Diffusion tensor magnetic resonance imaging of the heart is typically performed at millimetre-scale resolution, yielding only four to five voxels across the ventricular wall, limiting the measurement of local spatial variation in cardiomyocyte organization. Here we present a submillimetre in vivo cardiac diffusion tensor imaging method achieved during free breathing that facilitates voxel-level characterization of myocardial microstructure. We introduce a phenomapping framework that combines voxelwise diffusion magnitude and anisotropy with radial and circumferential gradients of cardiomyocyte helix angle to identify distinct microstructural environments. The approach was developed in healthy volunteers and applied to patients with severe aortic valve stenosis, who had preserved cardiac function and marked myocardial thickening. Comparisons to conventional resolution imaging, together with downsampling analyses and ex vivo and histological validation, show that these voxel-scale features are less optimally detected using standard techniques. Four data-driven microstructural classes, defined by combined diffusion properties and orientation gradients, were observed in both healthy and pressure-overloaded hearts. Despite substantial hypertrophy, pressure overload was associated with preserved cardiomyocyte spatial organization. This framework supports studies of myocardial microstructural remodelling in vivo.

Current techniques to image the microstructure of the heart with diffusion tensor MRI (DTI) are highly under-resolved. We present a technique to improve the spatial resolution of cardiac DTI by almost 10-fold and leverage this to measure local gradients in cardiomyocyte alignment or helix angle (HA). We further introduce a phenomapping approach based on voxel-wise hierarchical clustering of these gradients to identify distinct microstructural microenvironments in the heart. Initial development was performed in healthy volunteers (n=8). Thereader, subjects with severe but well-compensated aortic stenosis (AS, n=10) were compared to age-matched controls (CTL, n=10). Radial HA gradient was significantly reduced in AS (8.0±0.8°/mm vs. 10.2±1.8°/mm, p=0.001) but the other HA gradients did not change significantly. Four distinct microstructural clusters could be idenJfied in both the CTL and AS subjects and did not differ significantly in their properties or distribution. Despite marked hypertrophy, our data suggest that the myocardium in well-compensated AS can maintain its microstructural coherence. The described phenomapping approach can be used to characterize microstructural plasticity and perturbation in any organ system and disease.

During fibroproliferation, protein-associated extracellular aldehydes are formed by the oxidation of lysine residues on extracellular matrix proteins to form the aldehyde allysine. Here we report three Mn(II)-based, small molecule magnetic resonance (MR) probes that contain α-effect nucleophiles to target allysine in vivo and report on tissue fibrogenesis. We used a rational design approach to develop turn-on probes with a 4-fold increase in relaxivity upon targeting. The effects of aldehyde condensation rate and hydrolysis kinetics on the performance of the probes to detect tissue fibrogenesis noninvasively in mouse models were evaluated by a systemic aldehyde tracking approach. We showed that for highly reversible ligations, off-rate was a stronger predictor of in vivo efficiency, enabling histologically validated, three-dimensional characterization of pulmonary fibrogenesis throughout the entire lung. The exclusive renal elimination of these probes allowed for rapid imaging of liver fibrosis. Reducing the hydrolysis rate by forming an oxime bond with allysine enabled delayed phase imaging of kidney fibrogenesis. The imaging efficacy of these probes, coupled with their rapid and complete elimination from the body, make them strong candidates for clinical translation.

