Scan Pitch Research Articles

Optimization of multidetector array CT acquisition parameters for CT colonography.

Multidetector array computed tomography technology has increased the number of acquisition parameters that a user must select. This article examines the criteria by which detector collimation, reconstructed scan width, reconstruction scan interval, pitch, image noise, and patient dose can be optimized. A water phantom containing tissue-equivalent polyps in an air-filled tube was scanned using multiple acquisition parameter combinations. X-ray tube current was changed to independently match dose and noise to a single-detector array technique. Images were assessed in axial and three-dimensional formats. All polyps were visible in axial and three-dimensional images for all scans. Helical artifacts were noted at higher table speed values. The 5-mm-wide scans spaced at 3-mm intervals allowed visualization of the smallest polyps: 5 x 5 or 7 x 3 (diameter x height; mm). Our results indicate that thin-scan and low-noise techniques need not be used to visualize polyps of clinically relevant sizes.

Study of curing characteristicsof photopolymer used in solid laser diode plotter rapid prototyping system

For most rapid prototyping (RP) systems, stereolithography processes employ UV or diode pumped, solid state lasers to cure the associated photopolymer to build three-dimensional parts. However, such types of lasers are relatively expensive. Therefore a semiconductor laser has been used in the solid laser diode plotter RP system to cure a specific photopolymer DF2000.The DF2000 photopolymer is formulated from a base resin, hardening agent, and powder. The wavelength of the semiconductor laser used in the solid laser diode system is 680 nm and is in the red light range. In this research, the curing level of most of the visible wavelength spectrum generated by a lamp on the DF2000 photopolymer is investigated, using differential scanning photocalorimetry (DSPC). The DSPC results indicate that the curing effect of the photopolymer using blue light is better than that using red light. The results also show that the shorter the wavelength, the better the curing effect of the photopolymer. Hence, a blue semiconductor laser (405 nm) or a shorter wavelength laser, can be used instead of a red laser to increase the curing level of the photopolymer used in the SLP system. The quantitative effect of the SLP processing parameters on the curing level of the DF2000 photopolymer and the mechanical properties of the SLP test specimen were studied using the Taguchi method. The results show that the mechanical properties of a fabricated part are proportional to the degree of cure of the photopolymer. The results also indicate that the scanning pitch of the processing parameters is the most sensitive parameter of the SLP system to affect the curing level. Hence the curing characteristics of the photopolymer used in the SLP system can be used as an index of the mechanical properties of the fabricated part. In addition, using a shorter wavelength laser rather than a red laser can further improve the mechanical properties and fabrication speed of the part.

Characterization of artifact simulating aortic dissection in computed tomography imaging.

An artifact simulating aortic dissection has been seen in computed tomography (CT) and reported in numerous journals. The purpose of this study is to determine the origin. A phantom was constructed to simulate the motion of the ascending aorta during the cardiac cycle. Technique factors such as scan time, slice thickness, pitch, and reconstruction algorithms were examined for their effect on the simulated dissection appearance. Change in the angle of the simulated aorta with respect to the scanner axis was also studied. CT images displaying the simulated aortic dissection are obtained reproducibly. The amplitude of the artifact is more pronounced for increased scan time. The artifact amplitude is proportional to the displacement of the phantom. The simulated aortic dissection seems to be more pronounced when the scan time is comparable to the cycling time of aortic motion.

Curing Characteristics of the Photopolymer Used in the Solid Laser-Diode Plotter RP System

Most stereolithography (SL) processes employ ultraviolet (UV) or diode pumped solid state lasers to cure the associated photopolymer to build a 3D part. A UV or diode pumped solid state laser is more expensive in initial cost and maintenance than a semiconductor laser. A semiconductor laser is used in the solid laser-diode plotter (SLP) rapid prototyping system to cure a specific photopolymer (DF2000). The DF2000 photopolymer is formulated from a based resin, hardening agent, and powder. The wavelength of the semiconductor laser used in the SLP system is 680 nm and is in the range of red colour light. In this work, the curing effect of the visible wavelength spectrums generated by a lamp on the DF2000 photopolymer was investigated, using differential scanning photo calorimetry (DSPC). The DSPC result indicates that the curing degree of the photopolymer using blue light is better than that when using red light. The result also seems showing that the shorter the wavelength, the better the curing effect of the photopolymer. Hence, a blue semiconductor laser (405 nm) or a shorter wavelength laser or even a higher-power lamp, instead of a red laser, can be employed to increase the curing degree of the photopolymer used in the SLP system, The quantitative effect of the SLP processing parameters on the curing degree of DF2000 photopolymer and the mechanical property of the SLP test specimen was studied using the Taguchi method. The results show that the mechanical property of a fabricated part is proportional to the curing degree of the photopolymer. The results also indicate that the scanning pitch of processing parameters is the most sensitive parameter of the SLP system affecting the curing degree and, hence, also affecting the mechanical property. Therefore, the curing characteristics of the photopolymer used in SLP system could be used as an index of the mechanical property of a fabricated part. Also, the employment of a shorter wavelength laser rather than red laser can further improve the part mechanical property and fabrication speed of the part.

