Multi-Modal Imaging - Motivation, Synchronicity, Instrumentation & Data Quality Issues Flashcards
What is multi-modal imaging?
Simultaneous production of signals got more than one imaging technique
What is an example of multi- moral imaging?
One could combine using optical, magnetic and radioactive reporters to be detected by SPECT, MRI and PET
Who undergoes multiple imaging for any given condition?
Most (all?) patients in tertiary medical centres
What is multi-modal imaging used for?
Visualise various aspects of the patients condition:
- Brain morphology and pathology
- Brain metabolism
- Brain’s electrical activity
- Skull (for surgery)
Optimal use of this information can be achieved through multi-modal data fusion
What does multimodal imaging enable?
Examining more than one molecule at a time, so that cellular events may be examined simultaneously or the progression of these events can be followed in real time
What is multi-moral imaging a combination of?
Images or maps
- from different sources (instruments) or from the same scanners but using different sequences
- that show different aspect of the body’s structure or function (e.g. MR contrasts)
What is the fundamental assumption of multi-modal imaging?
All measurements (images) relate your the same phenomenon
- if you bring all of the data together and show it is in a fused image - co-registered side by side
- there is no time difference between the two
What are the two crucial consideration of multi-modal imaging?
- Space
2. Time
What is an example of multi-modal imaging?
- EEG-fMRI
- these are fMRI statistical maps superimposed on the structural scans showing both changes, fMRI changes into an EEG pattern showing patients with generalised epilepsy
- BOLD changes are correlated with the amount of generalised spike waves
- All the images are co-registered
What is a holding structure for surgical instrument?
The skull
Why is it difficult to segment the skull from fMRI?
Because CSF is quite dark - you can’t tell the difference between bone and CSF
What is fMRI and structural MRI?
- fMRI maps are always superimposed on structural MRI - done in SPM
- It is easy to believe the blob is exactly there
- This is the result of an operation that can fail - superimposition of 2 images can fail
- If the blob is off by 3cm - it can end up in The air, in the eye but if it is closer to where it should be
- A software always produces an answer
What is PET-CT?
- This is a merged instrument
- This is good for abdominals
- Abdominal imaging is difficult - the head doesn’t move but the abdomen always moves
- Big efforts to have two images acquired at the same time
What is the principle and aim of multi-modal imaging data
Ensure that all data is comparable
What are two equivalent ways of looking at multi-modal imaging?
All the information to be shown must…
- relate to the phenomenon of interest
- Be up to date
- Accuracy - being true to the reality
What are two considerations of multi-modal imaging data?
- Acquisition co-localisation
2. Acquisition synchrony
What are the fundamental underlying problem with multi-nodal imaging data?
- Images are powerful
- We tend to believe what we see
- Need to carefully consider how the multi-modal data is acquired, processed and displayed
- Most fused images are the result of lot of processing
What are examples of acquisition co-localisation?
- Same field of view or built-in co-registration: ‘PET-CT’
- post-acquisition co-registration unnecessary - Different fields of view: MRI & CT
- post-acquisition co-registration necessary
What is same fields of view or built-in co-registration: PET-CT?
- The subject doesn’t move, you acquire two images at the same time it is built in
- It is acquired at the same time at the same space
- It produced co-registered images by design
Different fields of view: MRI + CT
Co-registrations are required
What are the key operational questions of co-localisation?
- How precisely must the data be co-registered
(Often. Neglected consideration)
- aswell As possible given available means - Are the data from the same image space or not?
- decide on co-registration strategy
What are examples of same acquisition sessions ?
- Maintain field of view
- Subject immobilisation
- Sale scanning matrix - Change field of view
Different acquisition sessions
- Maintain field of view
- subject re-positioning
- recall scanning matrix (MRI) - Change field of view
What are the key operational questions for acquisition synchrony?
- What is the tome scale of the phenomenon in relation to data acquisition time’s?
- is the date ‘accurate’: is it up to dates - Are we interested in individual or averaged events
What is Acquisition synchrony?
- This is about what is happening in the subjects brain, are all my images up to date
- Or how quickly are things changing - can I use the structural MRI from a month ago to do surgery
- If I am to use the lesion in MRI -can I use that scan in the operating theatre to target lesion
- You might have some relevant information because you have analysed their old scan much more time to analyse the old scan
What is linearly related?
Neuronal response and BOLD response
What is an example study for the acquisition synchrony?
The Neuronal basis of BOLD decreases
Technique: simultaneous BOLD and micro-electrode neurophysiology in primates
What are the phenomena of interest and acquisition synchrony?
- Reproducible or slow events (e.g. evokes responses, brain structure/function)
- different data acquisition sessions - allow study of averaged, typical or slow effects - Simultaneous (synchronous) data acquisitions
- allow study of individual event
- possible dada degradation - Unpredictable (spontaneous), brief, unique events (e.g. epileptic spikes, seizures)
Simultaneous acquisition are necessary
- averaged effects and single realisations (individual events)
- possible data degradation
What is a downside; inference of synchronous multi-model acquisitions?
The combined instruments might interact
- possible interferences
- The introduction of a modality in the environment of another can lead to undesirable effects:
- performance degradation (data quality degradation)
- additional safety risks - Modifications or remedial post-hoc measures may be required
- hardware modifications
- acquisition protocol modifications
- additional data processing
What are example applications of multi-modal imaging?
- CT & MRI
- PET-CT
- FMRI & structural MRI
- FMRI & MRI: application in neuro-navigation
- EEG-fMRI
What is CT & MRI?
- Instrumentation: MR and CT scanners used in separate sessions
- Application: visualise soft tissue in relation to radio-opaque structures
- Brain vs. Bone or implanted objects - Synchrony requirement; low to medium, depending on the precise circumstances
- Co-localisation: post-hoc registration
- data quality issue: different geometric distortion between CT and MR
What is ‘PET-CT’?
Instrumentation: combined PET-CT instrumentation
Application: measure glucose intake in organs in oncology
Synchrony requirement: high in abdominal application
Co-localisation: same space
Motivation: perfect registration of moving tissues
Data quality issues: not the the best PET not CT but adequate for purpose
What is fMRI & structural MRI?
Instrumentation: MR scanner
Application: measure brain activity (haemodynamic) in relation to brain structure for functional mApping for neurosurgery
synchrony requirement; low to medium
Co-localisation: post-hoc registration
Data quality issue: different geometric distortion between MRI sequences
What is fMRI & MRI: application in neuro-navigation?
Additional considerations:
Synchrony requirement: low-Hugh
Co-localisation: co-registration of instruments with images
Data quality issue: image update
What is EEG-fMRI?
Instrumentation: combined EEG system - MR scanner
Application, measure haemodynamic of brain activity identified on EEG and in relation to brain structure: BOLD mapping and epileptic activity
Synchrony requirement: Hugh
Co-localisation requirement: low-medium; post-hoc registration
Data quality issue: interference between EEG and MR Systems
