BM402: Engineering In Medicine PDF

BM402: ENGINEERING IN MEDICINE 17th October 2024 M 2170 – South Campus MRI Functional MRI Applications of MRI and fMRI EEG Applications of EEG Multimodal Imaging MRI: ANATOMICAL SCAN Acıbadem Altunizade...

BM402: ENGINEERING IN MEDICINE 17th October 2024 M 2170 – South Campus MRI Functional MRI Applications of MRI and fMRI EEG Applications of EEG Multimodal Imaging MRI: ANATOMICAL SCAN Acıbadem Altunizade Hospital Siemens 3 T MR Scanner Sagittal view Axial view Healthy volunteer FMRI: FUNCTIONAL SCAN Functional networks Veer et al. 2010 MAGNETIC RESONANCE IMAGING: MRI The MRI scanner is essentially a giant magnet. The strength of the magnet is measured in a unit called Tesla (T). The earth’s magnetic field is around 0.00006 T. A 3 T MRI scanner is around 50,000 times stronger than the earth’s magnetic field! Most (clinical) MRI scanners used in hospitals and medical research clinics are 1.5 or 3 T, while some research scanners are at fields of 7 T, 10.4 T and 11.7 T. INSTALLATION OF 11.7 T Giant Magnet 11.7 T, NeuroSpin 16.03.2019, NIH, Bethesda, MD, USA 5 meters long, 5 meters in diameter, and It will require about 35,000 liters of helium to cool the weighs over 130 metric tons superconductive coils that create the magnetic field. ~380 tons of steel were needed to prevent the magnet’s field from interfering with other equipment in the building. Unboxing - World's Most Powerful Brain Scanner - YouTube HOW MRI WORKS HOW MRI WORKS HOW MRI WORKS HOW MRI WORKS HOW MRI WORKS Some Glossary B0: ↑ The MRI scanner’s main magnetic field. Precessional Frequency: ↑ The rate at which protons spin in a magnetic field. RF: ↑ Radio frequency pulse (also referred as B1) used to tip on resonance protons away from the B0 field. On Resonance: ↑ Have the same frequency. Fourier Transform: ↑ A mathematical calculation that is used to change the electrical current in a coil into an image. HOW MRI WORKS Some Glossary B0: ↑ The MRI scanner’s main magnetic field. Precessional Frequency: ↑ The rate at which protons spin in a magnetic field. RF: ↑ Radio frequency pulse (also referred as B1) used to tip on resonance protons away from the B0 field. On Resonance: ↑ Have the same frequency. Fourier Transform: ↑ A mathematical calculation that is used to change the electrical current in a coil into an image. The natural precession frequency of a spin system is also known as the Larmor frequency. HOW MRI WORKS: PRECESSION The natural precession frequency of a spin system is also known as the Larmor frequency. ω = γB where ω is the Larmor frequency in MHz, γ is the gyromagnetic ratio in MHz/tesla and γ is a constant specific to each specific nucleus or particle (e.g., H-1=42.58); and B is the strength of the static magnetic field in tesla. Larmor, 1857 – 1942 HOW MRI WORKS: FOCUSING OUR IMAGING Head coil HOW MRI WORKS: FOCUSING OUR IMAGING Head coil HOW MRI WORKS: IMAGE FORMATION Ridgway, 2010 FOURIER TRANSFORM Converting from k-space to image space In image space, the basic sampling unit is distance; in k-space, the basic sampling unit is spatial frequency (1/distance). Qualitatively speaking, a wider range of coverage in k-space results in higherspatial resolution in image space (i.e., smaller voxels). Dr. Seiji Ogawa Converting from k-space to image space Different parts of the k-space data correspond to different spatial-frequency components of the image. The center of k-space (B) provides low-spatial frequency information, retaining most of the signal but not fine details. The periphery of k-space (C) provides high spatial-frequency information, and thus more image detail, but it contributes relatively little signal to the image. Dr. Seiji Ogawa Converting from k-space to image space Different parts of the k-space data correspond to different spatial-frequency components of the image. The center of k-space (B) provides low-spatial frequency information, retaining most of the signal but not fine details. The periphery of k-space (C) provides high spatial-frequency information, and thus more image detail, but it contributes relatively little signal to the image. Dr. Seiji Ogawa FIRST MR IMAGE 2003 Nobel Prize in Physiology or Medicine was not awarded for the discovery of the medical applications of MR, but for the development of techniques for image formation. FIRST MR IMAGE 2003 Nobel Prize in Physiology or Medicine was not awarded for the discovery of the medical applications of MR, but for the development of techniques for image formation. On October 12, 2003, the Nobel Committee on Physiology and Medicine awarded the Nobel Prize to Paul Lauterbur and Sir Peter Mansfield for MRI. MRI BASICS As Rabi used a strong magnetic field to measure spin properties of nuclei, today’s MRI scanners use a strong magnetic field to induce changes in proton spin. Just as Bloch detected nuclear induction using transmitter and receiver coils, scanners now use similar coil systems to obtain MR signals. Configuration of the gradient coils used for spatial encoding in all three dimensions. Transceiver indicates And, just as Lauterbur manipulated the the RF system comprising a transmitter, coil and magnetic field strength using changing receiver (Coyne 2012). gradient fields to create an image, almost every current MRI study relies on magnetic gradients for image acquisition. 