Novel real-time R-wave detection algorithm based on the vectorcardiogram for accurate gated magnetic resonance acquisitions

Purpose: To investigate MRI of the fetal heart by way of a novel triggering method with the use of an MR-compatible cardiotocography (CTG) in an animal model. Materials and Methods:Fetal cardiac MRI was performed on four pregnant ewes on a 1.5 Tesla (T) MR system. A CTG was rendered MR compatible and its signal was used for the triggering of the fetal heart to perform cardiac cine MRI of the fetal heart with maternal freebreathing with cine steady-state free precession. The left ventricular volume and function were measured from the short-axis (view). The image quality of anatomical structures was assessed.Results: All cardiac valves and the foramen ovale could be visualized. Myocardial contraction was depicted in cine sequences. The average blood volume at the end systole was 1.7 mL (SD 6 0.12). The average volume at the end diastole was 4.6 mL (6 0.4); thus the average stroke volumes of the left ventricle were 2.87 mL (6 0.31) with ejection fractions of 60.53% (6 4.17). Conclusion:The newly developed MR compatible CTG could be used as a tool for cardiac triggering method of the fetal heart. This novel device might help fetal cardiac MRI technology in the future. THE RAPID DEVELOPMENT of cardiac MR imaging in the past few years has enabled many different investigations, for example investigations into coronary arteries and myocardial infarctions. In practice, twodimensional (2D) CINE steady-state free precession (SSFP) imaging is the most reliable and frequently used technique for left ventricular (LV) function assessment. To assess the LV function correctly, speed as well as synchronization of data acquisition with the cardiac cycle are required, so that artifacts due to cardiac motion and flow constraints that dictate the viable window for data acquisition are avoided. To avoid the artifacts caused by cardiac motion, it is customary that either finger pulse oximetry or electrocardiography (ECG) triggering/gating techniques are used so that data acquisition can be synchronized with the cardiac cycle.Although the use of MR imaging during pregnancy is limited to the second and third trimester, its diagnostic value has been increasing in recent years. In the field of fetal MR imaging, the evaluation of the fetal heart is one of the greatest challenges. Nowadays, the gold standard in fetal cardiac imaging is the use of ultrasound (US), because it can be obtained during the entire pregnancy; it is easy to use and thus more practicable. Both the measurement of the cardiac volume and the evaluation of volumetric changes with US are possible, and the technology has been improving. Because cardiac chambers do not lend themselves to geometric assumptions, it has always been difficult to calculate their dimensions, even though studies have shown that 3D US has a better reproducibility than 2D (1-4). To be able to do so, it is necessary to trace the volume of the cardiac chambers manually, due to the appearance of various US specific artifacts, such as speckles and acoustic shadowing, which appear when traced automaticall...

Section: Discussionmentioning

confidence: 99%

Cardiac MRI of the fetal heart using a novel triggering method: Initial results in an animal model

Yamamura

Kopp

Frisch

et al. 2012

“…The principal artifact was from turbulence patterns, some of which can be seen in Figure 1. The ECG gating technique with the automatic level control was extremely robust in this application, although more sophisticated "vectorcardiogram" monitoring may be useful in some studies (34), especially where the lead arrangement is not optimized solely for gating. Foreseeable improvements in the data consistency and segmentation algorithms should make these processing techniques less reliant on operator oversight.…”

Section: Discussionmentioning

confidence: 99%

Dobutamine stress cine‐MRI of cardiac function in the hearts of adult cardiomyocyte‐specific VEGF knockout mice

