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David J Collins

Publications and source records attributed to David J Collins.

11 recordsLinked to original sources
PubMed2007

Reference tissue quantification of DCE-MRI data without a contrast agent calibration.

The quantification of dynamic contrast-enhanced (DCE) MRI data conventionally requires a conversion from signal intensity to contrast agent concentration by measuring a change in the tissue longitudinal relaxation rate, R(1). In this paper, it is shown that the use of a spoiled gradient-echo acquisition sequence (optimized so that signal intensity scales linearly with contrast agent concentration) in conjunction with a reference tissue-derived vascular input function (VIF), avoids the need for the conversion to Gd-DTPA concentration. This study evaluates how to optimize such sequences and which dynamic time-series parameters are most suitable for this type of analysis. It is shown that signal difference and relative enhancement provide useful alternatives when full contrast agent quantification cannot be achieved, but that pharmacokinetic parameters derived from both contain sources of error (such as those caused by differences between reference tissue and region of interest proton density and native T(1) values). It is shown in a rectal cancer study that these sources of uncertainty are smaller when using signal difference, compared with relative enhancement (15 +/- 4% compared with 33 +/- 4%). Both of these uncertainties are of the order of those associated with the conversion to Gd-DTPA concentration, according to literature estimates.

Biophysical Phenomena↗
PubMed2006

Construction of open metal-organic frameworks based on predesigned carboxylate isomers: from achiral to chiral nets.

The four-connected carboxylate ligand N,N,N',N'-tetrakis(4-carboxyphenyl)-1,4-phenylenediamine (TCPPDA) exists as three stereoisomers: a pair of enantiomers (deltaD2- and lambdaD2-TCPPDA) and a diastereomer (C2h-TCPPDA). TCPPDA was predesigned for the construction of isomeric coordination networks. Reactions of M(NO3)2 (M=Cu, Zn, Co) or Nd(NO)3 with TCPPDA under solvothermal conditions gave rise to five novel porous metal-organic frameworks: [Cu2(D2-tcppda)(H2O)2].2 DMSO.6H2O (1), [Cu2(C2h-tcppda)(H2O)2].2DMSO.6H2O (2), [Co3(D2-Htcppda)2].4DEF.5H2O (3), [Nd2(D2-tcppda)(C2h-tcppda)0.5(DMSO)3]3 DMSO5 H2O (4), and [Zn4O(D2-tcppda)1.5].DMF.H2O (5) (DMSO=dimethyl sulfoxide, DEF=diethylformamide, DMF=dimethylformamide). Complexes 1 and 2 are supramolecular isomers, in which all the ligands adopt pseudotetrahedral (both deltaD2- and lambdaD2-TCPPDA) and rectangular (C2h-TCPPDA) geometries, respectively. Both compounds connect paddlewheel secondary building units (SBUs) to form three-dimensional porous networks possessing PtS and NbO nets, respectively. In 3, all ligands possess pseudotetrahedral (both deltaD2- and lambdaD2-TCPPDA) geometry and link hourglass SBUs to form a three-dimensional porous framework. Compound 4 contains all three stereoisomers (C2-, deltaD2-, and lambdaD2-TCPPDA), thus, has both pseudotetrahedral and rectangular geometries. D2-TCPPDA connects the binuclear neodymium units to generate a two-dimensional layer, further linked by C2h-TCPPDA to create a three-dimensional open framework. In 5, all the ligands possess pseudotetrahedral geometry (D2-TCPPDA), as found in 1 and 3. However, all the TCPPDA ligands in 5 appear as either the deltaD2 or the lambdaD2 form, thus, the whole structure is homochiral. Complex 5 crystallizes in the I4(1)32 space group and the octahedral SBU in 5 is connected by the enantiopure TCPPDA to generate a three-dimensional porous network possessing the corundum Al2O3 net. Complexes 1, 2, and 5 possess permanent porosity, and 4 and 5 exhibit strong luminescence at lambdamax=423 and 424 nm, respectively, upon excitation at 268.5 nm.

