Alternate Imaging: CT and MRI Flashcards
CT stands for
Computed Tomography (CAT Scan)
MRI stands for
Magnetic Resonance Imaging
Imaging that depicts a slice of the body
free from superimposition of overlying structures
Tomography
What are the 3 tomographic modalities?
CT
MRI
US (Ultrasound)
A 2D tiny square that represents the average number of
a voxel of tissue
Pixel
A 3D block of tissue represented on an image matrix
by a pixel and determined by the product of
pixel size and the thickness of the scan slice
Voxel
A voxel on an MRI represents
signal intensity
A voxel on a CT represents
the Hounsfield unit
Voxels on MRI depend on
transverse magnetization
Voxels on CT depend on
linear attenuation coefficient of tissue
Which tomographic modality would you use for
soft tissue evaluation?
MRI
Which tomographic modality would you use for
bone and lung evaluation?
CT
Which tomographic modality is the Gold Standard
for thoracic metastasis?
CT
How is long scale of contrast achieved on CT?
WIDE window
for low contrast
How is short scale of contrast achieved on CT?
NARROW window
for high contrast
How is a black area on a CT described?
Described as:
hypodense or hypoattenuating
How is a white area on a CT described?
Described as:
Hyperdense or hyperattenuating
Why would you CT a thoracic mass?
To see if it has metastasized
Which tomographic modality has
the highest levels of radiation exposure?
CT
Which tomographic modality is better for soft tissue detail?
MRI
How is a black area on an MRI described?
Described as Hypointense
How is a white area on an MRI described as?
Described as Hyperintense
What is the difference between a T1 and T2 MRI?
During the process of T1 relaxation,
protons reorient resulting in recovery of longitudinal magnetization.
During the process of T2 relaxation,
protons dephase (spin becomes desynchronized) resulting in decay of transverse magnetization.
Which MRI weighted imaging technique is best for
Anatomical overview?
T1
Which MRI weighted imaging technique is best for
diagnosis of pathology?
T2
T1 vs. T2 MRI:
Edema is dark in ____
T1
T1 vs. T2 MRI:
Edema is bright white in _____
T2
T1 vs. T2 MRI:
Free fluid is ______ on T1
dark
T1 vs. T2 MRI:
Free fluid is ____ on T2
bright
T1 vs. T2 MRI:
Fat is ____ on T1
bright
T1 vs. T2 MRI:
Fat is _______ on T2
intermediate gray
What does STIR stand for?
Short T1 Inversion Recovery
What does FLAIR stand for?
Fluid Attenuated Inversion Recovery
What type of MRI inversion recovery technique
would you use if you wanted to
selectively suppress fat (signal void black)?
STIR
What type of MRI inversion recovery technique
would you use if you wanted to
selectively suppress pure fluids (signal void black)?
FLAIR
What type of MRI inversion recovery technique
was used if free fluid appears WHITE?
STIR
What type of MRI inversion recovery technique
would you use if you wanted to
distinguish fat from fluids/edema?
STIR
(fat signal is removed,
fat appears black and edema appears white!)
What type of MRI inversion recovery technique
would you use if you wanted to
distinguish free fluid from edema?
FLAIR
(Free fluids appear black and edema appears white!)
