Comparative performance evaluation of a flat detector and an image intensifier angiographic system both used for interventional cardiology procedures in adult and pediatric patients

PurposeTo compare two angiography systems of different image capture technology, one with flat detector (FD) and one with image intensifier (II), in terms of entrance surface air kerma (ESAK) rate, detector dose (DD) rate and image quality (IQ), in interventional cardiology procedures concerning both adult and pediatric patients.Materials and methodsIn order to determine ESAK and DD rates, a digital dosimeter and polymethylmethacrylate (PMMA) plates were used. For the evaluation of IQ, two contrast objects (the Leeds TOR 18FG and a 5 mm-thick Aluminum plate) were used and two figures of merit were defined in fluoroscopy and cine acquisition modes. Measurements of ESAK, DD rates and IQ were made for various fields of view, pulse and frame acquisition rates.ResultsFor the particular setup used in this study was noted that ESAK values in the II system were generally larger than the respective values in the FD system (on average 70% for fluoro mode, 5 times for cine mode). When halving the fluoroscopy pulse rate, reduction in ESAK was not proportional, in fluoroscopy mode. Image quality evaluations indicated that II performs better in terms of low contrast sensitivity (LCS) and signal-to-noise ratio (SNR) than the FD system which performs better regarding high contrast resolution (HCR). However, when considering image quality in relation to ESAK the FD system performs better than the II system (with the exception of low thicknesses and zooms for high pulse rates in the fluoroscopy mode).ConclusionsThe FD system, generally, provides a better image quality–dose relation than the II system although II unit provides better LCS and SNR. This means that with the right adjustments to both systems, FD unit is able to provide same image quality with lower dose. However, newer technology does not automatically imply better image quality and further investigation is necessary for deriving safe conclusions for units which utilize different capture technology.     

Advantages of CCD detectors for de novo three-dimensional structure determination in single-particle electron microscopy

For three-dimensional (3D) structure determination of large macromolecular complexes, single-particle electron cryomicroscopy is considered the method of choice. Within this field, structure determination de novo, as opposed to refinement of known structures, still presents a major challenge, especially for macromolecules without point-group symmetry. This is primarily because of technical issues: one of these is poor image contrast, and another is the often low particle concentration and sample heterogeneity imposed by the practical limits of biochemical purification. In this work, we tested a state-of-the art 4 k x 4 k charge-coupled device (CCD) detector (TVIPS TemCam-F415) to see whether or not it can contribute to improving the image features that are especially important for structure determination de novo. The present study is therefore focused on a comparison of film and CCD detector in the acquisition of images in the low-to-medium ( approximately 10-25 A) resolution range using a 200 kV electron microscope equipped with field emission gun. For comparison, biological specimens and radiation-insensitive carbon layers were imaged under various conditions to test the image phase transmission, spatial signal-to-noise ratio, visual image quality and power-spectral signal decay for the complete image-processing chain. At all settings of the camera, the phase transmission and spectral signal-to-noise ratio were significantly better on CCD than on film in the low-to-medium resolution range. Thus, the number of particle images needed for initial structure determination is reduced and the overall quality of the initial computed 3D models is improved. However, at high resolution, film is still significantly better than the CCD camera: without binning of the CCD camera and at a magnification of 70 kx, film is better beyond 21 A resolution. With 4-fold binning of the CCD camera and at very high magnification (> 300 kx) film is still superior beyond 7 A resolution.     

Comparative bioacoustical study of diurnal and nocturanl rodents from closed ranges

Studies have been made on the evoked potentials at the level of the colliculus inferior in the nocturnal rodent Glis glis and diuranl one--Eutamias sibiricus. In G. glis, the evoked potentials were recorded in a wide range of sonic and ultrasonic frequencies up to 90 kc, while in E. sibiricus these potentials were recorded in a range of frequencies up to 60 kc. The auditory threshold curves for G. glis exhibited two areas of minimum thresholds-- a low frequency area and an area at a boundary between sonic and ultrasonic frequencies. Threshold curves for E. sibiricus have no clear sensitivity maximum. In G. glis, correlation between the spectrum of their communication signals and acoustic noise in the habitat was observed. The species investigated differ in the rate of the recovery of the evoked potentials to paired stimuli and in the values of critical summation time.     

