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PubMed2002

Comparison between high-resolution helical CT and pathology in breast examination.

PURPOSE: To determine whether high-resolution helical CT can show the architectural features of breast carcinomas of non-limited extent (non-BCLE) and to establish the CT characteristic morphology of non-BCLE. MATERIAL AND METHODS: We prospectively studied high-resolution helical CT of 136 invasive breast carcinomas before breast-conserving surgery. Non-BCLE were defined as ductal carcinomas in situ and invasive carcinomas beyond 1 cm from the edge of the dominant mass. Non-BCLE were defined as positive if enhanced beyond 1 cm from the edge of the focal enhancement on CT. After surgical resection, specimens were sliced in serial sections at 5-mm intervals, and the gross morphology and histology were correlated with the appearance of the preoperative CT lesion images. RESULTS: Non-BCLE were present in 47 invasive carcinomas. The sensitivity and specificity of non-BCLE evaluation by high-resolution helical CT were 70% and 89%, respectively. The morphology of non-BCLE on CT agreed with histologic findings. The morphological pattern on CT significantly correlated with intraductal tumor density adjacent to invasive tumor. CONCLUSION: Comparison of high-resolution helical CT with histologic data suggests that demonstration of a non-BCLE morphology can make the CT breast carcinoma local staging more accurate.

Breast↗

PubMed1992

Resolution of Pneumocystis carinii pneumonia in CD4+ lymphocyte-depleted mice given aerosols of heat-treated Escherichia coli.

Mice were thymectomized and depleted of CD4+ lymphocytes by treatment with monoclonal antibody to induce Pneumocystis carinii (PC) pneumonia (PCP). These mice were then exposed to aerosols of heat-treated Escherichia coli three times a week. Aerosol treatment for 10 d caused a slight reduction in numbers of PC nuclei in the lungs of mice, and treatment for 22 d resulted in nearly complete resolution of PCP. Large numbers of macrophages, polymorphonuclear leukocytes, and lymphocytes accumulated in lungs of aerosol-treated mice. Depletion of either CD8+ lymphocytes or asialo GM1+ cells that remained in the mice after CD4+ cell depletion had no effect on the ability of the mice to resolve PCP after E. coli aerosol treatments. However, depletion of Thy-1+ lymphocytes in these mice abrogated their ability to resolve PCP and reduced the numbers of macrophages that accumulated in the lungs. In addition, it was found that resolution of PCP induced by heat-treated E. coli aerosol treatments was also abrogated when mice were treated with polyclonal antibodies against tumor necrosis factor alpha (TNF-alpha). Thus, resolution of PCP in CD4+ lymphocyte-depleted mice by heat-treated E. coli aerosols was not dependent on either CD8+ or asialo GM1+ cells but was dependent on Thy-1+CD4-CD8- lymphocytes and on the participation of TNF. These results indicate that heat-treated E. coli aerosols can act as an immune response modifier by inducing resolution of PCP in mice by a mechanism not dependent on the presence of CD4+ lymphocytes.

Aerosols↗

PubMed1991

Resolution and information limitations from transducer arrays.

The factors limiting the resolution achievable with array-based imaging methods are considered. The limitations on beamwidth and field of view for beam scanning systems are first examined using plane wave diffraction theory, treating focusing and any array curvature as separable to the plane wave analysis. It is found that in all cases the number of half-beamwidths (maximum to null) across the field of view cannot exceed the number of electrically addressable elements in the array. The minimum beamwidth achievable by strong focusing is shown to be limited to twice the inter-element pitch. Digital reconstruction is then considered as an alternative to beam scanning. Here the number of image points recoverable across the field of view is equal to the number of elements in the array. The mathematical equivalence of the two methods is demonstrated, and the inference is made that the half-beamwidth represents a fundamental measure of lateral resolution. Alternative array configurations, suitable for CT methods, are then compared to probe arrays and it is found that the total number of resolution cells within a two-dimensional image is dependent on the pulse length and number of elements, rather than on the array configuration and imaging method. This again reveals the fundamental similarity of the various methods, essentially in combining position line information from the separate elements, albeit in different orders. Finally an expression for the information capacity of a scanning system is presented which relates the limitations on spatial and contrast resolution to the bandwidth and dynamic range of the system and the number of elements in the array.

