dental radiography and radiology

7/29/2019 Dental Radiography and Radiology

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Introduction:Dental Radiography and Radiology

Script 1

3-feb-2013

Welcome to the new course dent 325, the first course of oral radiology,

which is mainly about physics of radiation, and radiation protection. You can

check the syllabus for more information about the course.

Many books are recommended. But the main reference for you is DentalRadiography: Principles and Techniqueswhich is available in the book shop.

Midterm exam will be after the seventh lecture enshaAllah.The doctor will not give us slides as he said.

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Introduction:Dental Radiography and Radiology

What is the difference between radiography and radiology?

Radiography: it is the science of making the picture, how you canmake and capture a radiograph.The techniques involved in producing thevarious radiographic images.

Radiology: it is the science of interpretation, interpretation ofpathology on the radiograph. You are dealing with interpretation. Howeverafter the invention of the 3D imaging modalities we stopped to sayinterpretation it is more said visualization. Because we can see thedisease, we can rotate the image since they are 3D images. In the past weonly had 2D image like panorama. So we have to interpret, we have toimagine. But nowadays we have visualization.

For this year we are mainly concerned about how to make andcapture the image, and how to process the film.

As you can see here this is a bitewing radiograph, in which you can see themaxillary and mandibular teeth on the same film. I can see the enamel,dentine, pulp and high contrast amalgam fillings (the contrast or the densityof amalgam is higher than enamel).
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Q- Why enamel is radiopaque and why the pulp is radiolucent?Because enamel totally stops the X-ray so it looks radiopaque (white),While the pulp its mineral content is low comparable to enamel so it allows

all the X-ray to pass then it will be radiolucent.

Q- What will happen if we increase the dose of the radiograph?The enamel will start to become radiolucent; finally your image will beblack.

So the final image depends on your dose and also on thebody you are capturing.many factors we will take about them later on.

The amount the X-ray beam is stopped (attenuated) by an object

determines the radio density of the shadows. So we have radiopaque,radiolucentandgrayshadows,

The white or radiopaque shadowson a film represent thevarious dense structures within the object which have totally stoppedthe X-ray beam.


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The black or radiolucent shadowsrepresent areas where theX-ray beam has passed through the object and has not beenstopped at all.

The grey shadowsrepresent areas where the X-ray beam hasbeen stopped to a varying degree.

when you want to describe a lesion you say radiopaque lesion orradiolucent lesion.

The final image depends on many factors1.The material itself. The specific type of material of which the

object is made. The image of your hand will not be the same as the

image of microphone. Soft tissues is not like image of metal2.The thickness or density of the material. If you take a

radiograph for a kid. It is not like a radiograph for an adult.

3. The shape of the object.4. The intensity of the X-ray beam used. If you increase the

dose. You will have different radiographs. When you increase thedose the image will be darker. Finally you will burn you image. Sosometimes when you want to see small things like stones in salivaryglands we usually decrease the dose up to 50%. We also decrease

the dose when we want to make an image for a kid.5.The position of the object in relation to the X-ray beam

and film. If there is superimposition with other objects or not.6.The sensitivity of the film. The higher the sensitivity of the film

is the faster the film.


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This picture shows us that different materials give differentshadows

Here we have the same material with different densities.

Here we have different shapes and we have different final images


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Here we have different shapes and different levels of X-rays(dose). Look here we are increasing the intensity so the maximumintensity of X-ray will result in burning the object, we dont see theobject (a) any more unless the object is big like (d) in the figure sowe can see part of it.


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In the intraoral films the basic films like the periapical films you cansee

1- The main parts of the tooth( enamel, dentin , pulp)2- You can see the lamina Dura which is the cortical bone

surrounding the tooth3- You can see PDL (periodontal ligament) space which is between

lamina Dura and the tooth.4- You can see trabecular bone


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If you take cross sections you can see buccal and lingual cortical bonesurrounding the tooth.

In the intraoral films we can only see the 2D of the object we cant seethe whole tooth, if you want to see the whole tooth you have to take

another image like 3D image.

Limitations of 2D images1. Superimposition. We cant see the whole object, so we

have to imagine.Look at this house, different views gave different images

So this is the problem, that you see part of the object. So on your pictureyou may capture the caries but if you take it from another angle you maymiss it.


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Look here we detect radiopaque object in the nose but due to superimposition we couldnt know the exact location.

So we took another image from lateral view. And now we can see thatthis radiopaque object is a clip in the brain. And the arrows show the truelocation for the clip.

Look at this example. An object is in the middle of the head. The X-ray iscoming from behind of the patient and the final image was the same.

Although the object was in different places and in (d) was a different object.However the final image was the same.


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Look here when we take lateral view now we have different images forthe different places and for different shapes.

So side view can overcome the problem of superimposition sometimes.When we have fracture in the jaw one image is not enough so we

have to take 2 images perpendicular to each other or we need advancedimaging modalities. Like CT or MRI. 3D images or advanced images willsolve these problems.Look here I took side view image however I had similar images why?Because I have superimposition with another object.So not always I can solve the superimposition problem by taking anotherimage.


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Sometimes I have to go to advanced imaging and this is the best. Forexample a patient having trauma, go for advanced imaging dont hesitateto take advanced imaging modalities for the patient because it is veryimportant to know the exact extension of the fracture, I dont know if thisfracture only in the nose, only in the jaw or is it extending into the brain Ihave to know everything.

If I have a periapical image for an impacted tooth I cannot knowwhere this tooth is located? Lingual or buccal? I have to take anotherimage perpendicular to it like an occlusal radiograph. Now we will be ableto see the canines location. Or I can take 3D image.

