Intro Flashcards
Who pioneered medical imaging?
Wilhelm Röntgen 1895- research into X-rays
First imaged a hand
When was MRI scanning developed?
Between 1950-1973
First MR images of human tissue published 1977 by Peter Mansfield
Why are MRI scans different to a photo?
Photo is visible light pictures as seen by the eyes -we digest features of a photo by the contrast between colours and shadows
BUT
The contrast in an MRI scanner is differences in inherent magnetic properties in tissue, MRI is visualising these differences through high or low magnetic signal - scans visualise this difference in magnetic behaviour between brain matter, fat etc.
What is gandolinium?
A contrast agent used to highlight certain tissues or pathologies. This is called exogenous contrast.
MRI scans use natural properties of tissue to generate endogenous contrast (i.e. without any injections).
What are scan images made up of?
Numbers visualised with colour scales on top of them
Scans are made up of pixels which give coordinates with 3 numbers on them, the number next to it is the value of the pixel
What is the difference in value between dark and light pixels?
Darker pixels = lower value
Lighter pixels = higher value
When we process images what are we doing?
Manipulating sets of numbers
What is a matrix (sometimes known as 2 dimensional array)?
Square arrangement of numbers in columns and rows - in imaging, the numbers correspond to discrete pixel values.
Each box within the matrix also corresponds to a specific location in the image and corresponds to a specific area of the patient’s tissue
How many axes do MRI scans have?
3 - this means we are dealing with stacks of matrices
What are pixels/voxels?
These individuals numbers are the smallest details of an image and are the image pixels.
Each pixel quantifies an amount of physical space. In a structural brain MRI scan this may typically be 1mm x 1mm.
The size of the pixels is referred to as the spatial resolution of the scan
How is higher resolution linked to pixel size?
High resolution = smallers pixels = clearer image
Why are 3D scans different?
In these cases our numerical values refer to a 3D volume of anatomy rather than a “flat” square.
These numbers are called voxels rather than pixels.
How are MRI scans kept?
As computer files
Initially scan is generated in a “raw” format
Most common raw format is called DICOM
What do we do to raw data?
Convert it into other types of files that are more standardised and compatible with image processing tools
Most common is called “nifti” format (.nii) - this can be compressed down further into “nifti-gz” to save storage space
What two sets of information do image files contain?
The image itself and its “metadata”
