Electromagnetic Waves Overview

Electromagnetic Waves

• Electromagnetic (EM) waves are produced by accelerating charges.
• EM waves are also called electromagnetic radiation.
• EM waves consist of oscillating electric and magnetic fields that travel away from the accelerating charges.
• A changing magnetic field induces a changing electric field, and vice-versa.
• These changing fields form electromagnetic waves.
• EM waves can travel through vacuum, air and solid materials.
• EM waves in vacuum or in air travel at a speed of 3.00 × 10⁸ m/s.

Learning Objectives

• Lecture 1: Explain the electromagnetic spectrum, explain the properties of electromagnetic waves, and explain the medical uses of electromagnetic waves.
• Lecture 2: Explain what MRI is and how it works, explain the safety of using MRI, and explain the people who are not able to use MRI.

Introduction

• EM waves are produced only by accelerating charges.
• EM waves consist of oscillating electric and magnetic fields.
• A changing magnetic field produces a changing electric field, and vice versa.
• There are no electric waves or magnetic waves only electromagnetic waves.
• EM waves can travel through vacuum, air, and solid materials.

The Electromagnetic Spectrum

• EM waves exist at every frequency.
• The properties of EM waves and their interactions with matter depend on the frequency of the wave.
• The electromagnetic spectrum is traditionally divided into six or seven regions based on frequency and wavelength.

Visible Light

• Visible light is the part of the spectrum that can be detected by the human eye.
• For an average range, the frequencies of visible light are 430 THz to 750 THz, corresponding to wavelengths in vacuum of about 700-400 nm.
• White light can be separated by a prism into the colours red, orange, yellow, green, blue, and violet.
• Red has the lowest frequency (longest wavelength), and violet has the highest frequency (shortest wavelength).
• Lightbulbs, fire, the sun, and fireflies are sources of visible light.
• We see objects by the light they reflect.

Medical Applications of Visible Light

• Blue light treatment of jaundice in babies.
• Scanning laser ophthalmoscope (for examining the retina and optic nerve head).
• Photodynamic therapy (PDT) uses light energy and photosensitizing medications to treat certain types of cancer.

Endoscopy

• Endoscopy is a test to look inside the body using a long, thin tube with a small camera (endoscope).
• The endoscope is passed into the body through a natural opening such as the mouth.
• New approaches involve virtual endoscopy, using a high-resolution CT scan and a computer to show the internal organs as if viewed through an endoscope.

Infrared (IR)

• Infrared radiation (IR) is lower in frequency than visible light.
• IR extends from the low-frequency (red) edge of the visible spectrum to a frequency of about 300 GHz (λ ≈ 1 mm).
• IR waves are longer than visible light waves, but shorter than radio waves.
• IR is invisible to the human eye, but some animals can detect it.
• Thermal radiation given off by warm objects is primarily IR.
• IR is used in modern thermometers and thermography.

Medical Application of IR – Thermography

• Thermography uses infrared imaging to assess skin temperature.
• Assessing skin temperature is often used as an extension of a standard physical exam (especially for diagnosis and treatment plans).

Pulse Oximetry

• Pulse oximetry uses spectrophotometry to determine the proportion of hemoglobin that is saturated with oxygen.

Near Infrared Spectroscopy (NIRS)

• NIRS is a tool to assess oxygenation and hemodynamics in various organs like muscle and brain.

Ultraviolet (UV)

• UV radiation is higher in frequency than visible light.
• UV ranges in wavelength from about 10 nm to approximately 400 nm.
• UV is present in sunlight.
• UV exposure can lead to vitamin D production in moderate amounts, but excessive exposure can cause tanning, sunburn, and skin cancer.
• UV radiation can cause cataracts in the eyes.
• UV is used medically to treat certain skin conditions, for example psoriasis, vitiligo, and skin tumors of cutaneous T-cell lymphoma.

Microwaves

• Microwaves are part of the EM spectrum between radio waves and infrared.
• Microwaves are used in communication (cell phones, computer networks, satellite TV).
• Microwaves are used in radar.
• Microwave thermotherapy is used in cancer treatment.

X-rays and Gamma Rays

• X-rays and gamma rays have very short wavelengths and high frequencies.
• X-rays and gamma rays are used to produce images of the body's internal structures.
• X-rays are used to create images of bone, lungs, and other organs of the body and gamma rays are used for nuclear medicine.
• In conventional X-ray imaging, film records the amount of radiation that passes through tissue based on the density of the tissue.
• Computed tomography (CT) allows for cross-sectional images of the body structures.

Radiotherapy

• X-rays and other radiation damage DNA in rapidly dividing cells, this is why radiation therapy can be useful for killing cancer cells.
• Linear accelerators generate x-rays that rotate around the body to target radiation at the tumour, while minimizing damage to surrounding healthy tissues.

Radio Waves

• Radio waves are the lowest frequency and longest wavelength EM waves in the spectrum.
• Radio waves are extensively used for communication
• Common applications of radio waves in medicine are MRI (diagnostic imaging), RF ablation, and localized dielectric heating (shortwave diathermy).