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PubMed2005

[On the way to isotopic spatial resolution: technical principles and applications of 16-slice CT].

The broad introduction of multi-slice CT by all major vendors in 1998 was a milestone with regard to extended volume coverage, improved axial resolution and better utilization of the tube output. New clinical applications such as CT-examinations of the heart and the coronary arteries became possible. Despite all promising advances, some limitations remain for 4-slice CT systems. They come close to isotropic resolution, but do not fully reach it in routine clinical applications. Cardiac CT-examinations require careful patient selection. The new generation of multi-slice CT-systems offer simultaneous acquisition of up to 16 sub-millimeter slices and improved temporal resolution for cardiac examinations by means of reduced gantry rotation time (0.4 s). In this overview article we present the basic technical principles and potential applications of 16-slice technology for the example of a 16-slice CT-system (SOMATOM Sensation 16, Siemens AG, Forchheim). We discuss detector design and dose efficiency as well as spiral scan- and reconstruction techniques. At comparable slice thickness, 16-slice CT-systems have a better dose efficiency than 4-slice CT-systems. The cone-beam geometry of the measurement rays requires new reconstruction approaches, an example is the adaptive multiple plane reconstruction, AMPR. First clinical experience indicates that sub-millimeter slice width in combination with reduced gantry rotation-time improves the clinical stability of cardiac examinations and expands the spectrum of patients accessible to cardiac CT. 16-slice CT-systems have the potential to cover even large scan ranges with sub-millimeter slices at considerably reduced examination times, thus approaching the goal of routine isotropic imaging.

Cardiovascular Diseases↗

PubMed2003

Localization of jointless-2 gene in the centromeric region of tomato chromosome 12 based on high resolution genetic and physical mapping.

Abscission is a universal process whereby plants shed their organs, such as flowers, fruit and leaves. In tomato, the non-allelic mutations jointless and jointless-2 have been discovered as recessive mutations that completely suppress the formation of pedicel abscission zones. A high resolution genetic map of jointless-2 was constructed using 1,122 jointless F2 plants. Restriction fragment length polymorphism (RFLP) marker RPD140 completely co-segregated with the jointless-2 locus and mapped in a 2.4 cM interval between RFLP markers CD22 and TG618. To chromosome walk to jointless-2, all three markers were used to screen a bacterial artificial chromosome (BAC) library and contigs were developed. Intensive efforts to expand and merge the BAC contigs were unsuccessful because of the highly repetitive sequence content on the distal ends of each contig. To determine the physical distance between and the orientation of the three contigs, we used high resolution pachytene fluorescence in situ hybridization (FISH) mapping. The RPD140 contig was positioned in the centromeric region of chromosome 12 between two large pericentric heterochromatin blocks, about 50 Mb from the TG618 contig on the short arm and 10 Mb from the CD22 contig on the long arm, respectively. Based on high resolution genetic and physical mapping, we conclude that the jointless-2 gene is located within or near the chromosome 12 centromere where 1 cM is approximately 25 Mb in length.

Centromere↗

PubMed2004

High-resolution mapping of the Rym4/Rym5 locus conferring resistance to the barley yellow mosaic virus complex (BaMMV, BaYMV, BaYMV-2) in barley (Hordeum vulgare ssp. vulgare L.).

Soil-borne barley yellow mosaic virus disease--caused by a complex of at least three viruses, i.e. Barley mild mosaic virus (BaMMV), Barley yellow mosaic virus (BaYMV) and BaYMV-2--is one of the most important diseases of winter barley in Europe. The two genes rym4, effective against BaMMV and BaYMV, and rym5, additionally effective against BaYMV-2, comprise a complex locus on chromosome 3HL, which is of special importance to European barley breeding. To provide the genetic basis for positional cloning of the Rym4/Rym5 locus, two high-resolution maps were constructed based on co-dominant flanking markers (MWG838/Y57c10 - MWG010/Bmac29). Mapping at a resolution of about 0.05% rec., rym4 has been located 1.07% recombination distal of marker MWG838 and 1.21% recombination proximal to marker MWG010. Based on a population size of 3,884 F2 plants (0.013% recombination) the interval harbouring rym5 was delimited to 1.49+/-0.14% recombination. By testing segmental recombinant inbred lines (RILs) for reaction to the different viruses at a resolution of 0.05% rec. (rym4) and 0.019% rec. (rym5), no segregation concerning the reaction to the different viruses could be observed. AFLP-based marker saturation for rym4, using 932 PstI+2/MseI+3 primer combinations only resulted in three markers with the closest one linked at 0.9% recombination to the gene. Two of these markers detected epialleles arising from the differential cytosine methylation of PstI sites. Regarding rym5, profiling of 1,200 RAPD primers (about 18,000 loci) and 2,048 EcoRI+3/MseI+3 AFLP primer combinations (about 205,000 loci) resulted in one RAPD marker and seven AFLP markers tightly linked to the resistance gene. Flanking markers with the closest linkage to rym5 (0.05% and 0.88% recombination) were converted into STS markers. These markers provide a starting point for chromosomal walking and may be exploited in marker-assisted selection for virus resistance based on rym5.