Investigation of detector uniformity issues for Siemens Inspiration systems

PurposeDetector uniformity is an important parameter in digital mammography to guarantee a level of image quality adequate for early detection of breast cancer.Many problems with digital systems have been determined through the uniformity measurement, primarily as a result of incorrect flat-field calibration and artifacts caused by image receptor defects.The European guidelines suggest a method for the image uniformity assessment based on measurement of Signal-to-Noise ratio (SNR) and Pixel Value (PV) across a uniform image.Nineteen mammography systems from the same manufacturer installed in our organization incorporate an a-Se direct conversion detector. Since their installation, instability and inconsistency of image uniformity has attracted medical physicist attention.A number of different tests have been carried out in order to understand and establish reasons for this instability.MethodsThree different tests have been performed to evaluate the impact of the heel effect, detector temperature and ghosting on the uniformity images. All the tests are based on the acquisition of uniform images as suggested by the European Guidelines for Quality Assurance in Breast Cancer Screening and Diagnosis.ResultsResults show that an increase in detector temperature produces an increase of SNR and decrease of uniformity. A further decrease of uniformity ranging between 20% and 30% is due to the ghosting while a decrease of about 10% is due the heel effect.ConclusionsX-ray tube, system geometry and detector have an impact on the system uniformity and an understanding of the contribution of each is necessary in order to obtain comparable image quality among all the systems.     

Grid computing in image analysis

Diagnostic surgical pathology or tissue–based diagnosis still remains the most reliable and specific diagnostic medical procedure. The development of whole slide scanners permits the creation of virtual slides and to work on so-called virtual microscopes. In addition to interactive work on virtual slides approaches have been reported that introduce automated virtual microscopy, which is composed of several tools focusing on quite different tasks. These include evaluation of image quality and image standardization, analysis of potential useful thresholds for object detection and identification (segmentation), dynamic segmentation procedures, adjustable magnification to optimize feature extraction, and texture analysis including image transformation and evaluation of elementary primitives. Grid technology seems to possess all features to efficiently target and control the specific tasks of image information and detection in order to obtain a detailed and accurate diagnosis. Grid technology is based upon so-called nodes that are linked together and share certain communication rules in using open standards. Their number and functionality can vary according to the needs of a specific user at a given point in time. When implementing automated virtual microscopy with Grid technology, all of the five different Grid functions have to be taken into account, namely 1) computation services, 2) data services, 3) application services, 4) information services, and 5) knowledge services. Although all mandatory tools of automated virtual microscopy can be implemented in a closed or standardized open system, Grid technology offers a new dimension to acquire, detect, classify, and distribute medical image information, and to assure quality in tissue–based diagnosis.     

Image quality characteristics for virtual monoenergetic images using dual-layer spectral detector CT: Comparison with conventional tube-voltage images

PurposeTo investigate the image quality characteristics for virtual monoenergetic images compared with conventional tube-voltage image with dual-layer spectral CT (DLCT).MethodsHelical scans were performed using a first-generation DLCT scanner, two different sizes of acrylic cylindrical phantoms, and a Catphan phantom. Three different iodine concentrations were inserted into the phantom center. The single-tube voltage for obtaining virtual monoenergetic images was set to 120 or 140 kVp. Conventional 120- and 140-kVp images and virtual monoenergetic images (40–200-keV images) were reconstructed from slice thicknesses of 1.0 mm. The CT number and image noise were measured for each iodine concentration and water on the 120-kVp images and virtual monoenergetic images. The noise power spectrum (NPS) was also calculated.ResultsThe iodine CT numbers for the iodinated enhancing materials were similar regardless of phantom size and acquisition method. Compared with the iodine CT numbers of the conventional 120-kVp images, those for the monoenergetic 40-, 50-, and 60-keV images increased by approximately 3.0-, 1.9-, and 1.3-fold, respectively. The image noise values for each virtual monoenergetic image were similar (for example, 24.6 HU at 40 keV and 23.3 HU at 200 keV obtained at 120 kVp and 30-cm phantom size). The NPS curves of the 70-keV and 120-kVp images for a 1.0-mm slice thickness over the entire frequency range were similar.ConclusionVirtual monoenergetic images represent stable image noise over the entire energy spectrum and improved the contrast-to-noise ratio than conventional tube voltage using the dual-layer spectral detector CT.     

