bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantitative regional blood volume studies in rat myocardium in Vivo
Authors: Kahler Elke , Waller Christiane , Rommel Eberhard , Hiller Karl‐Heinz , Voll Sabine , Broich Andrea , Hu Kai , Schnackerz Klaus D. , Bauer Wolfgang R. , Ertl Greoug , Haase Axel 
Published: March 2007

AbstractMany pathophysiological processes in the myocardium are in close relation to changes of the regional blood volume and regional myocardial blood flow or perfusion. Only few methods exist to obtain quantitative values for these parameters. Quantitative regional blood volume (RBV) studies in rat myocardium are presented using snapshot fast low angle shot (FLASH) inversion recovery T1 measurements with two different blood pool contrast agents, gadolinium diethylenetriamin‐opentaacetic acid (Gd‐DTPA) albumin and Gd‐DTPA polyly‐sine. In contrast to previous attempts, each snapshot FLASH image acquisition was ECG‐triggered under breathhold conditions. To measure relaxation times shorter than a heart cycle, each T1 sequence was repeated two times with different delays between inversion pulse and first image acquisition. The experiments were performed on a Bruker Biospec 70/21 using a homogeneous transmitter coil and a circularly polarized surface receiver coil, a special ECG trigger unit, and a respirator that is controlled by the pulse program. Based on a fast exchange model RBVm maps were calculated from the relaxation time maps for different concentrations of the two blood pool contrast agents. A significant dependence of the RBV, values on blood T1 was found. This is in accordance with a model that has been developed recently relating the dependence of RBVm on T1 of blood to perfusion. For Gd‐DTPA albumin, the application of the model to the experimental data yields realistic values for RBV and perfusion. The values, which are in accordance with literature data, were obtained at highest contrast agent concentrations i.e., lowest relaxation times of blood (ca. 200 ms).
Quantification of the extraction fraction for gadopentetate across breast cancer capillaries
Authors: Daldrup Heike E. , Shames David M. , Husseini Waleed , Wendland Michael F. , Okuhata Yoshitaka , Brasch Robert C. 
Published: March 2007

AbstractTo quantify the extraction fraction, E, for gadopentetate across tumor capillaries, R3230 adenocarcinomas were implanted in the mammary fat pads of seven rats. The value of E was determined by using a two‐compartment tissue model in which the endothelial transfer coefficient, KPS (ml. min −1. cc−1 of tissue), was estimated from the model fitted to changes in R1 relaxation time (ΔR1; s−1) measured by dynamic three‐dimensional spoiled gradient recalled magnetic resonance imaging after injection of 0.1 mmol. kg−1 of gadopentetate dimeglumine. The plasma flow rate through the tumor capillaries, Fp, (ml. min−1·g−1 of tissue), was independently measured with fluorescent microspheres. E could be calculated by the relationship, E = KPS/Fp.The mean E for gadopentetate in the R3230 tumor was 0.197 ± 0.118 with a range of 0.123–0.454. The relatively small mean value of E for gadopentetate allows a fair approximation of the permeability surface area product by KPS in this R3230 tumor model.
39K NMR measurement of intracellular potassium during ischemia in the perfused guinea pig heart
Authors: Radford Nina B. , Babcock Evelyn E. , Richman Angela , Szczepaniak Lidia , Malloy Craig R. , Sherry A. Dean 
Published: March 2007

AbstractThe hyperfine shift reagent, TmDOTP5−, was used to resolve the 39K NMR resonances of intra‐ (Ki+) and extracellular (Ke+) potassium in isolated, perfused guinea pig hearts. [Ki+] as measured by 39K NMR was 25.9 ± 10.3 mM, compared with 114.4 ± 10.8 mM as measured by atomic absorption spectros‐copy (AAS) using TmD0TP5‐ as a marker of extracellular space. Thus, only approximately 23% of intracellular potassium was detected by 39K NMR using our experimental conditions. The area of the Ki+ signal increased during early ischemia then returned to baseline levels during reperfusion. In an effort to learn more about the Ki+ not detected by 39K NMR, hearts were perfused with a Rb+‐enriched, K+ ‐depleted buffer for an extended period. This resulted in loss of the entire 39K NMR signal, and Ki+, as measured by AAS, decreased from ∼60 to ∼6 to 7 μmol/g wet weight. When K+‐depleted hearts were subjected to global ischemia, a small 39K NMR signal reappeared, suggesting that at least a portion of the nonexchangeable Ki+ becomes detectable by NMR during ischemia. This newly visible K+ signal subsequently dissipated during reperfusion of ischemic hearts. We conclude that ischemia induces changes in the NMR visibility of 39K in perfused guinea pig hearts.
Characterization of flow emerging from a stenosis using MRI
Authors: Gach H. Michael , Lowe Irving J. 
Published: March 2007

