摘要:

AbstractAn NMR method to study on‐line mitochondrial function was developed. Mitochondria were maintained in a stable physiologic state in agarose beads that were continuously superfused with oxygenated buffer at 28°C. Oxidative function of both heart and liver mitochondria was evaluated with31P NMR at 9.4 T using pyruvate plus malate as substrate. This method allows clear resolution of adenosine triphosphate‐γ (ATPγ) and adenosine diphosphate‐β (ADPβ) phosphate signals, whereas a signals of ATP and ADP overlap. ATP production by mitochondria was documented to be very sensitive to different interventions (hypoxia, ischemia, carbonyl cyanide p‐(tri‐fluoromethoxy)phenylhydrazone (FCCP)) and depended on the ADP concentration in supervision medium. These data demonstrate that the new application of NMR to study mitochondrial function can discriminate, on‐line, between several physiologic and biochemical processes in intact physiologically sta

ISSN:0740-3194    

DOI:10.1002/mrm.1910390502

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

年代:1998

数据来源: WILEY

摘要:

AbstractThe feasibility of noninvasively assessing hemoglobin oxygen saturation of deep blood vesselsin vivoby measuring bloodT2* is investigated. Techniques for bloodT2* measurements in major arteries and veins in the presence of pulsatile blood flow are presented and validated using a flow phantom. Images of multiple TEs were collected in a paired fashion. Cardiac triggering was used to eliminate image artifacts caused by pulsatile arterial blood flow. Using these techniques, it was found that theT2* of arterial blood (199 ± 8 ms) is significantly greater than that of venous blood (108 ± 6 ms) in 10 volunteers, consistent with the fact that the oxygen saturation level of arterial blood is much larger than that of venous blood. Various oxygen saturation levels were createdin vivoin a pig and the bloodT2* was shown to increase with oxygen saturation levels over a wide range. Preliminary results of this study indicate that it is feasible to assess local oxygen saturation by measuring bloodT2* using the proposed technique

ISSN:0740-3194    

DOI:10.1002/mrm.1910390503

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

年代:1998

数据来源: WILEY

摘要:

AbstractAcquire multiple longitudinal locations in the lower extremity after a single contrast injection, appropriate table translation and contrast injection are required. An approximate model based on constant bolus velocity was developed to describe the space‐time course of a contrast bolus in the lower extremity. This model was verified in dynamic MR angiograms acquired in a group of patients using time‐resolved 2D MR digital subtraction angiography (MRDSA). From this contrast bolus passage model, a timing algorithm for table translation and contrast injection was developed for bolus chase MRDSA, subsequently validated in bolus chase 2D MRDSA experiments. All targeted major peripheral arteries were well depicted in bolus chase 2D MRDSA using this timing algorithm and a single 15‐ml contrast

ISSN:0740-3194    

DOI:10.1002/mrm.1910390504

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

年代:1998

数据来源: WILEY

摘要:

AbstractPreliminary results fromin vivosodium MRI of human patellar articular cartilage are presented. Sodium images generated of anin vitrobovine patella clearly distinguish the region of proteoglycan depletion from the region of healthy cartilage. This provides the first evidence that sodium imaging may be used to detect changes due to osteoarthritisin vivo.The process of optimizing imaging time and signal‐to‐noise ratio, as well as potential implications in the detection of osteoar‐thritic change, are disc

ISSN:0740-3194    

DOI:10.1002/mrm.1910390505

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

年代:1998

数据来源: WILEY

摘要:

AbstractIn the pulsed arterial spin labeling (ASL) techniques EPISTAR, PICORE, and FAIR, subtraction of two images in which inflowing blood is first tagged and then not tagged yields a qualitative map of perfusion. An important reason this map is not quantitative is that there is a spatially varying delay in the transit of blood from the tagging region to the imaging slice that cannot be measured from a single subtraction. We introduce here two modifications of pulsed ASL (QUIPSS and QUIPSS II) that avoid this problem by applying additional saturation pulses to control the time duration of the tagged bolus, rendering the technique relatively insensitive to transit delays and improving the quantitation of perfusion.

