Neuroradiology Free

**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