Principles of imaging 1

Question 1

What does the current do to x-ray image?

Answer 1

mAMPs determine the number of X-rays

Question 2

How do the cathode and anode interact on X-ray tubes?

Answer 2

Between anode and cathode there is a constant voltage applied which enables electrons to fly faster towards the anode

Question 3

What are the anode and cathode of an X-ray made of?

Answer 3

Tungsten

Question 4

How are X-rays directed in a safe and appropriate way?

Answer 4

The anode is positioned under an angle facing towards a small opening in the lead casing. this allows only certain X-rays to exit the machine

Question 5

How long should the distance between the tube and the patient be and why?

Answer 5

Cannot be shorter than 20cm. To avoid overradiating the patient.

Question 6

Why are some manufactured X-rays with longer spacer cones and others with shorter ones?

Answer 6

Some machines have smaller and others longer spacer cones. Depending on the position of the X-ray tube.

Question 7

What are the functions of the spacer cone?

Answer 7

Indicates where X-rays exit the machine to aim at patient

Keeps distance between patient and X-ray source

Question 8

What is the job of the aluminum disk in an X-ray?

Answer 8

Aluminum disk is placed behind the opening in the lead casing. To filter out the weaker X-rays as these X-rays would be absorbed by patient but are useless.

Question 9

How is the position of the anode indicated on the machine?

Answer 9

A small dot on the outer casing of the machine indicates where the anode is in the device. The distance between the anode and the spacer cone is usually between 20 and 40cm (never <20cm)

Question 10

What are the dimensions of the anode?

Answer 10

Anode is theoretically a point focus but reality is its dimensions are 0.4 x 0.4 mm.

Initially the anode is flat but over time it gets bent and becomes less clear.

This causes the focus to enlarge and instead of being the theoretically point focus, it turns into a line focus.

Question 11

What current is ideal for imaging?

Answer 11

7mAMPs ideal for imaging and this can go down to 4 without issue

Question 12

How are parallel, focused X-rays produced?

Answer 12

Image receptor should be placed as close as possible to the teeth and as parallel as possible to the axis of the teeth.

To achieve parallel X - rays a collimator is positioned in front of the aluminum filter. This collimator is either circular (cylinder shape of PID) or rectangular (beam shape of PID).

Question 13

Why is geometry important?

Answer 13

If the X - rays are not parallel, but diverging, the image
will be distorted severely and be very inaccurate
.

Question 14

What are the types of solid state sensors?

Answer 14

CCD Sensor same as the phone camera sensor. It converts X-rays into light energy that can be detected by this device.

CMOS-APS

Question 15

What digital image detectors are used in ohcwa and how do they work?

Answer 15

Photo-Stimulable Phosphor Storage Plates. They don’t caputre light, they capture energy from the X-rays.

Question 16

When were Solid State Sensors made?

Answer 16

1987 by a company called trophy

Question 17

What are the disadvantages to using Solid State Sensors?

Answer 17

Not available in any size

Actual size of sensor is different to size of captor

Easy to use, however, fast image acquisition time

Overexposure is possible and results in blooming

Question 18

What are the important limitations to using phosphor plates?

Answer 18

Latent image is captured – sensitive to white light (erases the latent image)

Can be scratched

Barrier envelopes required to prevent cross contamination

Question 19

What are the advantages to using phosphor plates

Answer 19

A photomultiplier tube catches the light and via an analogue digital converter the image is displayed on a computer screen

Very forgiving with regard to exposure time

Double images are possible

Re - usable (1000s x)

Question 20

How do solid state sensors compare to phosphor plates?

Answer 20

Solid state sensors give a better image overall

CCDs are bulky

Solid state sensors also don’t require a scanner

Phosphor plates damage easily and are bendable

Question 21

Which of the 2 types of imaging has better latitude of exposure time under optical densities between 0.3 and 2?

Answer 21

Phosphor plate has the widest latitude of exposure time under optical densities between 0.3 and 2

Question 22

What does a pixel represent?

Answer 22

a 3D cuboid or voxel of a patient’s tissues.

Depth of the pixel depends on the thickness of the part of the body being imaged.

Each pixel measures the total x-ray absorption throughout the whole of each voxel

Question 23

Why is it impossible to have perfect images using X-rays?

Answer 23

The system has a lot of inherent “noise” from scattering etc

The computer systems it is diplayed on are limited by 8 bit processing

Question 24

How is image manipulated on romexis?

Answer 24

Alteration in contrast (difference between black and white)

Alteration in brightness (degree of blackening)

Sharpening / smoothening (uses filters)

Inversion (positive image)

Embossing (pseudo 3D)

Magnification (limited as pixilation occurs with too much magnification)

Automated measurement (calibration required, but not in CBCT)

Pseudo colourisation (arbitrary)

Question 25

What are the features of the diagnostic monitor being used to view X-ray images?

Answer 25

Screen should never face a window

Sit in front of the monitor (less important today than in the past)

Laptops have a lower display intensity

Most of the recent displays will do for 2 dimensional X-ray diagnosis

Avoid reflection on the monitor (matt displays are best)

Avoid monitor facing light (window, artificial light source)

Make sure the monitor is clean

Test calibration regularly as monitor performance may
change