1.5 T 3T 7T MRI HARDWARE Static magnetic field Gradient coils Gradients are loops of wire or thin conductive sheets on a cylindrical shell Configuration of the gradient coils used for spatial lying just inside the bore of an MR scanner. encoding in all three dimensions (Coyne 2012). When current is passed through these coils a secondary magnetic field is created. This gradient field slightly distorts the main magnetic field in a predictable pattern, causing the resonance frequency of protons to vary in as a function of position. The primary function of gradients, therefore, is to allow spatial encoding of the MR signal. MRI HARDWARE Static magnetic field Gradient coils RF coils RF coils are the antennas of the MRI system and have two functions: first, to excite the magnetization by broadcasting the RF power (Tx‐Coil) and second to receive the signal from the excited spins (Rx‐Coil). MRI HARDWARE Static magnetic field Gradient coils RF coils Shimming coils Other necessary parts are the shimming coils that ensure the homogeneity of the static magnetic field; specialized computer systems for controlling the scanner; and the experimental task, and physiological monitoring equipment. BASICS OF MR IMAGE CONTRAST (T1, T2, T2*) T1 and T2 are inherent properties of tissues and are thus fixed for a specific tissue (at a given magnetic field strength). The parameter T2*, however, also depends on inhomogeneities in the main magnetic field, but again is fixed for a specific tissue within a given external magnetic environment. BASICS OF MR IMAGE CONTRAST (T1, T2, T2*) T1 and T2 are inherent properties of tissues and are thus fixed for a specific tissue (at a given magnetic field strength). The parameter T2*, however, also depends on inhomogeneities in the main magnetic field, but again is fixed for a specific tissue within a given external magnetic environment. RF OFF: The spins will go back to the lowest energy state. The spins will get out of phase with each other. Once the RF is turned off, the transverse magnetization vector begins to decay while the longitudinal component begins to recover. BASICS OF MR IMAGE CONTRAST (T1, T2, T2*) BASICS OF MR IMAGE CONTRAST (T1, T2, T2*) T1-weighted images are produced by using short acquisiton times; conversely, T2-weighted images are produced by using longer times. BASICS OF MR IMAGE CONTRAST (T1, T2, T2*) WM CSF CSF GM T1-weighted images are produced by using short acquisiton times; conversely, T2-weighted images are produced by using longer times. BASICS OF MR IMAGE CONTRAST (T1, T2, T2*) Time to Echo (TE) is the time between the delivery of the T2* image showing low signal area due RF pulse and the receipt of the echo signal. to old blood products.  T2*-sensitive sequences also form the basis for functional MRI (fMRI) using the BOLD (Blood Oxygen Level Dependent) technique ∙ Arteries, veins, capillaries: 2% brain 20% energy (oxygen supply)  T2*-sensitive sequences also form the basis for functional MRI (fMRI) using the BOLD (Blood Oxygen Level Dependent) technique ∙ Arteries, veins, capillaries: 2% brain 20% energy (oxygen supply)  T2*-sensitive sequences also form the basis for functional MRI (fMRI) using the BOLD (Blood Oxygen Level Dependent) technique Source: Jorge Jovicich, fMRIB Brief Introduction to fMRI Background: the birth of functional brain imaging Apparatus used by Mosso to record Increases in temperature in the cat visual Increase in CBF produced by hand changes in brain volume in patients cortex by shining light into the eye movement in the contralateral sensory with skull defects (Mosso, 1880). (Schmidt and Hendrix, 1938). motor cortex (Lassen et al., 1978) Recordings of brain expansion in response Increase in cerebral blood flow (CBF) to intracarotid infusion of a brain extract produced in the calcarine cortex and (Roy and Sherrington, 1890). superior colliculus by visual stimulation (Freygang and Sokoloff, 1958). Iadecola et al., 2017 FMRI TERMINOLOGY FMRI TERMINOLOGY RESTING STATE EXPERIMENT FUNCTIONAL MRI – TASK DESIGN  FUNCTIONAL MRI – TASK DESIGN Simplest task: eyes open & eyes closed Subtraction of the eyes-closed condition from the eyes-open condition identifies a BOLD signal intensity difference in the primary visual cortex (shown on the right).  