bluuebunny/crossref_metadata_2025 huggingface dataset:
Hadamard spectroscopic imaging technique as applied to study human calf muscles
Authors: Goelman Gadi , Walter Glenn , Leigh John S.
Published: March 2007

In vivo results obtained by the B1 insensitive Hadamard spectroscopic imaging multivolume technique used with a surface coil are shown. The functional behavior of different human calf muscles during exercise was determined and the Pi/PCr ratio in each calf muscle, during steady‐state conditions, was measured as a function of work level. Different levels of metabolic and physical activity were observed at the three calf muscles. © 1992 Academic Press, Inc.
Analysis of phospholipids in brain tissue by 31P NMR at different compositions of the solvent system chloroform‐methanol‐ water
Authors: Edzes Hommo T. , Teerlink Tom , Knaap Marjo S. Van Der , Valk Jaap
Published: March 2007

Brain phospholipids can be quantitated by high‐resolution 31P NMR of crude brain tissue extracts in the solvent system chloroform‐methanol‐water (+EDTA) which was introduced recently (P. Meneses and T. Glonek, J. Lipid Res. 29, 679 (1988)). Phospholipid resonance positions depend on the type of tissue extract and on solvent composition. The effects of systematic variation of the solvent system on phospholipid NMR profiles are presented. Resolution can be optimized by adjustment of the solvent composition. Virtually all phospholipid classes can be resolved, and the major phospholipids in brain: sphingo‐myelin and phosphatidyl‐choline, ‐serine, ‐inositol, ‐ethanolamine, and ‐ethanolamine plasmalogen can be quantitated easily. Additional resonances have been assigned to phosphatidylcholine plasmalogen, alkylacyl‐phosphatidylcholine and phosphatidylinositolbis‐phosphate. NMR offers a rapid method for quantitative analysis of the phospholipid composition in brain tissue which requires minimum sample handling.
Analysis of hybrid imaging techniques
Authors: Ortendahl Douglas A. , Kaufman Leon , Kramer David M.
Published: March 2007

Hybrid imaging techniques have been proposed as a means of decreasing imaging time without the cost and technical constraints of echo planar imaging. With this technique phase encoding measurements acquired at different echo times in more than one multiecho experiment are used to form a single image. This study analyzes the trade‐offs which occur in the selection of this technique over more conventional imaging in terms of signal/noise, contrast, resolution, imaging time, and efficiency. Hybrid imaging is shown to be advantageous when raw speed is essential such as in abdominal or pediatric imaging. When coverage rather than time becomes the important factor, hybrid imaging does not offer a significant advantage over conventional methods. T2 decay will also serve as a roll‐off filter which will reduce the spatial resolution, but not the noise, for short TE hybrid imaging.
Direct measurement of spin‐lattice relaxation times of Phosphorus Metabolites in Human Myocardium
Authors: Neubauer S. , Krahe T. , Schindler R. , Hillenbrand H. , Entzeroth C. , Horn M. , Bauer W. R. , Stephan T. , Lackner K. , Haase A. , Ertl G.
Published: March 2007

T1 values of phosphorus metabolites visible in human cardiac 31P‐MR spectra were determined in 12 volunteers at 1.5 T. Consecutive spectra were acquired with varying pulse repetition time (TR) from 1.6 to 24 s; volume selection was achieved with ISIS. T 1's of creatine phosphate (CP), [γ‐P], [α‐P], and [β‐P] ATP, 2‐3 diphosphoglycerate, and phosphodiesters were 6.1 ± 0.5, 5.4 ± 4 0.5, 5.5 ± 0.5, 5.8 ± 1.0, 7.6 ± 1.0, and 5.0 ± 1.0 s, respectively. CP/ATP ratios showed little change with varying TR; linear regression of CP/ATP vs TR was of borderline significance (r = 0.28, P = 0.06). T1'S for CP and ATP were also determined in standard solution (20 mM CP, 10 mM ATP) yielding TIcp of 8.7 ± 0.2 and T1[γ‐P]‐atpof 9.9 ± 0.7 s. Thus, T1'S for CP and ATP were similar at 1.5 T in both human heart and standard solution. In human cardiac 31P‐MR spectra, CP/ATP ratios may need little correction for partial saturation.
Automatic in vivo nmr data processing based on an enhancement procedure and linear prediction method
Authors: Diop A. , Briguet A. , Graveron‐Demilly D.
Published: March 2007

A new data processing method for in vivo NMR data quantitation is presented. This method (EPLPSVD) is based on the enhancement procedure (EP) proposed by J. A. Cadzow (IEEE Trans. Acoust. Speech Signal Process. 36, 49, 1988) followed by the usual linear prediction method using the singular value decomposition (LPSVD). The evaluation of this protocol is performed using synthesized 31P signals with different signal‐to‐noise ratios. A Monte‐Carlo simulation as a function of signal‐to‐noise ratio (SNR) has proved that EPLPSVD leads to unbiased estimated values of parameters. Then the Cramer‐Rao method yields reliable confidence intervals for the estimated parameters. The estimates of NMR parameters using EPLPSVD are reliable and accurate for SNR ≥ 1.2 while the LPSVD method failed for SNR ≤ 4. This protocol is applied to analyze automatically a series of 31P free induction decays obtained from the human gastrocnemius muscle during exercise. Spectral parameters with their confidence intervals, curves of relative intensity variations in phosphocreatine and inorganic phosphate, and pH curves are automatically provided.
A piezoelectric respiratory monitor for in vivo nmr
Authors: McKibben Charlton K. , Reo Nicholas V.
Published: March 2007

