bluuebunny/crossref_metadata_2025 huggingface dataset:
Biopsy needle susceptibility artifacts
Authors: Ladd Mark E. , Erhart Peter , Debatin Jörg F. , Romanowski Benjamin J. , Boesiger Peter , McKinnon Graeme C.
Published: March 2007

Understanding the appearance of thin metallic structures in magnetic resonance imaging is important for evaluating the potential role of MRI in guiding and monitoring percutaneous interventions. As most MR compatible instruments are made from materials with a susceptibility different from water, their visibility is enhanced beyond what is expected on the grounds of displaced water alone. Unfortunately, this artifactually enhanced visibility is not constant, but instead depends on a variety of factors. This article presents computer simulations of the image distortion resulting from magnetic susceptibility differences between a needle and the surrounding tissue. The simulations show not only an artifact size that is dependent on needle composition, orientation, and pulse sequence, but also a corresponding shift of the artifact center away from the actual center of the needle. These effects place limits on the accuracy of MRI‐guided needle tip placement.
Enhanced resolution of proton NMR spectra of malignant lymph nodes using magic‐angle spinning
Authors: Cheng Leo L. , Lean Cynthia L. , Bogdanova Anna , Wright S. Carter , Ackerman Jerome L. , Brady Thomas J. , Garrido Leoncio
Published: March 2007

Proton NMR spectroscopy has proven useful in the detection of cancer in lymph node tissue. However, due to the high fat content of this type of tissue, 2D 1H COSY measurements (requiring acquisition times of 4–5 h or longer) are necessary to obtain the spectral information necessary for diagnosis. T2‐filtered proton magic‐angle spinning (MAS) NMR spectros‐copy provides 1D spectra of lymph nodes in approximately 20 min with sufficient spectral resolution allowing for identification of changes in cellular chemistry due to the presence of malignant cells. MAS data from lymph nodes of five control and six rats with mammary adenocarcinoma (R13762) demonstrated increases in the signal intensity of resonances associated primarily with lactate (s̀ = 4.12 ppm) P < 0.0004, creatines/lysine (s̀ = 3.04 ppm) P < 0.0032, and glutamate/ glutamine (s̀ = 2.36 ppm) P < 0.0002 in metastatic compared with normal lymph nodes. The infiltration of lymph nodes by malignant cells is an important prognostic factor for many cancers. The rapid assessment of node tissue without the introduction of sampling errors (inherent in currently employed histological procedures) would allow postoperative therapy decisions to be made more efficiently.
Broadband decoupled, 1H‐localized 13C MRS of the human brain at 4 tesla
Authors: Gruetter Rolf , Adriany Gregor , Merkle Hellmut , Andersen Peter M.
Published: March 2007

Broadband proton decoupling of the entire 13C spectrum was possible within power absorption guidelines and resulted in the detection of narrow (as low as 2–3 Hz), natural abundance signals from metabolites such as myo‐inositol, glutamate, N‐acetyl‐aspartate, and glutamine from 72 cm3 volumes in the human brain. To overcome the chemical shift displacement error, three‐dimensional localization on the 1H z magnetization was combined with polarization transfer. Efficiency of the heteronuclear localization method was demonstrated by the elimination of all scalp lipid resonances. A signal‐to‐noise ratio of 5:1 for 0.07 mM [13C] was achieved in 12 min, which is approximately a fivefold improvement over the sensitivity reported at 2.1 Tesla.
Gd‐DTPA2− as a measure of cartilage degradation
Authors: Bashir Adil , Gray Martha L. , Burstein Deborah
Published: March 2007

Glycosaminoglycans (GAGs) are the main source of tissue fixed charge density (FCD) in cartilage, and are lost early in arthritic diseases. We tested the hypothesis that, like Na+, the charged contrast agent Gd‐DTPA2‐ (and hence proton T1) could be used to measure tissue FCD and hence GAG concentration. NMR spectroscopy studies of cartilage explants demonstrated that there was a strong correlation (r > 0.96) between proton T1 in the presence of Gd‐DTPA2‐ and tissue sodium and GAG concentrations. An ideal one‐compartment electrochemical (Donnan) equilibrium model was examined as a means of quantifying FCD from Gd‐DTPA2‐ concentration, yielding a value 50% less but linearly correlated with the validated method of quantifying FCD from Na+. These data could be used as the basis of an empirical model with which to quantify FCD from Gd‐DTPA2‐ concentration, or a more sophisticated physical model could be developed. Spatial distributions of FCD were easily observed in T1‐weighted MRI studies of trypsin and interleukin‐1 induced cartilage degradation, with good histological correlation. Therefore, equilibration of the tissue in Gd‐DTPA2‐ gives us the opportunity to directly image (through T1, weighting) the concentration of GAG, a major and critically important macromolecule in cartilage. Pilot clinical studies demonstrated Gd‐DTPA2‐ penetration into cartilage, suggesting that this technique is clinically feasible.
The NMR chemical shift pH measurement revisited: Analysis of error and modeling of a pH dependent reference
Authors: Ackerman Joseph J. H. , Soto Gabriel E. , Spees William M. , Zhu Zehua , Evelhoch Jeffrey L.
Published: March 2007