AbstractMRI ultra‐fast imaging techniques are used to characterize flow emerging from streamlined and abrupt stenoses inside cylindrical channels. Reattachment lengths of the shear boundary to the channel wall are measured using rotating ultra‐fast imaging sequence (RUFIS) in‐flow imaging. Velocity profiles of flow are created using velocity (sine and cosine)‐encoded RUFIS sequences. The sine‐encoded images permit one to identify reverse flow (i.e., eddies) that arise within the region of flow reattachment. The ratios of peak velocities (downstreamhpstream of the stenosis) derived from the cosine‐encoded images are used to identify the transition from the laminar to the turbulent regimen. Based on these experiments, the transition from the laminar to turbulent regimen occurs at a stenotic Reynolds Number of 350, whereas fully developed turbulence occurs at a stenotic Reynolds Number of 2600. These results are compared with the results from invasive studies.
3D Time‐resolved contrast‐enhanced MR DSA: Advantages and tradeoffs
Authors: Mistretta Charles A. , Grist Thomas M. , Korosec Frank R. , Frayne Richard , Peters Dana C. , Mazaheri Yousef , Carroll Timothy J. 
Published: March 2007

AbstractThe 3D TRICKS method for contrast‐enhanced, time‐resolved MR DSA has been recently described. In this paper, computer simulations are used to investigate the relative frame rate, temporal window, artery‐vein temporal separation, contrast‐to‐noise ratio, and spatial resolution of TRICKS and conventional scans for breath‐hold and non‐breath‐hold applications. For non‐breath‐hold applications, TRICKS can be coofigured to provide increased CNR or spatial resolution at an increased frame rate, but with a longer temporal window when compared with a series of conventional scans in which the central portion of k‐space is sampled at the same rate as for the TRICKS scans. For breath‐hold applications, TRICKS typically provides three images with 75% of the conventional single acquisition spatial resolution and is more tolerant of variations in contrast curve shape within the field of view.
Artifacts induced by concomitant magnetic field in fast spin‐echo imaging
Authors: Zhou Xiaohong Joe , Tan Steve G. , Bernstein Matt A. 
Published: March 2007

AbstractIt has been observed that fast spin‐echo (FSE) images with a large field of view (>40 cm) in certain directions exhibit unusual ghosting artifacts that cannot be eliminated with existing ghost removal methods. These artifacts have been related to a higher‐order magnetic field perturbation (known as the concomitant field, or Maxwell field) concomitant to the linear i‐maging gradient, in accordance with the Maxwell equations Several methods have been developed to eliminate or minimize the effects of the concomitant magnetic field by redesigning the FSE pulse sequences. In the slice‐selection direction, the gradient waveforms are made symmetrical about the refocusing RF pulses wherever possible. Surrounding the first refocusing pulse, such symmetry cannot be achieved due to the slice‐refocusing gradient, which is often combined with the left crusher. In this case, it is shown how crusher gradients can be reshaped to nullify the phase due to the concomitant field. In the phase‐encoding direction, the gradient amplitude is reduced and its duration is prolonged. Artifacts due to the readout gradient are eliminated by reshaping the prephasing lobe, while keeping its area fixed. In all the three directions, the gradient waveforms are adjusted so that they have minimal overlap. Selected methods have been implemented on a clinical scanner, and typically reduce the ghost intensities in phantom and human images by a factor of 3.
Functional burst imaging
Authors: Jakob Peter M. , Schlaug Gottfried , Griswold Mark , Lovblad Karl O. , Thomas Robert , Ives John R. , Matheson Jean K. , Edelman Robert R. 
Published: March 2007

AbstractA quiet magnetic resonance (MR) imaging technique for detecting changes in cerebral activity functions is presented. This single‐shot method, functional Burst imaging (FBI), combines elements of Burst imaging with an offset technique known as asymmetric spin echo (ASE). The FBI sequence has the unique feature of being nearly silent, because of the low number of gradient switching steps involved. Furthermore, this approach has the key advantage that it can be implemented on conventional MR systems. Established auditory and visual paradigms were used to evaluate whether FBI can detect changes in cerebral activity using a 1.5 Tesla MR system. In a second set of experiments, the FBI technique was used to evaluate cerebral activity changes during different sleep stages in humans. The results obtained demonstrate that the FBI sequence provides an alternative approach for functional imaging of brain activity in primary and secondary sensory areas of the human brain. Furthermore, in using this quiet MR technique, it was possible to scan continuously during different stages of human sleep without acoustic noise perturbation.
Single‐shot diffusion‐weighted trace imaging on a clinical scanner
Authors: Chun Terry , Uluğ Aziz M. , van Zijl Peter C. M. 
Published: March 2007