Quality of the image(later on we will have lectures about the quality)

General over view for now>>

We have something called contrast and spatial resolution andsharpness.

If you want to buy new TV , flat one you have to take care aboutresolution and contrast

What is contrast?It is the ability to differentiate between shades of grades of colors.Saturation of the colors. Do you want to have your TV saturated with colorsor you want it to be sharper.

What is resolution or spatial resolution specifically?It is the ability to separate two objects from the back ground.


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Which is better or more important?In fact no one can answer this question because both can affect eachother. And we are in need for both.

What is sharpness?

It is the ability to define an edge. Image geometry.

~~ To make an ideal radio graph we have to be sure of three things ~~1. The object and the film should be in contact or as close together as

possible. So to take a radiograph image you have to put the film asclose as possible to the tooth lingually.

2. The object and the film should be parallel to one another. Why? Toovercome problems of elongation or shortening

3. The X-ray tubehead should be positioned so that the beam meetsboth the object and the film at right angles.

These are the ideal characteristics to have an ideal radiograph. Howeverin daily practice we cannot give the ideal image. So we have to do somemodification to overcome these problems. Later on we will know them.

Look here this is the ideal image, if you can put a film in contact to atooth both are parallel to each other and the beam is perpendicular to both

this is the perfect image.

What will happen if your film is not parallel making an angle with thetooth? In this case we will have an elongated image.


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These are mistakes and the students make these mistakes in the clinicand asking why?

Why my image is foreshorted ? because the beam is perpendicular tofilm but not to the tooth.

Why the image distorted, elongated and fake? Because the beam isnot perpendicular to both like( c )this is distorted image

So elongation can result from incorrect placement of the film, the film isnot parallel to the tooth, elongation also results from insufficient verticalangulations (later on you will know).

Just to have an idea when we increase a dose (kilo voltage) this the kilovoltage peck (in the slide), this is the dose that we give it to the patient (inthe slide),, of course we also concern about Milliampere and the time, allof these factors will result in the final dose.

lets concern now on the kilo voltage ,when we increase kilo voltage weincrease the number (shades of grays) this is called SCALE OFCONTRAST ; long scale of contrast many shade of grays , however the


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contrast will be this(in the slide) if we have only black and white this will bethe highest contrast the(CT machine)which used in the medical field theyused a high kilo voltage for this reason they can see a soft tissue, howeverin dental field we use( CO beam(not sure)) only give 80 kilo voltage so weare not able to see the soft tissue .

Any increase in the Milliampere or time or kilo voltage will result indarker image. In the clinic the student sometimes plays with these factorsso as a result the image and the density will be affected.

What is density?Density: it is the degree of darkness of the film

What are the ideal characteristics of the x-ray beam?

1. Sufficiently penetrates we have a kid and we want to make an image

to the kid. and I only used 10 kilo voltage ,this will not make animage because it will not penetrate through the body, so I have toincrease it .

2. The x-ray must be parallel not divergent; because the divergent ofthe beam will result in magnification, in fact X-rays usually travel indivergent pathway, so how we can overcome this problem? By using

a device called collimatorto make it parallel then we can makethe image.

3. Produced from a point source, to reduce blurring of the edges of the

image, a phenomenon known as the penumbra effect.Penumbra effect it mean the blurring of edges, why we have blurring

edges? Because the x-ray source is not a point it is from tungsten plate so the

penumbra effect will result by using this plate. So how we can overcomethis penumbra? By tilting the target (of course you cant imagine what dowe mean by target next lectures you will know)

Now this the final point in this lecture which is:

Contrast, context and partial images.

When you have a radiograph and you have a pathology in thisradiograph the interpretation will be different among different observers.


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For example: I will say this is caries but if I give you the radiograph you willsay this is normal, why?

1) The power of eye.2) Surrounding environment will effect.

3) Perception (Experience), because I have an trained eye I can seethings in this radiograph that you cant see it, and also I have abackground that the caries will appear radiolucent and it appears in thisarea, so I have knowledge that makes it easy to detect caries. So this isthe perception depends on experience.

For example if I want to make a research in radiology and I want tosend it a journal to accept it. They will not accept it if I am the onlyobserver, why? Because at least they will need two observer, why?Because this is the problem of perception I can see there is an

abnormality and another observer will say no there is no abnormality soit depends.4) Context: look here if u see this image you will say this small square

is radiopaque is white ,however in the last image is radiolucant isblack so it depend on environment

what about this, here you will say this is B but when you looking hereyou will say this is number 13 why ?

Because in the first line was between letters so I consider it BWhile in the second line it is between numbers so I consider it 13.


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So in the mouth there is cortical bone, cancellous bone, vessels, sothis is normal anatomy any structure will be one of these. But in case youare looking on the maxillary sinus you will never say this is a tooth unlessthere is a problem. If there is something radiopaque most probably it is nota tooth because maxillary sinus is full of air, sometimes fluid, sometimes

mucosal thickening but it will not be a tooth.

THE END

Done by:Yousef Nasrawi & Sawsan Jwaied

Inspiration is one thing and you can't control it, but hardwork is what keeps the ship moving. Good luck means, workhard. Keep up the good workKevin Eubanks
http://www.brainyquote.com/quotes/authors/k/kevin_eubanks.htmlhttp://www.brainyquote.com/quotes/authors/k/kevin_eubanks.htmlhttp://www.brainyquote.com/quotes/authors/k/kevin_eubanks.html

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