ISSN:0740-3194    

DOI:10.1002/mrm.1910390506

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

年代:1998

数据来源: WILEY

摘要:

AbstractA new acquisition technique for rapid, whole‐brain functional MRI is presented. In this technique, several slices are simultaneously acquired using rosettek‐spacetrajectories and a gradient‐induced frequency modulation. This modulation together with the spectral properties of the rosette acquisition allow all slices to be reconstructed individually. In functional MRI studies, acquisition rates of 16.7 to 25 images/s were achieved, a threefold improvement over single‐slice acquisitions. The raw images showed some increase in noise. However, because this increase is mostly stationary, the functional activation maps showed only a slight increase in noi

ISSN:0740-3194    

DOI:10.1002/mrm.1910390507

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

年代:1998

数据来源: WILEY

摘要:

AbstractA new technique for magnetic resonance imaging of absolute perfusion changes that uses magnetically labeled tissue water proton spins as a freely diffusible tracer is described. It consists of unprepared basis (BA) images that serve as a reference and selective (SE) inversion prepared images that are sensitive to perfusion changes. In the present study, the BASE technique was applied to functional neuroimaging. BA and SE images were alternatingly and repeatedly acquired during periods of visual stimulation and control. Visual stimulation was achieved with an alternating black/white checkerboard operating at a frequency of 8 Hz. Maps of the absolute cerebral blood flow changes (ACBF) were calculated from the image intensities of the corresponding BA and SE images. The individual mean values of ACBF measured in five healthy volunteers ranged from 69 ± 18 to 99 ± 26 ml/min/100 g. Since the BASE technique does not require nonselective spin inversion, it can be used with small transmit/receive head coils (e.g., surface coils). In addition, the BASE technique is robust against a mismatch of the inversion and detection slice profile

ISSN:0740-3194    

DOI:10.1002/mrm.1910390508

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

年代:1998

数据来源: WILEY

摘要:

AbstractThe quantification of invivoMR spectra imposes severe problems because of low spectral resolution and poor signal‐to‐noise ratio. Maximum likelihood methods are often applied. However, with conventional spectrum analysis procedures, the search for a global minimum in a multidimensional space often terminates in only a local minimum. Heuristic optimization procedures are able to circumvent this difficulty. Two approaches, the genetic algorithm and the simulated annealing, have been adapted to the quantification of MR spectra. For evaluation purposes, the procedures have been applied to synthetic andin vivospectra with different noise levels. They both allowed a reliable spectrum quantification. The areas of most peaks were quantified reproducibly, although in some cases, the discrimination between spectroscopically almost identical metabolites (e.g., glutamate and glutamine) was not completely satisfactory. The two algorithms are found to be valuable alternative methods in the quantification ofin vivoMR spec

ISSN:0740-3194    

DOI:10.1002/mrm.1910390509

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

年代:1998

数据来源: WILEY

摘要:

AbstractThe purpose of this study was to measure the spatially varying31P MR signals in global and regional ischemic injury in the isolated, perfused rat heart. Chronic myocardial infarcts were induced by occluding the left anterior descending coronary artery eight weeks before the MR examination. The effects of acute global low‐flow ischemia were observed by reducing the perfusate flow. Chemical shift imaging (CSI) with three spatial dimensions was used to obtain31P spectra in 54‐/μl voxels. Multislice1H imaging with magnetization transfer contrast enhancement provided anatomical information. In normal hearts (n =8), a homogeneous distribution of high‐energy phosphate metabolites (HEP) was found. In chronic myocardial infarction (n =6), scar tissue contained negligible amounts of HEP, but their distribution in residual myocardium was uniform. The size of the infarcted area could be measured from the metabolic images; the correlation of infarct sizes determined by histology and31P MR CSI was excellent (P<0.006). In global low‐flow ischemia (n= 8), changes of HEP showed substantial regional heterogeneity. Three‐dimensional31P MR CSI should yield new insights into the regionally distinct metabolic consequences of various forms of myocard

ISSN:0740-3194    

DOI:10.1002/mrm.1910390510

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

年代:1998

数据来源: WILEY

摘要:

AbstractTumorous and contralateral rat brain was examined byin vivosingle voxel proton NMR spectroscopy. Magnetization transfer (MT) experiments cause attenuation of various metabolite signals. Selective saturation of immobile metabolites was achieved by pulsed RF preirradiation. The method is compared with continuous wave MT generation. In contralateral tissue, MT attenuation is detected for both the CH3and the CH2protons of (phospho‐)creatine (Cr + PCr) and for a signal at 3.44 ppm ascribed to taurine. Significant attenuation is also observed for a signal at 3.78 ppm that is commonly ascribed to the αCH proton of glutamate and glutamine (Glx); however, no effect is observed for the γCH2protons of Glx. Within implanted F98 glioma tumors, only the CH3signal of Cr + PCr shows significant MT attenuation. Although the MT effect detected for lactate in the tumors fails to reach significance, a significant effect is observed for the lactate signal acquired during 3 to 9 min postmor

ISSN:0740-3194    

DOI:10.1002/mrm.1910390511

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

年代:1998

数据来源: WILEY