Imaging Anatomy of the CNS

Basic Imaging Types X-ray CT (Computed Tomography) MRI (Magnetic Resonance Imaging) Angiography

X-ray Limited Use Evaluation of: Bones, fractures Calcification

X-ray

Computed Tomography

What is CT? X- ray study, therefore has risks. Beams of X-ray are shot through object, and received on the other side. This is done in a 360o manner. Computer reconstructions of each 360o turn gives us each image “slice”. Based on tissue density. Sections only in axial plane.

Magnetic Resonance Imaging

What is MR? Not an X-ray, electromagnetic (similar to microwave) Electromagnetic field aligns all the protons in the brain. Radiofrequency pulses cause the protons to spin. Amount of energy emitted from the spin is proportional to number of protons in the tissue. No ferromagnetic objects.

Angiography

Angiography Real time X-ray study Catheter placed through femoral artery is directed up aorta into the cerebral vessels. Radio-opaque dye is injected and vessels are visualized Gold standard for studying cerebral vessels.

Angiography AP Right ICA Lateral Right ICA

Angiography AP Right Vertebral

Planes of Section Axial (transverse) Sagittal Coronal (frontal) Oblique

What is an AXIAL section?

CT without contrast

Lateral ventricles

CT with contrast

CT bone window

Brain CT… Note that we take axial slices beginning from the skull base., parallel to a standard line (orbito-meatal or canthomeatal line). The thickness of the slice (the distance between a slice –picture- and the following slice –picture-) is 10mm or as determined. The skull base is a bony area with much small details, so we take the slices with less thickness (5mm) to show al the details. You have to recognize the following: 1- Cerebral hemispheres 2- Brainstem 3- Ventricular system 4- Basal ganglia and thalamus 5- Basal cisterns (subarachnoid space)

Cerebral Hemispheres (Lobes) & Brain Stem… Lobes in the cerebral hemispheres are the frontal, temporal, parietal, and occipital lobes. Note that the white matter appears grey, and the grey matter appears white. Brainstem is composed of the midbrian, pons & medulla oblongata.

Ventricular System… It is composed of the lateral ventricles, 3rd ventricle and the 4th ventricle. Remember that the ventricles contain the choroid plexuses which maybe normally calcified so appears white in CT. The lateral ventricle is composed of the frontal horn (anterior horn), ventricular body, occipital horn (posterior horn) and the temporal horn (inferior horn). Normally, the temporal horns can’t be seen in CT. So, when they appear we call them “prominent temporal horns”; If they are dilated, this indicates hydrocephalus. 4th ventricle is situated behind the pons.

Basal Ganglia & Thalamus… You need to recognize: 1- thalamus 2- caudate nucleus 3- lentiform nucleus 4- internal capsule (it’s anterior limb and it’s posterior limb)

Basal Cisterns (Subarachnoid Space)… They contain cerebrospinal fluid (CSF), so they normally appear black in brain CT. Basal cisterns are: 1- prepontine cistern 2- cerebellopontine cistern 3- interpeduncular cistern 4- ambient cistern 5- quadrageminal cistern 6- sylvian cistern (sylvian fissure)

CT Brain Bone Window… It’s done by just giving an order for the CT machine to give us a CT brain- bone window. You have to recognize the following: 1- Frontal, parietal, temporal & occipital bones (Bone appears white on CT scan). 2- Bone sinuses (Sinuses are full of air)

MRI Weighting T1 Weighted MRI T2 Weighted MRI

Axial T1

Axial T2

Axial FLAIR

Diffusion

Axial T1 with contrast

Brain MRI Most brain lesion are seen by T2 or FLAIR MRI. Usually, we use T1 MRI to visualize brain anatomy, while T2 MRI & FLAIR is used for visualizing brain pathology.

Coronal T1 with contrast

Coronal Brain MRI You have to recognize: 1- sella turcica: which contains the pituitary gland 2- cavernous sinus 3- sphenoidal sinus 4- optic chiasma

Body of lateral ventricle Sagittal T1 with contrast Genu Splenium Rostrum 4th ventriclr Sagittal T1 with contrast

Sagittal Brain MRI… In a sagittal MRI, you have to recognize: The Corpus callosum that is composed of: rostrum, genu, body and splenium.

Neck MRA

Brain MRA

Brain MRA

Brain MRA

Sagittal T1 Cervical spine

Sagittal T2 Cervical spine

Sagittal T1 dorsal spine

Coronal T1 Cervical spine