System Signal-to-noise Ratio Research Articles

Using a flat-panel detector in high resolution cone beam CT for dental imaging

Cone beam CT (CBCT) requires a two-dimensional X-ray detector. In the several CBCT systems developed for dental imaging, detection has been by the combination of an X-ray image intensifier and charge-coupled device (CCD) camera. In this paper, we propose a new CBCT system in which the detector is of the flat-panel type and evaluate its performance in dental imaging. We developed a prototype CBCT that has a flat-panel-type detector. The detector consists of a CsI scintillator screen and a photosensor array. First, the flat panel detector and image intensifier detector were compared in terms of the signal-to-noise ratio (SNR) of projected images. We then used these data and a theoretical formula to evaluate noise in reconstructed images. Second, reconstructed images of a bar pattern phantom were obtained as a way of evaluating the spatial resolution. Then, reconstructed images of a skull phantom were obtained. The SNR of the developed system was 1.6 times as high as that of a system with an image intensifier detector of equal detector pitch. The system was capable of resolving a 0.35 mm pattern and its field of view almost completely encompassed that of an image intensifier detector which is used in dentomaxillofacial imaging. The fine spatial resolution of the detector led to images in which the structural details of a skull phantom were clearly visible. The system's isotropically fine resolution will lead to improved precision in dental diagnosis and surgery. The next stage of our research will be the development of a flat panel detector system with a high frame acquisition rate.

Hard Disk Drive Capacity at High Magnetic Areal Density

Increases in recording areal density have propelled the disk drive industry in the last dozen years. Several studies and research programs strive to accomplish an areal density of 1 Tb/in/sup 2/. At present, the future of the hard disk drive technology appears predicated on monotonic and unbound areal density growth. The system consequences of using large areal densities are the subject of this paper. It is argued that the limited signal-to-noise ratio (SNR) predicted at 1 Tb/in/sup 2/, as well as the extreme mechanical demands on the system, will cause the user capacity not to grow linearly with areal density, as has been the case in the past. This is due, among other reasons, to the increased servo overhead, the increased error-correction code overhead, and the mechanical requirements that compel the reduction of the size of the mechanism. Without casting in doubt the feasibility of magnetic bit recording at 1 Tb/in/sup 2/, scaling laws nevertheless show that there may be limited rewards for the technical efforts directed toward accomplishing 1 Tb/in/sup 2/. Unless the system SNR can be maintained at about 18 dB, areal density gains will not result in proportional user-capacity gains.

Estimation of signal-to-noise ratio improvement in RF-interconnect

RF-interconnect (RFI) can greatly improve the signal-to-noise ratio (SNR) in a high-speed digital interface system by separating the data and the noise in the frequency domain and suppressing the switching noise by the highpass channel characteristics. Experimental characterisation results are presented of a prototype multi-I/O RFI channel. The potential SNR improvement is estimated to be 10 dB compared to conventional digital interface systems. The improved system SNR can lead to enhanced data rate with reduced signalling level in RFI.

Usefulness of Three-dimensional Contrast-Enhanced MR Angiography in the Evaluation of Pelvic and Lower Extremity Arteries

Purpose: To evaluate the feasibility and clinical usefulness of three-dimensional contrast-enhanced MR angiography (3D-CE-MRA) as a screening test in the evaluation of pelvic and lower extremity arterial diseases. Materials and Methods: Forty-four patients who underwent 3D-CE-MRA were included in this study. Coronal 3-dimensional gradient-echo, pre-and post contrast image were acquired with a dedicated peripheral vascular coil and moving-bed technique on a 1.5T MR system. Timing of start of data acquisition was determined by MR fluoroscopy technique, and 0.2mmol/kg Gd-DTPA was injected into an antecubital vein, at a rate of 1cc/sec with an autoinjector. For quantitative analysis, signal to noise ratio (SNR) and artery to soft tissue contrast to noise ratio (CNR) of lower extremities arterial system including lower abdominal aorta were calculated. For qualitative analysis, arterial systems were divided into six segments, and were evaluated in terms of conspicuity of arterial systems and the degree of venous enhancement by three- and four-point scale respectively. In eight patients who underwent both MR angiography and conventional angiography, the degree of the stenosis of MR angiography was compared with conventional angiography as standard reference. Imaging analysis was done by means of consensus between two experienced radiologists. Results: The mean time for the examination was about 15min (5 min). The mean SNR of arterial system was 26.511.6, and mean artery to soft tissue contrast to noise ratio (CNR) was 24.611.2. Among the total 525 arterial segments, 498 arterial segments (94.9%) could be demonstrated with good delineation of entire arterial tree. Good arterial imaging without or with minimal venous enhancement were demonstrated in 98.5% (260/264) in above knee and 89% (211/261) in below knee (p

