basic neuroimaging (ct and mri)

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Basic Neuroimaging (CT and MRI) Dr Sean E Mc Sweeney 2007/2008

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Page 1: Basic Neuroimaging (CT and MRI)

Basic Neuroimaging (CT and MRI)

Dr Sean E Mc Sweeney

2007/2008

Page 2: Basic Neuroimaging (CT and MRI)

Indications for CT scan:

1) Significant Head Injury

2) Acute Stroke

3) Acute Headache (to look for SAH)

Indications for MRI:

4) Progressive focal neurological deficit

5) Epilepsy

6) Infections

7) Degenerative diseases

Page 3: Basic Neuroimaging (CT and MRI)

Multislice Helical CT scanner

Page 4: Basic Neuroimaging (CT and MRI)

Basic CT Physics

CT overcomes superimposition of structures

Measures and records small differences in tissue density

Highly collimated x ray beam passes through the head – with different tissues attenuating this beam differently

Detectors on the other side gather information about attenuation characteristics and with mathematical algorithms compute an image

Page 5: Basic Neuroimaging (CT and MRI)
Page 6: Basic Neuroimaging (CT and MRI)

Normal CT Brain ScanCT Scan above the level of the lateral ventricles

Frontal Lobe

Falx Cerebri

Centrum Semiovale

Parietal Lobe

Without Contrast

With Contrast

Page 7: Basic Neuroimaging (CT and MRI)

Normal CT Brain ScanCT Scan at the level of the lateral ventricles

Frontal Lobe

Frontal Horn of Lateral Ventricle

Occipital Lobe

Head of Caudate Nucleus

Thalamus

Posterior Horn of Lateral Ventricle

Page 8: Basic Neuroimaging (CT and MRI)

Normal CT Brain ScanCT Scan at the level of the 3rd Ventricle

Without Contrast With Contrast

Sylvian Vessels

Ant + Post Limbs of the Internal Capsule

Temporal Lobe

Head of Caudate Nucleaus

Frontal Horn of Lateral VentricleLentiform Nucleus

Tectum of Midbrain

Confluence of Venous Sinuses (Torcula)

Page 9: Basic Neuroimaging (CT and MRI)

Normal CT Brain ScanCT Scan at the level of the 4th Ventricle

ACA

Temporal Lobe

MCA

Basilar Artery

Pons4th Ventricle

Without Contrast With Contrast

Page 10: Basic Neuroimaging (CT and MRI)

Tissue Hounsfield Unit

Air -1000

Fat -40 to -100

Fluid 0 to 20

Soft Tissue 20 to 100

White Matter 20 to 35

Grey Matter 30 to 40

Acute Hemorrhage 55 to 75

Bone 

1000

Black

White

Hounsfield Unit (CT Density)

Page 11: Basic Neuroimaging (CT and MRI)

Grey Matter

Example on CT

Air (-1000)Fluid CSF (0-20)

White MatterGrey Matter

Bone (1000)

Page 12: Basic Neuroimaging (CT and MRI)

Case Examples on CT

Lipoma (Fat) Calcification (in meningioma)

Acute hematoma

-80 HU 70 HU140 HU

Page 13: Basic Neuroimaging (CT and MRI)

Brain Windows vs. Bone Windows

CT of fibrous dysplasia of skull with brain and bone windows

Page 14: Basic Neuroimaging (CT and MRI)

Evolution of Hematoma on CT

Acute hematoma: 4 hrs

4 days

3 months after initial CT

Page 15: Basic Neuroimaging (CT and MRI)

Decreasing Density of Hematoma

• Acute : hyperdense (1 to 6 days)

• Subacute: isodense (6 to 12 days)

• Chronic : hypodense ( > 12 days)

Page 16: Basic Neuroimaging (CT and MRI)

Classic Infarct on CT

• Wedge shaped area of low density in right middle cerebral artery territory

ACAMCA

PCA

Page 17: Basic Neuroimaging (CT and MRI)

Acute Extradural hematoma

Page 18: Basic Neuroimaging (CT and MRI)

Extradural Hematoma - evolution

Acute extradural hematoma

Chronic epidural hematoma

Page 19: Basic Neuroimaging (CT and MRI)

Extradural Hematoma

• Extradural hematomas are located between the inner table of the skull and the dura.

