摘要:

AbstractWe 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 out

ISSN:0740-3194    

DOI:10.1002/mrm.1910290112

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractDifferences in the NMR detectability of39K in various excised rat tissues (liver, brain, kidney, muscle, and testes) have been observed. The lowest NMR detectability occurs for liver (61 ± 3% of potassium as measured by flame photometry) and highest for erythrocytes (100 ± 7%). These differences in detectability correlate with differences in the measured39K NMR relaxation constants in the same tissues.39K detectabilities were also found to correlate inversely with the mitochondrial content of the tissues. Mitochondria prepared from liver showed greatly reduced39K NMR detectability when compared with the tissue from which it was derived, 31.6 ± 9% of potassium measured by flame photometry compared to 61 ± 3%. The detectability of potassium in mitochondria was too low to enable the measurement of relaxation constants. This study indicates that differences in tissue structure, particularly mitochondrial content are important in determining39K detectability and measured relaxation ra

ISSN:0740-3194    

DOI:10.1002/mrm.1910290113

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractProtein in water solution increases magnetic relaxation rates of solvent nuclei to an extent that depends on magnetic field strength and molecular weight. Koenig and Schillinger (J. Biol. Chem.244, 3283 (1969)) showed that a small fraction of the water molecules in the first hydration shell, bound irrotationally with a residence lifetime in the range 01.1 to 10 us, would account for the phenomena. No experiments, as yet, have proven the existence of such long‐lived waters, nor yielded a value for their lifetime. Analogous measurements on solutions of both denatured and cross‐linked protein give data different from that of native protein, but much like results for tissue. By comparing proton and deuteron relaxation rates in solutions of native and cross‐linked protein, it is possible to demonstrate the existence of these relatively long‐lived waters; the data indicate that 1% of a monolayer of the waters of hydration of protein have lifetimes that cluster near 1 us and, it is argued, are held in place by multiple hydrogen bonds. Assigning shorter lifetimes for waters held by fewer bonds, it is possible to develop a unified view of relaxation of water nuclei in protein solutions and in tissue, and to relate it to recent crystallographic data on hydrated

ISSN:0740-3194    

DOI:10.1002/mrm.1910290114

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractWe present an analysis of how vessel curvature can create distortions in magnetic resonance images of flowing blood. Steady flow in curved vessels produces distortions of the vessel shape and intensity variations in the image due to motion during the interval between phase encoding or slice selection and the echo center. Even with steady flow, vessel curvature produces motion moments higher than velocity (acceleration, etc.), but use of a first order oblique flow compensated phase encoding gradient waveform reduced the distortion in the image. Numerical calculations of image distortions based on simple flow models are in good agreement with experimental results in a phantom.

ISSN:0740-3194    

DOI:10.1002/mrm.1910290115

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractAlthough hypoxia and metabolic acidosis have both been shown to impair cardic function, some workers have suggested that acidosis during a period of hypoxia will actually accelerate physiologic recovery from this insult. To address the interactions of metabolic acidosis and hypoxia further, isolated isovolumic rat hearts were exposed to normal perfusion conditions for 30 min to establish baseline conditions, then either continued normal conditions, metabolic acidosis, hypoxia, or combined acidosis and hypoxia for 30 min and subsequently reperfused under normal perfusion conditions for an additional 30 min. We observed that acidosis + hypoxia impaired recovery of cardic contraction more than acidosis or hypoxia alone following experimental perfusion. The combination of acidosis and and hypoxia also impaired cardiac energy metabolism more than acidosis or hypoxia alone as assessed by increases in tissue inorganic phosphate during experimental perfusion as well as during reperfusion. These data suggest that during hypoxia, acidosis appears to primarily impair cardic energy production as we have previously observed in the normoxic isolated rat heart. Therefore, in the intact beating heart, acidosis may not protect from hypoxic injury as has been suggested in simpler systems but may not protect from hypoxic injury as has been suggested in simpler systems but rather may exacerbate at.

ISSN:0740-3194    

DOI:10.1002/mrm.1910290116

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractProjection reconstruction has been implemented with self‐refocused selection pulses on a small bore, 2.0 T MR microscope, to allow imaging of lung parenchyma. Scan synchronous ventilation and cardiac gating have been integrated with the sequence to minimize motion artifacts. A systematic survey of the pulse sequence parameters has been undertaken in conjunction with the biological gating parameters to optimize resolution and signal‐to‐noise (SNR). The resulting projection images with effective echo time of<300 usec allow definition of lung parenchyma with an SNR improvement of ∼15 x over a more conventional 2DFT short echo gradient s

ISSN:0740-3194    

DOI:10.1002/mrm.1910290117

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractWe compared the abilities of three solutions (bicarbonate‐free glucose‐phosphate Ringer's solution (EP II), lactated Ringer's solution, and physiologic saline solution) to preserve pig cornea by measuring phosphate metabolites with31P NMR spectroscopy. EP II preserves corneal viability better than others, and preserving extracted cornea also is better than preserving the whole

ISSN:0740-3194    

DOI:10.1002/mrm.1910290118

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe rotating frame method of localized spectroscopy can be augmented by the inclusion of a refocusing pulse to enable the measurement of T2relaxation times. This technique is particularly appropriate for determining short relaxation parameters due to the absence of time consuming switched B0field gradients. We have evaluated the accuracy of this protocol by measuring localized T2s in the range of 1 to 20 ms. Preliminary data obtained from muscle and liver of normal and iron overloaded human subjects are also presented.

ISSN:0740-3194    

DOI:10.1002/mrm.1910290119

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThis report describes a noninvasive1H‐NMR method for measuring absolute temperatures (±0.2°C) in biological samples and, in particular, in cell culture perfusion systems, utilizing the linear temperature dependence of the water chemical shift relative to the temperature‐independent shift of one of the components of the biological medium, e.g., pyruvate, acetate, or lactate. The effects of flow on temperature can be monitored and appropriate adjustments of the temperature controller can be

ISSN:0740-3194    

DOI:10.1002/mrm.1910290120

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractWe describe a technique for measuring the time dependence and field distortions of magnetic fields due to eddy currents (EC) produced by time‐dependent magnetic field gradients. The EC measuring technique uses a sample with short T1,T2and many rf excitation pulses and free induction decays (FIDs) to measure the out‐of‐phase component of the FIDs, which are proportional to γΔB, the amount by which the signal is off resonance. The measuring technique is sensitive, easy to implement and interpret, and useful for setting preemphasis compensation n

ISSN:0740-3194    

DOI:10.1002/mrm.1910290121

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY