| | UltraSound - Technology Information Portal | Friday, 10 September 2010 |
| |
|
 | Info
Sheets |
| | | | | | | | | | | | | | |
 | Out-
side |
| | |
|
| | |
| |
Result : Searchterm 'Interference' found in 2 terms [ ] and 8 definitions [ ])
| | 1 - 5 (of 10) nextResult Pages : [1] [2] | | | | |
 |
US Resources |
|
| | | | | | | |  |
| Interference Artifact |   |
| |
|
|
Interference artifacts occur if decreasing of the echo amplitude is not exponential with penetration depth caused by inhomogeneous tissue layers and fluid or air-filled regions. If ultrasound waves have opposite phases, i.e. if the phase difference is 180°, their amplitudes will always be in opposite directions and their sum is a weaker wave. This is destructive interference and artifacts occur.
|
| | | | | |
| |
|
US Resources |
|
| | | | | |
|
| | |  |
| Huygens Principle | |
| |
|
Huygens principle states that an expanding sphere of waves behaves as if each point on the wave front were a new source of radiation of the same frequency and phase. The principle explains how a flat ultrasound transducer can transmit a narrow ultrasound beam, which in the near field is confined to the dimensions of the transducer surface.
Spherical wavelets are emitted from numerous point sources on the transducer surface. They interfere to form a narrow, slightly converging beam of ultrasound in the near field. The wavefronts in the beam are nearly parallel. A precondition for this interference is that the transducer surface is much larger than the ultrasound wavelength.
See also Interference Artifact.
|
| | | |
 Further Reading: |
Basics:
|
|
News & More:
| | | | |
| |
|
| |
| Linear Array Transducer | |
| |
|
Linear array transducer elements are rectangular and arranged in a line. Linear array probes are described by the radius of width in mm. A linear array transducer can have up to 512 elements spaced over 75-120 mm. The beam produced by such a narrow element will diverge rapidly after the wave travels only a few millimeters. The smaller the face of the transducer, the more divergent is the beam. This would result in poor lateral resolution due to beam divergence and low sensitivity due to the small element size.
In order to overcome this, adjacent elements are pulsed simultaneously (typically 8 to 16; or more in wide-aperture designs). In a subgroup of x elements, the inner elements pulse delayed with respect to the outer elements. The interference of the x small divergent wavelets produces a focused beam. The delay time determines the depth of focus for the transmitted beam and can be changed during scanning.
Linear arrays are usually cheaper than sector scanners but have greater skin contact and therefore make it difficult to reach organs between ribs such as the heart. One-dimensional linear array transducers may have dynamic, electronic focusing providing a narrow ultrasound beam in the image plane. In the z-plane (elevation plane - perpendicular to the image plane) focusing may be provided by an acoustic lens with a fixed focal zone.
Rectangular or matrix transducers with unequal rows of transducer elements are two-dimensional (2D), but they are termed 1.5D, because the number of rows is much less than the number of columns. These transducers provide dynamic, electronic focusing even in the z-plane.
See also Rectangular Array Transducer.
|
| | | |
| Further Reading: |
Basics:
|
|
News & More:
| | | |
| |
|
|
US Resources |
|
| | | | | | | 1 - 5 (of 10) nextResult Pages : [1] [2] |
| |
|
| |
 | Look
Ups |
| |
|
| | [last update: 2010-09-07 06:10:53] |
|
|
bottom
(.pdf)
Random Page
top