Automatic capture verification by charge-neutral sensing.

Automatic capture verification can prolong pulse generator longevity and increase patient safety. However, the detection of evoked response following pacing is complicated due to afterpotentials caused by polarization of electrodes. This study describes a new capture verification scheme, which neutralizes the charges between the pacing electrodes. The hypothesis of the charge-neutral sensing is that the afterpotentials in the ring and the tip are opposite in polarity when pacing in a bipolar mode between ring and tip. Summing the unipolar signals sensed at the tip and the ring should effectively cancel the afterpotentials. This scheme was implemented in an external computer based system and tested during pacemaker implant/replacement on 23 patients during VVI pacing (17 acutely implanted leads and 6 chronic leads). Surface ECG was recorded to provide a marker for capture and noncapture. The pacing voltage was gradually decreased until a noncapture beat was noted. To avoid fusion beats, the pacing rate was programmed approximately 50% higher than the intrinsic rate. The evoked response was high pass filtered and the integral average was calculated for both capture and noncapture beats. The system signal to noise ratio (SNR) was expressed as ratio of the minimum integral average of all capture beats to the maximum integral average of all noncapture beats. The system SNR was 8.6 +/- 1.3 (mean +/- S.E.M; range 1.5-22.8), indicating that the charge-neutral sensing method has, on average, a ninefold safety margin in providing capture verification. Further, evaluation is needed to fully assess this feature in patients with chronic leads.

Generation and reception of ultrasonic guided waves in composite plates using conformable piezoelectric transmitters and optical-fiber detectors

A condition monitoring nondestructive evaluation (NDE) system, combining the generation of ultrasonic Lamb waves in thin composite plates and their subsequent detection using an embedded optical fiber system is described. The acoustic source is of low profile with respect to the composite plate thickness, surface conformable, and able to efficiently launch a known Lamb wave mode, at operating frequencies between 100 and 500 kHz, over typical propagation distances of 100 to 500 mm. It incorporates both piezocomposite technology and interdigital design techniques to generate the fundamental symmetrical Lamb wave mode in both metallic and carbon-fiber composite plates. Linear systems and finite element modeling techniques have been used to evaluate the operation of the transducer structure, and this is supplemented by experimental verification of the simulated data. An optical fiber, either bonded to the surface or embedded across the length of the composite plate samples, is used to detect the propagating ultrasonic Lamb waves. Single mode silica fiber has been used in conjunction with a portable 633 nm Mach-Zehnder interferometer for signal demodulation and subsequent data acquisition. This hybrid system is shown to generate and detect the fundamental symmetrical Lamb wave (s(0)) in both carbon-fiber and glass-fiber reinforced composite plates. Importantly, the system signal-to-noise ratio (SNR) associated with the acoustic source compares favorably with s(0) Lamb wave generation using a conventional transducer and angled perspex wedge arrangement.

Reduction of fiber-nonlinearity-enhanced amplifier noise by means of phase-sensitive amplifiers

In optical fiber transmission systems near the zero-dispersion wavelength that use in-line erbium-doped fiber amplifiers (EDFA's), the enhancement of optical amplifier noise caused by four-wave mixing (FWM) in transmission fibers degrades signal-to-noise ratio (SNR) excessively. We theoretically show that the enhancement of amplifier noise by the FWM in transmission fibers can be effectively eliminated by implementing in-line phase-sensitive amplifiers (PSA's). Small-signal analysis of the nonlinear Schrödinger equation shows that the transmission distance limited by the SNR of an in-line PSA system is expanded four times more than that of an in-line EDFA system.

