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Physics OCR A'level > Ch27: Medical Imaging > Flashcards

Ch27: Medical Imaging Flashcards

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1
Q

What is the approximate range of wavelengths for X-Rays?

A

10^-8 to 10^-13 m

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2
Q

Approximately how many times more energy do X-ray photons have than visible light?

A

10-10 000 times more

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3
Q

How are X-ray photons produced?

A

Very fast moving electrons fired from a cathode and are slowed down by interaction with the atoms of a metal anode such as Tungsten. The kinetic energy of the electrons becomes high energy photons.

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4
Q

What is the energy gained by an electron when accelerated through p.d: V?

A

eV, where e is the elementary charge

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5
Q

How can we calculate the maximum energy of an X-ray Photon?

A

max X-ray energy = kinetic energy of electron

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6
Q

What is the equation for wavelength of an X-ray photon in relation to the electron that produced it?

A

λ = hc/eV

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7
Q

Name the 4 ways an X-ray photon can interact with matter.

A
  • Simple scatter
  • Photoelectric effect
  • Compton scattering
  • Pair production
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8
Q

Describe the effect of Simple scatter? What is its photon energy range?

A

Electrons in an atom scatter the X-ray to a different direction as the photon does not have enough energy to remove the electron.
< 20keV

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9
Q

Describe the Photoelectric effect?

A

A photon is fully absorbed by an electron and removes it from the atom with no left over photon.
<100keV

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10
Q

What is the typical voltage range for hospital X-ray machines?

A

30-100kV

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11
Q

Describe the effect of Compton scattering? What is the photon energy range?

A

A photon provides enough energy to remove an electron from an atom, with enough energy left over to allow a low energy photon to escape as well.
0.5-5MeV

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12
Q

Describe the effect of pair production? What is the photon energy range?

A

A photon interacts with a nucleus, the electromagnetic energy of the photon creates an electron and a positron which are ejected in opposite directions.
> 1.02MeV

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13
Q

What is an attenuation coefficient?

A

A value which describes how well a substance absorbs X-rays.

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14
Q

What is the equation for transmitted intensity of X-rays?

A

I = Io(e^-μx)

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15
Q

Why are contrast mediums used?

A

to increase absorption coefficients of soft tissues so their structure is visible in an X-ray.

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16
Q

What are the two most common contrast mediums for X-rays and how are they used?

A

Iodine: typically injected
Barium: typically eaten

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17
Q

What is the attenuation coefficient proportional to?

A

The attenuation coefficient is proportional to the cube of the atomic number (Z).

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18
Q

What does C.A.T stand for?

A

Computerised axial tomography

19
Q

What are the advantages and disadvantages of C.A.T scans?

A

A: produces a 3D image
D: High radiation exposure and long time to do (10-30 min)

20
Q

How are CAT scans done?

A

An X-ray tube produces a fan of x-rays which move 360 degrees around a patient while the patient also moves through the machine; producing slices which a computer puts together to form a 3D image.

21
Q

What are the key parts of a CAT scan machine?

A

Rotating gantry, X-ray tube, detector, patient bed, display, and computer.

22
Q

What are the parts of a gammas camera in order?

A

collimator, scintillator, light guide, photomultiplier tubes, circuits, computer, and display

23
Q

What is the most common medical tracer used with the gamma camera?

A

NaTcO4 (Tc-99)

24
Q

What is the function of a collimator in a gamma camera?

A

Only allows through photons travelling straight at the camera.

25
Q

What is the function of the scintillator in a gamma camera?

A

Turns gamma photons to visible light (only approximately 1 in 10)

26
Q

What are two common isotopes used in tracers for PET scans?

A

Fluorine-18 and Carbon-11

27
Q

What does P.E.T stand for?

A

Positron emission tomography

28
Q

How do Pet scans work?

A

An isotope ingested by the patient decays releasing a positron which almost immediately annihilates with an electron within the body, this creates two gamma photons in opposite directions. These are then detected by a ring of gamma cameras which determine where the two came from.

29
Q

What is the function of a gamma camera in a PET scan?

A

detecting gamma photons

30
Q

What are the advantages and disadvantages of a PET scan?

A

A: non invasive, can diagnose cancer, monitor brain function, and plan complex surgeries.
D: expensive, only used for complex patients

31
Q

What are the benefits of ultrasound imaging?

A

Non-ionising, non-invasive, quick

32
Q

What is the frequency range of medical ultrasound?

A

1-15MHz

33
Q

What device is used to generate and receive ultrasound?

A

An ultrasound transducer.

34
Q

What is the piezoelectric effect?

A

The creation of e.m.f in some crystals by stretching, compressing or distorting them. or vice versa

35
Q

How does a transducer generate ultrasound?

A

By running an alternating pd through a crystal to quickly stretch and compress it, producing an intense ultrasound signal.

36
Q

What is the typical frequency of ultrasound pulses?

A

5kHz pulses (of 5MHz ultrasound)

37
Q

What is the difference between A-scans and B-scans?

A

A scans scan only one direction, generating an oscilloscope reading. while B-scans produce 2D or 3D images.

38
Q

What is acoustic impedance?

A

The product of a substance’s density (p) and the speed of ultrasound in that substance (c)

39
Q

What is the equation for acoustic impedance?

A

Z = pc

40
Q

What is doppler imaging?

A

A process which uses the reflection of ultrasound off moving objects in the body (usually liquid) to determine their speed.

41
Q

What are some uses of doppler imaging?

A

Can reveal blood clots, identify narrowing of the walls of veins/arteries, and evaluate blood flow to transplanted organs.

42
Q

How can colour doppler scans be created?

A

A computer connected to the ultrasound transducer can assign colours for speed in different directions, such as in an umbilical cord.

43
Q

What is the equation associated with Doppler imaging? Define the terms.

A 
Δf = (2fvcosθ)/c
Δf: change in frequency
f: frequency of transmitted ultrasound
c: speed of sound in substance
v: velocity of object/fluid

Physics OCR A'level (19 decks)

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