Scanner Response Research Articles

Application of a color scanner for (60)Co high dose rate brachytherapy dosimetry with EBT radiochromic film.

Background.The aim of this study is to evaluate the performance of a color scanner as a radiochromic film reader in two dimensional dosimetry around a high dose rate brachytherapy source.Materials and methodsA Microtek ScanMaker 1000XL film scanner was utilized for the measurement of dose distribution around a high dose rate GZP6 60Co brachytherapy source with GafChromic® EBT radiochromic films. In these investigations, the non-uniformity of the film and scanner response, combined, as well as the films sensitivity to scanner’s light source was evaluated using multiple samples of films, prior to the source dosimetry. The results of these measurements were compared with the Monte Carlo simulated data using MCNPX code. In addition, isodose curves acquired by radiochromic films and Monte Carlo simulation were compared with those provided by the GZP6 treatment planning system.ResultsScanning of samples of uniformly irradiated films demonstrated approximately 2.85% and 4.97% nonuniformity of the response, respectively in the longitudinal and transverse directions of the film. Our findings have also indicated that the film response is not affected by the exposure to the scanner’s light source, particularly in multiple scanning of film. The results of radiochromic film measurements are in good agreement with the Monte Carlo calculations (4%) and the corresponding dose values presented by the GZP6 treatment planning system (5%).ConclusionsThe results of these investigations indicate that the Microtek ScanMaker 1000XL color scanner in conjunction with GafChromic EBT film is a reliable system for dosimetric evaluation of a high dose rate brachytherapy source.

Evaluation of a glassless photographic film scanner for high-gradient radiochromic film dosimetry

This study evaluates the performance of the Nikon Coolscan 9000 ED film scanner for high-gradient radiochromic film dosimetry. As a reference for comparison, analogue experiments were performed on the Epson Expression 10000XL flatbed scanner. Based on these results, a dosimetric protocol was established for the Nikon scanner and its overall performance for high-gradient dosimetry was evaluated. The Nikon scanner demonstrated a high sensitivity for radiochromic film dosimetry, resulting in more contrast in the digitized image. The scanner's optics also demonstrated excellent stability and did not necessitate warm-up scans prior to data acquisition. Moreover, negative effects of temperature changes of the film inside the scanner were shown to be limited. None of the digitized images showed significant disturbances by moiré-patterns, by virtue of the absence of a glass plate for film positioning. However, scanner response was found to vary considerably across the reading area, requiring an optical density-dependent correction procedure to be incorporated into the scanning protocol. The main limitation of the Nikon Coolscan 9000 ED transmission scanner remains its film size restriction to 6.2 × 20 cm2. Nevertheless, its excellent characteristics render it the preferential tool for high-gradient radiochromic film dosimetry in applications limited to small film sizes, such as dosimetry in the build-up region.

Enhancement of digital gamma activation autoradiography capabilities by means of computer analysis of the time series images

It has been demonstrated that pixel-by pixel processing of series of autoradiography images for revealing the dynamics of decay of the induced radionuclides is an efficient approach for mapping of radionuclides in the sample in activation autoradiography. Concepts of virtual scanner and corresponding software for linearization of dependence of optical density on scanner response (luminosity) have been introduced. The concept provides unification of the subsequent processing of autoradiograms, irrespective of the method as to how the digital image has been obtained. Algorithms and the software for estimation of decay parameters of a radionuclide mixture for each pixel using a series of coaxially positioned images have been developed. The software is able generate a set of the derivative meta-images allowing a conclusion to be made about the presence of the inclusions in question. To increase the reliability of radionuclide mapping it is suggested to use analysis of distribution of half-life values estimated for pixels of image zone(s) pointed by a special mask.

