Feb 3- Special Imaging Techniques Part 1

Question 1

Four important Special imaging techniques are:

Answer 1

• Multidirectional (conventional) tomography
• Computed tomography and cone beam CT
• Magnetic resonance imaging
• Nuclear imaging

Question 2

What is Multidirectional Tomography?

Answer 2

Movement of the x ray source and film or image receptor in opposite directions around a fulcrum.

This produces a (“slice”) of tissue - everything outside of this “slice” will be blurred and out of focus.

Question 3

What is Computed Tomography (CT) and what is Cone Beam Computed tomography? How do they differ?

Answer 3

CT - also called fan beam. this is the one used in the

hospitals a lot. Only takes a thin slice image. To get the

entire head you have to take several slices. you need multiple rotations, and therefore expose patient to more radiation. Here image resolution is high.

CBCT -

widely used in dentistry. cone shaped, can get image in one shot. Only need one rotation. This uses less radiation than computed. image is not as high in resolution.

Question 4

What is the standard format for image files?

Answer 4

DICOM ( Digital imaging and communications in medicine)

Question 5

With regard to image reformatting, what is primary reconstruction and secondary reconstruciton.

Answer 5

primary - what the computer makes for you. i.e. axial, coronal, and sagittal images

secondary - ones that you make after. i.e. panoramic viess, cross sections, sagital and coronal of TMJ

Question 6

Talking about primary reconstruction; what is the proper name for the x, y, and z axis?

Answer 6

X= axial section

Y = coronal or frontal section

Z = sagital section.

Question 7

How do the CT and CBCT differ in appearance?

Answer 7

because medical CT uses much higher doses of radiation and has a much smaller collumation than CBCT the images are much higher resolution and allow the view to distinguish between different tissue types

In CBCT radiation is much lower and collimation isn’t as fine and so the images are much lower resolution, have more noise (grainy) and only allow the distinguishing of boney structures

Question 8

What is the average annual dose of background radiation? How much comes from man made and natural sources?

Answer 8

Old number was 3600 uSv/ yr. About 20% of that is from man - made sources and 80% from natural sources.

Recent measurements in US suggest current average annual dose is around 6240 uSv with around 50% of that coming from man made sources.