bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of intravascular‐to‐extravascular water exchange on the determination of blood‐to‐tissue transfer constant by magnetic resonance imaging
Authors: Cao Y. , Brown S. L. , Knight R. A. , Fenstermacher J. D. , Ewing J. R. 
Published: January 2005

AbstractWater exchange across capillary walls couples intra‐ and extravascular (IV‐EV) protons and their magnetization. A bolus i.v. injection of an extracellular MRI contrast agent (MRCA) causes a large increase in the spin‐lattice relaxation rate, R1, of water protons in the plasma and blood cells within the capillaries and changes the effective relaxation rate R1eff in tissue via IV‐EV water exchange. An analysis of the effect of plasma‐red cell and IV‐EV water exchange on the MRI‐measured influx and permeability of capillaries to the MRCA is presented and focused on the brain and the blood–brain barrier. The effect of arrival of a bolus of an MRCA in the capillary on the relaxation rate R1eff in tissue via IV‐EV water exchange occurs more rapidly than the MRCA uptake in tissue and can dominate the initial time curve of the R1eff change before the MRCA uptake in tissue becomes significant. This raises the possibility that (tissue dependent) IV‐EV rate of exchange of water molecules can affect estimates of MRCA transfer constant. We demonstrate that an approach that considers IV‐EV water exchange and uses the theoretical model of blood–brain tracer distribution developed by Patlak et al. (J Cereb Blood Flow Metab 1983;3:1–7) can lead to an accurate estimate of the MRI‐determined influx rate constant of the MRCA and to an underestimation of the tissue blood volume. Magn Reson Med 53:282–293, 2005. © 2005 Wiley‐Liss, Inc.
MRI‐based technique for determining nonuniform deformations throughout the volume of articular cartilage explants
Authors: Neu C.P. , Hull M.L. , Walton J.H. , Buonocore M.H. 
Published: January 2005

AbstractArticular cartilage is critical to the normal function of diarthrodial joints. Despite the importance of the tissue and the prevalence of cartilage degeneration (e.g., osteoarthritis), the technology required to noninvasively describe nonuniform deformations throughout the volume of the tissue has not been available until recently. The objectives of the work reported in this paper were to 1) describe a noninvasive technique (termed the cartilage deformation by tag registration (CDTR) technique) to determine nonuniform deformations in articular cartilage explants with the use of specialized MRI tagging and image processing methods, 2) evaluate the strain error of the CDTR technique using a custom MRI‐compatible phantom material, and 3) demonstrate the applicability of the CDTR technique to articular cartilage by determining 3D strain fields throughout the volume of a bovine articular cartilage explant. A custom MRI pulse sequence was designed to tag and image articular cartilage explants at 7 Tesla in undeformed and deformed states during the application of multiple load cycles. The custom pulse sequence incorporated the “delays alternating with nutations for tailored excitation” (DANTE) pulse sequence to apply tags. This was followed by a “fast spin echo” (FSE) pulse sequence to create images of the tags. The error analysis using the phantom material indicated that deformations can be determined with an error, defined as the strain precision, better than 0.83% strain. When this technique was applied to a single articular cartilage explant loaded in unconfined compression, hetereogeneous deformations throughout the volume of the tissue were evident. This technique potentially can be applied to determine normal cartilage deformations, analyze degenerated cartilage, and evaluate cartilage surgical repair and treatment methodologies. In addition, this technique may be applied to other soft tissues that can be appropriately imaged by MR. Magn Reson Med 53:321–328, 2005. © 2005 Wiley‐Liss, Inc.
Ultrashort TE chemical shift imaging (UTE‐CSI)
Authors: Robson Matthew D. , Tyler Damian J. , Neubauer Stefan 
Published: January 2005