Medical Laboratory Science↗

PubMed1997

Influence of OSEM, elliptical orbits and background activity on SPECT 3D resolution recovery.

In maximum-likelihood expectation-maximization (MLEM) reconstruction of SPECT images, if both attenuation correction (AC) and detector response correction (DRC) are included, the reconstruction can be too time consuming to be clinically useful. With use of the ordered-subset expectation-maximization (OSEM) reconstruction, it has been reported that the reconstruction time can be substantially reduced. We investigated the reconstruction of point sources in a non-uniform attenuation medium in terms of the normalized FWHM of these sources. We compared MLEM versus OSEM reconstructions; circular versus elliptical orbits; and the presence versus the absence of background activity in the object. We found: (i) that OSEM does speed up the reconstruction by a factor of 10 over MLEM; (ii) that the resolution recovery does not depend on the type of orbit if both AC and DRC are included in the reconstruction; however, when there is background activity, a significant number of iterations are required to alleviate the effect of orbit; (iii) that background activity significantly slows down the resolution recovery of the point sources; and (iv) that if reconstruction only includes AC, and not DRC, changing orbit can change isotropy of recovered resolution, whereas introducing background activity may degrade the recovered resolution and also changes the isotropy.

Computer Simulation↗

PubMed1998

SPECT electronic collimation resolution enhancement using chi-square minimization.

An electronic collimation technique is developed which utilizes the chi-square goodness-of-fit measure to filter scattered gammas incident upon a medical imaging detector. In this data mining technique, Compton kinematic expressions are used as the chi-square fitting templates for measured energy-deposition data involving multiple-interaction scatter sequences. Fit optimization is conducted using the Davidon variable metric minimization algorithm to simultaneously determine the best-fit gamma scatter angles and their associated uncertainties, with the uncertainty associated with the first scatter angle corresponding to the angular resolution precision for the source. The methodology requires no knowledge of materials and geometry. This pattern recognition application enhances the ability to select those gammas that will provide the best resolution for input to reconstruction software. Illustrative computational results are presented for a conceptual truncated-ellipsoid polystyrene position-sensitive fibre head-detector Monte Carlo model using a triple Compton scatter gamma sequence assessment for a 99mTc point source. A filtration rate of 94.3% is obtained, resulting in an estimated sensitivity approximately three orders of magnitude greater than a high-resolution mechanically collimated device. The technique improves the nominal single-scatter angular resolution by up to approximately 24 per cent as compared with the conventional analytic electronic collimation measure.

Algorithms↗

PubMed1998

Comparison of frequency-distance relationship and Gaussian-diffusion-based methods of compensation for distance-dependent spatial resolution in SPECT imaging.

The goal of this investigation was to compare resolution recovery versus noise level of two methods for compensation of distance-dependent resolution (DDR) in SPECT imaging. The two methods of compensation were restoration filtering based on the frequency-distance relationship (FDR) prior to iterative reconstruction, and modelling DDR in the projector/backprojector pair employed in iterative reconstruction. FDR restoration filtering was computationally faster than modelling the detector response in iterative reconstruction. Using Gaussian diffusion to model the detector response in iterative reconstruction sped up the process by a factor of 2.5 over frequency domain filtering in the projector/backprojector pair. Gaussian diffusion modelling resulted in a better resolution versus noise tradeoff than either FDR restoration filtering or solely modelling attenuation in the projector/backprojector pair of iterative reconstruction. For the pixel size investigated herein (0.317 cm), accounting for DDR in the projector/backprojector pair by Gaussian diffusion, or by applying a blurring function based on the distance from the face of the collimator at each distance, resulted in very similar resolution recovery and slice noise level.