Base Sequence↗

PubMed2004

In vivo application of 3D-line skeleton graph analysis (LSGA) technique with high-resolution magnetic resonance imaging of trabecular bone structure.

Over the last several years magnetic resonance (MR) imaging has emerged as a means of measuring in vivo 3D trabecular bone structure. In particular, MR based diagnosis could be used to complement standard bone mineral density (BMD) methods for assessing osteoporosis and evaluating longitudinal changes. The aim of this study was to demonstrate the feasibility of using the 3D-LSGA technique for the evaluation of trabecular bone structure of high-resolution MR images, particularly for assessing longitudinal changes, in vivo. First, the reproducibility of topological 3D-LSGA based measurements was evaluated in a set of seven volunteers, and coefficients of variations ranged from 3.5% to 6%. Second, high-resolution MR images of the radius in 30 postmenopausal women from a placebo controlled drug study (Idoxifene), divided into placebo ( n=9) and treated ( n=21) groups, were obtained at baseline (BL) and after 1 year of treatment (follow-up, FU). In addition, dual X-ray absorptiometry (DXA) measures of BMD were obtained in the distal radius. Standard morphological measurements based on the mean intercept length (MIL) technique as well as 3D-LSGA based measurements were applied to the 3D MR images. Significant changes from BL to FU were detected, in the treated group, using the topological 3D-LSGA based measurements, morphological measures of volume of connected trabeculae and App Tb.N from MIL analysis. The duration of the study was short, and the number of patients remaining in the study was small, hence these results cannot be interpreted with regard to a true therapeutic response. Furthermore, the site (wrist) and the drug (idoxifene) are not optimal for follow-up study. However, this paper demonstrated the feasibility of using 3D-LSGA based evaluation coupled with in vivo high-resolution MR imaging as a complementary approach for the monitoring of trabecular bone changes in individual subjects.

Adult↗

PubMed2005

Three-dimensional texture analysis of cancellous bone cores evaluated at clinical CT resolutions.

The objective of this study was to determine if three-dimensional (3D) Haralick co-occurrence texture measures calculated from low-resolution CT images of trabecular bone correlate with 3D structural indices measured from high-resolution CT images. Thirty-three cubical regions of trabecular bone from human calcanei were analyzed using images obtained from a micro-computed tomography (micro-CT) scanner. 3D measures of bone architecture were calculated. The original images were then subsampled by factors of 5, 10, 15, and 20, and 3D texture features were calculated for each set of subsampled images. Linear regression models showed that co-occurrence texture features were significantly correlated with structural indices. Over 90% of the variation in three different structural indices was explained in two-variable regression models using texture features as predictors when the voxel side length was reduced by a factor of 10. Texture features calculated from clinical images may increase our ability to obtain trabecular bone architectural information when high-resolution images are unobtainable.

Aged↗

PubMed2002

High-resolution analytical TEM of nanostructured materials.

This paper briefly reviews the potential applicability of analytical transmission electron microscopy (TEM) to elucidate both structural and chemical peculiarities of materials at high lateral resolution. Examples of analytical TEM investigations performed by energy-dispersive X-ray spectroscopy (EDXS), electron energy loss spectroscopy (EELS), and energy-filtered TEM (EFTEM) are presented for different materials systems including metals, ceramics, and compound semiconductors. In particular, results are given of imaging the element distribution in the interface region between gamma matrix and gamma' precipitate in the nickel-based superalloy SC16 by energy-filtered TEM. For core-shell structured BaTiO(3) particles the chemical composition and even the chemical bonding were revealed by EELS at a resolution of about 1 nm. A sub-nanometer resolution is demonstrated by energy-selective images of the Ga distribution in the surrounding of (In,Ga)As quantum dots. Moreover, the element distribution in (Al,Ga)As/AlAs multilayers with linear concentration gradients in a range of about 10 nm was investigated by EDXS line-profile analyses and EFTEM.

