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Purpose: To evaluate reproducibility of total cerebral blood flow (CBF) measurements with phase contrast magnetic resonance imaging (pcMRI). Materials and Methods:We repeated total CBF measurements in 15 healthy volunteers with and without cardiac triggering, and with and without repositioning. In eight volunteers measurements were performed at two different occasions. In addition, measurement of flow in a phantom was performed to validate MR measurements. Results:A difference of 40.4 ml/minute was found between CBF measurements performed with and without triggering (P Ͻ 0.05). For repeated triggered measurements, the coefficient of variation (CV) was 7.1%, and for nontriggered measurements 10.3%. For repeated measurements with repositioning, the CV was 7.1% with and 11.2% without triggering. Repeated measurements at different occasions showed a CV of 8.8%. Comparing measured with real flow in the phantom, the triggered differed 4.9% and the nontriggered 8.3%. Conclusion:The findings of this study demonstrate that pcMRI is a reliable method to measure total CBF in terms of both accuracy and reproducibility. METHODS THAT CURRENTLY ARE USED to assess total cerebral blood flow (CBF) can be divided into two groups based on the underlying concepts. On the one hand, total CBF can be estimated based on information generated by flow in the capillaries; on the other hand, total CBF can be assessed by measuring flow in the supplying vessels of the brain. Methods that are based on measurements of flow in the capillaries are single positron emission computed tomography (SPECT), xenon-computed tomography (Xe-CT), and perfusion magnetic resonance imaging (MRI). Blood flow in the supplying vessels of the brain can be measured using Doppler ultrasound and phase contrast MRI (pcMRI). Advantages of both Doppler ultrasound and pcMRI are no need for using ionizing irradiation or administration of intravenous agents, and the possibility of repeated measurements on a short-term basis. However, limitations of Doppler ultrasound are its operator dependency and overestimation of total blood flow in a given vessel due to the fact that only the highest flow in the center of the vessel is assessed (1). Using pcMRI, total CBF can be assessed by simultaneously measuring flow in the internal carotid arteries and the basilar artery. As compared to Doppler ultrasound, pcMRI has the advantage of being operator independent and involving straightforward flow quantification. In addition, pcMRI can be added to morphologic MRI sequences, offering the option to correlate flow to morphology based on data generated during one examination.In vitro and in vivo studies have demonstrated that pcMRI provides reliable flow data (2-4). However, data on short-term and long-term reproducibility are scarce. Furthermore, there is an ongoing discussion whether total CBF should be measured using a cardiac-triggered or a nontriggered pcMRI technique (4 -6). Finally, using pc-MRI, considerable differences in total CBF have been found between healthy volunteers (7,8). ...

The relative contributions to gastric emptying from common cavity antroduodenal pressure difference ("pressure pump") vs. propagating high-pressure waves in the distal antrum ("peristaltic pump") were analyzed in humans by high-resolution manometry concurrently with time-resolved three-dimensional magnetic resonance imaging during intraduodenal nutrient infusion at 2 kcal/min. Gastric volume, space-time pressure, and contraction wave histories in the antropyloroduodenal region were measured in seven healthy subjects. The subjects fell into two distinct groups with an order of magnitude difference in levels of antral pressure activity. However, there was no significant difference in average rate of gastric emptying between the two groups. Antral pressure history was separated into "propagating high-pressure events" (HPE), "nonpropagating HPEs," and "quiescent periods." Quiescent periods dominated, and average pressure during quiescent periods remained unchanged with decreasing gastric volume, suggesting that common cavity pressure levels were maintained by increasing wall muscle tone with decreasing volume. When propagating HPEs moved to within 2-3 cm of the pylorus, pyloric resistance was found statistically to increase with decreasing distance between peristaltic waves and the pylorus. We conclude that transpyloric flow tends to be blocked when antral contraction waves are within a "zone of influence" proximal to the pylorus, suggesting physiological coordination between pyloric and antral contractile activity. We further conclude that gastric emptying of nutrient liquids is primarily through the "pressure pump" mechanism controlled by pyloric opening during periods of relative quiescence in antral contractile wave activity.

Purpose: To explore the potential of perfusion-corrected diffusion-weighted magnetic resonance imaging (MRI) in characterizing soft-tissue tumors. Materials and Methods:Diffusion-weighted MRI was performed in 23 histologically proven soft-tissue masses using a diffusion-weighted spin-echo sequence with diffusion gradient strengths yielding five b-values (0 -701 seconds/ mm 2 ). True diffusion coefficients and perfusion fractions were estimated and compared with apparent diffusion coefficients (ADCs).Results: ADC values of all tumors, subcutaneous fat, and muscle were significantly higher than true diffusion coefficients, indicating a contribution of perfusion to the ADC. True diffusion coefficients of malignant tumors (1.08 ϫ 10 -3 mm 2 /second) were significantly lower than those of benign masses (1.71 ϫ 10 -3 mm 2 /second), whereas ADC values between these groups were not significantly different. Conclusion:Perfusion-corrected diffusion-weighted MRI has potential in differentiating benign from malignant softtissue masses.

MR Z-spectroscopy allows enhanced imaging contrast on the basis of saturation transfer between the proton pools of cellular compounds and water, occurring via chemical exchange (chemical exchange saturation transfer, CEST) or dipole-dipole coupling (nuclear Overhauser effect, NOE). In previous studies, signals observed in the aliphatic proton region of Z-spectra have been assigned to NOEs between protons in water molecules and protons at the surface of proteins. We investigated a possible relationship between the signal strength of NOE peaks in Z-spectra obtained at B0 = 7 T and protein structure. Here, we report a correlation of NOE-mediated saturation transfer with the structural state of bovine serum albumin (BSA), which was monitored by fluorescence spectroscopy. Encouraged by CEST signal changes observed in tumor tissue, our observation also points to a possible contrast mechanism for MRI sensitive to the structural integrity of proteins in cells. Therefore, protein folding should be considered as an additional property affecting saturation transfer between water and proteins, in combination with the microenvironment and physiological quantities, such as metabolite concentration, temperature and pH.