Medical Uses

Medical Uses

1. Waves

   • Radiation
     • Radiation is energy that originates from a source
     • Ionising
       • Ionising means that it can knock electrons off of atoms and cause them to become ions.
       • X-rays
         • These are high energy EM waves that get absorbed by dense materials like bone and metal.
         • Medical Imaging
           • Fluoroscopy
             • Basic fluoroscopy works by placing a patient between an x-ray source and a fluorescent screen and an x-ray source. Different amounts of x-rays are absorbed by different parts of the body. The intensity will also vary depending on what they've passed in the body. The screen catches the x-rays that have passed through and fluoresces to show a live image on the screen- all due to the different intensities of rays caught. The higher the intensity, the brighter the screen.
             • Modern fluoroscopy now generally involves using an image intensifier to increase the brightness of the image seen (up to 5000 times brighter), meaning a lower dose of x-rays can be used. The screen is attached to a computer so that the images can be recorded.
             • This process is also used to diagnose problem with organs functioning. Because x-rays pass easily through soft tissue, the patient is given a 'contrast medium' by injection or ingestion. This substance improves the contrast of the image seen by 'enhancing' the soft tissue making it more visible. 
           • CAT Scans
             • Computerised Axial Tomography(CAT) scans use x-rays to produce images of 2d slices of the body. They use intense beams of x-rays that are strongly ionising. Unlike x-ray imaging, these can be used to image soft tissue as well as bones.
             • They can also make 3d images by 'stacking' the individual slices.
           • PET Scans
             • Positron Emission Tomography/ PET scanning is a technique to show tissue or organ function and can be used to help diagnose conditions. PET Scans show areas of damaged tissue in the heart by detecting areas of decreased blood flow. This can reveal coronary artery disease and damaged heart muscles due to heart attacks. They can also record blood flow and activity in the brain which helps to diagnose conditions like epilepsy. PET scans can also identify active cancer tumours by showing metabolic activity in tissue. Cancer cells have a much higher metabolism than healthy cells.
             • Instructions: 1. Inject the patient with a substance used by the body (like glucose) containing a        positron-emitting radioactive isotope with a short half-life so it acts as a tracer. Over an hour or so, it moves over the body. Use about 7mSv per PET scan.2. Positrons meet electrons and annihilate which emit 2 gamma rays moving in opposite directions which are detected. Enough of these can be used to pin-point the exact location of a tumour.3. The distribution of radioactivity matches up with metabolic activity because the cells with high metabolic rates will be using more of the substance containing the tracer. 
             • Isotopes used in PET scanning have short half-lives so they have to be injected close to where they'll be used by the cells that'll use them up. Some hospitals have their own cyclotrons to make isotopes on site otherwise if they had to be transported over a large distance, their activity could be too low to be useful.
             • Annihilation
               • This occurs when a particle and an antiparticle collide, e.g. an electron and a positron. When annihilation occurs, the particles are converted into energy which is given off in the form of gamma rays. These rays have the same mass but opposite velocities so the total momentum before the collision is zero - it needs to be zero because momentum is conserved. The total charge after the reaction must equal the total charge before the reaction. The total charge before the electron-positron collision is zero, gamma rays have no charge so the charge after the collision is also zero-the charge is conserved.
               • E = m x c^2 E is energy (in joules, J) m is mass (in kilograms, kg) c is the speed of light  -     (3x10^5 m/s)
           • X-ray Photographs
             • Radiographers take images using x-rays that are passed through a specific part of the body and meet a film developed to catch the x-rays that come through. These are usually used to diagnose things like broken bones. They use a type of ionising radiation and that means they can be a health risk to people who are exposed to them.
         • Electron Beams
           • To produce x-rays, all you need is a cathode, an anode, an evacuated gas tube and some thermionic emission. A filament acts as a cathode. It's heated which gives energy to its electrons and once they have enough, they "boil off"-the process is called thermionic emission. Electrons are then accelerated towards the anode by a potential difference between the two electrodes. Electron beams can be used to produce x-rays by making them collide with a metal target(the anode), causing them to lose some of their kinetic energy and convert into x-rays. The glass tube contains a vacuum to prevent electrons colliding with air particles that would knock them off target and decrease their energy. A lead casing is out around the tube to absorb some of the x-rays so they're only aimed at the thing in question.
