Medical Physics Chapter 7: Light in Medicine

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Questions and Answers

What is the definition of light?

Electromagnetic radiation that only travels in a vacuum

Electromagnetic radiation with a constant speed

Electromagnetic radiation with an electric charge

Electromagnetic radiation within the visible portion of the electromagnetic spectrum (correct)

What happens when a light beam meets a new material at an angle other than perpendicular?

It speeds up to the speed of light in a vacuum

It reflects off the material

It passes through the material unchanged

It bends, or is refracted (correct)

What is the result of a light photon being absorbed by a single molecule?

It is reflected back to the source

It causes a chemical change in the molecule (correct)

It produces interference and diffraction

It produces heat and light

What are the three categories of light studied in medicine?

Visible, ultraviolet, and infrared Signup and view all the answers

What is the name of the ratio of the speed of light in a vacuum to its speed in a given material?

Index of refraction Signup and view all the answers

What is the behavior of light when it is absorbed by a single molecule?

It behaves both as a wave and as a particle Signup and view all the answers

What is the result of light being absorbed by a molecule in the retina?

The molecule triggers an electrical signal to the brain Signup and view all the answers

What is the general appearance of light energy when it is absorbed?

It appears as heat Signup and view all the answers

What is the purpose of phototherapy in treating newborn jaundice?

To lower bilirubin levels through photo-oxidation Signup and view all the answers

What is the advantage of using ultraviolet light with wavelengths below 290 nm?

It is germicidal and can sterilize medical instruments Signup and view all the answers

What is the beneficial effect of UV light from the sun?

It converts molecular products in the skin into vitamin D Signup and view all the answers

What is a blacklight also referred to as?

Wood's lamp or ultraviolet light Signup and view all the answers

What is the definition of a premature infant?

A baby born before 37 completed weeks of gestation Signup and view all the answers

What is the application of lR light in medicine?

To weld a detached retina Signup and view all the answers

What is fluorescence?

The emission of lower-energy light photons Signup and view all the answers

What is the purpose of transillumination?

To detect hydrocephalus Signup and view all the answers

What is the application of fluorescence in medicine?

To detect porphyria Signup and view all the answers

What is the effect of ultraviolet photons compared to visible photons?

They have higher energies Signup and view all the answers

What is specular reflection?

Reflection of light from smooth surfaces Signup and view all the answers

What is used to treat jaundice in premature infants?

Phototherapy Signup and view all the answers

What is the unit of measurement for wavelengths of light?

Nanometers Signup and view all the answers

What is the wavelength range of visible light?

400-700 nm Signup and view all the answers

What is the wavelength range of ultraviolet light?

100-400 nm Signup and view all the answers

What is diffuse reflection?

Reflection of light from rough surfaces Signup and view all the answers

What is the primary purpose of a Wood's lamp in dermatology?

To diagnose skin conditions using ultraviolet light Signup and view all the answers

What is the wavelength of ultraviolet light used in a Wood's lamp?

365 nanometers Signup and view all the answers

What is the name of the type of IR photography that uses wavelengths of 700 to 900 nm to show patterns of veins just below the skin?

Reflective IR photography Signup and view all the answers

What is the primary cause of skin cancer in humans?

Ultraviolet light from the sun Signup and view all the answers

What is the name of the optical filter glass invented by Robert Williams Wood in 1903?

Wood's glass Signup and view all the answers

What is the term for a type of IR photography that uses the long IR heat waves emitted by the body to give an indication of the body temperature?

Thermograph Signup and view all the answers

What is the characteristic of a laser that makes it a unique light source?

Monochromatic light Signup and view all the answers

What is the abbreviation of the term that describes the process of light emission in a laser?

LASER Signup and view all the answers

Who proposed the basic theory for lasers?

Albert Einstein Signup and view all the answers

What is the result of concentrating laser energy in a small area?

The power density becomes very large Signup and view all the answers

Why is a specific laser wavelength used in medicine?

Because it is easily absorbed by tissue Signup and view all the answers

What is the primary use of lasers in ophthalmology?

Photocoagulation of the retina Signup and view all the answers

What type of imaging is being researched using lasers?

Three-dimensional imaging Signup and view all the answers

What is the unit of measurement for the energy of a typical laser pulse?

Millijoules Signup and view all the answers

What is the duration of a typical laser pulse used in medicine?

Less than a microsecond Signup and view all the answers

What is the potential use of lasers in cancer treatment?

To cure certain types of cancer Signup and view all the answers

Study Notes

Light in Medicine

Light is a form of electromagnetic radiation within the visible portion of the electromagnetic spectrum.
It has no electric charge and travels at the speed of light.

Properties of Light

The speed of light changes when it passes from one material to another, and this ratio is called the index of refraction.
Light behaves as both a wave and a particle, producing interference and diffraction, and can be absorbed by a single molecule.
When light is absorbed, its energy generally appears as heat, which is used in medicine to heat tissues.
When a photon is absorbed, a lower energy light photon is emitted, known as fluorescence, which is used in medicine for detection and diagnostic purposes.

Measurement of Light and its Units

The three categories of light (UV, visible, and IR) are defined in terms of their wavelengths, which are measured in nanometers (1 nm = 10-9 m).
Ultraviolet light has wavelengths from about 100 to 400 nm, visible light from about 400 to 700 nm, and infrared light from about 700 to over 104 nm.

Applications of Visible Light in Medicine

Visible light is used in phototherapy to treat jaundice in newborns, by lowering bilirubin levels in the blood through photo-oxidation.
Transillumination is used to detect hydrocephalus, pneumothorax, and other conditions in infants.

Applications of Ultraviolet and Infrared Light in Medicine

Ultraviolet light is used to sterilize medical instruments and to produce vitamin D in the skin.
Ultraviolet light is used in dermatology to diagnose skin conditions, and a Wood's lamp is used to emit UV-A light to diagnose skin conditions.
Infrared light is used in thermography to measure body temperature and in reflective IR photography to show patterns of veins just below the skin.

Hazards of Light

Ultraviolet light from the sun can cause sunburn and skin cancer, and the wavelengths that produce sunburn are around 300 nm.
Prolonged exposure to UV light can cause skin cancer, especially in people who have been exposed to the sun a great deal.

Laser in Medicine

A laser is a unique light source that emits a narrow beam of monochromatic and coherent light.
Laser is used in medicine to deliver energy to tissue, and the laser wavelength used should be strongly absorbed by tissue.
Lasers are used in ophthalmology for photocoagulation of the retina, and are also being used in medical research for special three-dimensional imaging called holography.

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Description

This quiz covers the basics of light and its properties, measurement units, and applications in medicine, including visible, ultraviolet, and infrared light, as well as laser technology.