Foundations Exam 2

mechanical energy traveling in longitudinal waves

• It travels faster in solid mediums
• slower in air

ultrasound transducers convert ultrasound energy into electrical energy and v.v.

piezoelectric elements (crystals), the transducer create the US beam and recieve the echos to produce the image

• mechanical
• medium has dramatic effect on waves
• measured in hertz
• higher frequency has better resolution and less penetration

• >20,000
• (higher frequency has better resolution and less penetration)

• transfer speed of sound through a medium
• stiffer the medium, higher (faster) propagation speed

• air
• water
• soft tissue
• bone

• provides depth information
• increasing PRF eliminates aliasing
• CW doesn't ailase but compromise for unknown depth

• pulsed doppler may have aliasing (increase PRF to get rid of)
• CW doesn't ailase but no depth known

• a primary beam will exit transducer
• beam will be moved thru body to produce image
• multiple images will produce a real-time exam

US outside the primary beam and may produce  (has to do with beam formation)

• US reflected when there is a change in tissue impedance
• greater the change=more relfection

• term that describes the medium characteristics
• an acoustic property of a medium that is related to its density and propagation speed

• Tissue interfaces can be specular or non-specular
• Specular should be imaged perpendicular (if imaged obliquely artifacts can occur)
• Non-specular can be imaged an any angle

• create most artifacts
• image at 90* (allows reflection to return to transducer and produce image)

• higher frequencies provide better axial and lateral resolution
• they attenuate at at higher rate
• ALWAYS use the highest frequency that provdes adequate penetration

lateral resolution is pimproved in the focal zone and by using multiple/wide focal zones

• where the beam is narrowest (aka focused) = best lateral resolution
• higher frequencies = narrower beam= better lat resolution

• cavitation
• thermal effects
• use lowest power for OB and limit spectral doppler on OB

• decreases in intensity as sound travels through medium
• diverges
• absportion
• relfections (creates image)

posterior enhancement due to low attenujation

shadows (aka bone)

• attenuation artifacts
• US beam makes the path more than once
• extra echoes go into image that don't represent true anatomy

• info on depth (aka time)
• horizontal beam location (beam direction)
• reflector amplitude (brightness) *represents anatomy*

• pulse determines power
• determined by the "pulser"
• rate at which sound is pulsed *rythm*
•  -limited by depth of imaging

lower PRF "power"

• processes electrical signals from transducer that represent reflections
• OPERATOR controls- amplificiation (gain & TCG), dynamic range, and harmonics

• increases intensity of reflections returning from deeper structures more than superficial structures
• used to compensate for attenuation

• time it took for relfections to come back
• controlled according to DEPTH

• increases intensity of all reflections on the image
• does NOT affect penetration

• number of grays available for display
• LARGER the number = more shades of gray = looow contrast
• PREPROCESSING fucntion

• preset for exams
• Vascular- lower DR, black and white
• Abdomen- medium DR, moderate # of grays
• Small parts- higher DR, lots of grays

• new frequency produced from initial sound wave
• will be a multiple of initial (fundamental) frequency

• receiving and processing only the harmonic signal
• reduces artifacts
• slightly poorer spatial resolution

• amplitude mode
• x & y axis based
• still used in opthamology

• brightness mode
• reflector brightness representative of reflector intensity

• motion mode
• show motion of structures on single frame
• AKA fetal hearbeat
• brightness reflections corresponds with intensity

• realtime imaging is created by moving the beam through the patient
• creates many scan lines per image and many images per second

• linear- rectangular FOV (best resolution b/c parallel scan lines)
• sector- wedge shaped FOV (poorest resolution) aka- pahsed array/ curvilinear transducers)

• deep as needed for area of interest
• no deeper

• start with gain in middle for each exam
• will not "reset" every exam
• different numbers on each machine

• makes image uniform
• vary b/w pts and exams
• will not "reset"

• automatic control that adjusts gain
• can be problematic and jsut needs to be OFF

• freq- highest possible that allows for penetration, adjust required for exam
• harm- help on "technically difficult exams", reduces artifacts

• place at area of interest
• if entire image important, put it at BOTTOM
• makes a biiig difference in image quality
• focal zones will imporve image but decrease frame rate

• to stop real time image
• will NOT save at this time

• saves current image onto machine hard drive
• at some point images will go to PACS

• rectangular
• groups of crystals
• parallel scan lines
• best resolution
• large footprint
• "linear"

• blunted sector
• groups of crystals
• scan line seperation-->downfall
• better than sector
• large footprint BUT better than linear
• "Curved"

• sector
• trapezoidal vector
• Individual crystals
• scan line seperation -->downfall
• small foot print
• "sector"

• sector or linear (usually sector)
• poor doppler b/c sloow

• time delays
• operator dependent

• HIGH frame rate = adv. w/ mocing structures = less scan lines= poorer resolution
• Lower fram rate = adv. w/ non moving structures = more scan lines= better resolution

increased depth= lower PRF = lower frame rate

• narrow FOV with zoom or sector size
• frame rate control

• controls preprocessing
• dynamic range control

• preprocessing
• improves resolution
• (use entire matrix less anatomy)

• manipulation of image (gray/B-color)
• cine-loop
• more bits/pix allows for more shades of gray

• post processing
• no improvement to image resolution
• displays pixels larger

number of frames per second displayed on the monitor