This report describes a simple electronic device employing a piezoelectric element which serves as a sensitive detector of motion. The device is useful as a monitor of respiratory motion for nuclear magnetic resonance animal experiments in vivo. It can also provide a trigger pulse for respiratory gating experiments.
T1 and t2 of ferritin at different field strengths: effect on mri
Authors: Vymazal Josef , Brooks Rodney A. , Zak Olga , Mcrill Connie , Shen Cynthia , Chiro Giovanni Di
Published: March 2007

Nuclear magnetic relaxation times T1 and T2 were measured in ferritin solutions at field strengths from 0.04 to 1.5 T.T1 was relatively constant, but 1/T2 increased linearly with field strength, in agreement with earlier MRI observations in the monkey brain. This finding supports the theory that ferritin is responsible for T2 shortening in brain nuclei containing iron. The linear dependence of 1/T2 on magnetic field is unique and not explained by present theories of the magnetic properties of ferritin.
An Investigation of Tumor 1H Nuclear Magnetic Resonance Spectra by the Application of Chemometric Techniques
Authors: Howells S. L. , Maxwell R. J. , Peet A. C. , Griffiths J.R.
Published: March 2007

1H nuclear magnetic resonance (NMR) spectra of tumors and normal tissue include signals from all hydrogen‐containing metabolites and can therefore be considered multicomponent multivariate mixtures. We have obtained 1H spectra from perchloric acid extracts of three normal tissues (liver, kidney, and spleen) and five rat tumors (GH3 prolactinoma, Morris hepatomas 7777 and 9618a, LBDS1 fibrosarcoma, and Walker 256 carcinosarcoma). We have applied several different chemometric methods to analyze the data. First, we used principal component analysis, cluster analysis, and an optimized artificial neural network to develop a classification rule from a training set of samples of known origin or class. The classification rule was then assessed using a set of unknown samples. We were able to successfully determine the class of each unknown sample. Second, we used the chemometric techniques of factor analysis followed by target testing to investigate the underlying biochemical differences that are detected between the classes of samples.© 1992 Academic Press,Inc.
A new approach to study cardiac motion: The optical flow of cine MR images
Authors: Amartu Sundar C. , Vesselle Hubert J.
Published: March 2007

We present a novel approach to study the intricate motion of the heart using the optical flow technique applied to cine MR images. The method uses image brightness variations between consecutive frames to compute in‐plane displacements or velocities of moving image features. The dense velocity field thereby obtained throughout the myocardial wall allows to not only characterize segmental left ventricular wall motion but also to resolve “fine” motion such as intramural differences in displacements and therefore in thickening. Other subtle features of systole like the descent of the base towards the apex or the counterclockwise rotation of the apex with respect to the base can also be detected by the algorithm. Contrary to other techniques proposed earlier, this noninvasive method presents the additional advantages of not requiring any special pulse sequence nor well defined endocardial and epicardial outlines.
Effect of glucose and confluency on phosphorus metabolites of perfused human prostatic adenocarcinoma cells as determined by31P MRS
Authors: Macdonald Jeffrey M. , Kurhanewicz John , Dahiya Rajvir , Espanol Maryceline T. , Chang Lee‐Hong , Goldberg Beth , James Thomas L. , Narayan Perinchery
Published: March 2007

A series of perfused cell31P MRS studies were conducted using a well established human prostate adenocarcinoma cell line (DU 145) at different phases of growth, and exposed to varying glucose concentrations during growth. The spectral characteristics of perfused DU 145 cells were compared with the same cells grown in nude mice (xenografts). Perfused DU 145 cells had lower levels of inorganic phosphate and phos‐phocreative relative to in vivo nude mice xenografts. 31P MR spectra obtained from perfused cells at different phases of growth and exposed to varying glucose concentrations during grown suggest that increases in diphosphodiester levels are associated with high glucose concentrations and confluency. Perfused DU 145 cells grown in 5.5 mm glucose and harvested at log phase of growth best reflected the phosphorus MR spectra of the same cell line grown in nude mice.
Correction of translational motion artifacts in multi‐slice spin‐echo imaging using self‐calibration
Authors: Zang L.‐H. , Fielden J. , Wilbrink J. , Takane A. , Koizumi H.
Published: March 2007

In this paper, we describe a method for detecting and correcting in‐plane bulk translational motion in multislice spin‐echo imaging using self‐calibration and postprocessing. A constant phase encoding offset between slices is used to evenly spread out the low spatial frequency echoes to allow accurate motion detection by self‐calibration. Motion detection in both x and y directions is achieved by interchanging the readout and phase encoding directions for the alternate slices. Displacements are determined by cross correlating the modulus of each 1D transformed echo with a reference box car function whose width equals that of the imaged object. In addition, phase errors induced by the velocity in the readout direction are estimated and corrected using the displacement data. The results obtained from knee studies at 0.5 T and 1.5 T show that the artifacts due to translational motions are significantly suppressed upon correction. The method does not require any additional pulses or time, and the data processing can be easily implemented.
Changes in double quantum filtered sodium intensity during prolonged ischemia in the isolated perfused heart
Authors: Hutchison R. B. , Huntley J. J. A. , Zhou H. Z. , Ciesla D. J. , Shapiro J. I.
Published: March 2007

Intracellular sodium (Nal) concentrations rose immediately and progressively during ischemia in the isolated heart. The intracellular double quantum filtered sodium coherence (DQ) intensity also increased during ischemia. However, when normalized for Nai, the DQ intensity began to fall after 40 min of ischemia, and remained depressed during reperfusion.
Noninvasive analysis of aldose reductase activities in rat testis: 3‐FDG NMR spectroscopy and imaging
Authors: Nakada Tsutomu , Kwee Ingrid L.
Published: March 2007