Williams¹,

Gerber²,

Giordano³

et al. 2001

A mouse model of non-necrotic vascular deficiency in the adult heart was studied using cine-magnetic resonance imaging (MRI) and other techniques. The mice lacked cardiomyocyte-derived vascular endothelial growth factor (VEGF) following a targeted knockout in the ventricular cardiomyocytes. Quantitative endothelial labeling showed that the capillary density was significantly reduced in the hearts of knockout mice. Gene expression patterns suggested that they were hypoxic. Semiautomated MR image analysis was employed to obtain both global and regional measurements of left ventricular function at 10 or more time points through the cardiac cycle. MRI measurements showed a marked reduction in ejection fraction both at rest and under low-and high-dose dobutamine stress. Regional wall thickness, thickening, and displacement were all attenuated in the knockout mice. A prolonged high-dose dobutamine challenge was monitored by MRI. A maximal response was sustained for 90 minutes, suggesting that it did not depend on endogenous glycogen stores. J. Index terms: VEGF; cine; dobutamine; mouse; heart THE RECENT PROLIFERATION of murine models of human heart disease has been remarkable (1) and is likely to continue. Although MRI has been elegantly applied by several groups to studies of the mouse heart (e.g., Refs. 2-5), it remains concentrated in relatively few centers. Cardiac MRI of the mouse, unlike of the rat (6), is not widespread in the pharmaceutical research setting, but that seems likely to change as the advantages of murine models increasingly outweigh their disadvantages. There are important biological differences between the hearts of different mammals, such as in calcium handling (7) and vascular anatomy (8), yet many of the perceived disadvantages of using mice as opposed to larger animal species are essentially technical in nature. This has spurred great efforts in adapting radiological, surgical, and physiological techniques to the temporal and spatial scale of the mouse heart (9,10).This paper describes MRI of the left ventricle (LV) under resting and stressed conditions in a mouse model of a non-necrotic vascular deficiency in the adult heart. This model may be of some value in designing and evaluating angiogenic therapies (11), and in understanding the pathophysiology of chronic ischemic conditions associated with coronary artery disease (12). The generation and preliminary phenotypic characterization of this mouse model has recently been described (13). Briefly, the Cre/lox system (14) was employed to generate a targeted knockout of vascular endothelial growth factor A (VEGF A) specific to the ventricular cardiomyocytes. VEGF A is a potent cytokine and mitogen involved in the formation and maintenance of blood vessels (15). Attempts to generate VEGF A knockouts by the more common germ-line strategies were confounded by the highly unusual embryonic lethality seen in VEGF A heterozygotes (16).The effect of the gene knockout was monitored directly (changes in VEGF A mRNA) and indirectly. Anticipating microvasc...

“…The vector electrocardiogram (VCG) was used in all studies for R-wave triggering (9). A gradient echo sequence was used to obtain the cine images of four-chamber view and four short-axis planes with 8-mm slice thickness.…”

Section: Cine Mrimentioning

confidence: 99%

Real‐time fast strain‐encoded magnetic resonance imaging to evaluate regional myocardial function at 3.0 Tesla: Comparison to conventional tagging

Korosoglou

Youssef

Bilchick

et al. 2008

Purpose:To compare the utility of the real-time technique fast strain-encoded magnetic resonance imaging (fast-SENC) for the quantification of regional myocardial function to conventional tagged magnetic resonance imaging (MRI). Materials and Methods:Healthy volunteers (N ϭ 12) and patients with heart failure (N ϭ 7) were examined using tagged MRI and fast-SENC at 3.0T. Circumferential strain was measured using fast-SENC in six endo-and six subepicardial regions in the basal-, mid-, and apical-septum and the basal-, mid-, and apical-lateral wall from the fourchamber view. These measurements were plotted to tagging, in corresponding myocardial segments.Results: Peak systolic strain (Ecc) and early diastolic strain rate (Ecc/second) acquired by fast-SENC correlated closely to tagged MRI (r ϭ 0.90 for Ecc and r ϭ 0.91 for Ecc/second, P Ͻ 0.001 for both). Both fast-SENC and tagging identified differences in regional systolic and diastolic function between normal myocardium and dysfunctional segments in patients with heart failure (for fast-SENC: Ecc ϭ -21.7 Ϯ 2.7 in healthy volunteers vs. -12.8 Ϯ 4.2 in hypokinetic vs. 0.6 Ϯ 3.8 in akinetic/dyskinetic segments, P Ͻ 0.001 between all; Ecc/ second ϭ 104 Ϯ 20/second in healthy volunteers vs. 37 Ϯ 9/second in hypokinetic vs. -16 Ϯ 15/second in akinetic/ dyskinetic segments, P Ͻ 0.001 between all). Quantitative analysis was more time-consuming for conventional tagging than for fast-SENC (time-spent of 3.8 Ϯ 0.7 minutes vs. 9.5 Ϯ 0.7 minutes per patient, P Ͻ 0.001). Conclusion:Fast-SENC allows the rapid and accurate quantification of regional myocardial function. The information derived from fast-SENC during a single heartbeat seems to be superior or equal to that acquired by conventional tagging during several heart cycles and prolonged breathholds.