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93 Cards in this Set
- Front
- Back
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When was CT imaging developed?
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1970's
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When were MRI scans developed?
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1980's
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Plain film analysis is used to evaluate...
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structures of the skull, facial bones, and sinus
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Plain film analysis is still used to detect...(5)
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fractures; abnormal calcifications; developmental abnormalities; osteolytic disorders; osteoblastic disorders
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CT & MRI imaging planes are similar to...
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the horizontal (axial), coronal, and sagittal planes used to describe basic neuroanatomy
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Sometimes the axial slices in CT scans are adjusted a few degrees off of the true axial plane. Why? (2 reasons)
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This enables the whole brain to be covered using fewer slices. This procedure also reduces radiation exposure to the eyes.
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MRI axial slices are usually true horizontal slices: True or False
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True
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Scout, or localizer images do what?
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They help the CT or MRI viewer see where the image slices are. These images should be included on all CT/MRI scans so that the exact angles can be documented.
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CT was developed directly from what technology?
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X-ray technology. So, similarly, CT measures the density of tissue.
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CT scans differ in what two ways from conventional X-rays?
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1) Rather than taking only one view, the CT X-ray beam is rotated around the patient and takes many different views; 2) The CT X-ray data are reconstructed by a computer to obtain a detailed image of all the structures in the slice (e.g., liquid, air, bone, soft tissue)
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Four facts about the single slice CT
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1) the scanner is shaped like a large ring; 2) the patient lies on the table & moves through the ring in small steps; 3) at each stop, X-rays are scanned through the patient and picked up by detectors on the opposite side of the ring; 4) the amount of energy absorbed depends on the density of the tissues traversed
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Three facts about the Helical CT
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1) the patient does not have to stop when moving through the scanner; 2) instead of single slices, up to 4 rows of detectors provide multiple overlapping slices; 3) These advances greatly improved the resolution and speed of the CT scan
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On a CT scan, white represents...
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dense structures, like bone
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On a CT scan, black represents...
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less dense materials, like air
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On a CT scan, hyperdense refers to...
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bright areas
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On a CT scan, hypodense refers to...
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dark areas
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On a CT scan, isodense refers to...
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intermediate density materials similar to brain tissue
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What color is CSF on a CT scan?
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Dark gray
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What color is fat tissue (subcutaneously just outside the skull) on a CT scan?
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nearly black
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What color is white matter on a CT scan?
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Slightly darker than celluar gray matter due to its high myelin content (gray matter is slighly lighter than white matter due to its high water content)
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Density in CT scans is often expressed in what unit?
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Hounsfield units (HU)
Water = 0 HU Air = -1000 HU |
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What do hemorrhages look like on a CT scan?
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It depends on how old the hemorrhage is.
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What does a fresh intracranial hemorrhage look like on a CT scan?
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It shows up as a hyperdense area relative to brain tissue.
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What does a one-week-old hemorrhage look like on a CT scan?
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isodense
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After a hemorrhage is 2-3 weeks old, what does it look like on a CT scan?
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hypodense
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Acute cerebral infarcts are readily detectable on CT scans: True or False
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False. Acute infarcts (the first 6-12 hours) are often not seen on CT scans. After 12 hours, cell death and edema lead to an area of hypodensity seen in the distribution of the occluded artery.
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What does a cerebral infarct that is weeks to months old look like on a CT scan?
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The brain tissue surrounding the infarct may shrink, producing a local area of prominent sulci or enlarged ventricles. However, persistent areas of hypodensity may be the result of gliosis and brain necrosis with replacement by CSF.
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What do neoplasms look like on a CT scan?
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They may be hypodense, hyperdense, or isodense, depending on the type or stage.
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What is helpful for visualizing neoplasms on a CT scan?
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intravenous contrast dye
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How do you detect mass effect on a CT scan?
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Look for localized compression of ventricles, effacement of sulci, or distortions in other brain structures (e.g., herniations)
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How does intravenous contrast in CT scans work?
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The contrast material contains iodine which is denser than brain and will therefore appear hyperdense in areas of increased vasularity or breakdown of the blood-brain barrier. Often, images are obtained with and without contrast for comparison.