Noninvasive investigation of aldose reductase activities in rat testis was performed using 3‐fluoro‐3‐deoxy‐D‐glucose (3‐FDG) and nuclear magnetic resonance (NMR) spectroscopy/imaging. Quantitative determination of testis aldose reductase activities, expressed as the sorbitol index, showed a value similar to that of brain. Sorbitol imaging demonstrated aldose reductase activities in testis to be confined primarily to the central region of this organ. The 3‐FDG 19F NMR method appears to have clinical potential in the evaluation of testicular function, especially that of spermatogenesis, noninvasively.
Development and characterization of an ergometer to study the bioenergetics of the human quadriceps muscle by 31P NMR spectroscopy inside a standard MR scanner
Authors: de Suso José M. Gonz Ález , Bernús Gema , Alonso Julio , Alay Albert , Capdevila Antoni , Gili Jaume , Prat Joan A. , Arús Carles
Published: March 2007

A description is given of an ergometer made of nonmagnetic materials which fits into a standard whole body MR magnet. T2‐weighted images show that exercise is highly specific for quadriceps muscles. The ergometer permits the noninvasive study of T2‐related changes in the proton images of the leg as well as changes occurring in muscle bioenergetics during exercise and recovery.
Nontriggered magnetic resonance velocity measurement of the time‐average of pulsatile velocity
Authors: Hofman Mark B. M. , Kouwenhoven Marc , Sprenger Michiel , van Rossum Albert C. , Valk Jaap , Westerhof Nico
Published: March 2007

The feasibility of the determination of the time‐average of pulsatile velocity obtained via a nontriggered magnetic resonance (MR) acquisition is studied. The advantage of this method, in comparison with a triggered acquisition, is a considerable reduction (≈15×) in acquisition time. However, pul‐satility causes image artifacts, known as ghosts, and the Fourier transform technique required for the imaging procedure accomplishes time‐averaging of the complex MR signal. Both effects can result in errors in the velocity determined. Calculations show that these errors depend on the velocity time function and the acquisition parameters. In vivo comparison of triggered and nontriggered MR velocity measurements in the femoral artery of volunteers (n = 7) shows larger statistical and systematic errors in the latter, which depend on the excitation angle. Therefore, this nontriggered average velocity measurement is only useful as a fast and rough estimation of the time‐averaged velocity.
In vivo1H chemical shift imaging of silicone implants
Authors: Pfleidere Bettina , Ackerman Jerome L. , Garrido Leoncio
Published: March 2007

In order to study the aging process (i.e., silicone migration, fat infiltration) of silicone (polydimethylsiloxane, PDMS) based biomaterials in living subjects by NMR imaging a hybrid 1H selective excitation and saturation chemical shift imaging technique (IR/CHESS‐CSSE) has been developed. This sequence allows selective mapping of the distribution of silicone protons in vivo, while suppressing the contributions of fat and water. Our results indicate that a combined inversion recovery and CHESS pulse, followed by a spoiler gradient, must be applied to suppress all contributions of fat protons to the NMR signal. The sensitivity of our experiments allows the detection of a chemically unchanged silicone concentration of 5% in a voxel of 0.9 mm3 at a signal/noise ratio of 2.
High‐Field MR microscopy using fast spin‐echoes
Authors: Zhou Xiaohong , Cofer Gary P. , Suddarth Steve A. , Allan Johnson G.
Published: March 2007

Fast spin‐echo imaging has been investigated with attention to the requirements and opportunities for high‐field MR microscopy. Two‐and three‐dimensional versions were implemented at 2.0 T, 7.1 T, and 9.4 T. At these fields, at least eight echoes were collectable with a 10 ms TE from fixed tissue specimens and living animals, giving an eightfold improvement in imaging efficiency. To reduce the phase‐encoding gradient amplitude and its duty cycle, a modified pulse sequence with phase accumulation was developed. Images obtained using this pulse sequence exhibited comparable signal‐to‐noise (SNR) to those obtained from the conventional fast spin‐echo pulse sequences. Signal losses due to imperfections in RF pulses and lack of phase rewinders were offset in this sequence by reduced diffusion losses incurred with the gradients required for MR microscopy. Image SNR, contrast, edge effects and spatial resolution for three k‐space sampling schemes were studied experimentally and theoretically. One method of sampling k‐space, 4‐GROUP FSE, was found particularly useful in producing varied T2 contrast at high field. Two‐dimensional images of tissue specimens were obtained in a total acquisition time of 1 to 2 min with in‐plane resolution between 30 to 70 μm, and 3D images with 2563 arrays were acquired from fixed rat brain tissue (isotropic voxel = 70 μm) and a living rat (isotropic voxel = 117 μm) in∼4.5 h.
In Vivo localized proton NMR spectroscopy of silicone
Authors: Pfleiderer Bettina , Ackerman Jerome L. , Garrido Leoncio
Published: March 2007

1H NMR localized spectroscopy (STEAM) can assess unambiguously the presence of free chemically unchanged silicone in animal tissue after injection of silicone oil. Although the signal—to—noise ratio obtained in 1H imaging is sufficient to detect the distribution of relatively large amounts of silicone in vivo, the specificity of silicone detection can be improved by using 1H localized spectroscopy techniques. The sensitivity of the STEAM experiments is sufficient to detect silicone at a concentration of 0.5% in a voxel of 27 mm3. Preliminary results from rats with silicone gel—filled implants show no detectable amounts of silicone in sites such as lymph nodes, the liver or the spleen, 3 or 6 months after implantation.
Stabilization of echo amplitudes in FSE sequences
Authors: Roux Patrick Le , Hinks R. Scott
Published: March 2007

