Physics 3.3 & 3.4
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| scanning | sweeping, steering the beam, automatically, real time sonography
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| scan lines | the transducer sends out scan lines, a complete scan of the ultrasound beam is called a frame, real-time sonography presents images(frames) in a rapid sequential format
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| 2 methods of sending out scan lines to form an image | mechanical, electronic
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| mechanical scanning | oscillating an element, spinning a group of elements, oscillating a mirror, mostly obsolete(some 3D and 4D)
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| electronic scanning | performed with arrays, dominate form of transducers
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| array | a grouping arrangement of parts forming a complete unit, EX. pages forming a book
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| transducer arrays | transducer assembly with many transducer elements (crystals)
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| types of arrays | linear (straight line), curved or convex (bowed out), annular (ring shaped)
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| linear array | linear sequenced array, linear sequential array
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| linear arrays contain.. | crystals (elements) in a straight line, 128 elements, each element is a wavelength wide
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| operation | applying voltage to groups of elements in succession, each group acts as a larger transducer element, sound beam moves across the transducer face from one end to the other and jumps back to the begininng to repeat
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| linear scanning | accomplished rapidly and consistently, no moving parts or coupling fluid
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| real-time linear scanning | the process must be accomplished rapidly, 30 times per second
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| aperture | the size of the group of elements that produces one scan line
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| width of image | equal to the length of the array, produces a rectangular image
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| rectangular image | paralell scan lines, produced by pulses that originate at different points across the face of the linear array transducer
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| firing sequence | how many elements are fired in each group? need to produce 250 scan lines per frame (image) for a good quality image
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| Facts: linear sequenced | aka linear sequential or linear array, rectangle shaped image, firing is sequential, electronic steering available, electronically focused
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| curved sequenced array | convex, curved sequential array, curvilinear array
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| construction | elements are in line but, the line has been curved, rather than straight
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| operation | idential to that of the linear sequenced array
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| curved images | pulses travel out in different direction due to curved shape, produced a SECTOR image
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| Facts; curved sequenced array | aka convex, curvilinear, or curved sequenced array, curved shaped image, wide near field, firing is sequenced, electronically focused
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| phased array | sector, vector or linear phased array, contains a compact line of elements, each element is 1/4 of a wavelength wide
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| operation | applying voltage pulses to all elements at almost the same time, usually less than 1 microsecond difference
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| phasing | applying voltage to all elements at almost the same time is termed phasing, the entire transducer is used to create one pulse
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| steering the beam | aka sweeping the beam, produced by phasing, time differences among the elements are changed continually creating a SECTOR shaped image
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| sector | phased array, sector image, "piece of pie shaped," common point of origin on the transducer face
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| vector | sector transducer in which the scan lines do not have a common point of origin
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| Facts: phased array | aka sector, vector, vector or sector shaped image, electronic steering and focusing, used for (cardiac, abdominal, neonatal, and endocavitary transducers)
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| focus by phasing | phasing can be used to focus the sound beam, an increase in curvature moves the focus closer to the transducer, a decrease in the curvature moves the focus deeper
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| control of focusing | provides electronic control of focus, the sonographer can change the focal depth
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| multiple focuses | one pulse can be focused at only one depth, to create a wide focus many (multiple) focuses must be used, multiple focuses require more time to create an image, slows down the frame rate
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| dynamic aperture | not all elements are used to generate all pulses, small aperture (less elements) are used for short focal depth, larger aperture (more elements) are used for longer focal depths
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| section thickness | slice thickness, section thickness, z axis, elevation axis, 3rd dimension of the ultrasound beam, the depth
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| two dimensional arrays | a single line of elements can electronically focus or steer only in the scan plane, focus can be achieved in the 3rd dimension, with at least 3 rows of elements phasing can be applied to focus the 3rd dimension electronically
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| two dimensional arrays have the ability to... | steer and focus in two dimensions
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| two dimensional arrays | with 100s or 1000s of elements have the ability to steer and focus in two dimensions rather than one, rapid electronic volume imaging is thus created
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| grating lobes | additional beam that are not contained in the sound beam, found only in multi-element transducers, can produce aritfacts
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| apodization | aka dynamic apodization, occurs continually, reduces grating lobes, varies the voltage to individual elements, less energy escapes out the sides of the element
