Multi-dimensional Excitation in MRI: New Development and Applications

In magnetic resonance imaging (MRI), multi-dimensional excitation can select signals from a specific spatial region and/or spectral component. The overall goal of this PhD project is to further develop MRI multi-dimensional excitation techniques to enable two new applications: (a) phosphorus (31P) imaging of selected metabolites at an ultra-high magnetic field of 9.4 Tesla (T) on human subjects, and (b) high-resolution high-b-value non-Gaussian diffusion imaging at 3 Tesla on tumor patients. Current in vivo 31P imaging techniques, such as magnetic resonance spectroscopy (MRS) and chemical shift imaging (CSI), are time-consuming ( >30 min) and unable to provide sufficient spatial coverage with adequate spatial resolution. We have developed a novel multi-dimensional excitation MRI technique to selectively excite specific phosphorous metabolites of interest. The images from the selected 31P metabolite (e.g., Phosphocreatine) have been acquired on human subjects within a clinically acceptable time (~10 min) and with adequate spatial coverage (e.g., 24×24×18 cm3) by utilizing the UIC’s state-of-the-art 9.4 T MRI scanner. This constitutes the first specific aim of the project. Second, non-Gaussian diffusion imaging, serving as a potentially powerful tool for probing tissue microstructures and micro-environment, is vulnerable to image distortion and low spatial resolution inherent to diffusion-weighted single-shot echo planar imaging (DW-ssEPI) pulse sequences. We have developed a new pulse sequence strategy by utilizing a novel 2D echo planar radiofrequency (EPRF) pulse with a tilted excitation plane. The new technique is able to zoom in the targeted region in vivo (e.g., the brain stem) with reduced field-of-view (FOV) in order to increase the spatial resolution while decreasing image distortion. The high-resolution and distortion-free diffusion images have been acquired from the brain stem of healthy human subjects and demonstrated on a non-Gaussian diffusion model known as the fractional order calculus (FROC) model. Moreover, we have applied the FROC model on three clinical applications. The new FROC parameters has shown clinical significance in differentiating the brain tumor grades in pediatric and adult patients, and in predicting the response of chemotherapy in gastrointestinal stromal tumors (GIST)

Effect of reduced proliferation in the SVZ on the generation of neuroblasts and their migration through the RMS.

<p>(A, B) Estimated number of DCX-ir neuroblasts in the SVZ (A) or RMS (B) of control mice (white bars), and mice 7 (grey bars) or 42 days (black bars) after 6-OHDA injections were performed to lesion the SNc (see <i>Protocol 1</i>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031549#pone-0031549-g002" target="_blank">Fig. 2A</a>). (C–M, S, T) BrdU (50 mg/kg i.p.) was administered twice daily for 3 consecutive days, beginning 7 days after 6-OHDA or sham injections, and mice were killed 6 days after the last BrdU administration (see <i>Protocol 2</i>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031549#pone-0031549-g002" target="_blank">Fig. 2B</a>). (C, D) Estimated number of BrdU+ cell bodies in the SVZ (C) or RMS (D) of control mice (white bars), and mice 15 days after 6-OHDA was injected (black bars). (E) Estimated number of BrdU+ cell bodies in the RMS of control or 6-OHDA injected mice, plotted according to distance rostral to the AC. Note the increase in BrdU+ cells in the SVZ of 6-OHDA injected animals. Photomicrographs showing BrdU-LI in the SVZ (F, G) and RMS (H, I) of control and 6-OHDA injected mice. Double-immunofluorescence confocal micrographs of BrdU- (red) and DCX-LI (green) in the SVZ (J, K) and RMS (L, M) of control (J, L) and 6-OHDA injected (K, M) mice. (S, T) Double-immunofluorescence confocal micrographs of BrdU- (red) and DCX-LI (green) in the SVZ of control (S) and 6-OHDA injected (T) mice, shown at higher magnification. Note increased number of double-labeled cells in the SVZ of 6-OHDA injected mice. (N–P) Photomicrographs of DCX-ir neuroblasts in the RMS of control mice (N), and 7 (O) or 42 days (P) after 6-OHDA injection into the SNc (see <i>Protocol 1</i>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031549#pone-0031549-g002" target="_blank">Fig. 2A</a>). (Q, R) Estimated number of GFAP-ir astrocytes in the SVZ of control mice (white bar), and 7 (grey bar) or 42 days (black bar) after 6-OHDA administration (Q) (see <i>Protocol 1</i>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031549#pone-0031549-g002" target="_blank">Fig. 2A</a>). (R) Double-immunofluorescence confocal micrograph of GFAP-LI (green) and Hoechst staining (blue) in the SVZ, the later providing a nuclear counter stain. In plots (A), (B) and (Q), white bars = control animals (n = 4), grey bars = mice 7 days after 6-OHDA injection (n = 4), and black bars = 42 days after 6-OHDA administration (n = 4). For control and lesion groups in plots C–E, n = 4. Control animals received injections of 0.9% NaCl into the SNc. Scale bars: I = 50 um, applies F–I; J = 20 um, applies J–M; P = 100 um. applies N–P; R = 10 um; T = 20 um, applies S, T. * corresponds to <i>P</i><0.05.</p