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What is one caveat regarding intracaranial hemorrhage and CT contrast?
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In suspected intracranial hemorrhage, it is very important to obtain a NONCONTRAST CT scan b/c small hemorrhages often appear on CT scans as whitish areas at the base of the brain. These areas could be masked by the normal hyperdense contrast material.
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What is myelography?
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A combination of a CT scan with a procedure in which a needle is introduced into the CSF which sends a contrast dye into the CSF. This allows for a better visual of nerve roots and impingements on the spinal CSF space.
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For a head trauma, which is better, CT or MRI?
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CT
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For lower cost, which is better, CT or MRI?
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CT
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For a subtle tumor or infarct, which is better, CT or MRI?
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MRI
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For a brainstem lesion, which is better, CT or MRI?
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MRI
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For a fresh hemorrhage, which is better, CT or MRI?
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CT
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For an old hemorrhage, which is better, CT or MRI?
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MRI
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When speed is needed, which is better, CT or MRI?
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CT
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When there is a skull fracture, which is better, CT or MRI?
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CT
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When a person has a pacemaker, which is better, CT or MRI?
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CT
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When anatomical detail is needed, which is better, CT or MRI?
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MRI
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When assessing low-contrast or small lesions such as MS plaques or low-grade astrocytomas, which is better, CT or MRI?
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MRI
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What is the only cranial nerve observable by CT scan?
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optic nerve
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In a non-urgent situation in which a single more definitive image method is desired, which is better, CT or MRI?
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MRI
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Which is better for first screening for head trauma or supsected intracranial hemorrhage, CT or MRI?
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CT
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MRI was developed from...
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Nuclear magnetic resonance.
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What happens during an MRI?
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A poweful magnetic field is applied that causes protons in the person to align their intrinsic spins in parallel with the magnetic field.
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Which protons are the ones relevant to conventional MRI?
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those protons forming hydrogen nuclei
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Brighter areas on an MRI are known as...
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hyperintense
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Darker areas on an MRI are known as...
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hypointense
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T1-weighted versus T2-weighted MRI images
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T1- looks like an anatomical brain section; it is better for identifying anatomy because the resolution is better.
T2- looks like a film negative; it is better for detecting pathological changes because while the resolution is poor, the contrast is good |
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Gray Matter appearance on T1- vs. T2-weighted MRI
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T1- Gray
T2- light gray |
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White Matter appearance on T1- vs. T2-weighted MRI
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T1- white (bright)
T2- dark gray |
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CSF/water appearance on T1- vs. T2-weighted MRI
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T1- Black
T2- white |
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Fat appearance on T1- vs. T2-weighted MRI
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T1- White
T2- Black |
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Air appearance on T1- vs. T2-weighted MRI
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T1- black
T2- black |
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bone/calcification appearance on T1- vs. T2-weighted MRI
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T1- black
T2- black |
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Edema appearance on T1- vs. T2-weighted MRI
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T1- Gray
T2- White |
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Demyelination/gliosis appearance on T1- vs. T2-weighted MRI
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T1- Gray
T2- White |
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In Proton density weighted images (a.k.a. first echo images)...
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The contrast between gray & white matter is reduced. But it is better at detecting abnormalities in the parenchyma such as small areas of edema or infarction.
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What are two factors that affect the intensity of MRI images/signals?
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1) the amount of hydrogen protons
2) Metallic implants can distort images |
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Intracranial hemorrhage on MRI: What is the characteristic course?
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1) On both T1 and T2, acute hemorrhage is hard to see b/c it is gray and looks like CSF
2) subacute hemorrhage looks white 3) Chronic hemorrhage looks dark. They also usually have a bright center with a dark rim. |
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Neuroangiography: definition
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The study of the central nervous blood vessels and related vasculature using radiographs during injection of a intravascular contrast medium. It is the gold standard for evaluating vasular diseases in the head, neck, & spine.
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Before the advent of MRI & CT, neuroangiography was used to...
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detect slight distortions in the patterns of blood vessels suggestive of intracranial mass lesions
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Now, neuroangiography is used to...(2)
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1) visualize lesions of blood vessels
2) assess the vascular anatomoy of tumors when planning neurosurgery |
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Lesions optimally seen by angiography include:
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Atherosclerotic plaques and other vessel narrowings
aneurysms AVMs |
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Is angiography invasive?
