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Characterization of high-intensity focused ultrasound (HIFU) systems using ex vivo tissues is an important part of the preclinical testing for new HIFU devices. In ex vivo characterization, the lesion volume produced by the absorption of HIFU energy is quantified as operational parameters are varied. This paper examines the three methods used for lesion-volume quantification: histology, magnetic resonance (MR) imaging, and numerical calculations. The methods were studied in the context of a clinically relevant problem for HIFU procedures--that of quantifying the change in the lesion volume with changing sonication time. The lesion volumes of sonicated samples of porcine liver were determined using the three methods, at focal intensities ranging from 800 W/[cm.sup.2] to 1700 W/[cm.sup.2] and sonication times between 20 s and 40 s. It was found that histology consistently yielded lower lesion volumes than the other two methods, and the calculated values were below magnetic resonance imaging (MRI) at high applied energies. Still the three methods agreed with each other to within a [+ or -] 10% difference for all of the experiments. Increasing the sonication time produced much larger changes in the lesion volume than increasing the acoustic intensity, for the same total energy expenditure, at lower energy (less than 1000 J) levels. At higher energy levels, (around 1500 J), increasing the sonication time and increasing the intensity produced roughly the same change in the lesion volume for the same total energy expenditure. [DOI: 10.1115/1.4001739] Keywords: HIFU, MRL lesion size, sonication time, histology

Following myocardial infarction, nonischemic myocyte death results in infarct expansion, myocardial loss, and ventricular dysfunction. Here, we demonstrate that a specific proapoptotic gene, Bnip3, minimizes ventricular remodeling in the mouse, [...]

Abstract Background In the conventional approach to arterial spin labeling in the rodent heart, the relative difference in the apparent T1 relaxation times corresponding to selective and non-selective inversion is related to perfusion via a two compartment model of tissue. But accurate determination of T1 in small animal hearts is difficult and prone to errors due to long scan times and high heart rates. In this study we introduce the theoretical frame work for an alternative method (SI-method) based purely on the signal intensity of slice-select and non-select inversion recovery images at a single inversion time at short repetition time. Methods A modified Bloch equation was solved to derive perfusion as a function of signal intensity of flow sensitized segmented gradient echo acquisitions. A two compartment fast exchanging model of tissue was assumed. To test the new technique first it was implemented on a flow phantom and then it was compared with the conventional T1 method in an in vivo study of healthy C57BL/6 mice (n=12). Finally the SI-method was used in comparison to a Late Gadolinium Enhanced (LGE) method to qualitatively and quantitatively assess perfusion deficits in an ischemia-reperfusion mouse model (n=4). Results The myocardial perfusion of healthy mice obtained by the SI-method, 5.6 ± 0.5 ml/g/min, (mean ± standard deviation) was similar (p=0.38) to that obtained by the conventional method, 5.6 ± 0.3 ml/g/min. The variance in perfusion within the left ventricle was less for the SI-method than that for the conventional method (p Conclusions The proposed signal intensity based ASL method with a segmented acquisition scheme allows accurate high resolution perfusion mapping in small animals. It’s short scan time, high reproducibility and ease of post process makes it a robust alternative to the conventional ASL technique that relies on T1 measurements.

Abstract Background Cardiac dysfunction in boys with Duchenne muscular dystrophy (DMD) is a leading cause of death. Cardiac resynchronization therapy (CRT) has been shown to dramatically decrease mortality in eligible adult population with congestive heart failure. We hypothesized that mechanical dyssynchrony is present in DMD patients and that cardiovascular magnetic resonance (CMR) may predict CRT efficacy. Methods DMD patients (n = 236) were stratified into 4 groups based on age, diagnosis of DMD, left ventricular (LV) ejection fraction (EF), and presence of myocardial fibrosis defined as positive late gadolinum enhancement (LGE) compared to normal controls (n = 77). Dyssynchrony indices were calculated based on timing of CMR derived circumferential strain (ecc). The calculated indices included cross-correlation delay (XCD), uniformity of strain (US), regional vector of variance (RVV), time to maximum strain (TTMS) and standard deviation (SD) of TTMS. Abnormal XCD value was defined as > normal + 2SD. US, RVV, TTMS and SD were calculated for patients with abnormal XCD. Results There was overall low prevalence of circumferential dyssynchrony in the entire DMD population; it increased to 17.1% for patients with abnormal EF and to 31.2% in the most advanced stage (abnormal EF with fibrosis). All but one DMD patient with mechanical dyssynchrony exhibited normal QRS duration suggesting absence of electrical dyssynchrony. The calculated US and RVV values (0.91 ± 0.09, 1.34 ± 0.48) indicate disperse rather than clustered dyssynchrony. Conclusion Mechanical dyssynchrony is frequent in boys with end stage DMD-associated cardiac dysfunction. It is associated with normal QRS complex as well as extensive lateral fibrosis. Based on these findings, it is unlikely that this patient population will benefit from CRT.

Abstract Background Although previous studies have helped define the natural history of Duchenne Muscular Dystrophy (DMD)-associated cardiomyopathy, the myocardial pathobiology associated with functional impairment in DMD is not yet known. The objective of this study was to assess the distribution of transverse relaxation time (T2) in the left ventricle (LV) of DMD patients, and to determine the association of myocardial T2 heterogeneity to the severity of cardiac dysfunction. DMD patients (n = 26) and normal control subjects (n = 13) were studied by Cardiovascular Magnetic Resonance (CMR). DMD subject data was stratified based on subject age and LV Ejection Fraction (EF) into the following groups: A (12 years, n = 5). LV mid-slice circumferential myocardial strain (εcc) was calculated using tagged CMR imaging. T2 maps of the LV were generated for all subjects using a black blood dual spin echo method at two echo times. The Full Width at Half Maximum (FWHM) was calculated from a histogram of LV T2 distribution constructed for each subject. Results In DMD subject groups, FWHM of the T2 histogram rose progressively with age and decreasing EF (Group A FWHM= 25.3 ± 3.8 ms; Group B FWHM= 30.9 ± 5.3 ms; Group C FWHM= 33.0 ± 6.4 ms). Further, FWHM was significantly higher in those with reduced circumferential strain (|εcc| ≤ 12%) (Group B, and C) than those with |εcc| > 12% (Group A). Group A FWHM was not different from the two normal groups (N1 FWHM = 25.3 ± 3.5 ms; N2 FWHM= 24.0 ± 7.3 ms). Conclusion Reduced EF and εcc correlates well with increased T2 heterogeneity quantified by FWHM, indicating that subclinical functional impairments could be associated with pre-existing abnormalities in tissue structure in young DMD patients.