Imaging Science and Imaging Processing Flashcards
(20 cards)
What is a medical image?
A representation of the human body that can be interpreted by an observer, the content depends upon the physics of the imaging process
Which is the best imaging modality?
Depends upon the clinical application.
What is a digital image?
Array of numbers mapped onto pixels of the output device. Information is so large that all information can rarely be seen in a single visualisation
What is windowing?
Selection of a range of data values and stretch these across available pixel values of the display device
What is a good quality image?
- Appropriate for the clinical application
- Optimised (balancing factors such as image quality, dose)
- Not necessarily the best possible image that can be acquired
What are measurable qualities of an image?
Contrast
Noise
CNR
Spatial resolution
Geometric linearity
What are the advantages and disadvantages of planar x-ray?
Anatomical
Quick
Inexpensive
Poor soft tissue contrast
What are the advantages and disadvantages of x-ray CT?
Anatomical
Quick
Reproducible
Good soft tissue contrast
Difficult to manipulate contrast
What are the advantages and disadvantages of MRI?
Anatomical
Functional
Exquisite soft tissue contrast
Can be slow
Not always reproducible
What are the advantages and disadvantages of NM?
Functional
No anatomical information
Low resolution
Slow
Potential for high dose
What are the advantages and disadvantages of PET/CT?
Anatomical
Functional
Whole body scans are easy
Expensive
Low resolution
What are the advantages and disadvantages of US?
Anatomical
Quick
Inexpensive
Difficult to interpret
What is image fusion?
Bringing images together into the same geometrical context on the same screen
What is the window width?
The range of the grayscale that can be displayed.
Why is windowing levels in CT standardised?
To provide consistency between patients and scanners
What is the window level?
The centre of grayscale range (window width)
Why is image processing done?
To aid interpretation of the image, by extracting details, calculations, improving visualisation, evaluating image quality (using phantoms)
How do you choose which imaging modality?
Usually start with the quickest and most available before choosing a more specialist technique. Often consider information from multiple modalities to develop an overall picture
What are the two steps involved in the analog to digital conversion of a signal?
- Sampling - Measure analog signal at discrete points (in time or space)
- Quantisation - Map signal to a pixel value
What is undersampling and how can it be avoided?
Not having a high enough sampling frequency to accurately represent the analog signal with a digital output. It can be avoided by increasing the sampling frequency.
