Course 111 - Diagnostic Imaging II - Study Guide

Speed of light

3×10⁸ m/s or 186,000 miles/s

Wavelength

Distance between two successive light waves

Frequency

How many waves pass a given point in one second

Amplitude

Height of wave

Absorption

Caused by impurities or loss

Specular Reflection

Angle of incidence is equal to angle or reflection

Diffuse Reflection

Angle of reflection is random

Scattering (Diffused)

Caused by impurities

Refraction

Bending of a wave when it enters a medium where its speed is different

Transmittance

Fraction of radiant energy that passes through a substance

LASER

Light Amplification by the Stimulated Emission of Radiation

L - Light

Type of electromagnetic radiation

Visible Light spectrum range

400 nm to 700 nm

Ocular Focus Region spectrum range

400 nm to 1,400 nm

Types of lights outside of visible spectrum

Infrared and ultraviolet

White Light

Contains all colors of the electromagnetic spectrum

A - Amplification

Taking small electronic signals and increasing it enough to have a useful output

SE

Stimulated Emission is a process that starts with spontaneous emission

Spontaneous Emission

Emission of light induced by an external energy source

Stimulated Emission

Emission of light after population inversion of the medium has been achieved by the spontaneously emitted photons

Spontaneous Emission process

electron in an excited state (higher energy level) naturally falls down to a lower energy level on its own, without any external influence. When it does this, it releases a photon (light).

Stimulated Emission process

electron in an excited state falls to a lower energy level because it is stimulated by an incoming photon (light)

Optical Resonator

A container that has an inner mirror-like finish to keep photons inside with Totally Reflective (TR) rear mirror and a Partially Reflective (PR) front mirror.

Population inversion

A state at which most of the atoms in the container have been stimulated

What is needed create laser light?

• Same wavelength

• Same energy source that excited them

• Same amplitude and wavelength

• In phase

Totally Reflective (TR) rear mirror

100% reflective

Partially Reflective (PR) front mirror

Typically 80-95% reflective

Radiation

Refers to all of the electromagnetic spectrum

Types of Surgical Laser Systems

• Gas

• Solid State

• Dye

• Diode

Devices used to deliver laser light

• Fiber optic cables

• Articulate arms

• Specialty glass components

CO₂ lasers

Referred as “Surgical laser” that achieves both cutting and hemostasis photothermally, operating at 10,600 nm infrared light CW

Argon lasers

• Blue-green light @ 488 nm and 514 nm

• Significant non-selective heating

Excimer laser

• disrupts the molecular bonds of surface tissue, causing ablation rather than burning or cutting

• Argon: Fluorine laser @ 192 nm

• Used in PRK and LASIK

YAG (Yttrium-aluminum-garnet)

Uses rare earth metals as lasing medium and operate in all types of modes

Nd:YAG lasers

• 1064 nm (sometimes 946 nm, 1120 nm, 1320 nm, & 1440 nm)

• Used for black tattoo ink and hair removal

KTP lasers

• Brilliant green light @ 532 nm

• CW to cut tissue

• Pulsed for vascular lesions

• Q-switched for red/orange tattoo removal

Er:YAG lasers

• 2940 nm

• Ablate tissue for cosmetic laser resurfacing

• Benefits include: short downtime, less invasive, & minimal thermal injury

• Also effective in tooth decay removal

Ho:YAG lasers

• 2070 nm

• Ablate bone and cartilage

  • Lithotripsy

  • ENT

  • Prostate

  • Orthopedics

Ruby lasers

• Red @ 694 nm

• Extensively used in tattoo and hair removal

Alexandrite lasers

• Chromium-doped solid-state laser

• Hair removal for light/olive colored skin

• Causes burns towards darker skin colored individuals

Pulsed Dye or Rhodamine Dye lasers

• Yellow @ 577-585 nm

• Peak absorption of hemoglobin in blood

• Causing unsightly purpura (black and blue marks)

Diode lasers

• "Injection Laser” or “Injection Laser Diode”

• Often used in dentistry

• 500-900 °C

Laser safety classifications

Levels 1, 2, 3, & 4

Class 2 lasers

• Limited to 1 mW

• Less than 250 ms of exposure is not hazardous

Class 3R lasers

• Limited to 5 mW in CW

• Momentary unintentional exposure is not considered hazardous

Class 3B lasers

• Can cause eye and tissue damage

• Equipped with a key switch and a safety interlock

Class 4 lasers

• Pulsed or CW

• reflected or diffused reflected beams are hazardous

• Greater than 0.5 W

Medical laser safety classification

Class 4 lasers

Nominal ocular hazard distance

Distance from source which intensity of energy per surface unit becomes lower than Maximum Permissible Exposure on cornea or skin

