Scan Period Research Articles

The application of large format, broadband quantum well infrared photodetector arrays to spatially modulated prism interferometers

The spatially modulated prism interferometer (SMPI) is a new type of imaging interferometer that has double the efficiency of conventional interferometers and only a fraction of the mass and volume. Its spectral resolution is independent of wavelength and slit width, an attribute made possible by generating interferograms at a pupil plane. It uses a large format, broadband quantum well infrared photodetector array to scan the interferograms digitally without moving any optical components. This enables the interferometer to make accurate measurements of target scenes that fluctuate during the scan period. Applications include detecting water sources on Mars, monitoring global warming and ozone depletion on Earth, monitoring pollution in cities, detecting chemical agents on the battlefield, and warning commercial aircraft of volcanic eruptions.

An evaluation of a steerable sidescan sonar for surveys of near-surface fish

A towed 330 kHz sector scanning sonar was evaluated for surveys of near-surface migratory salmonids ( Oncorhynchus sp.) and other fish in the Strait of Georgia near the mouth of the Fraser River near Vancouver, BC (Canada). Detection of large near-surface fish presents a serious challenge to conventional net trawls or echo-sounder surveys due to vessel avoidance behaviour by the fish. The sonar was towed beside a research vessel on a custom-built towfish at a nominal depth of 18 m. The optimum configuration was determined to be with the sonar scanning a 30° vertical sector oriented perpendicular to the tow direction, at a ping rate of 5 Hz and a sector scan period of 5 s. Fish were detected up to a range of 100 m, limited by systemic noise and backscattered reverberation from the sea surface. Some evidence of vessel-avoidance behaviour by the fish was observed. Near surface temperature and salinity gradients are shown to induce downwards refraction of the sonar beam, resulting in biases in apparent depth and target strength of the fish. A simple model of the sonar performance in this scanning mode, including beam-pattern effects, is used to generate curves of fish target detectability and beam-pattern induced bias as a function of range and fish target strength. After correction for refraction effects, beam-pattern bias, and detectability, the survey results show reasonable agreement with net trawl and riverine escapement data.

Temporal and Spatial Dynamics of Human Forebrain Activity During Heat Pain: Analysis by Positron Emission Tomography

To learn about the sequence of brain activation patterns during heat pain, we acquired positron emission tomographic (PET) brain scans at different times during repetitive heat stimulation (40 or 50 degrees C; 5-s contact) of each subject's left forearm. Early scans began at the onset of 60 s of stimulation; late scans began after 40 s of stimulation, which continued throughout the 60-s scan period (total stimulus duration 100 s). Each subject (14 normal, right-handed subjects; 10 male, 4 female; ages 18-42) used a visual analog scale to rate the perceived stimulus intensity (0 = no heat, 7 = pain threshold, 10 = barely tolerable pain) after each scan. The 40 degrees C stimulation received an average intensity rating of 2.19 +/- 1.22 (mean +/- SD) and the 50 degrees C an average rating of 8.93 +/- 1.33. During the scan sessions, subjects did not report a difference between early and late scans. To examine the effect of the duration of stimulation specifically, 8 of these subjects rated the perceived intensity of each of 20 sequential 5-s duration contact heat stimuli (40 or 50 degrees C; 100 s of stimulation). We used a graphical method to detect changes in perceived unpleasantness. There was no difference in perceived intensity or unpleasantness during the 40 degrees C stimulation. However, during 50 degrees C stimulation, perceived unpleasantness increased and subjects perceived the last five, but not the second five, stimuli as more intense than the first five stimuli. These psychophysical changes could be mediated by brain structures with increasing activity from early to late PET scans or that are active only during late scans. These structures include the contralateral M1/S1 cortex, bilateral S2 and mid-insular cortex, contralateral VP thalamus, medial ipsilateral thalamus, and the vermis and paravermis of the cerebellum. Structures that are equally active throughout stimulation (contralateral mid-anterior cingulate and premotor cortex) are less likely to mediate these psychophysical changes. Some cortical, but not subcortical, structures showed significant or borderline activation only during the early scans (ipsilateral premotor cortex, contralateral perigenual anterior cingulate, lateral prefrontal, and anterior insular cortex); they may mediate pain-related attentive or anticipatory functions. Overall, the results reveal that 1) the pattern of brain activation and the perception of heat pain both change during repetitive noxious heat stimulation, 2) cortical activity can be detected before subcortical responses appear, and 3) timing the stimulation with respect to the scan period can, together with psychophysical measurements, identify brain structures that are likely to participate in the perception of pain.