Calibration of GafChromic XR‐RV3 radiochromic film for skin dose measurement using standardized x‐ray spectra and a commercial flatbed scanner

In this study, newly formulated XR-RV3 GafChromic film was calibrated with National Institute of Standards and Technology (NIST) traceability for measurement of patient skin dose during fluoroscopically guided interventional procedures. The film was calibrated free-in-air to air kerma levels between 15 and 1100 cGy using four moderately filtered x-ray beam qualities (60, 80, 100, and 120 kVp). The calibration films were scanned with a commercial flatbed document scanner. Film reflective density-to-air kerma calibration curves were constructed for each beam quality, with both the orange and white sides facing the x-ray source. A method to correct for nonuniformity in scanner response (up to 25% depending on position) was developed to enable dose measurement with large films. The response of XR-RV3 film under patient backscattering conditions was examined using on-phantom film exposures and Monte Carlo simulations. The response of XR-RV3 film to a given air kerma depended on kVp and film orientation. For a 200 cGy air kerma exposure with the orange side of the film facing the source, the film response increased by 20% from 60 to 120 kVp. At 500 cGy, the increase was 12%. When 500 cGy exposures were performed with the white side facing the x-ray source, the film response increased by 4.0% (60 kVp) to 9.9% (120 kVp) compared to the orange-facing orientation. On-phantom film measurements and Monte Carlo simulations show that using a NIST-traceable free-in-air calibration curve to determine air kerma in the presence of backscatter results in an error from 2% up to 8% depending on beam quality. The combined uncertainty in the air kerma measurement from the calibration curves and scanner nonuniformity correction was +/- 7.1% (95% C.I.). The film showed notable stability. Calibrations of film and scanner separated by 1 yr differed by 1.0%. XR-RV3 radiochromic film response to a given air kerma shows dependence on beam quality and film orientation. The presence of backscatter slightly modifies the x-ray energy spectrum; however, the increase in film response can be attributed primarily to the increase in total photon fluence at the sensitive layer. Film calibration curves created under free-in-air conditions may be used to measure dose from fluoroscopic quality x-ray beams, including patient backscatter with an error less than the uncertainty of the calibration in most cases.

Scanner calibration revisited

BackgroundCalibration of a microarray scanner is critical for accurate interpretation of microarray results. Shi et al. (BMC Bioinformatics, 2005, 6, Art. No. S11 Suppl. 2.) reported usage of a Full Moon BioSystems slide for calibration. Inspired by the Shi et al. work, we have calibrated microarray scanners in our previous research. We were puzzled however, that most of the signal intensities from a biological sample fell below the sensitivity threshold level determined by the calibration slide. This conundrum led us to re-investigate the quality of calibration provided by the Full Moon BioSystems slide as well as the accuracy of the analysis performed by Shi et al.MethodsSignal intensities were recorded on three different microarray scanners at various photomultiplier gain levels using the same calibration slide from Full Moon BioSystems. Data analysis was conducted on raw signal intensities without normalization or transformation of any kind. Weighted least-squares method was used to fit the data.ResultsWe found that initial analysis performed by Shi et al. did not take into account autofluorescence of the Full Moon BioSystems slide, which led to a grossly distorted microarray scanner response. Our analysis revealed that a power-law function, which is explicitly accounting for the slide autofluorescence, perfectly described a relationship between signal intensities and fluorophore quantities.ConclusionsMicroarray scanners respond in a much less distorted fashion than was reported by Shi et al. Full Moon BioSystems calibration slides are inadequate for performing calibration. We recommend against using these slides.

SU‐FF‐I‐147: Monte Carlo Based Evaluation of 3D PET Quantification Inaccuracy for the Lung

Purpose: Our goal is to investigate the effect on PET accuracy of the various physical and instrumental phenomena using realistic Monte Carlo (MC) models of patient activity distributions and PET scanners. Methods and materials: Data from a lung PET/CT scan is used to create numerical voxelized phantom for realistic MC simulations using the GATE MC code. We compared the activity reconstructed from the simulations to the input (“true”) values. We investigated the effects of random coincidences, photon scatter and positional shift between transmission and emission scans on the degradation of 3D PET quantification accuracy. Results: When exact attenuation, scatter and random corrections are applied, the activity from the simulated scans deviated from the input by more than 50% for 25% of the voxels. Inaccuracy of the random and scatter corrections of 20% will add additional quantification errors of about 20% and 40% respectively. The attenuation correction (AC) adds random and scatter events to the high tissue density regions. AC based on misaligned transmission data causes pronounced changes in the activity distribution in regions that have a high density gradient such as at junctions between soft tissue, bone and lung. AC misalignment causes errors of the activity levels, which may exceed a factor of five around the ribs for 1.5 cm shift between the PET data and the AC image. Conclusions: MC methods are a useful tool in investigating PET scanner response to realistic distributions of the activity and the attenuation properties and in establishing the uncertainty in PET quantification in patient studies. The potential quantification errors due to possible misregistration and inaccurate scatter and random corrections have been determined as indicated above for the lung.Supported in part by NCI grant CA‐059017 and performed in part on the Physon cluster, funded by Bulgarian NSF contract DO‐1‐872.