Sickle Cell Disease (SCD) is characterized by severe hemolytic anemia and low Hct. This contributes to elevated cerebral cerebrometabolic strain, as evidenced by increased cerebral blood flow (CBF), increased blood oxygen extraction fraction (OEF), and increased incidence of silent cerebral infarct. Recent reports have shown that approved and experimental therapies ameliorate these physiological indicators of strain in SCD patients using advanced MRI-based techniques (Fields, et al., Blood, 2019; Hulbert, et al., Blood 2022), but the effect on these same MRI endpoints has not been demonstrated in animal models of SCD. The purpose of this work was to perform these same measurements in Townes SCD mice treated with tucaresol, which is known to increase the oxygen affinity hemoglobin, thus building a translational platform for non-invasive assessment of these endpoints to support characterization of novel therapies and their relationship to cerebrometabolic strain that leads to end organ damage in the brain. All animal procedures were performed under an IACUC-approved protocol. Forty-three male Townes SCD mice were assigned to two treatment groups (n=21 / 22, mean age = 8.1±0.8 / 8.4 ±0.6 weeks, mean weight = 26±2 / 26±2 g). Animals were anesthetized and scanned on a 9.4 T Bruker MRI scanner at MGH. CBF was measured using a pseudo-continuous arterial spin labeling sequence (pCASL) (Hirschler, et al., NMR in Biomedicine, 2018), and OEF was estimated from a T2 measurement in the superior sagittal sinus using a TRUST sequence (Wei, et al., Magn. Reson. Med., 2018) and a hematocrit measure which was taken from a tail vein bleed immediately following the scan. Following anesthesia recovery from the first imaging timepoint, animals were placed in cages according to group assignment and drinking water was replaced by one of two masked dosing solutions. prepared off-site by an independent team, containing either 1.14 mM tucaresol or pH and color-matched water. The tucaresol concentration was chosen to approximate an oral dose of 60 mg/kg/day comparable to a clinical dose and be consistent with previous studies. After two weeks of ad lib exposure to the dosing solutions, the scanning and blood sampling procedure was repeated. A terminal cardiac punch was also performed under anesthesia to assess tucaresol blood exposure. Due to technical challenges Hct measures were not performed in the first five animals from each group, and two animals had Hct measures at only the second timepoint. CBF is reported in whole bilateral striatum. Whole blood analysis revealed tucaresol exposures of 0.1-0.6 mM in the active arm. While still within the range for hemoglobin modification, the exposures were similar but somewhat lower than the exposures of 0.5-1.6 mM reported from oral gavage at 30 mg/kg twice per day in SCD mice (Knee et al. Blood, 2016). Table 1 shows CBF, Hct, and OEF values at baseline and after two weeks of dosing for each group. OEF values assume arterial oxygen saturation of 1. Spaghetti plots in figure 1 display changes in these values for individual animals. CBF elevations are observed very early in clinical SCD populations and begin to plateau as the disease progresses, but OEF has been shown to increase as the disease progresses (Juttukunda, et al., J. Magn. Reson. Imaging, 2019). As a result, therapeutic interventions in advanced disease may be expected to first affect OEF, with decreases in CBF to follow. That may, in part explain why a treatment effect was observed with OEF and not with CBF. Additionally, the proximity of the labeling plane of inflowing arterial blood to the brain tissue being perfused and the high carotid artery flow rate in these animals means that the CBF measure by pCASL MRI is considerably more challenging in mice than in humans. The sensitivity of MRI-derived OEF to therapeutic intervention in mice is similar to what has been reported in SCD patients, where elevated OEF is particularly associated with regions of the brain at highest risk for developing silent infarct. CBF and OEF are currently being evaluating for an approved HbS modifier (NCT05228821). The ability to use the same techniques in both mice and humans to non-invasively and quantitatively demonstrate the amelioration of the cerebrophysiological compensatory measures that precede end CNS organ damage is a valuable step in characterizing potential benefit of novel therapeutics beyond standard regulatory endpoints associated with pain crises.

Background The delivery of stem cells to the myocardium after ischemic injury has the potential to prevent left ventricular remodeling and heart failure. Ischemic injury, however, elicits a robust inflammatory response and the release of cytotoxic substances from infiltrating leucocytes. We aimed here to use a myeloperoxidase activatable gadolium chelate (MPO-Gd) [1], to quantify peroxidase activity in the myocardium in vivo after ischemic injury. We further aimed to determine, using bioluminescence imaging, whether the detected levels of MPO were compatible with cell survival.

