Medical Imaging

X-ray production and attenuation, CT scanning, ultrasound and acoustic impedance, and PET scanning.

Spec Points Covered
  • I can describe how X-rays are produced in an X-ray tube.
  • I can explain the attenuationThe reduction in intensityThe powerThe rate of energy transfer. Measured in watts (W). transmitted per unit area perpendicular to the wave direction. Measured in W m⁻². Proportional to amplitude squared. of radiation (such as X-rays) as it passes through a material, due to absorption and scattering. of X-rays and use I = I_0 $e^{-\mu x}.$
  • I can define the half-value thicknessThe thickness of material that reduces the intensityThe powerThe rate of energy transfer. Measured in watts (W). transmitted per unit area perpendicular to the wave direction. Measured in W m⁻². Proportional to amplitude squared. of X-rays to half its original value. and relate it to the attenuationThe reduction in intensityThe powerThe rate of energy transfer. Measured in watts (W). transmitted per unit area perpendicular to the wave direction. Measured in W m⁻². Proportional to amplitude squared. of radiation (such as X-rays) as it passes through a material, due to absorption and scattering. coefficient.
  • I can explain how contrast media and image enhancement improve diagnostic X-ray images.
  • I can describe the principles of CT scanning and explain how it produces cross-sectional images.
  • I can explain the production and detection of ultrasoundSound waves with frequencies above 20 kHz (beyond human hearing). Medical ultrasound typically uses 1-15 MHz. using piezoelectric transducers.
  • I can define acoustic impedanceThe product of the densityMass per unit volume of a material. Measured in kg m⁻³. of a medium and the speed of sound in that medium. Determines how much ultrasoundSound waves with frequencies above 20 kHz (beyond human hearing). Medical ultrasound typically uses 1-15 MHz. is reflected at a boundary. and use Z = $\rho$c.
  • I can calculate the fraction of ultrasoundSound waves with frequencies above 20 kHz (beyond human hearing). Medical ultrasound typically uses 1-15 MHz. reflected at a boundary using the impedance equation.
  • I can explain the difference between A-scans and B-scans in ultrasound imaging.
  • I can describe the principles of PET scanning, including positron-electron annihilationThe process in which a particle and its corresponding antiparticle collide and convert their combined rest mass into energyThe capacity to do work. Measured in joules (J)., typically producing two gamma photons. and the detection of gamma photonA quantum (discrete packet) of electromagnetic radiation. Its energy is proportional to its frequency. pairs.
  • I can compare the advantages and disadvantages of X-ray, CT, ultrasound, and PET imaging techniques.
Notes
01 X-rays are produced when high-speed electrons are decelerated rapidly on hitting a metal → 02 Attenuation Attenuation → 03 CT (Computed Tomography) scan CT (Computed Tomography) scan → 04 Ultrasound Ultrasound → 05 Acoustic impedance (Z) Acoustic impedance (Z) → 06 A-scan (Amplitude scan) → 07 PET (Positron Emission Tomography) PET (Positron Emission Tomography) → 08 X-ray → 09 X-ray attenuation → 10 Acoustic impedance →
Σ Key Equations Full Reference →
On Data Sheet
Not on Data Sheet
$$I = I_0 e^{-\mu x}$$
$$x_{1/2} = \frac{\ln 2}{\mu}$$
$$Z = \rho c$$
$$\frac{I_r}{I_0} = \left(\frac{Z_2 - Z_1}{Z_2 + Z_1}\right)^2$$
$$E = 2m_e c^2$$