A 256/spl times/256 pixel smart CMOS image sensor for line-based stereo vision applications

This paper presents a 256/spl times/256 pixel smart CMOS image sensor for line based vision applications. By combining the edge-based analog processing technique with an active pixel array, a dense and fast on-chip analog image processing has been achieved. The on-chip processing unit includes (1) an analog histogram equalizer, (2) a programmable recursive Gaussian filter, (3) a spatio-temporal differentiator, and (4) a local extrema extractor. An electronic shutter is applied to the active pixel sensor array in order to adapt the exposure time as a function of global illumination. The on-chip histogram equalizer extends the image into a constant and optimal range for all the following processing operators and gives a stable and predictable precision of the analog processing. A prototype chip has been designed and fabricated in a standard 0.8-/spl mu/m CMOS process with double poly and double metal, giving a pixel pitch of 20 /spl mu/m and die size of 7/spl times/7 mm/sup 2/. A line processing time is compatible with TV line scan period. The worst case power consumption measures 40 mA at 5 V.

The latitudinal distribution of solar wind magnetic holes

Using the fast latitude scan period of the Ulysses spacecraft, the occurrence of magnetic holes in the solar wind is investigated from −80° to +80° helio‐latitude. Near the ecliptic, the large average value and the large variations of the hole count rate appear to be correlated with interaction regions. It is found, however, that at 30°north and south latitude, approximately, the hole count rate drops to about 10% of that in the low latitude region and stays constant at this level to near the poles. The small but non‐zero hole count rate at high helio‐latitudes indicates that these holes were formed by processes other than the large scale dynamic solar wind features operating in the ecliptic region.

Characterisation of the Advanced Microwave Sounding Unit, AMSU-B

The Advanced Microwave Sounding Unit, AMSU-B, is a five channel microwave radiometer to be flown later this decade on the series of polar orbiting spacecraft NOAA-K, L and M. It will provide global data in support of synoptic weather forecasting by sounding the water vapour content of the atmosphere from the ‘window’ channels at 89 and 150 GHz to the strong resonance line at 183.3 GHz. It has a scan period of 2 2 3 seconds and provides 90 earth view pixels each of nominal beam width 1.1 degrees during earth scan. The key radiometric requirements of the instrument are to provide a temperature sensitivity of 1 to 1.2K depending on channel, a linearity within 0.3 of the temperature sensitivity and a beam efficiency of 95%. This paper describes the design of the AMSU-B, the ground based buy-off tests and results obtained for the Proto-Flight Model (PFM), Flight 2 (FM2) and Flight 3 (FM3) Models in the context of these requirements. The Engineering Model testing is described in reference /1/.

Focused ion beam insulator deposition

Focused ion beam (FIB) induced deposition of insulating films from TEOS, a SiO2 precursor, is reported. Deposition was typically carried out using a 30 kV beam of Ga+ ions with a range of ion beam currents from 40 to 2000 pA. The deposition rate was measured as a function of beam current density into the scanned area and scan period, with a typical rate of 0.3 μm3/nC being noted. An important application of the FIB is to repair integrated circuits enabling faster debugging and shorter design cycles. With the continuing trend toward devices containing more interconnect layers having narrower tracks and spaces, it is becoming increasingly difficult to access lower metal levels when they are completely covered by wide upper tracks. Localized FIB insulator deposition enables contact to lower level metal without first removing large areas of the upper metal layers which would otherwise be required. In such structures isolation resistances of more than 15 GΩ have been measured between the metal layers, corresponding to resistivities greater than 108 Ω cm, with a breakdown voltage for the material in the range of 20 to greater than 100 V/μm.

Anodic stripping voltammetry of selenium(IV) at a gold fiber working electrode

AbstractThe anodic stripping voltammetry of selenium (IV) in a gold fiber electrochemical flow cell is described. The cell is simple to construct and flexible in its operation. The nonlinear diffusional mass transport characteristics of such small diameter electrodes influence the anodic stripping voltammetry of Se(IV) with the result that significant deposition of metal ions occurs during the scan period from the deposition potential to the peak potential. Therefore, an extremely short deposition period of the order of 20 seconds can be employed at the gold fiber electrode. The system described resulted in a linear working range from 0–15 ng/mL, a detection limit of 0.5 ng/mL Se(IV) and a relative standard deviation of 6% at 5 ng/mL (n = 7) in pure solution.

