Biophysics Topics Final Exam PDF

1. Definition of biophysics, applied biophysics. Characterization of medical biophysics Biophysics: methods and theories from physics to study biological systems at every level – atoms, molecules, cells… Applied biophysics: how to apply results of the above investigations into human activity Medical...

1. Definition of biophysics, applied biophysics. Characterization of medical biophysics Biophysics: methods and theories from physics to study biological systems at every level – atoms, molecules, cells… Applied biophysics: how to apply results of the above investigations into human activity Medical biophysics: involves biophysical problems directly related to function and composition of the human body 2. Relationship between biophysics and medicine. Biophysical techniques and mechanisms Relationship between biophysics and medicine: principles and laws of the physics sciences to describe and investigate biological processes for the purpose of medical application Techniques and mechanisms: medical imaging technologies including MRI, CT, PET scans, sonograms for diagnosing diseases, treatment methods of kidney dialysis, radiation therapy, cardiac defibrillators, pacemakers, etc. 3. Basic properties of matter. Fundamental interactions in matter. Weak and strong interactions Basic properties of matter: • Corpuscular system – protons, neutrons, electrons • Mass, weight, volume and density 4 fundamental interactions in matter: What Range Strong between particles in atomic nucleus Long Weak β decay as a result of protons and neutrons Long Electromagnetic between particles and electric charge (repulsion, attraction) Short Gravitational force of attraction between elementary particles Short 4. Elementary particles of matter. Classification of particles Elementary particles of matter: those that can’t be discomposed into simpler mass Proton 1.6 × 10 charge −27 Neutron 1.6 × 10−27 Electron 9.1 × 10−31 Rest mass Spin nº +1 Photons 0 1 0 Leptons (neutrinos, electrons) ≈0 1/2 -1 Mesons between leptons and protons 0 Baryons (proton and neutron) high 1/2 or 3/2 Hadrons (mesons and baryons) formed by quarks Elementary particles also have antiparticles, having a ≠ spin nº, other quantum parameters – antimatter. 5. Quantum field theory, quantum properties of particles Quantum field theory: • Describes events on atomic scale. • Permits to describe macroscopic properties of matter (structure of atoms, molecules, macromolecules). • Quantum mechanics describes rotational and vibrational properties of molecules, interactions between molecules, chemical bonding, optical, electric and magnetic properties of solids Quantum properties of particles: • Macro world: continuous transitions between different values of physical quantities, such as energy. • Microworld: discontinuous, physical quantities describing states and processes are quantized. Particle has wave-duality. 6. Quantum processes absorption and emission Interaction of radiation with matter Absorption: photon hits an atom and the electron in lower energy level absorb the photon and jump up to the higher energy level. Emission: electron in atom falls from a higher energy level to a lower energy level, it emits a photon to carry of extra energy. 7. Uncertainty relations of Heisenberg The uncertainty principle says that we cannot measure the position (x) and the momentum (p) of a particle with absolute precision. Can be predicted from initial conditions. States that the more precisely the position of some particle is determined, the less precisely its momentum can be predicted from initial conditions, and vice versa. 8. Pauli exclusion principle. Wave-particle theory. Properties of atomic nucleus, potential barrier, atomic states Pauli exclusion principle: two electrons in an atom cannot have same quantum state (position, momentum, mass, spin) or same configuration. Wave-particle duality: in quantum mechanics, every particle or quantum entity may be described as a particle or as a wave. Light (electromagnetic waves, particle-like in packets (photons)) and electrons. Properties of atomic nucleus: • Nucleons = neutrons (no charge) + protons (+charged) bonded by strong interactions containing + charge • - charge is distributed in electron cloud • Nuclide is characterised by A, Z, N. • Isotopes: atoms of nuclei which have = number of protons but ≠ number of neutrons • Isomers: = number of protons and neutrons but ≠ energy state of nucleus • Isobars: are atoms of nuclei which have = number of nucleons (A) but ≠ number of protons (Z). 9. Hydrogen emission spectra Piece of evidence to show the quantized electronic structure of an atom. The hydrogen atoms of the molecule dissociate as soon as an electric discharge is passed through a gaseous hydrogen molecule. If the light is passed through a prism or diffraction grating, it is split into its various colours. What you would see is a small part of the hydrogen emission spectrum. Most of the spectrum is invisible to the eye because it is either in the infra-red or the ultra-violet. 10. General properties of atom, models of atom. Electromagnetic spectrum. Linear energy transfer Smallest unit into which matter can be divided without the release of electrically charged particles. The rest consists of a positively charged nucleus of protons and neutrons surrounded by a cloud of negatively charged electrons. The nucleus is small and dense compared with the electrons, which are the lightest charged particles in nature. Electrons are attracted to any positive charge by their electric force; in an atom, electric forces bind the electrons to the nucleus. Electromagnetic spectrum, the entire distribution of electromagnetic radiation according to frequency or wavelength. The entire electromagnetic spectrum, from the lowest to the highest frequency (longest to shortest wavelength), includes all radio waves. Linear energy transfer (LET) is the average amount of energy lost per unit track length in tissue by a particular type of radiation. Amount of energy that an ionizing particle transfers to the material traversed per unit distance. 11. Chemical bonding in terms of quantum theory • Ionic bonds: transfer of electrons (electrostatic forces) • Covalent bond: sharing of valence electrons • Metallic bond: sea of valence electrons • Hydrogen bond: interaction of hydrogen atoms • Van der Waals: called as dipole-dipole 12. Quantum numbers – principal, orbital, magnetic and spin quantum number Principal n designates principal electron shell, describes most probable distance of 1, 2, 3, 4 electrons from nucleus Angular orbital l determines the shape of an orbital 0, 1, 2, 3, (n-1) momentum Magnetic m determines the number of orbitals and their orientation within a subshell -l…, -1, 0, 1… l Spin s ½,-½ direction electron is spinning around its axis 13. Energetic processes in living systems, fundamental interactions, energy of light. Sources and conversions of energy. Energy in human organism Energetic processes in living systems: • Energy measure of the ability of a physical system to do work • Mechanics o kinetic energy (energy of motion) o potential energy (energy of position) Fundamental interactions – field of force: • Gravitational in bodies w great