Development of a quality assurance scattering phantom for cone beam optical CT

Standard water-based acrylic emulsion scattering solutions have been developed for use in optical scattering gel phantoms. These solutions display good uniformity and long term stability, and can be index matched to polymer gels through the addition of propylene glycol or molten gelatin. Preliminary quality assurance (QA) performed on the Vista cone beam optical computed tomography (OptCT) scanner (Modus Medical, London, ON) using these standard scattering solutions provides valuable information toward the establishment of protocols for scanner warm-up and dosimeter/bath temperature control. A characterization of Vista scanner response over a range of scattering concentrations indicates that improved dosimeter performance may be realized through lowering the %T concentration of the polymer gel into the linear response range of the scanner A gel molding process has been developed for these scattering solutions, with promising results obtained for early stage scattering gel phantoms.

Evaluation of an Epson flatbed scanner to read Gafchromic EBT films for radiation dosimetry

Gafchromic EBT (EBT) films are becoming increasingly popular due to their advantageous properties. When flatbed colour scanners are used for film dosimetry, a good quality control of the scanning device is a crucial step for accurate results. The proposal of this work was to fully assess the performance of the scanner Epson Expression 10000XL in order to quantify all parameters and needed corrections to minimize dose uncertainties. A standard step tablet, with 32 steps and optical densities from 0.06 to 3.8, was used to check the scanner linearity. The scanner warming-up effect and reproducibility were evaluated by performing 30 consecutive scans plus 20 scans in 15 min intervals. The scanning colour modes: 24 and 48 bits and scanning resolutions from 50 to 300 dpi were tested. A Wiener filter with different pixels regions was applied with the purpose of reducing the film noise. All scans were made in transmission mode with a constant film orientation. The red colour channel was posteriorly extracted from the images to maximize readout sensitivity. Two EBT films were irradiated, perpendicularly and parallel to beam incidence, with a 6 MV photon beam with doses that ranged from 0.2 to 3 Gy. A polynomial expression was used to convert optical density into dose. Dose uncertainty was quantified applying error propagation analysis. A correction for the non-uniform response of the scanner was determined using five films irradiated with a uniform dose. The scanner response was linear until an optical density of approximately 1 which corresponds to doses higher than those of clinical interest for EBT films. The scanner signal stabilized after seven readings. Scanner reproducibility around 0.2% was obtained either with the scanner warm or cold. However, reproducibility was significantly reduced when comparing images digitized with the scanner at different temperatures. Neither the colour depth mode, the scanning resolution, the multiscan option nor the Wiener filter had a significant effect on the shape of the calibration curve. However, a reduction in dose uncertainty was possible by selecting appropriate reading parameters. These are a 48 bit colour depth, a 75 dpi resolution and repeating the scan four times. Finally, the two dimensional Wiener filter applied to a 3 × 3 pixel region to the red component of the image reduced the experimental scan uncertainty to about 0.5% for doses higher than 0.5 Gy. Total scan uncertainty was less than 2% for a perpendicular calibration and reduced to less than 1% for a parallel calibration. A dose over-estimation of around 5% for clinical doses may be made if the image acquired is not corrected for the non-uniform response of the scanner. A protocol to read EBT films using the Epson Expression 10000XL scanner was established for IMRT verification. The contribution for the overall uncertainty in film dosimetry coming from the scanning process was estimated to be around 0.5% for doses higher than 0.5 Gy when reading parameters are optimized. Total scan uncertainty achieved is about 2% when using a perpendicular calibration. It can further be reduced if a parallel calibration is used.

