Introduction to Neuroimaging

Dr Mohamed El Safwany, MD.

Intended Learning Outcomes

The student should be able to recognize an introduction to neuroimaging.

Neuroimaging ModalitiesRadiography (X-Ray)

Fluoroscopy (guided procedures)

• Angiography

• Diagnostic

• Interventional

• Myelography

Ultrasound (US)

• Gray-Scale

• Color Doppler

Computed Tomography (CT)

• CT Angiography (CTA)

• Perfusion CT

• CT Myelography

Magnetic Resonance (MR)

• MR Angiography/Venography (MRA/MRV)

• Diffusion and Diffusion Tensor MR

• Perfusion MR

• MR Spectroscopy (MRS)

• Functional MR (fMRI)

Nuclear Medicine

• Positron Emission Tomography (PET)

“Duplex”

Radiography (X-Ray)

Radiography (X-Ray)

Disorders of spine:• Trauma• Degenerative Disorders• Post-opeerative

Fluoroscopy (Real-Time X-Ray)

Fluoro-guided procedures:• Angiography• Myelography

Fluoroscopy (Real-Time X-Ray)

Fluoroscopy (Real-Time X-Ray)Digital Subtraction Angiography

Fluoroscopy (Real-Time X-Ray)Digital Subtraction Angiography

Fluoroscopy (Real-Time X-Ray)

Myelography

Lumbar or cervical puncture

Inject contrast intrathecally with fluoroscopic guidance

Follow-up with post-myelo CT (CT myelogram)

Ultrasound

carotid

US transducer

Ultrasound

• Carotid stenosis• Vasospasm - Transcranial Doppler (TCD)• Infant brain imaging (open fontanelle = acoustic window)

• Noninvasive, well-tolerated, readily available, low cost• Quantitates blood velocity • Reveals morphology (stability) of atheromatous plaques

• Severe stenosis may appear occluded• Limited coverage, difficult through air/bone• Operator dependent

Indications:

Advantages:

Disadvantages:

Ultrasound – Gray Scale

Gray-scale image of carotid artery

Ultrasound – Gray Scale

Gray-scale image of carotid artery

Plaque in ICA

Ultrasound - Color Doppler

Peak Systolic Velocity (cm/sec) ICA Stenosis (% diameter)

125 – 225 50 – 70

225 – 350 70 – 90

>350 >90

Computed Tomography (CT)

Computed Tomography

A CT image is a pixel-by-pixel map of X-

ray beam attenuation (essentially

density) in

Hounsfield Units (HU)

HUwater = 0

Bright = “hyper-attenuating” or

“hyper-dense”

Computed Tomography

Typical HU Values:

Air –1000Fat –100 to –40Water 0Other fluids (e.g. CSF) 0–20White matter 20–35Gray matter 30–40Blood clot 55–75Calcification >150Bone 1000Metallic foreign body>1000

Brain

Computed Tomography

“Soft Tissue Window” “Bone Window”

Computed Tomography

Scan axially……stack and re-slice

in any plane“2D Recons”

CT Indications• Skull and skull base, vertebrae

(trauma, bone lesions)

• Ventricles

(hydrocephalus, shunt placement)

• Intracranial masses, mass effects

(headache, N/V, visual symptoms, etc.)

• Hemorrhage, ischemia

(stroke, mental status change)

• Calcification

(lesion characterization)

Skull and skull base, vertebrae

Fractures

Ventricles

Hydrocephalus

Intracranial masses, mass effects

Solid mass Cystic mass

Intracranial masses, mass effects

L hemisphere swelling Generalized swelling

Acute Hemorrhage

Intraparenchymal Subarachnoid Subdural Epidural

Acute Ischemia

Loss of gray-white distinction and swelling in known arterial territory

Calcification

Hyperparathyroidism

1. Rapid IV contrast bolus

2. Dynamic scanning during arterial phase

3. Advanced 2D and 3D Reconstructions: 2D multi-planar (sagittal, coronal) Volume–rendered 3D recons

CT Angiography

CT Angiography - HeadCircle of Willis

Aneurysms

Vascular Malformations

CT Angiography - Neck

Carotid

bifurcations

Vertebral arteries

Aortic arch

• Atherosclerosis

• Thromboembolism

• Vascular dissection

• Aneurysms

• Vascular malformations

• Penetrating trauma

CT Angiography - Indications

CT Perfusion CBV

CBF

MTT

Hemodynamic Parameters Derived From Concentration-Time Curves

Artery

VeinBolus arrival

Hemodynamic Parameter Maps

Transit Time (sec)

Blood Flow (mL/min/g)

Blood Volume (mL/g)

• Spinal CT immediately following conventional

myelogram

• Cross-sectional view of spinal canal along with spinal

cord and nerve roots

• Assess spinal stenosis/nerve root compression

(e.g. disc herniation, vertebral fracture,

neoplasm)

CT Myelography

CT Myelography

CT Myelography

Magnetic Resonance (MR)

Hydrogen proton in water or fat

MRI

COMPUTER

Magnetic Resonance Imaging

magnetic field

RF

Transmitter Receiver

RF = Radio Frequency energy Received

signal

“T1-weighted” “T2-weighted” w/ fat

suppression

Magnetic Resonance

Magnetic Resonance

Arachnoid Cyst

T2T1

NORMAL CYTOTOXIC EDEMA (Acute Ischemia)

Diffusion

MR Signal

Diffusion MR Imaging

Magnetic ResonanceImaging Diffusion

Highly sensitive to acute ischemia—

+ within a few hours!

No other imaging is more sensitive to acute ischemia

although perfusion imaging

reveals hypoperfused tissue

at risk for ischemia

Acute left MCA infarction

DWI

Magnetic Resonance Angiography

Axial “source” images… …reformatted to “maximum intensity projections” (MIP)

Multiple projections allow 3D-like displayNo need for IV contrast!

MRA Perfusion MR

Magnetic Resonance Angiography with Perfusion MR

Magnetic Resonance

Tissue contrast in MR may be based on:• Proton density

• Water/fat/protein content

• Metabolic compounds (MR Spectroscopy)

e.g. Choline, creatine, N-acetylaspartate, lactate

• Magnetic properties of specific molecules

e.g. Hemoglobin

• Diffusion of water

• Perfusion (capillary blood flow)

• Bulk flow (large vessels, CSF)

1. CT: Iodine-based

Iodine is highly attenuating of X-ray beam (bright on CT)

MRI: Gadolinium-based

Gadolinium is a paramagnetic metal that hastens T1 relaxation of nearby water protons (bright on T1-weighted images)

2. Tissue that gets brighter with IV contrast is said to “enhance” (Brightness, in and of itself, is not enhancement!)

3. Enhancement reflects the vascularity of tissue, but…

The blood-brain barrier keeps IV contrast out of the brain!

Enhancement implies BBB is absent or dysfunctional

Remember: Some brain anatomy lives outside the BBB

IV Contrast in Neuroimaging

EnhancementT1 T1+C

Hemorrhagic melanoma metastasis

Question

State three different orientations of the brain?

Assignments

5 Students will be selected for assignments.

Suggested Readings

Sutton’s Radiology

Thanks