           • Kinetic Energy Equation
             • Kinetic Energy, KE (in joules, J) Electronic charge, e (in coulombs, C) Accelerating Potential Difference, V (in volts, V) KE = e x V or KE=1/2 x m x v^2
           • Equation for current produced
             • Current, I (in amps, A) No. particles per sec. N (/s) Charge on each particle, q (coulombs, C) I = N x q
             • the electronic charge, e, is -1.6x10^(-19) C the charge of an electron, -1, is relative to -1.6x10^(-19)C. The relative charge is fine for comparing charges on different particles but in calculations like I=N x q, you need the actual value in coulombs
         • Intensity and Absorbtion
           • The intensity of radiation depends on distance from the source. Inverse square relationship: if you move twice as far from the source, the same radiation is being dpread over four times the area so you only receive 1/2^2=1/4 of the intensity
           • Thickness of materials affect x-ray absorption; the denser the material, the more radiation it absorbs. the thickness will also affect the amount of radiation absorbed; the thicker a material, the more x-rays that will be absorbed.
         • Treatments
           • Pros
             • Reason 1: Despite them being harmful, they're often the best choice to treat or diagnose a patient due to the benefits of using it outweighing the risks. e.g. it's better to properly diagnose a patient's injury than risk using the wrong treatment.
             • Reason 2: Hospitals try to limit exposure and reduce risk to the patient as much as possible
             • Reason 3: using x-rays is       non-invasive and means that the patient doesn't have to undergo incisions or surgery. This means that the procedures are quite quick.
             • Reason 4: Safer methods than x-ray imaging are used when possible to reduce the risk of exposure to the patient. However, when the x-ray imaging would be more beneficial to diagnosing a patient, doctors may decide with it instead.
           • Cons
             • Reason 1: x-rays can be harmful to us.
     • Non-ionising
       • Sound
         • Ultrasound
           • A sound with frequencies above 20kHz, a higher frequency than human hearing.
           • Pre-natal Scanning
             • Ultrasound imaging can be used to diagnose soft tissue problems and to perform pre-natal scans of a foetus in the womb. Ultrasound waves are reflected off the different issue boundaries, and the times and distributions of the echoes are processed by a computer to form a image on the screen.
           • Breaking Down Kidney Stones
             • Kidney stones are hard masses that can block the urinary tract and be extremely painful.
             • Ultrasound beams concentrate high energy waves at the kidney stones which then get turned into sand-like particles that are passed out in the urine. This is a good process because it means that patients don't need invasive surgery and its relatively painless.
           • Measuring the Speed of Blood Flow
             • Because ultrasound works in real time, it can show things changing and moving which makes it useful for investigating problems with blood flow - particularly in the heart and liver. Special machines can measure the speed of blood flow and identify any blockages in the veins and arteries.
       • Visible Light
         • Endoscopes
           • These reflect light along optical fibres and can be used to see inside the patient to investigate problems without the need for invasive surgery. They can be used for keyhole surgery
         • Lenses
           • Power and Lens Equation
             • power of lens = 1/focal length 1/f = 1/u + 1/v f is focal length, u is object distance, v is image distance
           • Snell's Law and Total Internal Reflection
             • n= sin I / sin r I is the angle of the incident ray r is the angle of the refracted ray n is the refractive index
             • If the angle of incidence (I) is less than the critical angle, most of the light passes out but a little bit of it is internally reflected. If the angle of incidence(I) is equal to the critical angle, the emerging ray comes out along the surface and there's also quite a bit of internal reflection. If the angle of incidence(I) is greater than the critical angle, no light comes out and all the light is internally reflected, i.e. total internal reflection.
             • Uses of Total Internal Reflection
               • Optical Fibres
                 • These carry visible light that can be used in medical diagnosis and communications technology. They work because of total internal reflection: light is reflected off the sides of a thin inner core of glass/plastic and the light is reflected repeatedly until it emerges at the other end. The fibres need to be narrow enough to keep angles above the critical angle and the fibre mustn't bend too sharply anywhere.
               • Endoscopes
                 • This is a thin tube containing optical fibres that let surgeons examine inside the body.  They consist of 2 bundles of optical fibres-one to carry light and the other to carry back an image so that it can be viewed. The image is seen through an eyepiece or is shown on a full-colour moving image on a TV.
                 • A big advantage with this procedure is that surgeons can perform many operations but cut only small holes into people - keyhole surgery. This wasn't possible before optical fibres.
         • The Eye
           • The Eye
           • Correcting Vision Defects
             • Short sight can be corrected with a diverging lenses. Long sight can be corrected with converging lenses.
