Diffusion-weighted MR imaging of the brain

1 Basics of Diffusion Measurements by MRI . . . . . . . . . . . . . . . . . . . . 1 1.1 Diffusion Imaging in MR . . . . . . . . . . 1 1.2 Diffusion Imaging of the Brain . . . . . . . 1 1.3 Magnetic Resonance Principles of Diffusion Imaging . . . . . . . . . . . . . 1 1.4 Apparent Diffusion Coefficient . . . . . . . 2 1.5 Diffusion Represents a Molecular Event . . 3 1.6 Requirements in Clinical Diffusion Imaging . . . . . . . . . . . . . . . 4 1.7 Setting the b-Value in Clinical DW Imaging . . . . . . . . . . . . . . . . . 4 1.8 Future Trends in Clinical DW Imaging . . . 5 References . . . . . . . . . . . . . . . . . . . . . . 5 2 Diffusion-Weighted Imaging of the Normal Brain . . . . . . . . . . . . 7 2.1 Introduction . . . . . . . . . . . . . . . . . 7 2.2 Adult Brain . . . . . . . . . . . . . . . . . . 7 2.2.1 Low Signal in Basal Ganglia . . . . 7 2.2.2 Diffusion-Weighted Imaging of Gray and White Matter . . . . . 7 2.2.3 Choroid Plexus . . . . . . . . . . . 7 2.3 Pediatric Brain . . . . . . . . . . . . . . . . 9 2.3.1 Diffusion-Weighted Imaging and ADC of the Pediatric Brain . . 9 2.4 Conclusion . . . . . . . . . . . . . . . . . . 10 References . . . . . . . . . . . . . . . . . . . . . . 10 3 Pitfalls and Artifacts of DW Imaging . . 11 3.1 Introduction . . . . . . . . . . . . . . . . . 11 3.2 Influence of ADC and T2 on the DW Appearance . . . . . . . . . . . 11 3.2.1 Concepts . . . . . . . . . . . . . . 11 3.2.2 Apparent Diffusion Coefficient Maps . . . . . . . . . . 11 3.2.3 Exponential Images. . . . . . . . . 11 3.3 Clinical Conditions . . . . . . . . . . . . . . 12 3.3.1 T2 Shine-through . . . . . . . . . . 12 3.3.2 T2 Washout . . . . . . . . . . . . . 15 3.3.3 T2 Blackout . . . . . . . . . . . . . 16 3.4 Artifacts . . . . . . . . . . . . . . . . . . . 18 3.4.1 Eddy Current Artifacts . . . . . . . 18 3.4.2 Susceptibility Artifacts . . . . . . . 18 3.4.3 N/2 Ghosting Artifact (Nyquist Ghost) . . . . . . . . . . 20 3.4.4 Chemical Shift . . . . . . . . . . . 20 3.4.5 Motion Artifacts . . . . . . . . . . 20 3.5 Conclusion . . . . . . . . . . . . . . . . . . 23 References . . . . . . . . . . . . . . . . . . . . . . 23 4 Brain Edema . . . . . . . . . . . . . . . . . 25 4.1 Characterization and Classification of Brain Edema . . . . . . . . . . . . . . . . 25 4.2 Definition and Classification of Cytotoxic Edema . . . . . . . . . . . . . 25 4.3 Pathophysiology of Cytotoxic Edema. . . . 25 4.3.1 Energy Failure . . . . . . . . . . . 25 4.3.2 Excitotoxic Brain Injury . . . . . . 27 4.4 Diffusion-Weighted Imaging and Cytotoxic Edema . . . . . . . . . . . . 28 4.4.1 Conditions that Cause Cytotoxic Edema, and Reversibility . . . . . . 29 4.5 Vasogenic or Interstitial Edema . . . . . . 35 4.5.1 Conditions that Cause Vasogenic Edema . . . . . . . . . . 364.6 Conclusion . . . . . . . . . . . . . . . . . . 37 4.6.1 Cytotoxic or Cellular Edema . . . 37 4.6.2 Vasogenic Edema . . . . . . . . . . 37 References . . . . . . . . . . . . . . . . . . . . . . 37 5 Infarction . . . . . . . . . . . . . . . . . . 39 5.1 Clinical Significance and Therapeutic Considerations for Brain Infarcts . . . . . . 39 5.1.1 Stroke Mimickers . . . . . . . . . . 39 5.1.2 Diffusion-Weighted Imaging. . . . 39 5.2 Diffusion-Weighted Imaging and Pathophysiology of Cerebral Infarction . . 39 5.3 Apparent Diffusion Coefficient . . . . . . . 40 5.3.1 Explanation for Restricted Diffusion. . . . . . . . . . . . . . . 