Week 1 Flashcards
What is a positron?
A positron is a particle of matter with the same mass as an electron but an opposite charge. It is a form of antimatter because, when a positron encounters an electron, the two completely annihilate to yield energy. Its not the same as a proton!
What theory and by whom led the evolution of modern physics?
Special Relativity by Albert Einstein.
What is special relativity?
Special relativity is an explanation of how speed affects mass, time and space. The theory includes a way for the speed of light to define the relationship between energy and matter — small amounts of mass (m) can be interchangeable with enormous amounts of energy (E), as defined by the classic equation E = mc^2.
What is general relativity and how does it differ from special relativity?
Special relativity applies to all physical phenomena in the absence of gravity. General relativity explains the law of gravitation and its relation to other forces of nature. It applies to the cosmological and astrophysical realm, including astronomy.
How special relativity explains Mario and Luigi’s disagreement?
- All is relative including time, so they are both correct.
- Simultaneity is not absolute - it depends on the observer.
What does the Bohr’s hydrogen model say?
Bohr model of the atom. In the Bohr model of the atom, electrons travel in defined circular orbits around the nucleus. The orbits are labeled by an integer, the quantum number n. Electrons can jump from one orbit to another by emitting or absorbing energy.
What was the shortage of the Bohr’s model?
It did not explain why a charged particle, the electron can stay in orbit around nucleus of opposite charge, the proton without crashing into nucleus itself.
What was Paul Dirac input?
He described quantum wave functions, that were added to De Brogile’s model relativistic effects.
What were 2 predictions from Dirac’s equation?
- Charged particles have a property of spinning (rotating around their axis).
- As charged particles they generate a magnetic field:
* certain strength
* certain direction
Water protons are the magnetic moment and basic principle behind MRI.
How does the water protons behave in terms of magnetic fields?
Generally they are directed randomly, resulting in null magnetization. However when the strong magnetic field is switched on, the spins will align to the direction of that magnetic field, and will spin with a rotating speed that will be dependent on the intensity of that magnetic field.
What are the four main components of MRI?
- Strong magnetic field.
- Gradient coils. These are magnetic fields that change linearly along X, Y, Z axes so that each point in the field of view has a slightly different magnetisation, hence different spinning frequency.
- Radio frequency coil that emits pulses. These pulses will excite the protons as long as the frequency of the excitation is the same as the one of the rotating spins. This excitation pulse will send the spins into a different state so that the net magnetisation resulting from all the spins will form an angle of 90 or 180 degrees with the direction of magnetic field.
- Radio frequency detector. Note that each spin in a different location will send a signal with very specific radio frequency.
What happens after the pulse is switched off?
The water protons will go back to their initial state, which means that their magnetisation decay back to what was before. The rate depends on the tissue the water protons are in.
By collecting these magnetic decays, at different frequencies, which correspond to different locations, a computer program will generate maps of magnetic relaxations, MRI images.
What is tractography and what for its used?
In neuroscience, tractography is a 3D modeling technique used to visually represent nerve tracts using data collected by diffusion MRI. It uses special techniques of magnetic resonance imaging (MRI) and computer-based diffusion MRI. The results are presented in two- and three-dimensional images called tractograms.
Diffusion tensor imaging tractography, or DTI tractography, is an MRI (magnetic resonance imaging) technique that measures the rate of water diffusion between cells to understand and create a map of the body’s internal structures; it is most commonly used to provide imaging of the brain.
`
What is angiography?
Magnetic resonance angiography–also called a magnetic resonance angiogram or MRA–is a type of MRI that looks specifically at the body’s blood vessels. Unlike a traditional angiogram, which requires inserting a catheter into the body, magnetic resonance angiography is a far less invasive and less painful test. Uses paramagnetic agents such as gadolinium.
What other molecules apart from water protons can give a magnetic resonance?
Creatinine, Choline, N-acetylaspartate produce resonance, and these can be explored using MRI radiofrequency signal to explore not space, but different molecular resonances.
What is heamoglobin?
It is the protein in blood that brings around oxygen to the peripheral tissues where oxygen is released.
What is BOLD effect? How it works?
Blood oxygenation level dependent. It depends on paramagnetic properties of hemoglobin.
Oxygen bound hemoglobin or not bound, changes its paramagnetic properties, hence difference in oxygenation can be readily imaged. Since oxygen consumption increases when a piece of brain tissue is particularly active, we can use BOLD effect to visualise brain functional activity when a subject performs a task in a scanner.
What is antimatter?
Antimatter, substance composed of subatomic particles that have the mass, electric charge, and magnetic moment of the electrons, protons, and neutrons of ordinary matter but for which the electric charge and magnetic moment are opposite in sign.
Who found positron in 1993?
Carl Anderson at Caltech lab.
