Introduction The measurement of the pulse-wave-velocity (PWV) is an important tool for the estimation of arterial stiffness and enables the early diagnosis of cardiovascular risks. In recent studies prospectively triggered MRI methods have been developed to quantify the PWV in the mouse model [1]. Measurements in the murine aorta are usually conducted at a high magnetic field B0 to provide higher SNR, which can cause problems with conventional triggering using ECG. For example, interferences with gradient eddy currents can reduce the quality of the trigger signal. In this work we present a retrospectively triggered measurement of the local PWV, which uses the centric k-space signal of a radial trajectory for navigation and is therefore independent of external triggering probes. The results are compared with a prospectively triggered radial PWV measurement.

Fig. 2: Correlation plot of individual PWV values obtained with the multisite TT-method and the QA-method for the control group (a) and the ApoE-/group (b). Comparison of local against regional elastic properties of the vessel wall in a murine atherosclerosis model by PWV measurements Alexander Gotschy, Volker Herold, Elisabeth Bauer, Gunthard Lykowsky, Christian Schrodt, Eberhard Rommel, Peter M. Jakob, and Wolfgang R. Bauer Department of Experimental Physics 5, University of Würzburg, Würzburg, Germany, Department of Internal Medicine I, University of Würzburg, Würzburg, Germany, Research Center Magnetic Resonance Bavaria (MRB), Würzburg, Germany

Introduction: Mouse models are increasingly used to investigate functional cardiovascular parameters. Pulse-wave velocity (PWV) is an important parameter for the evaluation of the arterial stiffness and cardiovascular risk. Several diseases such as hypertension and arteriosclerosis are associated with vascular remodeling and arterial stiffening. MRI methods have been used to quantify PWV in the murine aorta [1,2]. In this work we demonstrate the ability of high field MRI to quantify PWV in the right common carotid artery.

Introduction: Mouse models are increasingly used to investigate functional and cardiovascular parameters. Measurements of blood flow patterns, vessel wall strain and pulse wave velocity have been used for the evaluation of the arterial function and cardiovascular risk [1]. However noninvasive methods for measuring hemodynamic parameters such as blood pressure are not yet available. In this work we present an approach to noninvasively estimate the arterial pulse pressure by measuring the time dependant blood flow pulse and the local pulse wave velocity.

Mouse models are increasingly used to investigate functional and cardiovascular parameters. Pulse wave velocity (PWV) is an important parameter for the evaluation of the arterial and cardiovascular risk. Several diseases such as hypertension and arteriosclerosis are associated with vascular abnormalities and arterial stiffening. In this work we present two different methods to noninvasively examine the PWV at different sites in the murine aorta: a regional multipoint transit-time (TT) method and a local flow-area (QA) approach. Both methods were validated with a deformable vessel wall phantom.

Purpose 19-Fluorine (F) containing liposomes have recently been shown to accumulate in ischemia [1], tumor and abscess [2] models. These models suffer from confounding factors such as uncontrolled hemostasis, vascular damage and excessive necrosis. Non-ischemic sterile inflammation mouse models serve as well defined models of inflammatory processes [3], but have not yet been investigated using H/F-MRI. This study evaluates the capability of F-containing liposomes for imaging and quantifying inflammatory processes. Furthermore the uptake into activated atherosclerotic plaque macrophages of apoE mice is investigated

This work presents a method that allows for the assessment of 3D murine myocardial motion in vivo at microscopic resolution. Phase-contrast (PC) magnetic resonance imaging (MRI) at 17.6 T was applied to map myocardial motion in healthy mice along three gradient directions. High-resolution velocity maps were acquired at three different levels in the murine myocardium with an in-plane resolution of 98 mu m, a slice thickness of 0.6 mm, and a temporal resolution of 6 ms. The applied PC-MRI method was validated with phantom experiments that confirmed the correctness of the method with deviations of < 1.7%. Myocardial in-plane velocities between 0.5 cm/s and 2.2 cm/s were determined for the healthy murine myocardium. Through-plane velocities of 0.1-0.83 cm/s were measured. Velocity data was also used to calculate the myocardial twist angle during systole at different slices in the short-axis view.