A standard differential calculus‐based propagation of error treatment is applied to the traditional chemical‐exchange Henderson‐Hasselbalch NMR pH model in which the reference shift is pH independent. It is seen naturally from this analysis that (i) the error minimum in derived pH occurs in the region where pH and indicator pKa are equal and that (ii) the dynamic range, or difference between the limiting chemical shifts of acid and base forms of indicator species, determines the insensitivity of the technique to propagation of errors. To extend the useful pH range and utility of NMR pH determination methodology, a more general model is developed in which the internal reference species is also considered as having a pH‐dependent chemical shift. Data from standard solution pH titrations are fitted to both models and parameters are estimated for the normally observed family of ionizable phosphorus metabolites (ATP, inorganic phosphate, phosphoethanolamine and phosphocholine) and the xenometabolite 2‐deoxyglucose‐6‐phosphate with either phospho‐creatine, the α‐phosphate of ATP, or H2O taken as the 31P or 1H chemical shift internal reference species as well as with an external reference.
The determination of myocardial viability using Gd‐DTPA in a canine model of acute myocardial ischemia and reperfusion
Authors: Pereira Raoul S. , Prato Frank S. , Wisenberg Gerald , Sykes Jane
Published: March 2007

The partition coefficient of Gd‐DTPA was thought to vary with the amount of cellular membrane damage after an acute myocardial infarction. The relationship between the partition coefficient of Gd‐DTPA (λ) and the uptake of 201TI (as a marker of tissue viability) was studied 2 h to 3 weeks after reperfusion of a 2‐h occlusion to the left anterior descending coronary artery in a canine model. Gd‐DTPA was infused as a bolus followed by a prolonged constant infusion, and this infusion protocol was optimized such that the concentration of Gd‐DTPA was directly related to λ. After this infusion, MR images of excised hearts showed regions of increased signal intensity corresponding to increased Gd‐DTPA concentration. At all time points, λ and 201TI uptake were strongly negatively correlated indicating that λ is an accurate indicator of myocardial viability. Furthermore, λ in the infarcted regions was increased relative to normal regions after 2 h of reperfusion and stayed elevated up to 3 weeks. At all time points, λ in the infarcted and normal regions were significantly different. As well, this data showed a trend that λ in infarcted regions decreased monotonically from 1 day to 3 weeks. This trend was confirmed with MR imaging by examining the change in signal intensity of in vivo images from 4 days to 3 weeks in two animals. These results suggest that MRI with Gd‐DTPA could be used to measure the extent of myocardial damage after an acute myocardial infarction.
Noninvasive measurement of the pH inside the gut by using pH‐sensitive nitroxides. An in vivo EPR study
Authors: Gallez Bernard , Mader Karsten , Swartz Harold M.
Published: March 2007

The use of pH‐sensitive probes permits the measurement of the proton activity in biological systems by EPR spectroscopy. To illustrate the potential of this technique for in vivo purposes, the authors took advantage of the oral administration of nitroxides to monitor the pH value inside the stomach of mice after administration of different antacidics. The results indicate that EPR can be a valuable tool to characterize the pH in vivo in a continuous and noninvasive way.
Tumor 31P NMR pH measurements in vivo: A comparison of inorganic phosphate and intracellular 2‐deoxyglucose‐6‐phosphate as pHnmr indicators in murine radiation‐induced fibrosarcoma‐1
Authors: Soto Gabriel E. , Zhu Zehua , Evelhoch Jeffrey L. , Ackerman Joseph J. H.
Published: March 2007

Uncertainty regarding the intracellular/extracellular distribution of inorganic phosphate (Pi) in tumors has raised concerns that pH calculated from the tumor Pi chemical shift may not accurately represent the intracellular pH (pHin). This issue was addressed in subcutaneously transplanted murine radiation induced fibrosarcoma‐1 by directly comparing pH measured via Pi with pH measured via the in situ generated intracellular xenometabolite 2‐deoxyglucose‐6‐phosphate (2DG6P). In 131 comparative measurements employing eight tumor‐bearing mice under both control and hyperglycemic conditions (the latter to extend the range of tumor pH examined), the pH as derived from either 2DG6P or Pi showed only a small, but statistically significant, difference (0.07 ± 0.11 SD; P = 0.0001). Scatter in the comparative analysis over the pH range examined (ca. 5.5‐7.5) was not uniform. Above pH 6.6, 2DG6P indicated a pH lower than that of Pi by 0.088 ± 0.105 SD (n = 107, P = 0.0001); below pH 6.6, 2DG6P indicated a pH essentially identical to and not statistically different from that of Pi (mean difference 0.003 ± 0.128 SD (n = 24, P = 0.92)). Evidence is presented in support of this differential arising from a systematic measurement error due to peak overlap between 2DG6P and endogenous phosphomonoester species. These results support the use of Pi as a tumor 31P NMR pHin indicator, at least in RIF‐1 tumors under control and hyperglycemic conditions.
Three‐dimensional mapping of the static magnetic field inside the human head
Authors: Li Shizhe , Dardzinski Bernard J. , Collins Christopher M. , Yang Qing X. , Smith Michael B.
Published: March 2007

Finite element analysis was used to calculate the static magnetic field within the three‐dimensional head model. Localized field distributions were evaluated by using the magnetic field histogram technique. Experimental field maps and histograms of the human head were also obtained to validate the simulation results. Field deviations and gradients inside the human head cause NMR signal frequency shifts and line broadening, respectively. Voxels 2 × 2 × 0.5 cm may have frequency differences of more than 2.0 ppm. The linewidth of a single voxel may be broadened by more than 0.5 ppm. Calculated and experimental field maps are in excellent agreement. The global field distortion in the human head is primarily due to the susceptibility difference between air and tissues and their corresponding geometrical shapes.
High resolution measurement of cerebral blood flow using intravascular tracer bolus passages. Part I: Mathematical approach and statistical analysis
Authors: Østergaard Leif , Weisskoff Robert M. , Chesler David A. , Gyldensted Carsten , Rosen Bruce R.
Published: March 2007