Computer Simulation↗

PubMed2001

Resolution recovery for list-mode reconstruction in SPECT.

The purpose of the study was to evaluate the resolution recovery in the list-mode iterative reconstruction algorithm (LMIRA) for SPECT. In this study we compare the performance of the proposed method with other iterative resolution recovery methods for different noise levels. We developed an iterative reconstruction method which uses list-mode data instead of binned data. The new algorithm makes use of a more accurate model of the collimator structure. We compared the SPECT list-mode reconstruction with MLEM, OSEM and RBI, all including resolution recovery. For the evaluation we used Gaussian shaped sources with different FWHM at three different locations and three noise levels. For these distributions we calculated the reconstructed images for a different number of iterations. The absolute error for the reconstructed images was used to evaluate the performance. The performance of all four methods is comparable for the sources located in the centre of the field of view. For the sources located out of the centre, the error of the list-mode method is significantly lower than that of the other methods. Splitting the system model into a separate object-dependent and detector-dependent module gives us a flexible reconstruction method. With this we can very easily adapt the resolution recovery to different collimator types.

Algorithms↗

PubMed2003

The effect of water molecular self-diffusion on quantitative high-resolution MRI polymer gel dosimetry.

In polymer gel dosimetry, magnetic resonance imaging (MRI) is used to determine the spin-spin relaxation rate (R2) which in turn can be correlated with absorbed dose to provide a map of the spatial distribution of the absorbed dose in the irradiated dosimeter. High accuracy, precision and reproducibility of these dose maps are essential. Moreover, for dose verification around brachytherapy sources used for intravascular brachytherapy, a high spatial resolution is required (typically 0.01-0.1 mm). To achieve these microscopic resolutions, strong imaging gradients are applied. The Brownian motion of water molecules in the presence of these strong magnetic field gradients causes an attenuation of the MR signal. When using a multiple spin-echo sequence, this may result in a significant deviation in the measured R2. The diffusion-related change in R2 at high resolutions was investigated experimentally and correlated with predictions that were obtained numerically and algebraically. Diffusion weighting is determined by the self-diffusion coefficient D, and imaging parameters, quantified by the b-factor. The b-factor was calculated for a multiple spin-echo sequence for different gradient strengths and gradient pulse durations. The variations in R2 that were observed when changing the matrix size and slice thickness are explained. It is shown that a linear correlation between the matrix size and the variation in R2 is based on the diffusion weighting caused by the read-out gradients and slice selective gradients. In conclusion, the essence of taking into account molecular self-diffusion to quantify variations in the measured dose-R2 response when using high-resolution MRI in polymer gel dosimetry is emphasized.

Algorithms↗

PubMed2004

High resolution ultrasound elastomicroscopy imaging of soft tissues: system development and feasibility.

Research in elasticity imaging typically relies on 1-10 MHz ultrasound. Elasticity imaging at these frequencies can provide strain maps with a resolution in the order of millimetres, but this is not sufficient for applications to skin, articular cartilage or other fine structures. We developed a prototype high resolution elastomicroscopy system consisting of a 50 MHz ultrasound backscatter microscope system and a calibrated compression device using a load cell to measure the pressure applied to the specimen, which was installed between a rigidly fixed face-plate and a specimen platform. Radiofrequency data were acquired in a B-scan format (10 mm wide x 3 mm deep) in specimens of mouse skin and bovine patellar cartilage. The scanning resolution along the B-scan plane direction was 50 microm, and the ultrasound signals were digitized at 500 MHz to achieve a sensitivity better than 1 microm for the axial displacement measurement. Because of elevated attenuation of ultrasound at high frequencies, special consideration was necessary to design a face-plate permitting efficient ultrasound transmission into the specimen and relative uniformity of the compression. Best results were obtained using a thin plastic film to cover a specially shaped slit in the face-plate. Local tissue strain maps were constructed by applying a cross-correlation tracking method to signals obtained at the same site at different compression levels. The speed of sound in the tissue specimen (1589.8+/-7.8 m s(-1) for cartilage and 1532.4+/-4.4 m s(-1) for skin) was simultaneously measured during the compression test. Preliminary results demonstrated that this ultrasound elastomicroscopy technique was able to map deformations of the skin and articular cartilage specimens to high resolution, in the order of 50 microm. This system can also be potentially used for the assessment of other biological tissues, bioengineered tissues or biomaterials with fine structures.