• They are typically biconvex in shape because their outer border follows the inner table of the skull and their inner border is limited by locations at which the dura is firmly adherent to the skull.

• Epidural hematomas are usually caused by injury to an artery, although 10% of epidural hematomas may be venous in origin.

• The most common cause of an epidural hematoma is a linear skull fracture that passes through an arterial channel in the bone(middle meningeal artery).

• Epidural hematomas, especially those of arterial origin, tend to enlarge rapidly

Page 20: Basic Neuroimaging (CT and MRI)

Subarachnoid Haemorhage (SAH)

Acute Subarachnoid Haemorrhage in region of Circle of Willis (Yellow)

Page 21: Basic Neuroimaging (CT and MRI)

Subarachnoid Haemorhage

• CT without contrast– CT is the most sensitive imaging study in SAH .– Findings may be negative in 10-15% of patients with

SAH.– Maximum sensitivity is within 24 hours after the event;

sensitivity is 80% at 3 days, 50% at 1 week.– Look for evidence of hydrocephalus (trapped temporal

horns and "Mickey Mouse" appearance of ventricular system).

– Look for intraparenchymal clot, intraventricular hematoma, and interhemispheric hematoma

Page 22: Basic Neuroimaging (CT and MRI)

Hydrocephalus and SAH

• Haemorrhage can be seen in the ventricular spaces normally containing CSF, (dark grey replaced by white) which are dilated (Hydrocephalus) also the sylvian fissure are visable due to the presence of SAH.

Page 23: Basic Neuroimaging (CT and MRI)

CT Cerebral Angiography

• 3D CT Angiography of the Brain Allows Extremely Detailed and Precise Visualization of the Cerebral Vessels and the Circle of Willis that is Safe and Noninvasive

ACAMCA

CarotidPCA

Page 24: Basic Neuroimaging (CT and MRI)

Ct Angiography

A Subarachnoid hemorrhage in the right sylvian fissure (arrow), B, 3D volume-rendered image (lateral) shows inferiorly and posteriorly directed saccular aneurysm at the origin of the right posterior communicating artery (arrow). C,Preoperative right internal carotid digital subtraction angiogram shows corresponding saccular aneurysm. D, Angiogram shows successful clip placement in the posterior communicating artery aneurysm.

Page 26: Basic Neuroimaging (CT and MRI)

Acute Subdural

Acute subdural (White) on chronic (Yellow) and mass effect :midline shift (Red arrow)

Page 27: Basic Neuroimaging (CT and MRI)

Acute Subdural

• Subdural hematomas are located between the dura and the brain.

• Their outer edge is convex, while their inner border is usually irregularly concave (cresenteric).

• Subdural hematomas cross the intracranial suture lines; this is an important feature that aids in their differentiation from epidural hematomas.

• Subdural hematomas are usually venous in origin, although some subdural hematomas are caused by arterial injuries.

• The classic cause of a posttraumatic subdural hematoma is an injury to one of the bridging veins that travel from the cerebral cortex to the dura.

Page 28: Basic Neuroimaging (CT and MRI)

The MRI machine

1.5 Tesla magnet

Page 29: Basic Neuroimaging (CT and MRI)

Magnetic resonance imaging

• Magnetic resonance imaging is based on imaging of protons within the human body

• Images produced are based on a computer calculation of how protons within different soft tissues react to the application of a strong magnetic field and radiofrequency pulse

Page 30: Basic Neuroimaging (CT and MRI)

MRI Is Similar to an Orchestra

Different music can be produced by changing the parameters used

Page 31: Basic Neuroimaging (CT and MRI)

MRI Sequences - NORMALS

T1

T2

FLAIR

Page 32: Basic Neuroimaging (CT and MRI)

T1 vs. T2 Appearances

Page 33: Basic Neuroimaging (CT and MRI)

MRI Indications

• Neurology- acute cerebral infarction

- brain tumour

- white matter disease- spinal cord problems- posterior fossa-better than CT

- paediatric-avoids radiation

- head trauma

Page 34: Basic Neuroimaging (CT and MRI)

Acute Infarct: CT vs. MRI

CT very useful to r/o bleed

MRI can show acute infarcts: useful if thrombolytic therapy

being considered

DWI

Page 35: Basic Neuroimaging (CT and MRI)

Brain tumor-GBM

Page 37: Basic Neuroimaging (CT and MRI)

Multiple sclerosis

• MRIs typically demonstrate more than 1 hyperintense white matter lesion on T2.

