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 m and a slice thickness of 2 mm. The T 1 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 ⅐ 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 ⅐ 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 ⅐ 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. Over the past decade, the mouse animal model has become an essential part of medical basic research. This is due to the high degree of similarity between the mouse and the human genomes of about 97% (1) and the resulting high relevance of mouse animal studies for human basic research. Regarding cardiovascular research, magnetic resonance imaging (MRI) provides noninvasive and accurate assessment of cardiac structure and function (2). Since the viability and the capability of the myocardium are strongly influenced by its microcirculation, a full characterization of the myocardium requires a quantification of parameters such as the perfusion and the intracapillary or regional blood volume (RBV). In particular, perfusion is of paramount importance as a physiologic parameter, since it strongly determines the function of organs and the severity of many diseases.Heart diseases involving ventricular dysfunction and hypertrophy show significant alterations of the myocardial perfusion and transgenic mouse models may be well suited to elucidate the underlying fundamental mechanisms.For the assessment of cardiac perfusion in mice, only a few methods have been presented to date. One possible approach is the quantification of the coronary flow in the isolated mouse heart by ultrasonic flow probes (3). The injection of labeled microsphe...

Myocardial motion of healthy mice and mice with myocardial infarction was assessed in vivo by phase contrast (PC) cine MRI. The imaging module was a segmented fast low angle shot (FLASH) sequence with velocity compensation in all three gradient directions. To accomplish additional motion encoding, the spin phase was prepared using bipolar gradient pulses, which resulted in a linear dependence between the voxel velocity and spin phase. This method provided accurate quantification of the velocity magnitude and direction of the murine myocardium at a spatial resolution of 234 m and a temporal resolution of about 10 ms. The acquisition was EKG-gated and the mice were anesthetized by inhalation of 1.5-4.0 vol.% isoflurane at 1.5 l/min oxygen flow. To validate the MRI measurements, an experiment with a calibrated rotating phantom was performed. Deviations between MR velocity measurements and optical assessment by a light detector were lower than 1.6%. During our study, myocardial motion velocities between 0.4 cm/s and 1.7 cm/s were determined for the healthy murine myocardium across the heart cycle. Areas with myocardial infarction were clearly segmented and showed a motion velocity which was significantly reduced. In conclusion, the method is an accurate technique for the assessment of murine myocardial motion in vivo. MRI is a powerful tool for the in vivo examination of mice. Due to its high temporal and spatial resolution, MRI is well suited for the assessment of cardiac function (1).The mouse model has gained increased importance due to the potential of specific gene manipulations. Animals with gene overexpression, mutation, or knockout can easily be produced and the examination of the consequences of these modifications adds to the understanding of the function of certain gene products.In particular, the characterization of myocardial contractility is of major interest in cardiology research, since this parameter is a direct measure of the function and viability of the myocardium. MRI allows noninvasive assessment of quantities such as wall thickening, myocardial velocity, strain, and strain rate as indicators of contractility. Disease states like myocardial infarction result in impaired motion of the effected areas. Conventional cine MRI (2,3) allows visual estimation of the bulk motion of the myocardium, but does not yield exact quantitative information about regional wall motion except for wall thickening.One possible approach to obtain quantitative information about myocardial motion is myocardial tagging in combination with cine MRI (4,5). The basic principle of this method is the tracking of RF pulse-induced modulations of the magnetization in the myocardium over the heart cycle.One major intrinsic drawback of this approach is the low spatial resolution of motion information with respect to image resolution. The distance between adjacent tags has to be sufficiently large to ensure proper distinction between the tags in the image. This is particularly disadvantageous in the mouse heart, with its small dimen...

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 noninvasively 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 Ϯ 10 mL (100 g ⅐ minute) -1 (mean Ϯ standard error of the mean [SEM], N ϭ 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 ⅐ minute) -1 of the vasodilator adenosine by an intraperitoneal catheter. In this case, perfusion was significantly increased to 179 Ϯ 56 mL (100 g ⅐ minute) -1 (mean Ϯ SEM, N ϭ 6, P Ͻ 0.02). Mean basal perfusion in this subgroup was 96 Ϯ 26 mL (100 g ⅐ minute) -1 . Conclusion:Spin labeling MRI is a well-suited technique for the in vivo assessment of absolute perfusion in the murine skeletal muscle.

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.