The authors review the theoretical basis of determination of cerebral blood flow (CBF) using dynamic measurements of nondiffusible contrast agents, and demonstrate how parametric and nonparametric deconvolution techniques can be modified for the special requirements of CBF determination using dynamic MRI. Using Monte Carlo modeling, the use of simple, analytical residue models is shown to introduce large errors in flow estimates when actual, underlying vascular characteristics are not sufficiently described by the chosen function. The determination of the shape of the residue function on a regional basis is shown to be possible only at high signal‐to‐noise ratio. Comparison of several nonparametric deconvolution techniques showed that a nonparametric deconvolution technique (singular value decomposition) allows estimation of flow relatively independent of underlying vascular structure and volume even at low signal‐to‐noise ratio associated with pixel‐by‐pixel deconvolution.
High resolution measurement of cerebral blood flow using intravascular tracer bolus passages. Part II: Experimental comparison and preliminary results
Authors: Østergaard Leif , Sorensen Alma Gregory , Kwong Kenneth K. , Weisskoff Robert M. , Gyldensted Carsten , Rosen Bruce R.
Published: March 2007

This report evaluates several methods to map relative cerebral blood flow (rCBF) by applying both parametric and non‐parametric techniques to deconvolve high resolution dynamic MRI measurements of paramagnetic bolus passages with noninvasively determined arterial inputs. We found a nonparametric (singular value decomposition (SVD)) deconvolution technique produced the most robust results, giving mean gray:white flow ratio of 2.7 ± 0.5 (SEM) in six normal volunteers, in excellent agreement with recent PET literature values for age‐matched subjects. Similar results were obtained by using a model‐dependent approach that assumes an exponential residue function, but not for a Gaussian‐shaped residue function or for either Fourier or regularization‐based model‐independent approaches. Pilot studies of our CBF mapping techniques in patients with tumor, stroke, and migraine aura demonstrated that these techniques can be readily used on data routinely acquired by using current echo planar imaging technology. By using these techniques, the authors visualized important regional hemodynamic changes not detectable with rCBV mapping algorithms.
ROC methods for evaluation of fMRI techniques
Authors: Sorenson James A. , Wang X.
Published: March 2007

Receiver operating characteristic (ROC) methods provide a standardized and statistically meaningful means for comparing signal‐detection accuracy. A brief overview of ROC methods is presented. Example applications include a comparison of four different postprocessing algorithms operating on simulated fMRI time‐course data sets and on human null data sets to which a simulated fMR response had been added. ROC methods also were used to reanalyze one data set from a previously published work. Additional ROC methods that also may be useful for fMRI comparisons are described.
Optimization of spoiled gradient‐echo phase imaging for in vivo localization of a focused ultrasound beam
Authors: Chung Andrew H. , Hynynen Kullervo , Colucci Vincent , Oshio Koichi , Cline Harvey E. , Jolesz Ferenc A.
Published: March 2007

The parameters of a spoiled gradient‐echo (SPGR) pulse sequence have been optimized for in vivo localization of a focused ultrasound beam. Temperature elevation was measured by using the proton resonance frequency shift technique, and the phase difference signal‐to‐noise ratio (SNRδ ϕ) was estimated in skeletal muscle and kidney cortex in 10 rabbits. Optimized parameters included the echo time equivalent to T*2of the tissue, the longest repetition time possible with a 20‐s sonication, and the flip angle equivalent to the Ernst angle. Optimal SPGR phase imaging can detect a sonication beam with a peak phase difference of 0.55 radian, which corresponds to a temperature elevation of 7.3°C. The sonication beam can be localized within one voxel (0.6 × 0.6 × 5 mm3) at power levels that are below the threshold for thermal damage of the tissue.
Assessment of microvascular integrity in the isolated perfused rat liver by contrast‐enhanced MRI. Attenuation of reperfusion injury by conjugated deferoxamine
Authors: Colet Jean‐Marie , Cetiner Erol , Hedlund Bo E. , Muller Robert N.
Published: March 2007

Reperfusion of an ischemic organ can lead to miorocirculatory impairment caused, in part, by the generation of reactive free radicals. The iron‐catalyzed formation of these deleterious substances can be counteracted by strong metal chelators like deferoxamine. In this study, the protective effect of deferoxamme conjugate was evaluated by assessment of the hepatic microcirculation in the post‐ischemic phase. Assessment of the microvasculature was performed by MRI on the isolated perfused rat liver. The restriction of sinusoids subsequent to reperfusion injury was demonstrated by the use of a particulate superparamagnetic contrast agent trapped in the microvasculature. The protective effect of conjugated deferoxamine was evaluated by both MRI and release of alanine aminotransferase. Contrast‐enhanced MRI demonstrated a marked impairment of the microcirculation subsequent to the unprotected reperfusion of the ischemic tissue. This injury was attenuated by deferoxamine conjugated to hydroxyethylstarch (HES‐DFO).
Interpretation of flow encoding and quantification in MRI: Time domain versus frequency domain
Authors: Peeters Frank , Luypaert Robert , Eisendrath Henri , Osteaux Michel
Published: March 2007