AbstractA fundamental modification to the conventional chemical shift imaging (CSI) method is described that improves the imaging of species with short T2's (i.e., less than ∼2 ms). This approach minimizes the delay before each k‐space point is collected. This results in different time delays, Td, for different free induction decay (FID) acquisitions in k‐space. On a clinical 1.5T system this yields an effective delay due to transmit/receive switching of 70 μs and an echo time (TE) from the center of the excitation pulse to the center of k‐space of 170 μs, as compared with 1–2 ms for conventional CSI techniques. Using this method, the signal decay before acquisition is greatly reduced, thus enabling imaging of species with very short T2 (e.g., 200 μs) and increasing the signal‐to‐noise ratio (SNR) of species with intermediate T2. Increases in the SNR of the short T2 components of 23Na in the heart, and 31P acquisitions of bone are about 27% and 400%, respectively, compared to an optimized conventional CSI approach. The imperfections of this approach are also described, and the magnitude of the resultant image artifacts is quantified for different practical imaging situations. These artifacts were not found to be significant in the described applications. This new method allows us to obtain information on short T2 components without degrading the image quality from long T2 components. Magn Reson Med 53:267–274, 2005. © 2005 Wiley‐Liss, Inc.
Noninvasive MR thermometry using paramagnetic lanthanide complexes of 1,4,7,10‐tetraazacyclodoecane‐α,α′,α″,α‴‐tetramethyl‐1,4,7,10‐tetraacetic acid (DOTMA4–)
Authors: Hekmatyar S.K. , Hopewell Paige , Pakin Sait Kubilay , Babsky Andriy , Bansal Navin 
Published: January 2005

AbstractNoninvasive techniques to monitor temperature have numerous useful biomedical applications. However, MR thermometry techniques based on the chemical shift, relaxation rates, and molecular diffusion rate of the water 1H signal suffer from poor thermal resolution. The feasibility of MR thermometry based on the strong temperature dependence of the hyperfine‐shifted 1H signal from the paramagnetic lanthanide complex thulium‐1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetate (TmDOTA–) was recently demonstrated. The use of paramagnetic lanthanide complexes for MR thermometry can be further enhanced by improving the signal‐to‐noise ratio (SNR) of the observed signal. In this study, the use of lanthanide complexes of a methyl‐substituted analog of DOTA4–, 1,4,7,10‐tetramethyl 1,4,7,10‐tetra azacyclodoecane‐1,4,7,10‐tetraacetic acetate (DOTMA4–) was evaluated. DOTMA4– complexes have 12 magnetically equivalent methyl protons, which provide an intense and sharper resonance compared to the corresponding DOTA– complexes. Experiments with paramagnetic Pr3+, Yb3+, Tb3+, Dy3+, and Tm3+ complexes of DOTMA4– showed that the Tm3+ complex is most favorable for MR thermometery because of the high temperature dependence of its chemical shift and its relatively narrow linewidth. The chemical shift of the methyl 1H signal from TmDOTMA– was ∼60 times more sensitive to temperature than the water 1H shift and was insensitive to changes in concentration, pH, [Ca2+], or the presence of other ions and macromolecules. The application of TmDOTMA– for measuring temperature in a subcutaneously implanted tumor model was demonstrated. Lastly, the feasibility of obtaining 3D images from the methyl 1H resonance of TmDOTMA– was demonstrated in phantom and live animal experiments. Overall, TmDOTMA– appears to be a promising probe for MR thermometry in vivo. Magn Reson Med 53:294–303, 2005. © 2005 Wiley‐Liss, Inc.
Is there a change in water proton density associated with functional magnetic resonance imaging?
Authors: Jochimsen Thies H. , Norris David G. , Möller Harald E. 
Published: January 2005

AbstractIn a recent series of studies (see, for example, Stroman et al. Magn Reson Imag 2001; 19:827–831), an increase of water proton density has been suggested to correlate with neuronal activity. Owing to the significant implications of such a mechanism for other functional experiments, the functional signal changes in humans at very short echo times were re‐examined by spin‐echo EPI at 3 T. The results do not confirm the previous hypothesis of a significant increase in extravascular proton density at TE = 0. Instead, an alternative explanation of the effect is offered: The use of a low threshold to identify activated voxels may generate an artificial offset in functional contrast due to the inclusion of false‐positives in the analysis. Magn Reson Med 53:470–473, 2005. © 2005 Wiley‐Liss, Inc.
Ischemia‐induced ADC changes are larger than osmotically‐induced ADC changes in a neonatal rat hippocampus model
Authors: van Pul C. , Jennekens W. , Nicolay K. , Kopinga K. , Wijn P.F.F. 
Published: January 2005