Journal Article↗
PubMed2006

(10,3)-a Noninterpenetrated network built from a Piedfort ligand pair.

The Friedel-Crafts reaction of cyameluric chloride with toluene and subsequent oxidation have resulted in the synthesis of a benzoic acid functionalized tri-s-triazine derivative, s-heptazine tribenzoate (HTB). Photoluminescence and mass spectroscopy data indicate that, in solution, HTB molecules interact by face-to-face pi-pi stacking, forming dimers (the "Piedfort unit"). A porous metal-organic framework (MOF) with a (10,3)-a chiral network has been synthesized with these dimers at the three-connected nodes linking trinuclear zinc clusters. Within the network, the dimer can exist in either of two enantiomeric forms because of an angular offset in the stacking. The resulting MOF is neutral and noninterpenetrated and exhibits a high solvent-accessible volume (calculated 84%).

Benzoates↗
PubMed2006

Inter- and intraobserver variability in the evaluation of dynamic breast cancer MRI.

PURPOSE: To quantify variations within and between observers ascribable to manual region of interest (ROI) placement in patients with breast cancer undergoing dynamic MRI. MATERIALS AND METHODS: Expert and nonexpert observers independently outlined tumor ROIs on 30 dynamic T(1)-weighted (T(1)W) MRI scans on five occasions over two months. Lesion size (number of pixels) and kinetic parameter estimates, including the transfer constant (K(trans)), were calculated for each ROI placement. Inter- and intraobserver variability was assessed with respect to the interval between drawings, lesion morphology, and observer experience. RESULTS: For the nonexpert, the variability reduced with decreasing time intervals between ROI drawings (the coefficient of variance (wCV) values at two months, two weeks, one day, and same-day time intervals were respectively 11.6%, 10.7%, 4.8%, and 2.6% for lesion size, and 8.9%, 9.7%, 6.7%, and 3.2% for K(trans)). For the expert observer, the variability was smaller overall and more constant, but improved for same-day ROI placements (region size wCV: 7.5%, 6.2%, 7.1%, and 3.7%; K(trans) wCV: 5.4%, 5.3%, 5.6%, and 4.5%). CONCLUSION: Significant observer variability in manual ROI placement occurs in dynamic MRI of breast cancer. For serial patient studies, ROI placements should be outlined at the same sitting to minimize observer error.

Adult↗
PubMed2005

Synthesis and structure of cuboctahedral and anticuboctahedral cages containing 12 quadruply bonded dimolybdenum units.

The syntheses and structures of two clusters containing 12 Mo-Mo quadruple bonds, [Mo(24)(C(12)H(12)O(4))(24)](C(5)H(5)N)(12) and Mo(24)(C(8)H(4)O(4))(24), are reported. The 12 paddlewheel building blocks and 24 ligands self-assemble into cuboctahedral and anticuboctahedral polyhedra, respectively, depending on the manner in which the two halves of the cluster are aligned. These clusters contain twice as many dimolybdenum units as any previously reported cluster. Possible assembly mechanisms are also proposed.

Journal Article↗
PubMed2005

Localized COSY and DQF-COSY 1H-MRS sequences for investigating human tibial bone marrow in vivo and initial application to patients with acute leukemia.