Journal Article↗

PubMed2003

Application of GRAM and TLD to the resolution and quantitation of real complex multicomponent mixtures by fluorescence spectroscopy.

The application of the generalised rank annihilation method (GRAM) and the trilinear decomposition (TLD) method to the resolution and quantitation of fluorescence excitation-emission matrices of a ternary mixture of pesticides, carbendazim, fuberidazole, and thiabendazole, with overlapped spectra is described. The results obtained with both methods are compared and evaluated using measures of similarity (correlation coefficients) between the real and estimated spectra. Both approaches have been tested using augmented data matrices containing only two samples, but none of these methods succeeded completely in resolution of the system. When TLD was applied to augmented data matrices containing more than two samples better performance was achieved. To illustrate the application of both algorithms to real samples, they were used in the analysis of water samples containing the target pesticides. Again, TLD had an advantage over GRAM because the ability to analyse data from multiple (more than two) samples simultaneously allowed the resolution of the mixtures.

Benzimidazoles↗

PubMed2007

Multivariate curve resolution of rapid-scan FTIR difference spectra of quinone photoreduction in bacterial photosynthetic membranes.

Photosynthetic reaction centres and membranes are systems of particular interest and are often taken as models to investigate the molecular mechanisms of selected bioenergetic reactions. In this work, a multivariate curve resolution by alternating least squares procedure is detailed for resolution of time-resolved difference FTIR spectra probing the evolution of quinone reduction in photosynthetic membranes from Rhodobacter sphaeroides under photoexcitation. For this purpose, different data sets were acquired in the same time range and spectroscopic domain under slightly different experimental conditions. To enable resolution and provide meaningful results the different data sets were arranged in an augmented matrix. This strategy enabled recovery of three different species despite rank-deficiency conditions. It also results in better definition (identity and evolution) of the contributions. From the resolved spectra, the species have been attributed to: 1. the formation of ubiquinol, more precisely the disappearance of Q/appearance of QH(2); 2. conformational change of the protein in the surrounding biological medium; 3. oxidation of diaminodurene, a redox mediator. Because, moreover, results obtained from augmented data sets strategies enable quantitative and qualitative interpretation of concentration profiles, other effects, for example the consequence of repeated light excitation of the same sample, choice of illumination power, or the number of spectra accumulated could be compared and discussed.

Algorithms↗

PubMed2001

Determination of As, Cd, Cr, and Hg in SRM 2584 (trace elements in indoor dust) by high-resolution inductively coupled plasma mass spectrometry.

Standard reference material (SRM) 2584 (Trace Elements in Indoor Dust) was developed as a reference standard for evaluating field methods and for validating laboratory and reference methods for the assessment of lead contamination and exposure. In addition to lead, the toxic trace elements As, Cd, Cr, and Hg, at approximately 17, 10, 140, and 5 microg g(-1), respectively, have been certified in the SRM. These four analytes were successfully determined by use of high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS). Isobaric interferences at masses of As and Cr were resolved by using the high resolution mode (nominal 8000) and the medium resolution mode (nominal 3000), respectively, of the instrument. The effects of a significant drift in analyte sensitivity in the course of measurement were rectified by use of internal standardization, single spike standard addition, and an optimized analysis sequence. The results were compared with those obtained by instrumental neutron activation analysis (INAA) and isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS). The results for the quality control, SRM 2704 (Buffalo River Sediment), were in good agreement with the certified values, indicated by the uncertainty intervals of the measured values overlapping the certified intervals at 95% confidence level.

Arsenic↗

PubMed2001

Resolution of two-way data: theoretical background and practical problem-solving. Part 1: theoretical background and methodology.

This paper reviews recent progress in the resolution of two-way data obtained from hyphenated instruments. Special emphasis is placed on the solution of practical problems. Methods for estimating the number of chemical components both statistically and visually (the first step in solving the resolution problem) and methods for resolving the pure profiles (the second step in solving the resolution problem) are discussed in detail. To deal with real-world problems, pitfalls in the chemometric analysis of the two-way data from the instrumental measurements are also pointed out. Applications of methods for solving some difficult practical problems in environmental chemistry, pharmaceutical chemistry, and physical chemistry will be discussed in the second part of this paper.

Journal Article↗

PubMed1996

Surface analysis by scanning electrochemical microscopy: resolution studies and applications to polymer samples.

