X-rays/CT scan/Ultra Sound Flashcards
CT X
X-Ray: Series of x-ray images
CT A
Angles: Different angles are used
CT I
Image: To give the image of the slice
CT S
Slice: Repeated for many different slices
CT 3
3D: To build a 3D image
Formula for half life
Half life = ln(2) / decay constant
Formula for activity
A = Decay Constant * Number of undecided
How are x-rays produced?
Metal target bombarded with electrons, when ever a particle is accelerated it emits electromagnetic radiation
X-ray ratio between acceleration and wavelength
Inversely proportional
X-rays are emitted from?
The heated cathode
X-rays: How is intensity controlled?
Controlling rate of arrival of electrons at the anode by controlling the heat of the cathode
X-rays: How is hardness controlled?
Potential Difference
X-rays: How is sharpness controlled?
X-ray beam width, inversely proportional
X-rays: What are soft x-rays?
Set of peaks at longer wavelengths that don’t add to the image but increase background radiation, absorbed by using a aluminium window
X-rays: What absorbs more bone or muscle?
Bone
Formula for attenuation of X-rays
I = I * e ^-yx where y is a constant
What is HVT
Half value thickness, depth required to reduce intensity by one half
Steps for working out CT scan
Remove background, divide by number of scans-1
Formula for acoustic impedance
Z = pc where c is the speed of sound in a medium
What is acoustic impedance
The resistance sound waves encounter in a medium
Formula for intensity at a certain depth
I = I * e ^ -kx where k is the absorption constant
What is ultrasound used for
To gather information about internal structures of the body
How does ultrasound work
Monitoring pulses of ultrasound are sent into the body at regular intervals, the ultrasound is reflected on large changes in acoustic impedance, this reflected sound is mapped based on the time it took to return which produces an image
Why is cellulose gel used
To limit the large change of acoustic impedance at the boundary