Measurement of capillary basement membrane thickness by magnification on a rear opaque projection screen

2190 measurements of capillary basement membrane thickness were obtained from the images of magnified micrographs using a rear opaque projection screen. This method proved to be reproducible and reliable. The electron microscope magnification used, 2500x, permits sharp definition of structures in the resulting micrographs. Projection on the opaque rear screen magnified the image 16x, yielding a final magnification of 40,000x. This high final magnification of micrographs of good quality minimized the error in measurement. The use of a special dial caliper with pins attached allows an open field and decreases the subjective components of measurements. Moreover, this technique results in less stress for the persons performing the measurements.     

Tracking single particles: a user-friendly quantitative evaluation

As our knowledge of biological processes advances, we are increasingly aware that cells actively position sub-cellular organelles and other constituents to control a wide range of biological processes. Many studies quantify the position and motion of, for example, fluorescently labeled proteins, protein aggregates, mRNA particles or virus particles. Both differential interference contrast (DIC) and fluorescence microscopy can visualize vesicles, nuclei or other small organelles moving inside cells. While such studies are increasingly important, there has been no complete analysis of the different tracking methods in use, especially from the practical point of view. Here we investigate these methods and clarify how well different algorithms work and also which factors play a role in assessing how accurately the position of an object can be determined. Specifically, we consider how ultimate performance is affected by magnification, by camera type (analog versus digital), by recording medium (VHS and SVHS tape versus direct tracking from camera), by image compression, by type of imaging used (fluorescence versus DIC images) and by a variety of sources of noise. We show that most methods are capable of nanometer scale accuracy under realistic conditions; tracking accuracy decreases with increasing noise. Surprisingly, accuracy is found to be insensitive to the numerical aperture, but, as expected, it scales with magnification, with higher magnification yielding improved accuracy (within limits of signal-to-noise). When noise is present at reasonable levels, the effect of image compression is in most cases small. Finally, we provide a free, robust implementation of a tracking algorithm that is easily downloaded and installed.     

A novel approach to spot detection for two-dimensional gel electrophoresis images using pixel value collection

Separation of complex mixtures of proteins by two-dimensional gel electrophoresis (2-DE) is a fundamental component of current proteomic technology. Quantitative analysis of the images generated by digitization of such gels is critical for the identification of alterations in protein expression within a given biological system. Despite the availability of several commercially available software packages designed for this purpose, image analysis is extremely resource intensive, subjective and remains a major bottleneck. In addition to reducing throughput, the requirement for manual intervention results in the introduction of operator subjectivity, which can limit the statistical significance of the numerical data generated. A key requirement of image analysis is the accurate definition of protein spot boundaries using a suitable method of image segmentation. We describe a method of spot detection applicable to 2-DE image files using a segmentation method involving pixel value collection via serial analysis of the image through its range of density levels. This algorithm is reproducible, sensitive, accurate and primarily designed to be automatic, removing operator subjectivity. Furthermore, it is believed that this method may offer the potential for improved spot detection over currently available software.     