The absolute perfusion and the intracapillary or regional blood volume (RBV) in murine myocardium were assessed in vivo by spin labeling magnetic resonance imaging. Pixel‐based perfusion and RBV maps were calculated at a pixel resolution of 469 × 469 μm and a slice thickness of 2 mm. The T1 imaging module was a segmented inversion recovery snapshot fast low angle shot sequence with velocity compensation in all three gradient directions. The group average myocardial perfusion at baseline was determined to be 701 ± 53 mL (100 g · min)−1 for anesthesia with isoflurane (N = 11) at a mean heart rate (HR) of 455 ± 10 beats per minute (bpm). This value is in good agreement with perfusion values determined by invasive microspheres examinations. For i.v. administration of the anesthetic Propofol, the baseline perfusion decreased to 383 ± 40 mL (100 g · min)−1 (N = 17, P < 0.05 versus. isoflurane) at a mean heart rate of 261 ± 13 bpm (P < 0.05 versus isoflurane). In addition, six mice with myocardial infarction were studied under isoflurane anesthesia (HR 397 ± 7 bpm). The perfusion maps showed a clear decrease of the perfusion in the infarcted area. The perfusion in the remote myocardium decreased significantly to 476 ± 81 mL (100 g · min)−1 (P < 0.05 versus sham). Regarding the regional blood volume, a mean value of 11.8 ± 0.8 vol % was determined for healthy murine myocardium under anesthesia with Propofol (N = 4, HR 233 ± 17 bpm). In total, the presented techniques provide noninvasive in vivo assessment of the perfusion and the regional blood volume in the murine myocardium for the first time and seem to be promising tools for the characterization of mouse models in cardiovascular research. Magn Reson Med 53:584–592, 2005. © 2005 Wiley‐Liss, Inc.

A radio frequency (rf) coil combination of a birdcage resonator and a receive-only surface coil was developed for in vivo magnetic resonance imaging of mice at 7.0 T. Since this coil was designed for spin labeling perfusion measurements, the length of the birdcage resonator needed to be 110 mm at a diameter of 35 mm. This was challenging since this length extended 1/10 of the wavelength at the spectrometer Larmor frequency of 300.3 MHz. Symmetric drive with homogeneous B1 field was achieved by introduction of a new rf coupling scheme using an additional conductor path ring at zero potential. This design allowed a balanced drive of the coil without the use of an additional balun. The receive-only surface coil was realized as a single loop with a diameter of 24 mm. To avoid coupling between the coils, active decoupling using p-i-n diode switches was integrated. These switches showed good characteristics and the coil combination was not sensitive to effects such as contrast alterations, rf shielding of the transmit pulse by the receive coil, and possible receive coil destruction during transmission. The improved performance of the coil combination with respect to a stand-alone surface coil or a stand-alone birdcage resonator was demonstrated in phantoms and mice. In comparison with a stand-alone suface coil, the coil combination provided more uniform contrast behavior and an extended depth of view. In addition, the combination showed an improved signal-to-noise ratio with respect to a stand-alone birdcage resonator.

Purpose: To assess absolute perfusion in the skeletal muscle of mice in vivo with spin labeling magnetic resonance imaging (MRI) under normal and stress conditions.Materials and Methods: Absolute perfusion in the skeletal muscle of 27 C57BL/6 mice was assessed in vivo non-invasively by spin labeling MRI at 7.05 T. This technique was based on the acquisition of T1 maps with global and; slice-selective spin inversion in separate acquisitions. T1 mapping was performed by inversion recovery, snapshot fast low angle shot imaging. To guarantee proper spin inversion within the whole mouse, a dedicated radiofrequency (RF) coil combination was constructed. A birdcage resonator was used for transmission,. while detection of the MRI signal was achieved by a surface coil.Results: Basal perfusion in. the hindlimbs was determined to be 94 +/- 10 mL, (100 g.minute)(-1), (mean +/- standard error of the mean [SEM], N = 27). This value is in good agreement with perfusion values determined by invasive-techniques such as microspheres. A subgroup of six animals received a constant dose of 4 mg (kg.minute)(-1) of the vasodilator adenosine by an intraperitoneal catheter. In this case, perfusion was significantly increased to 179 +/- 56 mL (100 g.minute)(-1) (mean +/- SEM, N = 6, P < 0.02). Mean basal perfusion in this subgroup was 96 +/- 26 mL, (100 g.niinute)(-1).Conclusion: Spin labeling MRI is a well-suited technique for the in vivo assessment of absolute perfusion in the murine skeletal muscle.

Because of its complex geometry, assessment of right ventricular (RV) function is more difficult than it is for the left ventricle (LV). Because gene-targeted mouse models of cardiomyopathy may involve remodeling of the right heart, the purpose of this study was to develop high-resolution functional magnetic resonance imaging (MRI) for in vivo quantification of RV volumes and global function in mice. Thirty-three mice of various age were studied under isoflurane anesthesia by electrocardiogram-triggered cine-MRI at 7 T. MRI revealed close correlations between RV and LV stroke volume and cardiac output ( r = 0.97, P < 0.0001 each). Consistent with human physiology, murine RV end-diastolic and end-systolic volumes were significantly higher compared with LV volumes ( P < 0.05 each). MRI in mice with LV heart failure due to myocardial infarction revealed significant structural and functional changes of the RV, indicating RV dysfunction. Hence, MRI allows for the quantification of RV volumes and global systolic function with high accuracy and bears the potential to evaluate mechanisms of RV remodeling in mouse models of heart failure.