Scanner Characterization for Color Measurement of EP Printed Output

Typical automated print quality assessment tools use desktop scanners to analyze printed output. Unfortunately, due to the noncolorimetric properties of scanners, results can vary significantly depending upon the scanner used. This paper describes an investigation into using ICC (International Color Consortium) profiling as a tool to characterize the color response of a given scanner. The goal of this work is to create a scanner profile that can accurately measure the color of EP (electophotographic) printed output through the manipulation of targets, post processing refinement techniques, and the minimization of the effects of scanner non-uniformities. Targets with known color characteristics were created and scanned. Using open source software, ICC profiles were created from the scans to characterize a scanner's response to the colors in the targets. Through experimentation, it was determined that the maximum error of the profile can be minimized through post processing refinement. The main contributors to the average error were scanner nonuniformities and target characteristics, including uniformity, type, layout, and gamut. The results show that it is possible to, on average, characterize the output of a single EP printer to within 2 ΔE76 and the output of several EP printers to within 3 ΔE76. This is a quality level good enough to suggest that ICC profiling can be a fast, cost-effective solution toward obtaining reasonable color consistency across scanners, as well as a possible low-cost alternative to a spectrophotometer for specific applications.

Use of Standard Reference Material 2242 (Relative Intensity Correction Standard for Raman Spectroscopy) for microarray scanner qualification

As a critical component of any microarray experiment, scanner performance has the potential to contribute variability and bias, the magnitude of which is usually not quantified. Using Standard Reference Material (SRM) 2,242, which is certified for Raman spectral correction, for monitoring the microarray fluorescence at the two most commonly used wavelengths, our team at the National Institute of Standards and Technology (NIST) has developed a method to establish scanner performance, qualifying signal measurement in microarray experiments. SRM 2,242 exhibits the necessary photostability at the excitation wavelengths of 635 nm and 532 nm, which allows scanner signal stability monitoring, although it is not certified for use in this capacity. In the current study, instrument response was tracked day to day, confirming that changes observed in experimental arrays scanned are not due to changes in the scanner response. Signal intensity and signal-to-noise ratio (S/N) were tracked over time on three different scanners, indicating the utility of the SRM for scanner qualification.

Precautions and strategies in using a commercial flatbed scanner for radiochromic film dosimetry

The purpose of this study was to investigate the value of a commercially available flatbed scanner for film dosimetry with radiochromic film for external radiotherapy. The EPSON Pro 1680 Expression scanner was examined as a densitometer for two-dimensional film dosimetry with Gafchromic EBT film. An accurate and efficient scanning procedure was established. Possible drift and warm-up effects of the scanner were studied and the direct physical influence of the scanner light on the radiochromic film was assessed. Next, we investigated the scan field uniformity. Also, we examined if the accuracy of radiochromic film was improved by subtracting the optical density of the unirradiated blank film from the optical density of the irradiated film. To assess the accuracy of Gafchromic EBT film when the EPSON scanner was used as a densitometer, the depth dose of a 2 × 15 cm2 field and the in-plane and cross-plane profiles of a 15 × 15 cm2 field were measured and compared with diamond detector measurements. When taking consecutive scans, we found that the optical density taken from the first scan was about 1% higher than the optical density taken from subsequent scans. We attribute this to the warming up of the lamp of the scanner. Longer-term drift of the scanner was found to be absent. We found that the use of a correction matrix was necessary to correct for the non-uniform scanner response over the scan field. Subtracting the optical density of the unirradiated blank film from the irradiated film improves the precision of the Gafchromic EBT film. Depth dose and profile measurements with Gafchromic EBT film and the diamond detector are in agreement within 2.5%. The EPSON Pro 1680 Expression scanner is an excellent tool for accurate two-dimensional film dosimetry with Gafchromic EBT film provided that some precautions and corrections are taken into account.

