Introduction to Neuroimaging

1. Introduction to Neuroimaging Aaron S. Field, MD, PhD Assistant Professor of Radiology Neuroradiology Section University of Wisconsin–Madison Updated 7/17/07

2. 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 • Single Photon Emission Computed Tomography (SPECT) • 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”

3. Radiography (X-Ray)

4. Radiography (X-Ray) • Primarily used for spine: • Trauma • Degenerative Dz • Post-op

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

6. Fluoroscopy (Real-Time X-Ray)

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

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

9. Digital Subtraction Angiography Indications: • Aneurysms, vascular malformations and fistulae • Vessel stenosis, thrombosis, dissection, pseudoaneurysm • Stenting, embolization, thrombolysis (mechanical and pharmacologic) • Ability to intervene • Time-resolved blood flow dynamics (arterial, capillary, venous phases) • High spatial and temporal resolution • Invasive, risk of vascular injury and stroke • Iodinated contrast and ionizing radiation Advantages: Disadvantages:

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. Myelography Indications: • Spinal stenosis, nerve root compression • CSF leak • MRI inadequate or contraindicated • Defines extent of subarachnoid space, identifies spinal block • Invasive, complications (CSF leak, headache, contrast reaction, etc.) • Ionizing radiation and iodinated contrast • Limited coverage Advantages: Disadvantages:

12. US transducer carotid Ultrasound

13. 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:

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

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

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

17. Computed Tomography (CT)

18. 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”

19. 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 Attenuation: High or Low? • High: • Blood, calcium • Less fluid / more tissue • Low: • Fat, air • More fluid / less tissue Air –1000 Fat –100 to –40 Water 0 Other fluids 0–20 White matter 20–35 Gray matter 30–40 Blood clot 55–75 Calcification >150 Bone 1000 Metallic foreign body >1000

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

23. Computed Tomography

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

25. 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)

26. Skull and skull base, vertebrae Fractures

27. Skull and skull base, vertebrae Multiple Myeloma Osteoma

28. Ventricles Hydrocephalus

29. Intracranial masses, mass effects Solid mass Cystic mass

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

31. Acute Hemorrhage Intraparenchymal Subarachnoid Subdural Epidural

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

33. Calcification Hyperparathyroidism

34. 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

35. CT Angiography - Head

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

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

38. CT Angiography 3D Volume Rendering

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

40. CBV CBF MTT CT Perfusion

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

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

43. 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)

44. CT Myelography

45. CT Myelography

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

47. Magnetic Resonance Imaging

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

49. MRI Safety: The Magnet is Always On!

50. Magnetic Resonance Safety MRI Safety Test: Will it: Move? Torque? Get hot? Pass a current? Malfunction? Become a projectile? Get stuck in scanner? • Typically unsafe*: • Cardiac pacemakers (and other electrical devices) • Some older aneurysm clips • Metal fragments in orbit (1 case report) • Oxygen tanks, carts, chairs, stools, IV poles, gurneys, etc. • Some cosmetics, tattoos, jewelry, hairpins, etc. • Pager, watch, wallet, ID badge, pen, keys, pocketknife, etc. • Typically safe*: • Orthopedic hardware • Surgical clips, staples, sutures (older devices must be checked!) • Intravascular stents/filters * This is an incomplete list and there are many exceptions to every “rule” When in doubt, check it out!