Magnetic Resonance Imaging for Neurological Conditions. Lawrance Yip Department of Radiology Queen Mary Hospital

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1 Magnetic Resonance Imaging for Neurological Conditions Lawrance Yip Department of Radiology Queen Mary Hospital

2 Outline Strength and limitations of MRI for neurological conditions MR Imaging techniques and related applications Anatomy of MRI Brain Clinical cases

3 Magnetic Resonance Imaging MRI depends on magnetic properties of atomic nuclei Hydrogen is abundant in the body (>80% of body content is H 2 O) and has a large magnetic moment Hydrogen is the element most commonly used in MR imaging MRI is essentially measuring the spatial distribution of water within the body

4 Magnetic Resonance Imaging SNR=B o V(!N PE N PA N AV /BW) (1-e -TR/T1 ) e -TE/T2 SAR $ B 2 % 2 D " = # B o B = # 2 G 2 d 2 (' - d/3) B=µ o (1 + & m ) H S o = S o e -b(adc)

5 Four Steps of MRI Examination Patient is placed in a magnet A radiofrequency (RF) pulse is sent in by RF coils Patient emits a signal and received by RF coils Reconstruction of MR images using the raw data obtained

6 Strength of MRI for Neurological Conditions Non-invasive No radiation hazard

7 Strength of MRI for Neurological Conditions Non-invasive No radiation hazard Excellent soft tissue contrast CT T1-W MRI T2-W MRI

8 Strength of MRI for Neurological Conditions Non-invasive No radiation hazard Excellent soft tissue contrast Absence of beam hardening (streak) artifacts in skull base CT T2-W MRI T1-W MRI

9 Strength of MRI for Neurological Conditions Non-invasive No radiation hazard Excellent soft tissue contrast Absence of beam hardening (streak) artifacts in skull base Multi-planar imaging capability Axial Sagittal Coronal

10 Strength of MRI for Neurological Conditions Non-invasive No radiation hazard Excellent soft tissue contrast Absence of beam hardening (streak) artifacts in skull base Multi-planar imaging capability High safety profile of MR contrast media Gadolinium-based contrast medium Similar pharmacokinetics with iodinated X-ray contrast medium Provide contrast enhancement on T1- weighted images Mild allergic reaction: nausea, vomiting or uticaria Rate of severe allergic reaction = 1 in 400,000

11 MRI for Neurological Conditions Musculo-skeletal 10% Cardio-vascular 6% others 6% Body 10% Head & Neck 51% Spine 17% MRI Statistics by Region of Exam. DR, QMH 2007

12 Limitations of MRI for Neurological Conditions Relatively long imaging time compared with CT Immobilization Reassurance Sedation General anaesthesia

13 Limitations of MRI for Neurological Conditions Relatively long imaging time compared with CT Immobilization Reassurance Sedation General Anaesthesia All life-supporting equipment must be changed to MRI-safe ones before MRI examination Portable ventilator Physiological monitor Infusion pump

14 Limitations of MRI for Neurological Conditions Relatively long imaging time compared with CT Immobilization Reassurance Sedation General Anaesthesia All life-supporting equipment must be changed to MRI-safe ones before MRI examination Portable ventilator Physiological monitor Infusion pump Ferromagnetic objects must be removed from the patients and accompanying personnel before entering MRI scan room

15 Limitations of MRI for Neurological Conditions Relatively long imaging time compared with CT Immobilization Reassurance Sedation General Anaesthesia All life-supporting equipment must be changed to MRI-safe ones before MRI examination Portable ventilator Physiological monitor Infusion pump Ferromagnetic objects must be removed from the patients and accompanying personnel before entering MRI scan room Imaging artifacts from ferromagnetic objects Metallic fragment Dentures Surgical clip Aneurysm clip

16 Contra-indications of MRI Cardiac Pacemaker Intra-orbital metallic foreign bodies Non-MRI safe biomedical implants e.g. aneurysm clip, neurostimulator, artificial heart valve Claustrophobia

17 MRI Brain Imaging Techniques Structural (anatomical) imaging T2-weighted T1-weighted FLAIR (Fluid Attenuated Inversion Recovery) Post-contrast T1-weighted DWI (Diffusion Weighted Imaging) MR Angiography (MRA) MR Venography (MRV) MR Spectroscopy (MRS) Functional MRI (fmri)

18 MRI Brain T2-weighted image Tissue with high water content will be hyperintense e.g. CSF, gray matter Best demonstrate pathological conditions because most inflammatory and neoplastic processes will have increased water content and thus appear hyperintense

