Radiology lecture 1 – Introduction to Radiology
• CT:
o Used to visualize bone
o Trauma/fractures à contusions, brain herniations, soft tissue injuries
o Head and neck imaging
o Sinus diseases as well as temporal bone diseases
o ANGIOGRAPHY
§ Thrombi, etc
o Perfusion
§ Evaluate strokes
o Tumors
o WHERE YOU CAN’T USE MRI
o Superior sensitivity and specificity
§ Sensitivity: TRUE POSITIVES (can identify the diseased correctly)
§ Specificity: TRUE NEGATIVES (can identify the non-diseased correctly)
o Bone shows up bright, CSF is dark. Blood is bright. Infarcts are dark.
• MRI
o NO RADIATION (magnetic RESONANCE imaging)
o Neoplasms, ingection, hemorrhage, seizures, neurodegenerative disorders,
congenital anomalies
o T1
§ time in which the magnetization recovers
§ depends on SIZE of molecule
• Fatty acids, short t1 , brighter signal
• Water + protein, long t1, darker signal
• CSF: dark gray
• Gray matter è medium gray
• White matter è light gray
§ Poor contrast between normal / pathological
§ Lesions have increased water content therefore they are
HYPOINTENSE (darker signal)
o T2
§ time in which the protons DEPHASE
§ depends on how close to water / homogenous the magnetic field is
• Simple liquids à closest to water à longer T2 à brighter
• WATER/CSF IS BRIGHTEST
• Gray matter à light gray
• White matter à Dark gray
• Bone is DARK
§ Good contrast between normal and pathological
§ Lesions have increased water à brighter.
§ Bone is dark, as well as calcifications and fibrous tissue
, o HOW CAN YOU TELL IF IT IS T1 / T2 è look for CSF. CSF is white, then it is T2.
o FLAIR
§ Is a t2 image that suppresses the CSF signal
§ CSF à black
§ Gray matter à light gray
§ White matter à dark gray
§ Whats the point? è FLAIR increases the difference between the
bright CSF signal by suppressing it, and leaving the only brightness to
the lesions.
• STIR è Suppress the fat signal
• GRE
§ Gradient recall echo
§ Most sensitive technique for acute hemorrhage
§ Flowing blood à hyperintense
§ Hemorrhage à hypointense
• DWI
§ Diffusion weighted à seeing the random movement of molecules
§ The more the water moves, the darker the signal
§ Vasogenic edema + fluid collections à increase water motion à
Darker signal
§ Intracellular edema and hypercellular tumors à decrease water
motion à lighter signal
§ You can use a modified DWI called DTI to track axons
• Contrast
o CT – use iodine because it strengthens photons
o MR – use gandolinium as it reduces T1 times (brightens the signal)
o Shows the vessels/regions where blood – brain barrier is broken
• CT:
o Used to visualize bone
o Trauma/fractures à contusions, brain herniations, soft tissue injuries
o Head and neck imaging
o Sinus diseases as well as temporal bone diseases
o ANGIOGRAPHY
§ Thrombi, etc
o Perfusion
§ Evaluate strokes
o Tumors
o WHERE YOU CAN’T USE MRI
o Superior sensitivity and specificity
§ Sensitivity: TRUE POSITIVES (can identify the diseased correctly)
§ Specificity: TRUE NEGATIVES (can identify the non-diseased correctly)
o Bone shows up bright, CSF is dark. Blood is bright. Infarcts are dark.
• MRI
o NO RADIATION (magnetic RESONANCE imaging)
o Neoplasms, ingection, hemorrhage, seizures, neurodegenerative disorders,
congenital anomalies
o T1
§ time in which the magnetization recovers
§ depends on SIZE of molecule
• Fatty acids, short t1 , brighter signal
• Water + protein, long t1, darker signal
• CSF: dark gray
• Gray matter è medium gray
• White matter è light gray
§ Poor contrast between normal / pathological
§ Lesions have increased water content therefore they are
HYPOINTENSE (darker signal)
o T2
§ time in which the protons DEPHASE
§ depends on how close to water / homogenous the magnetic field is
• Simple liquids à closest to water à longer T2 à brighter
• WATER/CSF IS BRIGHTEST
• Gray matter à light gray
• White matter à Dark gray
• Bone is DARK
§ Good contrast between normal and pathological
§ Lesions have increased water à brighter.
§ Bone is dark, as well as calcifications and fibrous tissue
, o HOW CAN YOU TELL IF IT IS T1 / T2 è look for CSF. CSF is white, then it is T2.
o FLAIR
§ Is a t2 image that suppresses the CSF signal
§ CSF à black
§ Gray matter à light gray
§ White matter à dark gray
§ Whats the point? è FLAIR increases the difference between the
bright CSF signal by suppressing it, and leaving the only brightness to
the lesions.
• STIR è Suppress the fat signal
• GRE
§ Gradient recall echo
§ Most sensitive technique for acute hemorrhage
§ Flowing blood à hyperintense
§ Hemorrhage à hypointense
• DWI
§ Diffusion weighted à seeing the random movement of molecules
§ The more the water moves, the darker the signal
§ Vasogenic edema + fluid collections à increase water motion à
Darker signal
§ Intracellular edema and hypercellular tumors à decrease water
motion à lighter signal
§ You can use a modified DWI called DTI to track axons
• Contrast
o CT – use iodine because it strengthens photons
o MR – use gandolinium as it reduces T1 times (brightens the signal)
o Shows the vessels/regions where blood – brain barrier is broken
