Physics for Medicine: Imaging & Biomechanics

• Physics for medicine applies physics principles to medical diagnosis and treatment
• It encompasses various techniques, including medical imaging and biomechanics

Medical Imaging Techniques

• Medical imaging techniques visualize the human body for diagnostic and therapeutic purposes
• These techniques utilize different physical principles to generate images
• Examples include X-ray imaging, Computed Tomography (CT), Magnetic Resonance Imaging (MRI), Ultrasound imaging, Nuclear medicine imaging (PET and SPECT)
• X-ray imaging uses electromagnetic radiation to create images of bones and dense tissues
• CT combines multiple X-ray images to produce cross-sectional views of the body
• MRI uses magnetic fields and radio waves to visualize soft tissues
• Ultrasound imaging uses high-frequency sound waves to create real-time images
• Nuclear medicine imaging uses radioactive tracers to visualize organ function

Biomechanics in Medicine

• Biomechanics applies mechanical principles to biological systems
• It helps to understand the mechanics of human movement, tissue behavior, and implant design
• It is used in orthopedics, sports medicine, rehabilitation, and cardiovascular medicine
• Biomechanics involves studying forces, motion, and material properties in the body

Mechanics

• Mechanics is the study of forces and their effects on objects
• It is a fundamental branch of physics relevant to biomechanics
• Key concepts include:
  • Force: A push or pull that can cause a change in motion
  • Motion: Change in the position of an object over time
  • Newton's Laws of Motion: Describe the relationship between force, mass, and acceleration
  • Statics: Study of objects at rest or in equilibrium
  • Dynamics: Study of objects in motion

Torque

• Torque (rotational force) is the tendency of a force to cause rotation
• Torque is calculated as the product of the force and the lever arm (distance from the axis of rotation to the point where the force is applied)
• Torque = Force × Lever Arm
• Torque is a vector quantity, with direction perpendicular to both the force and the lever arm
• The unit of torque is Newton-meter (Nm)
• Torque plays a crucial role in understanding muscle action and joint movement

Centre of Gravity

• The center of gravity (CG) is the point where the entire weight of an object appears to act
• It is the point around which the object will balance
• The location of the CG depends on the object's shape and mass distribution
• For symmetrical objects with uniform density, the CG is at the geometric center
• The CG's position is important for stability and balance
• When the CG is within the support base, the object is stable
• If the CG falls outside the support base, the object will topple
• In human biomechanics, the CG changes with body posture and movement

Levers

• A lever is a rigid object that pivots around a fixed point called a fulcrum

• Levers are used to amplify force or increase displacement

• There are three classes of levers, based on the relative positions of the fulcrum, force (effort), and load (resistance):

  • First-class lever: Fulcrum is between the force and the load (e.g., seesaw, scissors)
  • Second-class lever: Load is between the fulcrum and the force (e.g., wheelbarrow, calf raise)
  • Third-class lever: Force is between the fulcrum and the load (e.g., biceps curl)

• The mechanical advantage (MA) of a lever is the ratio of the output force (load) to the input force (effort)

• MA = Load / Effort

• Levers in the human body:

  • Bones act as levers
  • Joints act as fulcrums
  • Muscles provide the force

• Most levers in the human body are third-class levers, which favor speed and range of motion over force amplification