Effects of nonideal input functions on PET measurements of pulmonary blood flow.

Regional pulmonary blood flow (rPBF) can be measured with an intravenous infusion of 15O-labeled water and positron emission tomography (PET). The current method depends on two assumptions related to the input of activity to the lung during the scan: 1) the pulmonary arterial tracer input is constant (i.e., a "step function" in shape), and 2) the scan begins at the instant of arrival of the step function. To determine the effect that departures from these assumptions might have on the measurement of rPBF, we performed a series of mathematical simulations for three different input functions: 1) a step function that arrived either 1 or 2 s before or after scan start; 2) a dispersed input function, with activity rising during the scan period; and 3) a combination of these two errors. Calculated values, based on the standard assumptions, were compared against the "known" values used in generating the simulated data. The results show that timing errors associated with starting the scan late cause an overestimation of rPBF, whereas timing errors due to low regional flow or departures from the assumed step input function both cause an underestimation of true rPBF. Thus, in actual practice, the combined errors probably partially offset one another. Except for states of truly high rPBF and low lung density, the errors remain less than 15% of the true value. We conclude that PET measurements of rPBF are not highly sensitive to these presumably common departures from the assumed pulmonary arterial input function to lung regions of interest.

Diagnostics of the plasma in a high power induction plasmatron by the intensity and broadening of spectral lines

A schematic of the measurement apparatus is depicted in Fig. i. The light flux from the discharge zone, exiting through a quartz window in the discharge tube, passes through lens L1 (FI = 900 mm) with diaphragm D1 (30 mm) placed at a focal length from the center of the plasma jet, and is directed on a scanning Fabry-Perot spectrometer. The radiation passing through the spectrometer is focused by means of lens L2 (F2 = 300 mm) with diaphragm D2 (30 mm) on the entrance slit of a MDP-23 monochromator. The radiation was detected using a PM-62 photomultiplier. The measuring scheme described above records radiation from the entire width of the plasma column, since the construction of the plasmatron does not permit application of an optical design in which the radiation is divided into several local sectors. However, previously completed measurements of the radiation intensity distribution using an Abelian transform procedure showed that the radiation density over the cross section of the plasma jet is virtually constant, having a sharp edge. Therefore, for a significant plasma column width, the contribution of the surface layers to the recorded radiation flux is negligibly small. It was also established that in the plasma under study, self-absorption is not significant. Measurements were made using an interferometer having the following characteristics: base L = 6.4  0.05 mm, reflection coefficient of the mirrors R = 0.86, diameter of the light orifice D = 30 mm. In the 800 nm spectral region these parameters corresponded to a free dispersion ~f.d. = 0.05 nm and a theoretical resolution ~ = 0.0025 nm. Hence, for operating linewidths A% = 0.01-0.02 nm the following relations are fulfilled: A%f.d. = 35 A% and ~% = 0.1-0.2 Ai. In this case, the profile of the spectral line is reliably recorded, optimal conditions being realized for the procedure whereby the true !ineshape is recovered from that observed. Wavelength scanning of the Fabry-Perot interferometer was accomplished using a piezoelectric ceramic support which displaced one of the mirrors by A~ = %/2. Account of factors distorting the line shapes was of critical importance. Distortion due to the time lag of the recorder was removed by the choice of the scan period. The widths of the entrance and exit slits of the monochromator were an order of magnitude less than values for which they would begin to affect the observed spectral contours (SI = $2 =

Kontrastmittel-CT des Mediastinums zur Lymphknotendiagnostik

In mediastinal lymphoadenopathy diagnostic problems arise if lymphomas are of the same density as cardial or vascular structures. For this reason, CT based on contrast enhancement must definitely ensure a significantly greater enhancement of vascular structures than of non-vascular ones during the entire scan period. We studied 4 groups of 20 patients each employing standardised CT examinations employing 100 ml. contrast medium in different concentrations (200 and 300 mg. iodine/ml., respectively) and an injection flow rate of 0.7 and 2.0 ml/s. The results show that higher iodine concentrations produce a significantly greater enhancement in the aorta than a lower iodine concentration independent of the flow rate. Although a lower flow rate slightly delayed the enhancement increase, this was nevertheless higher than 60 HU within a period of 4 minutes. Hence, we recommend to perform contrast enhanced CT of the mediastinum using lower flow rates (0.5-1.0 ml/s.) and a higher contrast medium concentration (300 mg. iodine/ml.).

