IT: medical image Flashcards
What is an image?
An array or matrix of square pixels (picture element) arranged in columns and rows
What does each picture element in a greyscale image (8-bit) have?
Assigned intensity that ranges from 0 to 255
What is an image (descriptive)?
- Measurements at multiple spatial locations
- Spatial measurements = measurements of distance, area and volume, these involve the first 2 dimension of image its width and height
- The measurements are often, but not always arranged on a 2D/3D grid
What is the key feature of an image?
Each measurement relates to a physical location in the patient
What can a 2D medical image be?
Either tomographic or a projection through a 3D object
What is tomographic image?
A slice through the object
What does projection images do?
Aggregate data over long lines
What are the 2 characteristic of projection images?
- Summation (projection x-ray)
2. Surface reflection and scattering in a photograph
What is an element of image usually called?
Pixel (single 2D slice/projection) or voxel (3D image)
What is each voxel sampling?
Some kind of average (usually a summation) of the contents of finite volume of object
What is point spread function?
Response of an imaging system to a point source or point object
What are examples of spatial size of samples?
- Partial volume effects
- Point spread function
- Slice profile
What does an image metadata involve?
Details relevant to image itself as well as information about its production
How is some metadata generated?
Automatically by device capturing image
What can image metadata be useful for?
Cataloging and contextualising visual information
How can you make an image more meaningful?
Store extra information alongside image array itself
Often stored in an image ‘header’
What are examples of image metadata?
- Geometry
- Patient details
- Exam logistics
- Exam parameters
- Relationship to other slices, series,exams,
- Archiving information
- Display information
Examples of geometry
- Sample spacing (voxel size, resolution, slice thickness)
- Orientation repetition
- Standard orientation to display
Example of patient details
- Name
- Hospital number
- Date of birth
- Ward
- History
- Indication
Example of exam logistics
- Hospital
- Scanner
- Date and time
- Radiographer
- Referring clinician
Examples of exam parameters
- Modality
- Flip angle
- TE/TR
- B value
- Dynamic timing
- RF pulse type
- Filters
Example of display information
- Window/level
2. colourmap
How are radiological images normally displayed?
As if the patient were in a standard orientation
What must you be certain about?
- Anatomy orientation
- Displayed orientation
- Handedness
How does dominant medical image format record orientation?
Using a well defined system with respect to the patient:
- x- positive: toward the patient’s left
- y- positive: toward posterior side
- z- positive: superior direction
known as LPS system
How is the actual orientation of image stored?
Recording the direction in co-ordinate system of unit vectors along row + column directions of each 2D image plane
What does handedness errors flip?
3D volumes without making any errors in axis identification, but rather ordering the slices wrongly
What does DICOM stand for?
Digital Imaging and Communication in Medicine
What are the features of DICOM?
- Dominant standard
- Both a file format and network protocol
- Used to share medical image data
- The standard for image data interchange
What is DICOM designed to do?
- Information model of real-world things - real world objects/concepts
- Allow devices to share data safely
What does DICOM provide?
Semantics for querying, sharing and storing images across a hospital network
What does HL7 transmit information about?
Primarily about patients:
- Admissions
- Appointments
- Transfers
- Test results