The classical CPMG sequence and its extension as an imaging sequence, fast spin echo (FSE, based on RARE), suffer from signal magnitude variations in the early echoes when the re‐focusing pulses are not set exactly to 180°. It has been suggested that by varying the value of the nutation angle of each refocusing pulse the signal magnitude could be made constant. This article describes an algorithm permitting the generation of sequences of nutation angles yielding series of echsoes with constant signal magnitudes. This result is then usesd to design selective pulses for the FSE imaging technique.
Measurement of the extraction efficiency and distribution volume for Gd‐DTPA in normal and diseased canine myocardium
Authors: Tong Chun Y. , Prato Frank S. , Wisenberg Gerald , Lee Ting Y. , Carroll Edwin , Sandler David , Wills Jane , Drost Dick
Published: March 2007

We have previously shown that the myocardial Gd‐DTPA concentration ([Gd‐DTPA]t(t)) after a bolus injection of Gd‐DTPA can be predicted by the Modified Kety Equation (MKE). If [Gd‐DTPA]t(t) can be determined by MRI and the data fit to the MICE, then the distribution volume (λ) of Gd‐DTPA and the myocardial flow (F) times the extraction efficiency (E), i.e., the FE product, can be determined. Therefore F can only be quantified if E is known. We measured the global E in vivo in normal canine myocardium, and measured E and λ, in vitro, locally in normal, acute ischemic (n = 5; coronary artery occlusion < 4 h), infarcted (n = 4; coronary artery occlusion, 6 days) and reperfused (n = 4; coronary artery occlusion 2 h, and reperfusion 2 h and 6 days) myocardium. Results indicate that E differs with F and with individuals and consequently, F cannot be quantified using the MKE unless the local E is also determined in vivo.
Predicting RF field penetration in heterogeneous bodies using a 3‐D finite element approach: Preliminary results
Authors: Petropoulos L. S. , Haacke E. M. , Brown R. W. , Boerner E.
Published: March 2007

We present preliminary results for a 3D finite element calculation to evaluate RF penetration in conducting dielectric materials at high field strengths. A tetrahedral mesh is used along with a Coulomb gauge constraint in a finite element method that yields excellent numerical stability at high frequencies. Accuracy is verified by comparisons with analytic solutions for single‐layer and multiple‐layer heterogeneous systems and for a 3D spherical model. We have also compared the finite element model with experimental results presented by Foo et al., Magn. Reson. Med. 23, (1992). Agreement is very good and argues for the usefulness of the method in the calculation of RF penetration and RF power deposition effects in heterogeneous objects.
Time of flight quantification of coronary flow with echo‐planar MRI
Authors: Poncelet Brigitte P. , Weisskoff Robert M. , Wedeen Van J. , Brady Thomas J. , Kantor Howard
Published: March 2007

Detection and quantification of flow of the left anterior descending (LAD) coronary artery in healthy volunteers are demonstrated using echo‐planar imaging (EPI). A time‐of‐flight TOF) model was used to derive coronary flow velocities from wash‐in curves, free of cardiac wall motion contamination. Short‐axis cardiac studies were performed using a gated, gradient echo EPI technique to limit the effect of cardiac wall motion on coronary vessel imaging. A series of 10 to 20 single or multislice images were acquired within a single breath‐hold. Real‐time cine series showed the LAD coronary artery with a detectability of 91% (n = 23) and revealed beat‐to‐beat variability in vessel position of a magnitude equal to or greater than its diameter. Flow velocity was measured in the proximal portion of the artery at rest and during exercise. The data demonstrated the known phasic pattern of LAD flow:‐Vsystole ≤ 5 cm/s and peak Vdiastole = 14 ± 3 cm/s (n = 11, V = mean laminar flow velocity). During isometric exercise, a LAD flow velocity increase (52 ± 24%) was detected in eight of nine subjects. The capacity of the EPI TOF method to detect flow velocity changes should prove clinically useful for future assessment of coronary flow reserve.
Migration and biodegradation of free silicone from silicone gel‐filled implants after long‐term implantation
Authors: Pfleiderer Bettina , Ackerman Jerome L. , Garrido Leoncio
Published: March 2007

In vivo1H NMR chemical shift imaging (CSI), 1H NMR localized spectroscopy (STEAM) and multinuclear NMR spectroscopy 29sl, 13C, 1H) were used to characterize the aging process of silicone gel‐filled implants in a rat model after long‐term implantation. Although no significant changes could be observed in the implants or surrounding tissue by in vivo 1H chemical shift imaging, in vivo 1H localized spectroscopy of the livers from the longer term population revealed the presence of silicone. Ex vivo 29Sl spectroscopy of the liver, spleen, and the capsule formed around the 9 and 12 month implants clearly demonstrated and confirmed for the first time that a significant amount of free silicone migrates from silicone gel‐filled implants. Also, these results show that silicones are not metabolically inert, and their biodegradation in tissue and within the implant can be monitored after 9 and 12 months by changes in the 29Sl chemical shifts seen in corresponding ex vivo spectra. The NMR findings are supported by those obtained by atomic absorption spectroscopy. Silicone aging changes not only the chemical composition of the gel, but also its proton T2 relaxation times, which increase with long implantation times. The three dimensional structure of the gel disintegrates (i.e., polymer chain rupture), increasing the molecular mobility of the polymer and, consequently, its protons T2 values. The relaxation data we obtained reflect this in vivo degradation, especially in the case of implant rupture. Additionally, small concentrations of fat in the silicone gel were found within the implants. The presence of these lipophilic substances also might increase the T2 values (plasticizer effect). These findings may assist in evaluating the implant integrity and disease symptoms related to their presence in humans.
The use of dietary loading of 133Cs as a potassium substitute in NMR studies of tissues
Authors: Philip Shehan B. , Mark Wellard R. , Adam William R. , Craik David J.
Published: March 2007

