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ULTRASOUND 3

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Created by: kkei

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