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| "tissue interface" - position within the tissue where the values of acoustic impedance change | ACOUSTIC BOUNDARIES
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| weakening of the sound as it propagates through a medium | ATTENUATION
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| Reduction in amplitude and intensity as sound travels | ATTENUATION
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| unit of attenuation | DECIBEL
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| Factors affecting attenuation | Medium and Frequency
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| ______will not only occur in the beam of sound produced by the transducer as it produces propagates through tissue, but also in returning ______ as the travel back to the transducer. | Attenuation, echoes
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| ______ frequencies are more attenuated than _____ frequencies. | HIGHER, LOWER
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| ____ frequency penetrates deeper than _____ frequency because they are attenuated to a "lesser" degree | LOWER, HIGHER
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| Where the molecules of the tissue are densely packed, attenuation will be much g____ than in l____ densely packed tissue | GREATER, LESS
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| If path length "increases", attenuation ____ | INCREASES
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| attenuation that occurs with each centimeter the sound wave travels | ATTENUATION COEFFICIENT
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| unit of attenuation coefficient | dB/cm
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| If the attenuation coefficient increases, attenuation _____. | INCREASE
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| For soft tissues, the typical value for attenuation coefficient is __. | 0.5 dB)cm.
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| term used to describe the average tissue that makes up the soft tissues of the human body (e.g., liver, kidney, spleen). | SOFT TISSUE
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| Process by which energy in the ultrasound beam is transferred to the propagating medium, where it is transformed into a different form of energy, mostly heat. The medium is said to absorb energy from the beam | ABSORPTION
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| The rate of absorption is directly ________ to the frequency. Higher frequency results in increased ultrasound absorption. | PROPORTIONAL
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| two large structures of significantly different acoustic impedance form an interface, the interface becomes a reflector and some of the wave energy is reflected back to the transducer | REFLECTION
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| the major interaction of interest for diagnostic ultrasound | INCIDENT ENERGY AND ECHO
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| the sound that hits an acoustic interface | INCIDENT ENERGY
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| reflected beam | ECHO
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| As we have seen, the percentage of incident energy that is reflected depends upon the _____ | ACOUSTIC IMPEDANCE MISMATCH
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| The "values of Z for the soft tissues" are quite similar to one another. We conclude that reflections at boundaries between soft tissue will give rise generally s__ e__. | SMALL ECHOES
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| The "Z value for bone" is several times higher than the soft tissue average.We conclude that reflection from gas/soft tissue interface gives rise to a l___e___. | LARGE ECHOES
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| The "value of Z for air (and other gaseous material)" is much lower than the soft tissue. We conclude that reflection from gas/soft tissue interface gives rise to a ____. | VERY LARGE ECHOES
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| ANOTHER FACTOR THAT AFFECTS THE STRENGTH OF THE REFLECTION IS THE SIZE OF THE REFLECTOR. Reflectors can either be ___ or ____. | SPECULAR OR DIFFUSE
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| - boundary is smooth and larger than the beam. - Angle of incidence = angle of reflection | SPECULAR REFLECTOR
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| - reflecting interface is irregular in shape and its dimensions are smaller than the diameter of the ultrasound beam. - Incident beam is reflected in many different directions. | DIFFUSE REFLECTOR
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| describe when the beam is perpendicular to the interface | NORMAL INCIDENCE
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| Denotes a direction of travel of the incident ultrasound that is not perpendicular to the boundary between two media | OBLIQUE INCIDENCE
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| - when an ultrasound waves strikes a boundary or interface between 2 small structures and the wave is scattered in different directions - responsible for providing the internal texture of organs in the image | SCATTERING
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| when the scatter in equal in all direction | RAYLEIGH SCATTERING
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| - change in direction of a sound beam as it enters the medium. - Transmission with a bend | REFRACTION
