Radioimaging of Brain and brainstem
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| Advantages of CT | Very fast imaging…seconds to minutes. (emergency situations) Post-processing reconstruction in multiple planes. Called multiplanar reconstruction (MPR) Patient does not have to be present Can be used in patients with implanted devices (unlike MRI).
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| Disadvantage of CT | Uses ionizing radiation (x-rays)
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| What are HUs? | Hounsfield Units (H.U.) Density measurement of a chosen area. 4,096 different shades of grey from pure white to pure black (+3071 to -1,024 Hounsfield units).
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| HUs of Gray vs. White? | Gray-35 HU White 25 HU
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| Hypodense vs. Hyperdense vs Isodense | Hypodense = decreased attenuation = dark Isodense = same attenuation Hyperdense = increased attenuation = white
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| CT requires contrast? | no, can be done with or without
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| Why are CT contrasts used? | Iodinated contrast agent injected I.V. (or intra-arterial). …Iodine molecules attenuate x-rays = white …Identify vasculature and vascularity. …Normal & abnormal tissues enhance differently.
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| What are contrast problems with CT | Potential problems rare: Allergic reaction Renal dysfunction
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| CSF vs. gray matter which is more attenuated (higher)? | gray
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| Skull is low or high density? | high
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| MRI made via what ? | magnetic field and radiofrequency
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| What is a high signal seen as? | bright (white)
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| What is low signal seen as? | dark
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| Advantages of MRI | Don't need iodinated contrast agent Great detail of soft tissue Can scan in any plane No ionizing radiation, so pretty safe
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| What contrast agent is occasionally used in MRI? | Gadolinium
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| Disadvantages of MRI | Scan time is long, so some pts automatically can't use it Implanted devices could malfunction Magnetic metals in pt? MRI can't be used
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| MRI: T1 | CSF is low signal
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| MRI: T2 | CSF is high signal
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| MRI: Pathology T2 or T1? | T2-most pathology has higher water content
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| MRI: Flair | Keeps CSF dark, but its a pathological finding of MRI
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| MRI: diffusion sequences | Very early ischemic stroke detection
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| White areas of MRI= | High signal
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