FUNCTIONAL CONNECTIVITY A term that appears frequently in the literature when discussing correlations in spontaneous blood oxygen level dependent (BOLD) fluctuations is ‘functional connectivity’ which may refer to any study examining inter-regional correlations in neuronal variability. Reading assignment (10 min break) @moodle Cognitive Impairment Cognitive impairment refers to a spectrum of difficulties in various cognitive domains, including memory, attention, language, executive function, and visuospatial skills. Cognitive Impairment Cognitive impairment is prevalent across different age groups and can occur as a result of various factors, including aging, neurodegenerative diseases (e.g., Alzheimer's disease), traumatic brain injury, psychiatric disorders, and other medical conditions. Cognitive Impairment & Neurological Cases Alzheimer's Disease (AD) Memory loss (especially recent ones) Difficulty with language (e.g., trouble finding words or understanding speech) Challenges with problem-solving and decision-making Changes in mood or behavior. Changes in the brain Amyloid Plaques Neurofibrillary Tangles Neuronal Loss Shrinkage of Brain Tissue Impaired Neurotransmission Cognitive Impairment & Neurological Cases Alzheimer's Disease (AD) Memory loss (especially recent ones) Difficulty with language (e.g., trouble finding words or understanding speech) Challenges with problem-solving and decision-making Changes in mood or behavior. Changes in the brain The hippocampus is a critical structure in the brain, primarily Amyloid Plaques involved in memory processes. Neurofibrillary Tangles Neuronal Loss Shrinkage of Brain Tissue Impaired Neurotransmission Cognitive Impairment & Neurological Cases Mild Cognitive Impairment (MCI) MCI represents an intermediate stage between the cognitive changes of normal aging and the more serious problems caused by Alzheimer's disease (AD) or other types of dementia. Memory Impairment Risk of Progression to Dementia (not all cases of MCI progress to Alzheimer's disease) Underlying Pathology: The underlying causes of MCI can vary and may include age-related changes, vascular issues, medication side effects, or early stages of neurodegenerative diseases such as Alzheimer's disease. Cognitive Impairment & Neurological Cases Working memory, visuospatial ability, attention, semantic understanding, and motor performance are areas where fMRI findings in AD have been discovered. The at-risk patients performed the fMRI tasks pretty well, which was a common aspect of the studies revealing evidence of elevated fMRI activity. Hyperactivity was seen primarily during successful memory trials in event-related fMRI experiments, suggesting that hyperactivity could be a compensatory strategy in the early stages of AD. Cognitive Impairment & Neurological Cases Cognitive Impairment & Neurological Cases Cognitive Impairment & Neurological Cases Face Recognition Visual Object Recognition Cognitive Impairment & Neurological Cases Parkinson's disease Parkinson's disease is associated with a range of motor and non-motor symptoms. Neurodegenerative disorder that primarily affects movement. It is characterized by a progressive loss of dopaminergic neurons in a region of the brain called the substantia nigra, leading to a shortage of dopamine, a neurotransmitter involved in regulating movement. The iron overload has been associated with the loss of dopamine-producing neurons. Cognitive Impairment & Neurological Cases Parkinson's disease T2-weighted Imaging: MRI sequences known as T2- weighted imaging are particularly sensitive to the presence of iron. Iron-rich structures in the brain, such as the basal ganglia and substantia nigra, appear hypointense (dark) on T2-weighted images due to the paramagnetic properties of iron. This dark signal intensity indicates the presence of iron deposits in these regions. The iron overload has been associated with the loss of dopamine-producing neurons. Jetlag Salivary cortisol levels in cabin crew after repeated exposure to jet lag were significantly higher than after short distance flights. Cho, K. et al. (2000) Jetlag One hypothesis suggests that significant high cortisol elevations induce hippocampal atrophy and deficits in hippocampus- dependent learning and memory. Therefore, the long-term effect of repeated jet lag on both the volume of the temporal lobe and hippocampus- dependent memory performance were tested in 20 healthy women employed by international airline companies. Compared the volume of the temporal lobe in two flight attendant groups with different jet lag recovery periods (n = 10 subjects in each group). Jetlag Subjects were assigned to groups based on their individual flight records: The short-recovery group had recovery intervals of less than 5 days between outward transmeridian flights across at least 7 times zones, whereas the long-recovery group had intervals of more than 14 days between outward transmeridian flights. Compared the volume of the temporal lobe in two flight attendant groups with different jet lag recovery periods (n = 10 subjects in each group). Jetlag Compared the volume of the temporal lobe in two flight attendant groups with different jet lag recovery periods (n = 10 subjects in each group). EEG basics Electro-encephalo-gram Brain Electrical Picture/Record sleeping EEG is the measurement of electrical patterns at the surface of the scalp which reflect cortical activity - commonly referred as “brainwaves”. EEG basics Electro-encephalo-gram Brain Electrical Picture/Record sleeping EEG is the measurement of electrical patterns at the surface of the scalp which reflect cortical activity - commonly referred as “brainwaves”. International 10-20 system 21 channel EEG Electrocorticography ECoG, iEEG Grid and stick electrodes Dr Kareem Zaghloul - Neural signatures of memory and information in the human brain EEG History Analysis – next week(s) EEG History EEG - brain rhythms