CT BRAIN for Medical and
Terminology used in CT.
• Section of the study (most commonly axial is
• Right and left side of the image.
• Density of a structure is taken relative to the
density of water and described as isodense,
hyperdense and hypodense.
• Location and anatomical structures involved.
• Should be able to formulate radiological
How to differentiate CT from MRI
• Bone is dense(white) on CT brain while hypo
intense(dark) on MRI(outer bright signals on
MRI are due to subcutaneous fats).
• Grey-white matter differentiation is clear on
MRI compared to the CT.
• Presence of periventricular lucent areas in
• MRI usually have multiple films compared to
commonly single in CT
• X-ray emitter and detector rotate in circular
• When radiation pass through exposed structure
they behave differently depending on the density
and physical properties.
• A visual representation of the raw data obtained
is called a sinogram which is raw form.
• The data must be processed using a form
of tomographic reconstruction which produces a
series of cross-sectional images.
• Unit used to measure the density are called as
• It can range on a scale from +3071 (most
attenuating) to −1024 (least attenuating) on
the Hounsfield scale.
• Contrast used for X-ray CT, as well as for plain
film X-ray, are called radiocontrasts.
Radiocontrasts for X-ray CT are, in general,
iodine-based. Often, images are taken both
with and without radiocontrast
• If you are pregnant or suspect that you may
be pregnant, you should notify your doctor.
Radiation exposure during pregnancy may
lead to birth defects
• Nursing mothers may want to wait 24 hours
after contrast material is injected before
• there is a risk for allergic reaction to the dye
• Patients with kidney failure or other kidney
problems should notify their doctor.
• patients taking the diabetes medication
metformin (Glucophage) should alert their
doctors before having IV contrast as it may
cause a rare condition called metabolic
When to prefer CT over MRI
• Trauma or acute emergency settings where
time is important.
• When ruling out bony injuries and bleeds that
are easily picked.
• Contraindications to MRI eg metallic objects.
• Claustrophobic patients.
• Cost and availibilty factors.
Modalities of CT used in brain
• Plain non contrast CT (with parenchymal and
• CT with contrast.
• CT perfusion.
• CT Angiogram.
• CT Venogram.
• CT with special cuts like orbit, Pituatrity fossa.
Anatomical Land marks.
• Cortex and division into various lobes.
• Subcortical structures including basal
• Pituatry area and cavernous sinus region.
• CSF system.
• Arterial and venous system.
• Two-dimensional CT images are
conventionally rendered so that the view is as
though looking up at it from the patient's feet.
• Hence, the left side of the image is to the
patient's right and vice versa, while anterior in
the image also is the patient's anterior and
Approach to CT
• Check name ,identification and date of study,
• Start from upper most or lower most cuts.
• Look from outside to inside or inside to
• Look for bones, sinuses,orbits.
• Extradural, subdural and meningeal details
and enhancement if contrast film.
Approach to the CT
• Look parenchyma for hypodensities
,hyperdensities, their location, shape,
homogenous/heterogenous,any mass effect
• Grey-white matter differentiation, any
enhacement if contrast film.
• Ventricles symmetry and cisterns any
• Contrast uptake.
• Choriod plexsus calcification and bone are the
do main hyperdensities that are present in
• Most commonly odema secondary to:
• Mass lesion.
• Fat containing structures.
• Paranasal sinuses and mastiod are structures that
are hypodense in normal cases.
Approach to the CT
• Explain the findings in systematic manner.
• Mention the Shape, size, density, location and
extent and any mass effects related to the
• Compare to the other side if applicable.
• Any contrast uptake.
• Formulate major or likely differentials related to
• What further imaging or test may be helpful to
clear likely diagnosis.
Causes of air
• Air filled spaces.
• Base of the skull fracture.
• Craniotomy or after other surgeries
Grey and white matter differentiation
• Normally Grey matter is outer denser
structure and white matter in inner
• Grey matter contains neurons cell bodies
while white matter contain axons with rich
fatty myelin sheath making it hypodense.
• This differentiation is loss in case of cerebral
Causes of cerebral odema
• Mass lesion.
• Metabolic causes.
• In true isolated cytotoxic oedema little change
is evident on CT as a mere redistribution of
water from extracellular to intracellular
compartments does not result in attenuation
changes. The changes colloquially ascribed to
'cytotoxic oedema' are in fact mostly due
to ionic oedema, and are described separately.
This is why brain CT is often normal in patients
with an acute ischaemic stroke.
• grey-white matter differentiation is
maintained and the oedema involves mainly
white matter, extending in finger-like fashion
• secondary effects of vasogenic oedema are
similar to cytotoxic oedema, with effacement
of cerebral sulci, with or without midline shift
Disoders of CSF spaces
• Hydrocephalus communicating and non
communicating including IIH,NPH.
• Loss of csf spaces usually secondary to
degenerative and other secondary processes.
• There are a number of different patterns of
cerebral herniation which describe the type of
• subfalcine herniation
• transalar herniation: ascending and descending
• transtentorial herniation
– downward: uncal herniation
– upward: ascending transtentorial herniation*
• tonsillar herniation*
• extracranial herniation
• Meningial enhancement and thickness,
extradural and subdural collection, with
associated communicating hydroceph.
• Focal parenchymal injury and abscess, mass
lesions with mass affects.
• Ventriculitis and diffuse cerebral odema.
• Tumors and masses.
• Congenital abnormalities.
• Toxic metabolic insults.
• Disections and aneurysms.
• Hypoxic injury.
• States where CT is useless.