physics.txt

comprises a single slap of PZT cut into a collection of separate pices called elements. Each active element is connected by a wire to its own electronic circuitry

• single,circular: disc shaped
• fan or sector-shape
• fixed or mechanical focusing
• damage - entire image lost

• Linear
• annular
• convex

• small footprint
• 100-300 elements, side by side, rectangular and narrow
• electronic steering (phasing)
• electronic beam focus
• damage - inconsistent focusing

always means adjustable or multi-focus

the electonics within the ultrasound system that create a pattern

• disc shaped element
• mechanical steering
• multiple focal zones (not adjustable)
• inner circle - shollow scan
• sector shape image
• damage - horizontal or side to side band

• large footprint
• 120 - 250 piezoelectric elements:
• some bur not all crystals are fired simultaneously
• transmit and receive focusing (electronic)
• rectangular image
• damage - vertical line

• 120-250 rectangular elements
• some but not all crystals are fired simultaneously
• electronic beam focus
• blunt sector shape
• damage - vertical line
• dynamic receiving focus

• 120-250 rectangular elements
• small footprint
• electronic beam steering
• electronic focusing
• trapezoidal image

accuracy in imaging

elevational resolution

• three dimensional space:
• side to side
• shallow to deep
• above and below

off axis sound beams from a single element transducer

off axis sound beams created by array transducers

stronger electrical signals are used to excite the innner crystals, annd progressiely weaker electrical spikes excite the outer crystals. this diminishes side lobes

changing the number of crystals along the face of the probe used to transmit pulses and receive reflctions

(number of elements used to receive reflected echoes.

• accuracy in time
• the ability to precisely position moving structures from instant to instant

determined by frame rate

higher frame rate improves temporal resolution

the ability of the system to create numerous frames each second

measured in Hz

determined by speed of sound and imaging depth

the time it takes to make a single image

inversely related to frame rate

imaging depth

number of pulses in each picture

shallow imaging increases frame rate and improves temporal resolution

pulses per frame and frame rate are inversely related

• multi vs. single focus
• sector size
• lines per angle of sector

negative effect on temporal resolution

improves accuracy of the individual image

superior lateral resolution

increase in sector size decreases temporal resolution

space between sound beams

high line density decreases temporal resolution

improved spatial resolution

a method of reporting the extent to which a signal can vary and still be accurately measured

measured in dB

relative measurement or ratio

• transducer 120
• receiver 100 - 120
• scan converter 40 - 50
• display 20 - 30
• archive 10 - 30

the creation of an image from sound reflctions at twice the frequency of the transmitted sound

arise from no -linear behavior

sound created by the transducer and transmitted into the body

the image created by rocessing reflections that have the same frequency as the transmitted sound

image created by processing reflections that are twice the fundamental frequency

proportional or symmetrical

systems respond in an even manner

irregular or disproportionate

system behaves unevenly

microbubbles that are entrapped in a shell that are ingested or injected into the circulation

have a different acoustic fingerprint than blood or tissue and therefore create strong reflections that actually "light up" blood chambers and vessels

• 1. safe
• 2. metabolically inert
• 3. long lasting
• 4. strong reflector of ultrasound
• 5. small enough to pass through capillaries

when an ultrasound pulse interacts with microbubbles, a small amount of energy in converted from the fundamental frequency to the harmonic frequency

contrast harmonics are created during reflection

uneven behavior caused when the microbubble within the sound beam grows or shrinks in relation to the pressure

the amount of contrast harmonics produced is estimated by MI

MI=peak negative pressure/sqaure roote of frequency

high frequency -less pressure- lower MI

high mechanical index - bubbles expand and break apart

nature of the outer shell

gas that fills the microbubbles

as a sound wave travels in the body, a miniscule amount of energy is converted from the fundamental frequency to the harmonic frequency

faster through compressions - slower through rarefactions