Course 111 - Diagnostic Imaging II - 2.1-4.1 - Ultrasounds, Laser Imaging, CR Plate Reader

Sound

Mechanical waveform energy that can travel through any medium

Sound waves

Created by vibrations, consisting of areas of compression and raraefactions

Echo

Sound waves that returned from the boundary of a medium or interface between two different tissue masses

Propagation

Oscillation (vibration) of molecules that result from a sound wave hitting a medium

What creates poor images using ultrasound applications

• Gaseous zones such as lungs and intestines

• Dense zones such as bone or metal impants

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

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 ]

Three interactions when ultrasound pulses passes through matter

• Absorption

• Reflection

• Refraction

Pulse duration

Length of time from the beginning to the end of the actual sound burst

Pulse Repetition Period (PRP)

Time from the start of one pulse to the start of another pulse

Pulse Repetition Frequency (PRF)

Number of pulses that occur per second

Duty factor

Percentage of the fraction of time that the ultrasound is sending out sound

Spatial Pulse Length (SPL)

Length of a single burst of sound in distance

Piezoelectric

Pressure electric

Focused transducer

Mechanically focused

Annular transducer

Transducer has crystals arranged in concentric rings with each producing different frequencies of sound

Phased transducer

Electronically focused

Lateral resolution

Ability to resolve objects side to side. Higher the frequency the greater the lateral resolution.

Axial resolution

Ability to resolve objects that lie above/below another. Higher the frequency, the lower the axial resolution is in larger patients

Depth of penetration

Higher frequencies are attenuated by tissue more than lower frequencies

Spatial resolution

Ability to distinguish two separate objects that are close together

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 transducer = blue

Blood flowing towards transducer = red

Ultrasound

Medical imaging technique that uses high frequency sound waves and their echoes

Piezoelectric Effect

Electric current that creates pressure forces

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 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 artifactsT

Types of ultrasound machines

• 2D

• 3D

• Doppler (CW or Pulsed)

• Duplex

• Triplex

Acoustic Shadowing (Artifact)

loss of information below an object because the greater portion of the sound energy was absorbed or reflected by the object

Enhancement (Artifact)

Increase in reflection from objects that lie behind a weakly attenuating structure

Reverberation (Artifact)

Unsuitable reflections generated when the sound wave strikes a highly reflective object creating artifacts that degrade the image, like ribs or strong muscles of the diaphragm

Side-lobe (Artifact)

Unwanted or unintended echoes that are received by the ultrasound probe from directions outside the intended area of focus.

“Mirroring” where sound energy is reflected off dense structures and displayed on screen as a double image

Common uses for ultrasound

• Obstetrics and gynecology

• Cardiology

• Urology

• Digestive system

• Endocrine system

• Lymphatic system

Safety/hazards in ultrasound imaging

• Heat

• Produces cavitation

• Prudent use during pregnancy

Limits in ultrasound imaging

• Trouble penetrating bone

• Poor perform with gas present

• Physique of patient

• Skills/experience of technician

Main types of laser-based printers

• Wet

• Dry

• Laser induced thermal

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

Laser images have undergone continuous improvements to offer…

better resolutions, stability, and processing speed

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)

Environment of use for laser imagers

• OB/GYN clinics

• Most radiology departments

Safety for laser imagers

• Draws large amounts of current, increased risk of electric shock

• Wet laser printers require PPE due to chemicals

• Needs to be located in well-ventilated room where the air supply complete changes once an hour

• Noisy, 45-55 dB on average with a high of 65 dB

Computed Radiography (CR) plate readers

• Opportunity to digitize most any traditional radiographic equipment image

• Efficient way to convert to digital

• Requires more ionizing radiation

Photostimulable Phosphor (PSP) plate

X-ray detector that uses electromagnetic waves to capture an image

Cassette

Housing that holds the PSP plate

Bucky

Tray in a table or wall stand of an X-ray system that holds a film, CR or digital cassette and a grid to minimize scatter radiation

Parts of a CR plate reader

• Plate

• Reader

• Workstation

PSP plate is typically ___ to ___ in depth

0.1 mm, 0.3 mm

How are electrons released in the PSP plate?

Electrons stored in the Fluoro compound (Storage phosphor) of the plate are stimulated of the laser that scans the plate inside the reader

Photomultiplier tube

Light (analog) is converted into an electronic signal (digital) and significantly amplified

Why the life of a PSP plate might be shortened?

• Scratches and abrasions

• Radiation fatigue or imprinting

• Dropped

The PSP plate is “erased” by exposing it to certain ___ or __ LED light waves so that it can be used again.

White, red

Advantages of CR plate reader systems

• Used anywhere X-ray film is used

• Save money

• Image manipulation after exposure

• Supports multiple X-ray rooms

Disadvantages of CR plate reader systems

• Delay between exposure and readout

• Labor intensive

• Detector is always on, prone to exposure

Main safety concerns for CR plate reader

• Care while handling lasers, needs glasses

• High voltage/current to power lasers

Using ultrasound, the monitor displays the ___ and ___ of the echoes, forming a two/three dimensional image

Distance, Intensities