40 5.4 Time Course of Infarction . . . . . . . . . . 40 5.4.1 Hyperacute (<6 Hours) . . . . . . 40 5.4.2 Acute (6 Hours to 3 Days) . . . . . 42 5.4.3 Subacute (3 Days to 3 Weeks) . . . 43 5.4.4 Chronic (3 Weeks to 3 Months) . . 44 5.5 Diffusion-Weighted Imaging and ADC Characteristics of Gray and White Matter Ischemia . . . . . . . . . 45 5.5.1 Relative ADC . . . . . . . . . . . . 45 5.6 Reversibility and Treatment . . . . . . . . . 45 5.7 Watershed Infarction. . . . . . . . . . . . . 47 5.8 Perfusion Versus Diffusion Imaging . . . . 48 5.9 Venous Infarction . . . . . . . . . . . . . . 48 5.9.1 Predisposing Factors . . . . . . . . 48 5.9.2 Pathophysiology . . . . . . . . . . 48 5.10 Small Vessel Infarcts . . . . . . . . . . . . . 50 5.11 Brain Stem and Cerebellar Infarcts . . . . . 51 5.12 Corpus Callosum Infarcts . . . . . . . . . . 52 5.13 Hemorrhagic Infarcts . . . . . . . . . . . . 53 References . . . . . . . . . . . . . . . . . . . . . . 54 6 Intracranial Hemorrhage . . . . . . . . . 55 6.1 Introduction . . . . . . . . . . . . . . . . . 55 6.2 Intraparenchymal Hemorrhages: Appearance and Evolution. . . . . . . . . . 55 6.2.1 Hyperacute Hematoma . . . . . . 55 6.2.2 Acute Hematoma . . . . . . . . . . 59 6.2.3 Early Subacute Hematoma . . . . 59 6.2.4 Late Subacute Hematomas . . . . . 62 6.2.5 Chronic Hematomas . . . . . . . . 62 6.3 Subarachnoid Hemorrhage . . . . . . . . . 62 6.4 Subdural and Epidural Hemorrhages . . . 64 6.5 Intraventricular Hemorrhage . . . . . . . . 65 6.6 Intra-tumoral Hemorrhage . . . . . . . . . 66 6.7 Hemorrhage Related to Vascular Malformation . . . . . . . . . . 67 6.8 Hemorrhage Related to Trauma . . . . . . 68 6.9 Conclusions . . . . . . . . . . . . . . . . . . 68 References . . . . . . . . . . . . . . . . . . . . . . 69 7 Vasculopathy and Vasculitis . . . . . . . 73 7.1 Definition . . . . . . . . . . . . . . . . . . . 73 7.2 Clinical Presentation . . . . . . . . . . . . . 73 7.3 Treatment . . . . . . . . . . . . . . . . . . . 73 7.4 Vasculitis of the CNS . . . . . . . . . . . . . 73 7.4.1 Characterization of CNS Vasculitis . . . . . . . . . . . . 73 7.4.2 Primary Angitis of the Central Nervous System . . . . . . 74 7.4.3 Giant Cell (Temporal) Arteritis . . 75 7.4.4 Takayasu’s Arteritis (Aortitis Syndrome) . . . . . . . . 78 7.4.5 Polyarteritis Nodosa . . . . . . . . 80 7.4.6 Churg–Strauss Disease . . . . . . . 80 7.4.7 Other Small Vessel Vasculitis. . . . 80 7.4.8 Collagen Vascular Diseases . . . . 80 7.4.9 Infectious Vasculitis . . . . . . . . 82 7.4.10 Drug-Induced Vasculitis, Including Illicit Drugs . . . . . . . 83 7.5 Vasculopathy of the CNS . . . . . . . . . . 84 7.5.1 Systemic Lupus Erythematosus . . 84 7.5.2 Moyamoya Disease . . . . . . . . . 86 7.5.3 Sickle Cell Disease . . . . . . . . . 86 7.5.4 Posterior Reversible Encephalopathy Syndrome . . . . 86 7.5.5 Hypertensive Encephalopathy . . . 87 7.5.6 Preeclampsia/Eclampsia . . . . . . 88 7.5.7 Immunosuppressive Drug-Induced Vasculopathy . . . . 89 7.5.8 Uremic Encephalopathy and Hemolytic Uremic Syndrome . . . 91 7.5.9 Thrombotic Thrombocytopenic Purpura . . . . . . . . . . . . . . . 92 7.5.10 Cerebral Amyloid Angiopathy . . . 92 7.6 Conclusion . . . . . . . . . . . . . . . . . . 92 References . . . . . . . . . . . . . . . . . . . . . . 93 8 Epilepsy . . . . . . . . . . . . . . . . . . . 95 8.1 Definition . . . . . . . . . . . . . . . . . . . 95 8.2 Classification . . . . . . . . . . . . . . . . . 95 8.3 Mechanisms and Pathophysiology of Epilepsy . . . . . . . . . . . . . . . . . . 