Background The left ventricle (LV) can tolerate pressure overload from hypertension or aortic stenosis for many years. In contrast, the right ventricle (RV) adapts to pulmonary hypertension only if this develops at birth, while in the adult heart severe and often fatal RV failure develops. We hypothesized that i) these divergent responses could be due to differences in myofiber architecture in the free walls of the LV and RV and that ii) adaptive changes to pressure overload would be seen in the LV but not the RV.

Brown adipose tissue (BAT) is the primary tissue responsible for nonshivering thermogenesis in mammals. The amount of BAT and its level of activation help regulate the utilization of excessive calories for thermogenesis as opposed to storage in white adipose tissue (WAT) which would lead to weight gain. Over the past several years, BAT activity in vivo has been primarily assessed by positron emission tomography-computed tomography (PET-CT) scan using 2-[18F]-fluoro-2-deoxy-D-glucose (18F-FDG) to measure glucose utilization associated with BAT mitochondrial respiration. In this study, we demonstrate the feasibility of mapping and estimating BAT volume and metabolic function in vivo in rats at a 9.4T magnetic resonance imaging (MRI) scanner using sequences available from clinical MR scanners. Based on the morphological characteristics of BAT, we measured the volume distribution of BAT with MRI sequences that have strong fat-water contrast. We also investigated BAT volume by utilizing spin-echo MRI sequences. The in vivo MRI-estimated BAT volumes were correlated with direct measurement of BAT mass from dissected samples. Using MRI, we also were able to map hemodynamic responses to changes in BAT metabolism induced pharmacologically by β3-adrenergic receptor agonist, CL-316,243 and compare this to BAT activity in response to CL-316,243 assessed by PET 18F-FDG. In conclusion, we demonstrate the feasibility of measuring BAT volume and function in vivo using routine MRI sequences. The MRI measurement of BAT volume is consistent with quantitative measurement of the tissue ex vivo.

BACKGROUND Aberrant accumulation of transition metals in the brain may have an early and important role in the pathogenesis of several neurodegenerative disorders, including Huntington disease (HD). OBJECTIVE To comprehensively evaluate and validate the distribution of metal deposition in the brain using advanced magnetic resonance imaging methods from the premanifest through symptomatic stages of HD. DESIGN Observational study. SETTING University imaging center. PARTICIPANTS Twenty-eight HD expanded gene carriers, 34 patients with symptomatic HD, and 56 age- and sex-matched healthy control subjects were included in the study. INTERVENTIONS Participants underwent magnetic resonance imaging for the quantification of the phase evolution of susceptibility-weighted images. MAIN OUTCOME MEASURES To verify the identity of the metals responsible for the changes in the phase evolution of the susceptibility signal in the brain and to assess correlations with systemic levels. Inductively coupled plasma mass spectrometry was used to measure transition metal concentrations in postmortem brains. RESULTS In the basal ganglia, progressive increases in the phase evolution were found in HD, beginning in premanifest individuals who were far from expected onset and increasing with proximity to expected onset and thereafter. Increases in the cerebral cortex were regionally selective and present only in symptomatic HD. Increases were verified by excessive deposition of brain iron, but a complex alteration in other transition metals was found. CONCLUSION An important and early role of altered metal homeostasis is suggested in the pathogenesis of HD.