The NMR probehead is a key element of the receiving chain of an NMR spectrometer. To optimize the signal-to-noise ratio the probehead must be adapted for the specific application. This article describes the basic physics and characteristics of NMR probeheads for in vivo applications in small animals and plants as well as quality control procedures on the workbench and in the NMR spectrometer. Various probeheads including volume coils, surface coils, double tuned coils, and microscopy coils are presented and illustrated by results of specific in vivo applications. (C) 2000 John Wiley & Sons. Inc.

A portable nuclear magnetic resonance (NMR) imaging system has been designed for noninvasive investigations of immobile objects, e.g., living plants in their natural environment, a human finger or similar objects not exceeding a diameter of 12 mm. The NMR spectrometer is equipped with a permanent magnet, flat biplanar gradient coils, and a battery powered amplifier network with a phase-encoding unit, capable of imaging experiments on volumes of (1 cm)3 with a spatial resolution of 63 μm. The total weight of the instrument is approximately 90 kg. First applications of this system include spin-echo images of phantoms and living plants in a greenhouse.

Many 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).

Many NMR measurements of cardiac microcirculation (perfusion, intramyocardial blood volume) depend on some kind of assumption of intracapillary-extravascular water exchange rate, e.g., fast exchange, The magnitude of this water exchange rate, however, is still unknown, The intention of this study was to determine a lower limit for this exchange rate by investigating the effect of perfusion on relaxation time, Studies were performed in the isolated perfused cardioplegic rat heart, After slice-selective inversion, the spin lattice relaxation rate of myocardium within the slice was studied as a function of perfusion and compared with a mathematical model which predicts relaxation rate as a function of perfusion and intracapillary-extravascular exchange rate, A linear relationship was found between relaxation rate T-(1) and perfusion P normalized by perfusate/tissue partition coefficient of water, lambda: Delta T-1 = m . Delta P/lambda with 0.82 less than or equal to m less than or equal to 1.06, Insertion of experimental data in the model revealed that a lower bound of the exchange rate from intra-to extravascular space is 6.6 s(-1) (4.5 s(-1), P < 0.05), i.e., the intracapillary lifetime of a water molecule is less than 150 ms (222 ms, P < 0.05), Based on this finding, the T-1 mapping after slice-selective inversion could become a valuable noncontrast NMR method to measure variations of perfusion.

The effect of perfusion on relaxation time in tissue has only been considered for first‐pass kinetics of NMR‐signal after application of contrast agents. The importance of perfusion on relaxation has not yet been studied for steady state conditions, i.e., when the intravascular relaxation rate is constant in time. The aim of this study is to develop a model in which T, relaxation is derived as a function of perfusion and intracap‐illary volume fraction ( regional blood volume ). Tissue is considered to be two‐compartment system, which consists of intracapillary and extravascular space. Intracapillary relaxation differs from relaxation in the arterial system due to diffusion‐exchange of magnetization from extravascular to intracapillary space. Perfusion tends to attenuate this difference and thus counteracts the effect on intracapillary relaxation. Relaxation in the extravascular space becomes a function of perfusion because extravascular and intracapillary magnetization are linked by diffusion. This dependence is presented in analytical form and a generic equation is derived. A T 1 experiment is considered in which all spins of tissue and blood are inverted at the beginning. Calculations are performed for the fast exchange model of tissue. Perfusion increases relaxation enhancement of intravascular contrast agents. This effect is considerable in highly perfused tissue like myocardium. The dependence of relaxation on perfusion implies an overestimation of the regional blood volume when the calculation of the latter is based on tissue models that neglect perfusion. The model presented here is applied to predict the effect of perfusion on T 1 imaging with FLASH‐pulse sequences because this technique has been proven to be a powerful method to obtain T 1 maps within a short time interval. For the fast exchange model, two algorithms are suggested that determine perfusion and regional blood volume from T 1 imaging in the presence and absence of intravascular contrast agents.

In single crystals the NQR nutation frequency depends on the relative orientation of the coil and the quadrupole axes. In powders the nutation lineshape is a superposition of spectra from the randomly oriented single crystals, so that powder patterns appear in such experiments if the reconstruction is performed by the Fourier transform method. In this paper an alternative reconstruction method of nutation spectra is suggested making use of the Hankel Transform. In this way the nutation spectra are simplified. Singularities arising with experiments for the determination of the asymmetry parameter eta can easily be resolved. In the particular case of an axially symmetric quadrupolar tensor and a homogeneous radiofrequency field one can reduce the powder pattern to a single line without heterogeneous broadening with respect to orientation. Further improvement of the nutation spectra can be achieved by taking advantage of the maximum entropy method, which strongly reduces apodisation and noise problems. Applications of the new data manipulation techniques to NQR imaging methods published elsewhere and 2D zero-field NQR spectroscopy are reported.