Introduction to Neuroimaging Aaron S Field, MD, PhD Assistant Professor of Radiology Neuroradiology Section University of Wisconsin–Madison Updated 7/17/07 Neuroimaging Modalities Magnetic Resonance (MR) Radiography (X-Ray) Fluoroscopy (guided procedures) • Angiography • Diagnostic • Interventional • Myelography Ultrasound (US) • Gray-Scale • Color Doppler “Duplex” Computed Tomography (CT) • CT Angiography (CTA) • Perfusion CT • CT Myelography • MR Angiography/Venography (MRA/MRV) • Diffusion and Diffusion Tensor MR • Perfusion MR • MR Spectroscopy (MRS) • Functional MR (fMRI) Nuclear Medicine • Single Photon Emission Computed Tomography (SPECT) • Positron Emission Tomography (PET) Radiography (X-Ray) Radiography (X-Ray) Primarily used for spine: • Trauma • Degenerative Dz • Post-op 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 Digital Subtraction Angiography Indications: • • • Aneurysms, vascular malformations and fistulae Vessel stenosis, thrombosis, dissection, pseudoaneurysm Stenting, embolization, thrombolysis (mechanical and pharmacologic) Advantages: • • • Ability to intervene Time-resolved blood flow dynamics (arterial, capillary, venous phases) High spatial and temporal resolution Disadvantages: • • Invasive, risk of vascular injury and stroke Iodinated contrast and ionizing radiation Fluoroscopy (Real-Time X-Ray) Myelography Lumbar or cervical puncture Inject contrast intrathecally with fluoroscopic guidance Follow-up with post-myelo CT (CT myelogram) Magnetic Resonance T2 T2 w/ fat suppression Magnetic Resonance T2 T2 w/ water suppression (T2-FLAIR) Magnetic Resonance Accentuating blood/calcium “blooming” T2 T2* Diffusion MR Imaging NORMAL CYTOTOXIC EDEMA (Acute Ischemia) Diffusion ↓ MR Signal ↑ Magnetic Resonance Imaging Diffusion Highly sensitive to acute ischemia— DWI + 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 Magnetic Resonance Angiography Axial “source” images… No need for IV contrast! …reformatted to “maximum intensity projections” (MIP) Multiple projections allow 3D-like display Time-Resolved MRA (TRICKS) IV contrast bolus reveals temporal dynamics Magnetic Resonance Angiography with Perfusion MR MRA 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) 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 IV Contrast in Neuroimaging Enhancement: Vessels Meninges pachy = dura lepto = pia-arachnoid Circumventricular organs (structures outside BBB) Pineal gland Pituitary gland Choroid plexus Absent/leaky BBB Some tumors Inflammation Infarction Enhancement T1 T1+C Hemorrhagic melanoma metastasis IV Contrast: Is it Indicated? Typically not Typically yes • • • • • • • • • Trauma R/O hemorrhage Hydrocephalus Dementia Epilepsy Neoplasm Infection Vascular disease Inflammatory disease Always best to provide detailed indication! Radiologist will protocol exam accordingly MR vs CT CT MR Advantages: Advantages: • Simpler, cheaper, more accessible • No absolute contraindications • Much broader palette of tissue contrasts (including functional and molecular) yields greater anatomic detail and more comprehensive analysis of pathology • Fewer pitfalls in interpretation • No ionizing radiation • Better than MR for bone detail • Direct multi-planar imaging Disadvantages: • IV contrast better tolerated (in most pts.) • Ionizing radiation Disadvantages: • IV contrast complications • Higher cost, limited access • Need recons for multi-planar • Difficult for unstable patients • Limited range of tissue contrasts • Several absolute contraindications (cardiac pacer, some aneurysm clips, etc.) • Tolerated by claustrophobics • Claustrophobics may need sedation • Image interpretation more challenging • Lacks bone detail Introduction to Neuroimaging Aaron S Field, MD, PhD Assistant Professor of Radiology Neuroradiology Section University of Wisconsin–Madison ... Fat Water Other fluids ? ?10 00 ? ?10 0 to –40 (e.g CSF) White matter Brain Gray matter Blood clot Calcification 0–20 20–35 30–40 55–75 >15 0 10 00 Bone Metallic foreign body >10 00 Computed Tomography... matter Gray matter Blood clot Calcification Bone Metallic foreign body ? ?10 00 ? ?10 0 to –40 0–20 20–35 30–40 55–75 >15 0 10 00 >10 00 Computed Tomography “Soft Tissue Window” “Bone Window” Computed Tomography... ICA Gray-scale image of carotid artery Ultrasound - Color Doppler Peak Systolic Velocity (cm/sec) 12 5 – 225 225 – 350 >350 ICA Stenosis (% diameter) 50 – 70 70 – 90 >90 Computed Tomography (CT)