Introduction to Neuroimaging

1. Introduction to Neuroimaging Dr Mohamed El Safwany, MD.

2. Intended Learning Outcomes • The student should be able to recognize an introduction to neuroimaging.

3. Neuroimaging Modalities • 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) • 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 “Duplex”

4. Radiography (X-Ray)

5. Radiography (X-Ray) • Disorders of spine: • Trauma • Degenerative Disorders • Post-opeerative

6. Fluoroscopy (Real-Time X-Ray) • Fluoro-guided procedures: • Angiography • Myelography

7. Fluoroscopy (Real-Time X-Ray)

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

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

10. Fluoroscopy (Real-Time X-Ray) Myelography Lumbar or cervical puncture Inject contrast intrathecally with fluoroscopic guidance Follow-up with post-myelo CT (CT myelogram)

11. US transducer carotid Ultrasound

12. Ultrasound Indications: • 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:

13. Ultrasound – Gray Scale Gray-scale image of carotid artery

14. Ultrasound – Gray Scale Plaque in ICA Gray-scale image of carotid artery

15. Ultrasound - Color Doppler Peak Systolic Velocity (cm/sec)ICA Stenosis (% diameter) 125 – 225 50 – 70 225 – 350 70 – 90 >350 >90

16. Computed Tomography (CT)

17. Computed Tomography A CT image is a pixel-by-pixel map ofX-ray beam attenuation(essentiallydensity)inHounsfield Units (HU) HUwater = 0 Bright = “hyper-attenuating” or “hyper-dense”

18. 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 1000 Metallic foreign body >1000 Brain

20. Computed Tomography “Soft Tissue Window” “Bone Window”

21. Computed Tomography Scan axially… …stack and re-slice in any plane “2D Recons”

22. 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)

23. Skull and skull base, vertebrae Fractures

24. Ventricles Hydrocephalus

25. Intracranial masses, mass effects Solid mass Cystic mass

26. Intracranial masses, mass effects L hemisphere swelling Generalized swelling

27. Acute Hemorrhage Intraparenchymal Subarachnoid Subdural Epidural

28. Acute Ischemia Loss of gray-white distinction and swelling in known arterial territory

29. Calcification Hyperparathyroidism

30. 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

31. CT Angiography - Head Circle of Willis Vascular Malformations Aneurysms

32. CT Angiography - Neck Carotid bifurcations Vertebral arteries Aortic arch

33. CT Angiography - Indications • Atherosclerosis • Thromboembolism • Vascular dissection • Aneurysms • Vascular malformations • Penetrating trauma

34. CBV CBF MTT CT Perfusion

35. Hemodynamic Parameters Derived From Concentration-Time Curves Bolus arrival Vein Artery

36. Hemodynamic Parameter Maps Transit Time (sec) Blood Flow (mL/min/g) Blood Volume (mL/g)

37. 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)

38. CT Myelography

39. CT Myelography

40. Magnetic Resonance (MR) Hydrogen proton in water or fat MRI

41. Magnetic Resonance Imaging Transmitter Receiver RF COMPUTER RF = Radio Frequency energy Received signal magnetic field

42. “T1-weighted” “T2-weighted” w/ fat suppression Magnetic Resonance

43. Magnetic Resonance T1 T2 Arachnoid Cyst

44. Diffusion MR Imaging NORMAL CYTOTOXIC EDEMA (Acute Ischemia) Diffusion  MR Signal 

45. 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

46. Magnetic Resonance Angiography Axial “source” images… …reformatted to “maximum intensity projections” (MIP) Multiple projections allow 3D-like display No need for IV contrast!

47. Magnetic Resonance Angiography with Perfusion MR MRA Perfusion MR

48. 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)

49. 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 barrierkeeps IV contrast outof the brain! • Enhancement implies BBB is absent or dysfunctional • Remember: Some brain anatomy lives outside the BBB

50. Enhancement T1 T1+C Hemorrhagic melanoma metastasis