Improving Signal-to-Noise Ratio in Susceptibility Weighted Imaging: A Novel Multicomponent Non-Local Approach

In susceptibility-weighted imaging (SWI), the high resolution required to obtain a proper contrast generation leads to a reduced signal-to-noise ratio (SNR). The application of a denoising filter to produce images with higher SNR and still preserve small structures from excessive blurring is therefore extremely desirable. However, as the distributions of magnitude and phase noise may introduce biases during image restoration, the application of a denoising filter is non-trivial. Taking advantage of the potential multispectral nature of MR images, a multicomponent approach using a Non-Local Means (MNLM) denoising filter may perform better than a component-by-component image restoration method. Here we present a new MNLM-based method (Multicomponent-Imaginary-Real-SWI, hereafter MIR-SWI) to produce SWI images with high SNR and improved conspicuity. Both qualitative and quantitative comparisons of MIR-SWI with the original SWI scheme and previously proposed SWI restoring pipelines showed that MIR-SWI fared consistently better than the other approaches. Noise removal with MIR-SWI also provided improvement in contrast-to-noise ratio (CNR) and vessel conspicuity at higher factors of phase mask multiplications than the one suggested in the literature for SWI vessel imaging. We conclude that a proper handling of noise in the complex MR dataset may lead to improved image quality for SWI data.     

An approach to minirhizotron root image analysis

Minirhizotrons speed up research on root demography, but image quality often hampers standardization of the image processing method. A simple procedure working on the blue band of colour images was tested on fibrous roots of sugarbeet (Beta vulgaris var. saccharifera). With respect to green and red, the blue band allows better detection of roots when their luminance is very similar to that of the background. The method makes use of an exponential algorithm of contrast stretching, which takes luminance frequency distribution into account. Based on a single threshold level, the procedure includes skeletonization. A minimum segment length was adopted to discriminate roots from extraneous objects. Although a specific minimum root length (MRL) value was calculated for each soil type, results show that a single value can be applied, indicating that this method can be profitably used for processing large samples of images. This revised version was published online in June 2006 with corrections to the Cover Date.     

Monte-Carlo simulation of a slot-scanning X-ray imaging system

We present a method for simulating slot-scanning X-ray imaging using the general-purpose Monte Carlo simulation package PENELOPE and penEasy Imaging. Different phantoms can be defined with the PENGEOM package, which defines bodies as combinations of volumes limited by quadric surfaces. The source-detector geometry, the position of the object, the collimator, the X-ray tube properties, the detector material and the pixel dimensions are defined. The output of the time-delay integration detector is simulated using sequential slot outputs derived from penEasy Imaging. The simulations are validated using tungsten and aluminium test objects, which are both simulated and imaged. The simulations are compared to the X-ray images using standard image quality metrics. The MTF, NPS and DQE curves show that the real and simulated X-ray images are comparable in terms of spatial resolution, noise and frequency information. The implementation can be modified to suit alterations in the system being simulated.     

Quantitative low-resolution analysis of colon mucosa

A general concept is presented for the analysis of histopathologically adenomatous structures at low levels of magnification. The algorithm is based upon structures of glands, not upon structures of single cells. Low microscopic magnification was used to assess the following parameters in colon mucosa: minimum diameter of glands, minimum distance to neighboring glands, number of neighbors, area of glands and circumference of glands. Twenty different specimens were analyzed for each of the following diagnostic groups: healthy tissue, tubulovillous adenoma and moderately to highly differentiated adenocarcinoma of the colon. Statistically significant differences (p less than or equal to 0.01) were obtained for each measured parameter for each group. The data indicate that low-resolution morphometry can be used successfully for the automatic separation of healthy, benign and malignant growths in adenomatous tissue.     

