Part II Flashcards
Function of the distance to the UTZ machine
Penetration into the deeper tissues [longer it takes, deeper]
Depth
Volume of returning echo/intensity
The louder the return echo, the brighter [quiter, darker]
Brightness
-provide energy to crystal
-known as the pulses
-function: control the rate of pulses emitted by the transducer or PRF & provides voltage
Transmitter
-produces and detects UTZ
-where piezoelectric effect occurs
Transducer
-range of frequency produced by a given transducer
-if broad - improve CR
-if narrow - speckle
Bandwidth
-“pressure electricity”
Piezoelectric
Explain PIEZOELECTRIC EFFECT
Electricity is applied to piezoelectric material → vibrates (expands & contracts) to produce mechanical sound or pressure waves → reflected waves (echoes) go back to transducer, thus converting mechanical back to electrical
Parts of a transducer
Physical housing
Electrica connections
Piezoelectric Elements
Backing Material
Acoustic Lens
Matching Layers
Structural support of the transducer that serves as the electrical and acoustic insulator
Physical Housing
Placed in front & back of crystal
Thin film of Ag and Au
Electrical Connections
-discovered by Jacques an Pierre (1820)
-mechanical force will induce some material to be electrically polarized
Piezoelectric Element
Piezoelectric element can be destroyed by exceeding beyond the [..]
Curie Temperature
Act as an electrode for non conducting piezoelectric element
Thin silver on sides
Reason for mechanical vibration: [..]
Crystal change in shape/produce sound waves
Piezoelectric Element
Natural: [..]
Man-made: [..]
- Quartz - first material used,
- Tourmaline - black mineral/prism crystals in granites and rocks
- Rochelle Salt/ Potassium Sodium Tartrate Tetrahydrate
- PZT- Lead Zirconate Titanate (also used in ceramic capacitors)
- Barium Titanate -piezoelectric material for microphones and transducer
- Lead Metaniobate - ceramics
-used to clean transducer because alcohol disrupts transducer
Ethyleneoxide
-reduce vibrating
-broadens the bandwidth and shorten the pulses
-improves axial resolution
Backing Material
Composition of backing material
Tungsten/ rubber in epoxy resin
Importance of backing material
- Eliminate back face vibration
- Control vibrations in front face
-located in front of transducer
-reduce the beam width of the transducer
-improv lateral resolution
Acoustic Lens
Materials of acoustic lens
Aluminum, Perspex, polystyrene
-interface between transducer and the tissue
-minimize acoustic impedance differences between the transducer
Matching Layer
-used between matching layer and patient’s skin to eliminate air pockets that could attenuate and reflect the UTZ beam
-hypoallergenic
Acoustic Coupling Gel
Types of transducer
Linear Array (Sequential)
Phased Array
Curvilinear Array
-produces beam by firing a subset of the total no of transducer elements as a group
-individual beams interact to produce collimated array
-f = 4 MHz
Linear Array (Sequential)
Linear Array example part of interests
Breast, thyroid, MSK, Obstetrics, Vessels
-produces a beam from all of the transducer elements fired with fractional time delays in order to steer and focus the beam
-f = 2-7.5 MHz
Phased Array
-diverge and allow wider field of view
-produce diverging images that originate in a curved arc
-f = 3.5 MHz
Curvilinear Array
Curvilinear Array example part of interests
-abdominal and obstetrical scanning
-deep lying structures
[utz beam properties]
-adjacent to transducer
-near field of UTZ beam
-used for UTZ imaging
Fresnel Zone
[utz beam properties]
-far field
-UTZ imaging does not extend to this area
Fraunhofer Zone
-region over which the beam id focused
Focal Zone
Distance from transducer toward focal zone
Focal length
-converging beam profile
-adjacent to the transducer face
-equal to focal distance
-at the end, region for best lateral resolution
Near Field
-diverging beam profile
-Fraunhofer Zone
-UTZ intensity decrease with distance
Far Field
Crystal relationship with near and far field
CRYSTAL NEAR FIELD FAR FIELD
NARROW decrease Increase
WIDE increase decrease
Frequency relationship with near and far field
FREQUENCY NEAR FIELD FAR FIELD
INCREASE long less
DECREASE short more
Types of Resolution
Spatial Resolution
Axial/Longitudinal
Lateral/Azimuthal
Elevation Resolution
Contrast Resolution
Temporal Resolution
Ability to differentiate two closely situated objects lying along axis of beam
Spatial Resolution
Ability to separate two objects along axis of beam
Axial/Longitudinal Resolution
-resolution in the plane perpendicular to the beam and transducer
-determined by slice thickness
-transducer directly related to elevation
Elevation/Azimuth Resolution
Ability of imaging system to differentiate between body tissues and display them as different shades of gray
Contrast Resolution
Display events that occur at different times as separated images
-frame rate
Temporal Resolution
Detects and amplifies voltage signals from the transducer
Receiver
-ability to compensate for attenuation of the transmitted beam as the sound wave travels through tissues in the body
-signals compensate for differences in echo strength
Time Gain Compensation (TGC)
-adapts the dynamic range of backscattered signal intensity (returning echoes/to correspond to the dynamic range of the display
Compression and Remapping of Data
Ratio of the highest to lowest amplitude
Dynamic range
Display UTZ signals depends on the different operational modes
CRT, LCD, LED
Image Display
Operational Modes
- A- Mode
- B- Mode
- Real-time
- M-mode
-Displays depth on the horizontal axis and echo intensity (pulse amplitude) on the vertical axis
-Displayed in CRT
-Echo, peaks and distance between various structures is measured
-Reliable in Axial Resolution
Static Imaging
A-mode (Amplitude)
-shows all the tissue travelled of the beam of UTZ scan
-2D
-appear as black and white images
-shown as series of dots in CRT
Static Imaging
B-Mode (Brightness)
-display changes in echo amplitude and position with time
-eval of rapidly moving structures (cardiac valves, chamber walls) -ultrasonic cardiography
-another way of displacing motion
-time on the horizontal axis and depth on the vertical axis
Real Time Imaging/Time Mode TM/ M-Mode (Motion)/ Position Mode PM)
-2D, real time, gray scale
-image is built by TZ pulses sent down a series of successive line scans
-entire image is created 15-60 times per sec
Real Time Imaging
B-Mode
He described Doppler Effect
Christian Johann Doppler
-based on Doppler effect
-“UTS Stethoscope”
Doppler Mode
-change in a frequency resulting from moving sound source
Doppler Effect
Identification of blood flow vessels
Doppler Ultasound
Explain STATIONARY TARGET (Doppler Effect)
-If reflecting interface is stationary, the backscattered UTS has the same frequency or wavelength as transmitted sound
-reflected and transmitted energy as equal
Explain TARGET MOTION towards transducer
-difference in reflected and transmitted frequencies in greater than zero
-use color map to display information based on the detection of frequent shifts from moving targets
-determine vessel if artery of vein
-shows arterial or venous supply of organ
-full of noise, limited sensitivity
Color Flow Doppler Imaging (CD)
BART
Blue away, Red towards
-uses color map to show distribution of the power/amplitude of the Doppler signal
-flow direction and velocity info are not provided
-noise is reduced with improved sensitivity for flow detection
Power Mode Doppler
-reduces noice and scatter of image
-improves spatial resolution
Tissue Harmonic Imaging
-combines images contained by isonating the target from multiple angles
-improves contrast
-speckle
Spatial Compunding
