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73 Cards in this Set
- Front
- Back
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Transducers convert one form of _____ into ______.
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Transducers convert one form of ENERGY into ANOTHER.
(sound into electricity and vice versa) |
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Piezoelectric effect
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Converting sound into electricity (the reflection/echo)
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Reverse piezoelectric effect
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Converting electricity into sound (the pulse/transmission)
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Three naturally occuring crystals...
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Quartz
Rochelle Salt Tourmaline |
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List man-made crystals ...
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Barium Titanate
Lead Metaniobate Lead Zirconate Titanate (PZT) (anything ending in -ate) |
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What is the most common crystal used in ultrasound transducer elements?
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PZY - lead zirconate titanate
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What is a curie point?
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360 degrees C
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What happens to the ceramic material of the crystal when it is heated about the Curie point?
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Above the Curie point the crystal loses its piezoelectric properties/becomes depolarized
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PZT crystals have ________ more propagation speed than the propagation speed of skin
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PZT crystals have 5-10 times more prop speed than skin
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Multiple layers of matching layers ________ sound _________.
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Multiple layers of matching layers IMPROVE sound TRANSMISSION.
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Why do we use gel or coupling agent before scanning?
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Gel eliminates the air layer & facilitates sound passage by matching impedences.
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List the effects of damping material.
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- Improves picture quality and Axial resolution
- Increases bandwidth (creates higher frequency) - Decreases sensitivity - Decreases Q factor - Reduces PD & SPL |
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Do CW transducers have backing material?
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No. They have NO image, NO PRF and NO aliasing
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Define bandwidth.
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Bandwidth is the range of frequencines contained in a pulse ultrasound, below and above the fundamental frequency.
Higher frequency = wider bandwidth Lower frequency = narrow bandwidth |
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In order to be useful, bandwidth must have at least _____% of the main intensity in the pulse.
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In order to be useful, bandwidth must have at least 50% of the main intensity in the pulse.
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List the features of low Q factor.
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Low Q factor results in:
-High damping -PD & SPL are shorter -Bandwidth is wider - Resolution is good so image is better |
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List the parts of a transducer.
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Parts of a transducer...
Cable, housing, damping material, PZT crystals, matching layers and the aperature or head of the Tx. |
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Matching layer helps to reduce ______ as the beam strikes the skin. Reflection occurs as a result of an impedance ____________.
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Matching layer reduces REFLECTION caused by impedance DIFFERENCES OR MIS-MATCH
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Low Q factor is good for image or high Q factor?
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Low Q factor have better image resolution. Specifically Axial resolution.
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What determines the length of the focal zone?
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The NZL is determined by the width of the beam and frequency of the Tx
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High frequency = _____ NZL
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High frequency Tx = longer NZL
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Increased width of TX = ______ NZL
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Increased width of Tx = Increased NZL
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Smaller diameter Tx = ________ divergence
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Smaller diameter Tx = Sudden divergence
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Wider diameter Tx - _________ divergence
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Wider diameter Tx = Less divergence. Near zone and far zones act similarly
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Which Tx will have least divergence?
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A wider diameter and higher frequency TX will have a longer NZL and the least divergence
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Which Tx will have the most divergence?
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A smaller aperature and lower frequency Tx will have a smaller NZL and more divergence
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A Tx with a 10mm aperature will display what width of the sound beam near NZL1, NZL2 and NZL3?
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A 10mm Tx will have a
NZL1 of 5 mm NZL2 of 10 mm NZL3 of 15 mm |
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At _____ the beam diameter equals the beam width,
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At NZL2 the beam diameter equals the beam width
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_______ and ______ determine the length of the focal zone.
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FREQUENCY and DIAMETER determine the length of the focal zone.
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Higher frequency TX = ____ NZL ____ focal zone and ____ divergence
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Higher frequency Tx has ...
longer NZL longer focal zone and less divergence |
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Wider diameter Tx = _____ NZL, _____ focal zone and _____ divergence
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Wider diameter TX has...
longer NZL longer focal zone and less divergence |
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Smaller diameter Tx = ____ NZL, ______ focal zone and _____ divergence
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Smaller diameter Tx has...
smaller NZL smaller focal zone and more divergence |
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Low frequency Tx = ____ NZL _______ focal zone and _______ divergence
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Lower frequency TX has...
smaller NZL smaller focal zone and More divergence |
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What are the synonyms for MAIN frequency?
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Primary
Center Main Natural Operating Resonant "Physics creates many nightmares occurring randomly" |
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Operating frequency: is determined by the ___________ of the ______ and the ___________ of the crystal.
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Operating frequency is determined by the propagation speed of the crystal and the THICKNESS of the crystal.
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Operating frequency FORMULA
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prop speed of PZT
--------------------------- 2(x) thickness of PZT |
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Thinner crystals produce _________ main frequency
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Thinner crystals produce HIGHER main frequency
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Thicker crystals produce _______ main frequency
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Thicker crystals produce LOWER main frequency
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Define switched transducer.