AbstractDiffusion‐weighted imaging (DWI) is frequently used to diagnose stroke. However, the origin of the observed reduction in the apparent diffusion coefficient (ADC) in the acute phase following ischemia is not well understood. Although cell swelling is considered to play an important role, it is unclear whether this can completely explain the large ADC decrease. We developed a method to induce in neonatal rat hippocampal slices both osmotic perturbations, which lead to cell swelling, and oxygen/glucose deprivation (OGD), which simulates ischemia. A perfusion system was used to provide the hippocampal slices with nutrients and oxygen to maintain slice viability, which was verified with the use of fluorescent dyes (live/dead staining). Upon induction of OGD, the ADC decreased to ∼57% of the initial value within 2 hr. The ADC reduction cannot fully be explained by changes due to cell swelling, since these led only to a maximum decrease of ∼83%. Therefore, in addition to cell swelling, other changes must contribute significantly to the ADC reduction. Magn Reson Med 53:348–355, 2005. © 2005 Wiley‐Liss, Inc.
Measurement and correction of transmitter and receiver induced nonuniformities in vivo
Authors: Wang Jinghua , Qiu Maolin , Yang Qing X. , Smith Michael B. , Constable R. Todd 
Published: January 2005

AbstractSignal intensity nonuniformities in high field MR imaging limit the ability of MRI to provide quantitative information and can negatively impact diagnostic scan quality. In this paper, a simple method is described for correcting these effects based on in vivo measurement of the transmission field B1+ and reception sensitivity maps. These maps can be obtained in vivo with either gradient echo (GE) or spin echo (SE) imaging sequences, but the SE approach exhibits an advantage over the GE approach for correcting images over a range of flip angles. In a uniform phantom, this approach reduced the ratio of the signal SD to its mean from around 30% before correction to approximately 6% for the SE approach and 9% for the GE approach after correction. The application of the SE approach for correcting intensity nonuniformities is demonstrated in vivo with human brain images obtained using a conventional spin echo sequence at 3.0 T. Furthermore, it is also shown that this in vivo B1+ and reception sensitivity mapping can be performed using segmented echo planar imaging sequences providing acquisition times of less than 2 min. Although the correction presented here is demonstrated with a simultaneous transmit and receive volume coil, it can be extended to the case of separate transmission and reception coils, including surface and phase array coils. Magn Reson Med 53:408–417, 2005. © 2005 Wiley‐Liss, Inc.
Imaging anisotropic and viscous properties of breast tissue by magnetic resonance‐elastography
Authors: Sinkus R. , Tanter M. , Catheline S. , Lorenzen J. , Kuhl C. , Sondermann E. , Fink M. 
Published: January 2005

AbstractMR‐elastography is a new technique for assessing the viscoelastic properties of tissue. One current focus of elastography is the provision of new physical parameters for improving the specificity in breast cancer diagnosis. This analysis describes a technique to extend the reconstruction to anisotropic elastic properties in terms of a so‐called transversely isotropic model. Viscosity is treated as being isotropic. The particular model chosen for the anisotropy is appealing because it is capable of describing elastic shear anisotropy of parallel fibers. The dependence of the reconstruction on the particular choice of Poisson's ratio is eliminated by extracting the compressional displacement contribution using the Helmholtz–Hodge decomposition. Results are presented for simulations, a polyvinyl alcohol breast phantom, excised beef muscle, and measurements in two patients with breast lesions (invasive ductal carcinoma and fibroadenoma). The results show enhanced anisotropic and viscous properties inside the lesions and an indication for preferred fiber orientation. Magn Reson Med 53:372–387, 2005. © 2005 Wiley‐Liss, Inc.
Detection threshold of single SPIO‐labeled cells with FIESTA
Authors: Heyn Chris , Bowen Chris V. , Rutt Brian K. , Foster Paula J. 
Published: January 2005

