Image receptors 1

Question 1

digital receptors are split into 2 types?

Answer 1

• Solid state sensors
• photo stimulable phosphor

Question 2

solid state sensors fall into 2 categories

Answer 2

CCD which stands for charge-coupled device, and CMOS, which stands complimentary metal-oxide semiconductor, these sensors work by converting light into electrons

Question 3

Describe PSP or photostimulable phosphor plates

Answer 3

are the type of receptor we use in the department. Images are produced by the interaction of x-rays with the phosphor layer on the plate, which is then scanned by a laser to produce the image. The extra-oral cassettes in the department are also PSP plates

Question 4

describe phosphor plates

Answer 4

The plate has 2 very different sides, a pale side which has the phosphor coating. The phosphor can be various compounds for example barium fluoride. This is the side on which the image is formed

the other side is black and shows the size of the film and the orientation dot. this is the back of the plate.

the plate is then placed in a protective bag before being used. You should be able to see the black side of the plate through the window of the bag

Question 5

describe stable excited state

Answer 5

the imaging plate is then placed into the patient’s mouth and the phosphor coating is exposed to x-rays which causes a reaction within the phosphor

Question 6

describe unstable excited state

Answer 6

the plate is then dropped into the vista scan unit where it is scanned by a red laser. The blue light which is then emitted is collected and then converted to an image

Question 7

describe latent image

Answer 7

So the phosphor layer on the plate is exposed to x-ray photons.The phosphors then store the radiation in local electron energies.

Question 8

describe Analogue to digital convertor or ADC

Answer 8

The plate is then inserted into the scanner and the phosphor layer is scanned by a red laser which causes the electrons to drop to lower energy levels by emitting blue light. This light is then detected by a photodetector and sent to a signal digitiser.

Question 9

describe grey-scale

Answer 9

he ADC converts the light to a digital signal, which is basically a numerical value assigned to each pixel according to the intensity of the light detected. Each pixel’s numerical value corresponds to a different shade of grey which forms the image on the monitor.

Question 10

describe charge couple device systems

Answer 10

The detector is made up of4 layers, a front cover, a scintillator layer which converts x-ray energy to light, a silicon wafer which converts the light into an electrical signal, and in this particular sensor, a back cover incorporating a cable to carry the signal to a PC

Question 11

describe the most recent digital detectors

Answer 11

wireless, so do not have to connect directly to the computer. This makes it easier for the patient and the image appears within seconds

Question 12

describe CMOS system (complimentary metal oxide semiconductor)

Answer 12

is very similar to CCD, the only difference being the photocells are electrically isolated therefore a signal is sent from each individual cell rather than a line of cells

Question 13

What is the issue with digital images ?

Answer 13

there is no orientation dot. This means when you have many images to look at it could be very easy to turn an image the wrong way and get a bit muddled up

Question 14

So which system is better?

Answer 14

CCD possibly better quality image ( low noise and more pixels) but CMOS catching up. CMOS cheaper to manufacture. CCD have been around longer therefore possibly more reliable. CMOS uses less power. CMOS - mobile phone camera CCD - high quality digital camera.

Question 15

How to tell if too much or too little exposure is given to patient from radiographic image?

Answer 15

If the image is too dark this is because too much radiation has been given (high exposure)

If the image is too pale this is because not enough radiation has been given (low exposure)

Question 16

What does too much exposure look like?

Answer 16

flat, very few shades of grey, no contrast. This is because the high radiation has caused too much light to be produced in each pixel, which means there is little variation in the electrical signals which are converted to form the image

Question 17

What does too little exposure look like?

Answer 17

white mottling on the image like the one on the bottom left. If not enough radiation has hit the receptor, nore action to produce light can occur, therefore no signal from that pixel will be produced and the computer cannot guess and make better what is just not here.

Question 18

What is the backup system for images at dental hospital?

Answer 18

in Dundee Dental Hospital we use an archive system called PACS – Picture Archiving and Communication System

Question 19

What are important things to note about radiographic images uploaded to PACS

Answer 19

Each image is given its own unique accession number which you can see on the top left. Images taken at DDH always start with T113H, and note all the icons at the top which allow you to manipulate the image or provide tools such as rulers for measuring pathology

Question 20

describe sizes for solid state digital receptors

Answer 20

tend to come in size 2 only, which can make x-raying anterior teeth more difficult due to the large size of the receptor

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