Polymethyl Methacrylate Thickness Research Articles

Simple Raman scattering sensor integrated with a metallic planar optical waveguide: effective modulation via minor structural adjustment

We report experimental realization of Raman spectra enhancement of copper phthalocyanine, using an on-chip metallic planar waveguide of the sub-millimeter scale. The oscillating ultrahigh order modes excited by the direct coupling method yield high optical intensity at resonance, which is different from the conventional strategy to create localized “hot spots.” The observed excitation efficiency of the Raman signal is significantly enhanced, owing to the high Q factor of the resonant cavity. Furthermore, effective modulation of the Raman intensity is available by adjusting the polymethyl methacrylate (PMMA) thickness in the guiding layer, i.e., by tuning the light–matter interaction length. A large modulation depth is verified through the fact that 10 times variation in the enhancement factor is observed in the experiment as the PMMA thickness varies from 7 to 23 μm.

Calculation of the contrast of the calcification in digital mammography system: Gate validation.

Validation of the Gate tool in digital mammography image simulation from the viewpoint of image quality (contrast of calcifications). The polymethyl methacrylate (PMMA) phantom containing aluminum foils in different thicknesses is used for measuring the contrast of calcifications in a real system. In this research, the phantom and mammography system have been simulated by the Gate tool with the maximum possible details. The contrast of the aluminum foil in simulations and practical method has been compared with each other and the standard errors in the mean (SEM) for various voltages of X-ray tube, aluminum foil, and PMMA thicknesses have been reported. Based on the obtained results, by increasing the X-ray tube voltage from 20 to 39 kVp, the image contrast has been decreased in both simulation and practical methods. The minimum and maximum average SEM of the contrast of the aluminum foils among various voltages between two simulations and practical methods for different PMMA thicknesses of 2, 4, and 6 cm have been reported as 0.0105 and 0.0117, 0.0049 and 0.0154, and 0.0037 and 0.0072, respectively. According to the SEM rate reported in this research for calculating the contrast of the aluminum foils in the mammography system based on simulation and practical methods, the capability of the Gate tool for simulating digital mammography system and the images created in it from the viewpoint of image contrast can be confirmed.

SANTA: Self-aligned nanotrench ablation via Joule heating for probing sub-20 nm devices

Manipulating materials at the nanometer scale is challenging, particularly if alignment with nanoscale electrodes is desired. Here we describe a lithography-free, self-aligned nanotrench ablation (SANTA) technique to create nanoscale trenches in a polymer like poly(methyl) methacrylate (PMMA). The nanotrenches are self-aligned with carbon nanotube (CNT) and graphene ribbon electrodes through a simple Joule heating process. Using simulations and experiments we investigate how the Joule power, ambient temperature, PMMA thickness, and substrate properties can improve the spatial resolution of this technique. We achieve sub-20 nm nanotrenches for the first time, by lowering the ambient temperature and reducing the PMMA thickness. We also demonstrate a functioning nanoscale resistive memory (RRAM) bit self-aligned with a CNT control device, achieved through the SANTA approach. This technique provides an elegant and inexpensive method to probe nanoscale devices using self-aligned electrodes, without the use of conventional alignment or lithography steps.

Patient and staff doses in paediatric interventional cardiology derived from experimental measurements with phantoms

The aim of this paper was to determine experimentally the entrance surface air kerma (ESAK) and kerma-area product (KAP) levels to patients and scatter doses at the cardiologist's eyes during paediatric interventional cardiology (IC) procedures for Chile, on the basis of measurements taken from X-ray systems characterization for different thicknesses of polymethyl methacrylate, together with the average values of fluoroscopy time and number of cine frames for ten paediatric IC procedures. The range of cumulative ESAK values when the different clinical procedures were simulated was from 2 to 1100 mGy. KAP values ranged from 0.30 to 150 Gy cm2. Scatter doses at cardiologist's eyes for the simulated procedures ranged from 0.20 to 116 µSv per procedure. Large differences between the X-ray systems were found in our study. Standardized guidelines in terms of X-ray system setting and protocols should be developed for hospitals that perform paediatric IC procedures in Chile.