AbstractMRI of superparamagnetic iron oxide (SPIO)‐labeled cells has become a valuable tool for studying the in vivo trafficking of transplanted cells. Cellular detection with MRI is generally considered to be orders of magnitude less sensitive than other techniques, such as positron emission tomography (PET), single photon emission‐computed tomography (SPECT), or optical fluorescence microscopy. However, an analytic description of the detection threshold for single SPIO‐labeled cells and the parameters that govern detection has not been adequately provided. In the present work, the detection threshold for single SPIO‐labeled cells and the effect of resolution and SNR were studied for a balanced steady‐state free precession (SSFP) sequence (3D‐FIESTA). Based on the results from both theoretical and experimental analyses, an expression that predicts the minimum detectable mass of SPIO (mc) required to detect a single cell against a uniform signal background was derived: mc = 5v/(Kfsl · SNR), where v is the voxel volume, SNR is the image signal‐to‐noise ratio, and Kfsl is an empirical constant measured to be 6.2 ± 0.5 × 10−5 μl/pgFe. Using this expression, it was shown that the sensitivity of MRI is not very different from that of PET, requiring femtomole quantities of SPIO iron for detection under typical micro‐imaging conditions (100 μm isotropic resolution, SNR = 60). The results of this work will aid in the design of cellular imaging experiments by defining the lower limit of SPIO labeling required for single cell detection at any given resolution and SNR. Magn Reson Med 53:312–320, 2005. © 2005 Wiley‐Liss, Inc.
Small tip angle three‐dimensional tailored radiofrequency slab‐select pulse for reduced B1 inhomogeneity at 3 T
Authors: Saekho Suwit , Boada Fernando E. , Noll Douglas C. , Stenger V. Andrew 
Published: January 2005

AbstractThis work presents a small tip‐angle 3D tailored RF slab‐select pulse for reducing the B1 field inhomogeneity at 3T. The compensated slice profile was determined from a B1 inhomogeneity map. SNR improvement and degree of artifact reduction were evaluated in a NiCl2 doped phantom and human brains. The technique was found to reduce inhomogeneities as large as 30% of the peak image magnitude in all three spatial directions in the brain using a standard head coil. Magn Reson Med 53:479–484, 2005. © 2005 Wiley‐Liss, Inc.
Echo time optimization for linear combination myelin imaging
Authors: Vidarsson Logi , Conolly Steven M. , Lim Kelvin O. , Gold Garry E. , Pauly John M. 
Published: January 2005

AbstractA 3‐echo linear combination myelin imaging method is presented. The echo times and weights are chosen such that the signal‐to‐noise ratio (SNR) of myelin–water is maximized, and signals from other white matter components are sufficiently suppressed. Interfering tissue water and cerebrospinal fluid (CSF) signals are much stronger than myelin due to their longer T2 and abundance. By carefully optimizing the echo times a 50‐fold tissue water suppression is achieved along with a 10‐fold CSF suppression. For comparison 4, 5, and 32 echo filters are also designed using the same method. The SNR efficiency of these filters is very similar. The 3‐echo filter design was validated by phantom scans. In addition, multislice in vivo myelin images were acquired from both a healthy volunteer and a multiple sclerosis patient. Total scan time was 5 min. A uniform T2 filter is also designed to pass all white matter species with uniform gain. The myelin–water fraction of the in vivo 3‐echo data set is then measured by dividing the myelin image by the uniformly filtered image. Obtained myelin–water fractions compare well with previous work. Magn Reson Med 53:398–407, 2005. © 2005 Wiley‐Liss, Inc.
Assessing linear time‐invariance in human primary somatosensory cortex with BOLD fMRI using vibrotactile stimuli
Authors: Nangini C. , MacIntosh B.J. , Tam F. , Staines W.R. , Graham S.J. 
Published: January 2005

AbstractThe assumption of linear time‐invariance (LTI) in the human primary somatosensory cortex (SI) is assessed for fMRI signals generated by variable‐duration vibrotactile stimuli. Predictions based on time‐shifted summation (TSS) of responses to 2 s stimuli overestimate observed BOLD signal amplitudes in response to longer‐duration stimuli, in agreement with previous findings in other primary sensory cortices. To interpret these results, we undertook an alternative approach for LTI assessment by characterizing BOLD signals using two biophysical models. The first model assumes that the input stimulus envelope is proportional to neural activity. The second assumes that neural activity exhibits both transient and steady‐state components, consistent with extensive electrophysiological data, and fits the experimental data better. Although nonlinearity remains evident for short stimulus durations, the latter model shows that the TSS procedure to assess LTI overestimates the BOLD signal because the temporal characteristics of neural activity have not been considered adequately. Further research to investigate the BOLD response to time‐varying neural activity is required. Magn Reson Med 53:304–311, 2005. © 2005 Wiley‐Liss, Inc.
Effects of the apparent transverse relaxation time on cerebral blood flow measurements obtained by arterial spin labeling
Authors: St. Lawrence K.S. , Wang J. 
Published: January 2005

