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 Radiography (X-Ray) Fluoroscopy (guided procedures) AngiographyAngiography DiagnosticDiagnostic InterventionalInterventional MyelographyMyelography Ultrasound (US) Gray-ScaleGray-Scale Color DopplerColor Doppler Computed Tomography (CT) CT Angiography (CTA)CT Angiography (CTA) Perfusion CTPerfusion CT CT MyelographyCT Myelography Magnetic Resonance (MR) MR Angiography/Venography (MRA/MRV)MR Angiography/Venography (MRA/MRV) Diffusion and Diffusion Tensor MRDiffusion and Diffusion Tensor MR Perfusion MRPerfusion MR MR Spectroscopy (MRS)MR Spectroscopy (MRS) Functional MR (fMRI)Functional MR (fMRI) Nuclear Medicine Single Photon Emission Computed Tomography (SPECT)Single Photon Emission Computed Tomography (SPECT) Positron Emission Tomography (PET)Positron Emission Tomography (PET) “Duplex”

3. Radiography (X-Ray)

4. Primarily used for spine: Trauma Trauma Degenerative Dz Degenerative Dz Post-op Post-op

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

6. Fluoroscopy (Real-Time X-Ray)

7. Digital Subtraction Angiography

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

9. Aneurysms, vascular malformations and fistulaeAneurysms, vascular malformations and fistulae Vessel stenosis, thrombosis, dissection, pseudoaneurysmVessel stenosis, thrombosis, dissection, pseudoaneurysm Stenting, embolization, thrombolysis (mechanical and pharmacologic)Stenting, embolization, thrombolysis (mechanical and pharmacologic) Ability to interveneAbility to intervene Time-resolved blood flow dynamics (arterial, capillary, venous phases)Time-resolved blood flow dynamics (arterial, capillary, venous phases) High spatial and temporal resolutionHigh spatial and temporal resolution Invasive, risk of vascular injury and strokeInvasive, risk of vascular injury and stroke Iodinated contrast and ionizing radiationIodinated contrast and ionizing radiation Indications: Advantages: Disadvantages: 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. Myelography Spinal stenosis, nerve root compressionSpinal stenosis, nerve root compression CSF leakCSF leak MRI inadequate or contraindicatedMRI inadequate or contraindicated Defines extent of subarachnoid space, identifies spinal blockDefines extent of subarachnoid space, identifies spinal block Invasive, complications (CSF leak, headache, contrast reaction, etc.)Invasive, complications (CSF leak, headache, contrast reaction, etc.) Ionizing radiation and iodinated contrastIonizing radiation and iodinated contrast Limited coverageLimited coverage Indications: Advantages: Disadvantages:

12. Ultrasound carotid US transducer

13. Ultrasound Carotid stenosisCarotid stenosis Vasospasm - Transcranial Doppler (TCD)Vasospasm - Transcranial Doppler (TCD) Infant brain imaging (open fontanelle = acoustic window)Infant brain imaging (open fontanelle = acoustic window) Noninvasive, well-tolerated, readily available, low costNoninvasive, well-tolerated, readily available, low cost Quantitates blood velocityQuantitates blood velocity Reveals morphology (stability) of atheromatous plaquesReveals morphology (stability) of atheromatous plaques Severe stenosis may appear occludedSevere stenosis may appear occluded Limited coverage, difficult through air/boneLimited coverage, difficult through air/bone Operator dependentOperator dependent Indications: Advantages: Disadvantages:

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

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

16. Ultrasound - Color Doppler Peak Systolic Velocity (cm/sec) ICA Stenosis (% diameter) 125 – 22550 – 70 125 – 22550 – 70 225 – 35070 – 90 225 – 35070 – 90 >350 >90 >350 >90

17. Computed Tomography (CT)

18. Computed Tomography A CT image is a pixel-by-pixel map of X-ray beam attenuation (essentially density) in Hounsfield Units (HU) HU water = 0 Bright = “hyper-attenuating” or “hyper-dense”

19. Computed Tomography Typical HU Values: Air–1000 Fat–100 to –40 Water0 Other fluids (e.g. CSF) 0–20 White matter20–35 Gray matter30–40 Blood clot55–75 Calcification>150 Bone1000 Metallic foreign body>1000 Brain

20. Computed Tomography Attenuation: High or Low? High: 1.Blood, calcium 2.Less fluid / more tissue Low: 1.Fat, air 2.More fluid / less tissue Air–1000 Fat–100 to –40 Water0 Other fluids0–20 White matter20–35 Gray matter30–40 Blood clot55–75 Calcification>150 Bone1000 Metallic foreign body>1000

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

23. Computed Tomography

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

25. CT Indications Skull and skull base, vertebrae Skull and skull base, vertebrae (trauma, bone lesions) (trauma, bone lesions) Ventricles Ventricles (hydrocephalus, shunt placement) (hydrocephalus, shunt placement) Intracranial masses, mass effects Intracranial masses, mass effects (headache, N/V, visual symptoms, etc.) (headache, N/V, visual symptoms, etc.) Hemorrhage, ischemia Hemorrhage, ischemia (stroke, mental status change) (stroke, mental status change) Calcification Calcification (lesion characterization) (lesion characterization)

