Image Reg

Question 1

What is contrast resolution?

Answer 1

The ability to image differences among low contrast tissues

Question 2

What is geometrical accuracy?

Answer 2

The ability to produce an image that is a geometrically correct
representation of the object imaged

Question 3

What is spatial resolution?

Answer 3

The ability to identify an object as distinct and separate from
another object

Question 4

What is Sensitivity?

Answer 4

The ability to detect differences in an object

Question 5

Specificity

Answer 5

The ability to accurately determine the nature of the imaged object

Question 6

What is a T1 weighted image?

Answer 6

spin-lattice or longitudinal relaxation
time.

Depicts anatomy well (low sensitivity for disease without contrast)

Question 7

What is a T2 weighted image?

Answer 7

spin-spin or transverse relaxation
time.
Depicts diseases with high water content well (low specificity though)

Question 8

What is a proton density weighted image?

Answer 8

Depicts anatomy and disease well (currently limited applications).
Higher spatial resolution than T1 and T2.

Question 9

What is a spin echo (SE) and fast/turbo SE.

Answer 9

INCREASES spatial resolution and reduce artifacts caused by magnetic field and inhomogeneties.

Fast SE is preferred for RT - it is faster and reduces motion artifacts

Question 10

What is a gradient echo?

Answer 10

Very short acquisition time minimises motion artifacts, DECREASE spatial
resolution; used for multi-phased imaging, oxygenation levels

Question 11

What is diffusion weighted imaging (DWI)

Answer 11

Differentiating between ↑cellular density (tumours) and ↓cellular
density (benign tissues inflammation necrosis

Question 12

What is the difference between a T1 and T2 image?

Answer 12

T1 fat is white

T2 fluid is white

Question 13

What colour is fat in a T2 fast spin echo (FSE) image

Answer 13

Fat is bright

Question 14

What are MRI limitations?

Answer 14

Image distortion due to non-uniformities
in the magnetic field

Image quality dependence on coils. ( this is a problem for RT imaging requirements e.g. fitting immobilisation under coils.

Poor imaging of cortical bone.

MRI distortion

Question 15

What common radionucleiode is used for PET scanning?

Answer 15

FDG (fluoro-D-glucose).

Question 16

What are the limitations of PET?

Answer 16

High uptake in benign pathologies.
Image resolution musch poorer than CT ( difficult to delineate tumour volumes).
PET is a metabolic image

Question 17

Why does PET have a poor image resolution?

Answer 17

PET uses a relatively large voxel size (0.4x0.4x0.4)
Images appear pixelated compared to CT.
(Difficult to define a geometric edge)

Question 18

What is semi-automated rigid image registration?

Answer 18

Use of automatic translational functions

to match landmarks and/or surfaces

Question 19

What is automates rigid image registration?

Answer 19

Use of algorithms to perform matching
based on statistical analysis or signal
processing of the voxel data of the two
image sets

Question 20

What are the 2 most common algorithms used in automated image registration?

Answer 20

Cross Correlation

Mutual Information

Question 21

What is cross correlation?

Answer 21

Used for registering an image with similar information.
Best suited to registering intra-modality images (CT-CT or MRI-MRI) registration.
Can be used CT-MRI

Question 22

What is mutual information?

Answer 22

Used for registering images with dissimilar information.
Technically this algorithm can be used for all multi-modality image registration.
Most commonly used for CT-PET or MRI-PET registration.