Summary of results, demonstrating the change in the number of cell bodies in the SVZ, RMS, GCL and GL of 6-OHDA injected animals when compared to control.

<p><i>Protocol 1</i>. A single dose of BrdU (150 mg/kg i.p.) was administered 2 hours prior to death, 7 or 42 days after the 6-OHDA or NaCl injections (n = 4 for each experimental group) (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031549#pone-0031549-g002" target="_blank">Fig. 2A</a>). First symbol represents 7 day group; second symbol corresponds to 42 day group. <i>Protocol 2</i>. BrdU (50 mg/kg, i.p.) was administered twice daily for 3 consecutive days beginning 7 days after 6-OHDA (n = 4) or NaCl (n = 4) injections into the SNc, and mice killed 6 days later (i.e. 15 days after 6-OHDA administration) (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031549#pone-0031549-g002" target="_blank">Fig. 2B</a>). <i>Protocol 3</i>. BrdU (50 mg/kg, i.p.) was administered twice daily for 5 consecutive days, beginning 8 days after 6-OHDA (n = 4) or NaCl (n = 4) was injected into the SNc, and mice killed 30 days later (i.e. 42 days after 6-OHDA administration) (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031549#pone-0031549-g002" target="_blank">Fig. 2C</a>). ↓ corresponds to reduced number of cell bodies in comparison to control; ↑ corresponds to increased number of cell bodies;  = corresponds to no statistical change in number of cell bodies. Numbers and letters in brackets refer to corresponding figure.</p

Counting frame dimensions and x, y co-ordinates for estimates of proliferating cells (Ki67, BrdU 2 hours), neuroblasts, migrating cells (DCX, BrdU 5 days), interneurons and mature cells (NeuN, TH, calbindin, calretinin, GABA, BrdU 30 days) in the SVZ, RMS and OB.

<p>Counting frame dimensions and x, y co-ordinates for estimates of proliferating cells (Ki67, BrdU 2 hours), neuroblasts, migrating cells (DCX, BrdU 5 days), interneurons and mature cells (NeuN, TH, calbindin, calretinin, GABA, BrdU 30 days) in the SVZ, RMS and OB.</p

The number of adult-born cells in the OB increases when precursor proliferation in the SVZ is reduced.

<p>BrdU (50 mg/kg i.p.) was administered twice daily for 5 consecutive days, beginning 8 days after 6-OHDA (or sham) injection, and mice killed 30 days after the last BrdU administration (i.e., 42 days after 6-OHDA injection; see <i>Protocol 3</i>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031549#pone-0031549-g005" target="_blank">Fig. 5C</a>). (A–G) Estimated number of BrdU+ cell bodies in the GCL of control (white bar) and 6-OHDA injected mice (black bar) (A). Photomicrograph of BrdU+ cell bodies in the GCL of control (B) and 6-OHDA injected (C) mice. (D) Estimated number of BrdU+ and GABA-ir double-labeled cell bodies in the GCL of control (white bar) and 6-OHDA injected mice (black bar). Photomicrograph of BrdU- (red) and GABA-LI (green) in the GCL of control (E) and 6-OHDA injected (F) mice. (G) Estimated number of BrdU+/GABA-ir co-expressing cell bodies expressed as a proportion of the total number of BrdU+ cell bodies in the GCL of control (white bar) and 6-OHDA injected mice (black bar). (H–M) Estimated number of BrdU+ cell bodies in the GL of control (white bar) and 6-OHDA injected mice (black bar) (H). Photomicrograph of BrdU+ cell bodies in the GL and EPL of control (I) and 6-OHDA injected (J) mice. (K) Double-immunofluorescence confocal micrographs of BrdU- (red) and TH-LI (green) in the GL of mouse with striatal/SVZ DA-depletion. (L) Estimated number of BrdU+ and TH-ir double labeled cell bodies in the GL of control (white bar) and 6-OHDA injected mice (black bar). (M) Estimated number of BrdU+/TH-ir co-expressing cell bodies expressed as a proportion of the total number of BrdU+ cell bodies in the GL of control (white bar) and 6-OHDA injected mice (black bar). In plots (A), (D), (G), (H), (L), (M), white bars = control animals (n = 4), and black bars = 6-OHDA-injected animals (n = 4). Control animals received injections of 0.9% NaCl into the SNc. In (G), (L) and (M) coex = co-expressing. Scale bars: C = 100 um, applies B, C; F = 40 um, applies E, F; I = 100 um, applies I, J; K = 10 um. * corresponds to <i>P</i><0.05.</p

