10-18b Intro to Imaging: CT & MRI Flashcards
How does Computed Topography Work? What is its unit?
Diff from radiograph x-rays b/c it is a three dimensional x-ray
images taken axially (transverse plane), info sent to computer, which reconstructs the image in any of the three planes
voxel: 3D pixel
higher density, more white (absorbed to a greater extent)
How does Computed Topography Work? What is its unit?
Diff from plain films b/c it is a three dimensional x-ray (can see tissue thickness)
images taken axially (transverse plane), info sent to computer, which reconstructs the image in any of the three planes
voxel: 3D pixel
higher density, more white (absorbed to a greater extent)
What is an advantage to CTs over plain filims?
one can distinguish b/w m. and fat due to 3D nature
most to least dense: prosthesis cortical bone spongy bone m. blood water fat (negative) soft tissues lungs air
What is one of the ways CTs are used? What is the advantage?
acute head trauma
quickly acquired and more routinely used
quickly ruling things in and out
thromboembolytic stroke: clot and can use clot buster
hemorrhagic stroke: no clot buster (white)
What is the second thing CTs are useful for?
complex fractures
needs more info for contrast quantification
What is the advantage of lung windowing?
sets the level to the HU of the observed tissue of interest
narrowing of the scale allows view of more details like tumors and other abnormalities
What is the advantage of lung windowing?
sets the level to the HU of the observed tissue of interest
narrowing of the scale allows view of more details like tumors and other abnormalities
What does bone windowing help with?
helps distinguish b/w cortical bone and spongy bone
What are the advantages to CT?
Acute intracranial bleeding differentiation
good for observing subtle/complex fractures/degenerative diseases in bone (spinal stenosis)
More available, less expensive, and quicker than MRI and more info than radiographs
can view heterotophic ossification: calcification in a place it shouldn’t be
Disadvantages to CT?
not as good for soft tissue differentiation
larger exposure to radiation than radiographs
pretty short, but radiographs are shorter
What is the tech for MRIs?
Images are produced by the interaction of hydrogen containing molecules within tissues and a magnetic field produced by the magnet. (unique images are produced b/c each tissue has diff amt. of hydrogen and relax at different rates)
First, the hydrogen lines up with the field of the magnet
Second, a radio wave is delivered to the tissue which causes the hydrogen nuclei to absorb energy and change its alignment within the magnet (resonance).
The radio pulses are stopped, the absorbed energy is released and measured by the computer detector.
How do you read a T1 MRI?
subcutaneous fat is white due to enormous water content, then m., then bone is black
What are the two parameters for MRIs? What do these determine?
Repetition Time (TR): Time b/w two consecutive radio wave pulses
Echo Time (TE): is the time selected to wait after the start of the TR to receive the signal or “echo” from the patient.
The accentuation of different tissues
What causes diff quality images of same tissues?
length and sequence of the pulses
What will a shorter TE produce?
T1 weighted image