26. Skull and skull base, vertebrae Fractures

27. 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. 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

35. CT Angiography - Head

36. Circle of Willis Aneurysms Vascular Malformations

37. CT Angiography - Neck Carotidbifurcations Vertebral arteries Aortic arch

38. CT Angiography 3D Volume Rendering

39. AtherosclerosisAtherosclerosis ThromboembolismThromboembolism Vascular dissectionVascular dissection AneurysmsAneurysms Vascular malformationsVascular malformations Penetrating traumaPenetrating trauma CT Angiography - Indications

40. CT Perfusion CBV CBF MTT

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

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

43. Spinal CT immediately following conventional myelogramSpinal CT immediately following conventional myelogram Cross-sectional view of spinal canal along with spinal cord and nerve rootsCross-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)Assess spinal stenosis/nerve root compression (e.g. disc herniation, vertebral fracture, neoplasm) CT Myelography

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

47. Magnetic Resonance Imaging

48. COMPUTER magnetic field RFTransmitterReceiver RF = Radio Frequency energy Received signal

49. MRI Safety: The Magnet is Always On!

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

51. Magnetic Resonance Excited protons relax back to equilibrium Relaxation rates depend on local molecular environment T1 T2

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

53. Arachnoid Cyst T2T1

54. Magnetic Resonance T2 T2 w/ fat suppression

55. Magnetic Resonance T2 T2 w/ fat suppression

56. Magnetic Resonance T2 T2 w/ water suppression (T2-FLAIR)

57. Magnetic Resonance T2T2* Accentuating blood/calcium “blooming”

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

59. Magnetic Resonance Imaging 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

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

61. Time-Resolved MRA (TRICKS) IV contrast bolus reveals temporal dynamics

62. MRA Perfusion MR MRA Perfusion MR Magnetic Resonance Angiography with Perfusion MR

63. Magnetic Resonance Tissue contrast in MR may be based on: Proton density Proton density Water/fat/protein content Water/fat/protein content Metabolic compounds (MR Spectroscopy) Metabolic compounds (MR Spectroscopy) e.g. Choline, creatine, N-acetylaspartate, lactate Magnetic properties of specific molecules Magnetic properties of specific molecules e.g. Hemoglobin Diffusion of water Diffusion of water Perfusion (capillary blood flow) Perfusion (capillary blood flow) Bulk flow (large vessels, CSF) Bulk flow (large vessels, CSF)

64. 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

65. 1.Vessels 2.Meninges pachy = dura lepto = pia-arachnoid 3.Circumventricular organs (structures outside BBB) Pineal gland Pituitary gland Choroid plexus 4.Absent/leaky BBB Some tumors InflammationInfarction IV Contrast in Neuroimaging Enhancement:

66. Enhancement T1 T1+C Hemorrhagic melanoma metastasis

67. IV Contrast: Is it Indicated? TraumaTrauma R/O hemorrhageR/O hemorrhage HydrocephalusHydrocephalus DementiaDementia EpilepsyEpilepsy NeoplasmNeoplasm InfectionInfection Vascular diseaseVascular disease Inflammatory diseaseInflammatory disease Typically not Typically yes Always best to provide detailed indication! Radiologist will protocol exam accordingly

68. MR vs. CT Advantages: Simpler, cheaper, more accessible Simpler, cheaper, more accessible Tolerated by claustrophobics Tolerated by claustrophobics No absolute contraindications No absolute contraindications Fewer pitfalls in interpretation Fewer pitfalls in interpretation Better than MR for bone detail Better than MR for bone detailDisadvantages: Ionizing radiation Ionizing radiation IV contrast complications IV contrast complications Need recons for multi-planar Need recons for multi-planar Limited range of tissue contrasts Limited range of tissue contrasts CTMR Advantages: Much broader palette of tissue contrasts (including functional and molecular) yields greater anatomic detail and more comprehensive analysis of pathology Much broader palette of tissue contrasts (including functional and molecular) yields greater anatomic detail and more comprehensive analysis of pathology No ionizing radiation No ionizing radiation Direct multi-planar imaging Direct multi-planar imaging IV contrast better tolerated (in most pts.) IV contrast better tolerated (in most pts.)Disadvantages: Higher cost, limited access Higher cost, limited access Difficult for unstable patients Difficult for unstable patients Several absolute contraindications (cardiac pacer, some aneurysm clips, etc.) Several absolute contraindications (cardiac pacer, some aneurysm clips, etc.) Claustrophobics may need sedation Claustrophobics may need sedation Image interpretation more challenging Image interpretation more challenging Lacks bone detail Lacks bone detail

69. Introduction to Neuroimaging Aaron S. Field, MD, PhD Assistant Professor of Radiology Neuroradiology Section University of Wisconsin–Madison