Medical imaging Flashcards

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1
Q

Define X-ray

A

Em radiation with wavelength ranging from 0.1 - 10 nm

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2
Q

Define x-ray tube

A

a peice of equipment that produces x ray photons by firing electrons from a beta cathode across a large p.d. in an evacuated tube. x-ray photons are produced when the electrons are decelerated by hitting the target metal of the anode

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3
Q

Define Thermionic emission

A

The release of electrons from the surface of a heated material

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4
Q

Define attenuation

A

The decrease of intensity of em radiation as it passes through matter or space

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5
Q

Define attenuation coefficient

A

A measure of the absorbtion of x ray photons by a substance. Also called absorbtion coefficient.

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6
Q

Define CAT scan

A

Computer Axial Tomography; x ray images taken in slices which are built up in softwhere to produce a 3-D image from which any 2-D image can be displayed

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7
Q

Define medical tracer

A

A compound labelled with a radioisotope that can be traced inside the body with a gamma camera

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8
Q

Define Collimator

A

Part of a gamma camera, a honeycomb of long thin tubes made from lead that absorbs any photons arriving at an angle to the axis of the tubes so that a clear picture is obtained

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9
Q

Define Scintillator

A

Part of a gamma camera, that produces thousands of visable photons when struck by a single gamma photon

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10
Q

Define Photomultiplier tube

A

A peice of equipment that converts a photon of visable light into an electric pulse

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11
Q

Define PET scan

A

Positron emission tomography scan; forms an image from the 2 gamma rays produced during the annihilation of a positron and an electron

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12
Q

Define Ultrasound

A

Sound that is higher frequency than the typical limit of human hearing (20kHz)

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13
Q

Define Ultrasound transducer

A

A device used both to generate and to recieve ultrasound which changes electrical energy into sound and sound into electrical energy

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14
Q

Define Piezoelectric effect

A

When electrical charge accumulates in a solid material due to an applied mechanical stress, producing a potential difference

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15
Q

Define Acoustic impedance

A

The product of the density and the speed of ultrasound in a substance

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16
Q

Define intensity reflection coefficient

A

The ratio of reflected intensity to incident intensity at a boundary

17
Q

Define coupling gel

A

A gel with acoustic impedance similar to that of skin smeared onto the transducer and the patients skin before an ultrasound scan in order to fill air gaps and ensure that almost all the ultrasound enters the patients body

18
Q

Define impedance matching

A

The use of two substances wih similar acoustic impedeance to minimise reflecion of sound waves at a boundary

19
Q

Define simple scatter

A

X ray photons in range of 1-20 keV
X ray ionises atom and bounces off
X ray machines have greater than 20keV

20
Q

Define Photoelectric effect

A

X ray photons less than 100keV
Photon is absorbed and electron is emitted
Dominant mechenism in x ray machines

21
Q

Define Compton scattering

A

X ray photons in range of 0.5-5 MeV
X ray photon frees electrons but also scatters with reduced energy
Radiographs need to be protected from compton scattering using a sheild

22
Q

Define pair production

A

X ray photons more than 1.02 MeV
Photon dissapears and positron pair is produced (electron and positron)