The traditional approach to flow effects in MRI is based on the gradient moment expansion. Recently, we have presented an alternative description by using linear response theory: the distortions of the velocity waveform induced by the gradient waveforms were analyzed in the frequency domain on the basis of the transfer function. In the present paper, we perform an analysis of flow encoding and quantification in the time domain, on the basis of the impulse response. The analysis shows that flow encoding should be interpreted as a weighted averaging process. Instantaneous flow encoding is determined by the centroid of the impulse response, but care should be taken regarding the physical meaning of the instant of encoding. The relationship of this approach to the frequency domain and gradient moment expansion approaches is clarified. By way of example, some interesting applications are investigated: asymmetrical phase encoding gradients to minimize misregistration and oscillating read‐out gradients for flow quantification. A variety of new applications are expected to derive from the combination of both the time and frequency domains.
Multisection T1‐weighted hybrid‐rare: A pulse sequence for MR imaging of the entire liver during suspended respiration
Authors: Jara Hernán , Soto Jorge A. , Yu Beverly , Hentzen Peter C. , van Yperen Gert H. , Yucel E. Kent
Published: March 2007

It is shown that the maximum average‐data‐collection‐speed (ADCS) of multisection 2D hybrid‐RARE sequences is independent of TR and TEeff, and a monotonically increasing function of echo‐train‐length (ETL). This result was used in the design of an optimized T1‐weighted hybrid‐RARE sequence that produces 20 images of the abdomen in 31 s divided into four breath‐hold periods. The resulting ADCS is 58 lines in k‐space per second. Twenty‐four subjects (2 healthy volunteers and 22 patients) were imaged with a protocol that also included: (a) breath‐hold T1‐weighted FLASH which acquires data at 34 lines in k‐space per second (49 s scan time), and (b) T1‐weighted conventional spin‐echo (9:44 minutes scan time) with respiratory compensation. The experiments show that this T1‐weighted‐hybrid‐RARE sequence has: (1) a level of T1 weighting that is comparable with the conventional sequences, (2) very low vulnerability to susceptibility artifacts, (3) high data acquisition efficiency, and (4) higher SNR than T1‐weighted‐FLASH. In conclusion, the T1‐weighted‐hybrid‐RARE sequence described herein is an efficacious and reproducible technique for rapid imaging of the upper abdomen during suspended respiration.
Citrate signal enhancement with a homonuclear J‐refocusing modification to double‐echo PRESS sequences
Authors: Mulkern Robert V. , Bowers John L. , Peled Sharon , Kraft Robert A. , Williamson Daniel S.
Published: March 2007

The citrate signal at field strengths of whole body imagers arises from two sets of two strongly coupled methylene protons. This causes citrate spectra acquired with standard in vivo localization schemes like the double‐echo point resolved echo spectroscopy (PRESS) sequence to have complicated dependencies on timing parameters. A homonuclear J‐refo‐cused version of the double‐echo PRESS sequence that has previously been shown to completely remove J‐modulations from weakly coupled AX systems is considered for its potential in acquiring signal from the strongly coupled AB system of citrate. An analytic solution to the problem is derived with the density matrix formalism and verified both numerically and experimentally for 7 T conditions. The general expression for the AB signal is applied to study the 1.5 T citrate signal where a substantial signal enhancement over conventional double‐echo PRESS sequences is predicted and verified for echo times in the 150 to 300 ms range.
Commutator filter: A novel technique for the identification of structures producing significant susceptibility inhomogeneities and its application to functional MRI
Authors: Lai Song , Reichenbach Jürgen R. , Haacke E. Mark
Published: March 2007

A robust postprocessing method to detect regions of magnetic field change is presented. High resolution gradient echo data is acquired to create a complex baseline image. From this image, two low resolution images are obtained by applying a low pass filter on the magnitude image and the complex image, respectively. Subtraction of the magnitude of the filtered complex image from the filtered magnitude image gives a new image called a commutator image in which regions of susceptibility‐induced field variation are greatly enhanced. Results on phantoms and applications to visualize paramagnetic venous blood vessels in the human brain are presented. The use of this technique on a 3D gradient echo data set represents a new approach to obtain an MR venogram. The application of this method to blood oxygenation level dependent (BOLD) functional brain MR imaging is demonstrated and the important role susceptibility plays in this model is verified.
Analysis of individual purine and pyrimidine nucleoside di‐ and triphosphates and other cellular metabolites in PCA extracts by using multinuclear high resolution NMR spectroscopy
Authors: Lutz Norbert W. , Yahi Nouara , Fantini Jacques , Cozzone Patrick J.
Published: March 2007

This work demonstrates thatindividualpurine and pyrimidine NDP and NTP can be assigned in high resolution31P NMR spectra from tissue extracts. To the best of our knowledge, it is shown for the first time that ATP, GTP, UTP, CTP, and the corresponding diphosphates can be quantitated in cell extracts without using HPLC or other biochemical methods. This work provides the basis for further optimization of nucleotide quantitation by31P NMR spectroscopy, and for a full assessment of this method. Furthermore, a new technique was developed for1H,31P, and13C NMR signal assignment and quantitation in cell extracts by using the same external reference capillary for all three nuclei. This allows for efficient, quantitative, multinuclear NMR spectroscopy without extract contamination by standard material.
Another interpretation of burst imaging as a variation of line projection imaging
Authors: Matsuda Tetsuya , Komori Masaru , Inoue Hiroshi , Hayashi Kohji , Kimura Toshihiko , Sasayama Shigetake
Published: March 2007

Burst imaging and DUFIS realize fast imaging without rapid switching of magnetic field gradients. In this paper, some new aspects of burst imaging are explored. Interestingly, when one‐dimensional Fourier transform is applied, Burst imaging becomes similar to line projection scanning, a concept proposed earlier by Mansfield and Maudsley (P. Mansfield, A. A. Maudsley, Planar spin imaging by NMR. J. Magn. Resort. 27, 101‐119 (1977)). The line scanning interpretation is applied to two‐dimensional Burst imaging, and the relationship between its two‐dimensional k‐space trajectory and line scanning interpretation is discussed.
Temporally resolved 3D phase‐contrast imaging
Authors: Wigström Lars , Sjöqvist Lars , Wranne Bengt
Published: March 2007

