bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in the activities of carbohydrate‐degrading enzymes with ripening in Musa paradisiaca
Authors: Iyare Osarose A , Ekwukoma Blessing O
Published: March 2007

The activities of phosphorylase (EC 2.4.1.1), amylase (EC 3.2.1.2) and invertase (EC 3.2.1.26) were monitored in the pulp and peel of post‐harvest plantain (Musa paradisiaca L) stored at 26 °C and at 14° respectively. There was a significant increase (P < 0.01) in the activities of the three enzymes in both the pulp and peel of plantain fingers stored at 26 °C as ripening progressed as assessed by the unpaired t‐test. The increase in amylase activity was more dramatic, thus suggesting a greater hydrolytic rather than phosphorolytic cleavage of starch. The enzyme activities in the plantain stored at 14 °C also increased with the post‐harvest storage period (P < 0.01) although the absolute values were less than those from the corresponding plantain fingers stored at 26 °C. The possible importance of these observations in the light of reducing the large wastage of M paradisiaca due to poor storage facilities, and thereby enhancing its shelf life and usefulness in the tropics, is discussed.
Release and chemical speciation of copper from anti‐fouling paints with different active copper compounds in artificial seawater
Authors: Sandberg J. , Odnevall Wallinder I. , Leygraf C. , Virta M.
Published: March 2007

Release rates of total copper in artificial seawater (without organic matter) from anti‐fouling paints of different active copper compounds range from 0.5 to 75 μg cm−2 day−1. Approximately 80% of the released total copper was determined to be electrochemically active (labile fraction) for all paints investigated. The remaining fraction is more strongly bonded non‐bioavailable copper complexes with species released from the paints. Model calculations, using MinteqA2, predicted only a small portion (≈ 6%) of the total copper released as free cupric ions (Cu(H2O)2+6), the most bioavailable form of copper. Similar results were obtained with bioassay testing using bacteria and yeast on released copper from massive copper sheet exposed at identical conditions. The large difference between the total and the bioavailable copper fraction emphasizes the importance of generating chemical speciation data for accurate decisions of potential adverse effects of copper release from anti‐fouling paints. The observed release of other metals and organic substances from the paint matrix, implies the importance to assess an integrated response from released species from paints of anti‐fouling, and not only from single ingredients.
Influence of fluoride concentration and pH on corrosion behavior of Ti‐6Al‐4V and Ti‐23Ta alloys in artificial saliva
Authors: Robin A. , Meirelis J. P.
Published: March 2007

Titanium alloys exhibit an excellent corrosion resistance in most aqueous media due to the formation of a stable oxide film and some of these alloys (particularly Ti‐6Al‐4V) were chosen for surgical and odontological implants for this resistance and their biocompatibility. Treatments with fluorides (F−) are known as the main method to prevent plaque formation and dental caries. Toothpastes, mouthwashes and prophylactic gels can contain from 200 to 20 000 ppm F− and can present neutral to acidic character, which can affect the corrosion behavior of titanium alloys devices present in the oral cavity. In this work, the behavior of Ti‐6Al‐4V and the new experimental Ti‐23Ta has been evaluated in artificial saliva of pH 2, 5 and 7 and different F− concentrations (0, 1000, 5000 and 10 000 ppm), through open‐circuit potential measurements, potentiodynamic polarization and electrochemical impedance spectroscopy. A defined correlation between pH and F− concentration settled the active or passive character of the materials. For both alloys, an active behavior was observed for pH 2 and 1000 to 10 000 ppm F− and for pH 5 and 5000 and 10 000 ppm F−. The passive behavior was observed for the other investigated conditions. The F− concentration increase and pH decrease reduced the corrosion resistance of the alloys and decreased the stability of their passive film. The corrosion behavior of both alloys was very similar, but the Ti‐23Ta alloy generally presented slightly higher corrosion resistance.
Intravascular heparin protects muscle flaps from ischemia/reperfusion injury
Authors: Li Xiaolu , Cooley Brian C. , Fowler J. David , Gould John S.
Published: March 2007

Heparin has been found to decrease ischemia/reperfusion injury in skeletal muscle and other tissue/organ systems. The timing of heparin administration to the muscle vasculature has not been explored. We investigated the use of heparinized blood as a washout solution during ischemia to reduce ischemia/reperfusion injury. A rat cutaneous maximus muscle free flap was subjected to a 10‐hr period of room temperature ischemia, then was heterotopically transplanted to the groin via microsurgical revascularization to the femoral vessels. In three experimental groups, flaps were subjected to brief ex vivo perfusion with autologous heparinized blood, at 2, 5, or 8 hr into the 10‐hr ischemic interval. In the two other groups, the flaps were not perfused, and the animals were systemically heparinized either before ischemia or before transplantation, respectively. A control group underwent no flap perfusion or systemic heparinization. After transplantation, flaps were given a 48‐hr period of in vivo reperfusion, then were harvested for evaluation. Flaps undergoing ex vivo perfusion or preischemic heparinization had no significant differences in weight gain (edema) compared with flaps receiving posttransplant heparinization or no heparinization (controls). The dehydrogenase staining of muscle biopsies was significantly faster (indicative of viable tissue) for perfused flaps and the flaps for which the animals received preischemic heparinization, when compared with flaps for which the animals received posttransplant heparinization or no heparinization. From these results, we conclude that heparin offers protection from ischemia/reperfusion injury when it can be introduced into the vascular network either prior to or during the ischemia period. These findings suggest the possibility of using heparinized washout solutions to enhance survival in amputated extremities. © 1995 Wiley‐Liss, Inc.
Natural history of digital replantation: A 12‐year prospective study
Authors: Povlsen B. , Nylander G. , Nylander E.
Published: March 2007