mass • Electromagnetic between particles and electric charge – electric field o Electric energy: energy of an electric charge in electric field (chemical bond, surface energy, elastic energy) o Magnetic energy: moving of electric charges Energy of light: Electromagnetic radiation. Consists of photons, which are produced when an object’s atoms heat up. Wavelength accounts for light’s colour and how it will interact with matter. Differs from energy of gamma rays, infrared radiation, radio waves only by different frequency of the oscillations processes. Properties of light energy: intensity, frequency, wavelength, polarization, phase. Sources and conversions of energy: Heat energy Mechanical energy Mechanical energy Electrical energy Electrical energy Mechanical energy Electrical energy Heat, acoustic, light energies • Phototrophic organisms – substantial part of received energy comes from the light energy • Chemotrophic organisms – capable of using energy obtained by oxidation and reduction of substances • Autotrophic organisms – use CO2 and H2O in presence of light energy to synthesize carbonaceous substances • Heterotrophic organisms – acquire C and necessary energy from autotropic sources, often by oxidative processes Energy in human organism: Stored in form of glucose, lipids, ATP → cellular respiration to access to it Needed for DNA replication, mitosis, meiosis, cell movement, endocytosis, exocytosis, and apoptosis. 14. Physical properties of light. Interactions of light with matter • Wave-particle duality • Arises from electron shell during transition from higher energy level to lower one due to a released photon • Stream of electromagnetic energy • Speed of light (in vacuum) c=2,9979·108 m/s • Absolute refractive index of a medium 𝑛 = 𝑐 𝑣 Interaction of light with matter is a fundamental process. If transmission is 100% → absorption is 0%. Absorption in range 1 to 99% rise to change in light intensity. • Law of rectilinear propagation light rays propagating through a homogenous transparent medium do so in straight lines • Law of reflection on reflection from a smooth surface, the angle of the reflected ray is equal to the angle of the incident ray • Snell’s law the ratio of the sines of incidence and refraction angles is constant for all incidences in any given pair of media for electromagnetic waves of a definite frequency 15. Physical principle of absorption spectrophotometry. Lambert-Beer law Interaction between the matter and electromagnetic radiation. Different type of radiation results in different physical and chemical effect in the compound. Different photon energy in every type of radiation results in different effects. Absorption spectrophotometry is based on the postulate that the decrease in intensity of light dI passing through absorbing solution (with the concentration c and thickness dx) is proportional to the intensity I of light entering −𝑑𝐼 = 𝑘 · 𝑐 · 𝑙 · 𝑑𝑥 𝐼 = 𝐼0 · 10−ε·x·c ɛ – molar absorption coefficient (chemical factors of the compounds) I – intensity of light leaving layer c – concentration of attenuating species I0 – original light intensity entering the layer x –total thickness of the absorbing layer in direction of light propagation Ratio of transmitted and incident light is transmittance 𝑇 = 𝐼/𝐼0 Lambert-Beer law relates the attenuation of light to the properties of the material through which light is traveling. 𝐴 = 𝜀·𝑐·𝑥 16. Physical principle of pulse oximetry. Vital signs Pulse oximetry is a non-invasive method which provides a continuous measurement of haemoglobin saturation (%) in arterial blood by oxygen molecules. Fe2+ oxidized to → Fe3+ (enables O2 molecules bound more easily) O2-Hb saturation curve Vital signs indicate a person’s vitality. The monitoring is the recording of the parameters of vital processes in the human body to determine the overall physical condition of the patient, identify any disease, the subsequent progress of recovery. 17. Respiratory system, oxygen transport. Gas exchange, elastic forces of the lungs. Work of breathing. Breathing resistance O2 is transported by Hb (in red blood cells) into the blood and carbon dioxide is removed from it. Diffusion of gases between air in lungs and blood proceeds in the direction from high to low concentration. Gas exchange or breathing can be separated in two processes • External respiration: gas exchange across the respiratory membrane in our lungs • Internal respiration: gas exchange in the respiratory membrane in the metabolizing tissues Elastic recoil means rebound of lungs after having been stretched by inhalation. Work of breathing is the energy expended to inhale and exhale a breathing gas. Breathing involves 3 types of resistance: • Elastic pressure of lungs and thoracic cage caused by elastic recoil of lung tissue, due to many elastic elements and method of their arrangement. • Non-elastic resistance of tissues complex viscous resistance of tissues produced by friction of lung tissue, thoracic cage, breathing muscles and organs in thoracic and abdominal cavity. • Airflow resistance of respiratory passageways denotes multiple resistances of respiratory passages impeding flow 18. Physical principle of pulse oximetry, scheme of pulse oximeter. Arterial oxygen saturation The level of arterial haemoglobin oxygenation is assessed by oxygen saturation in arterial blood 𝑆𝑎𝑂2 = [𝐻𝑏𝑂2 ] [𝐻𝑏𝑂2 ] + [𝐻𝑏] Lambert-Beer law if measure incident light intensity I0 and the intensity of light which pass the solution I Scheme of pulse oximeter: Foto diode Tissue Foto detector Amplifier Micro processor Display O2% OxHb 660nm, DeOxHb 940nm 19. Advantages and limitations of pulse oximetry. Formula for fractional and functional saturation. Absorption spectra of haemoglobin Advantages Limitations Fast method and no calibration needed Failure to detect problems of poor O2 delivery (anaemia) Don’t depend on the patient’s haemoglobin level Bad signal because of poor perfusion due to a low Tº Can lead to corrections in diagnosis and treatment Nail polish, excessive ambient light, patients with right- Assess need for supplemental O2 sided heart failure Absorption of spectra of haemoglobin – oxyhaemoglobin and deoxyhaemoglobin have different absorption spectrum 20. Radioactivity and radioactive decay law. The half-life – physical, biological and effective. Radioactive equilibrium Radioactivity is done by an atomic nucleus that is unstable; it "wants" to give up some energy (radiation) in order to shift to a more stable configuration. Radioactive decay law describes the dynamics of decay of radionuclides ∆𝑁 Decay rate ∆𝑁 ∆𝑡 − = 𝑁 · 𝜆 𝑁 Nº of nuclei that has decayed over a short time ∆𝑡 𝜆 Constant of disintegration Loss of elementary particles from unstable nucleus → more stable element 𝑁𝑡 = 𝑁0 · 𝑒 −𝜆·𝑡 𝑁0 Nº of particles in t0 𝑁𝑡 Total nº of particles 𝜆 Decay cte. [s-1] -sign = nº of decayed atoms decreases w time Half-life time it takes for 1/2 of substance to decay • Physical half-life time for ½ of substance to decay (radioactive and non-radioactive elements) 𝑇𝑃 • Biological half-life time needed for excreting ½ any radioactive substance from organism • Effective half-life physical and biological half-life 1 𝑇𝑒𝑓 = 1 𝑇𝑃 + = ln 2 𝜆𝑝 1 𝑇𝐵 Radioactive equilibrium exists when a radioactive nuclide is decaying at the same rate at which it is being produced 𝐷𝑒𝑐𝑎𝑦 𝑟𝑎𝑡𝑒 = 𝜆 · 𝑁 𝜆 Decay cte. 