Experimental myocardial infarction (MI) in mice is an important disease model, in part due to the ability to study genetic manipulations. MRI has been used to assess cardiac structural and functional changes after MI in mice, but changes in myocardial perfusion after acute MI have not previously been examined. Arterial spin labeling noninvasively measures perfusion but is sensitive to respiratory motion and heart rate variability and is difficult to apply after acute MI in mice. To account for these factors, a cardiorespiratory-gated arterial spin labeling sequence using a fuzzy C-means algorithm to retrospectively reconstruct images was developed. Using this method, myocardial perfusion was measured in remote and infarcted regions at 1, 7, 14, and 28 days post-MI. Baseline perfusion was 4.9 6 0.5 mL/gÁmin and 1 day post-MI decreased to 0.9 6 0.8 mL/gÁmin in infarcted myocardium (P < 0.05 versus baseline) while remaining at 5.2 6 0.8 mL/gÁmin in remote myocardium. During the subsequent 28 days, perfusion in the remote zone remained unchanged, while a partial recovery of perfusion in the infarct zone was seen. This technique, when applied to genetically engineered mice, will allow for the investigation of the roles of specific genes in myocardial perfusion during infarct healing. Magn Reson Med 63:648-657, 2010. V C 2010 Wiley-Liss, Inc.Key words: arterial spin labeling; myocardial perfusion; myocardial infarction; fuzzy C-means; mouse Mice are widely used as models of human disease in biomedical research. Similarities in the cardiovascular systems of mice and humans, the low cost of mouse studies, the relative ease of genetic manipulation of mice, and improved surgical techniques have led to increased use of mouse models of myocardial infarction (MI) (1-3). Cardiac MRI has been used to study structural and functional left ventricular (LV) remodeling in mice following MI (3-5). However, measurement of myocardial perfusion in mice by MRI during acute MI and subsequently during the processes of infarct healing and post-MI LV remodeling has not previously been performed.Arterial spin labeling (ASL) provides quantitative measurements of blood flow and has been used for quantification of cerebral blood flow (6,7) and myocardial perfusion (8-11) in humans. In small animals, ASL has been performed in both mice (12-15) and rats (16)(17)(18)(19)(20)(21)(22)(23)(24)(25). Prior murine studies have examined myocardial perfusion at baseline (12-15), with differing anesthesia (13), in response to a vasodilator (13,15), and for phenotyping of genetically altered mice (14,15). Only two prior studies have measured perfusion after MI in mice, and those measurements were restricted only to the remote myocardium at 4 weeks following MI (12,14). ASL has been more widely used in rats (22) and has been used to assess changes in myocardial perfusion in response to dobutamine (17), adenosine (25), methods of anesthesia (23,24), diabetes (18,19) and following coronary stenosis (20,21) and MI (20,21). Similar to mouse studies, measurements...

ObjectiveA number of promising experimental therapies for Duchenne muscular dystrophy (DMD) are emerging. Clinical trials currently rely on invasive biopsies or motivation-dependent functional tests to assess outcome. Quantitative muscle magnetic resonance imaging (MRI) could offer a valuable alternative and permit inclusion of non-ambulant DMD subjects. The aims of our study were to explore the responsiveness of upper-limb MRI muscle-fat measurement as a non-invasive objective endpoint for clinical trials in non-ambulant DMD, and to investigate the relationship of these MRI measures to those of muscle force and function.Methods15 non-ambulant DMD boys (mean age 13.3 y) and 10 age-gender matched healthy controls (mean age 14.6 y) were recruited. 3-Tesla MRI fat-water quantification was used to measure forearm muscle fat transformation in non-ambulant DMD boys compared with healthy controls. DMD boys were assessed at 4 time-points over 12 months, using 3-point Dixon MRI to measure muscle fat-fraction (f.f.). Images from ten forearm muscles were segmented and mean f.f. and cross-sectional area recorded. DMD subjects also underwent comprehensive upper limb function and force evaluation.ResultsOverall mean baseline forearm f.f. was higher in DMD than in healthy controls (p<0.001). A progressive f.f. increase was observed in DMD over 12 months, reaching significance from 6 months (p<0.001, n = 7), accompanied by a significant loss in pinch strength at 6 months (p<0.001, n = 9) and a loss of upper limb function and grip force observed over 12 months (p<0.001, n = 8).ConclusionsThese results support the use of MRI muscle f.f. as a biomarker to monitor disease progression in the upper limb in non-ambulant DMD, with sensitivity adequate to detect group-level change over time intervals practical for use in clinical trials. Clinical validity is supported by the association of the progressive fat transformation of muscle with loss of muscle force and function.