A conventional 3D phase contrast acquisition generates images with good spatial resolution, but often gives rise to artifacts due to pulsatile flow. 2D cine phase contrast, on the other hand, can register dynamic flow, but has a poor spatial resolution perpendicular to the imaging plane. A combination of both high spatial and temporal resolution may be advantageous in some cases, both in quantitative flow measurements and in MR angiography. The described 3D cine phase contrast pulse sequence creates a temporally resolved series of 3D data sets with velocity encoded data.
An alternative to GRASE: Toward spin‐echo‐like contrast with independent reconstruction of gradient‐echo images
Authors: Keller Paul J. , Karis John P. , Fram Evan K. , Heiserman Joseph E. , Drayer Burton P.
Published: March 2007

Multiple gradient echoes are generated for each RF echo of a Carr‐Purcell‐Meiboom‐Gill (CPMG) train. Independently, phase‐encoded fast spin‐echo images are obtained from the different gradient echoes. Presently, three images are formed from three gradient‐echoes from each of four RF echoes. The two peripheral gradient echo images are encoded for a late effective TE, then summed after reconstruction: this image has decreased fat intensity and increased susceptibility contrast compared with fast spin echo. The central gradient echoes yielded another image of intermediate contrast useful for neuroimaging. Raw data from the variously timed gradient echoes are not combined as they are in GRASE.
Arterial input functions from MR phase imaging
Authors: Akbudak Erbil , Conturo Thomas E.
Published: March 2007

A method is presented for obtaining high‐sensitivity arterial input functions following bolus intravenous contrast agent administration. Arterial contrast agent is monitored by phase reconstruction of single‐shot echo‐planar images. During bolus injections of a gadolinium (Gd) agent in a baboon, data were acquired at the mid‐abdominal aorta, and magnitude and phase‐shift images were reconstructed. Pair‐wise image subtraction was used to minimize phase aliasing. The phase‐based method is shown to have a significant potential improvement in sensitivity compared to the magnitude approach. The phase method also has a general linear response to concentration. This method may have potential utility in quantitative imaging of blood flow and contrast agent kinetics.
Visualization of dedicated catheters using fast scanning techniques with potential for MR‐guided vascular interventions
Authors: Bakker Chris J. , Hoogeveen Romhild M. , Weber Jan , van Vaals Joop J. , Viergever Max A. , Mali Willem P.
Published: March 2007

This paper reports the development of dedicated catheters and real‐time MR scan techniques for guiding vascular interventional procedures. By way of phantom experiments, it is shown that proper modification of the magnetic properties of catheters allows their conspicuous and consistent visualization in subsecond 2D gradient echo images and phase contrast angiograms. Dynamic scan times as low as 0.5 s could be achieved by exploiting the keyhole technique and purposeful postprocessing. The temporal resolution and spatial resolution of the resultant scan protocol shows promise for adequate tracking of catheter manipulation.
MR spectroscopic imaging and diffusion‐weighted MRI for early detection of kainate‐induced status epilepticus in the rat
Authors: Ebisum Toshihiko , Rooney William D. , Graham Steven H. , Mancuso Anthony , Weiner Michael W. , Maudsley Andrew A.
Published: March 2007

Previous studies have shown that reduction of N‐acetyl‐aspartate (NAA) is correlated with the degree of neuronal loss at 3 days after kainate‐induced status epilepticus in the rat. In this study, magnetic resonance spectroscopic imaging (MRSI), measurement of NAA and lactate, T2‐weighted MRI, and diffusion‐weighted MRI were used to study early alterations in rat piriform cortex at 12 and 26 h after kainate administration. The major findings are that decreased NAA signal, increased lactate signal, and decreased apparent diffusion coefficient (ADC) were observed at 12 h, with little evidence of histological and T2‐weighted MRI changes. These results support the hypothesis that NAA, lactate signals, and ADC provide sensitive methods for detection of early and minimal brain damage in vivo.
Finger printing of mycobacterium tuberculosis in patients with intracranial tuberculomas by using in vivo, ex vivo, and in vitro magnetic resonance spectroscopy
Authors: Gupta Rakesh K. , Roy Raja , Dev Ravi , Husain Mazhar , Poptani Harish , Pandey Rakesh , Kishore Janak , Bhaduri Amiya P.
Published: March 2007

In vivo, ex vivo, and in vitro proton magnetic resonance spectroscopy was performed in 12 patients with intracranial tuberculomas with an aim of detecting the biochemical constituents of Mycobacterium tuberculosis in a granuloma. One dimensional (1D) single pulse and spin‐echo sequences and 2D correlative spectroscopy were used for the ex vivo study to confirm the resonances seen on in vivo study. Spectroscopic studies of the perchloric acid and lipid extract of granuloma and M. tuberculosis were performed to look for similarity of resonance. In vivo study showed the presence of lipids at 0.9, 1.3, 2.0, 2.8 ppm, and phosphoserine at 3.7 ppm. All these resonances were confirmed on ex vivo study. In addition, distinct resonances of serine and phenolic lipids were seen on ex vivo and in vitro study of tuberculous granuloma, which have not been observed in other intracranial tumors. Lipid extract of granuloma and M. tuberculosis showed phenolic lipids at 7.1 and 7.4 ppm, a constituent of the cell wall of the bacteria in a tuberculoma. It appears that it may be possible to finger print the biochemicals of the cell wall of M. tuberculosis in a tuberculous granuloma and thus may help in detection and diagnosis of such lesions.
2D locally focused MRI: Applications to dynamic and spectroscopic imaging
Authors: Yao Lian , Cao Yue , Levin David N.
Published: March 2007

