The purpose of this work was to develop high-resolution cardiac magnetic resonance imaging techniques for the in vivo mouse model for quantification of myocardial function and mass. Eight male mice were investigated on a 7-Tesla MRI scanner. High-quality images in multiple short axis slices (in-plane resolution 117 microm2, slice thickness 1 mm) were acquired with an ECG-gated cine sequence. Left ventricular end-diastolic and end-systolic volumes and mass were calculated from segmented slice volumes. There was precise agreement of left ventricular mass determined ex vivo and by MRI. Intraobserver (5%) and interobserver (5%) variability of in vivo MR measurements were low.

Cardiovascular transgenic mouse models with an early phenotype or even premature death require noninvasive imaging methods that allow for accurate visualization of cardiac morphology and function. Thus the purpose of our study was to assess the feasibility of magnetic resonance imaging (MRI) to characterize cardiac function and mass in newborn, juvenile, and adult mice. Forty-five C57bl/6 mice from seven age groups (3 days to 4 mo after birth) were studied by MRI under isoflurane anesthesia. Electrocardiogram-gated cine MRI was performed with an in-plane resolution of (78-117 microm)(2). Temporal resolution per cine frame was 8.6 ms. MRI revealed cardiac anatomy in mice from all age groups with high temporal and spatial resolution. There was close correlation between MRI- and autopsy-determined left ventricular (LV) mass (r = 0.95, SE of estimate = 9.5 mg). The increase of LV mass (range 9.6-101.3 mg), cardiac output (range 1.1-14.3 ml/min), and stroke volume (range 3. 2-40.2 microl) with age could be quantified by MRI measurements. Ejection fraction and cardiac index did not change with aging. However, LV mass index decreased with increasing age (P < 0.01). High-resolution MRI allows for accurate in vivo assessment of cardiac function in neonatal, juvenile, and adult mice. This method should be useful when applied in transgenic mouse models.

Objective: Skin-sodium storage, as a physiologically important regulatory mechanism for blood pressure, volume regulation, and indeed survival, has recently been rediscovered. This prompted the development of MRI methods to assess sodium storage in humans ( 23 Na-MRI) at 3.0 Tesla. This work examines the feasibility of high in-plane spatial resolution 23 Na MRI in skin at 7.0 T. Methods:A two-channel transceiver RF coil array tailored for skin MRI at 7.0 T (f=78.5MHz) is proposed. Specific absorption rate (SAR) simulations and a thorough assessment of RF power deposition were performed to meet the safety requirements. Human skin was examined in an in vivo feasibility study using 2D gradient echo imaging. Normal male adult volunteers (n=17, mean ± SD = 46 ± 18 years, range: 20-79 years) were investigated.Transverse slices of the calf were imaged with 23 Na MRI using a high in-plane resolution of (0.9 x 0.9) mm 2 . Skin Na + content was determined using external agarose standards covering a physiological-range of Na + concentrations. To assess the intra-subject reproducibility, each volunteer was examined three to five times with each session including a 5 min walk and repositioning/preparation of the subject. Age-dependence of skin Na + content was investigated. Results:The 23 Na RF coil provides improved sensitivity within a range of 1 cm from its surface versus a volume RF coil which facilitates high in-plane spatial resolution imaging of human skin. Intra-subject variability of human skin sodium content in the volunteer population was <10.3%. An age-dependent increase in skin Na + content was observed, r = 0.78). Short abstractThis work demonstrates the feasibility of sub-millimeter in-plane spatial resolution 23 Na MRI in skin at clinically acceptable acquisition times at 7.0 T. Intra-subject variability of human skin sodium content in the volunteer population was <10.3%. An age-dependent increase in skin Na + content was observed (r = 0.78). Assigning sodium stores with 23 Na-MRI techniques could be improved at 7.0 T compared to current 3.0 T technology.-6 -

The purpose of the present study was the serial investigation of morphological and functional changes after left coronary artery ligation in the intact rat using cine-magnetic resonance imaging (MRI). MRI studies were performed 4, 8, 12, and 16 weeks after myocardial infarction (MI) with an echocardiogram (ECG)-triggered cine-fast lowangle shot (FLASH)-sequence in a 7-Tesla magnet. MI-size, left ventricular (LV) mass and volumes, cardiac index, ejection fraction (EF), and remote wall and scar thickness of 11 Wistar rats were compared to four sham-operated rats. Stress MRI with dobutamine (10 l/kg ؋ minute) was performed at 16 weeks. In MI groups (small MI < 30%, N ‫؍‬ 5, large MI > 30%, N ‫؍‬ 6), there was significant increase of LV mass (small MI ؉ 47.8% increase, large MI ؉ 74.1%) and wall thickness (large MI 1.21 ؎ 0.03 to 1.84 ؎ 0.07 mm). Scar thickness declined from four to 16 weeks (large MI 0.92 ؎ 0.06 to 0.38 ؎ 0.02mm, P < 0.05). End-diastolic volume of both MI groups was significantly elevated but increased further only in animals with large MI from four to 16 weeks (657.1 ؎ 38.6 to 869.7 ؎ 60.7 L, P < 0.05). Compared to sham, EF was significantly depressed in MI (large MI 31.5 ؎ 2.0%). Wall thickening declined from four to 16 weeks post-MI (large MI 50.9 ؎ 9.9 to 28.9 ؎ 4.4%, P < 0.05). During stress, sham and MI rats increased wall thickening from 66.5 ؎ 8.2 to 111.2 ؎ 6.7% and from 30.8 ؎ 4.3 to 47.5 ؎ 5.8%, respectively (P < 0.05). Hypertrophy was found in all animals with MI throughout the entire period of observation, whereas dilatation after four weeks was only detected in animals with large MI. These Index terms: MRI; heart; myocardial infarction; rat; remodeling CORONARY ARTERY DISEASE with subsequent myocardial infarction (MI) is the most frequent cause for the development of chronic heart failure (1). The morphological and functional features of left ventricular (LV) remodeling have been studied both in animal models (2,3) and in humans (4 -6). The rat model of MI with consecutive LV dilatation has proved to be particularly valuable for the investigation of the development of heart failure and its prevention (7,8). However, the progressive, complex changes of LV geometry of the model have yet to be followed by exact sequential magnetic resonance imaging (MRI) measurements. In addition, the initial size of the MI is unknown in studies that rely on post-mortem measurements, due to MI expansion and remodeling of surviving myocardium. Thus, the exact underlying mechanisms and the precise time course of LV remodeling are still not fully understood. The noninvasive and exact nature of MRI make it a valuable tool for cardiac studies (9 -16). Cine-fast lowangle shot (FLASH)-MRI has been shown to provide good spatial and temporal resolution for the validation of an infarction model of the rat heart (17). This study aimed to better understand the remodeling process following MI by evaluating LV mass, wall thickness, volumes, and function over a specified time course. METHODS Experimental ProtocolSixtee...

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