The purpose of the study was to evaluate the fate of the digital arterial anastomoses, resting total digital blood flow, and cold‐induced discomfort following digital replantation with two repaired arteries. The evaluation was done with a Doppler ultrasound of the anastomoses, temperature recording from the finger pulp at room temperature, and a questionnaire regarding the patient's impression of cold‐induced discomfort. At the 2‐year follow‐up all anastomoses were patent, but in two of the six patients one anastomosis was occluded at the 12‐year follow‐up. The replanted digits generally showed lower skin temperatures compared with controls at the 2‐year follow‐up but these had normalized 10 years later, even in digits with one of the two repaired arteries occluded. The number of patients with severe cold‐induced discomfort was unchanged during the observation period. Conclusions: The digital flow continues to increase after the first 2 years after replantation and may reach normal levels at room temperature; however, cold‐induced discomfort is not normalized. Total blood flow improvement is not affected by late arterial occlusion. © 1995 Wiley‐Liss, Inc.
Orthotopic liver retransplantation in rats
Authors: Goto Shigeru , Kamada Naoshi , Delriviere Luc , Kobayashi Eiji , Lord Roger , Ware Frances , Hara Yuzuru , Edwards‐Smith Catherine , Shimizu Yoshinori , Vari Frank
Published: March 2007

A surgical experience with a method of rat orthotopic liver retransplantation (OLRT), and a preliminary study of immunological responses after OLRT are reported. OLRT was performed on the same recipient after the first orthotopic liver transplantation (1st‐OLT) according to our original (Kamada's) cuff method. Replacement of the portal vein (PV) and infra‐hepatic vena cava (IHVC) cuffs was not technically difficult. However, there were no survivors from the first 6 retransplanted rats, mainly due to complications from defective supra‐hepatic vena cava (SHVC) anastomoses. Unlike the human intra‐abdominal SHVC, the posterior wall of the intraabdominal SHVC in rats is too short and fragile to perform an end‐to‐end anastomosis twice between donor and recipient SHVC. For a second group of seven retransplants, a modification of the SHVC anastomosis was made between donor and recipient SHVC in conjunction with the recipient's cuff diaphragm. This enabled reanastomosis to be secure, resulting in the improved 1‐week survival after isogeneic OLRT (85.7%). This OLRT model has been applied to the fully allogeneic combination for several immunological studies and led to novel findings. Thus, an experimental model of a rat orthotopic liver retransplant model has the potential to allow more valuable insights into the immunological study of chronic rejection, sensitization and chimerism following liver retransplantation. © 1995 Wiley‐Liss, Inc.
Derivative lymphatic microsurgery: Indications, techniques, and results
Authors: Campisi C. , Boccardo F. , Alitta P. , Tacchella M.
Published: March 2007

Microsurgical derivative procedures to treat chronic lymphedemas of the limbs are reported here. Techniques used consisted of lymphatic capsule‐venous anastomoses (in pediatric patients) and end‐to‐side lymphatic‐venous anastomoses. Results after more than 5 years showed improvement in about 70% of the cases. The importance of an accurate preoperative diagnostic evaluation and the precise indications for these microsurgical procedures are discussed. Some personal modifications of derivative microsurgical techniques and their advantages are also pointed out. © 1995 Wiley‐Liss, Inc.
Refinements in the one‐stage procedure for management of chronic osteomyelitis
Authors: Guelinckx Paul J. , Sinsel Nadja K.
Published: March 2007

Posttraumatic osteomyelitis remains a frequent problem and requires aggressive surgical treatment to be cured. Radical debridement of all involved soft and hard tissues, obliteration of dead space, and neovascularization of the involved area are obligatory for successful management of the disease. Microvascular free tissue transfer provides the necessary tissue bulk and neovascularization to reconstruct the resulting defect. The transplanted muscle can be optimally mobilized and adjusted in size to obliterate the dead space in contrast to local transposition flaps. This is facilitated by smoothening the bony cavity using a rotating drill system. With an optimal interface between the muscle and the wall of the cavity, small foci of infection can be eliminated. Moreover after free muscle transfer, the optimal environment for secondary bone reconstruction is created. These principles of radical debridement combined with muscle transfer for dead space obliteration, are generally accepted in literature. Nevertheless to achieve this goal several different treatment schedules of repetitive debridements, prolonged antibiotic regimes, and finally various flap transfers have been advocated. We present 16 patients with chronic osteomyelitis treated with radical debridement and immediate free muscle transfer using the latissimus dorsi muscle preferably. Postoperatively an antibiotic course of only 12 days was given. With a mean follow‐up of 2 years all patients remained symptom free. Therefore, our results indicate that this long‐term problem can be solved by a one‐stage procedure using a free flap combined with a short course of antibiotics. However definite conclusions should be reserved for 20 years. © 1995 Wiley‐Liss, Inc.
Volumetric NMR imaging with time‐varying gradients
Authors: Macovski Albert
Published: March 2007

A novel generalized processing system is described whereby, using time‐varying gradients, simultaneous data acquisition can be provided for all points in a volume. This is in sharp distinction to the sensitive‐point method where only the null region is imaged. It is shown that time‐varying gradients systems provide unique phase modulation functions which, when appropriately decoded, enable every point in the volume to be simultaneously imaged from a single FID signal. Methods are shown using the technique to provide simultaneously acquired, localized NMR spectra. Alternative gradient signals are considered including both periodic and aperiodic waveforms.
Design data for efficient axial gradient coils: Application to NMR imaging
Authors: Saint‐Jalmes Hervé , Taquin Jacques , Barjhoux Yves
Published: March 2007

