Medical Physics

How are x-rays produced?

• Electrons released from a heated filament accelerate towards a tungsten cathode. Upon collision with the cathode, the KE of the electrons is converted to X-ray Photons.
• Electrons released from a heated filament accelerate towards a tungsten anode. Upon collision with the anode, the KE of the electrons is converted to X-ray Photons.
• Electrons released from a heated filament accelerate towards a tungsten cathode. Upon collision with the cathode, the change in spin of the electrons causes the release of X-ray Photons.
• Electrons released from a heated filament accelerate towards a tungsten anode. Upon collision with the anode, the change in spin of the electrons causes the release of X-ray Photons.

In order to improve x-ray image quality and to minimise the radiation dosage...

• Keep the x ray source close to the patient.
  Have a lead grid to absorb scattered rays.
  Put the detection plate as close to the patient as possible.
• Keep the x ray source far away from the patient.
  Have a lead grid to absorb as many x rays as possible.
  Put the detection plate as close to the patient as possible.
• Keep the x ray source close to the patient.
  Have a lead grid to absorb as many x rays as possible.
  Put the detection plate as close to the patient as possible.
• Keep the x ray source far away from the patient.
  Have a lead grid to absorb scattered rays.
  Put the detection plate as close to the patient as possible.

Which of the following statements is true about X-rays?

• The anode is made of Tungsten
• The Cathode is made of Tungsten
• Both are made of Tungsten
• Neither are made of Tungsten

Which of these statements is false?

• The photoelectric effect occurs when a photon is absorbed by an electron, causing it to be ejected from its atom. This leaves a gap in the electron shell which is filled by another electron, giving out a photon.
• Compton scattering occurs when a photon knocks an electron to a higher orbital level, which causes the photon to lose energy and be scattered.
• Pair production occurs when a high energy photon decays into an electron and a positron.

Nuclear Tracers can be used to...

• Show areas of damaged tissues.
  Identify inactive cancer tumors.
  Show blood flow and activity in organs.
• Show areas of damaged tissues.
  Identify active cancer tumors.
  Show blood flow and activity in organs.
• Show areas of damaged bone.
  Identify inactive cancer tumors.
  Show blood flow and activity in organs.
• Show areas of damaged bone.
  Identify active cancer tumors.
  Show blood flow and activity in organs.

PET scanning involves...

• an electron-emitting radio-tracer being injected into the patient. This travels through the body and organs and emits electrons. These collide with positrons causing them to annihilate and release high energy gamma rays.
• an electron-emitting radio-tracer being injected into the patient. This travels through the body and organs and emits electrons. These collide with positrons causing them to annihilate and release high energy radio waves.
• a positron-emitting radio-tracer being injected into the patient. This travels through the body and organs and emits positrons. These collide with electrons causing them to annihilate and release high energy gamma rays.
• a positron-emitting radio-tracer being injected into the patient. This travels through the body and organs and emits positrons. These collide with electrons causing them to annihilate and release high energy radio waves.

The Piezoelectric Effect occurs when...

• you apply a p.d. across the crystal, which causes it to deform and vibrate at the same frequency. At the right frequency, this will cause the crystal to absorb ultrasound. It also turns an incoming sound wave into a constant voltage, so can be both a transmitter and receiver. 
• you apply an alternating p.d. across the crystal, which causes it to deform and vibrate at the same frequency. At the right frequency, this will cause the crystal to absorb ultrasound. It also turns an incoming sound wave into a constant voltage, so can be both a transmitter and receiver. 
• you apply an alternating p.d. across the crystal, which causes it to deform and vibrate at the same frequency. At the right frequency, this will cause the crystal to emit ultrasound. It also turns an incoming sound wave into an alternating voltage, so can be both a transmitter and receiver. 
• you apply an alternating p.d. across the crystal, which causes it to deform and vibrate at the same frequency. At the right frequency, this will cause the crystal to emit ultrasound. It also turns an incoming sound wave into a constant voltage, so can be both a transmitter and receiver. 

What are the crystals in a Gamma camera made of?

• Sodium Tartate
• Sodium Iodide
• Sodium Chloride
• Silver Nitrate 

The acoustic impedance of a medium is defined as...

• Z = pc where p is the density of the medium and c is the speed of sound within it. Z has units of kg/m2s
• Z = pc where p is the density of the medium and c is the speed of light within it. Z has units of kg/ms2
• Z = pc where p is the density of the medium and c is the speed of light within it. Z has units of kg/m2s
• Z = pc where p is the density of the medium and c is the speed of sound within it. Z has units of kg/ms2

The difference between an A-scan and a B-scan is...

• An A-scan sends a short pulse of ultrasound into the body while an electron beam sweeps down a cathode ray oscilloscope screen.
  In a B-scan, the electron beam sweeps across the screen rather than down.
• An A-scan sends long pulses of ultrasound into the body while an electron beam sweeps across a cathode ray oscilloscope screen.
  In a B-scan, the electron beam sweeps down the screen rather than across.
• An A-scan sends long pulses of ultrasound into the body while an electron beam sweeps down a cathode ray oscilloscope screen.
  In a B-scan, the electron beam sweeps across the screen rather than down.
• An A-scan sends a short pulse of ultrasound into the body while an electron beam sweeps across a cathode ray oscilloscope screen.
  In a B-scan, the electron beam sweeps down the screen rather than across.