Deviation of dopamine homeostasis is known to be associated with disorders like drug addiction and Parkinson's disease. As dopamine function is tightly regulated within the basal ganglia circuitry, cortical perturbation would lead to modulation of dopaminergic activity in the striatum. We proposed and tested if somatosensory activity such as forepaw stimulation could modulate dopaminergic function. Specifically, we tested in rats if electrical forepaw stimulation (EFS) could attenuate dopamine release in the brain if dopamine is excessive, and boost dopamine release if dopamine is deficient. We had previously demonstrated that EFS effectively attenuated excessive DA concentration in the striatum. We now show in this manuscript with fMRI that EFS boosted DA release on two DA deficient conditions: (1) with quinpirole challenge, and (2) partial Parkinsonism model (PD). Quinpirole alone decreased dopamine release and thus the cerebral blood volume (CBV) that was restored by EFS. EFS also succeeded in increasing CBV in the basal‐ganglia circuitry of the PD rats, but not in the controls. Context‐dependent connectivity analysis showed increased connectivity during the basal state in the PD rats, compared with the controls. This “enhanced” yet abnormal connectivity of PD rats was reduced post‐EFS. Our results suggest that EFS resets the deficient DA system by partially increasing DA release, in the meanwhile lessening the need for recruiting extra functional network in the basal ganglia circuitry. This study shows not only the capacity of peripheral stimulation to perturb neurotransmitter function, but also the potential of peripheral stimulation to restore neurotransmitter homeostasis. Synapse, 2012. © 2011 Wiley Periodicals, Inc.

Chronic use of cocaine is associated with lasting alterations in brain metabolism, circuitry, and receptor properties. We used neuroimaging with pharmacological magnetic resonance imaging to assess alterations in response to cocaine (0.5 mg/kg) in animals trained to self-administer cocaine on a fixed-ratio 5 schedule of reinforcement, as well as saline-yoked controls, after 28 days of cocaine abstinence. We fitted the cerebral blood volume (CBV) curves for full-width half-maximum (FWHM) as well as peak CBV response. There were significant increases in the FWHM of the response curves in the cocaine self-administering (SA) animals as compared with saline-yoked controls in the medial prefrontal cortex (mPFC) and the caudate/putamen (CPu), and increases in peak CBV in the M1 motor cortex, CPu, and pedunculopontine tegmental nucleus. Functional connectivity analysis showed increased correlations in the cocaine SA rats upon acute cocaine challenge, especially in the S1, mPFC, and thalamus. As D3 receptor expression is postulated to increase following chronic cocaine administration, we also examined the response to 0.2 mg/kg of the D3-preferring agonist 7-hydroxy-N,N-di-n-propyl-2-aminotetralin (7-OHDPAT). Cocaine SA animals showed a decreased overall CBV response to this drug, except in the globus pallidus. The hypothalamus showed a negative CBV change in response to cocaine challenge, similar to that noted with the D3 agonist, and showed a smaller response in the cocaine SA animals than in the controls. Given the good coupling of cerebral hemodynamics with dopamine dynamics previously observed with pharmacological magnetic resonance imaging, these data suggest that increased persistence of dopamine in the prefrontal cortex may be responsible for some of the behavioral alterations observed subsequent to chronic cocaine use.

Characterization of the ontogeny of the cerebral dopaminergic system is crucial for gaining a greater understanding of normal brain development and its alterations in response to drugs of abuse or conditions such as attention-deficit hyperactivity disorder. Pharmacological MRI (phMRI) was used to determine the response to dopamine transporter (DAT) blockers cocaine and methylphenidate (MPH), the dopamine releaser D-amphetamine (AMPH), the selective D1 agonist dihydrexidine, and the D2/D3 agonist quinpirole in young (<30 days old) and adult (>60 days old) rats. In adult rats, cocaine (0.5 mg/kg i.v.) or MPH (2 mg/kg) induced primarily positive cerebral blood volume (rCBV) changes in the dopaminergic circuitry, but negative rCBV changes in the young animals. Microdialysis measurements in the striatum showed that young rats have a smaller increase in extracellular dopamine in response to cocaine than adults. The young rats showed little rCBV response to the selective D1 agonist dihydrexidine in contrast to robust rCBV increases observed in the adults, whereas there was a similar negative rCBV response in the young and adult rats to the D2 agonist quinpirole. We also performed a meta-analysis of literature data on the development of D1 and D2 receptors and the DAT. These data suggest a predominance of D2-like over D1-like function between 20 and 30 days of age. These combined results suggested that the dopamine D1 receptor is functionally inhibited at young age.

Dopamine D3 receptors (D3R) may be important therapeutic targets for both drug abuse and dyskinesias in Parkinson’s disease; however, little is known about their functional circuitry.

