Introduction To Imaging Flashcards
What is an X-ray?
It is an electromagnetic pocket of energy with a wavelength of 0.1-10nm.
How does an X-ray machine work?
A cathode (negative and made from tungsten wire) is connected to a power supply and when a current is run through it heats up. There are lots of parts to reduce the heat of the process. Electrons roll off the cathode and form a cloud and they are attracted to the positive anode and some are turned to X-rays whilst the rest is heat. The rotor turns at high speeds whilst the bellow allows the structure to expand. The cathode and anode are in a vacuum and the whole production of x rays is thermionic emission.
What three things does the intensity of X-rays depend on in a machine?
The tube current
Atomic number of target
The tube voltage
What are the three interactions of X-rays with matter?
Scatter
Absorption
Transmission
What is attenuation and what three factors of matter does it change with?
It is the process by which radiation loses power as it travels through matter and interacts with it.
Atomic number
Density
Thickness
What is the order of attenuation coefficients?
Air
How does an ultrasound work?
The ultrasound releases high frequency sound pulses (1-20Mhz). These sound pulses travel through the matter until they hit an acoustic interface and they bounce back and the pressure wave constructs an image. There can be no gas bubbles between the skin and the device.
What is barium and what is it used to study? What are two complications that can arise from it?
It is a radio opaque contrast agent with a high atomic number so it absorbs more X-ray photons than surrounding tissues.
It’s used for swallow and meal to see the oesophagus, duodenum and stomach. It can be used to study the small bowel and large bowel.
Complications include bowel disturbance and colonic perforation at enema.
What does CT allow that X-ray doesn’t and what does it require to work?
It rotates so can give axial images and these images can be built up to form a complete image. It often is given either an oral or IV iodinated contrast.
What is ionising radiation?
A particle/wave that has sufficient energy to ionise a neutral atom.
