Help
Options
Question
"tissue interface"
- position within the tissue where the values of acoustic impedance change
- position within the tissue where the values of acoustic impedance change
click to flip
Didn't know it?
click below
click below
Knew it?
click below
click below
Don't know
Question
weakening of the sound as it propagates through a medium
Remaining cards (65)
Know
retry
shuffle
restart
0:00
Embed Code - If you would like this activity on your web page, copy the script below and paste it into your web page.
Normal Size Small Size show me how
Normal Size Small Size show me how
ULTRASOUND 3
| Question | Answer |
|---|---|
| "tissue interface" - position within the tissue where the values of acoustic impedance change | ACOUSTIC BOUNDARIES |
| weakening of the sound as it propagates through a medium | ATTENUATION |
| Reduction in amplitude and intensity as sound travels | ATTENUATION |
| unit of attenuation | DECIBEL |
| Factors affecting attenuation | Medium and Frequency |
| ______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 |
| ______ frequencies are more attenuated than _____ frequencies. | HIGHER, LOWER |
| ____ frequency penetrates deeper than _____ frequency because they are attenuated to a "lesser" degree | LOWER, HIGHER |
| Where the molecules of the tissue are densely packed, attenuation will be much g____ than in l____ densely packed tissue | GREATER, LESS |
| If path length "increases", attenuation ____ | INCREASES |
| attenuation that occurs with each centimeter the sound wave travels | ATTENUATION COEFFICIENT |
| unit of attenuation coefficient | dB/cm |
| If the attenuation coefficient increases, attenuation _____. | INCREASE |
| For soft tissues, the typical value for attenuation coefficient is __. | 0.5 dB)cm. |
| term used to describe the average tissue that makes up the soft tissues of the human body (e.g., liver, kidney, spleen). | SOFT TISSUE |
| 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 |
| The rate of absorption is directly ________ to the frequency. Higher frequency results in increased ultrasound absorption. | PROPORTIONAL |
| 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 |
| the major interaction of interest for diagnostic ultrasound | INCIDENT ENERGY AND ECHO |
| the sound that hits an acoustic interface | INCIDENT ENERGY |
| reflected beam | ECHO |
| As we have seen, the percentage of incident energy that is reflected depends upon the _____ | ACOUSTIC IMPEDANCE MISMATCH |
| 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 |
| 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 |
| 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 |
| ANOTHER FACTOR THAT AFFECTS THE STRENGTH OF THE REFLECTION IS THE SIZE OF THE REFLECTOR. Reflectors can either be ___ or ____. | SPECULAR OR DIFFUSE |
| - boundary is smooth and larger than the beam. - Angle of incidence = angle of reflection | SPECULAR REFLECTOR |
| - 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 |
| describe when the beam is perpendicular to the interface | NORMAL INCIDENCE |
| Denotes a direction of travel of the incident ultrasound that is not perpendicular to the boundary between two media | OBLIQUE INCIDENCE |
| - 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 |
| when the scatter in equal in all direction | RAYLEIGH SCATTERING |
| - change in direction of a sound beam as it enters the medium. - Transmission with a bend | REFRACTION |
| If the angle of incidence is 90 degrees, no refraction will occur. The physics of refraction are described by | SNELL'S LAW |
| two requirements for REFRACTION to ovcur are: | OBLIQUE INCIDENCE AND DIFF. PROPAGRATION SPEED ON EITHER SIDE OF THE BOUNDARY |
| 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 |
| convert one form of energy to another | TRANSDUCER |
| 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 |
| - contains individual components - Provides structural support and acts as an electrical and acoustic insulator | PHYSICAL HOUSING |
| - "Grounded electrode - " Protects patients from electric shock. | OUTSIDE ELECTRODE |
| - "Live Electrode - " Abuts against a thick backing block. | INSIDE ELECTRODE |
| - " transducer element" - most important component - Approx. 6-19 mm in diameter and 0.2-2 mm in thickness - Crystalline materials - dipolar molecules | PIEZOELECTRIC ELEMENT |
| naturally occurring material with piezoelectric properties | QUARTZ |
| - Commonly used materials - man made ceramic - more efficient, better sensitivity and can be easily shaped | LEAD ZIRCONATE TITANATE(PZT) |
| Greek term "piezo" means___ and Elektron ____ | To press and ember |
| - Was described 1880 by Pierre and Jacques Curies - some materials produced a voltage when deformed by an applied pressure. | PIEZOELECTRICITY |
| Eliminate the vibrations from the "back" face and to control the length of vibrations from the face of the crystals. | BACKING/DAMPING MATERRIAL |
| - Sandwiched between the piezoelectric crystal and the patient. - Has acoustic impedance value halfway between that of the crystal and soft tissue. | MATCHING LAYER |
| Area through which the sound energy emitted from the transducer travels | ULTRASOUND BEAM |
| 2 regions of Ultrasound beam | NEAR FIELD AND FAR FIELD/FRESNEL ZONE OR FRAUNHOFER ZONE |
| Region "nearest" the transducer face, characterized by a highly collimated beam with more uniform intensity. | NEAR FIELD(FRESNEL ZONE) |
| Region "farthest" from the transducer and characterized by the divergence of the beam with great variation in intensity. | FAR FIELD(FRAUNHOFER ZONE) |
| location where the beam reaches its minimum diameter | FOCUS OR FOCAL POINT |
| energy from the transducer that radiates at various amgles from the transducer face | SIDE LOBES |
| arrangement of crystals within the transducer | ARRAY |
| types of electronic array transducer | LINEAR ARRAY, CURVILINEAR(or SECTOR) ARRAY TRANSDUCER,PHASE ARRAY TRANSDUCER |
| physical size of yhe part of the ultrasound that contacts the patient | FOOTPRINT |
| width of the image that is seen on the screen | FIELD OF VIEW |
| produces parallel scan lines and has a rectangular field view | LINEAR ARRAY |
| - image superficial structures and vessels - operate at frequencies above 4MHz - used for vascular, small parts | LINEAR ARRAY |
| - similar to the linear areay but the transducer face is formed curve(convex) - "sector arrays" | CURVILINEAR ARRAY TRANSDUCER |
| - operate ar lower frequencies - 3.5 MHz - best suited to image deep lying strictures - application: abdominal and obstetric | CURVILINEAR ARRAY TRANSDUCERS |
| PHASED ARRAY | |
| transducer designed to enter the body via the vagina, rectum, esophagus or blood vessel(catheter-mounted type) | INVASIVE TRANSDUCERS |
| 1. ultrasound transducers should not be sterilized | TRANSDUCER CARE AND CLEANING |
| temperature at which polarization in a crystal is lost | CURIE POINT |
Created by:
kkei