PURPOSE: To develop 2D 1H-MRS measurement sequences for the evaluation of bone marrow lipids, and to assess these measurement sequences in healthy and diseased bone marrow. MATERIALS AND METHODS: Single-voxel localized variants of COSY and DQF-COSY 2D 1H-MRS sequences were developed for use at 1.5 T to investigate the biochemical composition of human bone marrow in vivo. The performance of each sequence was initially tested in vitro using lipid phantoms. An unsaturated lipid proton index was developed to interrogate the degree of unsaturation within the triacylglyceride (TAG) acyl chains. Localized 2D 1H-MRS data were obtained from the bone marrow of healthy controls (N = 6), patients presenting with acute leukemia (N = 6) and patients with acute leukemia in remission (N = 4). RESULTS: The COSY and DQF-COSY data recorded from all subject cohorts were similar, and the unsaturated lipid proton index did not reveal significant differences between patient groups. Variations in water content and measured relaxation times showed minor differences between the measurement groups. CONCLUSIONS: No significant differences were observed in the spectra obtained from bone marrow using the 2D 1H-MRS sequences. A novel unsaturated lipid proton index was developed.

Acute Disease↗
PubMed2005

Quantitative assessment of the hepatic pharmacokinetics of the antimicrobial sitafloxacin in humans using in vivoF magnetic resonance spectroscopy.

AIMS: To measure hepatic concentrations of the fluorine-containing antimicrobial, sitafloxacin, using in vivo(19)F magnetic resonance spectroscopy (MRS). METHODS: Data were acquired from eight healthy subjects at 2, 5, 8 and 24 h following doses of 500 mg day(-1) for 5 days using a (1)H/(19)F surface coil in a 1.5T clinical MR system. Tissue water was used as a reference. RESULTS: Estimated liver concentrations at 2 h were 15.0 +/- 4.0 microg ml(-1) (mean +/- 95% CI), compared with 3.54 +/- 0.58 microg ml(-1) in plasma (n = 6), and fell below threshold concentrations (2 microg ml(-1)) by 24 h. CONCLUSIONS: (19)F MRS is able to detect and quantify sitafloxacin in the liver. There was no evidence for the hepatic retention of the drug.

Adolescent↗
PubMed2003

Human gallbladder bile: noninvasive investigation in vivo with single-voxel 1H MR spectroscopy.

Proton (hydrogen 1) magnetic resonance (MR) spectroscopy was used to study model and porcine bile in vitro. The method was subsequently developed to facilitate the acquisition of in vivo 1H MR spectra from the gallbladder bile of 10 human volunteers. Signals attributable to phosphotidylcholine and conjugated bile acid protons were observed in eight of the 10 volunteers. Phosphotidylcholine concentrations were estimated, and five values (mean = 35.8 mmol/L, SD = 9.8) were within the expected range of levels in human bile. Findings in this preliminary investigation indicate that human gallbladder bile can be qualitatively and quantitatively studied noninvasively with 1H MR spectroscopy.

Adult↗
PubMedDate not supplied

Informatics in Radiology (infoRAD): Magnetic Resonance Imaging Workbench: analysis and visualization of dynamic contrast-enhanced MR imaging data.

Magnetic Resonance Imaging Workbench (MRIW) allows analysis of T1- and T2*-weighted dynamic contrast-enhanced magnetic resonance imaging data sets to extract tissue permeability and perfusion characteristics by using standard pharmacokinetic models. Parametric maps are calculated from individual pixel enhancement curves in regions of interest (ROIs) and displayed as color overlays on the anatomic images. User-defined ROIs can be saved to ensure consistency of later reanalysis. Individual parametric maps are visualized together with user-selected parameter time-series plots. The following selections are available: overall ROI enhancement curve and fit, histogram, and individual pixel enhancement curve and fit. Summary data (transfer constant, leakage space, rate constant, integrated area under the gadolinium curve after 60 seconds, relative blood volume, relative blood flow, and mean transit time) may be exported to permanent storage along with per-pixel results for statistical analysis. Numerical values for parameters are displayed below the plot for easy reference. The dynamic range of plots and parametric map overlays is interactively adjustable. Viewing individual enhancement curves and parametric maps allows radiologists to investigate the heterogeneity of contrast agent kinetics for lesion characterization and to scrutinize serial changes in response to therapy. MRIW is written in IDL, enabling it to be used on a variety of computer systems.

Computer Graphics↗