The effect of reduced precursor proliferation in the SVZ on subclasses of interneurons in the GCL and GL.

<p>The number of interneurons in the GCL and GL were estimated in animals administered with BrdU 2 hours prior to death (see <i>Protocol 1</i>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031549#pone-0031549-g002" target="_blank">Fig. 2A</a>). (A–C) Estimated number of GABA-ir cell bodies in the GCL of control mice (white bar), and mice 42 days after 6-OHDA injection (black bar) (A). Photomicrographs of GABA-LI in the GCL of control mouse (B) and 42 days after 6-OHDA injection (C). (D–F) Estimated number of calretinin-ir cell bodies in the GCL of control mice (white bar), and mice 42 days after 6-OHDA injection (black bar) (D). Photomicrographs of calretinin-LI in the GCL of control mouse (E) and 42 days after 6-OHDA injection (F). Estimated number of GABA-ir (G) and TH-ir (H) cell bodies in the GL of control mice, and mice 7 or 42 days following 6-OHDA injection. (I) Estimated number of GABA and TH double-labeled cell bodies in the GL of control mice, and mice 7 or 42 days after 6-OHDA injection. (J) Estimated number of GABA-ir/TH-ir co-expressing cell bodies expressed as a proportion of the total number of GABA-ir cell bodies in the GL of control mice, and mice 7 or 42 days after 6-OHDA injection. (K, L) Double-immunofluorescence photomicrographs of TH- (green) and GABA-LI (red) in the GL of control mice (K), and mice 42 days after 6-OHDA injection (L). Estimated number of calretinin-ir (M) and calbindin-ir (N) cell bodies in the GL of control mice, and mice 7 or 42 days after 6-OHDA injection. (O, P) Photomicrographs of calretinin-LI in the GL of control mice (O), and mice 42 days after 6-OHDA injection (P). (Q–S) Photomicrographs of calbindin-LI in the GL of control mice (Q), and mice 7 (R) or 42 (S) days after 6-OHDA injection. In plots (A) and (D), white bars = control animals (n = 4), and black bars = 6-OHDA-injected animals (n = 4). In plots (G–J), (M), and (N), white bars = control animals (n = 4), grey bars = mice 7 days after 6-OHDA injection (n = 4), and black bars = 42 days after 6-OHDA injection (n = 4). Control animals received injections of 0.9% NaCl into the SNc. In (J) coex = co-expressing. CalR = calretinin; CalB = calbindin. Scale bars: C = 100 um, applies B, C; F = 50 um, applies E, F; L = 50 um, applies K, L; P = 50 um, applies O, P; Q = 50 um, applies Q–S. * corresponds to <i>P</i><0.05.</p

Proliferation in the SVZ and RMS following 6-OHDA injections into the SNc.

<p>BrdU was administered 2 hours before animals were killed (see <i>Protocol 1</i>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031549#pone-0031549-g002" target="_blank">Fig. 2A</a>), and BrdU+ cells in the SVZ and RMS were quantified. (A–D) Estimated number of BrdU+ (A) and Ki67-ir (C) cell bodies in the SVZ. Estimated number of BrdU+ (B) and Ki67-ir (D) cell bodies in the RMS. (E–G) Photomicrographs of BrdU-LI in the SVZ of control mice (E), and mice 7 (F) or 42 days (G) after 6-OHDA was administered to deplete striatal DA. (H–J) Photomicrographs of Ki67-LI in the SVZ of control mice (H), and mice 7 (I) or 42 days (J) after striatal DA denervation. (K, L) Estimated number of NeuN-ir cell bodies in the GCL (K) and GL (L) of control mice, and mice 7 or 42 days after 6-OHDA administration. In plots (A–D) and (K), (L), white bars = control animals (n = 4), grey bars = mice 7 days after 6-OHDA injection (n = 4), and black bars = 42 days after 6-OHDA administration (n = 4). Control animals received injections of 0.9% NaCl into the SNc. CC, corpus callosum; LV, lateral ventricle; St, striatum; SVZ, subventricular zone; 7D, 7 days post 6-OHDA injection; 42D, 42 days post 6-OHDA injection. Scale bar in G = 50 µm, applies E–J. * corresponds to <i>P</i><0.05.</p

Neurogenesis in the adult rodent SVZ and OB.