A new coded-excitation ultrasound imaging system. II. Operator design

For pt.I see ibid. vol.43, pp.131-140 (1996). We introduced in pt. I a new approach for ultrasonic imaging using coded-excitation. Our formulation allows for the implementation of the imaging operator as a transversal filter bank with each filter designed to reconstruct scatterer distribution along one image line. This formulation allows for high-speed data acquisition when the reconstruction filters are utilized in parallel configuration. Furthermore, under high signal-to-noise ratio (SNR) conditions, our approach allows for spatial resolution that exceeds the resolution set by the diffraction limit. Ideally, the resolution limit for our system is set by the grid spacing in the region of interest (ROI). When the SNR of the system is finite, however, sensitivity to noise becomes a factor in image reconstruction quality. A trade-off exists between spatial and contrast resolutions with all elements of this trade-off captured by the singular value decomposition (SVD) of the imaging operator, G. In this paper, we demonstrate the use of the function given in pt.I in defining an optimal pseudo-inverse operator (PIO). The optimal PIO provides the highest spatial resolution at which the mean-square error (MSE) is minimized. We show that a design procedure for such an optimal image reconstruction operator is feasible, and we present an algorithm for operator design. Computer simulations are used to highlight the main features of the SVD-based operator design procedure; the SVD of the imaging operator consists of array-dependent (analytic) and code-dependent (nonanalytic) modes. The analytic modes yield a sine-like lateral point spread function (LPSF) of the imaging system. For a given SNR of the imaging system, a maximum number of modes (analytic and nonanalytic) can be used in the design of the imaging operator to minimize the LPSF width (i.e., maximize resolution) while minimizing the MSE. Finally, a two-dimensional cyst simulation is provided to demonstrate the potential advantage of our approach.

Methods to calculate the lens efficiency in optically coupled CCD x-ray imaging systems.

In lens-coupled CCD x-ray imaging, the lens efficiency is of critical importance for attaining an x-ray quantum-noise-limited system. However, the equations and the associated parameters of this process have not always been used properly in some of the literature. This can result in the incorrect estimation of the signal-to-noise ratio (SNR). In practice, it is found more convenient to use lens-coupling efficiency equations which assume that the scintillating screen is an extended Lambertian source, since the number of light photons emerging from various scintillating screens has been measured and reported by several investigators. This communication examines several of the most common types of lens-coupling efficiency equations and explains how to use them correctly with other parameters to calculate the SNR of a lens-coupled CCD x-ray imaging system.

Optimum design of optical storage media for drive compatibility

Interchangeability standards for writable optical data storage media allow considerable range in the design of media and optical devices. Naturally, the most reliable system performance occurs when the media design is made fully compatible with the particular characteristics of the drive. This paper treats design of the thin film structure of magneto-optical media for optimum readout compatibility with the drive. The methodology centers on maximization of system signal-to-noise ratio (SNR) under general conditions of system noise composition. We present simple models for the behavior of the various noise components in optical disk drives-medium, laser, shot, electronic. The total system noise model is supplied with relative component weights derived from experimental noise decomposition measurements on the physical system (drive or tester). By changing the relative weights of system noise components, one can readily identity optimum medium designs under different conditions of noise dominance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

OPTICAL AND MAGNETO-OPTICAL PERFORMANCE OF OPTIMIZED DISK STRUCTURES

We explore the relative magneto-optic readback performance of three magnetic materials for erasable optical data storage. We modeled the system signal-to-noise ratio (SNR) of optimal film structures incorporating either TbFeCo, a Co/Pt multilayer, or BiDy-substituted FeGa garnet as a function of the wavelength of the reading light beam. The complex indices of refraction and Voigt parameters of the three magnetic storage materials were determined experimentally over the spectral range 300-800 nm by regression fitting of data from variable angle of incidence ellipsometry and normal incidence Kerr spectroscopy to an appropriate optical model. Making specific comparisons of the read back performance at 450, 550, and 800 nm, we find that for the MO materials we have characterized, the performance of TbFeCo is superior to that of either Co/Pt or the garnet at 550 and 800 nm. Only at 450 nm did the Co/Pt give slightly higher SNR than the TbFeCo. The garnet showed improving SNR in passing from 800 nm to the shorter wavelengths, but it had lower performance than the metal films.