Updating national diagnostic reference levels for interventional cardiology and methodological aspects

The aim of this study is to propose national diagnostic reference levels (DRL) for updating in the field of interventional cardiology and to include technical details to help plan optimization.Medical physics experts and interventional cardiologists from 14 hospitals provided patient dose indicators from coronary angiography and percutaneous coronary interventions. Information about X-ray system dose settings and image quality was also provided.The dose values from 30,024 procedures and 26 interventional laboratories were recorded. The national DRLs proposed for coronary angiography and percutaneous coronary interventions were respectively 39 and 78 Gy·cm² for air kerma area product (P_KA), 530 and 1300 mGy for air kerma at reference point (K_a,r), 6.7 and 15 min of fluoroscopy time and 760 and 1300 cine images. 36% of the KAP meters required correction factors from 10 to 35%. The dose management systems should allow these corrections to be included automatically. The dose per image in cine in reference conditions differed in a factor of 5.5.Including X-ray system dose settings in the methodology provides an insight into the differences between hospitals. The DRLs proposed for Spain in this work were similar to those proposed in the last European survey. The poor correlation between X-ray systems dose settings and patient dose indicators highlights that other factors such as operation protocols and complexity may have more impact in patient dose indicators, which allows a wide margin for optimization. Dose reduction technology together with appropriate training programs will be determinant in the future reduction of patient dose indicators.     

Image analysis for monitoring the barley tempeh fermentation process

AIMS: To develop a fast, accurate, objective and nondestructive method for monitoring barley tempeh fermentation. METHODS AND RESULTS: Barley tempeh is a food made from pearled barley grains fermented with Rhizopus oligosporus. Rhizopus oligosporus growth is important for tempeh quality, but quantifying its growth is difficult and laborious. A system was developed for analysing digital images of fermentation stages using two image processing methods. The first employed statistical measures sensitive to image colour and surface structure, and these statistical measures were highly correlated (r=0.92, n=75, P<0.001) with ergosterol content of tempeh fermented with R. oligosporus and lactic acid bacteria (LAB). In the second method, an image-processing algorithm optimized to changes in images of final tempeh products was developed to measure number of visible barley grains. A threshold of 5 visible grains per Petri dish indicated complete tempeh fermentation. When images of tempeh cakes fermented with different inoculation levels of R. oligosporus were analysed the results from the two image processing methods were in good agreement. CONCLUSION: Image processing proved suitable for monitoring barley tempeh fermentation. The method avoids sampling, is nonintrusive, and only requires a digital camera with good resolution and image analysis software. SIGNIFICANCE AND IMPACT OF THE STUDY: The system provides a rapid visualization of tempeh product maturation and qualities during fermentation. Automated online monitoring of tempeh fermentation by coupling automated image acquisition with image processing software could be further developed for process control.     

A practical tool to evaluate dose distributions using radiochromic film in radiation oncology

PurposeTriple channel algorithm and specific procedures make more reliable radiochromic dosimetry for treatment planning verification and quality assurance in radiation therapy. A tool to obtain radiochromic dose distributions and compare them with the ones resulting from a treatment planning system was developed and applied.MethodsThe tool was developed as Microsoft Excel macro; it builds dose calibration curves against net optical density of Gafchromic EBT3 film, produces axial, coronal and sagittal dose maps and allows to evaluate them against dose distributions calculated by the Varian treatment planning system Eclipse using gamma index and gamma angle.ResultsThe net optical density standard errors of estimate of calibration curves at 6 MV Varian DBX600 linac energy were 0.2%, 0.4% and 0.2% for the red, green and blue channels. Tests of these curves by means of three independent eight dose points measurement series, at 15 MV and 6 MV Varian 2100C linac and at 6 MV DBX600 linac energies, showed less than 2% of dose errors for the red channel and less than 3% for the green channel in the range 100–450 cGy. The comparisons between dose distributions from Gafchromic EBT3 triple channel algorithm and the ones from Eclipse analytic anisotropic algorithm (AAA) showed values of gamma index 95th percentile between 0.6 and 1.0.ConclusionThe obtained results encourage the application of this tool in radiation therapy quality assurance.     