A new design for an axial magnetic field gradient is described. Implemented in a four‐coil configuration, it requires far less power than the conventional Maxwell pair, while maintaining the same field linearity. A practical design tool with a set of curves giving coil dimensions is proposed. Two realizations dedicated to NMR imaging are described and compared with the equivalent Maxwell pair. Substantial power reductions are achieved; in these cases, dc power is reduced by a factor of 5 and switching power by a factor of 15.
Magnetic field dependence of solvent proton relaxation in aqueous solutions of Fe3+ complexes
Authors: Koenig Seymour H. , Baglin Coral M. , Brown Rodney D.
Published: March 2007

It might appear that the Fe3+ ion would be particularly useful as an agent for enhancing contrast in NMR images since it has a relatively large magnetic moment and occurs in vivo in a variety of forms. Moreover, the concentration of Fe3+ changes locally in certain disease states (e. g., β‐thalassemia) and in trauma (formation of methemoglobin), and can be altered in the gastrointestinal tract by the ingestion of readily available dietary supplements. However, the Fe3+ ion is insoluble above pH ∼ 4, and soluble chelate and protein complexes of Fe3+ tend to sequester the ions from solvent; hence, the efficacy of Fe3+ ions for relaxing water protons ought to be low under typical physiological conditions. We report the magnetic field dependence of the relaxation rate of solvent protons (NMRD profiles) for solutions of a variety of Fe3+ complexes to demonstrate the phenomenology relevant to NMR imaging. From these data we make some estimates to show that, deposite the low relaxation rates of solvent protons in solutions of Fe3+ complexes, certain observed changes in image contrast are consistent, quantitatively, with inferences that can be drawn from solution data.
31P Surface‐Coil NMR Analysis of Metabolic Status in KHJJ Tumors
Authors: Adams Dorothy A. , Denardo Gerald L. , Denardo Sally J. , Conboy Claire B. , Morton Bradbury E.
Published: March 2007

Noninvasive monitoring of the effects of treatment on cancer tissue is fundamental to the development of rational radioimmunotherapy (RIT) schemes employing radiolabeled monoclonal antibodies or antibody fragments specific for human cancer. Recent advances in nuclear magnetic resonance spectroscopy make it an attractive candidate for sequential, topical monotoring by 31P NMR of metabolic events during RIT. Preliminary to this effort, we examined the metabolic competence of the well‐characterized, murine KHJJ tumor in situ in BALB/c mice using 31P surface‐coil NMR. The ATP/Pi ratio in tumor volumes ranging from 100 to 800 mm3 showed that tumors over this range of sizes were able to maintain high levels of ATP relative to Pi. As the tumor volume increased above 1 cm3, ATP/Pi levels indicated poor metabolic competence. This lack of metabolic competence was correlated with histological evidence of tissue necrosis and vascular disintegration. The T1 values of assigned phosphorus metabolites were established. Intracellular pH, as determined from the chemical shift of Pi, was found to vary in these tumors from 7.1 in rapidly metabolizing tissue to 6.6 in necrotic tumors.© 1985 Academic Press,Inc.
Truncation Artifacts in Magnetic Resonance Imaging
Authors: Wood Michael L. , Mark Henkelman R.
Published: March 2007

A method has been developed to reduce a magnetic resonance image artifact arising from the Fourier transformation of data truncated in the phase‐encoding direction. The discontinuity is eliminated between the phase of the complex data sample associated with the maximum negative phase‐encoding gradient and the phase of the maximum positive gradient sample. Images retain sharper edges than if low‐pass filtering is employed. The method is demonstrated on clinical images, then an explanation of the method is presented.© 1985 Academic Press,Inc.
Time‐Multiplexed Multislice Inversion‐Recovery Techniques for NMR Imaging
Authors: Park H. W. , Cho M. H. , Cho Z. H.
Published: March 2007

Multislice imaging techniques effectively applicable to inversion‐recovery (IR) imaging are developed and applied to human imaging. These new multislice IR imaging sequences employ the time‐multiplexing (TM) technique conventionally used in the slice‐by‐slice saturation‐recovery (SR) imaging. Two new time‐multiplexed multislice (TMM) IR imaging sequences are proposed and some of the experimental results obtained with the methods are presented.© 1985 Academic Press,Inc.
Water suppression in 1H magnetic resonance images by the generation of multiple‐quantum coherence
Authors: Dumoulin Charles L. , Vatis Dimitrios
Published: March 2007

Pulse sequences which generate multiple‐and zero‐quantum coherence and suppress the detection of single‐quantum coherence have ben used to greatly reduce the intensity of the water signal in NMR images. In the experiment, image signals having multiple‐quantum behavior add constructively while single‐quantum signals, such as the signal arising from water, are canceled. Since the generation of multiple‐quantum coherence is only a function of spin‐spin coupling, water suppression by this technique is independent of chemical shift. Consequently, suppression of the water resonance in a 1H NMR image can be accomplished in an inhomogeneous magnetic field provided that the excitation profile of the rf pulses is equal for all spins. Furthermore, variations in the T1 and T2 of coupled and uncoupled spins do not affect the efficiency of the multiple‐quantum filter. © 1986 Academic Press, Inc.
Rapid NMR imaging of dynamic processes using the FLASII technique
Authors: Frahm Jens , Haase Axel , Matthaei Dieter
Published: March 2007