Interframe Hierarchical Vector Quantization

An interframe hierarchical vector quantizer (IHVQ) is presented that is capable of encoding image sequence scenes at rates below 0.3 bit per pixel per frame. A regular decomposition quadtree method is used to segment the interframe differential signal into homogeneous regions of different block size. Small blocks representing high contrast moving boundaries (i.e., the impulsive component of the difference signal) are vector quantized, whereas large blocks typically representing smooth regions of the image are encoded by the local sample mean of the region. The IHVQ system has a signal-to-noise ratio (SNR) at least 2 dB higher than the SNR of the interframe mean-reconstructed quadtree coding system.

The intrinsic signal-to-noise ratio in NMR imaging.

The fundamental limit for NMR imaging is set by an intrinsic signal-to-noise ratio (SNR) for a particular combination of rf antenna and imaging subjects. The intrinsic SNR is the signal from a small volume of material in the sample competing with electrical noise from thermally generated, random noise currents in the sample. The intrinsic SNR has been measured for a number of antenna-body section combinations at several different values of the static magnetic field and is proportional to B0. We have applied the intrinsic and system SNR to predict image SNR and have found satisfactory agreement with measurements on images. The relationship between SNR and pixel size is quite different in NMR than it is with imaging modalities using ionizing radiation, and indicates that the initial choice of pixel size is crucial in NMR. The analog of "contrast-detail-dose" plots for ionizing radiation imaging modalities is the "contrast-detail-time" plot in NMR, which should prove useful in choosing a suitable pixel array to visualize a particular anatomical detail for a given NMR receiving antenna.

On the signal-to-noise ratio enhancement of the Doppler process

The output signal-to-noise ratio (SNR) of the ultrasound Doppler process, with and without the commonly used sample and hold circuit, is calculated rigorously, and confirmed by experiment. On the basis of this result it is shown that the use of pulsed Doppler processing without increase of the transmitted power enhances the output SNR of a pulse-echo system observing moving particles by the factor f r T t, where f r is the repetition rate of the pulse echo and Doppler systems and T t is the transit time of the particles across the range cell. If nonlinear losses are significant, then changing to continuous Doppler operation and lowering the peak transmitted power to maintain the average power constant can produce additional improvement in SNR due to reduced non-linear losses in the transducer and the propagation medium, as well as reduced requirements for transducer damping.

Signal-to-noise ratios of array receiving systems with internal losses

A formulation of the signal-to-noise ratio (SNR) for a typical antenna array receiving system that is more complete than those now available in the literature is presented. In addition to the external noise accepted by the array, it includes all forms of internal noise generated by the lossy components of the system. Distinct measurable factors account for distinct noise sources. For the analysis, it is shown that the actual lossy system can be replaced by an equivalent lossless system with appropriate attenuators. The formulation is used to design the combining network that will optimize the receiving system SNR for signals incident from a given direction in the presence of a known external noise distribution. The theory is applied to a specific array antenna receiving system operating under a variety of noise conditions, internal as well as external. A discussion of some typical results is presented.

Error Rate Bounds for Digital PAM Transmission with Phase Jitter and Intersymbol or Cochannel Interference

A simple method is presented for computing upper and lower bounds for binary PAM signaling over channels with phase jitter. Other impairments to reliable communication are taken to be additive thermal noise and intersymbol or cochannel interference. The important cases of binary and quadrature phase shift keying are cases for which the analysis presented is valid. The method consists of finding upper and lower bounds conditioned on the phase jitter, φ, in a form in which the auguments of the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> -functions involved are linear in <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\cos \phi</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sin \phi</tex> . When these functions are represented by a piecewise linear approximation, the average of these bounds can be given in closed form. In most cases 5 piecewise linear segments provides an error rate estimate that is accurate to at least 1 dB in system signal-to-noise ratio (SNR).