SU‐FF‐I‐54: A Monte Carlo Model of the Discovery ST PET Scanner

Purpose: To evaluate the accuracy of a GATE (Geant4 Application for Tomographic Emission) Monte Carlo model of a commercial PET scanner for purposes of simulating the generation, propagation, and detection of annihilation photons in PET scanners, and for evaluating image scatter fractions, resolution, sensitivity, and other scanning parameters. Methods: We compare GATE results to experimental data from a GE Discovery ST PET scanner. Our 3D PET simulation model of the GE Discovery ST scanner consists of 10,080 detectors grouped in modules and blocks following the vendor's specifications. NEMA'01 PET commissioning phantoms are also accurately modeled. More than 2 billion positron histories were followed to simulate measured PET scans of the NEMA phantom. Results: The simulated GE Discovery ST's radial sensitivity ratios for the NEMA'01 phantoms agree to within 0.6% of measured values ( versus , sensitivities R are in cps/kBq). The scatter fraction agreement is within 1.6% (the measured and simulated scatter fractions are 45.1% and 45.8% respectively). The model also accurately simulates the behavior of the time curves (measured peak true counts 338 kcps at 32.9 kBq/cc and simulated peak true counts 340 kcps at 32 kBq/cc). In addition, the spatial resolution of the scanner is simulated. Conclusions: The validated model accurately predicts scanner response and performance parameters, can be used to evaluate and improve PET resolution, image quality, and quantitative accuracy, and will aid in the determination of optimum scan parameters. In conjunction with CT images, the model can also be used to assess the accuracy of tumor segmentation for radiation therapy treatment planning. This work is sponsored in part by National Cancer Institute Grant PO1‐CA059017, by the summer fellowship program of the American Association of Physicists in Medicine, and by an internal seed grant.

Defining paramaters for an adaptative 3D Wiener filter in image restoration of SPECT cerebral blood flow studies: A novel approach

Multiple factors (attenuation, scattering, scanner response, etc) significantly degrade SPECT images. and multiple techniques have been proposed to correct for those and therefore yield more quantitatively exact SPECT studies, with the aim of improving clinical classification of patients as well as results from research using this technique. Application of a Wiener filter during reconstruction, which minimizes the mean square error between the original object and its estimate (the image), is a well-validated and relatively simple approach to this problem. Optimal use of this technique requires a priori information such as the point spread function (PSF) of the imaging system and the power spectrum ratio of the original object to image noise, but this information is not generally available. We have applied a new adaptation of this approach to cerebral blood flow studies obtained in SPECT with 99mTc labeled agents. Here, we start with a Gaussian function to model the PSF of the SPECT system, and a constant to replace the noise-to-signal power spectrum ratio 1. The PSF width and power-spectrum ratio are then iteratively optimized to improve image contrast between white and gray matter while keeping image mottle (or variance) within each region at a tolerable level (as defined in 2, 3). To track precisely the contrast and mottle, the white and gray matter regions are identified from an anatomical MRI of the same patient previously co-registered to the SPECT study 4. Simulation results with a realistic brain model (digital Hoffman phantom 5, with 3D Gaussian noise (at such count levels, Poisson noise would yield comparable results) and then blurred with a 3D Gaussian function to simulate an actual SPECT study) show marked contrast improvement while maintaining the mottle at an acceptable level: with object contrast between white and gray matter (as defined in 2) set at 0.427 and degraded to 0.074 post blurring, filtering increased contrast to 0.378, with the mottle (proportionally averaged for gray and white matter) actually decreasing (0.224 to 0.182). Tests conducted with actual clinical SPECT cases exhibit similar contrast improvement (0.045 to 0.104) with a limited (and still acceptable 2) mottle increase (0.198 to 0.276). We believe that this technique for defining the parameters of a 3D adaptive Wiener filter will be useful in clinical practice, where significant data degradation limits detection of anomalies with SPECT, because it automatically generates the best combination of those parameters, leading to significantly improved contrast quantification with little noise amplification.

Spectral characterization of a color scanner by adaptive estimation.

A new method of spectral characterization for color scanners by the use of adaptive estimation is proposed. It deals with estimation of high-dimensional reflectance vectors from low-dimensional scanner response vectors when the scanner departs from linearity. We first investigate the spectral linearity of the scanner, and then estimate the spectral reflectance adaptively based on the local statistics of a set of neighboring training samples. As the proposed characterization method does not utilize the mathematically recovered spectral responsivity, its inherent inaccuracy is not critical to the spectral characterization. Experimental results showed significant advantage of adaptive estimation when compared with other methods.

Free-space wavelength-multiplexed optical scanner demonstration.

Experimental demonstration of a no-moving-parts free-space wavelength-multiplexed optical scanner (W-MOS) is presented. With fast tunable lasers or optical filters and planar wavelength dispersive elements such as diffraction gratings, this microsecond-speed scanner enables large several-centimeter apertures for subdegree angular scans. The proposed W-MOS design incorporates a unique optical amplifier and variable optical attenuator combination that enables the calibration and modulation of the scanner response, leading to any desired scanned laser beam power shaping. The experimental setup uses a tunable laser centered at 1560 nm and a 600-grooves/mm blazed reflection grating to accomplish an angular scan of 12.92 degrees as the source is tuned over an 80-nm bandwidth. The values for calculated maximum optical beam divergance, required wavelength resolution, beam-pointing accuracy, and measured scanner insertion loss are 1.076 mrad, 0.172 nm, 0.06 mrad, and 4.88 dB, respectively.