Animals↗

PubMed2005

Photon-counting versus an integrating CCD-based gamma camera: important consequences for spatial resolution.

Charge-coupled devices (CCDs) coupled to scintillation crystals can be used for high resolution imaging with x-rays and gamma-rays. When the CCD images can be read out fast enough, the energy and interaction position of individual gamma quanta can be estimated by real-time image analysis of scintillation light flashes ('photon counting mode'). We tested a set-up in which an electron-multiplying CCD was coupled to a 1 mm thick columnar CsI crystal by means of a fibre-optic taper. We found that, compared to light integration, photon counting improves the intrinsic spatial resolution by a factor of about 3 to 6. Applying our set-up to Tc-99m and I-125 imaging, we were able to obtain intrinsic resolutions below 60 microm (full width at half maximum). Counting losses due to overlapping of light flashes are negligible for event rates typical for biomedical radio-nuclide imaging and do strongly depend on energy window settings. Energy resolution was estimated to be approximately 35 keV FWHM for a 1:1 taper. We conclude that CCD-based gamma cameras have great potential for applications such as in vivo imaging of gamma emitters.

Crystallography↗

PubMed2005

High-resolution temperature-based optimization for hyperthermia treatment planning.

In regional hyperthermia, optimization techniques are valuable in order to obtain amplitude/phase settings for the applicators to achieve maximal tumour heating without toxicity to normal tissue. We implemented a temperature-based optimization technique and maximized tumour temperature with constraints on normal tissue temperature to prevent hot spots. E-field distributions are the primary input for the optimization method. Due to computer limitations we are restricted to a resolution of 1 x 1 x 1 cm3 for E-field calculations, too low for reliable treatment planning. A major problem is the fact that hot spots at low-resolution (LR) do not always correspond to hot spots at high-resolution (HR), and vice versa. Thus, HR temperature-based optimization is necessary for adequate treatment planning and satisfactory results cannot be obtained with LR strategies. To obtain HR power density (PD) distributions from LR E-field calculations, a quasi-static zooming technique has been developed earlier at the UMC Utrecht. However, quasi-static zooming does not preserve phase information and therefore it does not provide the HR E-field information required for direct HR optimization. We combined quasi-static zooming with the optimization method to obtain a millimetre resolution temperature-based optimization strategy. First we performed a LR (1 cm) optimization and used the obtained settings to calculate the HR (2 mm) PD and corresponding HR temperature distribution. Next, we performed a HR optimization using an estimation of the new HR temperature distribution based on previous calculations. This estimation is based on the assumption that the HR and LR temperature distributions, though strongly different, respond in a similar way to amplitude/phase steering. To verify the newly obtained settings, we calculate the corresponding HR temperature distribution. This method was applied to several clinical situations and found to work very well. Deviations of this estimation method for the AMC-4 system were typically smaller than 0.2 degrees C in the volume of interest, which is accurate enough for treatment planning purposes.

Body Burden↗

PubMed2005

Resolution- versus sensitivity-effective diameter in pinhole collimation: experimental verification.

To account for photon penetration, the formulae used to calculate the geometric resolution of a pinhole collimator use an effective diameter d(e) rather than the physical diameter of the aperture. The expressions commonly used for d(e), however, were originally derived to include penetration in sensitivity calculations. To predict the full width at half maximum (FWHM) resolution of the point-spread function (PSF) of a knife-edge pinhole collimator, we have previously proposed simple expressions for a resolution-effective diameter d(re). Unlike those for d(e), expressions for d(re) predict both a dependence on the polar angle of the source (theta) and a non-isotropic PSF. In this paper, the new theory was tested by measuring experimentally the FWHM of the PSF. Results confirm the theoretical predictions that (a) d(re) provides the best estimates of the experimental FWHM as a function of theta and of the direction in the plane of the pinhole, (b) Paix's expression for d(e) tends to overestimate the FWHM, (c) Anger's is a better approximation, but still cannot predict the dependence on theta, and (d) the FWHM decreases with decreasing theta, i.e. resolution improves for sources at the edge of the field-of-view.