Gua Sha is a traditional Chinese folk therapy that employs skin scraping to cause subcutaneous microvascular blood extravasation and bruises. The protocol for bioluminescent optical imaging of HO-1-luciferase transgenic mice reported in this manuscript provides a rapid in vivo assay of the upregulation of the heme oxygenase-1 (HO-1) gene expression in response to the Gua Sha procedure. HO-1 has long been known to provide cytoprotection against oxidative stress. The upregulation of HO-1, assessed by the bioluminescence output, is thought to represent an antioxidative response to circulating hemoglobin products released by Gua Sha. Gua Sha was administered by repeated strokes of a smooth spoon edge over lubricated skin on the back or other targeted body part of the transgenic mouse until petechiae (splinter hemorrhages) or ecchymosis (bruises) indicative of extravasation of blood from subcutaneous capillaries was observed. After Gua Sha, bioluminescence imaging sessions were carried out daily for several days to follow the dynamics of HO-1 expression in multiple internal organs.

We studied the metabolic responses to different DA concentrations elicited by four doses of D‐amphetamine (AMPH, 0, 0.25, 0.5, 1.0, or 3.0 mg/kg). We compared the degree of DA release (via microdialysis) with striatal cAMP activity and whole brain maps of cerebral blood volume (rCBV) changes (via pharmacological MRI, phMRI). Results: AMPH increased DA release in the caudate/putamen (CPu) and cAMP activity in the CPu, nucleus accumbens (NAc), and medial prefrontal cortex (mPFC) in a linear dose‐dependent manner ( P < 0.0001). The cAMP data suggest that, postsynaptically, signal transduction induced by D1 receptor is stronger than that of D2 receptor at the higher doses (1–3 mg/kg). phMRI showed that, while higher doses of AMPH (3 mg/kg ( n = 7) and 1 mg/kg ( n = 6)) induced significant rCBV increases in the CPu and NAc, the degree of rCBV increase was much smaller with AMPH of 0.5 mg/kg ( n = 6). In contrast, AMPH of 0.25 mg/kg ( n = 8) induced significant rCBV decreases in the anteromedial CPu and NAc. The sign switch of rCBV in response to AMPH from low to high doses likely reflects the switching in the balance of D2/D3 stimulation vs. D1/D5 stimulation. In conclusion, degree of postsynaptic signal transduction is linearly correlated to the extracellular DA concentration. However, the presynaptic binding may dominate the overall DA innervation at the lower range of DA concentration. Synapse 63:764–772, 2009. © 2009 Wiley‐Liss, Inc.

Our previous fMRI and microdialysis measurements showed that electroacupuncture (EA) at LI4 was effective in alleviating excessive cerebral dopamine release induced by D-amphetamine (AMPH) in rats. We now compare the effect of EA in adjusting excess dopamine release at two stimulating frequencies (2 Hz versus 100 Hz at LI4) and at two acupoints (forepaw (LI4) versus hindpaw (ST36), at 2 Hz). fMRI measurements of relative cerebral blood volume (rCBV) were used to monitor the brain activity of "rest", followed by AMPH challenge, 10 min "rest", and then 20 min of EA. Results: EA at LI4 and ST36 significantly attenuated the AMPH-induced rCBV increases in the striatum, S1 cortex, and thalamus. Frequency: EA at 100 Hz induced greater attenuation of rCBV than EA at 2 Hz in the S1, insula, anterior cingulate cortices, dorsolateral striatum, and thalamus. Acupoints: EA at LI4 modulated a broader area in the medial anterior striatum while EA at ST36 modulated a more site-specific area in the dorsolateral striatum. in the thalamus, EA at LI4 showed greater attenuating effect than EA at ST36 did. However, in the insular cortex, EA at ST36 showed stronger attenuation. Conclusion: EA at both LI4 and ST36 was effective in restoring dopamine homeostasis from an excess state, with the most effective response at LI4 with 100 Hz, while the responses to 2 Hz EA at LI4 and ST36 showed slightly different spatial distribution of MR signal. This therefore provided insight into the neurophysiological basis of electroacupuncture effects in cortical and subcortical circuits. (C) 2008 Elsevier Ireland Ltd. All rights reserved.