FLASH (Fast Low‐Angle SHot) imaging is a new method for rapid NMR imaging which has been demonstrated to provide abdominal images without artifacts due to respiratory or peristaltic motions. The sequence typically employs 15° radiofrequency excitation pulses and acquires a free induction decay signal in the form of a gradient echo. Here FLASH images are recorded in the presence of dynamic processes with time constants even smaller than the measuring time of about 2 s for an image with a 128 × 128‐pixel resolution. Experiments are carried out on flow phantoms and on rabbits yielding heart images without gating of the cardiac motion. © 1986 Academic Press, Inc.
Observation of intracellular potassium and sodium in the heart by NMR: A major fraction of potassium is “invisible”
Authors: Fossel Eric T. , Hoefeler Herbert
Published: March 2007

Using 39K and 23Na NMR in conjunetion with extracellularly localized shift reagents, we have determined the intracellular concentrations of NMR visible sodium and potassium in isolated, perfused rat hearts. We find this concentration to be 9.9 mM/kg cell water for sodium and 31 mM/kg cell water for potassium. Values of activity determined by ionsensitive microelectrodes are in good agreement with our sodium value but do not agree with our potassium value. Our results mean that a major pool of intracelluar potassium is, on average, signifieantly immobilized and that the mobile NMR visible faction (31mM/kg) is not in exchange with the NMR invisible pool (114mM/kg). The immobilized fraction is characterized by T2 values which are too short to be observed by our conventional spectrometer. This fraction is, therefore, said to be “invisible” under our experimental conditions. © 1986 Academic Press, Inc.
Myocardial high energy phosphate metabolism in closed chest dog: Creation of an animal model
Authors: Osbakken Mary , Ligeti Laszlo , Clark B. J. , Bolinger Lizann , Subramanian Hari , Schnall Mitchell , Leigh Jack , Chance Britton
Published: March 2007

A chronic closed chest dog model was developed to study myocardial metabolism with NMR spectroscopy. Cardiac windows were surgically created in 10 dogs by removal of two ribs and accompanying skeletal muscle. Marlex mesh was sewn between the two exposed ribs, and fascia and skin were closed. 31P spectra were obtained using a surface coil placed into the surgically created pouch and using routine NMR pulsing techniques. © 1986 Academic Press, Inc.
Cardiac transfer function relating energy metabolism to workload in different species as studied with 31P NMR
Authors: Ligeti Laszlo , Osbakken Mary D. , Clark Bernard J. , Schnall Mitchell , Bolinger Lizann , Subramanian Hari , Leigh Jack S. , Chance Britton
Published: March 2007

Cardiac metabolism was studied with 31P NMR in 7 dogs and 4 cats to determine whether animals adapted for different life‐styles (stalk and sprint vs endurance running) respond to increased work loads (heart rate × blood pressure product) with different high‐energy phosphate kinetics. Hearts were exposed via a left lateral thoracotomy under Nembutal anesthesia (40 mg/kg). Two‐turned solenoid surface coils were placed on the left ventricles; pacing wires were sutured into the left ventricular apeces. The femoral artery and vein were canulated for blood pressure and arterial blood gas monitoring and fluid and drug infusion, respectively. Animals were placed in a plexiglass holder into a 2.1‐T, 31‐cm‐bore, superconducting magnet. 31P spectra were obtained from the heart using respiratory and electrocardiogram gating. Cardiac work loads were changed by pacing the heart at 4, 4.5, and 5 Hz. Heart rate × blood pressure product “work” was correlated with Pi/PCr ratios. Dog hearts were more resistant than those of cats to changes in Pi/PCr with increasing work load. It is possible that animals adapted to different life‐styles may have cardiovascular systems which are metabolically and mechanically adapted for different forms of stress. These differences may be elicited and effectively delineated using in vivo NMR techniques during various physiological interventions, such as pacing. The basis for these differences may be related to cardiac microvasculature or to intrinsic differences in enzyme kinetics. Delineation of these mechanisms may be helpful in the understanding of the physiological basis of cardiac function in health and disease. © 1987 Academic Press. Inc.
Frequency‐modulated radiofrequency pulses in spin‐echo and stimulated‐echo experiments
Authors: Kunz Dietmar
Published: March 2007

Frequency‐modulated of pulses based on a linear frequency sweep are studied experimentally in spin‐echo and stimulated‐echo sequences. It turns out that these FM pulses generate a quadratic phase perpendicular to the selected slice and that the quadratic phases of the FM pulses in a spin‐echo or stimulated‐echo sequence may compensate each other if sweep velocity and gradients are suitably chosen. For a complete rephasing, a formula is given and supported by measured slice profiles. Slice profiles of excellent rectangularity are obtained. Finally, it is shown that with this technique images can be obtained using pulses of increased bandwidth and reduced peak power compared with the AM situation. © 1987 Academic Press, Inc.
SYS‐FLASH. Systemic saturation in FLASH MR imaging
Authors: Matthaei Dieter , Haase Axel
Published: March 2007

A simple modification of FLASH (Fast Low Angle SHot) MR imaging, which results in a variable reduction of the intensity of flowing blood and flow artifacts in transaxial tomograms, is reported. Here a nonselective radiofrequency pulse of variable flip angle is used before the acquisition of each projection in FLASH imaging to saturate flowing blood within the whole volume (Systemic Saturation = SYS‐FLASH). © 1987 Academic Press, Inc.
Flow suppression in rapid FLASH NMR images
Authors: Frahm Jens , Merboldt Klaus‐Dietmar , Hänicke Wolfgang , Haase Axel
Published: March 2007

