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Classification of Head CT After Trauma
Grading system for brain injury based on cistern compression and midline shift
Diffuse Injury Grade CT Appearance Mortality
I Normal intracranial appearance 9.6%
II Basal cisterns present. Midline shift <5mm. No lesions. 13.5%
III Basal cisterns compressed or absent. Midline shift <5mm. No lesions >25cc. 34%
IV Midline shift >5mm. No lesions >25cc. 56.2%
Hounsfield Units Scale
Table with radiodensity measurements of important structures on CT scan
Basic Densities Hounsfield Units
Air at STP -1000 Hounsfield basic density
Water 0 Hounsfield basic density
Fat -60 to -120 Hounsfield basic density
Compact Bone +1000 Hounsfield basic density
Cranial Structures
Brain (Grey Matter) +30 to +40
Brain (White Matter) +20 to +35
Cerebral edema +10 to +14
CSF +5
Cranial Bone +600
Blood clot +75 to +80

Acute SDH, EDH, SAH;

Hct<23% → isodense to brain
Enhanced vessels +90 to +100
MRI Abbreviations
Abbreviation Description
T1WI Spin-lattice relaxation time – expresses realignment time of tissue’s proton spin
T2WI Spin-spin relaxation time – time constant for transverse magnetization decay (true T2)
T2* Observed time constant of transverse magnetization decay (observed T2)
TR Repetition time
TE Echo time
TI Inversion time
FLAIR Fluid-attenuated inversion recovery
FSE Fast spin echo
STIR Short TI inversion recovery
Temporal Changes in Signal Characteristics for Blood on MRI
Time T1 Weighted Image T2 Weighted Image
Acute Gray Black
Subacute White White
Chronic Black Black

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