AbstractThe single‐shot trace‐weighted acquisition scheme for isotro‐pic diffusion imaging suggested by Mori and van Zijl Magn. Reson. Med. 33, 41–52 (1995) was implemented on a clinical scanner in combination with echo‐planar imaging. The results on phantoms and seven volunteers show that good‐quality multiplanar isotropic diffusion‐weighted images can be obtained within seconds and absolute Dav images within 10–40 s, depending on the number of gradient strengths used. However, care has to be taken in using this type of multi‐bipolar‐gradient sequence to avoid measurement of artifactual diffusion constants due to background gradient interference. It is outlined how to test for this interference and how to optimize for the correct experiment.
Strategy for lipid suppression in lactate imaging using STIR‐DQCT: A study of hypoxic‐ischemic brain injury
Authors: Nakai Toshiharu , Rhine William D. , Okada Tomohisa , Stevenson David K. , Spielman Daniel M. 
Published: March 2007

AbstractIn vivo lactate detection using gradient enhanced double quantum coherence transfer (DQCT) was significantly improved by addition of short‐time‐inversion‐recovery (STIR). Phantom studies demonstrated lipid suppression down to the background noise level with 33% loss of lactate signal. In vivo studies using a rabbit model of hypoxic and unilateral‐ischemic brain injury showed reduction down to 29 ± 11% in lipids with inversion times between 140 and 170 ms. Lactate signals on the ischemic side were 51 ± 53% higher than the nonischemic side at the peak of hypoxia. STIR‐DQCT can be a useful robust method of obtaining metabolic maps of lactate in vivo.
A technique for determining the spatial relationship between the rotator cuff and the subacromial space in arm abduction using MRI and 3D image processing
Authors: Graichen Heiko , Bonel Harald , Stammberger Tobias , Heuck Andreas , Englmeier Karl‐Hans , Reiser Maximilian , Eckstein Felix 
Published: March 2007

AbstractAn MR imaging‐based technique for three‐dimensional determination of subacromial space width in relation to the rotator cuff in arm abduction is presented. Five volunteers were examined in an open MRI in seven arm positions, and coronal images were obtained with a gradient‐echo sequence. 30 reconstruction of the bones and the supraspinatus was performed, and the minimal spatial distances between acromion, clavicle, and humerus were calculated. The closest contact between the supraspinatus and the anterior ioferior part of the acromion occurred at 90° abduction in internal rotation. The technique presented allows investigation of the morphological basis of the impingement syndrome.
Coronary flow and flow reserve in canines using MR phase difference and complex difference processing
Authors: Wedding Kristin L. , Grist Thomas M. , Folts John D. , Maalej Nabil , Vigen Karl K. , Peters Dana C. , Osrnan Hashirn , Mistretta Charles A. 
Published: March 2007

AbstractCoronary artery disease continues to be the leading cause of death for adults in the United States. Magnetic resonance imaging (MR) has the potential to dramatically impact the diagnosis of heart disease by noninvasively providing a wide range of anatomic and physiologic information. Previous re search has shown that coronary flow, one component of a complete examination, can be accurately measured in the left anterior descending artery in viva The current work validates MR flow measurements in canine circumflex arteries using transit time ultrasound as a standard. The circumflex artery experiences greater in‐plane motion and is a more stringent test for flow measurement accuracy. This work also com pares two methods of processing MR velocity data, phase difference and complex difference techniques, and examines the sources of error present in the animal validation model. Phase difference processing with a 30% magnitude threshold best matched the mean ultrasound flow values (30% PD = 1.04 × US + 1.49, r = 0.94), but it was very sensitive to vessel boundary identification. The complex difference process was less sensitive to vessel boundary identification and correlated well with the transit time ultrasound despite systematic un‐derestimations. The reasons for the discrepancies are shown to stem from a number of possible sources including variabil ity of the ultrasound standard, low signal‐to‐noise ratios in the MR images, sensitivity of the MR technique to vessel bound ary identification, and motion artifacts in the images.
Continuous assessment of perfusion by tagging including volume and water extraction (CAPTIVE): A steady‐state contrast agent technique for measuring blood flow, relative blood volume fraction, and the water extraction fraction
Authors: Zaharchuk Greg , Bogdanov Alexei A. , Marota John J. A. , Shimizu‐Sasamata Masao , Weisskoff Robert M. , Kwong Kenneth K. , Jenkins Bruce G. , Weissleder Ralph , Rosen Bruce R. 
Published: March 2007