Muscle damage, edema, and fat infiltration are hallmarks of a range of neuromuscular diseases. The T 2 of water, T 2,w , in muscle lengthens with both myocellular damage and inflammation and is typically measured using multiple spin-echo or Carr-Purcell-Meiboom-Gill acquisitions. However, microscopic fat infiltration in neuromuscular diseases prevents accurate T 2,w quantitation as the longer T 2 of fat, T 2,f , masks underlying changes in the water component. Fat saturation can be inconsistent across the imaging volume and removes valuable physiological fat information. A new method is presented that combines iterative decomposition of water and fat with echo asymmetry and least squares estimation with a Carr-Purcell-Meiboom-Gill-sequence. The sequence results in water and fat separated images at each echo time for use in T 2,w and T 2,f quantification. With knowledge of the T 2,w and T 2,f , a T 2 -corrected fat fraction map can also be calculated. Monte-Carlo simulations and measurements in phantoms, volunteers, and a patient with inclusion body myositis are demonstrated. In healthy volunteers, uniform T 2,w and T 2 -corrected fat fraction maps are present within all muscle groups. However, muscle-specific patterns of fat infiltration and edema are evident in inclusion body myositis, which demonstrates the power of separating and quantifying the fat and water components. Magn Reson Med 66:1293-1302, 2011. V C 2011 Wiley Periodicals, Inc.Key words: water-fat separation; T 2 relaxometry; muscular dystrophy; edema Neuromuscular diseases commonly involve a range of skeletal muscle pathologies including inflammation, muscle wasting, and fat infiltration (1,2). As the molecular and genetic basis of many of these diseases becomes increasingly understood, there is a need for reliable methods to sensitively monitor disease progression and response to new treatments. For example, gene therapies have shown promise in the potential treatment of the disabling and eventually fatal condition Duchenne muscular dystrophy (3,4).MRI is emerging as a suitable method to monitor neuromuscular disease due to its sensitivity to key processes in the diseased muscle such as edema and fat infiltration (5,6). In contrast to muscle biopsy, which currently provides an established indicator of disease, MRI offers a repeatable, noninvasive, whole-organ approach for use in longitudinal clinical trials. Furthermore, MRI can quantify physical properties such as T 2 relaxation times and fat fractions within affected muscles.The T 2 of skeletal muscle increases with both damage and edema (7-9). Together, these ''edema-like'' regions appear bright on T 2 weighted imaging. In mouse models of limb girdle muscular dystrophy, T 2 values are elevated relative to controls, although following gene therapy T 2 values return to near-control levels (10). T 2 measurements in mouse models are simplified by the lack of fat infiltration that hallmarks these diseases in human patients. In humans, invasive replacement of muscle fibers in dystrophic muscle by fa...

Purpose To explore the use of iterative decomposition of water and fat with echo asymmetry and least-squares estimation Carr-Purcell-Meiboom-Gill (IDEAL-CPMG) to simultaneously measure skeletal muscle apparent fat fraction (AFF) and water T2 (T2,w) in patients with Duchenne muscular dystrophy (DMD). Materials and Methods In twenty healthy volunteer (HV) boys and thirteen subjects with DMD, thigh muscle AFF was measured by Dixon and IDEAL-CPMG, with the IDEAL-CPMG also providing T2,w as a measure of muscle inflammatory activity. A subset of subjects with DMD was followed up during a 48-week clinical study. The study was in compliance with the Patient Privacy Act and approved by the Institutional Review Board. Results AFF in the thigh muscles of subjects with DMD was significantly increased compared to HV boys (p < 0.001). Dixon and IDEAL-CPMG AFF strongly correlated (r = 0.92) and were in good agreement. Muscle T2,w measured by IDEAL-CPMG was independent of changes in AFF. Muscle T2,w was higher in the biceps femoris and vastus lateralis muscles of subjects with DMD (p < 0.05). There was a strong correlation (p < 0.004) between AFF in all thigh muscles and six-minute walk distance (6MWD) in subjects with DMD. Conclusions IDEAL-CPMG allowed independent and simultaneous quantification of skeletal muscle fatty degeneration and disease activity in DMD. IDEAL-CPMG AFF and T2,w may be useful as biomarkers in clinical trials of DMD as the technique disentangles two competing biological processes.

