Abstract only
Introduction:
Macrophage activity in the heart after myocardial infarction (MI) has previously been assessed by iron-particle cardiac magnetic resonance (CMR) that produces negative ...contrast. We hypothesized that a new multimodal, liposomal agent with both Gd-DTPA and fluorescent DiI dye could be used for positive contrast macrophage tracking.
Methods:
Multimodal liposomes (ML) were prepared with Gd-DTPA-bis-stearylamide and DiI then filtered to ∼0.3 μm size. Nine C57Bl/6 mice were subjected to 1h coronary occlusion followed by up to 7d of reperfusion. ML volumes of 50μl were injected IV on Day 2 post-MI for monocyte/macrophage phagocytosis. Mice were studied by CMR 2–4h after Day 2 injection and daily until Day 7 post-MI. CMR included inversion-recovery (IR) to image ML followed by IP infusion of Gd-DTPA and more IR to image the entire infarct (IF). After final imaging, hearts were removed for Mac2 immunostaining & fluorescence microscopy.
Results:
Day 2 IR CMR 2–4h after ML injection revealed strong signal enhancement in the spleen with none in the heart. In all mice from Day 3–7, ML signal enhancement marked the LV anterior wall in IF regions (Fig A
). The ML contrast peaked at Day 5 and decreased by Day 7 post-MI (Fig B
). In mice euthanized at Days 4 & 7, ML-enhanced regions corresponded well with regions containing macrophages as labeled by anti-Mac2 (Fig C
) and DiI (Fig D
)
Conclusions:
ML can assess the accumulation of macrophages in the heart until at least Day 7 post-MI. The Gd tag provides specific positive contrast and the fluorescent tag expedites histological confirmation. This improves over iron-based agents that preclude complementary CMR imaging in regions containing iron.
Following coronary occlusion, a need exists to differentiate infarct (MI) from salvaged area (SA) that together defines the area at risk (AAR). T2-weighted cardiac MRI (T2w CMR) detects myocardial ...edema that delineates the AAR, while late gadolinium-enhanced (LGE) CMR delineates the MI. Past T2w CMR studies have been performed in larger animals, but not in mice. We developed a T2w CMR method for mice to quantify post-MI MR. For this, we measured inhomogeneities in mice at 7 Tesla to develop a T2w CMR sequence resistant to artifacts, and applied it in vivo in mice to quantify MR and SA. Inhomogeneity maps in mice hearts quantified Δω at ±1000 Hz and ΔB1 at ±19%. The sequence design used T2 prep with an adiabatic pulse Malcolm Levitt train, and gradient echo readout. In vivo imaging included three post-MI mice groups with different occlusion times. Group one (60 minute occlusion) was imaged for four days, and had an AAR = 45.7 ± 2.6 (mean ± SEM) % LV mass that was significantly larger than MI = 33.2 ± 1.5% LV mass (p < 0.001). Group two (20–30 minute occlusion) was imaged from hour-3 through day-33. Day-2 AAR = 34.0 ± 2.8% LV mass and also significantly larger than MI = 18.7 ± 2.4% LV mass (p < 0.0001). The AAR contrast to noise ratio was 48.5 ± 3.8 over normal myocardium. Both AAR and MI from short occlusion were significantly smaller than from long occlusion (p < 0.012 and p < 0.00003 respectively). Short occlusion had significantly higher 46.4 ± 4.8% of AAR salvaged (SA) than long occlusion with 27.1 ± 1.6 salvaged (p < 0.0005). Group three (20 minute occlusion) was imaged on day-2, then sacrificed for histological AAR confirmation. There was linear agreement (R² = 0.86), and small −1.6% bias between T2w and histological AAR. Interobserver analysis of T2w AAR by independent analysts showed linear agreement (R² = 0.91) and low −0.15% bias between analysts. T2w CMR in mice may investigate short and long-term individual genetic pathways and pharmaceutical strategies for increasing the SA after MI.
The default mode network (DMN) in humans has been extensively studied using seed-based correlation analysis (SCA) and independent component analysis (ICA). While DMN has been observed in monkeys as ...well, there are conflicting reports on whether they exist in rodents. Dogs are higher mammals than rodents, but cognitively not as advanced as monkeys and humans. Therefore, they are an interesting species in the evolutionary hierarchy for probing the comparative functions of the DMN across species. In this study, we sought to know whether the DMN, and consequently its functions such as self-referential processing, are exclusive to humans/monkeys or can we also observe the DMN in animals such as dogs. To address this issue, resting state functional MRI data from the brains of lightly sedated dogs and unconstrained and fully awake dogs were acquired, and ICA and SCA were performed for identifying the DMN. Since anesthesia can alter resting state networks, confirming our results in awake dogs was essential. Awake dog imaging was accomplished by training the dogs to keep their head still using reinforcement behavioral adaptation techniques. We found that the anterior (such as anterior cingulate and medial frontal) and posterior regions (such as posterior cingulate) of the DMN were dissociated in both awake and anesthetized dogs.
Motion artifact suppression is an important task in the medical imaging field. Motion during data acquisition can produce blurred images and artifacts. The calculation load for previous motion ...correction methods is relatively high. In order to decrease computational complexity, an
efficient motion correction method is proposed based on fast robust correlation. Fast robust correlation is a computationally efficient search algorithm for translational image matching in the frequency domain. This method calculates the matching surface using a series of high-speed correlations
by defining a kernel with sinusoidal terms. The proposed method corrects motion distorted images by aligning translational motion between images formed by neighboring frequency segments. Due to the ineffectiveness of the squared difference kernel to detect motion between partial-Fourier images,
the absolute value kernel is proposed, which can be easily approximated by sinusoidal terms. Total variation of the sum of partial-Fourier images is chosen as the new match criterion. FFTs are used to calculate correlations for computational speed. Experimental results show that the proposed
method can reduce image motion artifacts effectively and efficiently.
