Flashcards in Lecture 6: Neuroradiology Deck (9):
Roughly explain the functioning of a computed tomography.
An x-ray beam rotates around the head of a patient with detectors measuring the amount of x-ray that makes it through the body.
Name advantages and disadvantages of CT.
Advantages: fast, non-invasive, no contra-indications, good contrast for bone, air, CSF, fat, blood and calcification.
Disadvantages: suboptimal contrast for grey and white matter, x-ray contamination.
By definition, what is the Houndfield Unit (HU) of water? What does the HU measure?
The HU of water is 0. It measures the density relative to water.
Roughly explain the functioning of an magnetic resonance imaging scanner.
A magnetic field is used to align hydrogene protons in the body. Radio frequency waves are absorbed by the protons and then emitted as a signal. A radio frequency coil picks up the signal and transmits it to the computer. The computer processes the data and an image is generated.
Describe the main differences seen in MRI being either T1 or T2 weighted.
In T1 weighted scans, tissue with lower density is darker (e.g. CSF being black) while tissue with higher density appears brighter (e.g. white matter).
In T2 weighted scans, tissue shows the exact opposite pattern with high-density tissue being darker than low-density tissue.
Name advantages and disadvantages of MRI.
Advantages: good contrast for grey and white matter, fat and CSF, unlimited slice orientation.
Disadvantages: slower than CT, contra-indications (e.g. pacemaker), not always available, low contrast for bone, air and metal.
What are indications for T1-weighted scans, in comparison to T2-weighted scans.
T1: anatomical information
T2: pathological signal
Name the main differences in characteristics of an epidural and a subdural bleeding.
Epidural: mostly lense-shaped, involvement of middle meningeal artery, often due to traumatic skull fracture, seen in younger people.
Subdural: mostly crescent-shaped, venous in origin, not always traumatic, mostly seen in elderly and very young (baby).