133Cs NMR chemical shifts and relaxation times have been measured for tissue samples in vitro and in vivo from rats which have been fed on a high cesium, low potassium diet, which leads to a predominantly intracellular distribution of this ion, similar to that of K
+. The high sensitivity, large chemical shift range, and narrow linewidths of 133Cs, compared with 39K, allow chemical shift differences to be observed between tissues, and in subcellular organelles such as mitochondria. For example, in vitro tissue chemical shifts, relative to 150 mM CsCl, are 1.06 ± 0.11 ppm for liver, 0.02 ± 0.05 ppm for brain, 1.76 ± 0.20 ppm for erythrocytes, and −0.13 ± 0.02 ppm for plasma. T1 and spin‐echo T2 values range from 1.26 ± 0.05 s (T2), and 0.028 ± 0.006 s (T2) for liver, to 6.49 ± 0.19 s and 1.12 ± 0.03 s for plasma. 133Cs relaxation times show the same relative trends between tissues as are observed in 39K tissue Studies.
A molecular theory of relaxation and magnetization transfer: Application to cross‐linked BSA, a model for tissue
Authors: Koenig Seymour H. , Brown III Rodney D.
Published: March 2007

Homogeneous soft tissue, as regards its magnetic relaxation properties, is well‐modeled by solutions of cross‐linked protein (see Koenig and Brown, Prog. NMR Specfr. 22,487 (1991)). Interactions at the solute‐solvent interface alter the hydrodynamics of solvent water, and also couple the solute and solvent proton Zeeman energy reservoirs, giving hydrodynamic and cross‐relaxation contributions to water proton relaxation that respond differently to deuteration of solvent. We report measurements of the magnetic field dependence of 1/T1, of water protons in cross‐linked bovine serum albumin (BSA), for partially deuterated solvent and, in order to separate these two contributions, of 1/T1, of deuterons. The major experimental finding is that, in addition to recently identified water‐binding sites on protein (covering ∼0.2% of the surface) with water lifetimes of about 1 μs, there is another group of sites with lifetimes of about 23 ns, covering ∼2% of the surface, which are evident in both proton and deuteron data. In addition, we have formulated a theory of interfacial proton‐proton magnetic interactions which—with these four parameters, plus two that quantify the protein‐water coupling at each site—can account for all the proton and deuteron data, in both native and cross‐linked BSA.
Dendrimer‐based metal chelates: A new class of magnetic resonance imaging contrast agents
Authors: Wiener Erik , Brechbiel M. W. , Brothers H. , Magin R. L. , Gansow O. A. , Tomalia D. A. , Lauterbur P. C.
Published: March 2007

We have developed a new class of magnetic resonance imaging contrast agents with large proton relaxation enhancements and high molecular relaxivities. The reagents are built from the polyamidoamine form of Starburs™ dendrimers in which free amines have been conjugated to the chelator 2‐(4‐isothiocyanatobnenzyl)‐6‐methyl‐diethylenetriaminepenta‐acetic acid. The dendrimer gadolinium poly‐chelates have enhancement factors, i.e., the ratlo of the relaxivity per Gd(III) ion to that of Gd(III)‐diethylenetriaminepentaacetic acid, of up to 6. These factors are more than twice those observed for analogous metal‐chelate conjugates formed with serum albumins, polylysine, or dextran. One of the dendrimer‐metal chelate conjugates has 170 gadolinium ions bound, which greatly exceeds the number bound to other macromolecular agents reported In the literature, and has a molecular relaxivity of 5,800 (mM · s)−1, at 25 MHz, 20°C, and pH of 7.4. We observed that these dendrimer‐based agents enhance conventional MR images and 3D time of flight MR angiograms, and that those with molecular weights of 8,508 and 139,000 g/mole have enhancement half lives of 40 ± 10 and 200 ± 100 min, much longer than the 24 ± 4 min measured for Gd(III)‐diethylenetriaminepentaacetic acid. Our results suggest that this new and powerful class of contrast agents have the potential for diverse and extensive application in MR imaging.
Effect of vitreous fluidity on the measurement of blood‐retinal barrier permeability using contrast‐enhanced MRI
Authors: Berkowitz Bruce A. , Wilson Charles A. , Tofts Paul S. , Peshock Ronald M.
Published: March 2007

Breakdown of the blood‐retinal barrier (BRB), frequently an early clinical sign in retinopathy, can be accurately determined using contrast‐enhanced MRI. However, increased vitreous fluidity with age and disease may affect the accuracy of the MRI method. We compared the permeability surface area product per area of leaky retina in eyes with normal vitreous (5.42 ± 0.48 × 10−4 cm/min, mean ± SEM, n = 5) to the contralateral gas‐compressed vitrectomized eyes (5.41 ± 0.54 × 10−4 cm/min, n = 5). The effect of vitrectomy was not significant (P = 0.325) using a Wilcoxon matched pairs signed rank test on the signed differences of the PS' values.
BOLD MRI monitoring of changes in cerebral perfusion induced by acetazolamide and hypercarbia in the rat
Authors: Graham G. D. , Zhong J. , Petroff O. A. C. , Constable R. T. , Prichard J. W. , Gore J. C.
Published: March 2007