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Yes: It requires local anesthesia and catheter insertion, typically in the femoral artery
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Provide three techniques for visualizing blood vessels that are less invasive than an angiography:
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1) Doppler ultrasound
2) Magnetic Resonance Angiography (MRA) 3) Spiral CT Angiography (CTA) However, these techniques are not as sensitive or specific. |
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Doppler ultrasound: definition
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used to measure flow and lumen diameter of large blood vessels in the head & neck; it is best for assessing atherosclerotic narrowings & is not good at detecting aneurysms or other vascular abnormalities
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Magnetic Resonance Angiography (MRA): definition
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detects direction and speed of blood flow; major vessels can be seen but smaller, branches cannot; it is used to detect decreased or absent arterial blood flow caused by atherosclerotic narrowing, thrombosis or dissection; can detect some aneurysms
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Spiral CT angiography (CTA):
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involves the rapid injection of IV contrast in conjunction with a helical CT to obtain images of blood vessels quickly; it can be used in patients where an MRA is contraindicated
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Therapeutic Neuroradiography (3)
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1) Wada Test
2) Treatment of brain aneurysms and AVMs- fill them with glue-like material via the angiography catheter 3) Stroke- current trials are underway in which thrombolytic agents are infused at the site of a clot to try and reestablish perfusion |
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Ultrasonography: definition
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Uses sound waves above audible levels to generate diagnostic medical images
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When is ultrasonography indicated?
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When the target area is not blocked by bone or air. It is very useful in pediatrics b/c of the lack of ionizing radiation.
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Ultrasonography is not useful for detecting...
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extra-axial hemorrhages, masses, or white matter
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In adults, ultrasonography can be used to detect...
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vascular lesions of the head and neck
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EEG
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It is the original method for measuring brain activity and is useful in evaluating for seizure activity and in detecting widespread abnormality in brain function.
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Is an EEG good at detecting focal brain lesions?
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No. Its sensitivity and spatial resolution for detecting focal brain lesions is poor.
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Evoked potential
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It is similar to an EEG. The brain's electrical activity is recorded in response to specific stimuli.
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Name five imaging techniques that produce images based on blood flow or dynamic blood flow volume (i.e., metabolic activity):
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1) Xenon regional cerebral blood flow mapping (Xe rCBF);
2) Positron Emission Tomography (PET); 3) Single photon emission computerized tomography (SPECT); 4) Dynamic contrast functional MRI (perfusion MRI); 5) Blood oxygen level dependent functional MRI (BOLD fMRI) |
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What neuroimaging technique based on metabolic activity is particularly useful in evaluating brain tumors?
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PET scans: high grade neoplasms demonstrate increased metabolism while low grade neoplasms demonstrate decreased activity.
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Name four functional MRI (fMRI) techniques:
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1) Perfusion MRI;
2) BOLD fMRI; 3) Diffusion MRI; 4) Magnetic Resonance Spectroscopy (MRS) |
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How does Perfusion MRI work?
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It involves the rapid injection of gadolinium and rapid measurements with "echo planar" imaging to produce an image of dynamic blood volume.
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How does BOLD fMRI work?
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It measures relative changes in oxy- and deoxyhemoglobin, which occur with changes in regional cerebral blood flow.
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How does Diffusion MRI work?
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It uses rapid echo planar imaging and strong gradients to measure the diffusion coefficient of water in brain tissue.
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How does MRS work?
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It can be used to detect local concentrations of certain chemicals in the brain including some neurotransmitters.
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Which fMRI technique may eventually replace the WADA test?
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BOLD fMRI
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Which fMRI technique can detect early areas of ischemia long before conventional MRI imaging?
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Diffusion MRI
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Ictal-Interictal SPECT Difference Imaging:
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It can be used to indirectly measure regional brain activity during seizures and to help localize their region of onset.
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What does Ictal-Interictal SPECT Difference Imaging look like between seizures?
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It shows decreased regional cerebral blood flow between seizures.
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What does Ictal-Interictal SPECT Difference Imaging look like ictally?
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It shows increased regional cerebral blood flow ictally.
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