Effects of AFM tip-based direct and vibration assisted scratching methods on nanogrooves fabrication on a polymer resist

This study proposes two atomic force microscope (AFM) tip-based direct nanoscratching methods including single-pass scratching and multi-pass scratching compared with a vibration-assisted scratching method to fabricate nano-grooves on the surface of the polymethylmethacrylate (PMMA) thin-film resist. In order to protect the AFM tip from wearing and optimize the subsequent etching process, the machined depth is expected slightly less than the PMMA thickness to prevent the tip directly contacting with the silicon substrate and obtain better process results. First, single-pass scratching tests are performed on films with different thickness employing varied normal loads. Results show that the machined depths of the grooves cannot be obtained slightly less than the thickness of the film very easily when scratching with single-pass method, 50–120nm in the present study, which may not be very suitable for the following etching process. Multi-pass and vibration-assisted methods are then utilized to solve this limitation of the machined depth in single-pass process. The machined depths using the multi-pass method are dependent on scratching times and the applied normal loads. Moreover, the depth closed to the thickness of the film can be obtained by enlarging the number of the scratching cycles. However, with a longer scratching time, large tip wear can be found. For vibration assisted method, the machined depths are controlled by the vibration amplitude and the applied normal load. With the vibration in z direction increasing, the machined depth can be enlarged comparing with the single-pass, which makes the fabrication process be feasible. In addition, the vibration-assisted method contributes to less tip wear during the machining process.

Mean glandular dose in six digital mammography services in Santiago, Chile: preliminary reference levels.

The purpose of this paper was to estimate mean glandular dose levels (DG) in six digital mammography systems in Santiago, Chile, and to propose preliminary reference levels to execute mammography in Chile. The study was carried out assessing two direct digital systems and four computer-based radiography (CR) systems. Estimates of DG were calculated for different thicknesses of polymethyl methacrylate according to the quality control protocol in digital mammography of the Spanish Society of Medical Physics and NHSBSP Equipment Report 0604 Version 3. DG values ranged between 0.64 and 7.26 mGy for a range of 20- to 70-mm thickness, respectively. Thirty-six per cent of DG was higher than the acceptable dose level and 100 % of DG was higher than the desirable level. It is therefore necessary to optimise doses. The initial proposal to establish dose reference levels for DG would range between 0.90 and 6.40 mGy for a thickness range of 20 to 70 mm.

Image simulation and a model of noise power spectra across a range of mammographic beam qualities

The aim of this work is to create a model to predict the noise power spectra (NPS) for a range of mammographic radiographic factors. The noise model was necessary to degrade images acquired on one system to match the image quality of different systems for a range of beam qualities. Five detectors and x-ray systems [Hologic Selenia (ASEh), Carestream computed radiography CR900 (CRc), GE Essential (CSI), Carestream NIP (NIPc), and Siemens Inspiration (ASEs)] were characterized for this study. The signal transfer property was measured as the pixel value against absorbed energy per unit area (E) at a reference beam quality of 28 kV, Mo/Mo or 29 kV, W/Rh with 45 mm polymethyl methacrylate (PMMA) at the tube head. The contributions of the three noise sources (electronic, quantum, and structure) to the NPS were calculated by fitting a quadratic at each spatial frequency of the NPS against E. A quantum noise correction factor which was dependent on beam quality was quantified using a set of images acquired over a range of radiographic factors with different thicknesses of PMMA. The noise model was tested for images acquired at 26 kV, Mo/Mo with 20 mm PMMA and 34 kV, Mo/Rh with 70 mm PMMA for three detectors (ASEh, CRc, and CSI) over a range of exposures. The NPS were modeled with and without the noise correction factor and compared with the measured NPS. A previous method for adapting an image to appear as if acquired on a different system was modified to allow the reference beam quality to be different from the beam quality of the image. The method was validated by adapting the ASEh flat field images with two thicknesses of PMMA (20 and 70 mm) to appear with the imaging characteristics of the CSI and CRc systems. The quantum noise correction factor rises with higher beam qualities, except for CR systems at high spatial frequencies, where a flat response was found against mean photon energy. This is due to the dominance of secondary quantum noise in CR. The use of the quantum noise correction factor reduced the difference from the model to the real NPS to generally within 4%. The use of the quantum noise correction improved the conversion of ASEh image to CRc image but had no difference for the conversion to CSI images. A practical method for estimating the NPS at any dose and over a range of beam qualities for mammography has been demonstrated. The noise model was incorporated into a methodology for converting an image to appear as if acquired on a different detector. The method can now be extended to work for a wide range of beam qualities and can be applied to the conversion of mammograms.