Algorithms↗

PubMed1991

The resolution of transcranial Doppler scanning: a method for in vitro evaluation.

The circle of Willis may be examined using low frequency pulsed Doppler ultrasound transmitted through the thin squamous temporal bone or 'acoustic windows' of the skull. The thickness and shape of these windows affect the characteristics of the ultrasound beam and partly determine the spatial resolution of transcranial Doppler scanning. We have studied the effects of temporal bone on the ultrasound beam and sample volume characteristics of the EME Transcan 2 MHz transducer using a stepper motor, computer-controlled ultrasound plotting system. The lateral and axial spatial dimensions of the sample volume, and a direct estimate of the lateral resolution of the system, were determined at various depths of interest using Doppler targets. The results in this initial study of a small number of specimens indicates a decrease in sample width, and hence an increase in lateral resolution, presumably due to the lensing effect of the skull cusping. The estimated lateral resolution of the system is of the order of 4 mm.

Aged↗

PubMed2002

A comparison of methods for measurement of spatial resolution in two-dimensional circular EIT images.

The literature concerning measurement of spatial resolution in electrical impedance tomography (EIT) is vague. Different groups often use their own method or a modified version of a better known method, thus hindering a generalized resolution measurement which could be useful for gauging the performance of one system against another. Measurement of spatial resolution in EIT is further complicated by its spatial variant nature and hence cannot be expressed simply with a single parameter as it can be in other imaging modalities (such as nuclear medicine or MRI for example). If the performance of each acquisition and image reconstruction system in EIT is to be compared objectively then there needs to be a common standard. In this paper the results of different methods for calculating spatial resolution are compared and an improved method is proposed which aims to fulfil this role.

Algorithms↗

PubMed2005

Spatial resolution improvement of 3D EIT images by the shrinking sLORETA-FOCUSS algorithm.

This paper describes the use of the shrinking sLORETA-FOCUSS algorithm to improve the spatial resolution of three-dimensional (3D) EIT images. Conventional EIT yields inaccurate, low spatial resolution images, due to noise, the low sensitivity of boundary voltages to inner conductivity perturbations and a limited number of boundary voltage measurements. The focal underdetermined system solver (FOCUSS) algorithm produces a localized energy solution based on the weighted minimum-norm least-squares (MNLS) solution. It was successfully applied for the spatial resolution improvement of EIT images of simulated and tank data for a 2D homogeneous circular disc. However, due to the fact that a 3D mesh system contains many more elements, much more memory is required to store the weighting matrix. In order to extend the work to 3D, the shrinking-FOCUSS method is utilized to shrink the solution space as well as the weighting matrix in each iteration step. The solution of the standardized low resolution electromagnetic tomography algorithm (sLORETA) is adopted as the initial estimate of the shrinking-FOCUSS. The effectiveness is verified by implementing the new algorithm on tank data for a three-dimensional homogeneous sphere.

Algorithms↗

PubMed2006

Comparison of resolution, contrast, and color differentiation among fiberoptic and digital flexible cystoscopes.