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| vector array | phasing applied to linear sequenced array, used to steer pulses in various directions, initiate pulses at various starting points across the array, allows more elements to be used, thus larger aperture and focal depth
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| type of images | scan lines originates from different points across the front of the transducer, they travel out in different directions, shaped similar to a sector image but has a flat footprint
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| parallelograms | created when phasing is applied to linear sequential arrays, used in color flow imaging
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| annular array | consists of several concentric ring shaped transducers, focused by phasing
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| focusing | focus is cone shaped, reduces section thickness, no grating lobes
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| steering | annular arrays cannot steer the beam, the beam is steered mechanically
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| hybrid transducer | steered mechanically, focused electronically
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| electronic focusing | transmit focus, dynamic focus
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| dynamic focus | "listening focus," set at a particular depth, echoes that are received from that depth are focused, continually changes as the tissues are scanned
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| 3D transducers | aka volume scanning, multiple 2D images placed next to each other, allows user to see height, width and depth, 3 ways to create (freehand, mechanical transducer, electronically)
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| freehand | transducer is moved in a parallel fashion, 2D images are stacked together to form 3D volume
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| mechanical | transducer is moved in a sweeping or fan motion, the 2D images are lined together to form a 3D image
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| electronic array | aka 2D array or matrix array, real-time volume imaging, transducers have up to 10,000 elements,
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| 4D imaging | 3D imaging in real-time, limited frame rate
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| resolution | ability to see structures as they really are
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| types of resolution | detail (spatial), temporal, contrast
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| resolutions | contrast and temporal resolution relate more directly to the instrument, detail resolution relates more directly to the transducer
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| detail(spatial) resolution | the ability of the system to distinguish between two closely spaced objects, quality of the detail of the image
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| detail resolution | axial, lateral, elevational, contrast
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| values | detail resolution is a numerical value
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| the smaller the numerical value(number)... | the better the detail resolution
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| axial | L longitudinal
A axial
R range
D depth
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| defintion | the minimum reflector separation required along the sound path, PARALLEL to the sound path, the minimum distance two reflectors can be parallel to the beam and still appear on the screen as two separate dots
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| axial resolution = | 1/2 SPL
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| there must be a distance of at least 1/2 the SPL between... | 2 structures for each structure to be recorded
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| axial resolution = | SPL divided by 2
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| to improve axial resolution... | the SPL must be reduced
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| SPL = | # of cycles x wavelength
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| reduce wavelength | higher frequency
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| reduce # of cycles | more damping material
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| useful frequency range | 2 to 15 MHZ, 2 for penetration, 15 the best resolution, must determine both
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| imaging depth | equals 60 divided by the frequency, frequency limits imaging depth
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| lateral resolution | minimum separation between tow reflectors that can produce two separate echoes, reflectors are in a plane perpendicular to the sound beam
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| lateral resolution cont... | L lateral
A azimuthal
T transverse
A angular
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| lateral resolution equals... | beam width
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| beam diameter | is determined by both the frequency and the diameter of the element, higher frequency = shorter NZL (best lateral resolution at the focus)
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| value | numerical value, the smaller the number the better the resolution, less distance is needed between the structures to image both the structures
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| distance | if a distance less than a beam width separates two structures in the perpindicular plane, the two structures will be combined, only one echo will be imaged
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| improvement by... | focusing
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| the best axial and lateral resolution is obtained at the... | focus. transducers have better axial resolution than lateral
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| elevational resolution | 3rd dimension of the ultrasound beam, depends on the transducer element height, aka (slice thickness plane, section thickness plane, elevational plane)
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| improvement by... | focusing. most commonly with a lens
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| contrast resolution | the ability to differentiate one shade of gray from another, related to equipment
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| temporal resolution | the ability to display structures in real time, related to equipment
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| equipment | contrast resolution plays a big part in overall resolution, the best transducer resolution will be of no value without good equipment resolution
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