<p>Schematic sagittal view of the adult mouse brain. 1) Adult-born olfactory precursors (stem cells/transit amplifying cells) proliferate primarily within the SVZ where they 2) differentiate into immature neurons (neuroblasts). 3) Neuroblasts then migrate tangentially along the RMS toward the main OB, which requires 2–6 days. Arrow indicates the direction of neuroblast migration through the RMS. 4) On days 5–7 after birth, adult-born neuroblasts migrate radially towards the granular, periglomerular and external plexiform cell layers of the OB. 5) 15–30 days after birth, adult-born cells in the OB mature to form local interneurons that display extensive dendritic arborizations (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031549#pone.0031549-Ming1" target="_blank">[9]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031549#pone.0031549-Abrous1" target="_blank">[10]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031549#pone.0031549-Petreanu1" target="_blank">[32]</a>). GCL, granular cell layer; GL, glomerular layer; RMS, rostral migratory stream; SVZ, subependymal zone.</p

Eco-Friendly Superhydrophobic Coupling Conversion Coating with Corrosion Resistance on Magnesium Alloy

An eco-friendly superhydrophobic conversion coating is fabricated to enhance the corrosion resistance of the AZ31B Mg alloy by combining the deep eutectic solvent pretreatment and electrodeposition. The coral-like micro–nano structure formed by reacting deep eutectic solvent and Mg alloy provides a structural basis for constructing a superhydrophobic coating. Cerium stearate with low surface energy is deposited on the structure, providing the coating’s superhydrophobicity and the corrosion inhibition effect. Electrochemical test results demonstrate that the as-prepared superhydrophobic conversion coating (water contact angle at 154.7°) with a 99.68% protection effect significantly improves anticorrosion properties for the AZ31B Mg alloy. The corrosion current density decreases from 1.79 × 10–4 A·cm–2 of Mg substrate to 5.57 × 10–7 A·cm–2 of the coated sample. Besides, the electrochemical impedance modulus reaches the value of 1.69 × 103 Ω·cm2 and increases approximately 23 times in magnitude compared with the Mg substrate. Furthermore, the corrosion protection mechanism is attributed to the coupling effect of water-repellency barrier protection and corrosion inhibition, resulting in excellent corrosion resistance. Results demonstrate a promising strategy for the corrosion protection of Mg alloys by replacing the chromate conversion coating with the superhydrophobic coupling conversion coating

Comparative Sequence Analysis of the <em>Ghd7</em> Orthologous Regions Revealed Movement of <em>Ghd7</em> in the Grass Genomes

<div><p><em>Ghd7</em> is an important rice gene that has a major effect on several agronomic traits, including yield. To reveal the origin of <em>Ghd7</em> and sequence evolution of this locus, we performed a comparative sequence analysis of the <em>Ghd7</em> orthologous regions from ten diploid <em>Oryza</em> species, <em>Brachypodium distachyon</em>, sorghum and maize. Sequence analysis demonstrated high gene collinearity across the genus <em>Oryza</em> and a disruption of collinearity among non<em>-Oryza</em> species. In particular, <em>Ghd7</em> was not present in orthologous positions except in <em>Oryza</em> species. The <em>Ghd7</em> regions were found to have low gene densities and high contents of repetitive elements, and that the sizes of orthologous regions varied tremendously. The large transposable element contents resulted in a high frequency of pseudogenization and gene movement events surrounding the <em>Ghd7</em> loci. Annotation information and cytological experiments have indicated that <em>Ghd7</em> is a heterochromatic gene. <em>Ghd7</em> orthologs were identified in <em>B. distachyon</em>, sorghum and maize by phylogenetic analysis; however, the positions of orthologous genes differed dramatically as a consequence of gene movements in grasses. Rather, we identified sequence remnants of gene movement of <em>Ghd7</em> mediated by illegitimate recombination in the <em>B. distachyon</em> genome.</p> </div