3D-CT画像における形状の歪みについて : 再構成関数の影響

Three-dimensional computed tomography is distorted in the Z-direction because of the partial volume effect. This distortion depends on slice width, helical scanning pitch, interpolation, reconstruction function, and reconstruction interval. We studies the effect of the reconstruction function on distortion by scanning high- and low-contrast phantoms in which an acrylic ball was set on expandable polystyrene in Japanese isinglass. We found that, if the acrylic ball was larger than the slice width, a three-dimensional image could be reconstructed without distortion by setting the threshold between the acrylic ball's CT numbers and the CT numbers of the acrylic ball's surroundings(air or Japanese isinglass). The image was not dependent on the reconstruction function. However, the three-dimensional size of the acrylic ball was smaller than the ball's actual size. Further, with the reconstruction function in which the edge was emphasized, distortion and the change caused by the threshold were larger than with the normal reconstruction function. This was because the style of the profile curve on the axial-transverse direction(X-Y direction)was affected by emphasizing the edge.

Performances of Novel Nozzle-Scan Coating Method

A novel dispenser-nozzle-scan coating (NS-coating) method was developed. NS-coating is very useful for reducing the coated volume and its cost. This method has two stages. The first stage is to form a fluid film on the substrate. The second stage is the vacuum drying process to evaporate the solvent with agitation to improve the thickness uniformity. In the first stage, one of the most important parameters of NS-coating is the relationship of the contact angle of the fluid film on the substrate surface to the scan pitch of the dispenser nozzle. The start and end positions of dispensation are also important in terms of avoiding projection. With selecting the solvent of a resist solution on the anti-reflection-layer (ARL) surface and optimizing the start and end positions of dispensation, the thickness uniformity of less than 2% was obtained in the solid state.

Directivity analysis of ultrasonic waves on surface defects using a visualization method

Ultrasonic testing uses the directivity of the ultrasonic wave, which propagates in one direction. The directivity is expressed as the relationship between the propagation direction and its sound pressure. The directivity of an ultrasonic wave is related to the choice of probe arrangement, testing sensitivity and scanning pitch, and correct measurement of defect size and location. This paper investigated the directivity of ultrasonic waves, which are scattered from a slit defect located in simulated butt weld joint using a visualization method. When the defect size was smaller than the wavelengths, clear directivity in the reflected wave was observed. When the ratio of defect size to wavelength is greater than 1.5, measured directivities almost agree with the theoretical directivity. The directivity of shear waves scattered from the slit defect varied according to probe direction (Far defect, Near defect). The angle of reflection wave became similar to angle of incidence as the height of excess metal in welded joint increased.

Dynamic error characteristics of touch trigger probes fitted to coordinate measuring machines

This paper discusses the dynamic error characteristics of touch trigger probes used with coordinate measuring machines. During the investigation, a number of important parameters have been identified, including measurement speed, probe longitude, approach distance, probe latitude, stylus length/stylus tip diameter, probe orientation, operating mode (scanning and nonscanning), scan pitch, preload spring force (gauging force), probe type, and the surface approach angle. This paper presents the detailed experimental design and the results obtained from the systematic experiments. These results have led to some useful recommendations for the reduction of the probe dynamic errors. Some of these recommendations included the selection of the optimum measurement speed, the setting of the preload spring force, and the choice of the probe type.

Ramp test objects for slice sensitivity profile measurement in spiral CT.

Spiral CT is increasingly becoming a routine imaging technique in the UK. The ability to scan whole organs within a single breath-hold often demands that the scan pitch (ratio of the patient translation distance per tube rotation (d) to the collimated slice thickness) be increased within technically acceptable limits. It is known that the full width at half maximum height (FWHM) of the slice sensitivity profile (SSP), degrades with increasing scan pitch and also varies with interpolation algorithm. Published literature frequently reports values for FWHM of the SSP for spiral acquisitions which have been measured with a ramp test tool. However, it has previously been shown that a ramp is inappropriate for SSP measurements in spiral CT. This is because of the physical basis of the premise for this measurement and the large artefacts generated by the application of the interpolation algorithm to the ramp spiral projection data. We present experimental evidence confirming the unsuitability of the ramp test tool in spiral CT. A cyclical variation (d/2) of the data is demonstrated; the magnitude of the measured SSP being dependent upon scan pitch and the interpolation algorithm used, as well as on the longitudinal position of the reconstruction plane.