𝑁 Atoms available to decay 21. Artificial and natural radioactivity. Classification of quarks. Particle conversion in term of quarks Natural Artificial Spontaneous Induced, produced by changing original ratio p + / n0 Initial material: unstable Initial material: stable Radioactive isotopes: thorium, uranium, actinium Radioactive isotopes: neptunium, used in medicine I-127 A quark is a type of particle that constitutes matter. Quark Spin Charge Baryon nº Mass Up – U ½ +2/3 1/3 1.7-3.3 MeV Down – D ½ -1/3 1/3 4.1-5.8 MeV Charm – C ½ +2/3 1/3 1270 MeV Strange – S ½ -1/3 1/3 101 MeV Top – T ½ +2/3 1/3 172 GeV Bottom – B ½ -1/3 1/3 4.19 GeV 22. Radioactive series. Alpha decay. Gamma decay. Beta decay and shell electron capture. Alpha (α) decay unstable atomic nuclei dissipate excess energy by spontaneously ejecting an alpha particle Beta (β) decay during electron emission proton nº +1, neutron º -1, nº of nucleons unchanged Beta + (β) decay during positron emission proton changes into neutron. Nº of nucleons is preserved but nº of proton decreases Shell electron capture beta decay. Nucleus captures electron from K shell. Proton changes into neutron. Neutrino released. Gamma (ȣ) decay atomic nucleus emits a quantum of electromagnetic radiation – ȣ photon 23. Radiotracers in nuclear medicine, critical organ, activity Radiotracers are drugs used in nuclear medicine to highlight internal organs or veins Isotope Half-life Max positron energy Production method 11 0.96 1.1 Cyclotron 13 1.19 1.4 Cyclotron 15 1.70 1.5 Cyclotron 18 0.64 1.0 Cyclotron 68 1.89 1.7 Generator 82 3.15 1.7 Generator C N O F Ga Rb Critical organ is any organ in which radioactive isotopes may become enriched. Are considered critical if their function is important for functioning of whole organism. 24. Radionuclide imaging and diagnostics. Scintillation detector and gamma camera Utilizations such as: tracing, radioimmunoassay, examination of organs physiology, imaging of organs and body. A scintillator is a material that exhibits scintillation, the property of luminescence, when excited by ionizing radiation. The gamma camera can detect scintillations (flashes of light) produced when gamma rays, resulting from radioactive decay of single photon emitting radioisotopes, interact with a sodium iodide crystal at the front of the camera. 25. Biophysics of ionizing radiation. Processes of ionization and radiation 26. Electron binding energy. Interaction of corpuscular nuclear radiation Is the energy required to remove an electron from an atom, a molecule o an ion. Energy necessary to ionize an atom. It depends on element to which electron is bound and shell within which it resides in ground state. Interaction of corpuscular nuclear radiation: charged particles of nuclear radiation directly ionize atoms of medium • α particles create large number of ions along their path, quick loss of energy • β particles fast electrons and positrons ionize the medium in terms of braking and characteristic Xray radiation • Neutrons indirect ionization through elastic and non-elastic impact into nucleus 27. Primary and secondary radiation. Direct and indirect effect of ionizing radiation Primary radiation (original) at anode X-Ray. Loss in the energy of it has quantity LET. Secondary radiation in matter due to Compton scattering (which was irradiated by 1ary radiation). Produced more when snapshot object is bulky and by higher values of anode voltage. Main factors which determine final effect of ionizing radiation: radiation dose, method of exposure, type of radiation and metabolic state of body during exposure Direct based on ionization of molecules crossed over by photons or other particles. Consequently, there is a release of chemical bonds or even disintegration of affected molecules. Direct effect prevails in cells with low water content. Indirect molecule doesn’t absorb radiation energy, it receives indirectly from other molecules, which absorbed energy before. It is a 2dary effect of water radiolysis products, with formation of aggressive free radicals, which are responsible for radiation damage of biologically important molecules. 28. Application of radioactivity in medicine. Radioactive isotopes in radiotherapy Mammography: a technique using X-rays to diagnose and locate tumours of the breasts Densitometry: uses a very small dose of ionizing radiation to produce pictures of inside of body to measure bone loss • Iodine-131 • Strontium-89 and Samarium-153 • Radium-223 29. Teletherapy, brachytherapy and contact therapy. Megavoltage therapy. • Teletherapy external beams of radiation are used to target the cancer • Brachytherapy radioactive sources are placed into or near the cancer • Contact therapy delivers radiation directly on to the tumour with a small margin • Megavoltage therapy emits photons with an average energy greater than 1 million electron volts (1 MeV) 30. Water radiolysis. DNA damage by nuclear radiation Exposure of cells to ionizing radiation induces high-energy radiolysis of H20 water molecules into H+ and OH- radicals. These radicals are themselves chemically reactive, and in turn recombine to produce a series of highly reactive combinations such as superoxide (H02) and peroxide (H202) that produce oxidative damage to molecules within cell. Ionizing radiation directly affects DNA structure by inducing DNA breaks, could not allow DNA to replicate correctly, changing chemical structure of bases, breaking sugar-phosphate backbone, breaking hydrogen bonds connecting base pairs. All these changes induce cell death and mitotic failure. 31. Biological effect of radiation and dose equivalent. Risks and diseases caused by ionizing radiation. Protection against ionizing radiation • Physical stage ionization and excitation of molecules (10-13 s) • Physical-chemical stage interaction of ions with molecules with present dissociation of molecules and formation of free radicals (10-10 s) • Chemical stage fibber breaks in DNA (10-6 s) • Biological stage overall functional and morphological changes (seconds-years) Dose of ionizing radiation • Minimum lethal dose: death of a single individual from an exposed group • Median lethal dose: death of 50% of exposed individuals • Absolute lethal dose: death of all exposed individuals within time T Dose equivalent is quantity describing the actual relative biological effect of radiation Risks and diseases: • Acute sickness whole body/big part • Chronic diseases fatigue, weakness, changes in blood • Local effect of radiation dermatitis Protection against ionizing radiation: DISTANCE!!! • α particles – several cm in air, clothing, or paper • β particles – several m in air, protection by aluminium 3-5 mm sheet metal or 5 mm of lead • neutrons – material containing lot of hydrogen 32. Interaction of ionizing radiation with matter. Photoelectric effect, Compton scattering, electronpositron pair production 𝐼 = 𝐼0 · 𝑒 −𝜇𝑑 𝐼 transmitted beam intensity 𝑑 thickness of absorbent 𝜇 mass absorption coefficient Relationship between the thickness of the absorbing material and the absorption coefficient of the material defines half-value layer