Atherosclerosis is a complex disease whose spatial distribution is hypothesized to be influenced by the local hemodynamic environment. The use of transgenic mice provides a mechanism to study the relationship between hemodynamic forces, most notably wall shear stress (WSS), and the molecular factors that influence the disease process. Phase contrast MRI using rectilinear trajectories has been used to measure boundary conditions for use in computational fluid dynamic models. However, the unique flow environment of the mouse precludes use of standard imaging techniques in complex, curved flow regions such as the aortic arch. In this article, two‐dimensional and three‐dimensional spiral cine phase contrast sequences are presented that enable measurement of velocity profiles in curved regions of the mouse vasculature. WSS is calculated directly from the spatial velocity gradient, enabling WSS calculation with a minimal set of assumptions. In contrast to the outer radius of the aortic arch, the inner radius has a lower time‐averaged longitudinal WSS (7.06 ± 0.76 dyne/cm2 vs. 18.86 ± 1.27 dyne/cm2; P < 0.01) and higher oscillatory shear index (0.14 ± 0.01 vs. 0.08 ± 0.01; P < 0.01). This finding is in agreement with humans, where WSS is lower and more oscillatory along the inner radius, an atheroprone region, than the outer radius, an atheroprotective region. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.

Background Manganese-enhanced MRI (MEMRI) has the potential to identify viable myocardium and quantify calcium influx and handling. Two distinct manganese contrast media have been developed for clinical application, mangafodipir and EVP1001-1, employing different strategies to mitigate against adverse effects resulting from calcium-channel agonism. Mangafodipir delivers manganese ions as a chelate, and EVP1001-1 coadministers calcium gluconate. Using myocardial T1 mapping, we aimed to explore chelated and nonchelated manganese contrast agents, their mechanism of myocardial uptake, and their application to infarcted hearts. Methods T1 mapping was performed in healthy adult male Sprague-Dawley rats using a 7T MRI scanner before and after nonchelated (EVP1001-1 or MnCl2 (22 μmol/kg)) or chelated (mangafodipir (22–44 μmol/kg)) manganese-based contrast media in the presence of calcium channel blockade (diltiazem (100–200 μmol/kg/min)) or sodium chloride (0.9%). A second cohort of rats underwent surgery to induce anterior myocardial infarction by permanent coronary artery ligation or sham surgery. Infarcted rats were imaged with standard gadolinium delayed enhancement MRI (DEMRI) with inversion recovery techniques (DEMRI inversion recovery) as well as DEMRI T1 mapping. A subsequent MEMRI scan was performed 48 h later using either nonchelated or chelated manganese and T1 mapping. Finally, animals were culled at 12 weeks, and infarct size was quantified histologically with Masson's trichrome (MTC). Results Both manganese agents induced concentration-dependent shortening of myocardial T1 values. This was greatest with nonchelated manganese, and could be inhibited by 30–43% with calcium-channel blockade. Manganese imaging successfully delineated the area of myocardial infarction. Indeed, irrespective of the manganese agent, there was good agreement between infarct size on MEMRI T1 mapping and histology (bias 1.4%, 95% CI −14.8 to 17.1 P>0.05). In contrast, DEMRI inversion recovery overestimated infarct size (bias 11.4%, 95% CI −9.1 to 31.8 P=0.002), as did DEMRI T1 mapping (bias 8.2%, 95% CI −10.7 to 27.2 P=0.008). Increased manganese uptake was also observed in the remote myocardium, with remote myocardial ∆T1 inversely correlating with left ventricular ejection fraction after myocardial infarction (r=−0.61, P=0.022). Conclusions MEMRI causes concentration and calcium channel-dependent myocardial T1 shortening. MEMRI with T1 mapping provides an accurate assessment of infarct size and can also identify changes in calcium handling in the remote myocardium. This technique has potential applications for the assessment of myocardial viability, remodelling, and regeneration.