Resolution studies of scanning electrochemical microscopy (SECM) have been performed in the feedback mode and in the generator/collector mode at circular model structures. A quantitative correlation of the loss in resolution and the increase in distance between tip and sample is found. Measuring a band electrode of just 500 nm width, the high sensitivity of the SECM in identifying chemically active sites is proven. Applied to polymer samples, the chemical composition was determined in the feedback mode at high lateral resolution. The difference in electrical conductivity allows one to distinguish between doped and undoped parts of a polyaniline film. By scanning above a blend consisting of polypyrrole and polypropylene, a map of the local chemical composition was obtained. In this context, the influence of the tip overpotential on the image is discussed.

Journal Article↗

PubMed1998

Manipulation and molecular resolution of a phosphatidylcholine-supported planar bilayer by atomic force microscopy.

The morphology of supported planar bilayers has been investigated below phase transition temperature by atomic force microscopy in contact and tapping mode. The bilayers were formed by the vesicle-spreading technique. In contact mode at low scanning forces of about 1 nN true molecular resolution could be achieved for supported phosphatidylcholine bilayers. The resolution was confirmed by experiments that captured the location, average area of individual lipid headgroups and the manipulation of the bilayer surface. Repeated scanning in contact mode shifted the random topology of the surface consecutively to a striped pattern. Height profiles of defect-containing bilayers were analyzed. The shape of the defects became smooth by repeated scanning. The height profiles allowed the estimation of the indentation of the tip into the surface-adsorbed membrane. In tapping mode a disordered pattern of headgroups became visible. Our morphological data at molecular resolution suggest that the native arrangement of the choline head-groups is disordered, free of large packing defects and becomes ordered in Schallamach waves by scanning in contact mode.

Lipid Bilayers↗

PubMed2001

High-resolution blood oxygen-level dependent MR venography (HRBV): a new technique.

Our purpose of this study was to demonstrate the clinical potential and spatial resolution of a new MRI technique: high-resolution blood oxygen-level dependent venography (HRBV), in well-known intracranial vascular lesions, such as cavernous and venous angiomas, and venous sinus thrombosis. HRBV provides unique high-resolution information on veins without administration of contrast medium. The data are independent of conventional findings on MRI and potentially useful in characterising and demonstrating the architecture of vascular lesions of the brain.

Adult↗

PubMedDate not supplied

Spontaneous resolution of the septal defects in atrioventricular septal defect.

It is known that atrial septal defects of the secundum type and ventricular septal defects may undergo spontaneous closure. However, it is not well recognized that atrioventricular septal defects may infrequently also undergo spontaneous resolution. We report one case of complete atrioventricular septal defect that underwent spontaneous closure of the ventricular component. We also describe one case of partial atrioventricular septal defect with almost complete spontaneous resolution of the interatrial communication. Presence of shunting across the defects is demonstrated by color Doppler echocardiography, along with later absence of shunting. The rate of spontaneous resolution is estimated.

Echocardiography, Doppler, Color↗

PubMed2002

Imaging of dopamine transporters in rats using high-resolution pinhole single-photon emission tomography.

To date, the vast majority of investigations on the dopaminergic system in small animals have been in vitro studies. In comparison with in vitro studies, single-photon emission tomography (SPET) or positron emission tomography (PET) imaging of the dopaminergic system in small animals has the advantage of permitting repeated studies within the same group of animals. Dopamine transporter imaging is a valuable non-invasive tool with which to investigate the integrity of dopaminergic neurons. The purpose of this study was to investigate the feasibility of assessing dopamine transporter density semi-quantitatively in rats using a recently developed high-resolution pinhole SPET system. This system was built exclusively for imaging of small animals. In this unique single-pinhole system, the animal rotates instead of the collimated detector. The system has proven to have a high spatial resolution. We performed SPET imaging with [(123)I]FP-CIT to quantify striatal dopamine transporters in rat brain. In all seven studied control rats, symmetrical striatal binding to dopamine transporters was seen 2 h after injection of the radiotracer, with striatal-to-cerebellar binding ratios of approximately 3.5. In addition, test/retest variability of the striatal-to-cerebellar binding ratios was studied and found to be 14.5%. Finally, in unilaterally 6-hydroxydopamine-lesioned rats, striatal binding was only visible on the non-lesioned side. Quantitative analysis revealed that striatal-to-cerebellar SPET ratios were significantly lower on the lesioned (mean binding ratio 2.2 +/- 0.2) than on the non-lesioned (mean ratio 3.1 +/- 0.4) side. The preliminary results of this study indicate that semi-quantitative assessment of striatal dopamine transporter density using our recently developed high-resolution single-pinhole SPET system is feasible in living rat brain.