d1/2 → thickness of matter that will stop half of the photons Photoelectric effect an incoming photon interacts with nucleus of an atom, causing ejection of outer electron of atom (photoelectron) = ionization of the atom Compton scattering incoming photon ejects an outer shell electron, yielding a Compton electron. Incident photon loses its energy and changes its direction – Compton photon. Electron-positron, pair production formation of electron and positron, from a pulse of electromagnetic energy traveling through matter 33. Detectors of ionizing radiation, scintillation counter Scintillator is appropriate choice of crystal (NaI) coupled to a photodetector for a detection of the visible light. Involves the conversion of high-energy photons into visible light via interaction with a scintillating material 34. Physical principle of Nuclear Magnetic Resonance Imaging. Gyromagnetic ratio of nucleus NMRI is a medical technique used in radiology to visualize detailed internal structures of human body. Based on the absorption and emission of energy in the radiofrequency (RF) range of the electromagnetic spectrum. Gyromagnetic ratio of nucleus: Relation between the magnetic moment μ and the spin vector of the nucleus: ȣ – gyromagnetic ratio [Hz.Tesla-1] describes the ratio of mechanic and magnetic properties of the nucleus For proton 𝛾 = 𝑒 𝑚𝑃 𝑒 elementary charge 𝑚𝑃 proton weight 35. Protons in external magnetic field, Larmor precessing frequency The proton magnetic moments with all possible phases describe a conus with known radius and height 𝛾 𝑣 Larmor precessing frequency [MHz] The frequency of that precessing motion: 𝑣 = 2𝜋 𝐵 𝛾 gyromagnetic ratio [MHz / Tesla] 𝐵 strength of EMF [Tesla] 36. Transversal and longitudinal magnetisation and relaxation, resonance phenomena and its conditions in NMR imaging Longitudinal magnetisation Mz is the projection of sum vector of magnetization M to the axis z Transversal magnetisation Mxy is the projection of sum vector of magnetization M to the plane xy Resonance phenomenon in MRI it uses a strong external magnetic field provided by a superconducting magnet and radiofrequency radiation to generate tomographic images in any plane. 37. Relaxation times in NMR imaging Relaxation time during which system is restored to 63% of equilibrium after the RF pulse turned off. • Spin-spin (transversal) relaxation time (T2) • Spin-lattice (longitudinal) relaxation time (T1) Depends on type of nucleus, RF (field strength), Tª, micro viscosity of matter, presence of large molec, presence of paramagnetic ions or molec. Reflects properties of surroundings of magnetic nucleus and provides info about tissue. 38. Signal and its acquisition in NMR imaging, factors that influence the signal intensity Image contrast is difference in the strength of NMR signal from different locations Difference is caused by relative density of nuclei (protons), differences in relaxation times, other factors (specialised NMRI). ΔΘ ΔΘ magnetic induction flux NMR signal acquisition 𝑈𝑖 = − Δ𝑡 𝑈𝑖 electric voltage Δt relaxation time Factors that influence signal intensity • hydrogen density • relaxation time • basic pulse sequence parameters • flow • use of contrast medium 39. Spatial information of NMR signal, position encoding of patient body Signal in NMR measurements contains two information: • Nº of nuclei ib small volume of human body – proportional to amplitude of signal • properties of surroundings of nucleus – relaxation time Position encoding of patient body: patient is placed in non-homogenous magnetic field → causing different Larmor frequencies Low signal is coming from: air, bones, calcified tissues Strong signal from: free body fluids, fat tissues Increase of proton density: bleeding, edema, some kinds of tumors Decrease of proton density: calcification, other kinds of tumors Gz splits the body to slices Shortly lasting Gy diphase the precessions of nuclei in y direction →Phase Encoding Gy changes the precession frequency in x direction → Frequency Encoding 40. Possible hazards of NMRI Can arise from Acute hazards Subacute hazards static magnetic field Projectiles Changes in Ez kinetics varying magnetic fields Implants Nerve conductivity radiofrequency fields Pacemakers Cardiac changes Claustrophobia Pregnancy 41. Principle of medical X-Ray imaging. Physical characterization of X-Ray. Production of X-Ray Formation of X-ray image is subject to partial absorption of X-rays by passing matter. Made up of electrical parts such as X-ray tube, control panel and image intensifier and mechanical parts which change the position of the patient towards to X-ray system. The source of high voltage for feeding X-ray tube consist of: transformer that changes the relatively low mains voltage to the voltage necessary, a rectifier which changes the current for the flow of electrons into direct current that gives half-waves which can cause unwanted production controlled by the circuit of smoothing. X-ray imaging begins with a beam of high energy electrons crashing into a metal target and x-rays are produced The electrons are accelerated by a very high electric voltage in the space between the hot cathode also called filament and the cold anode. The electrons are suddenly decelerated in a target which is part of the anode. A small part of the liberated energy is transformed into high-energy photons who are the X-rays. 42. Braking and characteristic X-Ray. Duan-Hunt Law. Exposure time Braking: energetic electron passes by the nucleus and is accelerated / decelerated (and its trajectory is changed) while producing a continuous spectrum of X-rays Characteristic: energetic photon or particle can kick one of the inner shell electrons out of its place release of characteristic X-ray radiation in the form of a photon Duan Hunt Law yields that minimum wavelength (or maximum frequency) of X-rays that can be emitted by Bremsstrahlung in an X-ray tube by accelerating electrons through an excitation voltage U into a metal target. 𝜆𝑚𝑖𝑛 = ℎ𝑐 𝑒𝑈 Exposure time: time of patient’s exposure to the beam of generated X-ray photons. Modified to account for the equipment’s sensitivity (or quality), type of tissue to be irradiated (soft, hard), patient’s age and type of projection. Milliseconds-seconds 43. Linear and mass attenuation coefficient. Half value layer LAC describes how effective the material is in absorbing the X-ray (rate at which incident photons are modified from an X-ray beam per unit distance of material travelled). Dependent on the X-ray’s energy. MAC measure of the probability of the interaction that occurs between incident photons and the matter of the unit mass per unit area water has three distinct phases (liquid, gaseous, and solid) even though they consist of the same molecule. Each of these has different values of LAC. Their MAC’s, however, are the same. Half value layer a penetration depth at which the intensity of the incident beam decreases to half its original value (measure of the quality of the X-ray beam) 44. Interaction of X-Rays with matter. Intensity of attenuated X-Ray. Image formation contrast, noise Highly dependent on energy of the X-ray beam, the atomic number of the target, and its electron density. Strength of these interactions depends on the energy of the X-rays and the elemental composition of the material. • Photoelectric absorption • Compton scattering • Rayleigh scattering Intensity of the beam is affected by beam quality (kVp) as well as beam quantity (mAs). Is also affected by distance between the x-ray tube and the exposed area such that if the distance is increased, beam intensity decreases following inverse square low. Image formation is reliant on the differential absorption of the X-ray beam as it penetrates different types of tissue (contrast). Resulting image is made via chemical reactions occurring near the film, originally quite like darkroom procedures used in photography. Contrast is the difference in density or difference in the degree of greyness between areas of the radiographic image. Noise is a random fluctuation in image intensity about its mean value. 