Week 1. 2 Brain Imaging of Communication Disorders-Q PDF

Brain imaging of communication functions Imaging methods Neurophysiological methods 1. ( can be combined with imaging): Cerebral angiography 1. Electroencephalography (EEG) 2. Computed Tomography (CT) 3. Magnetic Resonance Imaging (MRI) 4. Functional MRI 5. Positron Emission Tomography (PET) 2. Magn...

Brain imaging of communication functions Imaging methods Neurophysiological methods 1. ( can be combined with imaging): Cerebral angiography 1. Electroencephalography (EEG) 2. Computed Tomography (CT) 3. Magnetic Resonance Imaging (MRI) 4. Functional MRI 5. Positron Emission Tomography (PET) 2. Magnetoencephalography (MEG) Other methods ( for lateralization/ localization of cortical function): 1. WADA Test 2. Electrical stimulation mapping Date Your Footer Here 1 Imaging methods 1. Cerebral Angiography Use X-ray to examine the arteries and veins - look for blockages and other vascular problems ( Aneurysms, stenosis, tumor, hemorrhage, blood vessels inflammation) Previously: Catheter through the femoral artery is used to reach the area of interest in the vascular system. A contrast agent is injected and navigated by x-ray fluoroscopy. Fig. 3.1 Right carotid angiogram obtained before a Wada test, demonstrating the carotid bifurcation. The internal carotid artery is to the left. Limitations: - Catheter may damage a blood vessel or dislodge an embolus - Contrast agent may cause allergic reaction and may worsen rental impairment Date Your Footer Here 2 Imaging methods 1. Cerebral Angiography Currently: Angiography is used with CT and MRI. The contrast is administered intravenously. Vessels are visualized by CT and MRI… No catheter is needed so all associated risks are avoided Fig. 3.1 Right carotid angiogram obtained before a Wada test, demonstrating the carotid bifurcation. The internal carotid artery is to the left. Date Your Footer Here 3 Imaging methods 2. Computed Tomography (CT) 3D representations constructed from series of X-ray images. Helps to visualize structures at different depths within the body Differences in tissues density show different colors and shades in the scan Date High density body area (e.g., bone) White in color Low density body area (e.g., water) Black in color Your Footer Here 4 Imaging methods 2. Computed Tomography (CT) Advantages: - CT can detect lesions at structural levels and ideal for detecting abnormalities such as bone fracture, and ventricular abnormalities - CT has a high spatial resolution - CT can be used with angiogram ( called ACT) to detect arterial structure abnormalities Disadvantages: - Moderate to high exposure to radiation, repeated exposure may increase risk of cancer - In early stage of ischemic stroke, CT may appear normal or show only subtle changes. - The risk of use contrast agent Date Your Footer Here 5 Imaging methods 3. Magnetic Resonance Imaging (MRI) Use strong magnetic and radio waves and it interacts with hydrogen atoms and protons found in the body tissues T1-Weighted MRI T2-Weighted MRI FLAIR MRI Several types or sequences of MRI: Date T1-Weighted MRI T2-Weighted MRI FLAIR MRI Diffusion weighted MRI (dMRI) Your Footer Here 6 Imaging methods CT CT T1-Weighted MRI CT Angiogram T2-Weighted MRI FLAIR MRI Different types of MRI compared to CT The case: 65 years old patient with left MCA FLAIR MRI Date T2-Weighted MRI Your Footer Here DWI MRI Apparent diffusion coefficient 7 Imaging methods Advantages of MRI Also, it is saver than CT for pregnant women and children because it does not involve radiation Disadvantages of MRI 1. 2. 3. 4. Date Cost Time, it takes 15 to 60 minutes + the loud noise Sensitive to movements, thus, requires sedation for some cases (e.g., children) Not suitable for people with metal implants (e.g., pacemaker) 8 Imaging methods 4. Functional MRI (fMRI). It is technique that produce images of metabolic functions - Use Blood oxygen level dependent (BOLD) contrast to locate brain activity associated with a specific task - When you perform a task (any task), the brain area(or areas) involved in that task requires more blood flow. fMRI is used to locate the brain area correlated with the task by detecting the level of blood flow. Applications (examples): Use to locate language, sensorimotor, and visual functions Advantages: Evaluate brain function, safe technique, and high image resolution Disadvantages: Difficult to interpret the results sometimes ( correlating a behavior to a specific brain region) Date Your Footer Here 9 Imaging methods 4. Functional MRI (fMRI) A. Verbal fluency task B. Reading task Date Your Footer Here 10 Imaging methods 5. Positron Emission Tomography (PET) It is a nuclear medicine technique that produces a three-dimensional image of metabolic processes, blood flow, or receptor density within the body. Use a small dose of a radioactive tracer( a positron-emitting chemical) injected intravenously. Applications: It can detect disease processes before structural changes Use to evaluate brain tumors and early stage of Alzheimer’s disease or Parkinson’s Disadvantages: Date The exposure to radioactive tracer, cost, and time ( takes one to two hours) Your Footer Here 11 Neurophysiological methods 1. Electroencephalography (EEG) Measure electrical brain activities within the cerebral cortex It is commonly used to diagnose epilepsy, but it is also used in language research Advantages: low cost, high temporal resolution, safe Disadvantages: poor spatial resolution, and it is hard to detect activities of deep brain structures Date Your Footer Here 12 Neurophysiological methods Date Your Footer Here 13 Neurophysiological methods 2. Magnetoencephalography (MEG) It has magnetic sensors to measure magnetic fields produced by electrical currents in the brain. It is usually used with MRI to localize source of brain activity Also, it can be combined with EEG to locate source of seizure in the brain used in language research Advantages: high temporal resolution, safe, and it is directly measure brain function ( unlike fMRI) Disadvantages: poor spatial resolution, and it is hard to detect activities of deep brain structures 14 Other cortical function lateralization methods 1. WADA test Intracarotid amobarbital procedure Induce temporary paralysis of one side of the brain by injecting internal carotid artery. Language and memory measures are taken before and after the procedure. Test the dominance hemisphere and lateralization (i.e., language lateralization) It is an invasive test 15 Other cortical function lateralization methods 2. Electrical stimulation mapping Use Small electrical pulses that interfere with cortical activity in one area for a brief amount of time causing disruption of a specific behavior ( language, motor, or sensory function) It is used during brain surgeries (e.g., tumor) to ensure saving critical function such as language while doing excision of tumor. It is commonly used in awake craniotomy procedure It is also considered as an invasive method 16