X-Rays, ECGs & Oximetry Flashcards
What are x-rays used for?
To produce images of the bones and organs in a body
In the process of molecules becoming ionised what happens to the x-rays?
As x-rays pass through body tissue they are absorbed by molecules malik them ionised. In this process x-rays lose energy and eventually cannot ionise any more tissue
How are x-rays produced?
A heated cathode produces electrons and the potential difference between this an the anion cause the electrons to accelerate towards the anode.
In the anode is a tungsten target, and when the electrons collide wth this, some of the energy converts to x-rays
Only a small amount of energy is converted to x-rays. What is the rest of the energy converted to?
Heat
What is the formula (with units) used to calculate the current in an x-ray tube?
Current (ampere, A) = number of particles per second (1/second, 1/s) x charge carried by each electron (coulomb, C)
OR
I = N x q
What do the electrons gain in an x-ray electron beam?
Kinetic energy
What is the unit of potential difference?
Volts (V)
What does one coulomb of electric charge gain when it is accelerated through a potential difference of one volt?
One joule of energy
What formulae can be used to calculate kinetic energy?
KE = eV
OR
KE = 1/2mv^2
What are x-rays?
Electromagnetic waves with a very short wavelength
In KE = 1/2mv^2, what do KE, m and v stand for, with units?
KE = kinetic energy (joules, J) m = electron's mass (kg) v = velocity of electron (m/s)
True or False: KE = ev = 1/2mv^2
True!
What is the mass of an electron?
9.1 x 10^-31kg
What is the inverse square law?
Area increases with the square of distance so intensity decreases with the square of distance.
Which scan produces a 2D image and which scan produces a 3D image?
Conventional x-rays produce a 2D image and CAT scans produce a 3D image (of the internal structure)
What do fluoroscope a (which use x-ray images on a screen) all doctors to do?
See real time image of a patients internal condition
What are the advantages of an x-ray?
1) X-rays can help give a reliable diagnosis and make sure treatment is fast and accurate
2) X-rays are non invasive (patients do not require operation to see what’s happening in their bodies
What are the disadvantages of an x-ray?
1) X-rays can kill and damage living cells
2) Risks are greater for babies and young children, so exposure is kept to the minimum
What are action potentials?
They are electrical signals that control the heart muscles
What are action potentials generated by and why?
The hearts natural pacemaker in order to make the heart beat at the correct rate to supply the body with needed oxygen
What measures the changing electrical signals in the heart?
An ECG (electrocardiogram)
What can an ECG show?
If a heartbeat is abnormal and can allow doctors to diagnose any problems with a patients heart
What are the five deflections observed in ones heart beat labelled as?
PQRST
A normal ECG shows the heart is beating regularly. The pulse rate is the frequency of this signal. What is the formula to calculate this?
f = frequency (hertz, Hz) T = time period (seconds, s) f = 1/T
The pulse rate is usually given as bpm, what does this mean and what must you do to calculate the frequency?
bpm means beats per minute. In this case, in order to find the frequency, one must multiply it by 60
What is the average resting pulse of an adult?
72bpm
How does a pulse oximetry measure the patients heart rate?
As the heart beats, the volume of blood in a fingertip varies, and the amount of light passing through the finger also varies. This allows heart rate to be measured.
How does a pulse oximetry measure the patients oxygen levels?
The difference between the amount of infrared light and visible light passing through the fingertips depends on how much oxygen the blood is carrying, allowing oxygen content to be calculated.
In KE = ev, what do KE, e and V stand for, with units?
KE = Kinetic Energy (joules, J) e = charge on electron (coulomb, C) V = accelerating potential difference (volts, V)