To evaluate MRI methods for estimating cerebrovascular reserve, we computed changes in the R2* and R2, transverse relaxation rate and apparent diffusion coefficient (ADC) at 2.0 Tesla in five rats after administration of 30 mg of acetazolamide and in four rats during inhalation of 20% carbon dioxide gas. Significant decreases in R2*, corresponding to increases in gradient echo MRI signals, occurred in both the acetazolamide (average change −8.3%, P = 0.005) and the carbon dioxide (−2.7%, P = 0.009) treated animals. The computed values for R2 and ADC were unchanged. The magnitude of the gradient echo MRI changes observed should permit anatomic mapping of blood flow reactivity patterns in normal human subjects and in patients at risk for cerebrovascular disease.
Method for the quantitative assessment of contrast agent uptake in dynamic contrast‐enhanced MRI
Authors: Hittmair Karl , Gomiscek Gregor , Langenberger Karl , Recht Michael , Imhof Herwig , Kramer Josef
Published: March 2007

In previous papers relative signal intensity increase was used as a quantitative assessment parameter for contrast uptake in contrastenhanced MRI. However, relative signal intensity increase does not only reflect contrast uptake but depends also on tissue parameters (native T1 relaxation time) and sequence parameters (repetition time and flip angle); thus, the contrast uptake cannot be assessed accurately using relative signal intensity increase. Based on an analysis of the contrast behavior of spoiled gradient echo sequences, a method is described in this paper that overcomes the limitations of relative signal intensity increase measurement. A parameter, called “enhancement factor” (EF) is introduced that approximates differential T1 relaxation rate. The enhancement factor scales linearly with contrast uptake and is independent of tissue and sequence parameters. The additional measurement time involved in determining the enhancement factor is less than 1 min and computation is straightforward. The practicality of the new method was confirmed by phantom measurements using T1‐weighted and proton density‐weighted spoiled gradient echo sequences (FLASH‐2D). Enhancing tissues were simulated by water phantoms doped with increasing concentrations of Gd‐DTPA.
Validation of 13C NMR measurements of liver glycogen in vivo
Authors: Gruetter Rolf , Magnusson Inger , Rothman Douglas L. , Avison Malcolm J. , Shulman Robert G. , Shulman Gerald I.
Published: March 2007

The natural abundance 13C NMR intensity of the glycogen C1 resonance was measured in the surgically exposed liver of rabbits in vivo (n = 17) by integration from 98 to 104 ppm and compared double blindedly to the subsequent biochemical measurement. Coil loading was measured each time from a reference sphere at the coil center and the NMR Intensity was normalized accordingly. For quantification, the normalized NMR intensity was calibrated using aqueous glycogen solutions ranging from 110 to 1100 μmol glucosyl units/g (n = 14). An in vivo range from 110 to 800 pmol glucosyl unit/g wet weight was measured with a highly linear correlation with concentration (r = 0.85, P < 0.001). The in vivo NMR concentration was 0.95 ± 0.05 (mean ± standard error, n = 17) of the concomitant enzymatic measurement of glycogen content. We conclude that the 13C NMR signal of liver glycogen C1 is essentially 100% visible in vivo and that natural abundance 13C NMR spectroscopy can provide reliable noninvasive estimates of in vivo glycogen content over the physiological range of liver glycogen concentrations when using adequate localization and Integration procedures.
Short TE phosphorus spectroscopy using a spin‐echo pulse
Authors: Lim Kelvin O. , Pauly John , Webb Peter , Hurd Ralph , Macovski Albert
Published: March 2007

In vivo phosphorus spectroscopy requires very short acquisition delays in order to capture the signal from components with short transverse relaxation times (T2). The echo time typical of standard slice selective spin‐echo pulses are too long for this application, so hard pulse, free induction decay (FID) acquisitions have frequently been used instead. With FID, however, there is an interval between the time of coherence and data acquisition (acquisition delay), with resulting baseline distortions. In this paper we describe the design of a new short TE, slice‐selective, composite spin‐echo pulse with echo times as short as 2.5 ms. With a long TR, fully relaxed, multislice spectra can be collected. This technique will be useful for assessing, in vivo, changes in brain phospholipid activity associated with psychiatric and neurological diseases.
Multipoint K‐space point mapping (KPM) technique for NMR microscopy
Authors: Cho Zang H. , Ro Yong M.
Published: March 2007

An extended version of point mapping in k‐space for microscopic imaging applications is analyzed and described. Because the method can offer a number of advantages over the other conventional techniques due to the short echo time (TE), the technique is ideally suited for microscopic imaging where field in homogeneity dependent signal degradation is one of the main causes of image resolution degradation (1–3). Another application area is the case of imaging in a highly inhomogeneous situation such as the fringe field imaging (Z.H. Cho, E. Wong, US. Patent) #5023554 (1990). The first original point mapping technique described by Nauert et al. (1) and Emid and Creyghton (2) is analyzed as a k‐space point mapping technique, and the original technique is extended to a multipoint k‐space point mapping (MKPM) technique. With the extended MKPM technique, much faster microscopic imaging that is free of susceptibility and diffusion effects can be performed (4–6). To examine this idea, computer simulations are performed and their results are given.
Dynamically adaptive MRI with encoding by singular value decomposition
Authors: Zientara Gary P. , Panych Lawrence P. , Jolesz Ferenc A.
Published: March 2007

A new MRI spatial encoding method based upon the singular value decomposition (SVD) and using spatially selective RF excitation is described. This encoding technique is particularly; applicable to dynamic adaptive MRI, because it provides a near minimal set of spatial encoding profiles computed using an image estimate that is determined from a previously obtained image. Experimental results are presented for two cases, which exemplify its potential use in different dynamic imaging tasks. SVD‐encoded MRI has demonstrated to be a highly efficient encoding scheme.
Relaxivity corrected response modulated excitation (RME): A T2‐corrected technique achieving specified magnetization patterns from an RF pulse and a time‐varying magnetic field
Authors: Pearlman Justin D. , Wieczorek Tad J.
Published: March 2007