• Lesions may be observed anywhere in the CNS white matter (supratentorium, infratentorium, and spinal cord).

• Typical locations for MS lesions include the periventricular white matter, brainstem, cerebellum, and spinal cord.

• Ovoid lesions perpendicular to the ventricles are common in MS and occasionally are called Dawsons fingers.

• Perhaps the most specific lesions in MS are noted in the corpus callosum at the interface with the septum pellucidum

• Proton density (PD) MRI has an advantage over standard T2 imaging because, on PD series, MS lesions remain hyperintense while CSF signal is suppressed

Page 38: Basic Neuroimaging (CT and MRI)

HSV Encephalitis

Page 39: Basic Neuroimaging (CT and MRI)

Spinal Cord Lesion on CT

Ewing’s sarcoma arising from the cervical spine

Page 40: Basic Neuroimaging (CT and MRI)

Spinal Cord Lesion on MRI

Ewing’s sarcoma arising from the cervical spine with cord compression

T1 sagittal T1 sagittal C + T2 sagittal

Page 41: Basic Neuroimaging (CT and MRI)

Cord astrocytoma

T1 T1, with contrast

T2

Page 42: Basic Neuroimaging (CT and MRI)

Acoustic Neuroma

Page 43: Basic Neuroimaging (CT and MRI)

Blood Products

Acute hematoma best seen on CT

Subacute and chronic hematoma better evaluated on MRI

Primary (hypertensive) bleeds occur in the basal ganglia; for bleeds at other locations, hunt for a cause

Page 44: Basic Neuroimaging (CT and MRI)

Subacute Hematoma on MRIRight paraasagittal T1WI Left paraasagittal T1WI

(normal side)

Axial FLAIR image Axial T2 image

Page 45: Basic Neuroimaging (CT and MRI)

Chronic Resolved Hematoma

Now shows “slit” like cavity with hemosiderin stain

Page 46: Basic Neuroimaging (CT and MRI)

Advantages of MRI v CT

• No ionising radiation• Multiplanar imaging capability• Non-invasive vascular imaging• Cardiac imaging• Excellent contrast resolution-much better

than CT• No streak artifacts from bone• Safer contrast agent (Gadolinium)• Molecular imaging

Page 47: Basic Neuroimaging (CT and MRI)

Disadvantages of MRI v CT

• More expensive

• More motion sensitive

• Limited availability

• Contraindicated in certain patients

• Acute haemorrhage difficult to see (SAH)

Page 48: Basic Neuroimaging (CT and MRI)

Contraindications for magnetic resonance imaging

• Cranial metal i.e. head, brain, orbit

• Pacemaker

• History of metalwork, shrapnel

• Claustrophobic

Page 49: Basic Neuroimaging (CT and MRI)

Positron Emission Tomography

Page 50: Basic Neuroimaging (CT and MRI)

What is Positron Emission Tomography (PET)

• Positron emission tomography (PET scan) is a diagnostic examination that involves the acquisition of physiologic images based on the detection of radiation from the emission of positrons.

• Positrons are emitted from a radioactive substance administered to the patient. The subsequent images of the human body developed with this technique are used to evaluate a variety of diseases

Page 51: Basic Neuroimaging (CT and MRI)

PET Scanning

• F-18 2 fluoro-2 deoxy-D-glucose (FDG) is a glucose analog labeled with positron-emitting fluorine-18.

• Most malignant tumors are metabolically active and take up increased FDG relative to normal tissue.

• FDG is highly sensitive in identification of malignant tumors.

Page 52: Basic Neuroimaging (CT and MRI)

PET-CT

• PET-CT is the fusion of functional and anatomic information acquired almost simultaneously.

• By combining the structural anatomic information with functional data, we are able to visualize form and function

Page 53: Basic Neuroimaging (CT and MRI)

PET-CT

Page 54: Basic Neuroimaging (CT and MRI)

Lung cancer with metastatic mediastinal lymph nodes

Page 55: Basic Neuroimaging (CT and MRI)

Lung cancer with metastatic Adrenal mass

Page 56: Basic Neuroimaging (CT and MRI)