Nominal ocular hazard area

Depends on the area around the laser and refers to all space around the laser

Class 3B and 4 lasers have five main safety features:

• Key switch

• safety interlock dongle

• power indicator

• aperture shutter

• emission delay

Safe use regulations adopted by CDRH

• ANSI Z136.1 - American National Standards for the Safe Use of Lasers

• ANSI Z136.3 - American National Standards for the Safe Use of Lasers in Health Care

Cornea absorbs ___ and ___ waves which can cause severe pain, conjunctivitis and/or corneal damage

Far ultraviolet (180-315 nm), Far infrared (1,400-100,000 nm)

Safety glasses/goggles must have the correct…

Optical Density (OD) and wavelength

Biohazard for lasers

• Burns

• Fire/Explosion

• Electrical

• Chemical - dye lasers

• Laser plume

How to assure maximum flow rate of the smoke evacuator?

• Within 5 cm of the treatment site

• Change filters regularly

Adult imaging frequencies tend to be around…

2-3 MHz

Pediatric imaging frequencies tend to be around…

5-14 MHz

Frequencies above ___ are used for shallow to microscopic depth imaging

20 MHz

Period

Time to complete one cycle

Wavelength

Distance of complete one cycle

Speed

How fast sound waves move through the medium

What determines sound speed through a media:

• Material’s density

• Stiffness

Speed is inversely proportional to ___

Density

Average speed of sound in soft tissue

1,540 m/s

Amplitude

Maximum displacement of a particle or pressure wave

What determines amplitude?

How hard the electrical pulse strikes the ultrasound crystal

Power

Strength of the sound wave measured in Watts [ W ]

Intensity

Rate that energy travels through a medium [ W/cm² ]

Doppler Effect

Change in frequency of a wave in relation to an observer moving relative to the wave source. Moving closer to the sound source (transducer), the slightly higher frequency.

BART

Blue Away Red Towards

Blood flowing away from the transducer in Ultrasound is the color…

Red

Blood flowing towards the transducer in Ultrasound is the color…

Blue

Basic parts of ultrasound

• Transducer probe

• Pulse generator

• Computer

• Display

Transducer probe

In direct contact with the patient with two functions:

• Produce an ultrasound pulse

• Receive the returning echoes

Piezoelectric crystal

Active element of the transducer

Transducer also contains a backing block, which…

dampens the movement of the piezoelectric crystal

Pulse generator

Set and change the frequency and duration of the ultrasound pulses

Computer

Sends electrical current to the transducer probe to emit sound waves. Responsible for all calculations involved in processing data

A-mode (Amplitude)

Least often used where the display looks like an oscilloscope trace. Distance between the spikes represent the distance between the interface

B-mode (Brightness)

Most common where the echoes are represented as dots to form an image and the display would look like a two-dimensional monochrome picture

C-mode (A & B)

Determines depth of abnormality and scans in a spiral starting from the marked location

M-mode (Motion)

Rhythmically moving structures

Pulse-inversion mode

Makes gasses and other non-linear substances stand out

Harmonic mode

Provides better contrast resolution, reduced noise, improved lateral resolution, and reduced artifacts

Safety/hazards in ultrasound imaging

• Heat

• Produces cavitation

• Prudent use during pregnancy

Dynamic range

Max and min measurable light intensities

Photothermography

Formation of images using a combination of heat and light, either simultaneously or sequentially

Intensifying screen

Intensifies the effect of the X-ray photon by producing a larger number of light photons

Latent image

Invisible image produced on a photosensitive material by the exposure to light

Dry laser imagers operation

• Computer controls the position and intensity of laser beam as it scans in raster-fashion across the surface of the film

  • Optical modulator sits in the laser beam path and rapidly adjust the laser intensity as the beam scans the film

Dry laser imagers characteristics

• Installation and maintenance are simple, since water connections and drains are not necessary

• Sensitive to heat, should not be stored near or projected through a heat source

Wet laser imagers operation

First exposed to a laser beam and then processed using standard wet chemistry film methods

Wet laser imagers characteristics

Have higher installation and operating cost due to waste management and disposal.

Laser induced thermal operations

Creates a picture by detecting infrared radiation due to heat

Laser induced thermal characteristics

• Expensive and require strict environmental controls

• Film kept @ 60-100 K

• Often used in thermography (Veterinary medical testing used to provide a diagnosis)

Parts of a CR plate reader

• Plate

• Reader

• Workstation

Plate

A photostimulable phosphor plate that is stored inside a cassette

Reader

Reads the latent image on the PSP plate with a laser to form the digital image that is sent to the workstation

Workstation is also known as…

Acquisition station