Rapid FLASH (fast low angle shot) NMR images are very sensitive to flow phenomena. In particular, a steady reflow of unsaturated spins from outside the imaging plane results in high image intensities which depend on the flip angle, the repetition time, and the flow velocity. Here we describe a technique that suppresses these signals by saturating remote spins prior to entering the imaging plane, e.g., by intercalating the FLASH sequence with slice‐selective 1–2‐1 pulse packages. Experiments have been carried out on phantoms and human extremities. Flow artifacts in the phase‐encoding direction of the images are strongly reduced. Vascular structures may be easily delineated using difference images obtained with and without flow suppression.
Changes in nuclear magnetic resonance (T2) relaxation of limb tissue with bed rest
Authors: Leblanc Adrian , Evans Harlan , Schonfeld Ernesto , Ford Joseph , Schneider Victor , Jhingran Satish , Johnson Philip
Published: March 2007

Bed rest is used to simulate the effects of weightlessness on human physiology. A spinecho procedure was used to image the lower leg of 15 normal male volunteers before and after 5 weeks of horizontal bedrest. In addition to noninvasively measuring muscle size changes, accurate T2 images were produced to investigate possible relaxation time changes immediately (2–4 h) and 1–2 days after bed rest. Subcutaneous fat showed no change in T2, bone marrow showed a decrease, and muscle showed no change immediately after bed rest but increased 1–2 days following reambulation. © 1987 Academic Press, Inc.
Detection of myocardial infarction in the mini‐pig using NMR imaging
Authors: Checkley D. , Loveday B. E. , Waterton J. C. , Zhu X. P. , Isherwood I.
Published: March 2007

Spin‐echo images of 10 myocardial infarcts in nine mini‐pigs were obtained at 30 h, 3 days, and approximately 10 days postinfarction. Infarcts were not detected at all at 30 h in five out of five cases examined. At 3 days postembolization (six cases) one infarct was certainly detected, whilst at 10 days (nine cases) all infarcts were seen as high‐signal areas in long TE spin‐echo sequences. After 2 weeks no further infarct signal change was detected (three cases), but myocardial thinning became more evident. Using techniques similar to those reported here, early postinfarct changes in the dog have been detected by other authors. Possible reasons for this difference between pig and dog are discussed. © 1987 Academic Press, Inc.
Transverse relaxation of solvent protons induced by magnetized spheres: Application to ferritin, erythrocytes, and magnetite
Authors: Gillis Pierre , Koenig Seymour H.
Published: March 2007

Since 1/T2 of protons of tissue water is generally much greater than 1/T1 at typical imaging fields, small single‐ion contrast agents–such as Gd(DTPA), which make comparable incremental contributions and therefore smaller fractional contributions to 1/T2 compared to 1/T1–are not as desirable for contrast‐enhancement as agents that could enhance 1/T2 preferentially. In principle, such specialized agents will only be effective at higher fields because the field dependence (dispersion) of 1/T1 is such that it approaches zero at high fields whereas 1/T2 approaches a constant value. The residual 1/T2 is called the “secular” contribution and arises from fluctuations in time–as sensed by the protons of diffusing solvent or tissue water molecules–of the component of the magnetic field parallel to the static applied field. For solutions or suspensions of sufficiently large paramagnetic or ferromagnetic particles (⋧250 Å diameter), the paramagnetic contributions to the relaxation rates satisfy 1/T2 ≫ 1/T1 at typical imaging fields. We examine the theory of secular relaxation in some detail, particularly as it applies to systems relevant to magnetic resonance imaging, and then analyze the data for solutions, suspensions, or tissue containing ferritin, erythrocytes, agar‐bound magnetite particles, and liver with lowdensity composite polymer‐coated magnetite. In most cases we can explain the relaxation data, often quantitatively, in terms of the theory of relaxation of protons (water molecules) diffusing in the outer sphere environments of magnetized particles. The dipolar field produced by these particles has a strong spatial dependence, and its apparent fluctuations in time as seen by the diffusing protons produce spin transitions that contribute to both 1/T1 and /T2 comparably at low fields, for the larger particles, because of dispersion, the secular term dominates at fields of interest. On the basis of the agreement of theory with data for solutions of small paramagnetic complexes, large magnetite particles, and liver containing low‐density polymer‐coated magnetite agglomerates, it is argued that the theory is sufficiently reliable so that, e.g., for ferritin–for which 1/T2 is unexpectedly large–the source of its large relaxivity must reside in nonideal chemistry of the ferritin core. For blood, it appears that diffusion through intracellular gradients determines 1/T2. © 1987 Academic Press, Inc.
T2‐weighted contrasts in rapid low flip‐angle imaging
Authors: Bendel Peter
Published: March 2007

Expressions for the contrast‐to‐noise (C/N) behavior in images obtained from rapid low flip‐angle excitation pulses are derived, taking into account both T1‐ and T2‐dependent contrasts. It is shown, and demonstrated experimentally, that images with T2‐weighted contrasts can be efficiently acquired with such sequences, by a suitable choice of TR, TE and tip angle. © 1987 Academic Press, Inc.
Detection of malignant tumors: Water‐suppressed proton nuclear magnetic resonance spectroscopy of plasma
Authors: Dowd Terry L. , Kaplan Barry A. , Gupta Raj K. , Aisen Philip
Published: March 2007