5. PET検査の技術的問題点 : 脳神経核医学検査の技術的問題点 : 第45回総会シンポジウム

Positron emission tomography (PET) measures quantitative values of physiological and biochemical functions by means of quantitative measurements of tracer concentrations in vivo and sophisticated tracer labeled by positron emitting radioisotopes (^<11>C, ^<13>N, ^<15>O, and ^<18>F). In order to achieve quantitative measurements as a clinical diagnostic tool we should remind several points to maintain data quality in routine PET study as follows: That is, cyclotron and radio-synthesis system should be managed properly, physical characteristics of PET device should be known to convert tracer concentration to physiological functions, maintenance of PET devices should be done properly, and circumstances of subject side should be kept to be comfortable to keep steady positron for rather long scan period.

Interdome interactions in cutaneous type I receptors.

The encoder characteristics of cat, hairy skin, slowly adapting Type I receptors were studied by activating them with 'swept period' grating stimuli. A typical stimulus featured a minimum scan period of 0.3 mm, a maximum scan period of 2.0 mm, and a total of 40 grates. Using these stimuli, single domes could easily encode the temporal frequency (1/period*scan velocity) of a grate, regardless of the scan velocity or direction. Receptors with multiple domes could not encode the temporal frequency of a swept-period stimulus unless the instantaneous grate period matched a receptor's intrinsic ability to encode the stimulus. When this criterion was met, the temporal frequency of the stimulus was encoded in the bursting rate of the receptor's action potential event stream.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Neutral beam line ion beam raster scanning with a dipole magnet

An ion beam raster scanning method utilizing a wide gap dipole magnet has been developed at the Oak Ridge National Laboratory that can reduce the time-averaged amplitude of the ion beam power density on the ion beam dump by factors of 3 to 6. Time-varying in-phase and out-of-phase modulation current components are used in the dipole magnet coils in order to generate a time-varying magnetic field shape and magnitude whose magnetostatic central surface position oscillates between the two magnet iron poles. This time-varying three-dimensional (3-D) magnetic field shape deflects the ion beam onto an ion dump and can be programmed to produce a raster scan pattern that depends on the coil current modulation pattern. The 3-D magnetic field produced by an iron yoke system has been computed for different coil current ratios using a finite-element integral method. Ion orbit equations do not need to include the small space-charge forces present in the beam used for these purposes. The time-averaged amplitude of beam dump power densities should be lowered by a factor of 6 by sharing the beam impact pattern over a larger area with a short raster scan period compared to the ion dump thermal time constant.

Practical aspects involved in the design and set up of a 0.15 T, 6-coil resistive magnet, whole body NMR imaging facility

Many technical and logistical questions must be addressed when planning the installation of an NMR imaging system. These considerations become particularly significant when the facility is being established within an existing medical center complex. This paper presents a report on the practical aspects and experience obtained in siting a 6-coil 0.15 T resistive magnet system. The topics discussed include: floor loading; ferromagnetic environment; the effect of iron on the magnet field strength and homogeneity characteristics; shimming procedures; temperature stability requirements; rf shielding; and effects of the magnetic field on common medical instrumentation and magnetic media. It was found that the field shift as a function of the distance of a steel mass from the center of the magnet exhibited an ( 1 r ) 5.2±0.5 to ( 1 r ) 4.2±0.3 dependence for axial and radial positions respectively which, as expected, is somewhat weaker than the ( 1 r ) 6 dependence expected by point dipole approximations. Field distortions caused by the presence of ferromagnetic material in radial positions may be essentially fully compensated with first order transverse shim coils (most conveniently, the x and y imaging gradient coils could be used). Axially distributed material requires, in addition to first order z-gradient correction, higher order axial shim compensation. The temperature stability of the magnet system over the scan period must be better than 0.2°C to insure that temperature-induced field fluctuations are less than the intrinsic static inhomogeneity: and, ideally, below 0.01°C to reduce these fluctuations to less than those caused by power supply instability.

