Neuroimaging Flashcards
medical imaging used to be limited to a small number of elite hospitals associated with teams of researchers who provide the expertise for its application and interpretation but now…
this is changing since commercial vendors are now offering products that make advanced brain imaging accessible to a much wider range of physicians and insti- tutions.
To treat a brain tumor patient using invasive surgery and/or radiotherapy, there are three key issues
- Where is the tumor ad how far has it spread
- How bad is it? (pathology/heterogenous or not/where is it most aggresive
• What’s at risk? Is there eloquent cortex or key white matter (tracts) near with key fnx?
overall clinical goal:
effective treatment with minimal risk of causing neurological deficits that could compromise the patient’s quality of life.
“deck” of 5 different types of imag- ing information layered into a single view that provides the surgeon with detailed infor- mation for planning a maximal resection of the tumor without damaging gray and white matter structures critical for vision.
Advanced imaging advantage
This shows the anatomy at high resolution with good gray/white matter differentiation.
T1-weighted magnetic resonance image (MRI).
Issue with T1 weighted magnetic resonace image MRI
However, some types of pathology are not well differentiated in this type of image.
(SPoiled, Gradient Recalled at steady state)
SPGR
The deck allows you to individually adjust each type of image and to re-arrange their stacking order. You can think of this as analogous to a deck of cards in which you can re-arrange the order of the cards.
SPGR
an MRI image that highlights the tumor better. This type of image also reveals edema within the tumor and surrounding tissue. However, the gray/white matter anatomy is less well de- fined.
(Fluid Attenuated Inversion Recovery = FLAIR
We can “threshold” the FLAIR image to allow the detailed SPGR anatomy to show through thus getting both the detailed anatomy and a good image of the tumor bed.
Multiparameter Imaging: Threshold FLAIR + SPGR
_______ is a mathematical manipulation of the image so that only voxels with intensities above the threshold limit are displayed.
Thresholding
= a small 3-dimensional imaging volume or the 3-dimensional equivalent of a “pixel”,
Voxel
The more voxels the _____ the spatial reso- lution, that is, the more detial in the MR im- age.)
higher
Functional MRI provides images of highly localized changes in blood flow and oxygenation that are driven by changes in net neural activity due to a sensory, motor or cognitive event.
BOLD fMRI: Brain Function
______ triggers local vasodilation and resultant increase in highly oxygenated hemoglobin
in BOLD fMRI: Brain Function
Neural activity
BOLD fMRI: Water protons within the blood and tissue are induced to emit radio frequency signals that are ________when the local magnetic field created by the scanner is undisturbed but _______when the local field is disrupted by the presence of poorly oxygenated hemoglobin.
high (strong) are low (weak)
(BOLD fMRI) Neural activity causes increased blood flow which removes poorly oxygenated hemoglobin which allows
the protons to emit a strong signal.
How neural activity triggers the
blood flow changes is poorly under- stood and may reflect a complex interplay of excitatory and inhibitory effects and may reflect both
post- synaptic and action potential activity.
in BOLD fMRI the fMRI signals are slow compared to ______so typically reflect changes in neural activity integrated over several seconds.
neural events
technique for mapping the representation of the visual field in a relatively short scanning session of 10-15 min.
fMRI Mapping of the Visual Field
How do you get a visual stimulus for fMRI Mapping of the Visual Field
visual stimulus = flickering, checkered annulus slowly ex- pands over a 32 second period and then repeats 5 times during the fMRI scan.
In the fMRI of the occipital cortex, we see the layout of the visual field eccentricity with the center of gaze represented at the
occipital pole
In the fMRI of the occipital cortex, we see the layout of the visual field eccentricity with the more eccentric locations represented
represented more anteriorly.
The colors in the fMRI of the visual field identify
locations in the visual field not the amplitude of the fMRI response.
By adding distance contours, you show an estimated
“no-fly zone” around the tumor
Different colors within the no-fly zone mark “shells” at different distances from the tumor: Red orange yellow green
Red < 5 mm,
orange < 10 mm,
yellow < 15 mm,
green < 20 mm.
Gray and white matter structures within _____mm of a resection site are likely to be at risk for damage caused by the surgery.
5-10
When looking at a no-fly zone we see the peripheral visual field is in the red zone around the tumor.. would the physician opt for compete excision of the tumor?
Yes, Loss of vision in the peripheral visual field is often well tolerated so the surgeon and patient may elect to accept such a functional loss to ensure complete excision of the tumor.
When evaluating imaging, doc noticices the close proximit of white matter tracts along the margin of the tumor including optic radiations. Why do those tracts show up green?
these are optic radiations which are supplying the visual input that is driving the fMRI
activity in the occipital cortex
arterio- venous malformation (AVM) in the ______These typically congenital malformations of the vasculature can ____ or _____
precentral sulcus
bleed or induce epileptic activity.
Tx option for AVM
surgical removal
superior longitudinal fasciculus is also known as
arcuate fasiculus
connects Wiernicke’s and Broca’s speech are- as in the temporal and frontal lobes respectively
arcuate fasiculus
Option a surgeon can use when the the tumor is close to structures for movement and language function
Gamma knife
__________is essential in complicated cases to allow the surgeon to plan both the route of access to the tumor and the key structures “at risk”
Advanced multiparamter imaging
Advanced multiparameter imaging allows sugeons to be more or less aggressive
allows them to be MORE aggressive with the resection because they don’t have to guess where the crucial structures are located.
Treatment was to involve sub-threshold electrical stimulation of the face area in motor cortex using epi- dural electrodes, (direct visualization was not possible)
What kind of tx was this?
Therapeutic brain stimulation
placement of the electrodes in therapeutic brain stimulation is critical not only to achieve maximum therapeutic effect but also
avoid stimulation of other nearby areas
fMRI data can be used to
identify the optimal location of the stimulating electrodes relative to the fiducial markers on the scalp.
Once a surgical plan is constructed, key images showing the critical features of the case are loaded into a system for
intra-operative navigation.
Such systems can track the location of a surgical instrument (eg. aspi- rator) relative to the images of the brain thereby assisting the surgeon in orienting to features that are invisible to the naked eye but that are
evident in the medical images
intra-operative navigation
______ is rapidly affecting all stages of health care from diagnosis to treatment planning to treatment delivery and follow up monitoring for tumor recurrence
medial imaging technology
capabilities are currently rudimentary but will advance rapidly allowing custom “shaping” of the radiation field… the purpose is
to maximally impact the tumor while minimizing dosage to eloquent cortex nearby