Average linewidths of methyl and methylene proton resonances of plasma lipoproteins from healthy controls and untreated cancer patients were measured in water‐suppressed proton spectra obtained at 400 MHz. In contrast to a previous report (E. T. Fossel, J. M. Carr, and J. McDonagh, N. Engl. J. Med. 315, 1369 (1986)) no statistically significant difference (P > 0.5) was found between the average linewidths in plasma samples from 20 normal controls (36.0 f 6.4 Hz) and 17 untreated cancer patients (34.6 ± 6.3 Hz). When the effect of lactate was removed by graphical extrapolation, a small but marginally significant (P = 0.08) difference was observed between the average linewidths of the normal controls (35.1 ± 5.8 Hz) and untreated cancer patients (31.8 ± 5.2 Hz). However, there was still a large overlap between the two groups. In addition, substantial day to day variations in the linewidths of samples from the same individuals were observed. We conclude that these measurements cannot be used to detect cancer.
19F magnetic resonance imaging of the reticuloendothelial system
Authors: Ratner Adam V. , Hurd Ralph , Muller Holde H. , Bradley‐Simpson Beverly , Pitts William , Shibata J Dean , Sotak Chris , Young Stuart W.
Published: March 2007

In this study sequential1H and19F magnetic resonance imaging methods were used to map the distribution of fluorinated compoundsin vivo.An intravenously administered emulsion of perfluorooctylbromide (PFOB), an agent known to localize in the reticuloendothelial system, was detected in the liver and spleen of all studied hamsters and mice using19F MRI. Lungs and salivary glands were also affected in some animals. Using a G. E. NMR CSI 2‐T spectroscopy/imaging system, projection19F images were obtained in 4 to 8 min. Subsequent mouse studies using a thick‐slice driven equilibrium pulse sequence produced19F images with an improved signal‐to‐noise ratio in a shorter acquisition time. With PFOB,19F MRI has the capability of detecting macrophages in the reticuloendothelial system and in other sites where macrophages congregate. This is the first report where the reticuloendothelial system was specifically imaged in live animals and where driven equilibrium imaging techniques have been applied to19F MRI. © Academic Press, Inc.
Continuous distributions of NMR relaxation times applied to tumors before and after therapy with X‐rays and cyclophosphamide
Authors: Kroeker Randall M. , Stewart Cindy A. , Bronskill Michael J. , Henkelman R. Mark
Published: March 2007

In vivo measurements of T1 and T2 values in two experimental tumors growing in the legs of mice were made during tumor growth and after treatment of the tumor with either X‐rays or cyclophosphamide. The T1 and T2 values were obtained by fitting the data to continuous distributions of relaxation times. This technique gives broad distributions of relaxation times which are characterized by a number of peaks with characteristic T1 and T2 values. Before treatment, the TI and T2 values increased before a palpable tumor mass could be detected. The response to subcurative doses of either treatment method was a reduction in the T1 and T2 values and a parallel reduction in tumor weight. Although local recurrence was characterized by the same pattern of tumor growth as was observed before treatment, therapy was found to give higher relaxation time values than those measured in untreated tumors. The higher relaxation time values of tumor‐bearing legs were the result of redistribution of the peaks in the distribution and not changes in the relaxation times of the individual peaks. © 1988 Academic Press, Inc.
Time‐resolved magnetic resonance angiography
Authors: Dumoulin C. L. , Souza S. P. , Walker M. F. , Yoshitome E.
Published: March 2007

A time‐resolved phase contrast magnetic resonance angiography technique is described. This technique provides a series of angiograms obtained at different phases of the cardiac cycle. Such a series of angiograms can be used to evaluate blood flow dynamics. For example, turbulent flow in the regions of vessel bifurcations is easily demonstrated and followed during systole and diastole. Retrograde flow can also be observed. Dynamic angiography can be particularly useful in distinguishing transient image features, such as signal voids due to turbulent flow, from static features arising from vessel morphology. © 1988 Academic Press, Inc.
Saturation and inversion transfer studies of creatine kinase kinetics in rabbit skeletal muscle in vivo
Authors: Hsieh Paul S. , Balaban Robert S.
Published: March 2007

The steady‐state kinetics of the creatine kinase reaction in rabbit skeletal muscle in vivo was investigated using inversion and saturation magnetization transfer techniques. Both techniques determined the forward rate of this reaction (creatine phosphate ATP) as approximately 0.3 s−1. This corresponds to a flux of 10 μmol creatine phosphate/s/g muscle. The saturation transfer technique underestimated the reverse reaction by approximately 56%. This result is likely due to the participation of ATP in other interactions in skeletal muscle not involving creatine phosphate. © 1988 Academic Press, Inc.
The modification of the RF field distribution of surface coils by weakly conducting saline samples
Authors: Hanstock C. C. , Lunt J. A. , Allen P. S.
Published: March 2007

The modification of the RF field distribution of a surface coil, which is brought about by both loading and skin effect conditions arising from the proximity of weakly conducting saline samples, is demonstrated. A procedure for the calibration of the depth of the spectral acquisition region in depth‐pulse localized in vivo spectroscopy is shown to be acceptable. © 1988 Academic Press, Inc.
Improved sensitivity of proton MR to oxygen‐17 as a contrast agent using fast imaging: Detection in brain
Authors: Hopkins A. L. , Haacke E. M. , Tkach J. , Barr R. G. , Bratton C. B.
Published: March 2007

