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Introduction to Neuroimaging
Dr Mohamed El Safwany, MD.
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Intended Learning Outcomes
The student should be able to recognize an introduction to neuroimaging.
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Neuroimaging Modalities
Radiography (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”
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Radiography (X-Ray)
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Radiography (X-Ray) Disorders of spine: Trauma Degenerative Disorders
Post-opeerative
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Fluoroscopy (Real-Time X-Ray)
Fluoro-guided procedures: Angiography Myelography
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Fluoroscopy (Real-Time X-Ray)
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Fluoroscopy (Real-Time X-Ray) Digital Subtraction Angiography
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Fluoroscopy (Real-Time X-Ray) Digital Subtraction Angiography
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Fluoroscopy (Real-Time X-Ray)
Myelography Lumbar or cervical puncture Inject contrast intrathecally with fluoroscopic guidance Follow-up with post-myelo CT (CT myelogram)
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carotid US transducer Ultrasound
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Ultrasound Indications: Advantages: Disadvantages: 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 Advantages: Disadvantages:
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Ultrasound – Gray Scale Gray-scale image of carotid artery
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Ultrasound – Gray Scale Gray-scale image of carotid artery
Plaque in ICA Gray-scale image of carotid artery
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Ultrasound - Color Doppler
Peak Systolic Velocity (cm/sec) ICA Stenosis (% diameter) 125 – – 70 225 – – 90 > >90
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Computed Tomography (CT)
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Bright = “hyper-attenuating” or “hyper-dense”
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”
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Computed Tomography Typical HU Values: Air –1000 Fat –100 to –40
Water 0 Other fluids (e.g. CSF) 0–20 White matter 20–35 Gray matter 30–40 Blood clot 55–75 Calcification >150 Bone Metallic foreign body >1000 Brain
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“Soft Tissue Window” “Bone Window”
Computed Tomography “Soft Tissue Window” “Bone Window”
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…stack and re-slice in any plane
Computed Tomography Scan axially… …stack and re-slice in any plane “2D Recons”
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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)
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Skull and skull base, vertebrae
Fractures
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Ventricles Hydrocephalus
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Intracranial masses, mass effects
Solid mass Cystic mass
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Intracranial masses, mass effects
L hemisphere swelling Generalized swelling
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Acute Hemorrhage Intraparenchymal Subarachnoid Subdural Epidural
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Acute Ischemia Loss of gray-white distinction and swelling in known arterial territory
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Calcification Hyperparathyroidism
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CT Angiography Rapid IV contrast bolus
Dynamic scanning during arterial phase Advanced 2D and 3D Reconstructions: 2D multi-planar (sagittal, coronal) Volume–rendered 3D recons
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Vascular Malformations
CT Angiography - Head Circle of Willis Vascular Malformations Aneurysms
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CT Angiography - Neck Carotid bifurcations Vertebral arteries
Aortic arch
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CT Angiography - Indications
Atherosclerosis Thromboembolism Vascular dissection Aneurysms Vascular malformations Penetrating trauma
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CT Perfusion CBV CBF MTT
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Hemodynamic Parameters Derived From Concentration-Time Curves
Bolus arrival Vein Artery
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Hemodynamic Parameter Maps
Transit Time (sec) Blood Flow (mL/min/g) Blood Volume (mL/g)
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CT Myelography 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)
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CT Myelography
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CT Myelography
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Magnetic Resonance (MR) Hydrogen proton in water or fat
MRI
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Magnetic Resonance Imaging
RF Transmitter Receiver RF = Radio Frequency energy COMPUTER Received signal magnetic field
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“T2-weighted” w/ fat suppression
Magnetic Resonance “T1-weighted” “T2-weighted” w/ fat suppression
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Magnetic Resonance T1 T2 Arachnoid Cyst
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CYTOTOXIC EDEMA (Acute Ischemia)
Diffusion MR Imaging NORMAL CYTOTOXIC EDEMA (Acute Ischemia) Diffusion MR Signal
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Magnetic Resonance Imaging Diffusion DWI
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
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Magnetic Resonance Angiography
Axial “source” images… …reformatted to “maximum intensity projections” (MIP) Multiple projections allow 3D-like display No need for IV contrast!
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Magnetic Resonance Angiography with Perfusion MR
MRA Perfusion MR
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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)
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IV Contrast in Neuroimaging
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) Tissue that gets brighter with IV contrast is said to “enhance” (Brightness, in and of itself, is not enhancement!) 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
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Hemorrhagic melanoma metastasis
Enhancement T1 T1+C Hemorrhagic melanoma metastasis
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Question State three different orientations of the brain?
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Assignments 5 Students will be selected for assignments.
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Suggested Readings Sutton’s Radiology
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Thanks
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