AbstractPrevious modeling studies have predicted that a significant fraction of the signal in arterial spin labeling (ASL) experiments originates from labeled water in the capillaries. Provided that the relaxation times in blood and tissue are similar, ASL data can still be analyzed with the conventional one‐compartment Kety model. Such studies have primarily focused on T1 differences and have neglected any differences in transverse relaxation times (T2 and T). This is reasonable for studies at lower fields; however, it may not be valid at higher fields due to the stronger susceptibility effects of deoxygenated blood. In this study a tracer kinetic model was developed that includes T differences between capillary blood and tissue. The model predicts that a reduction in blood T at higher fields will attenuate the capillary contribution to the ASL signal. This in turn causes an underestimation of CBF when ASL data are analyzed with the one‐compartment Kety model. We confirmed this prediction by comparing ASL data collected at 1.5 and 4 T, and at multiple gradient echoes (19, 32, 45, and 58 ms). A decrease in resting‐state CBF with echo time (TE) was observed at 4 T, but not at 1.5 T. These results suggest that at higher fields AST data should be collected using gradient‐echo techniques with short TEs, or with spin‐echo techniques. Furthermore, the sensitivity of the CBF measurements to venous T may affect the interpretation of concurrent ASL/BOLD studies. Magn Reson Med 53:425–433, 2005. © 2005 Wiley‐Liss, Inc.
Mitigation of susceptibility‐induced signal loss in neuroimaging using localized shim coils
Authors: Hsu Jung‐Jiin , Glover Gary H. 
Published: January 2005

AbstractCorrection of magnetic field distortions is essential for obtaining accurate brain blood‐oxygen‐level‐dependent functional magnetic resonance imaging (fMRI) activation maps. The present work introduces an active shimming method that utilizes the magnetic field generated by resistive shim coils placed in the mouth to locally homogenize the magnetic field in the inferior portion of the frontal lobe, where the field is most seriously distorted. The shimming field can be optimized in situ patient by patient for the region of interest of the scanner operator's choice. The method at 1.5 T is shown to be effective in reducing field inhomogeneity and in recovery of fMRI signal. For example, in a region of interest approximately of 149 cm3, a coil of simple geometry can reduce the root mean square of the magnetic field by more than 50% and the recovered signal increases the extent of activation detected in a breath‐holding fMRI experiment. Magn Reson Med 53:243–248, 2005. © 2005 Wiley‐Liss, Inc.
MR spectroscopic evidence for glial increase but not for neuro‐axonal damage in MS normal‐appearing white matter
Authors: Vrenken H. , Barkhof F. , Uitdehaag B.M.J. , Castelijns J.A. , Polman C.H. , Pouwels P.J.W. 
Published: January 2005

AbstractQuantitative single‐voxel, short echo‐time (TE) MR spectroscopy (MRS) was used to determine metabolite concentrations in the cerebral normal‐appearing white matter (NAWM) of 76 patients with multiple sclerosis (MS), and the WM of 25 controls. In NAWM of all MS disease types (primary progressive, relapsing‐remitting, and secondary progressive), the concentration ratio of total N‐acetyl‐aspartate (tNAA)/total creatine (tCr) was decreased compared to controls. Remarkably, this was entirely due to an increase of tCr in MS patients, whereas there was no difference in tNAA. Separate quantification of the two tNAA components yielded no significant difference in NAA (N‐acetyl‐aspartate), while the concentration of NAAG (N‐acetyl‐aspartyl‐glutamate) was slightly—but significantly—elevated in MS patients. Myo‐inositol (Ins) was strongly increased in MS patients, and choline‐containing compounds (Cho) were mildly increased. There were no metabolite differences between disease types, and no correlations with disability scores. The results are supported by measures of spectral quality, which were identical for patients and controls. In conclusion, MS NAWM containing very little perilesional tissue is characterized by increased glial cell numbers (increase of Ins and tCr) without evidence of axonal dysfunction (normal NAA). Further studies should elucidate the mechanism underlying increased NAAG in MS NAWM. Magn Reson Med 53:256–266, 2005. © 2005 Wiley‐Liss, Inc.
Muruganandham et al. In Vivo Tumor Lactate Relaxation Measurements by Selective Multiple‐Quantum‐Coherence (Sel‐MQC) Transfer, Magn Reson Med 2004;52:902‐906
Authors: Muruganandham Manickam 
Published: January 2005

AbstractThe original article to which this Erratum refers was published in Magnetic Resonance in Medicine (2004) 52(4) 902–906.