The potential utility of H217O as a contrast agent has been demonstrated in biological solutions and isolated tissues but its use has been impaired by the need to run heavily T2‐weighted spin‐echo images. By choosing an appropriate steady‐state free precession experiment sensitive to T1/T2, we have improved the available contrast‐to‐noise. per unit time by more than a factor of 5. This allows easy measurement of the proton effects for concentrations as low as 0.4% H217O in less than 1 min. Injection into small animals produces a marked reduction in the overall image intensity. Consecutive imaging at the rate of one every 52 s has been used to follow the rate of change in brain image intensity immediately after injection. © 1988 Academic Press, Inc.
Quantitative magnetic resonance imaging of estradiol‐induced pituitary hyperplasia in rats
Authors: Rudin M. , Briner U. , Doepfner W.
Published: March 2007

Magnetic resonance imaging (MRI) has been used for the determination in vivo of rat pituitary size. In midsagittal T2‐weighted sections the pituitary, having a lower T2 value than the surrounding tissue, was visible with pronounced contrast. The size has been estimated by pixel counting. A close correlation (r = 0.96) with the pituitary weights determined postmortem has been obtained, demonstrating the reliability of the in vivo method. Using MRI the effects of Sandostatin, a somatostatin analog, on the pituitary size have been monitored in a rat model of prolactinoma (estradiol‐induced hyperplasia of the pituitary). Treatment with Sandostatin over 4 weeks resulted in a 40% reduction of the hyperplastic pituitaries. These results have been confirmed by determination of pituitary weights postmortem. However, due to a large interindividual variation in size of hyperplastic pituitaries, more animals are required to reach statistical significance when only endpoints of treatment can be measured. In contrast, MRI allows one to monitor individually the drug effects over a long period of time, eliminating interindividual variations. © 1988 Academic Press, Inc.
Problems in the assessment of magnesium depletion in the rat byin vivo31P NMR
Authors: Adam William R. , Craik David J. , Hall Jon G. , Kneen Malea M. , Wellard R. Mark
Published: March 2007

Priorin vitrostudies, utilizing31P nuclear magnetic resonance (31P NMR) to measure the chemical shift (σ) of β‐ATP and lengthening of the phosphocreatine spin‐spin (T2) relaxation time, suggested an assessment of their efficacy in measuring magnesium depletionin vivo.Dietary magnesium depletion (M2+↓) produced markedly lower magnesium in plasma (0.44 vs 1.13 mmol/liter) and bone (130 vs 190 μmol/g) but much smaller changes in muscle (41 vs 45μmol/g, P0.01), heart (42.5 vs 44.6 μmol/g), and brain (30 vs 32 μmol/g). NMR experiments in anesthetized rats in a Bruker 7‐T vertical bore magnet showed that in Mg2+↓rats there was a significant change in brain β‐ATP shift (16.15 vs 16.03 ppm,P< 0.05). These chemical shifts gave a calculated free [Mg2+] of 0.71 mM(control) and 0.48mM(Mg2+↓). In muscle the change in β‐ATP shift was not significant (Mg2+↓15.99 ppm, controls 15.96 ppm), corresponding to a calculated free MP of 0.83 and 0.95mM, respectively. PhosphocreatineT2(Carr‐Purcell, spin‐echo pulse sequence) was no different with M2+↓in musclein vivo(surface coil) (Mg2+↓136, control 142 ms) or in isolated perfused hearts (Helmholtz coil) (control 83, Mg2+↓92 ms).31P NMR is severely limited in its ability to detect dietary magnesium depletionin vivo.Measurement of β‐ATP shift in brain may allow studies of the effects of interaction in group studies hut does not allow prediction of an individual magnesium status. © 1988 Academic Press, Inc.
Intravoxel incoherent motion imaging using steady‐state free precession
Authors: Le Bihan Denis
Published: March 2007

IVIM MR imaging is a method which generates images of diffusion and perfusion in vivo. Until now, intravoxel incoherent motion (IVIM) images have been obtained using spin‐echo sequences with extragradient pulses, resulting in long acquisition times (typically 2 × 8 min 32 s). A new method is proposed here, using steady‐state free precession (SSFP), which allows IVIM images to be obtained in a couple of minutes. Phantom studies showed that the sensitivity of SSFP to IVIMs is much greater than that of spin echoes. In vivo images are shown. © 1988 Academic Press, Inc.
31P and 1H magnetic resonance spectroscopy of acute alcohol cardiac depression in rats
Authors: Auffermann Wolfgang , Camacho S. Albert , Wu Shao , Litt Lawrence , Parmley William W. , Higgins Charles B. , Wikman‐Coffelt Joan
Published: March 2007

Cardiac depression in the isolated rat heart perfused with 4% ethanol was correlated with intracellular phosphate energetics and tissue water distributions. Energy metabolites were assessed using 31P magnetic resonance spectroscopy (MRS) and correlated to the mitochondrial redox state using epicardial surface fluorometry. Changes in myocardial water compartmentation were measured by using 1H NMR spectroscopy with an extracellular chemical‐shift reagent (DyTTHA) and correlated to results of 2D echocardiography (2DE). During alcohol perfusion there was a significant decrease in developed pressure and in coronary flow. No change was seen in ATP, PCr, pHi, Pi, or NADH. After withdrawal of alcohol from the perfusate cardiac function reverted to control values without a depletion of energy levels. During alcohol perfusion 'H MRS showed a marked redistribution of water from the intra‐ to the extracellular space, corresponding to a 35% left ventricular wall thinning confirmed by 2DE. The results indicate that acute alcohol cardiac depression is related to a dehydration of myocardial cells, but is not associated with intracellular acidosis or energy depletion. 0 1988 Academic Press, Inc. © 1988 Academic Press, Inc.
Suppression of radiofrequency interference in cardiac gated MRI: A simple design
Authors: Shetty Anil N.
Published: March 2007

