Image Acquisition

Question 1

What is frame mode imaging ?

Answer 1

Image parameters are set before imaging, usually stored as protocols, i.e. mat size, mag, mat depth, e window and termination condition

Question 2

What is list mode imaging?

Answer 2

Data is stored as x,y,z and t
Can rebin/frame as desired (flexible)
Inc post-processing time
No check Im during imaging
Option not always available

Question 3

What is static imaging?

Answer 3

Images are displayed as a matrix
Little or no post-pro
Take diff angle views to get more info

Question 4

Why is whole body imaging used?

Answer 4

Easier to interpret than multiple statics

Question 5

How are whole body images created?

Answer 5

1)Step and shoot:
Series of static images
Digitally stitched together

2) Single sweep
Scan speed pre-selected
Counts stored in pos mat based on cam position at the time of recording

Question 6

What is dynamic imaging?

Answer 6

A series of sequential static frames
Used to image rapidly changing distribution within the patient
ex. renography

Question 7

What is cardiac gated imaging?

Answer 7

Several frames acquired covering the cardiac cycle
Acquired over many cycles
Can bin counts based on phases

Question 8

What is SPECT?

Answer 8

3D GC projection imaging

Question 9

What are the issues with 2D imaging?

Answer 9

2D view of a 3D object
There is no depth information
Overlying structures are superimposed leading to a loss of contrast compared to 3D

Question 10

How are planar images motion corrected? (4 steps)

Answer 10

1 Produce line images from a dynamic sequence (compress along each row/clm)
2 Stack the line images and est x/y motion from the deviations in pos of max I
3 Translate each frame according to the disp co-ords
4 Sum the translated frames

Question 11

How are SPECT images motion corrected?

Answer 11

Review sinograms and linograms for discontinuities

The shift req to realign the components is then calculated and the projections are translated

Question 12

What are the limitations of motion correction?

Answer 12

Reduces spatial res as req interpolation
Out of plane motion cannot be corrected
Distribution changes can confound the algorithms

Question 13

How are colour scales used?

Answer 13

Help simplify diagnosis by maximising visible contrast

Question 14

Describe Filtered Back Projection

Answer 14

Back Project each planar image onto three dimensional image matrix
More views – better reconstruction
1/r blurring, even with infinite number of views
So must apply a ramped filter to remove the blur

Question 15

How does using a ramp filter effect projection images?

Answer 15

Gives increases weighting to higher spatial frequencies

But, amplifies noise

Question 16

How can ramp filters be improved?

Answer 16

Multiply with another function to rolls off the ramp effect at higher frequencies
For example, mult by a gaussian