Animals↗

PubMed2006

Quantification of FDG PET studies using standardised uptake values in multi-centre trials: effects of image reconstruction, resolution and ROI definition parameters.

PURPOSE: Standardised uptake values (SUVs) depend on acquisition, reconstruction and region of interest (ROI) parameters. SUV quantification in multi-centre trials therefore requires standardisation of acquisition and analysis protocols. However, standardisation is difficult owing to the use of different scanners, image reconstruction and data analysis software. In this study we evaluated whether SUVs, obtained at three different institutes, may be directly compared after calibration and correction for inter-institute differences. METHODS: First, an anthropomorphic thorax phantom containing variously sized spheres and activities, simulating tumours, was scanned and processed in each institute to evaluate differences in scanner calibration. Secondly, effects of image reconstruction and ROI method on recovery coefficients were studied. Next, SUVs were derived for tumours in 23 subjects. Of these 23 patients, four and ten were scanned in two institutes on an HR+ PET scanner and nine were scanned in one institute on an ECAT EXACT PET scanner. All phantom and clinical data were reconstructed using iterative reconstruction with various iterations, with both measured (MAC) and segmented attenuation correction (SAC) and at various image resolutions. Activity concentrations (AC) or SUVs were derived using various ROI isocontours. RESULTS: Phantom data revealed differences in SUV quantification of up to 30%. After application-specific calibration, recovery coefficients obtained in each institute were equal to within 15%. Varying the ROI isocontour value resulted in a predictable change in SUV (or AC) for both phantom and clinical data. Variation of image resolution resulted in a predictable change in SUV quantification for large spheres/tumours (>5 cc) only. For smaller tumours (<2 cc), differences of up to 40% were found between high (7 mm) and low (10 mm) resolution images. Similar differences occurred when data were reconstructed with a small number of iterations. Finally, no significant differences between MAC and SAC reconstructed data were observed, except for tumours near the diaphragm. CONCLUSION: Standardisation of acquisition, reconstruction and ROI methods is preferred for SUV quantification in multi-centre trials. Small unavoidable differences in methodology can be accommodated by performing a phantom study to assess inter-institute correction factors.

Algorithms↗

PubMedDate not supplied

Preoperative assessment of local tumor extent in advanced rectal cancer: CT or high-resolution MRI?

BACKGROUND: We compared high-resolution magnetic resonance imaging (MRI) with computed tomography (CT) in the assessment of tumor infiltration in surrounding structures for locally advanced primary and recurrent rectal cancer. METHODS: Twenty-six patients with operable, locally advanced rectal cancer (15 recurrent and 11 primary) were evaluated with conventional pelvic CT and 1.5-T high-resolution MRI with a quadrature phased-array coil. The images were scored for invasion of nine neighboring pelvic structures, and the results were compared with surgical and histologic findings. RESULTS: A total of 234 structures in 26 patients was evaluated for tumor invasion. For MRI the, sensitivity was 97% and the specificity 98%; for CT, the sensitivity was 70% and the specificity was 85%. The difference in performance was statistically significant (p<0.001). The failure most frequently made on CT was the false-positive prediction of pelvic floor and piriform muscle invasion (14), whereas MRI showed only four false-positive predictions. MRI correctly predicted all four cases of sacral bone invasion, three of which were missed by CT. MRI was accurate in 20 patients (80%) and CT in only five patients (19%). CONCLUSION: High-resolution MRI using a quadrature phased-array coil is highly accurate and superior to CT in predicting tumor infiltration in surrounding structures for locally advanced primary or recurrent rectal cancer and is recommended in the preoperative work-up of these tumors.

Adenocarcinoma↗

PubMedDate not supplied

High-resolution MR imaging evaluation of hepatocellular carcinoma.

PURPOSE: To determine the utility of high-resolution MR imaging for hepatocellular carcinoma. MATERIALS AND METHODS: High-resolution MR images with a 512 matrix in a right to left frequency encoding direction were obtained in 20 consecutive patients with known or suspected hepatocellular carcinoma (HCC). Six series of breath-hold images of the entire liver [T1- and T2-weighted fast spin echo sequences, T1-weighted fast low-angle shot gradient echo sequence and three-phased contrast-enhanced dynamic study using the latter) were obtained using a phased-array multicoil. RESULTS: HCC was depicted in 15 patients on the MR images, and the diagnosis was confirmed at pathology in 13 and at imaging in the other two. In the remaining five patients, HCC was correctly ruled out with MR imaging. CONCLUSION: High-resolution MR imaging is a promising method in the evaluation of HCC.

Adolescent↗

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