Precision Tone Reproduction Curve Measurement Technique for High Image Quality and Halftone Design Applications

We show that an extremely accurate tone reproduction curve (TRC), insensitive to noise in the printer and the media, can be measured using a scanner. In the scannerbased approach, two patterns are written. The first contains as many as 15,000 extremely small patches of the 256 addressable gray levels randomly placed on paper. The random placement averages over the noise and the mean of each patch gives an estimate of the TRC. The second pattern consists of 256 narrow strips with a high spatial frequency modulation between two adjacent gray levels for each strip. The scanner response at the modulation frequency for each strip gives the change in gray level between each halftone. The absolute values of the TRC from the first measurement are adjusted to best agree with the slope measurements, resulting in a highly accurate TRC measurement.

Identification and sizing of particle defects in semiconductor-wafer processing

An experimental study of the sizing of submicron particles on semiconductor wafers is presented. The objective of the study was to determine the accuracy of a state-of-the-art optical wafer scanner, by comparing its size response with that of two well established techniques, namely, differential mobility analysis (DMA) and secondary electron microscopy (SEM). Test particles used include polystyrene–latex spheres and SiO2, Si3N4, W, and Cu particles of 64, 107, and 202 nm nominal (DMA) sizes. The scanner-indicated sizes using the oblique and normal operational modes were compared to the DMA sizes and to average sizes determined from the SEM images. Results show that the scanner-indicated size is comparable to the SEM-indicated size. However, both the scanner size and SEM size exhibit large distributions for a given nominal (DMA) size. The discrepancies are due to a combination of factors such as the effects of particle shape and material, and the presence of larger, doubly charged particles among those analyzed. A comparison of the normal and oblique scanner operational mode results for the scanner further show that the normal mode undersizes particles somewhat. These results collectively indicate that accurate sizing of complex and unknown submicron sized particles on semiconductor wafers is not an easy task. A thorough understanding of the scanner response to a variety of process particles is essential for the meaningful interpretation of scanning results.

Bulk density calibration for X-ray tomographic analyses of marine sediments

A calibration procedure is presented for generating bulk density profiles of intact marine sediment cores using X-ray computed tomography (CT). Developed using both artificial and natural marine sediment samples, the correlation is strong with an R2 value of 0.98. Similar experiments with carbonate sediments were also strongly linear, but offset from the terrigenous curve, illustrating the influence of sediment chemistry on scanner response. Comparison between newly computed densities for both sediment types with those from individually calibrated cores during our previous CT studies reveals good correspondence between the data sets.

A convenient procedure for quantitative analysis of stained or immunostained blotting membranes by densitometry

A convenient method for analysing the information provided by blotting membranes is described. The membranes are first air dried at room temperature, copied to transparency film and the intensity of the bands on the transparency is determined by densitometry. The results show a linear correlation between the amount of protein present and the final scanner response.

Minimum-volume transforms for remotely sensed data

Scatter diagrams for multispectral remote sensing data tend to be triangular, in the two-band case, pyramidal for three bands, and so on. They radiate away from the so-called darkpoint, which represents the scanner's response to an un-illuminated target. A minimum-volume transform may be described (provisionally) as a nonorthogonal linear transformation of the multivariate data to new axes passing through the dark point, with directions chosen such that they (for two bands), or the new coordinate planes (for three bands, etc.) embrace the data cloud as tightly as possible. The reason for the observed shapes of scatter diagrams is to be found in the theory of linear mixing at the subfootprint scale. Thus, suitably defined, minimum-volume transforms can often be used to unmix images into new spatial variables showing the proportions of the different cover types present, a type of enhancement that is not only intense, but physically meaningful. The present paper furnishes details for constructing computer programs to effect this operation. It will serve as a convenient technical source that may be referenced in subsequent, more profusely illustrated publications that address the intended application, the mapping of surface mineralogy.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>