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| If the angle of incidence is 90 degrees, no refraction will occur. The physics of refraction are described by | SNELL'S LAW
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| two requirements for REFRACTION to ovcur are: | OBLIQUE INCIDENCE AND DIFF. PROPAGRATION SPEED ON EITHER SIDE OF THE BOUNDARY
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| As a beam of ultrasound travels through it will diverge. This divergence will result in the same power spread over larger area. The intensity of the beam will therefore be reduced | DIVERGENCE
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| convert one form of energy to another | TRANSDUCER
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| G E N E R A L C O M P O S I T I O N O F A N UL T R A S O U N D T R A N S D U C E ivL | PHYSICAL HOUSING
, ELECTRODES, PIEZOELECTRIC ELEMENTS
BACKING MATERIAL
, IMPENANCE MATCHING LAYER
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| - contains individual components - Provides structural support and acts as an electrical and acoustic insulator | PHYSICAL HOUSING
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| - "Grounded electrode - " Protects patients from electric shock. | OUTSIDE ELECTRODE
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| - "Live Electrode - " Abuts against a thick backing block. | INSIDE ELECTRODE
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| - " transducer element" - most important component - Approx. 6-19 mm in diameter and 0.2-2 mm in thickness - Crystalline materials - dipolar molecules | PIEZOELECTRIC ELEMENT
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| naturally occurring material with piezoelectric properties | QUARTZ
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| - Commonly used materials - man made ceramic - more efficient, better sensitivity and can be easily shaped | LEAD ZIRCONATE TITANATE(PZT)
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| Greek term "piezo" means___ and Elektron ____ | To press and ember
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| - Was described 1880 by Pierre and Jacques Curies - some materials produced a voltage when deformed by an applied pressure. | PIEZOELECTRICITY
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| Eliminate the vibrations from the "back" face and to control the length of vibrations from the face of the crystals. | BACKING/DAMPING MATERRIAL
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| - Sandwiched between the piezoelectric crystal and the patient. - Has acoustic impedance value halfway between that of the crystal and soft tissue. | MATCHING LAYER
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| Area through which the sound energy emitted from the transducer travels | ULTRASOUND BEAM
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| 2 regions of Ultrasound beam | NEAR FIELD AND FAR FIELD/FRESNEL ZONE OR FRAUNHOFER ZONE
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| Region "nearest" the transducer face, characterized by a highly collimated beam with more uniform intensity. | NEAR FIELD(FRESNEL ZONE)
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| Region "farthest" from the transducer and characterized by the divergence of the beam with great variation in intensity. | FAR FIELD(FRAUNHOFER ZONE)
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| location where the beam reaches its minimum diameter | FOCUS OR FOCAL POINT
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| energy from the transducer that radiates at various amgles from the transducer face | SIDE LOBES
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| arrangement of crystals within the transducer | ARRAY
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| types of electronic array transducer | LINEAR ARRAY, CURVILINEAR(or SECTOR) ARRAY TRANSDUCER,PHASE ARRAY TRANSDUCER
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| physical size of yhe part of the ultrasound that contacts the patient | FOOTPRINT
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| width of the image that is seen on the screen | FIELD OF VIEW
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| produces parallel scan lines and has a rectangular field view | LINEAR ARRAY
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| - image superficial structures and vessels - operate at frequencies above 4MHz - used for vascular, small parts | LINEAR ARRAY
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| - similar to the linear areay but the transducer face is formed curve(convex) - "sector arrays" | CURVILINEAR ARRAY TRANSDUCER
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| - operate ar lower frequencies - 3.5 MHz - best suited to image deep lying strictures - application: abdominal and obstetric | CURVILINEAR ARRAY TRANSDUCERS
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| PHASED ARRAY
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| transducer designed to enter the body via the vagina, rectum, esophagus or blood vessel(catheter-mounted type) | INVASIVE TRANSDUCERS
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| 1. ultrasound transducers should not be sterilized | TRANSDUCER CARE AND CLEANING
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| temperature at which polarization in a crystal is lost | CURIE POINT
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