Shared Flashcard Set

Details

SPI Examination Review
Sonographic Priniciples and Instrumentation
68
Health Care
Professional
01/28/2010

Additional Health Care Flashcards

 


 

Cards

Term
piezoelectric effect
Definition
property of certain crystals to emit energy by expanding and contracting when pressure from a returning sound beam is applied
Term
reverse piezoelectric effect
Definition
property of certain crystals to expand and contract when an electrical current is applied, creating a mechanical sound wave
Term
PZT
Definition
lead zirconate titanate
Term
Curie point
Definition
temperature at which piezoelectric crystals lose magnetic properties (300-400 degrees Celsius)
Term
What happens to a crystal if heated above Curie point?
Definition
loses piezoelectric properties
Term
autoclave
Definition
heat sterilization
Term
How to calculate transducer frequency (MHz)
Definition
crystal propagation speed (mm/us) / 2x crystal thickness (mm)
Term
thickness of typical pulsed elements
Definition
.2 - 1 mm
Term
propagation speeds of typical pulsed elements
Definition
4-8 mm/us
Term
How is frequency determined in PW US?
Definition
by crystal
Term
How is frequency determined in CW US?
Definition
by electrical voltage applied to the element
Term
What does damping material do?
Definition
reduces # cycles in pulse, pulse duration, SPL and improves axial resolution
Term
dynamic damping
Definition
electronic suppressing of ringing by applying a voltage of opposite polarity to the crystal after the pulse
Term
bandwidth
Definition
difference between highest & lowest frequency found in a pulse; measured in MHz
Term
How to increase bandwidth
Definition
limit amount of ringing in the crystal (damping material)
Term
Q Factor
Definition
describes homogeneity of beam frequency
Term
How is Q-Factor related to bandwidth and axial resolution?
Definition
inversely
Term
How q-factor is related to frequency
Definition
directly
Term
How to calculate q-factor
Definition
operating frequency / bandwidth
Term
matching layer
Definition
decreases the impedance difference between the crystal and the skin
Term
matching layer thickness
Definition
1/4 wavelength
Term
Huygen’s Principle
Definition
all points on a wave are a source for the production of spherical secondary wavelets (determines direction of the sound beam)
Term
constructive interference
Definition
Wave amplitudes reinforce each other, building a wave of even greater amplitude
Term
destructive interference
Definition
Waves intersect “out-of-phase.” The peak of one wave lines up with the trough of the other
Results in a decreased amplitude or a canceling out of the wave altogether
Term
focal width
Definition
1/2 beam diameter
Term
How is focal length related to frequency and crystal diameter?
Definition
directly
Term
How is the amount of widening in the far zone related to frequency and crystal diameter?
Definition
inversely
Term
resolution
Definition
ability to distinguish close objects
Term
types of resolution
Definition
temporal, contrast, detail
Term
temporal resolution
Definition
ability to distinguish closely spaced events in time
Term
contrast resolution
Definition
ability of the equipment’s gray scale display to distinguish between echoes of slightly different intensities
Term
detail resolution
Definition
ability to distinguish 2 adjacent objects as 2 distinct objects
Term
3 types of detail resolution
Definition
axial, lateral, elevational
Term
other names for axial resolution
Definition
LARD - longitudinal, axial, range, depth
Term
other names for lateral resolution
Definition
LATA - lateral, angular, transverse, azimuthal
Term
longitudinal resolution
Definition
ability to distinguish 2 structures laying one on top of the other, parallel to the path of sound travel
Term
How to calculate axial resolution
Definition
1/2 SPL (mm)
Term
How to improve axial resolution
Definition
higher frequency and less ringing (damping)
Term
lateral resolution
Definition
resolution perpendicular to the beam path; minimum distance of 2 structures lying next to each producing 2 echoes
Term
What determines lateral resolution?
Definition
beam diameter
Term
How to improve lateral resolution
Definition
focusing and higher frequency
Term
elevational resolution
Definition
thickness of the tissue perpendicular to the scan plane
Term
Other names for elevational resolution
Definition
section thickness, Z-axis, elevational axis, or out-of-plane focusing
Term
Increased slice thickness:
Definition
Decreases spatial resolution (ability to detect & display adjacent entities)
Causes slice thickness artifacts
Reduces ability to detect small low-contrast lesions
Term
2 types of electronic focusing
Definition
transmit and receive
Term
transmit focusing
Definition
uses interference phenomena by delaying (phasing) the electrical pulses to each crystal to cause the wavefronts to converge at variable focal points
Term
receive focusing
Definition
crystal elements are timed to be sensitive to listening at a particular depth (using the range equation)
Term
dynamic focusing
Definition
time delays at reception to process returning echoes and optimize image quality
Term
sequential electronic beam focusing
Definition
applied to individual beams to improve lateral & slice thickness resolution
Term
phasing electronic transmission focusing
Definition
Delays the pulse to the crystals so they are pulsed in an outer to inner method
Term
beam steering
Definition
Delaying the electronic pulse to each crystal causes the wave fronts to be steered at various angles by the wave interference phenomenon
Term
apodization
Definition
Transmit/receive technique using different pulses across aperture of linear array to reduce the intensity of grating/side lobes
Maximum voltages are at the center & lower voltages toward boundary
Term
subdicing
Definition
Crystal element divided into many smaller sub-elements wired together to form original size element - reduces grating lobes
Term
dynamic aperture
Definition
aperture increases to maintain a constant focal width during echo reception
Term
aperture
Definition
Transducer surface size producing beam
Term
mechanical steering
Definition
fixed focus crystal mechanically steered to produce a sector image; crystal is physically rocked or rotated through an arc sweeping the beam back & forth over the region being scanned
Term
side lobes
Definition
weaker beams of sound traveling out from a single element in directions different than that the main beam
Term
annular array
Definition
Concentric rings of crystals on a motor assembly that rotated back & forth that created a curved top/blunted sector image
Term
Transducer that provides the thinnest beam of all probes
Definition
annular array
Term
advantages of annular array
Definition
superior image quality
small footprint (tight windows)
narrowest beam thickness
Term
disadvantages of annular array
Definition
mechanical parts wear out
mechanical system provide limited Doppler capability
vibrations from probe can be annoying to the user & the patient
Term
linear array advantages
Definition
no moving parts to wear out
better lateral resolution
faster frame rates
Term
disadvantages to linear array
Definition
larger footprint creates loss of body contact & cannot be used in small windows
Term
advantages to curved linear array
Definition
no moving parts to wear out
better lateral resolution
faster frame rates
larger field of view
Term
disadvantages to curved linear array
Definition
hard to use in small windows due to larger footprint
Term
advantaged to phased arrays
Definition
no moving parts to wear out
better lateral resolution
faster frame rates
larger field of view
small footprint
Term
disadvantages to phased linear arrays
Definition
expensive
limited near field of view
grating lobe artifacts
Term
vector array
Definition
Combine linear & phased technologies to produce a trapezoidal-shaped image
Supporting users have an ad free experience!