks high and

magnified

8. To examine the extent of Large lesions

9. To Evaluate Trauma. & fractures of the mandible and the

bilateral/contra-lateral condyle fracture

10. Examination of the sinuses, nasal cavity and the orbit

11. Before and after implants: usually when the patient comes to you and

he wants to do an implant, you can start by taking a panoramic radiographor periapical radiograph However, panorama is not enough because

panorama tells you if there is bone but you have to do another test by

cone beam CT to make sure.

- If panorama shows you that there is no bone then you have to stop and

ask the patient to go home.

*Advantages:1) Comfortable for the patient because there is no film inside the mouth

2) Easy to use for the incooperative patient like edentulous patients,children, old people.

3) Less exposure if you want to compare it with CMS (complete mouth

survey)


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4) Wide coverage for mandible and maxilla

5) Reduce superimposition in anatomical structures

*Disadvantages

1) Equipment cost: Initial cost of the machine is relatively high.

2) Image quality: The images of the radiograph are not sharp compared to

intra-oral images, the resolution of the panoramic image is 4 lines per

millimeter but the intra oral is 5 times sharper than panorama.

3) Objects outside the focal trough may not be evident.

4) Age limitation: Not suitable for children under 5 years of age because

of the relatively long exposure time.

5) Dark room processing (like students in the center because there is no

safe light they have to change the film in the dark each time).

6) Changing of the bite block because of hygienic purposes. It has to be

sterilized and covered.

7) Minimal bone changes cannot be detected in the panoramic radiograph

due to super imposition.

*Patient preparation

1. Explain the radiographic procedures to be performed.

2. Place lead apron, without thyroid collar in order not to block the x-

ray beam and also double sided lead apron is recommended (one thatprotect the patient from the front and the back.

3. Remove all objects from the head and neck area like earrings,

necklaces, eyeglasses, complete and partial dentures

4. Instruct the patient to Stand or sit (as tall as possible) with straight

back, the vertebral column must be straight to prevent white shadow to

appear over the middle of the radiograph (superimposition).


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Dr. Louie Hammad

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5. Patient must bite a plastic bite block, the front teeth should be placed in

end to end position in the notch found on the bite block, and this groove

will align the teeth and the jaw in the focal trough area.*COMMON ERRORS

1-Ghost image: it is a radiopaque artifact seen on panoramic film thatis produced when a radiodense object penetrated twice by the X-ray

beam.

-This object is located between the source of x-ray and the rotational

center appears on the radiograph as an object indistinct, higher and

magnified

Ghost Image:

Opposite side

Same shape

Larger

Projected higher on film

Less distinct


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Dr. Louie Hammad

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*Ghost Images summary:1. Image from other side of patients jaw that is seen as a blurred shadow

2. Results from radiodense objects left on patient during exposure

3. Resembles its real counterpart in shape

4. Found on opposite side of film as blurred, enlarged and higher than

actual object


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Dr. Louie Hammad

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2) Wearing thyroid collar might block the x-ray beam

-Usually we let the patients wear a lead apron. This prevents photons

from interacting with any area that we dont want it to appear on the

radiograph.

-The lead apron should not be extended upward also thyroid collar should

be avoided because It will be imaged on the film and making it useless

Lead apron shadow


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Dr. Louie Hammad

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3) Patient positioning errors

-The most crucial factor in getting a

correct image is patient position.

-The patient should be in correct

antero-posterior position. The patient

should not be too far forward or too far

backward. The patient should be in the

natural head position.

-The patient should also be correctly

positioned on the midsagittal plane. His

head should not be tilted or twisted...

Why?

-Because tilting or twisting the head

will cause one side to be closer to the

film while the other is farther away

from the film, this will cause magnification of the image( One side of the

image will have small teeth while the other will have larger teeth).

- To prevent this, some x-ray machines have a light which indicates the

midsagittal plane. This light will divide the nose into two equal parts and

this will help keep the midsagittal plane respected.

-Usually there is a chin rest on the x-ray machines. If the chin is down,

the upper teeth are closer to the source of x-ray. This will cause

magnification. Again there is a line on the machine that represents the

Frankfort plane or the occlusal plane. This plane should be parallel to thefloor.

*If the head is turned to the left or to the right side

-If the head turned to the right side: the right side will be smaller in

size than the left side


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Dr. Louie Hammad

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-If we look at the pic we notice that the width of the ramus in the right

side is smaller

Structures smaller on the side to which head is

turned; larger on opposite side.


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Dr. Louie Hammad

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*Note: When you see that there is deference in the width between the

right ramus and the left one, you must know that the patient's head was

tilted.

-Always the side next to image receptor is smaller and the opposite side is

larger.

*In both tilted and twisted we will have deference in the ramus

width, so how can we differentiate between them?

I f twistedthe 2 ramus at the same level( one ramus is larger thanthe other and the angles at the same level so it is twisted )

I f tiltedone is higher than the other ( so if one ramus higherthan the other and one is larger than the other it is tilted )

-So the deference between twisted and tilted is the level of angles!!!!!!!!

*If the patient is too far forward

So the anterior teeth will be closer to image receptor so we will have

minimum magnification decreasing of the size of ant teeth. plus the

cervical spine will be super imposed on the ramus.


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Dr. Louie Hammad

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*If the patient is too far backward

So the distance between the teeth and the image receptor will increase,

the ant teeth will be larger than the normal size.


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Dr. Louie Hammad

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*If the back is not erect this will produce a ghost image of the spine on

the film. This will be pyramid shaped, opaque, and in the middle. This

will often be a technical mistake. The image will be radio opaque and the

radiograph will be useless.


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Dr. Louie Hammad

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Shadow of vertebral column, usually

from patient not standing straight

*If the chin is down

So the anterior teeth will be close to image receptor and the lower border

of the mandible will give us acute angle (slightly curved), anterior teeth

smaller, the spine is superimposed on the ramus


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Dr. Louie Hammad

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Mandibular incisors shortened, V-shaped mandible

HEAD TIPPED DOWN


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If the chin is up:

Then the lower border of the mandible will look flat or Reverse smile, the

anterior teeth away so they will be magnified.

-If the chin is up then the hard palate will be superimposed on the apexesof the anterior teeth ((usually the hard palate appear above the apexes of

the anterior teeth))

HEAD TIPPED UP

Squared-off mandible, palate superimposed over maxillary teeth

-Exaggerated smile line of the mandible due to chin tilted down

so the incisor will appear smaller


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Dr. Louie Hammad

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-We also instruct the patient to swallow and hold the tongue on the palate.

If there is a gap between the palate and the tongue, then there is going to

be an air space. This air space will not interact with the photons passing

and these photons will interact and expose the crystals on the film and

will cause radiolucency on the film


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Dr. Louie Hammad

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Palatoglossal Air Space

-If the patient moves during exposure then the result will be unclear

image

-If the radiograph is not clear it's either thepatient move or the tube head

move.


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Dr. Louie Hammad

*Why the patients move?

-Usually all the patients think that the panoramic radiograph needs few

seconds like in peripical radiograph

-We must instruct the patient that the panorama will take from 1825

sec

Static electricity; caused by removing film from box

or cassette too quickly, creating static discharge

Tongue ring

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