Monte Carlo-based assessment of the trade-off between spatial resolution,field-of-view and scattered radiation in the variable resolution X-ray CT scanner

ObjectiveThe purpose of this work is to evaluate the impact of optimization of magnification on performance parameters of the variable resolution X-ray (VRX) CT scanner.MethodsA realistic model based on an actual VRX CT scanner was implemented in the GATE Monte Carlo simulation platform. To evaluate the influence of system magnification, spatial resolution, field-of-view (FOV) and scatter-to-primary ratio of the scanner were estimated for both fixed and optimum object magnification at each detector rotation angle. Comparison and inference between these performance parameters were performed angle by angle to determine appropriate object position at each opening half angle.ResultsOptimization of magnification resulted in a trade-off between spatial resolution and FOV of the scanner at opening half angles of 90°–12°, where the spatial resolution increased up to 50% and the scatter-to-primary ratio decreased from 4.8% to 3.8% at a detector angle of about 90° for the same FOV and X-ray energy spectrum. The disadvantage of magnification optimization at these angles is the significant reduction of the FOV (up to 50%). Moreover, magnification optimization was definitely beneficial for opening half angles below 12° improving the spatial resolution from 7.5 cy/mm to 20 cy/mm. Meanwhile, the FOV increased by more than 50% at these angles.ConclusionIt can be concluded that optimization of magnification is essential for opening half angles below 12°. For opening half angles between 90° and 12°, the VRX CT scanner magnification should be set according to the desired spatial resolution and FOV.     

The relationship between cancer detection in mammography and image quality measurements

PurposeTo investigate the relationship between image quality measurements and the clinical performance of digital mammographic systems.MethodsMammograms containing subtle malignant non-calcification lesions and simulated malignant calcification clusters were adapted to appear as if acquired by four types of detector. Observers searched for suspicious lesions and gave these a malignancy score. Analysis was undertaken using jackknife alternative free-response receiver operating characteristics weighted figure of merit (FoM). Images of a CDMAM contrast-detail phantom were adapted to appear as if acquired using the same four detectors as the clinical images. The resultant threshold gold thicknesses were compared to the FoMs using a linear regression model and an F-test was used to find if the gradient of the relationship was significantly non-zero.ResultsThe detectors with the best image quality measurement also had the highest FoM values. The gradient of the inverse relationship between FoMs and threshold gold thickness for the 0.25 mm diameter disk was significantly different from zero for calcification clusters (p = 0.027), but not for non-calcification lesions (p = 0.11). Systems performing just above the minimum image quality level set in the European Guidelines for Quality Assurance in Breast Cancer Screening and Diagnosis resulted in reduced cancer detection rates compared to systems performing at the achievable level.ConclusionsThe clinical effectiveness of mammography for the task of detecting calcification clusters was found to be linked to image quality assessment using the CDMAM phantom. The European Guidelines should be reviewed as the current minimum image quality standards may be too low.     

Interactive and automated application of virtual microscopy

Virtual microscopy can be applied in an interactive and an automated manner. Interactive application is performed in close association to conventional microscopy. It includes image standardization suitable to the performance of an individual pathologist such as image colorization, white color balance, or individual adjusted brightness. The steering commands have to include selection of wanted magnification, easy navigation, notification, and simple measurements (distances, areas). The display of the histological image should be adjusted to the physical limits of the human eye, which are determined by a view angle of approximately 35 seconds. A more sophisticated performance should include acoustic commands that replace the corresponding visual commands. Automated virtual microscopy includes so-called microscopy assistants which can be defined similar to the developed assistants in computer based editing systems (Microsoft Word, etc.). These include an automated image standardization and correction algorithms that excludes images of poor quality (for example uni-colored or out-of-focus images), an automated selection of the most appropriate field of view, an automated selection of the best magnification, and finally proposals of the most probable diagnosis. A quality control of the final diagnosis, and feedback to the laboratory determine the proposed system. The already developed tools of such a system are described in detail, as well as the results of first trials. In order to enhance the speed of such a system, and to allow further user-independent development a distributed implementation probably based upon Grid technology seems to be appropriate. The advantages of such a system as well as the present pathology environment and its expectations will be discussed in detail.