Conventional magnetic resonance images have uniform spatial resolution across the entire field of view. A method of creating MR images with user‐specified spatial resolution along one dimension of the field of view was described recently by the authors. This paper presents the 2D generalization of this technique, which allows the user to specify arbitrary spatial resolution in arbitrary 2D regions. These images are reconstructed from signals that sparsely sample the k‐space representation of the image. Therefore, locally focused images can be acquired in less time than that required by Fourier imaging with uniformly high resolution. In this paper the authors show how to increase the temporal resolution of dynamic imaging (e.g., interventional imaging) by using high resolution in areas of expected change and lower resolution elsewhere. Alternatively, by matching the local spatial resolution to the expected edge content of the image, it is possible to avoid the localized truncation artifacts that mark Fourier images reconstructed from the same number of signals. For example, the authors show how proton spectroscopic images of the head may be improved by using high resolution in the neighborhood of scalp lipids that might otherwise cause truncation artifacts.
Biexponential diffusion attenuation in various states of brain tissue: Implications for diffusion‐weighted imaging
Authors: Niendorf Thoralf , Dijkhuizen Rick M. , Norris David G. , van Lookeren Campagne Menno , Nicolay Klaas
Published: March 2007

Diffusion‐weighted single voxel experiments conducted at b‐values up to 1 × 104 smm−2 yielded biexponential signal attenuation curves for both normal and ischemic brain. The relative fractions of the rapidly and slowly decaying components (f1, f2)are f1 = 0.80 ± 0.02, f2 = 0.17 ± 0.02 in healthy adult rat brain and f1 = 0.90 ± 0.02, f2 = 0.11 ± 0.01 in normal neonatal rat brain, whereas the corresponding values for the postmortem situation are f1 = 0.69 ± 0.02, f2 = 0.33 ± 0.02. It is demonstrated that the changes in f1 and f2 occur simultaneously to those in the extracellular and intracellular space fractions (fex, fin) during: (i) cell swelling after total circulatory arrest, and (ii) the recovery from N‐methyl‐D‐aspartate induced excitotoxic brain edema evoked by MK‐801, as measured by changes in the electrical impedance. Possible reasons for the discrepancy between the estimated magnitude components and the physiological values are presented and evaluated. Implications of the biexponential signal attenuation curves for diffusion‐weighted imaging experiments are discussed.
Improving MR quantification of regional blood volume with intravascular T1 contrast agents: Accuracy, precision, and water exchange
Authors: Donahue Kathleen M. , Weisskoff Robert M. , Chesler David A. , Kwong Kenneth K. , Bogdanov Alexei A. , Mandeville Joseph B. , Rosen Bruce R.
Published: March 2007

The goal of this work was to develop a comprehensive understanding of the relationship between vascular proton exchange rates and the accuracy and precision of tissue blood volume estimates using intravascular T1 contrast agents. Using computer simulations, the effects of vascular proton exchange and experimental pulse sequence parameters on measurement accuracy were quantified. T1 and signal measurements made in a rat model implanted with R3230 mammary adenocarcinoma tumors demonstrated that the theoretical findings are biologically relevant; data demonstrated that over‐simplified exchange models may result in measures of tumor, muscle, and liver blood volume fractions that depend on experimental parameters such as the vascular contrast concentration. As a solution to the measurement of blood volume in tissues with exchange that is unknown, methods that minimize exchange rate dependence were examined. Simulations that estimated both the accuracy and precision of such methods indicated that both the inversion recovery and the transverse‐spoiled gradient echo methods using a “noexchange” model provide the best trade‐off between accuracy and precision.
Pharmacokinetic changes induced by vasomodulators in kidneys, livers, muscles, and implanted tumors in rats as measured by dynamic Gd‐DTPA‐enhanced MRI
Authors: Su Min‐Ying , Wang Zhiheng , Roth Gerald M. , Lao Xiaoyan , Samoszuk Michael K. , Nalcioglu Orhan
Published: March 2007

The effects of three physiologically different vasomodulators, angiotensin II (a vasoconstrictor), hydralazine (a vasodilator), and histamine (a permeability modulator), on the pharmaco‐kinetics of entry of small molecules (measured by Gd‐DTPA concentration) into normal and abnormal tissue were studied in rats implanted with R3230 AC tumors. Sequential dynamic Gd‐DTPA‐enhanced MRI studies, one before and one after vasomodulator administration, were performed, and the signal intensities of various tissues analyzed. Angiotensin II (6 μg/kg) reduced blood flow in tumors, but increased it in muscles. Hydralazine (5 mg/kg) reduced blood flow in tumors, kidneys, and livers, and slowed Gd‐DTPA clearance from tumors, livers, and muscles. Histamine (25 μg/kg) increased renal blood flow, hastening Gd‐DTPA clearance causing reduced measurable blood flow in tumors and muscles. By simultaneously monitoring the effects in various tissues, the pharmacokinetic effect of each drug in the entire body could be obtained.
Lactate, N‐acetylaspartate, choline and creatine concentrations, and spin‐spin relaxation in thalamic and occipito‐parietal regions of developing human brain
Authors: Cady Ernest B. , Penrice Juliet , Amess Philip N. , Lorek Ann , Wylezinska Marzena , Aldridge Richard F. , Franconi Florence , Wyatt John S. , Reynolds E. Osmund R.
Published: March 2007

