Neuroradiology COPY Flashcards
What is plain film analysis used to evaluate? What does it detect?
structures of the skull, facial bones, and sinus Fractures; abnormal calcifications; developmental abnormalities; osteolytic disorders; osteoblastic disorders
CT & MRI imaging planes?
the horizontal (axial), coronal, and sagittal planes used to describe basic neuroanatomy
Sometimes the axial slices in CT scans are adjusted a few degrees off of the true axial plane. Why? (2 reasons)
-Enables the whole brain to be covered using fewer slices. -This procedure reduces radiation exposure to the eyes.
MRI axial slices are true horizontal slices: True or False
True
CT scans differ in what two ways from conventional X–rays?
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)
Four facts about the single-slice CT
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
On a CT scan, what does white represent?
dense structures, like bone
On a CT scan, what does black represent?
less dense materials, like air
On a CT scan, what does hyperdense refer to?
bright areas
On a CT scan, what does hypodense refer to?
dark areas
On a CT scan, what does isodense refer to?
intermediate density materials similar to brain tissue
On a CT scan, what shade is CSF?
Dark gray
On a CT scan, what color is fat tissue just outside the skull (subcutaneous)?
nearly black
On a CT scan, what color is white matter?
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)
Density in CT scans is often expressed in what unit?
Hounsfield units (HU) Water = 0 HU Air = –1000 HU
What do hemorrhages look like on a CT scan?
It depends on how old the hemorrhage is: Fresh intracranial hemorrhage shows up as a hyperdense area relative to brain tissue. One-week old hemorrhage looks isodense. Older hemorrhage (2-3 weeks) looks hypodense.
Are acute cerebral infarcts readily detectable on CT scans?
No, 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.
What does the cerebral infarct look like when it’s weeks to months old on a CT scan?
The brain tissue surrounding the infarct may shrink, producing a local area of prominent sulci or enlarged ventricles. Persistent areas of hypodensity may be the result of gliosis and brain necrosis with replacement by CSF.
What do neoplasms look like on a CT scan?
They may be hypodense, hyperdense, or isodense, depending on the type or stage.
What is helpful for visualizing neoplasms on a CT scan?
IV contrast dye