45. Conventional X-Ray imaging – radiography, fluoroscopy, digital subtraction angiography. Mammography. Densitometry. Radiography static imaging technique in which X-ray image is captured either on a film (old-school) or digitally. Most common. Contraindications: pregnancy. Fluoroscopy procedure for dynamic viewing of patient’s X-ray images with high temporal resolution. Continuous imaging using X-ray beam from the tube towards detector, both of which are placed together on a solid piece of equipment to ensure their relative stability. It’s the only technique to image dynamically. Contraindications: pregnancy, allergic reactions to contrast agents, prior problems with kidneys. Digital Subtraction Angiography an imaging technique used to visualize the interior of blood vessels and organs of the body. Contraindications: pregnancy, allergic reactions to contrast agents, previous problems with kidneys. Mammography radiographic examination that is designed for detecting breast pathology, particularly breast cancer. Soft X-Rays used. Dose must be limited as the breast is radiosensitive. Specialized X-ray tube. Contraindications: pregnancy, breast implants, age < 40 yrs., symptoms of breast cancer. Densitometry is a special spectrophotometer that measures light transmitted through a solid sample such as a cleared or transparent but stained gel. Used for measure bone loss. 46. Principles of computed tomography. Definition of voxel unit. Radiation dose. Hounsfield unit. Principles of computed tomography • Image is not only shadow projected on film and shade • All planes of patient that are in parallel with the X-ray film overlap • There is a projection of a 3D volume on a 2D surface • Due to overlapping structures called summing, images do not show very high contrast • Bones and cavities are easily recognizable Voxel unit = unit of graphic information that defines a point in 3D space Measuring radiation dose: Exposure, KERMA, absorbed and equivalent dose, effective dose Hounsfield unit of linear attenuation. Each pixel can be assigned a precise value of HU. 𝐻𝑈(𝑥) = 1000 × 𝜇(𝑥) − 𝜇𝐻2 𝑂 𝜇𝐻2 𝑂 47. Physical principle of positron emission tomography imaging. Positron interactions with matter. Energy emitted positron Nuclear medicine functional imaging technique, molecular level • Short-lived positron-emitting radiotracer (radionuclide + compound) is introduced into the body • Radioactive decay of tracer indirectly causes creation of gamma rays • β+ radiation decay Positron interactions with matter and energy emitted positron 1. Emission from the nucleus 2. Positron loses kinetic energy by interactions with the surrounding matter 3. Deflection in the positron path 4. Positron and electron are practically at rest, they collide and annihilate. 5. 2 γ-ray photons are given off at opposite directions. Each photon energy = 0.511 MeV. e− + e+ → γ + γ 48. Physical principle of annihilation process in PET. Radiotracers in PET imaging Annihilation occurs when a subatomic particle collides with its respective antiparticle to produce other particles, such as an electron colliding with a positron to produce two photons. PET radiotracer is a type of radioligand (radioligand is a radioactive biochemical substance for diagnosis) that is used for the diagnostic purposes via positron emission tomography imaging technique. Examples of radiotracers: Mefway, nifene, MPPF in neurology. 49. Coincidence detection in PET. Line of response. Types of coincidence events In a PET camera, each detector generates a timed pulse when it registers an incident photon. These pulses are then combined in coincidence circuitry, and if the pulses fall within a short time-window, they are deemed to be coincident. Line of response: path between two detectors used to localize the tracer Types of coincidence events: • True 2 photons are generated by positron annihilation event and lie on line of response LOR • Accidental 2 positron annihilation locations are assigned to one LOR • Scattered wrong LOR is detect 50. Detection system in PET – scintillation detectors. Pulse creation and processing Scintillator crystal - converts gamma photons into visible photons, which can be detected using fast photomultiplier Photomultiplier (PMT) - converts incoming light photons to accelerated, amplified electrons – current Pulse creation and processing: each detector generates a timed pulse when it registers and incident photon. These pulses are then combined in coincidence circuity, and if the pulses fall within a short time-window, they are deemed to be coincident. In the diagnostic section, radiopharmaceuticals are detected with gamma camera, which give a very accurate picture of the area. Located around the perimeter of scintillation detectors the registration of the incident photon generates timed pulses 51. Clinical application of PET. Limitations and advantages of PET Oncology for cancer diagnosis and management, cardiology and cardiac surgery, neurology, and psychiatry. Limitations: time. Consuming, PET scanning can give false results, Resolution structures may not be as clear as MRI, if a person is obese may not fit. Benefits: PET imaging gives answer how well organs and tissues are functioning, and nuclear medicine is less expensive and gives more precise and useful information. 52. Physical characteristics of ultrasound and ultrasound imaging. Propagation of ultrasound matter. Characterization of longitudinal and shear waves Physical characteristics of diagnostic ultrasound and ultrasound imaging are determined by ultrasonic properties of tissue. Propagation and attenuation are the most important parameters. REFLECTION: when passing through medium, the part of US beam reflexes on an interface PROPAGATION SPEED OF US REFRACTION: the US strikes the boundary of two tissues at an oblique angle. SCATTERING: it occurs when the US beam meets the small object ACOUSTIC IMPEDANCE: US velocity vs. density of the medium in which the US is passing through, i.e., the greater impedance, the denser material ATTENUATION In a longitudinal wave, particles of medium move parallel to wave’s direction of travel. In a longitudinal wave, each particle of matter vibrates about its normal rest position and along the axis of propagation, and all particles participating in the wave motion behave in the same manner, except that there is a progressive change in phase of vibration—i.e., each