Previous studies of the brains of normal infants demonstrated lower lactate (Lac)/choline (Cho), Lac/creatine (Cr), and Lac/N‐acetylaspartate (Naa) peak‐area ratios in the thalamic region (predominantly gray matter) compared with occipitoparietal (mainly unmyelinated white matter) values. In the present study, thalamic Cho, Cr, and Naa concentrations between 32–42 weeks' gestational plus postnatal age were greater than occipito‐parietal: 4.6 ± 0.8 (mean ± SE), 10.5 ± 2.0, and 9.0 ± 0.7 versus 1.8 ± 0.6, 5.8 ± 1.5, and 3.4 ± 1.1 mmol/kg wet weight, respectively: Lac concentrations were similar, 2.7 ± 0.6 and 3.3 ± 1.3 mmol/kg wet weight, respectively. In the thalamic region, Cho and Naa T2s increased, and Cho and Lac concentrations decreased, during development. Lower thalamic Lac peak‐area ratios are principally due to higher thalamic concentrations of Cho, Cr, and Naa rather than less Lac. The high thalamic Cho concentration may relate to active myelination; the high thalamic Naa concentration may be due to advanced gray‐matter development including active myelination. Lac concentration is higher in neonatal than in adult brain.
Effect of 6‐aminonicotinamide on the pentose phosphate pathway: 31P NMR and tumor growth delay studies
Authors: Koutcher Jason A. , Alfieri Alan A. , Matei Cornelia , Meyer Kristen L. , Street James C. , Martin Daniel S.
Published: March 2007

6‐aminonicotinamide (6AN) has been shown to enhance radio‐sensitivity in vitro, although previous in vivo studies failed to show an effect. 31P NMR spectra were obtained by using a one‐dimensional chemical shift imaging technique on a first generation transplant of the CD8FI spontaneous mammary carcinoma tumor model. Spectra were obtained both before and 10 h after treatment with 6AN (20 mg/kg). Changes in pH, nucleoside triphosphate/inorganic phosphate, and phosphocreatine/inorganic phosphate measured at 10 h post‐6AN were not significant. A new peak was detected 10 h post‐6AN, which was assigned to 6‐phosphogluconate (6PG), indicating inhibition of the pentose phosphate pathway (PPP). Based on the spectral data demonstrating inhibition of the PPP at 10 h post‐6AN, tumor‐bearing mice were irradiated (15 Gy × 3 fractions) on Days 1, 10 or 11, and 21 10 h after administration of 6‐aminonicotinamide (20 mg/kg). Tumor‐bearing mice receiving 6AN alone (20 mg/kg × 3), radiation alone (15 Gy × 3), or saline were also studied. Tumor growth delay studies indicated that 6AN alone induced a small but significant tumor growth delay (4.3 ± 0.8 days). Radiation alone induced a tumor growth delay of 34.5 ± 2.7 days. Treatment with 6AN followed by radiation induced a tumor growth delay of 57.0 ± 3.8 days. This was significantly greater than the TGD values for treatment with 6AN alone or radiation (P < 0.01). No complete regressions were noted after treatment with 6AN or radiation alone. Concomitant therapy with 6AN plus radiation yielded 6/28 complete regressions (21%), which was significantly greater than radiation (P < 0.05) or 6AN alone (P < 0.01) on this mammary carcinoma.
Toward a quantitative assessment of diffusion anisotropy
Authors: Pierpaoli Carlo , Basser Peter J.
Published: March 2007

Indices of diffusion anisotropy calculated from diffusion coefficients acquired in two or three perpendicular directions are rotationally variant. In living monkey brain, these indices severely underestimate the degree of diffusion anisotropy. New indices calculated from the entire diffusion tensor are rotationally invariant (RI). They show that anisotropy is highly variable in different white matter regions depending on the degree of coherence of fiber tract directions. In structures with a regular, parallel fiber arrangement, water diffusivity in the direction parallel to the fibers (D| ≈ 1400–1800 × 10−6 mm2/s) is almost 10 times higher than the average diffusivity in directions perpendicular to them ((D + D⊥′)/2 ≈ 150–300 × 10−6 mm2/s), and is almost three times higher than previously reported. In structures where the fiber pattern is less coherent (e.g., where fiber bundles merge), diffusion anisotropy is significantly reduced. However, RI anisotropy indices are still susceptible to noise contamination. Monte Carlo simulations show that these indices are statistically biased, particularly those requiring sorting of the eigenvalues of the diffusion tensor based on their magnitude. A new intervoxel anisotropy index is proposed that locally averages inner products between diffusion tensors in neighboring voxels. This “lattice” RI index has an acceptably low error variance and is less susceptible to bias than any other RI anisotropy index proposed to date.
Unraveling diffusion constants in biological tissue by combining Carr‐Purcell‐Meiboom‐Gill imaging and pulsed field gradient NMR
Authors: van Dusschoten Dagmar , Moonen Chrit T. W. , de Jager P. Adrie , Van As Henk
Published: March 2007