We have reworked the theory of RF excitation to enable correction for relaxivity while designing response‐modulated excitation (RME) to achieve specifled magnetization targets. This results in a significant improvement in the ability to achieve a specified target magnetization, especially if excitation time is long or T2 is short. The methods presented may also be used to improve the quality of spatial‐spectral pulses as well as localized spectroscopy, real‐time imaging, real‐time localized velocity, and noninvasive pressure measurement.
Metabolic loss of deuterium from isotopically labeled glucose
Authors: Ben‐Yoseph Oded , Kingsley Peter B. , Ross Brian D.
Published: March 2007

The isotopically substituted molecule (6‐13C, 1, 6, 6‐2H3)glucose was evaluated to determine whether metabolic 2H loss would prevent its use in quantitating pentose phosphate pathway (PPP) activity. PPP activity causes the C1 of glucose to be lost as CO2, while C6 can appear in lactate. 2H NMR analysis of the lactate produced from this glucose can distinguish (3‐2H)‐lactate (from C1 of glucose) from (3‐13C, 3, 3‐2HZ)lactate (from C6 of glucose). 2H NMR spectroscopic analysis of medium containing (4‐13C, 1,6,6−2H3) glucose after incubation with cultured rat 9L glioma cells suggested a 30.8 ± 2.1% PPP activity as compared with 6.0 ± 0.8% from separate, parallel incubations with (1‐13C)glucose and (6‐13C)glucose. Subsequent experiments with other isotopically labeled glucose molecules suggest that this discrepancy is due to selective loss of 2H from the C1 position of glucose, catalyzed by phosphoman‐nose isomerase. Failure to consider 2H exchange from the C1 and C6 positions of glucose can lead to incorrect conclusions in metabolic studies utilizing this and other deuterated or tritiated glucose molecules.
The effect of high performance gradients on fast gradient echo imaging
Authors: Reeder Scott B. , McVeigh Elliot R.
Published: March 2007

The effect of gradient system performance on segmented k‐space gradient echo imaging is presented. Three cases were investigated. First, an ideal system that has infinite slew rates and unlimited maximum gradient strengths was considered. Second, a “high speed” imaging system (2.3 (G/cm), 23 (G/cm)/ms) was considered. These two cases were compared with a “conventional” imaging system (1(G/cm), 1.67 (G/cm)/ms). It was found that substantial increases in SNR can be achieved (≈︁ 45%) by using high speed versus a conventional gradient system, for a TR of 6 ms. For trapezoidal gradient waveforms, there exists an optimum maximum gradient strength for a given slew rate, and any increase in gradient strength above this optimum will not be utilized by an optimized sequence. These studies have shown that increasing TR without decreasing the bandwidth is not a good way to increase SNR for constant scan time.
Noninvasive MRI Thermometry with the Proton Resonance Frequency (PRF) Method: In Vivo Results in Human Muscle
Authors: Poorter John De , Wagter Carlos De , Deene Yves De , Thomsen Carsten , Ståhlberg Freddy , Achten Eric
Published: March 2007

The noninvasive thermometry method is based on the temperature dependence of the proton resonance frequency (PRF). High‐quality temperature images can be obtained from phase information of standard gradient‐echo sequences with an accuracy of 0.2°C in phantoms. This work was focused on the in vivo capabilities of this method. An experimental setup was designed that allows a qualitative in vivo verification. The lower‐leg muscles of a volunteer were cooled and afterwards reheated with an external water bolus. The temperature of the bolus water varied between 17°C and 37°C. The in vivo temperature images can be used to extract the temperature in muscle tissue. The data in the fat tissue are difficult to interpret because of the predominance of susceptibility effects. The results confirm the method's potential for hyperthermia control.
Compensation of Diffusion Effects in T2 Measurements
Authors: Deichmann Ralf , Adolf Holger , Kuchenbrod Erwin , Nöth Ulrike , Schwarzbauer Christian , Haase Axel
Published: March 2007

Measurements of the transverse relaxation time T2 are usually conducted with the Carr Purcell Meiboom Gill (CPMG) pulse sequence, which causes T2‐weighted magnetization. Diffusion effects are a common source of error in measurements of this kind, because the incoherent motion of spins in external magnetic field gradients distorts T2 weighting of the transverse magnetization. As a result, inaccurate T2‐values are obtained. In this work, we present a method which completely compensates for the effect of diffusion.
Water‐Macromolecular Proton Magnetization Transfer in Infarcted Myocardium: A Method to Enhance Magnetic Resonance Image Contrast
Authors: Scholz Thomas D. , Hoyt Robert F. , Deleonardis John R. , Ceckler Toni L. , Balaban Robert S.
Published: March 2007

Water proton nuclear magnetic resonance relaxation times and magnetization transfer (MT) parameters of rat hearts were studied 24 h or 4 weeks after ligation of the left coronary artery or sham operation. Compared with sham‐operated controls, measured relaxation times (T1sat' and T2) of both acute and chronic myocardial infarction increased. The MT effect significantly decreased in the infarcted myocardium. The changes in relaxation times and MT effect were significantly greater in chronic infarcts compared with acute infarcts. Improvements in calculated image contrast between normal and infarcted tissue were supported by images of ex vivo hearts with chronic infarction. Image contrast was increased at short echo times in the presence of macromolecular proton pool irradiation. Exploiting changes in tissue MT following myocardial infarction to enhance contrast between normal and infarcted tissue should allow improved identification and characterization of infarcted myocardium.
In vivo Oximetry Using EPR and India Ink
Authors: Goda Fuminori , Liu Ke Jian , Walczak Ted , O'Hara Julia A. , Jiang Jinjie , Swartz Harold M.
Published: March 2007

