ND - Medical Imaging and VEP - Week 4 Flashcards
What is an alternate name for the coronal plane in imaging?
Frontal plane
What kind of exposure does tissue and bone give in an x-ray film?
Bone - little to no exposure
Tissue - high exposure
What kind of exposure does dense tissue such as muscle give in an x-ray film?
Little to moderate exposure
Are x-rays mutagenic?
Yes
What kind of resolution is given by an x-ray?
Coarse
What is the first 3D imaging technique?
CT scan
How are CT scans carried out and with what kind of beam?
X-rays in a fan beam, which rotates
What kind of resolution is given by an MRI scan and what kind of tissue is it good for?
High resolution images
Great for non-calcified tissue
List the basic principles behind how an MRI scan works (7).
-Body is made up largely of water
-Hydrogen nuclei become aligned in the magnetic field
-MRI applies a strong magnetic field to align the proton spins
-A radio frequency is applied that varties the magnetic field
-Protons absorb energy from this variable current and flip spin states
-When turned off, the proton return to ground state, which varies depending on tissue density and results in the emission of RF energy
-A 2D image is reconstructed from this emitted energy
Define the two components of a structural MRI. Explain what they describe. Do these signals vary between tissue? What does this result in?
T1 - longitudinal relaxation time
T2 - transverse relaxation time
Both describe different aspects of how the protons return to equilibrium after RF is pulsed
They vary between tissues resulting in different image qualities
Explain how different image types are created with an MRI.
Image sequence varies the repetition time and time to echo
Define repetition time.
Amount of time between successive pulse sequences on the same slice
Define time to echo.
The time between the delivery of the RF pulse and the receipt of the echo signal
What structures have the following colour on a T1-weighted image:
Black (3)
Dark (3)
Grey (2)
White (2)
Black
-air
-bone
-calcium
Dark
-cerebrospinal fluid
-oedema
-most lesions
Grey
-grey/white matter
White
-fat
-blood
What structures have the following colour on a T2-weighted image:
Black (3)
Dark (2)
White (4)
Black
-air
-calcium
-bone
Dark
-grey/white matter
White
-cerebrospinal fluid
-blood
-oedema
-most lesions
Define FLAIR in MRI structural imaging. What is it created with (2) and what does it result in (2)?
Fluid attenuation inverted recovery
Created by long time to echo and long repetition times
Abnormalities remain but CSF is attenuated
What does diffusion weighted imaging for MRI measure and what condition is it good for?
Measures the movement of water molecules within a voxel of tissue
Very good for visualising stroke
Describe the basic principles of 1H magnetic resonance spectroscopy (4).
Each proton can be visualised at a specific chemical shift
This depends on its chemical environment
It is dictated by neighbouring protons within the molecule
Metabolites can be characterised by their unique set of 1H chemical shifts.
What does magnetic resonance spectroscopy allow for? What benefit does this have?
Allows chemical composition analysis of an area of the brain to be determined
This can lead to better development of cancer medicine (different tumours have different metabolic composition)
What are contrast media?
A substance with different attenuation properties to tissue
List two examples of contrast media and what kind of imaging technique they are used for.
Iodine, barium sulphate (CT)
Gadolinium (MRI)
Describe how digital subtraction angiography is carried out.
Image of a region taken with contrast media is subtracted from image taken before contrast media, leaving medium defined outcome
What is digital subtraction angiography good for when coupled with CT scans? What about when coupled with MRI?
CT - good for vessels
MRI - good for vascular rich structures
Describe how PET scans work (3). What is it good for imaging? What is given to the patient beforehand?
Small amount of liquid radioactive substance is injected - most commonly fluorodeoxyglucose
It gives off energy as gamma rays
PET scans show how/where sugar is being used by the body
Tumours need a lot of sugar, so it is good for cancer imaging
Which kind of patients can electrodiagnostic methods be particularly useful?
Uncooperative patients
-infants
-special needs/disability
List three components of an electroencephalogram.
Visual evoked potential
Visual evoked response
Visual evoked cortical potential
How is a visual evoked potential carried out and in reference to what?
Skin electrodes placed in reference to bony landmarks
What types of stimuli are used when measuring visual evoked potential and why?
A varying stimulus because it is the change that evokes a response
What does a visual evoked potential measurement test (2)?
It tests the visual pathway and visual cortex
What responses are amplified in a visual evoked potential?
Macular responses
What are visual evoked potentials serial to?
ERG
Consider an ERG. What does P50 and N95 correspond to and what conditions can it be useful for?
P50 - inner retina - maculopathy
N95 - ganglion cells - optic neuropathy
What are the fullfield ERG, P50 ERG, and VEPs like in diseases that affect the macula?
Normal fullfield ERG
Abnormal ERG P50
Delayed pattern VEP
What are the fullfield ERG, P50 ERG, and VEPs like in diseases that affect retinal ganglion cells?
Normal fullfield ERG
Abnormal ERG N95
Delayed, abnormal pattern VEP
Consider a patient with unexplained vision loss who has abnormal pattern VEP and normal PERG. What is a possible disease they have?
Optic nerve dysfunction
Consider a patient with unexplained vision loss who has abnormal pattern VEP, abnormal PERG, normal P50, and abnormal N95. What is a possible disease they have?
Optic nerve dysfunction
Consider a patient with unexplained vision loss who has abnormal pattern VEP, abnormal PERG, abnormal P50, and normal ERG. What is a possible disease they have?
Macular dysfunction
Consider a patient with unexplained vision loss who has abnormal pattern VEP, abnormal PERG, abnormal P50, and abnormal ERG. What is a possible disease they have?
Retinal dysfunction
