P3 topic 2 Flashcards
what does CAT stand for?
computerised axial tomography
what are CAT scabs commonly used to diagnose?
tumours, blood clots, Alzheimer’s disease
why are CAT scans different from conventional 2D X-ray scans?
they can also show the structure of soft tissue in the body- they produce a 3-dimensional image of the inside of the body
how are risks of CAT scans reduced?
x-rays are ionising radiation and can damage healthy cells- short exposure times minimises risks
how does a CAT scan create an image?
during a CAT scan, X-rays are passed through the body from all directions as the X-ray source rotates around the body in a spiral path- detectors produce images of slices of the body to build up a 3D image
what are fluoroscopes used for?
to obtain real-time moving images of the internal structure of organs in the body, usually used for diagnosing problems with the digestive system
how do fluoroscopes work?
the patient first has to drink a chalky fluid containing barium sulfate, which is opaque to x-rays- when x-rays are passed through the body to a detector, the passage of the ‘barium meal’ can be viewed on a monitor and the doctors can identify any problems
what do radiographer a wear to protect their bodies?
lead is a good absorber of x-rays, so radiographers wear lead-lined aprons to protect their bodies
inverse square law
the intensity of EM radiation decreases with distance from its source- intensity is inversely proportional to the square of the distance from the source
what is used to produce x-rays to treat cancer?
a linear particle accelerator (linac) is used, so that the energy and intensity of the x-rays can easily be controlled, to ensure that the patient receives the correct dose- x-rays produced from a linac can also easily be switched off, unlike gamma rays from radioactive sources
what can x-rays be used for in hospitals?
CAT scans and fluoroscopes
what’s an evacuated tube?
a glass vessel with no air inside (a vacuum)
what happens if a potential difference is applied across an and a cathode in an evacuated tube?
a beam of electrons can be forced to flow
thermionic emission
emission of electrons from the surface of a heated metal- a low voltage supply (6 v) heats up the filament at the cathode and causes the electrons in the filament to gain enough energy to escape
what causes the electrons to be accelerated towards the positive by charged anode?
a high voltage supply (500 v) applied between the cathode and the anode
when is there a flow of charge or electric current?
if there are electrons moving
why does this have to be done in a vacuum?
if there is any air in the tube the electrons will collide with air molecules and lose energy, so it has to be a vacuum- this arrangement is sometimes know as a thermionic diode
X-ray tube
similar to a thermionic diode, but a higher potential difference (about 100 000 V) is needed between the anode and the cathode
what is the anode in an X-ray tube made of?
a high melting point metal, such as tungsten- it’s known as the target
what is another precaution put in place in x-ray machines?
when the electrons strike the target at a very high speed, about 1% of their energy is converged to X-rays and the rest is converted to heat- as there is so much heat produced, the target needs to be cooled by circulating water, otherwise it may melt
how can the frequency of the x-rays produced be increased?
by increasing the accelerating potential difference between the cathode and the anode