Recent advances in electron paramagnetic resonance (EPR) oximetry have established the use of the particulate materials fusinite and lithium phthalocyanine (LiPc) as probes for measurement of oxygen tensions in tissues in vivo with a sensitivity and accuracy that is relevant for studying pathophysiological processes. India ink, another potentially very useful new probe for EPR oximetry, shares the critical properties of fusinite and LiPc and has the additional advantage of already having been widely used clinically with no apparent toxicity. The line width is particularly sensitive to changes in oxygen tension of less than 30 mmHg; in this range the line broadening/unit of pO2 is much greater than that of fusinite and LiPc. Over the range of biological conditions that can occur in vivo, the response of the EPR spectrum of India ink to pO2 is independent of pH, oxidants, reductants, and the nature of the medium. In this paper we describe the relevant properties of India ink and its use to measure pO2 in vivo in experimental animals and a human subject.
Rotating Frame RF Current Density Imaging
Authors: Scott Greig C. , Joy Michael L. G. , Armstrong Robin L. , Mark Henkelman R.
Published: March 2007

RF current density imaging (RF‐CDI) is a new MRI technique for imaging the Larmor frequency current density parallel to B0 in electrolytic media. To extend the use of RF‐CDI to biological tissue for generating conductivity contrast, the sensitivity must be increased and the data requirements reduced. A rotating frame approach, in which a large B1 field is applied simultaneously as a rotary echo with RF current, is proposed to meet these requirements. Rotating frame magnetic fields are encoded in the phase of an MRI image. Trials have now been performed with this sequence in a three‐compartment cylindrical phantom containing doped water or mineral oil for detecting displacement, conduction and fringe field currents. In a postmortem rat study, 85.56 MHz RF currents injected by implanted electrodes created tissue dependent contrast because of the electrical properties of tissue. A sensitivity and artifact analysis was also performed. The sensitivity of this method is determined by the maximum RF pulse duration. SAR limits pose an upper bound on this time and B1, whereas the avoidance of phase artifacts imposes a lower bound on B1.
Phase Constrained Encoding (PACE): A Technique for MRI in Large Static Field Inhomogeneities
Authors: Kim Jae K. , Plewes Donald B. , Mark Henkelman R.
Published: March 2007

In spin echo imaging, magnetization is assigned to a location defined by its frequency of rotation. In the presence of a static magnetic field inhomogeneity, however, this location does not correspond to the true location of the magnetization. This paper describes a magnetic resonance imaging technique called phase constrained encoding (PACE) that assigns magnetization to its true location through the use of a spin echotrain and alternating readout gradients. Small artifactual sidebands occur in the point spread function but can be minimized or eliminated using higher gradient strengths, more echoes, and/or additional acquisitions. Implementation of a simple version of this technique confirms simulations.
Localized proton NMR spectroscopy in the striatum of patients with idiopathic parkinson's disease: a multicenter pilot study
Authors: Holshouser Barbara A. , Komu Markku , Möller Harald E. , Zijlmans Jan , Kolem Heinrich , Hinshaw David B. , Sonninen Pirkko , Vermathen Peter , Heerschap Arend , Masur Harald , Rinne Urpo K. , Koster Ad De , Tosk Jeffrey M.
Published: March 2007

Single voxel proton MRS was used to study brain metabolism in the striatum of patients diagnosed with idiopathic Parkinson's disease (PD). Peak metabolite ratios in long echo time spectra were evaluated in 151 patient spectra and 97 age‐matched control spectra collected at four participating institutions using identical hardware and clinical protocols. Combining data from all ages (27–83 years old) showed no significant difference between patient and control ratios. However, in an elderly subset of patients (51–70 years old), a significant decrease in striatal N‐acetylaspartate (NAA)/choline (Cho) was observed. Also, a significant decrease in the mean NAA/Cho ratio was observed in patients versus controls for patients not being treated with Sinemet (Du Pont Pharm, Wilmingon, DE) (hereafter referred to as levodopa/carbidopa). This result is consistent with the hypothesis that NAA may provide a reversible spectroscopic marker for neuronal dysfunction, although a prospective follow‐up study will be needed to confirm this. Quantitation of MRS would be useful to exclude the possibility that a change in Cho levels affected the NAA/Cho ratios.
The use of a priori knowledge to quantify short echo in vivo1h mr spectra
Authors: Stanley Jeff A. , Drost Dick J. , Williamson Peter C. , Terry Thompson R.
Published: March 2007

In vivo 1H MR spectra of the prefrontal cortex acquired with the stimulated echo acquisition mode (STEAM) TE = 20 ms sequence were quantified to determine relative levels of cerebral metabolites. A priori knowledge of spectra from individual metabolites in aqueous solution was incorporated into a frequency domain quantification technique. The accuracy and precision of modeling these metabolites were investigated with simulated spectra of varying signal‐to‐noise ratios (SNRs) and relative metabolite levels. The efficacy of modeling in vivo data was tested by quantifying 10 repeated measures of two consecutively acquired in vivo spectra (an 8−cm3 volume of interest (VOI) and a 4−cm3 VOI positioned within the 8−cm3 VOI) on the same normal subject. The differences in levels of glutamate (Glu), phosphocreatine plus creatine (PCr+Cr) and choline‐containing compounds (Cho1 between spectra from the 8− and 4−cm3 VOIs corresponded with the expected differences observed in the proportions of gray matter within the VOIs (estimated from 1H images). Correcting for the T1 and T2 relaxation, the estimated concentrations of N‐acetylaspartate, PCr+Cr, Cho1, Glu, and glutamine were consistent with previous in vivo and in vitro reports.