Control of the distribution of surface plasmon local field by altering the surrounding material

The field distribution of the surface plasmon (SP) around a silver nanowire greatly influences its applications for both spectrum enhancement and nano-waveguide. This paper demonstrates the change of the SP local field distribution of a silver nanowire on glass substrate with the refractive index of the covering medium by numerical simulation. The hot energy site is observed focusing on the interface between the nanowire and the surround material of larger refractive index. Moreover, we also find that the surface plasmon field becomes more confined as the refractive index between the substrate and medium has a larger gap, while a homogeneous distribution of the surrounding dielectric material around the nanowire shows a uniform local field distribution with a larger surface plasmon propagation length. The change of related parameters, such as effective index, mode area, and propagation length are also comprehensively investigated against the refractive index for nanowires with 100, 200, 300nm diameter. Considering the wide use of polymethyl methacrylate (PMMA) material, the field distribution of silver nanowire partially imbedded in PMMA against the PMMA thickness is also studied.

Effect of Optical Properties Characteristic Polymethylmethacrylate Using UV Laser Direct-Structuring

Polymethylmethacrylate (PMMA) material has excellent characteristics, such as being light weight, low cost, ease of machining, and optical quality, which are useful in numerous applications such as backlit LCD display panels, lens optics, and other photoelectric fields. Laser machining of polymerization material results in a superior machining quality, high accuracy, high speed, and high reproducibility, produces a small variety of products, reduces mold costs, and enables the rapid manufacture of products based on complex graphics by processing different depths and widths of the 3D structure. This paper presents the fabrication of symmetrical array microstructures on PMMA material by using a UV laser system. The PMMA material dimensions and thickness were 20 x 20 mm and 1 mm, respectively. Regarding the machining quality, the laser pulse energy, pulse repetition frequency, and fill spacing were adjusted. For the experiments, a semiconductor laser source (635 nm/5 mW/TEM00) and a beam profiler were used to measure the characteristics of a laser beam passing through the microstructures. The microstructure pitches and morphologies also affected the light uniformity. After laser machining, the surface morphology and the light transmittance were measured using a spectrophotometer.

Validation of simulation of calcifications for observer studies in digital mammography

Studies using simulated calcifications can be performed to measure the effect of different imaging factors on calcification detection in digital mammography. The simulated calcifications must be inserted into clinical images with realistic contrast and sharpness. MoCa is a program which modifies the contrast and sharpness of simulated calcification clusters extracted from images of mastectomy specimens acquired on a digital specimen cabinet at high magnification for insertion into clinical mammography images. This work determines whether the use of MoCa results in simulated calcifications with the correct contrast and sharpness. Aluminium foils (thickness 0.1–0.4 mm) and 1.60 µm thick gold discs (diameter 0.13–0.8 mm) on 0.5 mm aluminium were imaged with a range of thicknesses of polymethyl methacrylate (PMMA) using an amorphous selenium direct digital (DR) system and a powder phosphor computed radiography (CR) system (real images). Simulated images of the tests objects were also generated using MoCa. The contrast of the aluminium squares and the degradation of the contrast of the gold discs as a function of disc diameter were compared in the real and simulated images. The average ratios of the simulated-to-real aluminium contrasts over all aluminium and PMMA thicknesses were 1.03±0.04 (two standard errors in the mean) and 0.99±0.03 for the DR and CR systems, respectively. The ratio of the simulated-to-real degradations of contrast averaged over all disc diameters and PMMA thicknesses were 1.007±0.008 and 1.002±0.013 for DR and CR, respectively. The use of MoCa was accurate within the experimental errors.