Subjects with Duchenne Muscular Dystrophy (DMD) suffer from progressive muscle damage leading to diaphragmatic weakness that ultimately requires ventilation. Emerging treatments have generated interest in better characterizing the natural history of respiratory impairment in DMD and responses to therapy. Dynamic (cine) Magnetic Resonance Imaging (MRI) may provide a more sensitive measure of diaphragm function in DMD than the commonly used spirometry. This study presents an analysis pipeline for measuring parameters of diaphragmatic motion from dynamic MRI and its application to investigate MRI measures of respiratory function in both healthy controls and non-ambulant DMD boys. We scanned 13 non-ambulant DMD boys and 10 age-matched healthy male volunteers at baseline, with a subset (n = 10, 10, 8) of the DMD subjects also assessed 3, 6, and 12 months later. Spirometry-derived metrics including forced vital capacity were recorded. The MRI-derived measures included the lung cross-sectional area (CSA), the anterior, central, and posterior lung lengths in the sagittal imaging plane, and the diaphragm length over the time-course of the dynamic MRI. Regression analyses demonstrated strong linear correlations between lung CSA and the length measures over the respiratory cycle, with a reduction of these correlations in DMD, and diaphragmatic motions that contribute less efficiently to changing lung capacity in DMD. MRI measures of pulmonary function were reduced in DMD, controlling for height differences between the groups: at maximal inhalation, the maximum CSA and the total distance of motion of the diaphragm were 45% and 37% smaller. MRI measures of pulmonary function were correlated with spirometry data and showed relationships with disease progression surrogates of age and months non-ambulatory, suggesting that they provide clinically meaningful information. Changes in the MRI measures over 12 months were consistent with weakening of diaphragmatic and inter-costal muscles and progressive diaphragm dysfunction. In contrast, longitudinal changes were not seen in conventional spirometry measures during the same period. Dynamic MRI measures of thoracic muscle and pulmonary function are, therefore, believed to detect meaningful differences between healthy controls and DMD and may be sensitive to changes in function over relatively short periods of follow-up in non-ambulant boys with DMD.

Aims The aim of this study is to quantify altered myocardial calcium handling in non-ischaemic cardiomyopathy using magnetic resonance imaging. Methods and results Patients with dilated cardiomyopathy (n = 10) or hypertrophic cardiomyopathy (n = 17) underwent both gadolinium and manganese contrast-enhanced magnetic resonance imaging and were compared with healthy volunteers (n = 20). Differential manganese uptake (Ki) was assessed using a two-compartment Patlak model. Compared with healthy volunteers, reduction in T1 with manganese-enhanced magnetic resonance imaging was lower in patients with dilated cardiomyopathy [mean reduction 257 ± 45 (21%) vs. 288 ± 34 (26%) ms, P &lt; 0.001], with higher T1 at 40 min (948 ± 57 vs. 834 ± 28 ms, P &lt; 0.0001). In patients with hypertrophic cardiomyopathy, reductions in T1 were less than healthy volunteers [mean reduction 251 ± 86 (18%) and 277 ± 34 (23%) vs. 288 ± 34 (26%) ms, with and without fibrosis respectively, P &lt; 0.001]. Myocardial manganese uptake was modelled, rate of uptake was reduced in both dilated and hypertrophic cardiomyopathy in comparison with healthy volunteers (mean Ki 19 ± 4, 19 ± 3, and 23 ± 4 mL/100 g/min, respectively; P = 0.0068). In patients with dilated cardiomyopathy, manganese uptake rate correlated with left ventricular ejection fraction (r2 = 0.61, P = 0.009). Rate of myocardial manganese uptake demonstrated stepwise reductions across healthy myocardium, hypertrophic cardiomyopathy without fibrosis and hypertrophic cardiomyopathy with fibrosis providing absolute discrimination between the healthy myocardium and fibrosed myocardium (mean Ki 23 ± 4, 19 ± 3, and 13 ± 4 mL/100 g/min, respectively; P &lt; 0.0001). Conclusion The rate of manganese uptake in both dilated and hypertrophic cardiomyopathy provides a measure of altered myocardial calcium handling. This holds major promise for the detection and monitoring of dysfunctional myocardium, with the potential for early intervention and prognostication.