particle completes its cycle of reaction later. The S waves, also called shear waves, can travel only through solid materials. They produce an up-and-down or sideto-side motion at right angles to the direction of wave propagation. They occur in an elastic medium when it is subjected to periodic shear. Shear is the change of shape, without change of volume, of a layer of the substance, produced by a pair of equal forces acting in opposite directions along the two faces of the layer. If the medium is elastic, the layer will resume its original shape after shear, adjacent layers will undergo shear, and the shifting will be propagated as a wave. 53. Characterization of the transducer beam profile. Classification and characterization of ultrasound transducers The beam profile from a typical transducer is often thought of as a column of energy originating from the active element area that travels as a straight column for a while and then expands in diameter and eventually dissipates, like the beam from a spotlight. The ultrasound waves (pulses of sound) are sent from the transducer, propagate through different tissues, and then return to the transducer as reflected echoes. The returned echoes are converted back into electrical impulses to form the ultrasound image presented on the screen. 54. Description of drawing piezoelectric effect based on piezoelectric crystals. Propagation speed. Half way thickness Is the ability of certain materials to generate an electric charge in response to applied mechanical stress. Thickness of the crystal determines the frequency of the scan head. Ultrasound machines assume sound waves travel at a speed of 1540 m/sec through tissue. Half-value thickness, is the thickness of the material at which the intensity of radiation entering it is reduced by one half. 55. Ultrasound interactions with the tissue. Reflection, attenuation, refraction, scattering Reflection occurs when the waves pass between two tissues of different acoustic speeds and a fraction of the wave bounces back. Attenuation energy loss through interactions between ultrasound waves and soft tissues which occurs due to absorption and scattering events Refraction occurs if it travels between tissues with different propagation speeds. Scattering when a sound wave strikes a structure with a different acoustic impedance to the surrounding tissue and which is smaller than wavelength of incident sound wave 56. Intensity based effect of ultrasound. Energy transfer. Ultrasound safety and risks, thermal index and mechanical index Interaction of US w biological tissues depends on its intensity, at high intensities active interactions take place. Passive interactions take place at low intensities. US has a remarkable record for patient safety with no significant adverse bioeffects reported in the literature. MI: an estimate of the maximum amplitude of pressure in the body TI: measure of an ultrasound beam's thermal bioeffects 57. Biological effect of ultrasound. Thermal, cavity and mechanical effects The biological effect of ultrasound refers to the potential adverse effects the imaging modality has on human tissue Thermal: all sound energy attenuated by tissues must be converted to other forms of energy. The majority of this is turned into heat. Mechanical: refers to damage caused by actual oscillation of the sound wave on tissue Cavitation caused by the oscillation of small gas bubbles within the US field. Sometimes these bubbles can grow and collapse generating very high energies next to the tissue. 58. Ultrasonography, A, M and B imaging modes A mode (Amplitude mode): basic pulse-echo system is used for measuring the depth of echo-producing boundaries in one direction M mode (Motion mode): used for examination of moving boundaries. Provides a single line of information at a higher frame rate than can be obtained by two-dimensional echocardiography B mode (Brightness mode): a 2D ultrasound image display composed of bright dots representing the ultrasound echoes 59. Principles of Doppler ultrasound imaging. Doppler shift frequency, Doppler shift equation. Continuous wave Doppler and pulsed wave Doppler. Doppler works by measuring sound waves that are reflected from moving objects. Doppler frequency shift is the difference between transmitted and received echoes. Doppler shift equation shows the relationship of Doppler frequency shift to target velocity ∆𝑓 = (𝑓0 − 𝑓𝑟 ) = 2𝑓0 𝑣 cos 𝜃 𝑐 Continuous wave uses separate transmitting and receiving transducer. Can be only used for flow measurement of superficial vessels. Pulsed wave provides information about position of examined structure. Is able to measure blood-flow in deep located vessels. 60. Artefacts in ultrasonography Transducer produces sound waves that bounce off body tissues and make echoes. 61. Physical characteristics of laser – absorption, spontaneous emissions, stimulated emission Characteristics of laser light: coherent, monochromatic, collimation, high intensity, continuous, or very short pulse. Absorption of a photon causes an electron to be pushed to a higher energy level. The energy change depends on the frequency of a photon. f=(E1-E2)/h Spontaneous emission of a photon occurs when an electron falls from a higher energy level to a lower and in the process emits a photon with a frequency by falling from E1 to E2 Stimulated emission is triggered by another photon of the same frequency as the emitted ones. The electron is displaced from higher energy state to a lower state. 62. Characterization of laser light. Wavelength and photon energy • Coherent photons are in the same phase • Monochromatic all photons same wavelength • Collimation laser light has a direction • High intensity depends on the pumping power and the efficiency of the LASER mechanism • Continuous or very short pulses Colour of a laser determines the energy of the individual quanta of light according to 𝐸𝑝ℎ𝑜𝑡𝑜𝑛 = ℎ × 𝑣 = ℎ×𝑐 𝜆 1,24 Energy in eV can be calculated from the wavelength in m using 𝐸[𝑒𝑉] = 𝜆[𝜇𝑚] Indirect proportionality of wavelength and energy 63. Laser active medium. Population inversions, metastable state, metastable energy AM – substance capable to produce laser radiation (keeps atoms in metastable position = population inversion). Amplifies the light. Can be gases, glasses, semiconductors. Population inversion is a system (atoms or molecules) exists in a state with more members in an excited state than in lower energy states. Metastable state is an excited state of an atom or other system with a longer lifetime than the other excited states 64. Laser parameter. Three level and four level laser systems. Laser wavelength is determined by the AM, but the energy and the spot size can be influenced. Assumption 1 – laser with an operating power of P: 𝐸 = 𝑃 × 𝑡 varying the operating time t allows a desired quantity of energy E to be radiated into the system. Assumption 2 – energy density fluence rate F: F=A where the area A usually is circular 𝐴 = 𝜋𝑟 2 keeping the fluence constant, the energy used defines the spot size. 65. General laser construction. Laser pumps 1. 2. 3. 4. 