The subcortical response to peripheral somatosensory stimulation is not well studied. Prior literature suggests that somatosensory stimulation can affect dopaminergic tone. We studied the effects of electrical stimulation near the median nerve on the response to an amphetamine-induced increase in synaptic dopamine. We applied the electrical stimulation close to the median nerve 20 min after administration of 3 mg/kg amphetamine. We used fMRI and microdialysis to measure markers of dopamine (DA) release, together with the release of associated neurotransmitters of striatal glutamate (Glu) and gamma-aminobutyric acid (GABA). Changes in cerebral blood volume (CBV), a marker used in fMRI, indicate that electrical stimulation significantly attenuated increased DA release (due to AMPH) in the striatum, thalamus, medial prefrontal and cingulate cortices. Microdialysis showed that electrical stimulation increased Glu and GABA release and attenuated the AMPH-enhanced DA release. The striatal DA dynamics correlated with the CBV response. These results demonstrate that electrical stimulation near the median nerve activates Glu/GABA release, which subsequently attenuate excess striatal DA release. These data provide evidence for physiologic modulation caused by electroacupuncture at points near the median nerve.

Rat subventricular zone (SVZ) stem cells were labeled with superparamagnetic iron oxide particles (SPIO) to follow their fate and migratory potential with magnetic resonance imaging (MRI) and positron emission tomography (PET). Labeled cells were transplanted into either the right rostral migratory stream (RMS) or striatum of normal adult Sprague-Dawley rats and serially followed for 3 months. Minimal migration of the cells implanted into the striatum was observed after 3 weeks whereas SVZ cells implanted into the RMS migrated toward the olfactory bulb at 1 week post-transplantation. PET studies of glucose metabolism using (18)F-FDG demonstrated enhanced glucose utilization in the striatum of transplanted animals. PET studies conducted 3 months after transplantation showed elevated accumulation of (11)C-raclopride (dopamine receptor type 2) and (11)C-CFT (dopamine transporter) binding in the striatal grafts. Implanted SVZ cells did not induce significant inflammation as identified by PET using (11)C-PK11195, a ligand detecting activated microglia. Histological analysis identified viable SPIO-labeled cells (some of which were nestin-positive) 7 weeks post-transplantation, suggesting a prolonged presence of undifferentiated neural stem cells within transplants. In addition, double immunostaining for neuronal and astrocytic markers (NeuN and GFAP) indicated that differentiation into neuronal and astrocytic phenotypes also occurred. Thus, combining MRI and PET enables monitoring of cell migration and metabolism non-invasively in vivo for extended periods of time.

Nicotine is one of the most addictive substances known. To better understand the mechanisms of action, we mapped the regional brain response to nicotine administration using pharmacologic magnetic resonance imaging (phMRI) in rats. We measured the regional response of relative cerebral blood volume (rCBV) in rats to a challenge of 0.07 mg/kg (0.43 μmol/kg) of nicotine. The areas of the brain with significant and reproducible changes in the rCBV response were (in descending order of magnitude) infralimbic cortex, hippocampus (subiculum), agranular insular/pyriform cortex, visual cortex, interpeduncular area, nucleus accumbens, cingulate cortex, thalamus, and septum. This pattern of response is consistent with stimulation of both cholinergic and dopaminergic neuronal pathways and is consistent with the known behavioral properties of nicotine. The peak CBV response to nicotine occurred between 9 and 13 min depending upon brain region, and the average full width half‐maximum of the rCBV response was 27 min. The high spatial and temporal resolution of the phMRI technique lends itself well to further, more detailed, studies of nicotine dynamics. Synapse 60:152–157, 2006. © 2006 Wiley‐Liss, Inc.