Clinical Applications of Diffusion Imaging in Neuroradiology No disclosures Stephen F. Kralik Assistant Professor of Radiology Indiana University School of Medicine Department of Radiology and Imaging Sciences Outline Basics of Diffusion Imaging Free environment Complex environment Basic concept of diffusion imaging Clinical applications of diffusion imaging in neuroradiology Diffusion Imaging uses the motion of water to explore the the microstructure of biological tissues. Water molecules encounter different structures in the human body which affect the freedom of movement. Basics of Diffusion Imaging The purpose of Diffusion-weighted imaging (DWI) is to create contrast within the anatomy based on the movement of water. DWI is usually performed with a single shot echo echo planar (EPI) sequence. DWI uses application of diffusion gradients to each side of 180 pulse. The first gradient dephases the spins of the water molecules, while the second gradient rephases Result: Faster water motion = weaker signal Slower/Immobile water motion = stronger signal. Basics of Diffusion Imaging The degree of diffusion weighting (b-value) is increased by increases in: Gradient amplitude Application time Time between the two gradients The sensitivity to the detection of diffusion is limited the direction of the gradients. Acquisition requires gradients oriented in 3 directions to create a global diffusion. The diffusion image will have both a T2 and a diffusion component.
Basics of Diffusion Imaging By acquiring images with 2 b-values (b=0 and b=1000 s/mm2), the apparent diffusion coefficient (ADC) can be calculated and the ADC image no longer has a T2 component. ADC = reduced water motion Most Clinically important Pathology ADC = increased water motion Outline Basic concept of diffusion imaging Clinical applications of diffusion imaging in neuroradiology DWI Clinical applications: Neuroradiology Diffusion Imaging: Brain Stroke Infection Tumor Trauma Brain Neck Spine Diffusion Imaging: Brain Stroke Infection Tumor Trauma Stroke Most important use of diffusion in neuroradiology Stroke is the 4 th leading cause of death in the U.S. About 800,000 new strokes per year (1 every 4 seconds) Stroke is caused by either a reduction of blood flow or oxygen to the brain or rupture of blood vessel in the brain Brain cells do not receive enough oxygen to function
Stroke Normal Brain: 22 billion neurons, 150 trillion synapses, 84,500 miles of length of myelin fibers Each minute of stroke loses: 1.9 million neurons, 14 billion synapses, and 7.5 miles of myelin fibers Stroke: DWI Most sensitive imaging test for detection of acute stroke Demonstrates the size and location of an acute infarct before any other MRI sequence Most centers will perform MRI with diffusion to diagnose/confirm presence or absence of acute stroke after a CT scan has excluded acute hemorrhage 61 year old with acute gait abnormality 61 year old with acute gait abnormality DWI more sensitive for acute stroke than noncontrast CT 70 year old with acute left sided weakness Large right MCA infarct. DWI characterizes extent of infarct
70 year old with acute left sided weakness 3 days of left hand weakness Infarct visible on FLAIR and CT ADC isointense in subacute phase of infarct New on set of weakness. Prior history of stroke. New on set of weakness. Prior history of stroke. Old infarct visible on T2 and FLAIR. Is there acute infarct present? No diffusion restriction present. Old infarct has increased diffusion due to loss of brain tissue 30 yo with Lupus and acute neurological deficits. Is there acute stroke present? DWI demonstrates multiple infarcts and multiple vascular territories.
Catheter Angiography demonstrated vasculitis as the etiology 6 day old baby with seizures. Evaluate for acute ischemia 6 day old baby with seizures. Evaluate for acute ischemia 52 yo found down. Unresponsive on ventilator. Evaluate for anoxic injury Symmetric reduced diffusion in the basal ganglia and thalami indicates hypoxia/hypoperfusion etiology What is the cause of the T2 signal hyperintensity? 52 yo found down. Unresponsive on ventilator. Evaluate for anoxic injury Mimic 45 yo with acute seizure Symmetric acute ischemia to the white matter from anoxic injury
Summary DWI is uniquely valuable for evaluation of acute stroke DWI will demonstrate restricted diffusion in acute infarct. Pattern of infarcts can indicate mechanism Diffusion Imaging: Brain Stroke Infection Tumor Trauma Some types of infections, most commonly bacterial, may become organized within a confined space The motion of water can become restricted within this confined space Multiple ring enhancing brain masses. What is the etiology? Bacterial Abscesses 17 year old with orbit infection.?