Evaluation of patient doses and lens radiation doses to interventional cardiologists in a nationwide survey in Chile

The objective of this study was to perform a nationwide survey in Chile to determine dose levels to patients and staff in four risk scenarios during cardiac catheterisation procedures. Different phantom thicknesses of polymethyl methacrylate (PMMA) were used to simulate adult patients. Scenario 1: 10-min fluoroscopy and 800 cine frames for 20 cm of PMMA; Scenario 2: 10-min fluoroscopy and 800 cine frames for 28 cm of PMMA; Scenario 3: 30-min fluoroscopy and 2400 cine frames for 20 cm of PMMA; Scenario 4: 30-min fluoroscopy and 2400 cine frames for 28 cm of PMMA. The average values regarding dose-area product and scattered doses at the cardiologist eye lens achieved for the four scenarios were 94, 249, 281, 747 Gy cm(2) and 0.3, 0.8, 0.9 and 2.5 mSv, respectively. Large variations in radiation doses received by both patients and staff for the same type of procedure suggest that optimising procedure protocols and using the most effective types of protective devices may substantially reduce the dose values found here.

Where should we measure the entrance air kerma rate during acceptance testing of the automatic dose control of a fluoroscopic system?

In Japan, the entrance air kerma rate (EAKR) to a patient cannot exceed 50 mGy/min in conventional fluoroscopy. However, it is unclear where the EAKR should be measured. We obtained the tube potential and tube current as a function of polymethylmethacrylate (PMMA) thickness, and the EAKR at the interventional reference point (IRP) was measured from the trajectory. The EAKR at the point established by the U.S. Food and Drug Administration (FDA) was calculated from EAKR at the IRP. The EAKR at the IRP exceeded the limit at a PMMA thickness of 22-28 cm. However, the EAKR did not exceed the limit at the FDA point. If the EAKR to a patient is being verified to meet the recent Japanese ruling, the EAKR should be measured at the FDA point, and if the EAKR is being evaluated for determination of the skin dose, it should be monitored at the IRP.

A study to determine the differences between the displayed dose values for two full-field digitalmammography units and values calculated using a range of Monte-Carlo-based techniques:a phantom study

Modern full-field digital mammography (FFDM) units display the mean glandular dose (MGD) and the entrance or incident air kerma (K) to the breast following each exposure. Information on how these values are calculated is limited and knowing how displayed MGD values compare and correlate to conventional Monte-Carlo-based methods is useful. From measurements done on polymethyl methacrylate (PMMA) phantoms, it has been shown that displayed and calculated MGD values are similar for thin to medium thicknesses and appear to differ with larger PMMA thicknesses. As a result, a multiple linear regression analysis on the data was performed to generate models by which displayed MGD values on the two FFDM units included in the study may be converted to the Monte-Carlo values calculated by conventional methods. These models should be a useful tool for medical physicists requiring MGD data from FFDM units included in this paper and should reduce the survey time spent on dose calculations.

