Roadmap Consensus on Carotid Artery Plaque Imaging and Impact on Therapy Strategies and Guidelines: An International, Multispecialty, Expert Review and Position Statement.

Current guidelines for primary and secondary prevention of stroke in patients with carotid atherosclerosis are based on the quantification of the degree of stenosis and symptom status. Recent publications have demonstrated that plaque morphology and composition, independent of the degree of stenosis, are important in the risk stratification of carotid atherosclerotic disease. This finding raises the question as to whether current guidelines are adequate or if they should be updated with new evidence, including imaging for plaque phenotyping, risk stratification, and clinical decision-making in addition to the degree of stenosis. To further this discussion, this roadmap consensus article defines the limits of luminal imaging and highlights the current evidence supporting the role of plaque imaging. Furthermore, we identify gaps in current knowledge and suggest steps to generate high-quality evidence, to add relevant information to guidelines currently based on the quantification of stenosis.

Adaptive optical processor.

The transversal filter is widely used in digital data processing. In this paper, we describe a method for using optically tapped, Bragg cell delay lines to implement a general adaptive linear prediction algorithm. Flexibility is achieved through changing the electronic signals. The implementation is in the Fourier domain so that the wide bandwidth of the Bragg cells can be fully used. A high dynamic range can be achieved because the system is interferometric and linear in light amplitude.

Interferometric spectrum analyzer.

Dynamic range is a key performance parameter for spectrum analyzers. The dynamic range of a Bragg cell power spectrum analyzer is generally limited by the dynamic range of self-scanned photodetector arrays. Interferometric techniques can be used to increase the dynamic range; but it is at the expense of increasing the number of photodetectors required, when the interference is introduced in the spatial domain, or a large photodetector bandwidth, when the interference is introduced in the temporal domain. In this paper we describe an interferometric approach wherein a second Bragg cell generates a spatially modulated reference waveform to produce an interference term that has a constant temporal frequency for all spatial frequencies. The advantages of this approach are lower photodetector bandwidth, improved dynamic range, improved cross talk suppression, more efficient use of the Bragg cell time-bandwidth product, immunity to scattered noise, and improved short pulse detectability. The chief disadvantage is the need for a discrete element photodetector array; when such arrays become available in hybrid or integrated packages, an additional advantage will be that of parallel postdetection processing.

Packing density in holographic systems.

The holographic packing density is derived for any plane in a coherently illuminated optical system. The gain in packing density relative to the object plane is given. A two-lens optical system in which a condenser lens provides high packing densities and an imaging lens provides sufficient resolution is superior to a system in which a single lens performs both functions.

Design relationships for holographic memories.

The maximum capacity of a block-oriented, random-access memory is determined primarily by the geometrical parameters of the lenses required to create a Fourier transform of a spatial bit pattern and to image the reconstructed bits onto a photodetector array. Furthermore, the maximum packing density is determined primarily by the same parameters. Several important relationships are developed that are useful in the preliminary design of holographic memories.

The use of film nonlinearities in optical spatial filtering.

Optical data-processing systems that use spatial filters for detecting two-dimensional signals are usually arranged so that the data are placed in a space domain and the signals to be detected are placed in a frequency domain as holographically recorded Fourier transforms. We propose to interchange the roles of the data and the signal by introducing the data into the system as a Fourier transform hologram and by placing the signal in the space plane. Furthermore, the nonlinear behavior of the film used to record the Fourier transform hologram can be used to good advantage. These modifications combine to give a system that (1) acts as an adaptive filtering system because the noise suppression part of the matched filter is based on a specific noise sample rather than on averages of many noise samples, (2) is less sensitive to the position of the element that must be changed to perform a search for the scale or orientation of the signal, and (3) may reduce the aberrations that are sometimes caused by spatial carrier-frequency functions. Experimental results support the theoretical conclusions.

The effects of small displacements of spatial filters.

In a coherent optical system any displacement of a spatial filter from its optimum position degrades the performance of the system. In this paper the performance of a matched filtering system is related to the degree of displacement for both uniform and nonuniform noise spectral densities. Static displacements of the filter normal or parallel to the optical axis are treated, as well as random motion of the filter normal to the optical axis. Displacements normal to the optical axis cause the performance to decrease more rapidly than those parallel to the axis. For both kinds, the positioning tolerances are more critical when the noise spectral density is nonuniform. A dual frequency-plane optical precessor is described; this processor helps overcome the tolerance problem when the noise is nonuniform because the fixed part of the matched filter can be placed in one frequency plane and the changeable part in another.

Correction of lens aberrations by means of holograms.

Holograms are made of a wavefront emerging from a lens having spherical aberration. The hologram, when used in combination with the lens, serves as a corrector plate for the lens. Experimental results are given, followed by a third-order analysis.

Practical considerations for the use of spatial carrier-frequency filters.

The article discusses several practical problems in the use of spatial carrier-frequency filters in coherent optical systems, and describes an interferometric system that offers many practical advantages in constructing such filters. Also described is an optical configuration that can easily search for the scale of a signal, as well as its location and orientation. The use of a prism in the optical configuration simplifies the search for the orientation and scale of the signal. The spatial carrier-frequency filter introduces some aberrations, but only astigmatism and distortion remain uncorrected. The necessary magnitude of the spatial carrier frequency depends upon the size of the signal and of the input data. A natural extension of this consideration leads directly to a corresponding requirement on the spatial carrier frequencies for multiplexed filters.