Imaging brain structure and function Flashcards
What is the basic idea of a CT scan?
X-rays are passed through the patient and the relative rate of absorbance is measured by a detector.
Different tissues absrbed different amounts fo radiation (measured in Hounsfiled units) allowing algorithm to calculate the pattern of tissues creating the image.
What is meant by the CT window?
A tissue specific contrast/brightness setting that can be chosen to highlight certain structures e.g bone, soft tissue, stroke, brain etc
Can be displayed and set at a given range of HU.
Can give a median level of HU.
What is a CT algorithm?
What is the purpose of it?
A set of instruction used to take the absorption data collected by the CT machine and form the image by condensing information to look at specialised tissues.
Aim to improve image quality and reduce artefacts.
Used to put the information together into an image, usedula as digital CT detects more information that what can be shown on a screen or detected by the human eye.
What two settings must be correct and aligned to get a good CT image?
The CT window - what range of absorbance to focus on
The CT algorithm- to convert the absorbance data back into the image/
What is the key difference in image when looking at a type 1 and a type 2 MRI?
TYpe 1 - suppreses water and highlights fat - hence CSF is black
Type 2 - highlights fat hence CSF is white (so is fat)
What do the different signals suggest the tissue is made of in a type 1 MRI?
Black - air, CSF, corticoal bone, flow void
Dark grey - gret matter, edema, fluids, tendons and muscle
Light grey - white matter, cysts, proteinaceous materials
White - fat, contrast and methemoglobulin
What do the different signal intesntisties suggest the structure is on a T2 MRI?
Black - air, cortical bone, flow void
Dark grey - white matter, ligaments, tendons, sclerosis.
Light grey - grey matter, edema, mucosa
White - Fat, CSF, fluids, proteinaceous material, oxyhemoglobin.
What is important to remember about the terminology T1 and T2 MRI?
An MRI can be weighted towards measuring mostly T1 decay or T2 deacy, hence is a T1/T2 weighted MRI but neither becomes the defining signal, other signals will also contribute.
What is an MRI?
Uses strong magenetic fields and radio waves to alter the spin and axis/alignment of spin of protons, can measure the change is magnetism of protons to produce a signal intensity.
What is a proton density MRI?
Measures the concentration of protons (mobile hydrogen atoms). (opposed to the characteristics/magnetism of these protons)
Good for imaging soft tissue such as MSK.
What is the use of Gadolinium contrast in an MRI?
Can be injected into the body, highlights the fluid location by enhancing its signal.
Useful for pathology where fluid may be in the wrong place due to odema, blockage, haemorrhage etc.
What is meant by a FLAIR or Fluid Attenuated Invasion Recovery on an MRI?
Complete alongside another MRI alrgorithm.
The addition of an extra radio pulse at the correct time can manipulate the signal received so that a chosen tissues signal can be removed.
Used used to remove CSF in brain.
What is a diffusion weighted MRI?
When extrad magentic gradients are applied either side of radial pulses
This means tissues with high diffusion loose signal much more quickly (darker).
Whilst areas of reduced diffusion are highlighted (white)
This is great for spotting iscaemia
What is the most appropriate imaging algorithm for an MRI for MS?
T2 flair - cancel out CSF (appears black), new lesions appear white
Or a T1 with galdonium contact (will not show old lesions as well)
What is an EEG for brain imaging?
Involves recording electrical potentials through the scalpy.
Electrical potentials relate to the activity in the cortex
Each electrode placed on the scalp and records the activity of 1000s of neurons.
Works in pairs to be compared to activity of others.