Effects of breast thickness and lesion location on resolution in digital magnification mammography

This study aimed to examine the resolution effects of breast thickness and lesion location in magnification mammography by evaluating generalized modulation transfer function (GMTF) including the effect of focal spot, effective pixel size, and the scatter. Polymethyl methacrylate (PMMA) thicknesses ranging from 10 to 40 mm were placed on a standard supporting platform that was positioned to achieve magnification factors ranging from 1.2 to 2.0.As the magnification increased, the focal spot MTF degraded, while the detector MTF improved. The GMTF depended on the trade-off between the focal spot size and effective pixel size. Breast thickness and lesion location had little effect on the resolution at high frequencies. The resolution of small focal spot did improve slightly with increasing PMMA thickness for magnification factors less than 1.8. In contrast, system resolution decreased with increasing PMMA thickness for magnification factors greater than 1.8 since focal spot blur begins to dominate spatial resolution. In particular, breast thickness had a large effect on the resolution at lower frequencies. A low-frequency drop effect increased with increasing PMMA thickness because of the increase in scatter fraction. Hence, the effect of compressed breast thickness should be considered for the standard magnification factor of 1.8 that is most commonly used in clinical practice. Our results should provide insights for determining optimum magnification in clinical application of digital mammography, and our approaches can be extended to a wide diversity of radiological imaging systems.

Evaluating phantom image quality parameters to optimise patient radiation dose in dental digital radiology

Our objective was to obtain images of a predictable level of quality using an intraoral X-ray system with digital imaging, avoiding patient overexposure. A polymethylmethacrylate (PMMA) physical test phantom was imaged at different exposure times and at various PMMA thicknesses using a dental imaging coupled charge device. Two identical regions of interest (ROIs) were chosen in every image file, and quality was numerically evaluated by measuring high-contrast spatial resolutions, low-contrast thresholds and signal-to-noise ratios. In addition, three practitioners proposed personal quality scores by image inspection. Numerical contents in the ROIs, related to the image quality, were plotted against exposure time. From here, a simple expression linking the exposure time with the thickness to obtain images of comparable quality was deduced. As a result, the optimum exposure time for imaging with a predictable level of quality can be inferred. The potential effect could imply savings above 1000 man Sv, roughly 20 % of the collective dose due to dental imaging, over a population of 1540 millions.

Determination of equivalent breast phantoms for different age groups of Taiwanese women: An experimental approach

Polymethylmethacrylate (PMMA) slab is one of the mostly used phantoms for studying breast dosimetry in mammography. The purpose of this study was to evaluate the equivalence between exposure factors acquired from PMMA slabs and patient cases of different age groups of Taiwanese women in mammography. This study included 3910 craniocaudal screen/film mammograms on Taiwanese women acquired on one mammographic unit. The tube loading, compressed breast thickness (CBT), compression force, tube voltage, and target/filter combination for each mammogram were collected for all patients. The glandularity and the equivalent thickness of PMMA were determined for each breast using the exposure factors of the breast in combination with experimental measurements from breast-tissue-equivalent attenuation slabs. Equivalent thicknesses of PMMA to the breasts of Taiwanese women were then estimated. The average +/- standard deviation CBT and breast glandularity in this study were 4.2 +/- 1.0 cm and 54% +/- 23%, respectively. The average equivalent PMMA thickness was 4.0 +/- 0.7 cm. PMMA slabs producing equivalent exposure factors as in the breasts of Taiwanese women were determined for the age groups 30-49 yr and 50-69 yr. For the 4-cm PMMA slab, the CBT and glandularity values of the equivalent breast were 4.1 cm and 65%, respectively, for the age group 30-49 yr and 4.4 cm and 44%, respectively, for the age group 50-69 yr. The average thickness of PMMA slabs producing the same exposure factors as observed in a large group of Taiwanese women is less than that reported for American women. The results from this study can provide useful information for determining a suitable thickness of PMMA for mammographic dose survey in Taiwan. The equivalence of PMMA slabs and the breasts of Taiwanese women is provided to allow average glandular dose assessment in clinical practice.

