Question | Answer |
What is ionising radiation? | Radiation that has enough energy to knock electrons out of their shells in an atom, causing it to become a positively-charged particle |
What is the strength of an X-ray dependent on? | Its frequency and its energy |
How does the strength of ionising radiation change over distance? | It decreases according to the inverse square law, i.e. if the distance is doubled, the intensity is reduced by four times (two squared) |
What are CAT scans and how are they done? | CAT scans are X-ray images that show a slice through the body. An X-ray source is moved round a patient in a circle and X-rays are detected by a detector opposite the source to build up many cross-sectional views of the body. image built up on computer |
What are CAT scans used for? | They are used for diagnosing cancers- unusual areas of brightness or darkness can indicate tumours or small areas of dead tissue |
What determines how many X-rays are absorbed by a medium? | Its density - on an X-ray photo, dark areas are where lots of X-rays have been detected because not many have been absorbed, and light areas are where not many X-rays have been detected because more have been absorbed |
What are fluoroscopes and how do they work? | Fluoroscopes show the patients organs working - they consist of an X-ray source and a detector attached to a digital video camera with the patient placed in between |
What are the advantages and disadvantages of using CAT scans and fluoroscopes for diagnosis? | Advantages: painless for the patient, non-invasive, can eliminate the need for a biopsy.
Disadvantages: they give a dose of radiation that is equivalent to up to 10 years of background radiation- increased risk of developing cancer |
How does an X-ray machine work? | • Thermonic emission of electrons from a heated wire filament (cathode)
• Electrons accelerate towards the anode when there is a big potential difference
• Electrons collide with metal anode and some energy is converted into X-rays |
What is the tube evacuated? | The tube is evacuated so that the electrons don’t collide with other particles as they cross the tube |
Why is the cathode at a high temperature? | A cathode with a higher temperature emits more electrons so more X-rays are produced |
Why is the beam of charged particles in an X-ray machine equivalent to an electric current? | When electrons flow form the cathode to the anode, they complete the circuit so the movement of charged particles is equivalent to an electric current |
How do you calculate the current in the X-ray machine? | Current in the X-ray machine (amperes) = number of particles flowing each second x charge on each particle (coulombs) |
How do you calculate the kinetic energy of the electrons in an X-ray machine? | The kinetic energy of an electron (joules) = charge on an electron (1.6 x 10-19 coulombs) x potential difference (volts) |
What is an action potential? | An action potential is an electrical signal sent to each muscle cell in the heart to tell it when to contract |
Why does the human body conduct electricity? | Because it contains a high proportion of water with salts dissolved in |
What is an ECG? | An ECG is an electrocardiogram, a picture of the heart electrical signals, built up through the detection of action potentials |
What is the characteristic shape of an ECG? | P wave = action potential spreads across both atria (small bump). QRS wave = action potential spreads up ventricle walls (large peak). T wave = contraction spreads up from base of ventricles (small bump) |
What are ECGs used for? | ECGs can be used to work out how fast the heart is beating and how well it is working |
What type of graph paper are ECGs printed on? | ECGs are printed on graph paper with a horizontal scale of 0.2 seconds for each larger square |
How do you work out the frequency of the heartbeat in beats per minute? | 1. Work out the time period of a heartbeat on the ECG
2. Use the equation: frequency (Hz) = 1 / time period (s)
3. Multiply the frequency by 30 |
What is pulse oximetry? | Pulse oximetry is used to measure a person’s pulse rate |
What does a pulse oximeter consist of? | Consists of: LED emitting red light, LED emitting infrared radiation & detector. |
How does a pulse oximeter work? | It works out the pulse by looking at time interval between the peak points of infrared absorbance, which occur after each heart beat, because a heart beat releases more oxygenated blood into the arteries which absorbs more infrared radiation. |
What is the percentage oxygen saturation? | The amount of oxygen that the blood is carrying - this is calculated by a pulse oximeter by comparing the absorbance of the two LEDs |