A simple design is proposed to suppress the noise pickup in the ECG leads from RF and gradient pulses during NMR imaging. The ECG signal is passed through a low‐pass filter and a common‐mode‐rejection amplifier to reduce erroneous signal generated by the electrical ground loops. The output is gated through a CMOS switch to blank the preamplifier from the NMR during data acquisition. © 1988 Academic Press, Inc.
Rapid31P spectroscopy on a 4‐T whole‐body system
Authors: Hardy C. J. , Bottomley P. A. , Roemer P. B. , Redington R. W.
Published: March 2007

Initial31P spectroscopy results from a 4‐T whole‐body system are reported. Localized spectra from the human head, liver, and calf were obtained using DRESS, slice‐inter‐leaved DRESS, and volume 3DFT spectroscopic imaging techniques. Substantial reductions in data acquisition times to 10 s–4 min were achieved relative to previous similar experiments at 1.5 T. Some gain in spectral resolution (as measured in ppm) was also realized in the head. © 1988 Academic Press, Inc.
In vivo1H NMR spectroscopy of an intracerebral glioma in the rat
Authors: Remy C. , Von Kienlin M. , Francois A. , Benabid A. L. , Decorps M.
Published: March 2007

High‐resolution 1H surface coil NMR spectroscopy (MRS) was used to evaluate in vivo the cerebral metabolism changes in rat brain induced by a glial tumor growing in situ. Tumor cells (C6 glioma cells) were stereotaxically placed in the right hemisphere superficially. 1H MRS was performed using 5‐mm surface coils implanted over the right hemisphere and the water was suppressed using a binomial sequence. As the intracerebral tumor size increased, there was a marked decrease in the N‐acetyl aspartate level and an increase in the 1.3 ppm peak. Edition of this peak showed that lactate increased but lipids increased much more than lactate. Moreover the ratio between the choline‐phosphocholine and creatine‐phosphocreatine peaks changed. This study demonstrates that high‐resolution surface coil 1H MRS can be used to monitor changes in metabolism associated with growth of an experimentally induced rat brain tumor in situ. © 1989 Academic Press, Inc.
Magnetization transfer contrast (MTC) and tissue water proton relaxation in vivo
Authors: Wolff Steven D. , Balaban Robert S.
Published: March 2007

In this study the exchange between 1H magnetization in “free” water (1Hf) and that in a pool with restricted motion (1Hr) was observed in tissues in vivo using NMR saturation transfer methods. Exchange between these two pools was demonstrated by a decrease in the steady‐state magnetization and relaxation times of 1Hf with radiofrequency irradiation of 1Hr. The pseudo‐first‐order rate constant for the movement of magnetization from 1Hfto 1Hr was ∼ Is−1 in kidney and ∼3s−1 in skeletal muscle in vivo. Proton NMR imaging demonstrated that this exchange was tissue specific and generated a novel form of NMR image contrast. The extent of exchange between 1Hf and 1Hr as well as the topological correlation ofthe exchange with relaxation weighted images suggests that this pathway is a major determinant of the observed relaxation properties of water 1H in vivo. © 1989 Academic Press. Inc.
A comparison of double‐tuned surface coils
Authors: Fitzsimmons J. R. , Brooker H. R. , Beck B.
Published: March 2007

The combined acquisition of proton images and localized spectra is considered essential to the practical application of NMR techniques to human and animal research. Double‐tuned surface coils which have been introduced to the literature are intended to address the problem: however, a careful evaluation of available designs is lacking. The “trap” method, the loop gap resonator design, and the transformer‐coupled double‐tuned design are evaluated here using bench tests of signal intensity and Q as well as signal‐to‐ noise measurements on a 2‐T imager/spectrometer. Comparisons are made relative to optimized single‐tuned circuits of the same size for both protons at 85 MHz and phosphorus at 34 MHz. The results suggest that the “trap” design and the transformer coupled design are very efficient (98%) in the low‐frequency mode (34 MHz) while the loop gap resonator is relatively inefficient (82%). In the high‐frequency mode (85 MHz) the loop gap resonator is 75% efficient while the “trap” design and the transformer coupled coil are closer to 50% efficient. © 1989 Academic press. Inc. © 1989 Academic Press, Inc.
Assessment of the NMR visibility of intraerythrocytic sodium by flame photometric and ion‐competitive studies
Authors: Nissen Henrik , Jacobsen Jens Peter , Hørder Mogens
Published: March 2007

23Na nuclear magnetic resonance (NMR) studies of intraerythrocytic sodium concentrations were performed at 37°C and the accuracy of the method was evaluated through concomitant emission flame photometric analysis. NMR visibility of intraerythrocytic sodium was estimated to be 75 ± 3%. Verification of the presence of an NMR invisible intraerythrocytic sodium pool and assessment of the mechanisms explaining this invisibility was achieved by measurement of 23Na NMR signal intensities and T1 relaxation times of erythrocyte hemolysate during ion‐competitive sodium release from association sites. Signal intensities after addition of small quantities of K+ and Mg2+ to the hemolysates were significantly larger than that expected from dilution of the sample, implying that the additions have resulted in the release of formerly invisible sodium. Furthermore, the intensities following the addition of K+ were significantly larger than those after the addition of Li+ and choline+. This signifies a specificity of the association sites at which sodium has decreased visibility. Increased T1 values following the additions confirmed the release of bound sodium. © 1989 Academic Press, Inc.