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Radiology > X ray unit and films Revision Questions > Flashcards

X ray unit and films Revision Questions Flashcards

1
Q

What does an xray unit consist of?

A 
X rays tube head
Collimator
Positioning arm
Control Panel 
Circiutary
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2
Q

Filament - cathode

A

Made of tungsten and negatively charged
Goes through step down transformer - low voltage and high current
z = 74, mp = 3210 degrees

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3
Q

Target - anode

A

Positively charged and made of tungsten
Converts electrons to xray photons
effective area = 0.7mm^2

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4
Q

Target surround

A

copper and effective heat conductor

z=24, mp = 1080 degrees

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5
Q

Shielding

A

lead surround to absorb xrays trying to get out of tube head
Z = 82
Ensure does rate in vinicity >7.5uSvh^-1

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6
Q

Evacuate glass envelope

A

Evacuated glass and vacuum prevents risk of interaction of electrons with air atoms prior to meeting target

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7
Q

Filtration

A 
Alluminium 
allows high energy electron through but not low ones
Z = 13
1.5mm <=70kv
2.5mm >70kv
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8
Q

Collimator

A

lead
Controls the shape of the xrays beam
max beam = 60mm

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9
Q

Spacer cone

A

a beam indicating device
Controls the distance between the focus to skin
100mm<60kv
200mm>60kv

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10
Q

What does rectangular collimation do?

A

Controls the shape, size of the xray beam

Dose reduction, improved quality, fewer rejects

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11
Q

Compoenents of an intra oral film?

A

Radiographic film
Protective paper (black) - protects the radiographic film from light from light exposure, damage fingers and saliva
Lead foil - absorbs any excess xray photons - furthers away from tube - lets xrays get to the patient
Outer wrapper

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12
Q

What is the structure of the radiogrpahic film?

A

Transparent plastic base - supports the emulsion
Adhesive - attaches the emulsion to the plastic base
Emulsion - silver bromide in gelatin
Protective coating of clear gelation - shields the emulsion from mechanical damage

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13
Q

What does film holder packet consist of?

A

Connecting rod
bite block
image receptor support
beam aiming deveice with rectangular devices

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14
Q

Where is the xray dot located

A

convex faces tube head
Placed occulsally so does not superimpose over tooth

PA - dot bottom of film holder
BW - top of holder

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15
Q

What is a latent image?

A

A hidden image that becomes visible once beam is processed

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16
Q

Steps of fim processing

A

Developing - converts sentitised crystals to black metallic silver patches
Washing - removes resisdual developer solution
Fixing - removes non-sensitised crystals and hardens emulsion
Washing - removes reisdual fixer solution
Drying - removes water so film is ready to be handled

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17
Q

Advantages of self developing film

A

No dark room or processing facilities required

Faster time to complete

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18
Q

Disadvatnages of self devleoping films

A 
No lead foil
Easily bent
Expensive
Poor quality
image detoeriiates more rapidly over time
Difficult in positoning holders
19
Q

Advantages for digital xrays

A 
no need for chemical processing
easy back up of images
images can be manipulated
no processing faults
easy storage and archiving
images can be integrated with patient notes
easy transfer of images
low radiaiton dose
20
Q

Disadvatanges of xrays

A

worse resolution
risk of data loss
hard copy print outs tend to have decreased image quality
image enhancment can increase misleading images
requires a diagnositic level computer monitor for viwing images

21
Q

Brown/green stains

A

inadqueate fixing time

Non sensititsed crystals are left behind

22
Q

crazed pattern

A

film dired too quickly over a strong heat source

23
Q

Presence of crystals

A

insufficient washing after fixing

24
Q

Black lines

A

film bent

25
Q

black spots

A

film splashed with fixer before developing

26
Q

Fading image

A

inadequate fixing time

27
Q

faint image

A

developer solution too weak, too cold temp

left in for too short a period

28
Q

Why can cone cutting occur

A

incorrect assembly of receptor holder
incorrect allingment between xray tube and recptor holder
incorrect orientation of the rectangualr collimation

29
Q

What is film speed

A

amount of xray exposure required to produce an adequate image

30
Q

What affects film speed

A

number and size of hallide crystals

larger crystals, faster film but pooer image quality

31
Q

Proclined teeth - angulation of tube head

A

increases

32
Q

Retroclined teeth - angulation of tube head

A

decreases

33
Q

Ideal projection geometry

A

image recpetor and object in contact and parallel
parallel beam of xrays
xray beams perpendicular to object and image recptor

34
Q

Paralleling techinque

A

Film parallel to long axis of tooth, xray beam perpendicular to long axis of tooth
Image size same as actual tooth

Problem - divergent xrays - long distance between image recpetor and tooth so potential for magnification - use long axis x-ray focus to skin distance to reduce magnification @20cm

35
Q

Bisecting angle technique

A

angulation of long axis of tooth determined, angle bisected at right angles with the xray beam
Still uses long xray focus to skin distance @20cm

36
Q

What are head positions for maxiallry occlusal

A

Mid sagittal plane perpendicular to the floor
Occlusal plane horizontal
Ala tragus line horizontal and parallel to floor (runs from ala of nose to upper border of tragus of ear)

37
Q

Anterior teeth horizontally wider

A

patient too far back in machine

canine behind the guidance marker

38
Q

Posterior teeth horizontally wider

A

patient rotated in machine

39
Q

Anterior teeth, out of focus

A

Patient postioned too far back in machine

40
Q

Molars larger on one side

A

Head rotated to one side

Patient not biting symmetrically between incisors on bite peg

41
Q

Vertical/horizontal distortion

A

patient moved

42
Q

<90 degrees

A

elongate tooth

43
Q

> 90 degrees (steep)

A

Shortens tooth

Radiology (6 decks)

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