AbstractA new technique, CAPTIVE, that is a synthesis of arterial spin labeling (ASL) blood flow and steady‐state susceptibility con trast relative blood volume imaging is described. Using a single injection of a novel, long half‐life intravascular magnetopharma‐ceutical with a high tissue:blood susceptibility difference (Δ χ) to ΔR1 ratio, changes in tissue transverse relaxivity (ΔR2 or ΔR2*) that arise from changes in blood volume were measured, while preserving the ability to measure blood flow using traditional T1 ‐based ASL techniques. This modification permits the contin uous measurement of both blood flow and blood volume. Also, because the contrast agent can be used to remove the signal from intravascular spins, it is possible to measure the first‐pass water extraction fraction. Contrast‐to‐noise is easily traded off with repetition rate, allowing the use of non‐EPI scanners and more flexible imaging paradigms. The basic theory of these measurements, several experimental scenarios, and validating results are presented. Specifically, the PaCO2‐reactivity of mi‐crovascular and total relative cerebral blood volume (rCBV), ce rebral blood flow (CBF), and the water extraction‐flow product (EF) in rats with the new contrast agent MPEG‐PL‐DyDTPA is measured, and the values are concordant with those of previous literature. As an example of one possible application, continuous flow and volume measurements during transient focal ischemia are presented. It is believed that CAPTIVE imaging will yield a more complete picture of the hemodynamic state of an organ, and has further application for understanding the origins of the BOLD effect.
Changes of intracellular sodium T2 relaxation times during ischemia and reperfusion in isolated rat hearts
Authors: van Emous Jan G. , van Echteld Cees J. A. 
Published: March 2007

AbstractThe effect of ischemia and reperfusion on transverse relax ation (T2) of intracellular Na+ (Na+i) was measured with 5‐min time resolution in isolated rat hearts. Nai T2 relaxation was biexponential with 28 ± 7% fast (T2f)and 72 ± 7% slow (T2s) decay. This ratio was constant throughout the protocol. Dur ing 20 min of ischemia, Nai T2s increased from 18.9 ± 2.7 ms to 26.4 ± 1.1 ms (P < 0.001), whereas T2f did not change significantly (3.1 ± 1.8 versus 2.3 ± 1.6 ms during control), and Na+i increased from 9.0 ± 1.0 to 19.5 ± 1.0 mmol/liter (P < 0.001). T2s and Na+i declined again during reperfusion. Changes in T2s relaxation correlated significantly (r = 0.73, P < 0.001) with the time course of Na+i.
Total brain N‐acetylaspartate concentration in normal, age‐grouped females: Quantitation with non‐echo proton NMR spectroscopy
Authors: Gonen Oded , Viswanathan A. Kasi , Catalaa Isabelle , Babb James , Udupa Jayaram , Grossman Robert I. 
Published: March 2007

AbstractThe intra‐individual and inter‐individual variations of the global N‐acetylaspartate (NAA) concentration were measured in a cohort of five 42 ± 5 year‐old normal females. The total NAA signal from the whole head was obtained with non‐localized non‐echo proton spectroscopy (1H‐MRS) and con verted into absolute mole amounts using phantom replace ment. Since NAA is assumed to be present only in neurons, its concentration was obtained by dividing these mole amounts with the brains' volume, calculated from high resolution MRI. The key feature of the procedure is its near‐complete sup pression of the intense subcutaneous and bone marrow lipids' signals, whose chemical shifts neighbor and underlay the NAA. This was achieved by exploiting the lipids' much shorter T1s, compared to that of NAA, for destructive interference of their signals in co‐addition following alternating, nonselective 180° inversions. The average global, inter‐individual NAA concentration in that group was found to be 10.63 mM with a 95% confidence interval of 10.43–10.82 mM.
Adiabatic water suppression using frequency selective excitation
Authors: de Graaf Robin A. , Nicolay Klaas 
Published: March 2007