19 MRI Brain T1-weighted image Adipose tissue, blood products or proteinacious fluid will appear hyperintense e.g. yellow bone marrow, intracerebral lipoma Tissue with high water content will appear hypointense e.g. CSF, gray matter Higher signal-to-noise ratio and less susceptible of MR imaging artifacts compared with T2-W image Useful in characterization of lesions

20 MRI Brain FLAIR (Fluid Attenuated Inversion Recovery) T2-W image with suppression of signal from normal CSF Increased sensitivity for detection of intracerebral lesions especially those adjacent to cerebral ventricles and sulci

21 MRI Brain Post-contrast T1-weighted image Normal brain tissue will not have contrast enhancement due to presence of Blood Brain Barrier (BBB) Normal dosage = 0.2ml / Kg of body weight Indications Brain tumour Brain metastasis Inflammatory process e.g. brain abscess, encephalitis Multiple sclerosis

22 MRI Brain Maxillary Sinus Medulla Oblongata Cerebellum Vertebral Arteries Pre-medullary Cistern

23 MRI Brain Pons Cerebello-pontine Cistern 4 th Ventricle Temporal Lobe Basilar Artery Pre-pontine Cistern Cerebellum Cerebellar Vermis

24 MRI Brain Frontal Lobe Sylvian (Lateral) Fissure Temporal Lobe Quadrigeminal Cistern Third Ventricle Substantia Nigra Red Nucleus Occipital Lobe Superior Sagittal Sinus

25 MRI Brain Frontal Lobe Genu of Corpus Callosum Sylvian (Lateral) Fissure Lentiform Nucleus Temporal Lobe Splenium of Corpus Callosum Longitudinal fissure Caudate Nucleus Lateral Ventricle Internal Capsule Thalamus Third Ventricle Occipital Lobe

26 MRI Brain Longitudinal Fissure Body of Corpus Callosum Lateral Ventricle Septum Pellucidum

27 MRI Brain Frontal Lobe Falx Cerebri Pre-central Gyrus (motor stripe) Central Sulcus Post-central Gyrus (sensory stripe) Parietal Lobe

28 Corpus Callosum Thalamus MRI Brain Occipital Fissure 4 th Ventricle Pons Medulla Oblongata Cerebral Aqueduct Optic Chiasma Cerebellum Infundibulum

29 MRI Brain Falx Cerebri Parietal Lobe Tentorium Cerebelli Dentate Nucleus Cerebellum

30 MRI Brain Falx Cerebri Parietal Lobe Tentorium Cerebelli 4 th Ventricle Cerebellum

31 MRI Brain Longitudinal Fissure Lateral Ventricle 3 rd Ventricle Temporal Lobe Sylvian Fissure

32 MRI Brain Diffusion weighted imaging (DWI) Sensitive to random thermal motion of tissue water molecules (Brownian movement) Mobility of water molecules MR signal intensity DWI can depict location and extent of acute ischemic stroke during initial critical hours after onset of disease process Useful in triage patients for appropriate interventional treatments

33 Imaging Principles of DWI Hypoxic ischaemia leads to failure of ATP-dependent Na + /K + pump and loss of ion homeostasis Intracellular influx of sodium, calcium, and chloride ions accompanied by the movement of water from the extracellular space Cl - Cell Na + Cytotoxic Oedema H 2 O Ca ++

34 Imaging Principles of DWI Normal tissue Ischaemic tissue Freely diffusing extracellular water molecules Increased restrictions of water molecules

35 Diffusion Weighted Imaging CT & conventional MRI are insensitive to acute ischemic stroke during the initial critical hours after the onset of symptoms Motion of water molecules is restricted immediately after stroke onset and ischaemic region is visualized as hyperintense area in comparison to the surrounding normal brain T2-W DWI

36 MR Angiography (MRA) Non-invasive No IV contrast medium is required for demonstration of intracranial vessels e.g COW Demonstrate patency, course and morphology of intracranial vessels e.g. cerebral aneurysm, arteriovenous malformation, vascular stenosis 3D data acquisition with submillimeter spatial resolution

37 MR Angiography (MRA)

38 MR Angiography (MRA) Superior Cerebellar Artery Anterior Cerebral Artery Basilar Artery Middle Cerebral Artery Anterior Inferior Cerebellar Artery Posterior Inferior Cerebellar Artery Internal Carotid Artery Vertebral Artery

39 Cerebral Aneurysm

40 MR Angiography (MRA) Extra-cranial carotid and vertebral vessels can be demonstrated by contrast-enhanced MRA technique Bolus injection of MR contrast medium Data acquisition during arrival of contrast bolus at the vessel-of-interest 3D data acquisition