17 year old with orbit infection. Empyema! 15 year old with scalp swelling.?? 15 year old with scalp swelling. Empyema! An abscess or empyema may require emergent surgical drainage Acute abscesses will demonstrate central restricted diffusion. Following treatment with antibiotics and/or drainage, abscesses will generally no longer restrict on DWI Diffusion Imaging: Brain Stroke Infection Tumor Trauma Brain tumors may demonstrate a wide range of appearances More malignant tumors tend to have less intracellular free water motion due to larger nucleus:cytoplasm ratio
Brain tumors may demonstrate a wide range of appearances appearances on the histology The more tightly packed the tumor cells, the greater the restriction of extracellular water motion Two different patients. Which one has the benign tumor? A B Low grade tumor - JPA High grade tumor - Medulloblastoma Patient A Patient B An 11-month-old boy with atypical teratoid/rhabdoid tumor WHO GRADE 4. A 12-month-old child with desmoplastic infantile ganglioglioma WHO GRADE 1 Diffusion Imaging for Tumor Grading of Supratentorial Brain Tumors in the First Year of Life Kralik et al. AJNR Am J Neuroradiol 35:815 23 Two different patients. Which one has the benign tumor? A B Conclusion: ADC maps can differentiate high- versus lowgrade neoplasms for supratentorial tumors presenting in the first year of life, given the significant negative correlation between ADC values and tumor grade.
Two different patients. Which one has the benign tumor? Ring enhancing mass. Is this an abscess? A B Benign Malignant Peripheral diffusion restriction NOT central restriction Brain Metastasis Ring enhancing mass. Is this an abscess or metastasis? Infiltrative diffusion restriction Glioblastoma Multiforme In general, the DWI correlates with histopathology, tumor cellularity, and grading of benign vs malignant Some tumors may have similar post contrast appearance, however, drastically different DWI appearance A few potential exceptions to the rule
Epidermoid cysts may demonstrate restricted diffusion due to the internal complexity of the cyst Epidermoid Cyst - Benign Diffusion Imaging: Brain DWI: Trauma 24 yo with acute trauma/mva Stroke Infection Tumor Trauma DWI: Trauma In the setting of acute trauma, small areas of diffusion restriction in the white matter can indicate diffuse axonal injury (DAI) DWI Clinical applications: Neuroradiology Brain Neck Spine
DWI: Neck DWI Orbit: Tumor Which patient s tumor is benign? Patient 1 Patient 2 Increasing investigation into the utility of DWI for neck pathology Main focus is with tumor differentiation, or complications of infections 7-week-old girl with history of bump on the left eye lid 22-month-old girl with history of right eye swelling Patient 1 DWI Orbit: Tumor Patient 2 DWI Orbit: Tumor 7-week-old girl with history of bump on the left eye lid Final Diagnosis: Infantile hemangioma. 22-month-old girl with history of right eye swelling Final Diagnosis: Rhabdomyosarcoma. DWI Temporal Bone: Cholesteatoma versus effusion or granulation tissue? DWI Temporal Bone: Cholesteatoma versus effusion? EPI DWI
DWI Temporal Bone: Cholesteatomas are similar to epidermoid cysts, and should demonstrate restricted diffusion Problem: temporal bone creates artifact limiting visualization on DWI Solution: non-epi DWI DWI Temporal Bone: AJNR Am J Neuroradiol 32:430 36 Mar 2011 DWI Temporal Bone: Cholesteatoma versus effusion? DWI Clinical applications: Neuroradiology T2 HASTE Diffusion Final Diagnosis: Cholesteatoma Brain Neck Spine DWI: Spine Increasing interest in DWI for spinal pathology DWI: Spine Acute Infarct Main areas of utility include detection of acute spinal cord infarct, spinal infection, and spinal cord tumors Challenges: small region surrounded by bone, motion from CSF/breathing/ swallowing
DWI Spine: Infection Is this fluid an abscess? DWI Spine: Infection Is this fluid an abscess? Epidural Abscess Summary DWI provides unique information in neuroradiology DWI has most frequent application for acute stroke Not everything that shows restricted diffusion is an acute stroke Diffusion can be utilized to provide identification of infection and tumor in the brain, neck, and spine