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Real-time scanners had rather standard appearance, sizes and fabrication. They are usually portable on 4 wheels with the monitor on the top of the console and rows of receptacles at the bottom to accomodate a variety of scanner probes.
See some of these scanners here. By the mid s curvilinear or convex abdominal transducers have come into the market which have a better fit to the Obstetric abdomen and have a wider field of view further from the transducer face.
Curvilinear arrays have completely replaced the linear configuration by the late s. Prior to the s, B-scan ultrasound images made steady progress in resolution and quality, but the improvements were not dramatic and except for a few really top-end brands, most had felt that images in the late s did not have significant improvements over those in the early 80s.
During this period, techiques for resolution and overall image enhancement centered around: See a brief discussion on the linear and phased-array principles. The machine shook the ultrasound community with its excellent resolution and clarity and also the price.
Many other companies followed on similar system designs. The early to mid- s was the time with the heaviest proliferation of standard-setting good quality machines. By the early s there were over 45 large and small diagnostic ultrasound equipment manufacturers worldwide.
Image quality saw real improvements in the early s. It is interesting to note that the availability of new and effective technologies to ultrasound scanners had also progressively stemmed from advances in technology in other areas of science such as radar navigation, telecommunications and consumer electronics.
Such included the rapid developments in cellular telephones, micro-computers, digital compact and versatile disk players, and high definition TVs. The very high-speed digital electronics required for ultrasound application had become available at an affordable costs.
The ultrasound imaging market alone would not have supported the development of these new technologies. Model number of scanners made after from important manufacturers are listed here with the year in which they were marketed. The new developments in the s which has lead to some real enhancement in image quality and resolution include: The entire signal processing chain becomes digital.
The entire signal chain which includes: Previously the beamformer employing analog delay lines and the signal processing stages are usually analog in their operation. The digital change-over was based on the very powerful computer platforms that were only available after the mid s. The processor in the newer highend machines has the power equivalent of roughly 40 Pentium tm processors, executing some 20 to 30 billion operations per second.
Most of the processing are also programmable software-based rather than hardware-based and allow for much more versatility and finer adjustments in the manipulation of beam signals.
Signals from and to the transducer elements are digitized before any signal processing, which is one of the most important advancement in ultrasound technology in the 90s. It opened the venue for dealing with some of more difficult areas in ultrasound physics.
Superfast digital beamformers allow for many times the number of focal points along the beam and produce microfine focal points on receive to the size of a screen pixel. Digital beamforming also reduces noise in the signal processing by several hundred folds producing a much cleaner picture.
Extensive use of refined broad-band wide aperture transducers, improving both definition of tissue textures and dynamic range.
With wide aperture transducers, transmit and receive apodization also allowed for the electronic reduction of the lateral array elements sidelobes. In the early s there was much improvements in transducer material design and fabrication technology allowing for higher frequency transducers, improved sensitivity and contrast resolution.
The number of channels in high-end systems went up to and more recently to and 2-D arrays in several high-end systems allowing for extremely wide aperture on transmission and reception. In ultrasound physics, the lateral resolution is the product of the wavelength and the f-number.
The f-number equals the depth of the returning echo divided by the aperture of the beam.
Therefore lateral resolution will be best smallest if there is a large aperture and short wavelength higher frequency. Too large an aperture will slow the frame rate considerably and requires very fast computation and parallel processing.
This has been made possible with the more recent digital electronics and the very powerful super-processors see above. Many slightly older ultrasound systems are capable of using low f-numbers on reception at an affordable cost. However, they often employed large f-numbers on transmit in order to cover a large area.
Significant improvement in lateral resolution requires low f-numbers both on transmit and receive. The resulting improvements in lateral resolution can be as much as 4 times.
The phase data in returning ultrasound echoes, in addition to the amplitude data are processed in what is known as coherent image processing. The technique produced twice the amount of data from which to create ultrasound images of high resolution.
The frame rate is also increased.One purpose of Proposition 21 is application of the maximum penalty and longest imprisonment available based on the status of the crime. (Voter Pamphlet, at ). Justice Kennard argued that Proposition 21 unconstitutionally invaded a judicial function for three main reasons.
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Online Library of Liberty. A collection of scholarly works about individual liberty and free markets. A project of Liberty Fund, Inc. In March , the California Proposition 21 Juvenile Crime Policy was passed.
Its main purpose was to tighten the laws on juvenile gang related crimes thus making it possible to prosecute minors in adult courts. The problem that was identified by the sponsors of this proposition was the gradual increase of juvenile crimes in the state.
Proposition 8; Eliminates Rights of Same-Sex Couples to Marry. Initiative Constitutional Amendment.