             • Sight can also be corrected using contact lenses or laser eye surgery. Contact lenses: these sit on the cornea and are shaped to compensate for the fault. Like glasses, these can be converging or diverging. Laser eye surgery: a laser can be used to vaporise tissue, changing the shape of the cornea. Slimming it makes it less powerful and can improve short sight. Changing the shape so that it's more powerful can improve long sight. The surgeon can precisely control how much tissue the laser takes off, completely correcting the vision.
       • Infrared
         • A type of EM radiation
         • Pulse Oximeter
           • This uses light to check the oxygen percentage in the blood.
           • In their arteries, healthy people normally have at least 95% oxhaemoglobin and no more that 5% reduced haemoglobin.
           • Pulse Oximetry
     • Intensity
       • Intensity of radiation is dependent on the distance from the source and what it's passing through. Generally, the more dense the medium, the more radiation absorbed, decreasing the intensity of the radiation. The main equation to remember is: Power = Intensity x Area
     • Particle Radiation
       • Neutron Radiation
         • Neutrons are more penetrating than alpha or beta and sometime gamma. Unlike alpha, beta and gamma, neutrons aren't directly ionising but they can be absorbed by the nuclei of atoms in the substances they pass through which will make them radioactive. The radioactive nuclei then emit ionising radiation- therefore the name 'indirectly ionising'.
         • Neutrons are absorbed best by light nuclei. Hydrogen is the lightest of all so hydrogen-rich materials such as water, polythene or concrete are used to make neutron radiation shielding. Neutron absorption often makes nuclei emit gamma radiation, so some nice thick lead can be added to neutron radiation shielding to shield against gamma radiation too.
       • Positron Radiation
         • This is positively charged beta radiation. The positron is the antiparticle of the electron (their charge is the only difference; +1 instead of -1). Positrons have the same properties of electrons: they're light and fast moving and moderately ionising but can be stopped by a sheet of thin metal. But positrons are obliterated in spectacular fashion as soon as they meet an electron-called annihilation.
     • Tracers
       • Some radioactive tracers are used as tracers to diagnose some medical conditions. The tracers are injected or swallowed. A detector then follows their path around the body. A computer reads these messages from the detector to create an image which shows where the strongest reading of radiation is coming from. A well-known example is iondine-131 which is absorbed by the thyroid gland. It gives out radiation which can be detected to show whether the thyroid gland is taking in iodine like it should. Only isotopes that emit beta or gamma are used because they can pass out of the body. They also have short half-lives to reduce the amount of radioactivity inside the patient.
     • Dangers
       • Ionisation caused by radiation can kill a cell completely or damage it so it can't divide-causing tissue damage. Radiation can also alter genetic material in a cell, causing mutations. It can also make the cell divide and grow uncontrollably-making a cancer. That's why it's important to limit a person's exposure to radiation
       • Any exposure to radiation increases the risk of tissue damage and cancer. For treatments and diagnostics, patients are given the lowest possible doses and have short exposure time. Lead shielding is also worn to protect areas not being treated. Medical personnel must also limit their exposure to radiation; the intensity decreases with distance, so staff need to stay behind lead shielding and away from the source. Also, the amount of radiation needs to be closely monitored.
     • Radiation Therapy
       • Radiation can be used internally or externally to treat tumours. Internal radiation therapy is when a radioactive substance is placed inside the body into or near a tumour by ways such as injecting or implanting a small amount of radioactive substance. This method gives a high dose of radiation to a small part of the body so damage to normal tissue surrounding the tumour is limited.
       • Tumours can also be treated externally using high-energy x-rays or gamma rays aimed at the tumour. The radiation is carefully focused at the tumour, but some damage is still done to surround healthy cells.
       • Internal radiation therapy is shorter than using external sources, usually by up to 6 weeks which reduces the number of visits the patient has to make to hospital as well as time they have to wait to undergo any further planned treatment, e.g chemotherapy. Internal treatments may cause the patient to emit radiation after the source is inserted so they may have to limit contact with people until it's removed, which can sometime be 7 days later. With external sources, it only lasts a few minutes and the patient does emit any radiation afterwards.
       • Internal treatments generally have no side effects although there can be some discomfort from the implant. However, external treatments like radiotherapy can have short and long term effects. Some uses of internal and external radiation therapy overlap, but they're often used to treat different parts of the body.
       • Development
         • Some radioactive medical techniques are relatively new in the medical world. That means we don't full understand the   long-term benefits and side-effects. New techniques are often tested first on cells grown in a lab, then on animals. Once they've been tested on animals and come out OK, they need to be tested on people and are placed in clinical trials.