958.4 Magnetic Resonance Imaging of Epilepsy 96 8.4.1 Diffusion-Weighted Imaging in Epilepsy . . . . . . . . . . . . . 97 8.4.2 Magnetic Resonance Signal Alterations in Epilepsy . . . . . . 98 8.4.3 Ictal Stage to Periictal Stage . . . 99 8.4.4 Status Epilepticus . . . . . . . . . 100 8.4.5 Cytotoxic Edema in Status Epilepticus . . . . . . . 101 8.4.6 Other Imaging Techniques for Epilepsy . . . . . . . . . . . . 103 8.5 Hemiconvulsion–Hemiplegia Epilepsy Syndrome . . . . . . . . . . . . . 103 8.6 Focal Lesion in the Splenium of the Corpus Callosum in Epileptic Patients . . . . . . . . . . . . 103 8.7 Conclusion . . . . . . . . . . . . . . . . . 103 References . . . . . . . . . . . . . . . . . . . . . 105 9 Demyelinating and Degenerative Disease. . . . . . . . 107 9.1 Demyelinating Disease . . . . . . . . . . . 107 9.1.1 Multiple Sclerosis . . . . . . . . . 107 9.1.2 Acute Disseminated Encephalomyelitis . . . . . . . . . 112 9.1.3 Progressive Multifocal Leukoencephalopathy . . . . . . . 112 9.2 Degenerative Disease . . . . . . . . . . . . 113 9.2.1 Wallerian or Transneuronal Degeneration. . . . . . . . . . . . 113 9.2.2 Creutzfeldt–Jakob Disease . . . . 114 9.2.3 Amyotrophic Lateral Sclerosis . . 116 9.3 Conclusion . . . . . . . . . . . . . . . . . 116 References . . . . . . . . . . . . . . . . . . . . . 117 10 Toxic and Metabolic Disease . . . . . . 119 10.1 Toxic Disease . . . . . . . . . . . . . . . . 119 10.1.1 Chemotherapy-Induced Leukoencephalopathy . . . . . . . 119 10.1.2 Heroin-Induced Spongiform Leukoencephalopathy . . . . . . . 119 10.1.3 Cocaine, Phencyclidine Hydrochloride,Amphetamines and Related Catecholaminergics . 119 10.1.4 Central Pontine Myelinolysis and Extrapontine Myelinolysis . . 122 10.1.5 Wernicke Encephalopathy . . . . 123 10.1.6 Marchiafava–Bignami Disease . . 124 10.2 Metabolic Disease . . . . . . . . . . . . . . 125 10.2.1 Mitochondrial Encephalopathy . 125 10.2.2 Phenylketonuria . . . . . . . . . . 126 10.2.3 Other Metabolic Diseases and Leukodystrophies. . . . . . . 126 References . . . . . . . . . . . . . . . . . . . . . 129 11 Infectious Diseases . . . . . . . . . . 131 11.1 Overview of Brain Infections. . . . . . . . 131 11.2 Bacterial Brain Abscess . . . . . . . . . . . 131 11.3 Septic Emboli . . . . . . . . . . . . . . . . 132 11.4 Brain Abscess Caused by Unusual Bacteria . . . . . . . . . . . . . . 133 11.4.1 Differential Diagnosis . . . . . . 133 11.5 Bacterial Abscess in the Extra-Axial Space . . . . . . . . . . . . . . 137 11.5.1 Differential Diagnosis . . . . . . 137 11.6 Bacterial Vasculitis . . . . . . . . . . . . . 141 11.7 Toxoplasmosis . . . . . . . . . . . . . . . 141 11.7.1 Differential Diagnosis . . . . . . 143 11.8 Disseminated Aspergillosis . . . . . . . . 145 11.9 Herpes Encephalitis . . . . . . . . . . . . 145 11.10 Human Immunodeficiency Virus Infection . . . . . . . . . . . . . . . 146 References . . . . . . . . . . . . . . . . . . . . . 147 12 Trauma . . . . . . . . . . . . . . . . . . . 149 12.1 Introduction . . . . . . . . . . . . . . . . . 149 12.2 Diffuse Axonal Injury. . . . . . . . . . . . 149 12.2.1 Location . . . . . . . . . . . . . . 149 12.2.2 Computed Tomography and MR Imaging. . . . . . . . . . 154 12.2.3 Diffusion-Weighted Imaging . . . 154 12.3 Brain Contusion. . . . . . . . . . . . . . . 154 12.3.1 Location . . . . . . . . . . . . . . 154 12.3.2 Computed Tomography and MR Imaging. . . . . . . . . . 