nuc med Flashcards

1
Q

Parallel hole type

A

most common

Allows only radiation parallel to the septa to strike the crystal

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2
Q

Low energy collimator.

A

Is used to image energies of up to 200 Kev.
Has thin septa
Can therefore have more smaller holes giving better resolution

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3
Q

Medium energy collimator

A

Has thicker septa so that the more penetrating gamma rays are absorbed
Has fewer holes than a low energy collimator giving poorer resolution

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4
Q

High Resolution Collimator

A

Has a large number of long holes thus restricting the angle of view of each hole.
Gives better resolution as each point is imaged by fewer holes.
Loses sensitivity as less radiation reaches the crystal.

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5
Q

High Sensitivity Collimator

A

Has fewer short holes, each hole having a wide angle of view.
Gives poor resolution as each point is imaged by more holes
Has higher sensitivity as more radiation reaches the crystal.

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6
Q

Other Types of Collimator

A

Diverging Hole
Converging Hole
Pin Hole

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7
Q

The Crystal

A

Sodium Iodide activated with Thallium.
Photons striking crystal interact by Compton or PE
Produce a scintillation: blue/UV light

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8
Q

Light Guide

A

Provides optical coupling between crystal and PM tubes

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9
Q

Photo Multiplier Tubes

A

Several PM tubes will detect each scintillation
Produce small electrical signal from each scintillation
Amplify it maintaining proportionality
The sum of all the signals remains proportional to the energy of the incident photon (z pulse)

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10
Q

Pulse Height Analyser

A

Remember the z pulse is now proportional to the ENERGY of the incident photon.
PHA “looks” at the z pulse corresponding to each scintillation
Rejects the pulse if outside set limits (window)
Is a filter for scatter
Is not perfect

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11
Q

ADC

A

x, y and z signals are analogue
ADC processes the signal into digital form
Suitable for computer processing

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12
Q

Choice of collimator

A

Hi Resolution……..Bone scans, SPECT

- Hi Sensitivity…….Dynamic/ short frame times

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13
Q

Information density

A

Information density- number of photons collected over region of interest

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14
Q

Computer matrix

A

Computer matrix

-number of pixels in the image-fewer pixels = coarse image-no point in more than 256 x 256 pixels

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15
Q

Spatial Resolution

A
Ability to image two  adjacent point sources as separate points
-Dependent on:
Intrinsic resolution  (Ri)
Collimator (Rc)
Scatter component (Rsc)
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16
Q

Scatter

A

Surrounding tissue produces Compton scatter
Some scattered photons will reach crystal.
Some will be within the 20% energy window.
Degrades the image
Worse at increasing depth

17
Q

SPECT problem and solution

A

Problem-background activity in surrounding tissues and the increased amount of scatter limits the resolution and target to background ratio of the organ being imaged.
Solution-SPECT (Single Photon Emission Computed Tomography)

18
Q

Advantages of SPECT

A

Increased “pick up” of deep lesions
Localisation
Correlate with CT
Estimate volumes

19
Q

Disadvantages of SPECT

A
Requires special equipment
Careful setting up
Strict QC
Patient Co-operation
Acquisition times 15-30 minutes
20
Q

Field uniformity

Linearity:

A

Field uniformity
Uniform response over whole field of view
Intrinsic (without collimator) Extrinsic (with collimator)
Linearity:Ability of a gamma camera to image a straight line in x and y planes

21
Q

Intrinsic Uniformity

A
Remove collimator
Point source at least 5 x FOV from camera
Collect 5-10 million counts
Inspect images for defects
Use software to calculate uniformity
Do at least weekly
22
Q

Extrinsic Uniformity

A

Place “flood phantom” on collimator
Collect 5-10 million counts
Inspect images for defects
Use software to calculate uniformity

23
Q

Linearity

A
Point source at least 5 x FOV from camera
Place bar phantom on camera face
Acquire image
Inspect
Check  lines are not distorted
Check resolution