An investigation of the experimental conditions and characteristics of a nano-wear test

A point contact microscope (PCM) is used to conduct nano-wear tests that can characterize the wear durability of ultra thin films (5 nm-1000 nm) and micromachine parts. The test procedures are described in detail. The descriptive characterization parameters are defined as wear depth or critical wear cycle. The test has nanometer and nano-Newton resolution with good repeatability, and it is able to evaluate the tribological properties of thin films without the outside influence of geometry or distortion effects from the substrate. Nano-wear tests on a gold (Au) film show that the experimental conditions, including loading force, number of scan cycles, scan speed, scan pitch and tip type have significant influence on the test results. Therefore, this method is a relative characterization method, i.e. it is useful for comparing the relative wear durability of different materials under the same test conditions.

CdTe semiconductor X-ray imaging sensor and energy subtraction method using X-ray energy information

A multichannel X-ray imaging sensor using a CdTe compound semiconductor radiation detector was developed. Both the digital X-ray imaging and energy-information-generating analyzing method were studied. The X-ray imaging sensor consisted of 512-channel CdTe detector elements at a pitch of 0.2 mm. X-ray photons were directly detected using a photon-counting method and high- and low-energy images were obtained simultaneously. The specific resolution was obtained over 2.5 line pairs/mm in the channel direction and 1.6 line pairs/mm in the scanning direction with a scanning pitch of 0.2 mm. The energy subtraction method was found to be effective in distinguishing an object's component materials.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Ultrasonic inspection for long defects in thick steel components

A model calculation is presented to demonstrate that very long defects should play a negligible role in the assessment of the failure of pressure vessels of pressurised water reactors. The calculations are of the probability that very long defects could remain in the vessel undetected if ultrasonic inspection of the vessel is undertaken with 45° shear-wave pulse-echo and Tandem techniques to a standard at least as good as achieved in the PISC round robin trials. The probability calculated is that of incorrectly accepting referable defects, and hence is relevant to probabilistic analysis of pressure vessel failure. It is, therefore, correctly more conservative than functions concerned with the capability of ultrasonic detection only, since the aim is to provide results which are pessimistic estimates of the failure frequency. A full probabilistic fracture mechanics assessment is not made since we show that the chance of incorrectly accepting a very long defect ( 12 mm × 80 mm ) in a plate 219 mm thick would be about 10 −4 or less provided an ultrasonic scan pitch of 10 mm or less is used and the estimate of ultrasonic reliability is taken to be that due to team-to-team variation. However, this value is believed to lie below that determined by other considerations, such as human error. We conclude that the chance of accepting unacceptable, very long, defects is limited by these other sources of error. Hence the contribution of very long defects to pressure vessel failure will be very small.

磁気プリンタにおけるマルチヘッド記録

This paper describes a new multiple-channel head and a scanning method using the head in the magnetic printer.The head records spaced multiple lines each rotation of the magnetic drum and moves along the axial direction of the drum. The head has multiple channels with different track widths. The track widths of the preceding channels are wider than those of the succeeding channels. The latent images of the preceding channels are partly overlapped by the succeeding channels, whereby a high quality copy having a solid black is realized. A formula is presented which determines the track pitch of the head according to the number of channels and the scanning pitch. From experiments we found that the track width of the last succeeding channel should be set to be about 10 micrometers narrower than the desired toner image width.

Quantitative Evaluation of Proximity Effect in Raster-Scan Exposure System for Electron-Beam Lithography

The proximity effect in a raster-scan for electron-beam lithography system was evaluated by Monte Carlo calculation and verified by experiments. It was revealed that the reduction in the beam diameter below the scanning pitch, which links into the shortening of drawing time, is more effective in decreasing the proximity effect than the reduction in the resist thickness. From the calculated results, it was found that the error in Iinewidth definition due to the proximity effect was less than 10 percent at a linewidth of 1.5/spl mu/ m with scanning pitch of 0.5 /spl mu/m, beam diameter of 0.2 /spl mu/m, and PMMA resist of 1.0-/spl mu/m thickness.

Quantitative evaluation of proximity effect in raster-scan exposure system for electron-beam lithography

The proximity effect in a raster-scan for electron-beam lithography system was evaluated by Monte Carlo calculation and verified by experiments. It was revealed that the reduction in the beam diameter below the scanning pitch, which links into the shortening of drawing time, is more effective in decreasing the proximity effect than the reduction in the resist thickness. From the calculated results, it was found that the error in linewidth definition due to the proximity effect was less than 10 percent at a linewidth of 1.5 µm with scanning pitch of 0.5 µm, beam diameter of 0.2 µm, and PMMA resist of 1.0-µm thickness.