BACKGROUND AND PURPOSE: Advances in electro-optics continue to improve the urologist's ability to perform minimally invasive procedures. While the development of flexible fiberoptic cystoscopes more than 20 years ago greatly impacted the practice of urology, distal-sensor digital technology may represent the next step in the evolution of endoscopy. We compared a new distal-sensor digital flexible cystoscope with two standard fiberoptic flexible cystoscopes. MATERIALS AND METHODS: We evaluated the resolution, contrast, and color discrimination of a new ACMIICN distal-sensor digital cystoscope with >165,000 effective pixels in its clear aperture (viewing area), a new ACMI-ACN II fiberoptic cystoscope with <15,000 pixels in its clear aperture, and a Storz 1127 office fiberoptic cystoscope. Five subjects compared each cystoscope across 13 test parameters. RESULTS: There was no difference in the performance of the two fiberoptic cystoscopes. The ICN cystoscope was statistically superior to one or both fiberoptic cystoscopes across 12 of the 13 tests, including color differentiation between shades of dark red (P < 0.05), contrast discrimination along a 15-step grayscale gradient (P < 0.001 compared with the 1127 fiberoptic cystoscope only), resolution at 10 mm (7.52 line pairs/mm [lp/mm] (ICN) nu 3.58 lp/mm for both fiberoptic cystoscopes; (P < 0.001), and clear resolution of a 1-mm target at a distance of 6.1 cm (ICN) nu 3.3 cm (1127) and 3.8 cm (ACN II) (P < 0.001). CONCLUSIONS: The ICM distal-sensor all-digital cystoscope was clearly superior to two representative fiberoptic cystoscopes in vitro in terms of resolution, contrast discrimination, and red color differentiation. In-vivo performance remains to be assessed.

Calibration↗

PubMed1986

Densitometric scanning of high-resolution electrophoresis of serum: methodology and clinical application.

The recent introduction of high-resolution electrophoresis into many clinical laboratories has expanded the information available about protein abnormalities. While most laboratories interpret high-resolution electrophoresis patterns by direct visual examination of the stained electrophoresis strips, much useful information can be attained by supplemental densitometric scanning of these preparations. In the present report, we detail a method to perform densitometric scanning of high-resolution electrophoresis strips, and compare these results to those performed by standard cellulose acetate electrophoresis. Further, we evaluate the quantitative information by comparing the results from the densitometer scans with nephelometric quantification of specific monoclonal proteins. The present method gives a correlation coefficient of 0.97 when the gamma region densitometric scan is compared to the quantification of IgG by nephelometry in patients with known gamma-migrating IgG monoclonal gammopathies. Further, twofold dilution studies of these specimens showed excellent linearity. By providing objective, reliable, quantitative information, densitometric scanning of high-resolution electrophoresis strips is a useful adjunct to direct visual examination of these specimens.

Blood Protein Electrophoresis↗

PubMed2025

Unicorn: enhancing single-cell Hi-C data with blind super-resolution for 3D genome structure reconstruction.

MOTIVATION: Single-cell Hi-C (scHi-C) data provide critical insights into chromatin interactions at individual cell levels, uncovering unique genomic 3D structures. However, scHi-C datasets are characterized by sparsity and noise, complicating efforts to accurately reconstruct high-resolution chromosomal structures. In this study, we present ScUnicorn, a novel blind super-resolution framework for scHi-C data enhancement. ScUnicorn uses an iterative degradation kernel optimization process, unlike traditional super-resolution approaches, which rely on downsampling, predefined degradation ratios, or constant assumptions about the input data to reconstruct high-resolution interaction matrices. Hence, our approach more reliably preserves critical biological patterns and minimizes noise. Additionally, we propose 3DUnicorn, a maximum likelihood algorithm that leverages the enhanced scHi-C data to infer precise 3D chromosomal structures. RESULTS: Our evaluation demonstrates that ScUnicorn achieves superior performance over the state-of-the-art methods in terms of Peak Signal-to-Noise Ratio, Structural Similarity Index Measure, and GenomeDisco scores. Moreover, 3DUnicorn's reconstructed structures align closely with experimental 3D-FISH data, underscoring its biological relevance. Together, ScUnicorn and 3DUnicorn provide a robust framework for advancing genomic research by enhancing scHi-C data fidelity and enabling accurate 3D genome structure reconstruction. AVAILABILITY AND IMPLEMENTATION: Unicorn implementation is publicly accessible at https://github.com/OluwadareLab/Unicorn.

Single-Cell Analysis↗