CARDIAC IMAGING EXPLORATION

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. 4D mouse heart imaging technique that allows for high throughput imaging and/or high resolution scanning. We developed this as a tool to apply to mouse models of heart failure. Multi-spectral imaging with three-dimensional rosette trajectories Elizabeth Bucholz1,2, Jiayu Song1,3, G. Allan Johnson1,2, Ileana Hancu4 1Center for In Vivo Microscopy, Duke University, 2Department of Biomedical Engineering, Duke University, 3 Department of Electrical and Computer Engineering, Duke University, 4GE Global Research Center, Niskayuna, NY 2D intersecting k-space trajectories have been previously demonstrated to allow fast multi-spectral imaging. Repeated sampling of k-space points leads to destructive interference of the signal coming from the off-resonance spectral peaks; on resonance data reconstruction yields images of the on-resonance peak, with some of the off- resonance energy being spread as noise in the image. A shift of the k-space data by a given off-resonance frequency brings a second frequency of interest on resonance, allowing the reconstruction of a second spectral peak from the same k-space data. Given the higher SNR per unit time characteristic of a 3D acquisition, we have extended the concept of intersecting trajectories to three dimensions. A 3D, rosette-like, pulse sequence was designed and implemented in a clinical, 1.5T scanner. An iterative density compensation function was developed to properly weight the 3D intersecting trajectories before Fourier transformation. Three volunteers were scanned using this sequence, and separate fat and water images were reconstructed from the same imaging dataset. Elizabeth Bucholz, Ketan Ghaghada, Yi Qi, Srinivasan Mukundan, G. Allan Johnson, Four-dimensional MR microscopy of the mouse heart using radial acquisition and liposomal gadolinium contrast agent, Magnetic Resonance in Medicine, in press, 2008. MR microscopy has become an important tool for small animal cardiac imaging. In relation to competing technologies (micro-CT and ultrasound), MR is limited by spatial resolution, temporal resolution, and acquisition time. All these limitations have been addressed by developing a 4D (3D plus time) radial acquisition sequence. The signal-to-noise has been optimized by minimizing the echo time (300 ¿s). The temporal resolution and throughput have been improved by center-out trajectories resulting in TR < 2.5 ms. The contrast has been enhanced through the use of a liposomal blood pool agent that reduces T1 of the blood to < 400 ms. We have developed protocols for three specific applications: a) high-throughput with spatial resolution of 87x87x352 ¿m3 (voxel volume=2.7 nL) and acquisition time of 16 minutes; b) high-temporal resolution with spatial resolution of 87x87x352 ¿m3 (voxel volume=2.7 nL); temporal resolution at 4.8 ms and acquisition time of 32 minutes; and c) high-resolution isotropic imaging at 87x87x87 ¿m3 (voxel volume=0.68 nL), and acquisition time of 31 minutes. The 4D image arrays allow direct measure of cardiac functional parameters dependent on chamber volumes, e.g. ejection fraction, end diastolic volume, and end systolic volume.