Microcomputer-Based Performance-Monitoring and Recording System for a Solar Heating System

ABSTRACT A microcomputer-based on-line performance monitoring system was designed and used to monitor and record the performance of solar collectors in a solar heating system. Features of the system included the use of a small single-board computer, a high-level language (BASIC), signal conditioning, digital integration, pulse counting with direct conversion to flow rate or wind speed, incorporation of regression equations and variable sampling and printout rates. Parameters measured were collector inlet temperature, temperature rise across the collector, ambient temperature, insolation, flow rate through the collector, and wind speed. The on-line system printed out integrated values in convenient units each scan period along with the computed efficiency, time of day, and solar time. The procedure that was used to monitor the collector performance could also be used to monitor heat flow to other parts of this or a similar system.

Technical aspects and clinical applications of CT/X, a dynamic CT scanner.

CT/X is an X-ray computed tomographic scanner system designed for research in the clinical applications of rapid sequence scanning. The minimum scan time is 1.5 sec, and up to 18 images of the same cross section can be derived from scans taken over a 30 sec time interval. With this high image rate, the transit of a bolus of iodinated contrast medium can be followed through any cross section of the body. Rapid sequence scanning through a series of contiguous levels can also be performed, and 12 levels can be scanned in less than 50 sec. The short aggregate scan period minimizes the likelihood of interslice patient motion resulting in high quality multiplanar images. To fully exploit this capability, an imaging facility capable of reformatting axial transverse display data into a plane of arbitrary orientation has been incorporated into the system. A computer-electrocardiographic interface is also provided for use in retrospective cardiac gating. The capabilities of the scanner are illustrated with selective clinical studies.

Gated computed tomography of the heart

Since the inception of computed tomography (CT), we have been keenly interested in the possibility of imaging the myocardium in the axial dimension in vivo. Initial efforts at quantitive myocardial imaging were of necessity performed in vitro in the original EMI brain scanner (1). Combined with a study of whole blood in vitro, it became apparent that individuals with a normal hematocrit.would not show a significant difference between the density of the myocardium and blood without the use of a contrast agent. To study the myocardium in vivo would require either an ultrashort scan period (less than S0 msec (2)) or data acquisition at synchronized periods during the heart cycle (gating). With the advent of faster scan cycles in currently available commercial equipment, the initial thrust at in vivo myocardial imaging became possible. The potential advantages of myocardial imaging are numerous and include the ability to differentiate the myocardium from the blood pool which would permit volume analysis, determination of ejection fraction, study of akinesis and dyskinesis, evaluation of ischemic myocardium and, ultimately, the visualization of the lumen of coronary arteries. A noncatheter, low risk technique which could accurately portray the lumina of coronary arteries would be of inestimable public health value. The technologic considerations involved in achieving this task are, however, formidable. The history of scanning of the heart is brief but relevant. The myocardium has been imaged by CT in vivo since the advent of CT body scanning (3). Because early scanners required 60 to 180 traverses and the total scan took from 2 to 7 rain, the image of the myocardium was necessarily one that averaged during multiple cardiac contractions. The chamber wall, blood pool, fat surrounding the myocardium as well as the pericardium, septa and valves were not resolved because of systolic-diastolic motion blurring. The image was further degraded by respiratory motion (2). In addition, artifacts were created by cardiac pulsations transmitted to the high density diaphragm and subjacent structures which interface with the low density lung parenchyma. Clearly, an approach was needed wherein the subject would be apneic and the cardiac structures could be imaged in fractions of a second. Wood (4) and Ritman et al (5) were first to propose a cardiac scanning device with a multiple x-ray tube-detector array to scan the myocardium in fractions of a second. To date, such a device remains theoretically possible; however, it has not been accomplished in the laboratory. In vitro investigations of myocardial perfusion by Adams et al (6) are reported to show minute differences in attenuation coefficients of recently infarcted myocardium. In other experiments, Aifidi et al (2) and Ter-Pogossian et al (7) showed that CT angiocardiography using positive contrast agents was feasible in intact sacrlfi~:ed animals.

The effects of biological motion on CT resolution

A variety of periodic and aperiodic psyiologic motions affect the quality of CT images. This study was initiated to estimate what an optimal scan period should be in the design of CT units. Ultrashort scan periods were experimentally similated in the heart and liver to approximate the parameters of future technology.

Pulsating aurora in high‐latitude satillite photographs

Pulsating aurora has been identified in DMSP photographs. Its unique zebra‐stripe appearance is due to the interaction of the aurora pulsation period with the imaging device's raster scan period. It most commonly, but not exclusively, occurs on the equatorward edge of the auroral oval after midnight and is positively correlated with global magnetic activity. Pulsating aurora also occurs on the poleward leading edge of midnight sector surges.