A diffusion‐weighted multi‐spin‐echo pulse sequence is presented, which allows for simultaneous measurement ofT2, the fractional amplitude, and the diffusion constant of different fractions. Monte Carlo simulations demonstrate an improvement of this sequence with respect to the accuracy of diffusion constant and fractional amplitude for slow exchange. Examples are shown for a simple phantom containing two fractions. In addition, experiments on cat brain in healthy condition and following occlusion of the middle cerebral artery show that the fractional amplitude and the diffusion constant of cerebral spinal fluid and normal brain tissue can be analyzed within each pixel with acceptable accuracy.
Diffusion of metabolites in normal and ischemic rat brain measured by localized 1H MRS
Authors: van der Toorn Annette , Dijkhuizen Rick M. , Tulleken Cees A. F. , Nicolay Klaas
Published: March 2007

The apparent diffusion coefficient (ADC) of choline‐containing compounds (Cho), creatine and phosphocreatine (Cre), N‐acetyl‐aspartate (NAA), lactate, and water was measured in normal rat brain, and in the ischemic and contralateral region of rat brain approximately 3 and 24 h after induction of focal cerebral ischemia. After 3 h of ischemia, the ADC of Cre and NAA in the ischemic region had significantly decreased by 29% and 19%, respectively (P < 0.05). Lactate ADC was also obtained in the ischemic region. After 24 h of focal ischemia, no ADC values could be measured for NAA, Cre and Cho in the ischemic region because their concentrations had become too low. The ADCs of lactate and water in the ischemic volume were virtually identical at 3 and 24 h after occlusion. The experiments suggest that the ADC decrease of water after induction of ischemia is partly caused by changes in the diffusion characteristics of the intracellular compartment.
Improved image registration by using fourier interpolation
Authors: Eddyy William F. , Fitzgerald Mark , Noll Douglas C.
Published: March 2007

This paper presents a technique for performing two‐dimensional rigid‐body image registration for functional magnetic resonance images (fMRI). The method provides accurate motion correction without local distortion. The approach is to perform the translation and rotation in the Fourier domain. For images sampled on a grid, such as in echo‐planar imaging (EPI), one potential stumbling block to this approach is the computational burden of reconstruction, since the rotated image will no longer be on the Cartesian grid. A method of approximating rotations via local translations (shearing) is presented, which keeps the data on the Cartesian grid. This can provide quite accurate approximations with only a moderate amount of computation. A mean squared error (MSE) criterion is used for determining the registration parameters. This method is tested on several sets of simulated images and shown to have an accuracy ranging from 0.02 to 0.3 pixels for images with SNRs ranging from 100 to 10, respectively. They techniques have been tested on several sets of images. They are shown to work well on real subjects, for both echo‐planar and spiral data acquisition schemes. The techniques are used in an activation study in which the subject moved his head during image collection. After use of this registration technique, the activation is easily detected.
Curved slice imaging
Authors: Börnert Peter , Schäffter Tobias
Published: March 2007

Curved slice imaging based on multidimensional RF pulses is introduced and discussed. This new approach makes it possible to image curved anatomical structures by using MRI. The 2D RF or 3D RF pulses used can be tailored to excite or refocus transverse magnetization of a previously defined arbitrarily curved slice profile in a 3D space. These RF pulses can be integrated into all standard MRI sequences to perform slice selection. The final curved slice image is obtained as a projection of the curved slice magnetization onto a selected imaging plane. The problem of ambiguities arising due to this projection process is addressed. Phantom and in vivo experiments were performed to illustrate the advantages and limitations of this approach.
Effects of polar sampling in k‐space
Authors: Lauzon M. Louis , Rutt Brian K.
Published: March 2007

Magnetic resonance imaging allows numerous k‐space sampling schemes such as cartesian, polar, spherical, and other non‐rectilinear trajectories. Non‐rectilinear MR acquisitions permit fast scan times and can suppress motion artifacts. Still, these sampling schemes may adversely affect the image characteristics due to aliasing. Here, the Fourier aliasing effects of uniform polar sampling, i.e., equally spaced radial and azimuthal samples, are explained from the principal point spread function (PSF). The principal PSF is determined by assuming equally spaced concentric ring samples in k‐space. The radial effects such as replication, smearing, truncation artifacts, and sampling requirements, are characterized based on the PSF.
A method for the calculation of currents on shielded gradient coils
Authors: Carlson Joseph W. , Zha Leping
Published: March 2007

Alternate expressions for the current density on the shielding surface of a gradient coil are derived for cylindrical, planar, and hyperbolic gradient coils. For the planar and hyperbolic geometries, these expressions allow more rapid high‐precision calculations of current densities than the conventional solution.
TmDOTP5−: A substance for NMR temperature measurements in vivo
Authors: Zuo Chun S. , Bowers John L. , Metz Kenneth R. , Nosaka Toshihisa , Sherry A. Dean , Clouse Melvin E.
Published: March 2007

The chemical shifts of 31P and 1H in thulium 1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetrakis(methylene phosphonate) (TmDOTP5−) are approximately two orders of magnitude more sensitive to temperature than are water proton and 19F shifts. In the physiologically relevant pH range, the 31P and 1H chemical shifts of TmDOTP5− are linear functions of temperature between 25 and 47°C. The results indicate that using TmDOTP5− can provide measurements of temperature in vivo that are significantly more accurate than methods based on water and fluorocarbon chemical shifts.
Correction for distortion of echo‐planar images used to calculate the apparent diffusion coefficient
Authors: Haselgrove John C. , Moore James R.
Published: March 2007

An algorithm for correcting the distortions that occur in diffusion‐weighted echo‐planar images due to the strong diffusion‐sensitizing gradients is presented. The dominant distortions may be considered to be only changes of scale coupled with a shear and linear translation in the phase‐encoding direction. It is then possible to correct for them by using an algorithm in which each line of the image in the phase‐encoding direction is considered in turn, with only one parameter (the scale) to be found by searching.