5. Gain medium Laser pumping energy High reflector Output coupler Laser beam Laser pumps Pumps Source Electromagnetic Electromagnetic radiation Electric Electric discharge Chemical Chemical reaction Thermal Heat 66. Construction and working of Ruby laser, He-Ne laser, CO2 laser Electrons in Chromium→higher energy level after transferring part of the energy to the crystal lattice→ a lower metastable level After some period, the electrons from state E2 fall into E1 by releasing energetic photons The light beam induces further transitions from metastable levels, takes in more photons, thereby amplifying it and finally passing out through the semipermeable mirror He-Ne laser CO2 laser 67. Classes of lasers and laser products I safe, light is contained in an enclosure and do not pose hazard (in CD players) II safe during normal use; the blink reflex of eye will prevent damage. Up to 1 mW power (laser pointers) III a up to 5 mW, small risk of eye damage within time of blink reflex. Beam seconds cause damage on retina III b immediate eye damage upon exposure IV can burn skin, and in some cases, even scattered light can cause eye and/or skin damage 68. Laser hazards and safety AEL (Accessible Emission Limit) and MPE (Maximum Permissible Exposure) • Radiation hazard: dangerous for eyes and skin • Retinal hazard: Corneal hazard with H2O absorption, 400-1400 nm • Skin hazards: 230-380 nm most dangerous. From range of 700-1000 nm (IR) may cause burning the skin. • Chemical hazard: CO and CO2 lasers contain toxic gases Safety: protection glasses, distance 69. Application of lasers in medicine Angioplasty, cancer diagnostics and treatment, cosmetic dermatology (skin resurfacing, hair and tattoo removal), dermatology melanoma treatment, laser mammography, medical imaging, microscopy, ophthalmology (laser photocoagulation), optical coherence tomography, plastic surgery. 70. Laser – tissue interaction. Absorption and scattering. Optical • Transmission • Reflection • Absorption strongly depends on the type of tissue and the wavelength of the incident light. • Scatter o inelastic scattering (loss of energy of photon and change of wavelength) in fluorescence, phosphorescence o elastic scattering (no loss of energy) Thermal • Thermal conduction • Thermal capacity 71. Photothermal, photoacoustic and photochemical effect. • Photothermal: - Light energy transformed and dissipated as heat – most lasers - Photoablation- heats so quickly and thoroughly that tissue is ablated - CO2, Er:YAG • Photoacoustic / Photomechanical: - Occurs so fast that shock wave is created – Q switched • Photochemical: - Light energy starts chemical reaction – Photodynamic therapy 72. Laser thermal effect on tissue – coagulation, carbonization, vaporization and ablation Thermal interactions mainly excite vibrational and rotational states of the molecules in the tissue Coagulation denaturation (structural change) of biomolecules (in particular proteins) that may be more or less pronounced and can ultimately lead to detachment of the epidermis. Carbonization Vaporization radiation being absorbed strongly by water and therefore by tissues as well. Tissue is evaporated by the laser light Ablation removing atoms from a solid by irradiating it with an intense continuous wave or pulsed laser beam. 73. Selective thermolysis and photodynamic therapy Selective thermolysis: selective parts of the skin (blood vessels, pigment) can be zapped when the right wavelength is used. The target must be destroyed fast, before it has a chance to cool. Photodynamic therapy: cytotoxic action of a photosensitive species bound to a cell and excited by an appropriate light source. 74. Conversion of energy in living systems – phototrophic, chemotrophic, autotrophic, heterotrophic organisms • Phototrophic organisms – comes from the light energy • Chemotrophic organisms –energy obtained by oxidation and reduction of substances • Autotrophic organisms – use CO2 and H2O in presence of light energy to synthesize carbonaceous substances • Heterotrophic organisms – acquire carbon and necessary energy by oxidative processes 75. Basic properties of water and its functions in organisms Basic properties: • High relative permittivity of water (polar character of molecules) • Good solvent of polar substances because it’s a bipolar and has hydrogen bonds • Easily dissociate (weak hydrogen bonds) • Solvation envelope around polar molecules ions water molecules which group together • Specific heat capacity (huge quantities of water on Earth ensure thermal stability) • Latent heat of evaporation • Good heat conductor Function in organism: • Efficient solvent of ionic compounds and polar substances. • Environment in which most biochemical reactions occur • Reactants in many biochemical reaction • Facilitates transport process (e.g., Diffusion) • Influences mechanical properties of cells and tissues (affects the shape of cells) • Stabilization of functional molecular structures because of solvation envelopes • Thermoregulation due to its high values of heat conductivity, specific heat capacity and latent heat of evaporation 76. Composition of the cell membrane and its function. Active transport. Work against the electrochemical gradient F(x): distinguish intracellular and extracellular components, barrier to transport of ions and molecules • Phospholipids – polar and non-polar region • Integral membrane proteins • Peripheral proteins • Transmembrane proteins • Cytoskeletal proteins Active transport is the movement of molecules from a region of lower concentration to a region of higher concentration, particles move against the concentration gradient, using energy released during respiration. To move substances against a concentration or an electrochemical gradient, the cell must use energy. This energy is harvested from ATP that is generated through cellular metabolism. Active transport mechanisms, collectively called pumps or carrier proteins, work against electrochemical gradients. 77. Generation and recording of membrane potential. Resting membrane potentials and equilibrium potentials Generation Recording of membrane potential is made by glass microelectrodes. Electrode is filled with electrolyte solution (3M KCl) inserted through surface membrane. Tip diameter of the recording electrode 0.5 µm prevents the cell damage. Second reference electrode is placed into external environment of the This method is used in the determination of electrochemical parameters such as ions concentration Na, K, Ca, H, Resting membrane potential. The ion channels provide a circuit for movement of charge across the cell membrane to create the separation of charge Ci = ci* Equilibrium potentials if ion concentrations in both compartments are the same then there is no net flux of K+ ions. The one-way flux of K+ ions is the same in either direction. 