14. Medical Imaging & VEP Flashcards
X-rays are ... radiation which is detected by a ... placed behind the patient with a .... Soft tissues will give ...; bones give ... and dense muscular tissue give .... This result in bones appearing ... and soft tissues appearing ....
X-rays are body penetrating radiation which is detected by a film placed behind the patient with a anti-scatter grid. Soft tissues will give high exposure; bones give little to no exposure and dense muscular tissue give little to moderate exposure. This result in bones appearing white and soft tissues appearing dark.
What would X ray of the orbit show?
Ocular bone structures: circle of thin orbital bones and sinus, including eyebrow, bridge of nose and cheekbone
What are the reasons for visualising the orbital bones and sinuses with X-ray?
- After injury or trauma e.g. blowout fracture
- Changes to structure e.g. due to cancer: carcinoma
- Foreign bodies - some can embed further back in the eye
- Brain stem-spine/ CNS - observe gross change
- Used as a screening tool for metal foreign bodies prior to orbital MRI
Computed tomography (CT) scans uses ... and is the first .... The ... source produces a ... beam, where the source and the detectors ... the patient. Similar to X-rays, it is best at detecting ..., but can also image ....
Computed tomography (CT) scans uses X-ray and is the first 3D imaging technology. The X-ray source produces a fan beam, where the source and the detectors rotate around the patient. Similar to X-rays, it is best at detecting body structures, but can also image soft tissues.
If a visual field defect respects the vertical midline, what does it infer?
Defects that respect the vertical midline signifies that there is a cortical defect.
Magnetic Resonance Imaging (MRI) is results in high ... images and is great for ... tissues. MRI relies on the fact that human bodies are ... and therefore ... become aligned in a magnetic field. MRI applies a very strong ... (... to ...T) to .... MRI also applies a ... current that varies the magnetic field. Protons absorb energy from this ... and .... When turned off, the protons ..., but this process varies depending on ... and result in the emission of .... This emitted ... is used to create 2D images.
Magnetic Resonance Imaging (MRI) is results in high resolution images and is great for non-calcified tissues. MRI relies on the fact that human bodies are made up largely of water and therefore hydrogen/ protons become aligned in a magnetic field. MRI applies a very strong magnetic (1.5 to 3T) to align the proton spins. MRI also applies a radio frequency current that varies the magnetic field. Protons absorb energy from this variable current and flip their "spins". When turned off, the protons return to normal state, but this process varies depending on tissue density and result in the emission of RF energy. This emitted RF energy is used to create 2D images.
T1 and T2 both describe different aspects of how the .... after the applied ... pulse.
T1 is the ... and T2 is the .... T1 and T2 signals vary between ... resulting in .... To create different image types, image sequence varies the ..., which is the amount of time between ... and ..., which is the time between the ... and the receipt of the echo signal.
T1 and T2 both describe different aspects of how the protons return to equilibrium after the applied radio frequency pulse. T1 is the longitudinal relaxation time and T2 is the transverse relaxation time. T1 and T2 signals vary between tissues resulting in different image qualities. To create different image types, image sequence varies the Repetition Time (TR), which is the amount of time between successive pulse sequences applied to the same slice and Time to Echo (TE), which is the time between the delivery of the RF pulse and the receipt of the echo signal.
How do T1-weighted images and T2-weighted images differ?
T1-weighted images:
* Black = air, bone, calcium
* Dark = CSF, oedema, most lesions
* Grey = white & grey matter
* Bright = fat & blood
T2-weighted images:
* Black = air, calcium, bone
* Dark = white matter & grey matter
* Bright = CSF, blood, oedema, most lesions
FLAIR in MRI stands for ..., which is created by long ... and long .... Abnormalities remain ... but CSF is ....
FLAIR in MRI stands for fluid attenuation inverted recovery, which is created by long TE (echo time) and long TR (repetition time). Abnormalities remain bright but CSF is attenuated.
Diffusion weighted MRI imaging measures the ... within a voxel of tissue. This method is very good for visualising ....
Diffusion weighted MRI imaging measures the movement of water molecules within a voxel of tissue. This method is very good for visualising stroke.
Contrast mediums introduce substance with different ... to tissues.
In CT scans, ... and ... are used.
In MRI, ... is used, but water may also be sufficient for ....
Digital subtraction angiography (DSA) can be used in ... and .... The image of region take with ... is subtracted from ..., this therefore leaves a medium defined outcome for ... imaging.
Contrast mediums introduce substance with different attnetuation properties to tissues.
In CT scans, iodine and barium sulphate are used.
In MRI, gadolinium is used, but water may also be sufficient for stomach imaging.
Digital subtraction angiography (DSA) can be used in CT and MRI. The image of region take with medium is subtracted from image taken before injection of medium, this therefore leaves a medium defined outcome for vascular imaging.
PET scans stands for ... which utilise a small amount of ... injection, commonly ... (FDG). FDG gives off energy in form of ... and the scan shows where and how FDG sugar .... For example, ... require substantial sugar to grow, therefore this is used for .... The range of agent used depends on ... e.g. ... PET scan for Alzheimer’s disease.
PET scans stands for Positron Emission Tomography which utilise a small amount of liquid radioactive substance injection, commonly fluorodeoxyglucose (FDG). FDG gives off energy in form of gamma rays and the scan shows where and how FDG sugar is being utilised by the body. For example, tumours require substantial sugar to grow, therefore this is used for cancer imaging. The range of agent used depends on specific conditions being investigated e.g. amyloid-beta PET scan for Alzheimer’s disease.
Electrodiagnostic methods are used clinically for ... and also for determination of ... in uncooperative px, such as .... Scientifically, electrodiagnostic methods can ... determine properties and behaviours of ... and ....
Electrodiagnostic methods are used clinically for diagnosis or prognosis for diseases and also for determination of visual function in uncooperative px, such as infants and people with disability. Scientifically, electrodiagnostic methods can non-invasively determine properties and behaviours of retinal cells and visual pathways.
VEP is .... It is recorded using ... placed onto .... There are two basic grid patterns:
* ... (10/20) - either 10% or 20% of ..., which accounts for ...
* ... (QS) - 5cm steps along ...
VEP requires a ... stimulus because it is the ... that evokes a response
* Flash VEP - ...
* Pattern VEP - high contrast ... grating/ ... grid
VEP is visually evoked potential. It is recorded using skin electrodes placed onto bony reference landmarks. There are two basic grid patterns:
* Ten-twenty (10/20) - either 10% or 20% of total distance, which accounts for different head sizes
* Queen's square (QS) - 5cm steps along Z- or C-lines
VEP requires a varying stimulus because it is the change that evokes a response
* Flash VEP - flashes white light onto the retina
* Pattern VEP - high contrast sinusoidal grating/ checkerboard grid
VEP is used to test ... and .... PVEP P100 is used particularly for ... and ... disease, such as ..., where time delays are detected. Amplitudes of these responses ... due to the variability in .../ dipole directions/ ... of skin electrodes.
VEP is used to test visual pathway and visual cortex. PVEP P100 is used particularly for demyelination and inflammatory disease, such as multiple sclerosis, where time delays are detected. Amplitudes of these responses vary between individuals due to the variability in cortical folding/ dipole directions/ conductance of skin electrodes.