Radiation dose and image quality for paediatric interventional cardiology systems. A national survey in Chile

Radiation dose and image quality for paediatric protocols in all five X-ray fluoroscopy systems used for interventional cardiology procedures existing in Chile have been evaluated. Entrance surface air kerma (ESAK) and image quality using a test object (TO) and polymethyl methacrylate (PMMA) phantoms have been measured for the typical paediatric patient thicknesses (4-16 cm of PMMA). Images from fluoroscopy (low (FL), medium and high) and cine (CI) modes have been archived in DICOM format. Signal-to-noise ratio (SNR), figure of merit (FOM) and high-contrast spatial resolution (HCSR) have been computed from the images. The ratio between the maximum and the minimum value of ESAK per frame for a given fluoroscopy mode between the five systems ranges from 2 to 5 and from 14 to 38 for CI mode. SNR, FOM and HCSR showed a great variability for the different acquisition modes (AMs) and PMMA thickness. In the near future, it is urgent to upgrade Chilean legislation on radiation protection to incorporate quality assurance programmes that will allow us to evaluate and optimise the X-ray systems used in medical applications. Increments in doses per frame when increasing phantom thickness and when used CI runs instead of FL runs can be considered by the cardiologist in the good management of patient dose and allow them to select the best imaging AM during clinical procedures.

Temperature elevation during simulated polymethylmethacrylate (PMMA) cranioplasty in a cadaver model

The aims of this study were to: (i) obtain temperature measurements during in vitro polymerisation of polymethylmethacrylate (PMMA) disks of a range of thicknesses; and (ii) obtain tissue temperature measurements at various locations within a skull defect during a simulated PMMA cranioplasty procedure using a cadaver. In vitro, higher temperatures were recorded with increasing PMMA thickness. During the simulated cranioplasty, the maximum temperature was observed inside the PMMA sample, with nearby tissues being exposed to temperatures of greater than 50 °C over prolonged periods. There is conflicting information in the literature concerning the sensitivity of brain tissue and bone to elevated temperatures. Preoperatively fabricated PMMA cranioplasty prostheses are recommended.

Further factors for the estimation of mean glandular dose using the United Kingdom, European and IAEA breast dosimetry protocols

The United Kingdom, European and IAEA protocols for breast dosimetry in mammography make use of s-factors which allow for the use of different target/filter combinations. To supplement the existing protocols, a Monte Carlo computer program has been used to calculate s-factors for mammography using a tungsten target with silver filters of thicknesses 50–75 µm and for the same target filtered with 0.5 mm aluminium. The dosimetry protocols use slabs of polymethyl methacrylate (PMMA) of specified thicknesses to simulate the exposure of typical breasts. The equivalent thickness of PMMA has been calculated using a simplified approach for a wider range of x-ray spectra and for breast thicknesses of 2–11 cm. The results show that for the tungsten/silver target/filter combination, a single s-factor of 1.042 can be used with the protocols, but when the tungsten target is filtered with 0.5 mm of aluminium, it is necessary to select from a tabulation of s-factors against breast thickness. The equivalent thicknesses of PMMA for a given breast thickness show some dependence on beam quality and the values obtained differ from those presently used in the dosimetry protocols by an amount which depends upon breast thickness and half value layer (HVL). For the extreme case of an 11 cm breast and an HVL of 0.62 mm Al, the use of the protocol thickness would give rise to an error of 10%, but for breast thicknesses of 6 cm or less, the error is typically 2–3%.

Criteria to optimise a dynamic flat detector system used for interventional radiology

An analysis of the relationship between image quality and incident air kerma has been carried out for a dynamic flat detector X-ray system used for interventional radiology. A phantom of polymethyl methacrylate (PMMA) to simulate patients and two different image test objects, Leeds TOR 18FG and NEMA XR 21, were used to evaluate the quality of the obtained images. Measurements were made simulating clinical configuration with different PMMA thicknesses (16, 20, 24 and 28 cm), available fields of view of 22, 31, 42 and 48 cm (diagonal dimension), in the three default fluoroscopy modes and in one of the most used digital subtraction angiography image acquisition modes. The obtained results are being used to help in the optimisation of clinical procedures.