AbstractA new method for B1‐insensitive water suppression using adiabatic RF pulses is described. The transition zone of the inversion profile of adiabatic full passage (AFP) pulses is used for frequency‐selective excitation followed by dephasing of the excited water with magnetic field gradients. Several im provements of AFP pulses, which also have implications for other applications, are described. The technique was evalu ated by simulations based on the Bloch equations (including relaxation), in vitro experiments and an in vivo verification on neonatal and adult rat brain.
3D MR coronary artery segmentation
Authors: Cline Harvey E. , Thedens Daniel R. , Irarrazaval Pablo , Meyer Craig H. , Hu Bob S. , Nishimura Dwight G. , Ludke Siegwalt 
Published: March 2007

AbstractCoronary arteries are segmented from the blood pool using mathematical morphology operations from a 3D magnetic resonance spiral acquisition on a continuously breathing healthy volunteer. The segmented volume is maximal intensity projected at different views to yield coronary angiograms showing the left anterior descending artery (LAD), right coro nary artery (RCA), and left circumflex artery (LCX). Magnetic resonance coronary angiography provides a retrospective ro tating view of the coronary artery tree that complements oblique reformatted sections.
FAIR excluding radiation damping (FAIRER)
Authors: Zhou Jinyuan , Mori Susumu , van Zijl Peter C. M. 
Published: March 2007

AbstractIt is shown that the flow‐sensitive alternating inversion recov ery (FAIR) technique is complicated by the effect of radiation damping, leading to problems in calibrating this method on phantoms and to inaccuracies in measured flows. A modified scheme called FAIRER (FAIR excluding radiation damping) is proposed, which suppresses the damping effects by employ ing very weak magnetic field gradients (0.06 G/cm) during the inversion recovery, spin‐echo, and predelay periods. Results on phantoms and in vivo on cat brain are presented that demonstrate that FAIRER effectively solves these problems.
Changes of myocardial high‐energy phosphates with the cardiac cycle during acute or chronic myocardial stress
Authors: Illing Barbara , Horn Michael , Urban Bert , Strömer Hinrik , Schnackerz Klaus , de Groot Mark , Haase Axel , Hu Kai , Ertl Georg , Neubauer Stefan 
Published: March 2007

AbstractWhether changes of cardiac high‐energy phosphate concen trations occur over the cardiac cycle remains controversial. The hypothesis was that such cyclical changes are accentu ated during acute or chronic myocardial stress. Isolated rat hearts were perfused under four conditions: (1) control, (2) inotropic stimulation by doubling of perfusate [Ca2+], (3) acute hypoxia (buffer Po2 ∼ 150 torr), and (4) failing, chronically infarcted hearts. 31P‐MR spectra were obtained at seven time points of the cardiac cycle. Under control conditions, cyclical changes (“cycling”) of ATP (11 ± 3%*, *P < 0.05) and phos‐phocreatine (9 ± 2%*) were detected, inorganic phosphate cycling did not reach statistical significance. At high [Ca2+] perfusion, cycling of phosphocreatine (9 ± 5%*) was not accentuated, cycling of ATP and inorganic phosphate did not reach significance. During acute hypoxia, cycling of ATP (10 ± 4%*) and inorganic phosphate (11 ± 4%*) occurred, but cyclical changes of phosphocreatine were not significant. In chronically infarcted hearts, the extent of cyclical changes of ATP, phosphocreatine, and inorganic phosphate was not accentuated. Thus, in perfused rat heart, small oscillations of high‐energy phosphates during the cardiac cycle are detect able, but such changes are not accentuated during acute or chronic stress. The concentrations of high‐energy phosphates over the cardiac cycle are tightly regulated.
In vivo neuronal tract tracing using manganese‐enhanced magnetic resonance imaging
Authors: Pautler Robia G. , Silva Afonso C. , Koretsky Alan P. 
Published: March 2007

AbstractDevelopment of efficient imaging techniques to trace neuro nal connections would be very useful. Manganese ion (Mn2+) is an excellent T1 contrast agent for magnetic resonance imaging (MRI). Four reports utilizing radioactive Mn2+ in fish and rat brain indicate that Mn2+ may be useful for tracing neuronal connections. Therefore, the purpose of this work was to determine if Mn2+ can be used as an in vivo MRI neuronal tract tracer. The results indicate that topical admin istration of MnCI2 solution to the naris of mice as well as to the retinal ganglion cells via intravitreal injection leads to en hancement of contrast along the respective pathways. There fore, application of Mn2+ to neurons allows the use of MRI to visualize neuronal connections.