78. The Nernst equation for resting membrane potential. Donnan equilibrium 𝑈= 𝑅×𝑇 𝑐 U potential difference, membrane voltage × 𝑙𝑛 c/c* randomly selected ratio 𝑧×𝐹 𝑐∗ F Faraday constant 96 487 C/mol z charge of an ion 𝑙𝑛 𝐶 ∗𝐾+ 𝐶 ∗𝐶𝑙− = ln 𝐶𝐾`+ 𝐶𝐶𝑙− 79. The Goldmann equation for resting membrane voltage for sodium, potassium and chloride ions 𝑈= 𝑅×𝑇 𝑃𝐾+ · [𝐾+]𝑒𝑥𝑡 + 𝑃𝑁𝑎+ · [𝑁𝑎+]𝑒𝑥𝑡 + 𝑃𝐶𝑙− · [𝐶𝑙−]𝑖𝑛𝑡 × 𝑙𝑛 𝑧×𝐹 𝑃𝐾+ · [𝐾+]𝑖𝑛𝑡 + 𝑃𝑁𝑎+ · [𝑁𝑎+]𝑖𝑛𝑡 + 𝑃𝐶𝑙− · [𝐶𝑙−]𝑒𝑥𝑡 80. Definition and function of action potential. Origin of action potential Action potential: membrane potential rapidly depolarizes and repolarizes back to the resting membrane potential. Functions: • provide how electrical excitation can travel significant distances along specific neuronal structures known as axons • trigger rapid influx of Ca2+ into cell for triggering a cellular response (neurotransmitter, hormone release, muscle contraction) Origin of action potential • Action potential initiated chemical agents/small change in electric voltage on membrane • Starts with the opening of Na channels – their permeability increases 500 times • Na penetration inside the cells – depolarization • K+ channels are opened and K flows from the cell whereby the rapid change of potential is stopped – repolarization • Lower values of potential than resting values hyperpolarization • During which the membrane is hyperpolarized is refractory phase 81. Peak potential of Na and K ions. Conditions for starting action potential • Must be reached a threshold level of depolarization range -50 to -30 mV for different cell types • Suprathreshold depolarizing currents initiate an action potential • The height of the potential above zero is known as the overshoot. This is known as the afterhyperpolarization. • After a neuron fires an action potential there is a brief period during which it is impossible to fire another action potential. This is known as the absolute refractory period 82. Propagation of action potential. Rate of propagation Origin of action potential is influencing propagation of AP Na+ channels open if the value of resting membrane potential changes by at least 15 mV. Transfer of ions along the opposite sides of the membrane are local currents Either does not originate at all or it does originate and then it always has the same magnitude Rate of propagation is variable and depends on the structure and on nerve fibres. Action potential propagates between the gaps by leaps 83. Synaptic transfer, electrical and chemical synapses. Excitatory and inhibitory synapses Transfer between nerve or nerve-target cell. Are found in CNS between sensory and motor neurons, smooth and cardiac muscle and elsewhere. Electrical: electrical ions flow directly between cells. Chemical: using chemical messengers. The activity of synapses results in: • triggering of the action potential on postsynaptic membrane – synaptic excitation • worsening of the conditions for its origin – synaptic inhibition 84. Types of intermolecular and intramolecular interactions. Phase states of matter Intramolecular interactions hold atoms together in a molecule, whereas intermolecular interactions hold molecules together. → ELECTROMAGNETIC origin (physics) Intermolecular (van der Waals interactions, hydrophilic, Hydrophobic interactions, Hydrogen bonds) Effects of non-bonded interactions: • STATIC effect: formation of tertiary structure of proteins, conformation of oligomers • DYNAMIC effect: recognition of proper partners in reactions, formation of supramolecular complexes, aggregates Phase states of matter: GASES: distances between the particles are large – attractive (cohesive) forces are weak – shape and volume is not preserved LIQUIDS: molecules are in contact (touch) nonpolar molecules – disperse cohesive forces polar molecules – dipole cohesive forces preserve volume – adopt the shape of vessel – practically incompressible SOLIDS: strong cohesive forces, limited mobility vibrations around equilibrium positions, preserve the shape and volume, internal structure, all types of interactions occur PLASMA: is a mixture of atomic nuclei, free electrons, ions 85. Classification of dispersive systems Disperse Dispersed medium phase Gaseous Gaseous Liquid Solid Coarse dispersions Colloid dispersions Analytic dispersions Mixtures (Air) Liquid Aerosol (rain, inhalation spray) Aerosol (fog, drugs) Vapor of liquid in gas Solid Aerosol (dust) Aerosol (smoke) Vapor of solid in gas Gaseous Bubble, foam Foam (whipped cream) Solution (oxygen in water) Liquid Emulsion (milk, hand cream) Emulsion (oil in water) Solution (ethanol in water) Solid Suspension (chalk in water) Lyosol (blood) Solution (glucose in water) Gaseous Dry foam (dry sponge) - inclusion Dry foam (polystyrene) Solution (H in metal catalysers) Liquid Bubbles (wet sponge) - inclusion Solid foam Solution (amalgam) Solid Solid mixture (granite) Solid sol (glass w colloid Solid solution (alloy) gold) 86. Henry’s law. Dalton’s law. Solubility of O2 in blood, partial pressures of O2 and CO2 of the body. Exchange of respiratory gases. Decompression sickness Henry’s law 𝐶𝑝 = 𝑃𝑝 · 𝛼 Dalton’s law 𝑝 = 𝑝1 + 𝑝2 … 𝑝𝑁 Two mechanisms of Oxygen solvation in blood: • physical solubility (O2 in plasma or red blood cells 1,5%) • chemical solubility (O2 bound to haemoglobin 98,5%) 𝐶𝑝 – concentration of the dissolved gas in liquid 𝑃𝑝 – partial pressure of the gas above the liquid 𝛼 – concentration solubility coefficient ç N− nº of components of analytic dispersion 𝑝1 – partial pressure of i-th gas 𝑝 – pressure of gas mixture Partial pressure of O2 99,7 mmHg Partial pressure of CO2 35-45 mmHg Exchange of respiratory gases follows the direction of pressure gradient Decompression sickness is a disorder in which nitrogen dissolved in the blood and tissues by high pressure forms tiny bubbles in the blood and body tissues as pressure decreases 87. Colloidal dispersions and their physical properties. Lyophilic and lyophobic colloid solutions • Water solutions of biopolymers (proteins, DNA, ... in the human body) • Micellar – association colloids (soap, phospholipids) • Heterogenous systems (sol) Lyophilic (hydrophilic) – having strong affinity for the solvent (water) Lyophobic (hydrophobic) – having repulsion towards the solvent (water) - (liquid form – lyophobic sol, solid form - gel) 88. Electric properties of liquid colloidal dispersions. Electrokinetic potential Preparation methods: • Dispergation • Condensation Stability is provided by: • Solvation (hydration) envelope • Electric charge Electrokinetic potential ζ (zeta) and φ0 – the potential of the surface of the colloidal particle relative to infinity 89. Cohesive forces, surface tension, liquid viscosity, shear stress Surface tension is surface force acting perpendicular to the length l of the surface of the liquid 𝛿 = 𝐹2 𝐼 Liquid viscosity influences the real liquid flow. Is caused by intermolecular force of cohesion and molecular momentum exchange. Slower layer of liquid slows down the faster layer – on contact surface S acts force F – creates shear stress. Einstein’s equation for viscosity: 𝜂𝑠 = 𝜂0 · (1 + 𝑘 · 𝑐) ηs viscosity of the dispersion system η0 viscosity of the dispersion medium C volume concentration of the dispersed phase k constant 𝑑𝑢 Shear stress τ (tau): express the action of forces between two layers of liquid. 𝜏 = 𝜇 𝑑𝑦 𝜇 Viscosity 𝑑𝑢 𝑑𝑦 Rate of shear 90. Viscosity of blood Blood is a colloidal dispersion viscose-elastic fluid with disperse particles with electric double-layer and electric charges on the inner surface of the vessels. Blood viscosity depends on temperature, flow rate, cross-section of vessel, physical properties of the internal walls of the blood vessels, systole, diastole, content of blood 91. Diffusion. First and second Fick’s law of diffusion through membrane. Diff