Introduction and Imaging Flashcards
Apical
Pertaining to the tip or apex
Basal
Pertaining to the bottom or base
Rostral
Situated towards the nose or brow
Basilar
Pertaining to the skull base
Qualities of CT scan-
How does it work?
2D or 3D
Contrasting agent
X-ray based. Computer detects signal strength exiting opposing side of tissue.
Creates 2D image
Iodine used as contrasting agent in brain and neck
180 degree ar
CT advantages and disadvantages
Advantage
-Cheap relative to MRI
Disadvantages
- Joints and some tissues don’t age well
- Can only 1-2 times a year max
What colors are these structures in a CT scan and why?
Bone, Acute blood Enhanced tumor Subacute blood Muscle Grey matter White matter Cerebrospinal fluid Air, Fat
Dense structures appear white.
Medium density structures are grey
Low density structures are black
Sends signal. If it can go straight through = not dense. Black.
Sends signal. If it can’t go straight through = very dense. White.
Bone, Acute blood - very white Enhanced tumor - very white Subacute blood - light grey Muscle - light grey Grey matter - light grey White matter -medium grey Cerebrospinal fluid - medium grey to black Air, Fat - Very black
Which is more dense? White or grey matter?
Grey matter is more dense. Will appear lighter than white matter in CT scan
What does MRI stand for
Magnetic resonance imaging
How does MRI create a 2-dimensional image
Based on how Hydrogen atoms, or protons, spin.
The machine has a north and south pole used to create a magnetic field. The field causes Hydrogen atoms to spin in the same/specific direction instead of allowing them to spin freely. Once the magnetic field shuts off, the machine picks up how long it takes for the spin to go back to normal. The Hydrogen atoms give off energy as their magnetic field return to baseline.
T1 weighted MRI vs T2 weighted MRI
T1: Created from cancelled atoms returning to baseline.
T2: Created from enhanced atoms returning to baseline. Once the machine turns off, the Hydrogen atoms will try to go back to normal. Over time, one of the adjacent H atoms will change orientation slightly.
Is T1 weighted or T2 weighted MRI used more commonly?
T2 weighted. Especially for edema- produces a light brighter image.
What colors are these structures in an MRI and why?
Bone Air Muscle Grey matter White matter Fat Cerebrospinal fluid Edema Tumor Infarct Ischemia
Bone- Very black in T1 and T2
Air- Very black in T1 and T2
Muscle- Dark grey in T1 and T2
White matter- Light grey in T1 and dark grey in T2
Grey matter- Dark grey in T1 and light grey in T2
Fat- White in T1 and grey in T2
Cerebrospinal fluid- Very black in T1 and very white in T2
Tumor- Variable
Infarct (necrosis) - Dark grey in T1 and light grey/white in T2
Ischemia(artery blockage or build up)- Dark grey in T1 and light grey/white in T2
White mater is lighter than grey matter in ____ MRI
Grey matter is lighter than white matter in ____ MRI
T1
T2
Where is white and grey matter located at in the brain
White- Center
Grey- Peripheral (more dense)
What does MRA stand for
Magnetic resonance angiography
How does MRA work
Looks at vasculature in the neck or brain and can determine if there is stenosis (spinal narrowing) or plaque.
This is not ordered often and a little more expensive.
An alternative method used is ultrasound.
What is the basis of a fMRI
Functional MRI works by taking advantage of the higher magnetism of deoxyhemoglobin compared to oxyhemoglobin. Therefore, you can tell which areas of the brain require more or less oxygen meaning more or less metabolic activity. 2D.
Compare fMRI and PET Price Agents used Resolutions Duration/patient requirements
fMRI:
- cheaper due to use of MRI
- No radioactive or contrasting agent
- High resolution
- Complete stillness or 45 minutes. Lous.
PET:
- More expensive bc it requires a special machine
- Radioactive agent injected
- Low resolution
- Subject can move freely and only lasts 5-10 minutes.
When to order an x-ray
- Cheaper than a CT
- Fractured bones
- Tissue changes ex: tumor in lungs
- only need 2D image
What does PET scan stand for
Positron emission tomography
What is a PET scan
-A FANCY CT scan that is VERY expensive (5-10k)
Which 2 scans have the ability to track metabolic activity
PET scan through use of glucose
fMRI through use of deoxy and oxyhemoglobin
How does a PET scan work
When A mix of isotopes and glucose are injected into the body, metabolically active tissue will take up the glucose. Once the isotope begins to decay, the PET scan will pick up the released energy from the decay.
More metabolically active- more bright and vibrant colors.
When to ordre a PET scan
- Seizures
- TBI
- Schizophrenia
- Tumor/cancer cells
- Movement disorders
All of these will display an abnormal level of metabolic activity in the brain. Although expensive, this test is quick and the patient is allowed to move around more freely than compared to an fMRI.