         • There are ethical arguments that go with this: Some people argue that it is unethical to test new treatments or drugs on animals.  A new technique could have harmful side effects. Patients should be aware of possible side effects before agreeing to take part in medical tests. But doctors don't know for sure what all the side effects could be. Lots of ill patients may want to get onto a medical trial but places are limited. When a trial seems to show that a new technique works, how long before it's offered to everyone.
       • Ethics
         • Radiation is both useful and dangerous and we have to think whether the benefits of using it to diagnose or treat an illness outweigh the associated risks to the patients involved. Even when precautions are taken, using radiation to kill off cancerous cells will always cause some damage to normal cells which can lead to side effects. For example: radiotherapy can cause hair loss, sickness and skin irritation which are all minor side effects that generally last as long as the treatment.
         • However, there are other more serious side effects that may appear moths or years after radiotherapy treatment has ended that could significantly affect someone's life, e.g bowel damage or infertility. Some people may argue that if a person's quality of life could be seriously reduced after treatment, then it may not be worth undergoing the treatment in the first place. Some people may refuse treatment because of the risk of getting these side effects.
         • In some rare cases, the patient may even develop a second cancer caused by the radiation used to treat the first one. But without the first treatment, the person's life expectancy may be dramatically shorter. Radiotherapy doesn't always lead to a cure but it can often reduce the suffering of a patient who is close to death. Treatment that reduces the suffering without curing the illness is called palliative care.

2. Particles

   • Gasses and Pressure
     • in general: (pressure x volume) / temp (in K) = constants
     • Many gasses, like nitrogen and oxygen, are store in canister under pressure in hospitals. Flow rate is the volume of gas per unit time released from a gas bottle. The pressure outside a gas bottle will typically be 1atmosphere (atm). Stored gasses are kept at a much higher atmospheric pressure to ensure a high flow rate. Storing at high pressures also means you can store more gas in a small volume.
     • The difference in pressure between inside and outside of a gas bottle is what causes the gas to flow- when the pressures are equal, the gas has no reason to go anywhere. So no gas canisters will be fully empty. Gas canisters need to be made of materials that are strong enough to hold gasses under high pressures without buckling or splitting, e.g. steel or carbon reinforced aluminium
   • Pacemakers
     • A pacemaker is a device that is used to regulate heart beat. The heart pumps blood and creates a lub-dub rhythm due to a potential difference that first goes across the artria then to the ventricles. When there is an irregularity in the heart's natural rhythm when compared to the norm, a pacemaker is fitted in order to balance and help correct the problem. They do this by sending out electric pulses across the heart using small electrodes that are attached to the heart.
     • The pacemakers can be fitted with minor surgery and only a small incision is needed to be made to insert the pacemaker. However the artificial pacemakers are powered by batteries and will eventually need replacing when the battery looses power. Many modern pacemakers can also be programmed externally, meaning the pacemaker's settings can be changed without the patient having to undergo surgery again.
     • Some modern pacemakers are able to monitor things like breathing and temperature also and then use this information to adjust your heart rate to match whatever activity you're doing.
   • Cyclotrons
     • A cyclotron is a type of particle accelerator which uses a magnetic field to accelerate particles to very high energies along circular paths. A use of this process involving particle accelerators is to bombard atoms with protons to turn them into isotopes that are used in medical tracers.
   • Electricity and the Body
     • Electrocardiographs
       • The heart is a pump made of muscle which is split up into 4 chambers - the atria at the top and the ventricles at the bottom. When the heart beats, an action potential passes through the atria making them contract. A fraction of a second later, the same happens to the ventricles. Once the action potential has passed, the muscle relaxes. These weak electrical signals on the skin are sensed by the electrocardiograph which records these signals. For accurate readings, the patient should lie or sit still and relax.
       • The results are shown on an electrocardiograph and these are used to look at the action of the heart. How to calculate heart rate: Frequency = 1/ time period (secs) if you multiply the answer by 60, you get heart beats per minute.
     • Potential Differences
       • The potential difference is a voltage. The potential difference across the cell membrane of a muscle at rest id called the resting potential. The potential difference can be measured using tiny needle electrodes. The resting potential of a muscle is about -70mV.
       • When a muscle cell is stimulated by an electrical signal, the potential difference changes from -70mV to +40mV. This increased potential is called ACTION POTENTIAL. This action potential passes down passes down the length of the cell, making the muscle cell contract.