41 CE-MRA of Extracranial Carotid & Vertebral Arteries

42 CE-MRA of Extracranial Carotid & Vertebral Arteries 90% stenosis of Lt ICA Complete occlusion of Lt ICA

43 MR Venography (MRV) Non-invasive No IV contrast medium is required for demonstration of intracranial dural venous sinuses e.g. superior sagittal sinus, transverse sinus and straight sinus Demonstrate patency and course of dural venous sinuses

44 MR Venography (MRV) Superior Sagittal Sinus Inferior Sagittal Sinus Basal Vein of Rosenthal Basal Vein of Rosenthal Great Vein Of Galen Straight Sinus Confluence of Sinus Transverse Sinus

45 MR Venography (MRV)

46 MR Spectroscopy (MRS) The strength and promise of MRS come from its unique ability to allow non-invasive in-vivo measurement of biochemical components of tissue for differential diagnosis Differences in chemical bondings of various metabolites cause very small differences in the local tissue magnetic field and resonant frequency A plot of the resonant frequencies can be used to identify different chemicals present in a sample

47 Clinical Applications of MRS Ischaemic stroke Brain abscess Brain tumour Alzheimer s disease Hepatic encephalopathy Metabolic disorders NA: N-acetyl aspartate Glx: Glutamine / Glutamate Cr: Creatine Cho: Choline mi: Myo-inositol Normal MR Spectrum of Brain Tissue

48 MR Spectroscopy (MRS) Normal white matter Astrocytoma

49 MR Spectroscopy (MRS) Normal tissue Ischaemic stroke

50 Age Related Changes T1-W T2-W FLAIR T1-W T2-W FLAIR

51 Acute Ischemic Stroke (I) CT T2-W DWI CT T2-W DWI

52 Acute Ischemic Stroke (II)

53 Chronic Cerebral Infarct T1-W T2-W DWI T1-W T2-W DWI

54 Stroke Imaging DWI Chronic Cerebral Infarct DWI Acute Cerebral Infarct

55 Brain Abscess (I) T2-W T1-W DWI T1-W Post-Gd T2-W T1-W DWI T1-W Post-Gd

56 Brain Abscess (II)

57 Brain Metastasis (I) T2-W T2-W T2-W FLAIR FLAIR

58 Brain Metastasis (II) T1-W Post-Gd T1-W Post-Gd T1-W Post-Gd T1-W Post-Gd

59 Glioblastoma Multiforme (GBM) (I) T2-W T2-W FLAIR FLAIR T1-W T1-W T1-W

60 Glioblastoma Multiforme (GBM) (II) T1-W Post-Gd T1-W Post-Gd T1-W Post-Gd T1-W Post-Gd

61 Meningioma T2-W T2-W T1-W Post-Gd T1-W T1-W

62 Multiple Sclerosis (MS) T2-W T2-W T2-W T1-W Post-Gd T1-W T1-W FLAIR

63 Fetal MR Imaging MRI is a valuable complement to obstetric ultrasound when additional information is required for treatment decisions during pregnancy Non-invasive No known biological effect on fetus MR contrast agent is usually not recommended except clinical benefit outweigh risk

64 Fetal MR Imaging Dandy Walker Malformation

65 Fetal MR Imaging Hydrocephalus

66 Functional MRI (fmri) Functional brain mapping Localization of sensorimotor areas in cerebral cortex for neuro-surgical planning Plan the extent of surgical resection Accurate pre-surgical assessment of the risks and benefits of surgery Psycho-neurological research

67 Functional MRI (fmri) Fast imaging techniques to monitor rapid signal changes secondary to cortical activation Echo Planar Imaging (EPI) Specific neuronal activation paradigm Dedicated software tools for image analysis Blood Oxygen Level Dependent (BOLD) contrast contributes to signal variation

68 Blood Oxygen Level Dependent (BOLD) Regional increase of cerebral blood flow that accompanies cortical activation increases regional delivery of oxygen in excess of demand Change in ratio of oxyhaemoglobin and deoxyhaemoglobin will lead to variation in MRI signal Resting Cortical Activation

69 Functional MRI (fmri) On On On Right finger tapping Off Off Off Left finger tapping

70 Functional MRI (fmri) Right finger tapping Left finger tapping

71 Summary MRI is the imaging modality of choice for investigation of neurological conditions Non-invasive Excellent gray / white matter differentiation Multi-planar imaging capability High safety profile of MR contrast medium DWI is essential for stroke imaging MRA allows non-invasive demonstration of cerebral vasculature MRS provides non-invasive assessment of biochemical components of cerebral lesions

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