156 12.3.3 Diffusion-Weighted Imaging Findings . . . . . . . . . 156 12.4 Hemorrhage Related to Trauma . . . . . . 156 12.4.1 Computed Tomography and MR Imaging. . . . . . . . . . 157 12.4.2 Diffusion-Weighted Imaging . . . 157 12.5 Vascular Injuries . . . . . . . . . . . . . . 159 References . . . . . . . . . . . . . . . . . . . . . 16013 Brain Neoplasms . . . . . . . . . . . . . 161 13.1 Introduction . . . . . . . . . . . . . . . . . 161 13.2 Gliomas . . . . . . . . . . . . . . . . . . . 161 13.2.1 High-Grade Tumors . . . . . . . . 161 13.2.2 Peritumoral Infiltration . . . . . . 168 13.2.3 Treatment Response . . . . . . . . 168 13.3 Epidermoid Tumors and Arachnoid Cysts . . . . . . . . . . . . 169 13.4 Primitive Neuroectodermal Tumors. . . . 171 13.5 Meningiomas . . . . . . . . . . . . . . . . 172 13.6 Malignant Lymphomas . . . . . . . . . . . 174 13.7 Craniopharyngiomas . . . . . . . . . . . . 175 13.8 Metastases . . . . . . . . . . . . . . . . . . 176 13.9 Conclusion. . . . . . . . . . . . . . . . . . 178 References . . . . . . . . . . . . . . . . . . . . . 178 14 Pediatrics . . . . . . . . . . . . . . . . . . 181 14.1 Water Content of the Pediatric Brain . . . 181 14.2 Normal Structures . . . . . . . . . . . . . 181 14.3 Anisotropy. . . . . . . . . . . . . . . . . . 182 14.4 Infarction and Ischemia . . . . . . . . . . 182 14.4.1 Moyamoya Disease . . . . . . . . 184 14.4.2 Sickle Cell Disease . . . . . . . . . 184 14.4.3 Hypoxic Ischemic Encephalopathy . . . . . . . . . . 184 14.5 Trauma . . . . . . . . . . . . . . . . . . . 186 14.5.1 Battered Child Syndrome . . . . . 186 14.5.2 Diffuse Axonal Injury and Brain Contusion . . . . . . . 189 14.6 Encephalopathies . . . . . . . . . . . . . . 189 14.6.1 Mitochondrial Encephalopathy . 189 14.6.2 Acute Necrotizing Encephalopathy . . . . . . . . . . 190 14.6.3 Hypertensive Encephalopathy . . 190 14.7 Infections . . . . . . . . . . . . . . . . . . 191 14.7.1 Encephalitis . . . . . . . . . . . . 191 14.7.2 Brain Abscess . . . . . . . . . . . 193 14.8 Brain Tumor . . . . . . . . . . . . . . . . . 194 14.9 Dysmyelination and Demyelination . . . . 195 14.9.1 Pelizaeus–Merzbacher Disease . . 195 14.9.2 Vanishing White Matter Disease . 196 14.9.3 Metabolic or Toxic Leukoencephalopathies . . . . . . 196 14.9.4 Multiple Sclerosis . . . . . . . . . 197 14.9.5 Osmotic Myelinolysis . . . . . . . 197 14.10 Conclusion. . . . . . . . . . . . . . . . . . 199 References . . . . . . . . . . . . . . . . . . . . . 199 15 How to Use This Book . . . . . . . . . 201 Table 1 Differential diagnoses for lesions with a high diffusion signal associated with low ADC and iso intense T2 signal . . . . . . . . . 202 Table 2 Differential diagnoses for lesions with a high diffusion signal associated with iso-high ADC and a high intense T2 signal . . . . . . . 203 Table 3 Differential diagnoses for lesions with a high diffusion signal associated with a low ADC and high intense T2 signal . . . . . . . 208 Table 4 Differential diagnoses for lesions with an iso diffusion signal associated with a high ADC and high intense T2 signal . . . . . . . . 218 Table 5 Differential diagnoses for lesions with a low diffusion signal associated with a high ADC and high intense T2 signal . . . . . . . . 219 Table 6 Differential diagnoses for lesions with a low diffusion signal associated with a high ADC and iso intense T2 signal . . . . . . . . . 221 Table 7 Differential diagnoses for lesions with artifacts . . . . . . . . . . . . . . . 222