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Individual elements are fired one at a time, wait for the returning echo and then the next element is fired. (solo relay race)
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Define segmental transducer.
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Groups of elements are fired simultaneously, wait for the returning echo and then the next group is fired. (group relay race)
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Define Array
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Array is a collection of active elements or crystals in a single Tx
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Define Phased array.
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Phased array is when all elements in an array are fired as a complete group but with a time delay. By changing the delay pattern you may steer the beam. Phased array do not wait for returning echoes.
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Define Vector array.
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Phasing applied to a linear array in order to provide steering. Can be linear and/or fan shape. Also can be Trapozoid and flat top sector shapped. Has electronic steering and focusing.
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Linear phased array.
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Voltage pulses are applied to the element with a slight time delay so that the resulting pulse is sent in a specific path or direction. Uses time delay technique. Has electronic focusing and steering. Shape-flat top sector
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Linear sequential array.
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Voltage pulses are applied to groups of elements in succession. One group of elements fires at a time, waits for echo and then the next group goes.
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The effect of a defective crystal in a Mechanical Tx..
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Mechanical Tx crystal defect destroys the entire image (only have 1 crystal)
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The effect of defective crystal in linear switched Tx
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Linear switched Tx crystal defect results in vertical line drop.
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The effect of defective crystal in linear phased array Tx
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Linear phased array Tx crystal defect results in poor steering and focusing
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The effect of defective crystal in Annular phased Tx
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Annular phased Tx crystal defect results in horizontal line drop out
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The effect of defective crysal in Convex sequential Tx ...
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Convex sequential Tx crystal defect results in vertical line drop
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The effect of crystal defect in Convex phased Tx ...
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Convex phased Tx crystal defect results in poor steering and focusing
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The effect of crystal defect in a Vector Tx ...
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Vector Tx crystal defect results in poor steeriing and focusing
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Define Beam Steering.
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Beam steering is when voltage pulses are applied in rapid progression from left to right, the resulting ultrasound pulse is directed to the right creating an ELECTRIC SLOPE
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Define beam focusing.
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Electronic focusing of the beam is achieved with a curved pattern of phased delay. ELECTRIC CURVE moves the end of the near zone towards the Tx and narrows the beam. A deeper curve = shallow focusing. A wider curve = deeper focusing.
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List the other ways to describe Axial resolution.
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LARRD
Longitudial, Axial, Radial, Range, Depth |
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Formula for Axial resolution.
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SPL/2
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Axial resolution is _______ and can only be changed by changing the ______ of the Tx.
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Axial resolution is CONSTANT and can only be changed by changing the FREQUENCY of the Tx.
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Axial resolution is direction associated with ________.
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Axial resolution is directly associated with SPL and FREQUENCY (which controls SPL)
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Smaller Axial Resolution Number = _______________
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A smaller axial resolution number = a BETTER image due to SMALLER SPL
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If there are 6 cycles of 2 mm wavelength in a pulse, what will be the axial resolution?
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6 mm
number of cycles (6) times the wavelength (2) equals the SPL and then divide by 2 |
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List the other ways to describe lateral resolution.
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Lateral resolution aka LATA
Lateral, Angular, Transverse, Azimuthal (same synonyms as oblique incidence) |
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Lateral resolution is _____ and is determined by the ____ of the beam.
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Lateral resolution is NOT CONSTANT and is determined by the WIDTH of the beam.
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Formula for lateral resolution.
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Lateral resolution = width of the beam
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The damping material in a trasducer improves ______ resolution but has NO effect on _____ resolution.
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The damping material in a transducer improves AXIAL resolution but has NO effect on LATERAL resolution.
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List the various modes of focusing a transducer.
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Various modes of Tx focusing...
Internal = Electronic focusing or curved elements External = Lens or mirrors |
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Define aperature.
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Aperature is the width of the elements involved in a pulse. it is the opening through which pulses are coming and echoes are received.
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Define dynamic focusing.
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Dynamic focusing is the ability of the Tx to selectively receive echoes from different depts. It is automatic. AKA apodization = limiting or restricting activation of elements.
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If elements of a phased array are pulsed in rapid succession from right to left, the beam is steered ________
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If elements of a phased array are pulsed in rapid succession from right to left, the beam is steered LEFT
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If elements of a phased array are pulsed in rapid succession from left to right, the beam is steered ______
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If elements of a phased array are pulsed in rapid succession from left to right, the beam is steered to the RIGHT
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If the elements of a phased array are steered from outside to in, the beam is ______-
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If the elements of a phased array are steered from outside to in, the beam is FOCUSED IN THE CENTER
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A Tx with an NZL of 6 cm ______ be focused at 15 cm.
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A Tx with an NZL of 6 cm CANNOT be focused at 15 cm. (15 cm is in its far zone)
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Can you focus a Tx with an NZL of 5 cm at 15 cm?
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No. 15 cm is in its far zone.
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The focal point is the end of NZL one? True or false
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The focal point IS the end of NZL one.
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