Manganese‐enhanced MRI of rat brain based on slow cerebral delivery of manganese(II) with silica‐encapsulated MnxFe1–xO nanoparticles

In this work, we report a monodisperse bifunctional nanoparticle system, MIO@SiO₂‐RITC, as an MRI contrast agent [core, manganese iron oxide (MIO); shell, amorphous silica conjugated with rhodamine B isothiocyanate (RITC)]. It was prepared by thermal decomposition and modified microemulsion methods. The nanoparticles with varying iron to manganese ratios displayed different saturated magnetizations and relaxivities. In vivo MRI of rats injected intravenously with MIO@SiO₂‐RITC nanoparticles exhibited enhancement of the T₁ contrast in brain tissue, in particular a time‐delayed enhancement in the hippocampus, pituitary gland, striatum and cerebellum. This is attributable to the gradual degradation of MIO@SiO₂‐RITC nanoparticles in the liver, resulting in the slow release of manganese(II) [Mn(II)] into the blood pool and, subsequently, accumulation in the brain tissue. Thus, T₁‐weighted contrast enhancement was clearly detected in the anatomic structure of the brain as time progressed. In addition, T₂*‐weighted images of the liver showed a gradual darkening effect. Here, we demonstrate the concept of the slow release of Mn(II) for neuroimaging. This new nanoparticle‐based manganese contrast agent allows one simple intravenous injection (rather than multiple infusions) of Mn(II) precursor, and results in delineation of the detailed anatomic neuroarchitecture in MRI; hence, this provides the advantage of the long‐term study of neural function. Copyright © 2013 John Wiley & Sons, Ltd.     

Rapid simultaneous acquisition of T1 and T2 mapping images using multishot double spin‐echo EPI and automated variations of TR and TE (ms‐DSEPI‐T12)

A rapid method of simultaneous T₁ and T₂ measurement is presented which uses a segmented echo‐planar readout with varying repetition times (TR) and echo times (TE). This method is useful in T₁ mapping for analysis of dynamic contrast enhanced MRI (DCE‐MRI), where T₁ can be used to estimate contrast agent concentration. In the application of this method to dynamic imaging, the equilibrium magnetization is measured on pre‐contrast images and incorporated into post‐contrast T₁ calculations for improved accuracy. Simultaneous T₂ measurement allows correction of T₂ effects in the T₁ map which may occur at high contrast agent concentrations, and is performed without significant imaging time penalty. Phantom and in vivo results show the usefulness of this technique for analysis of contrast enhancement kinetics. Accurate rapid contrast agent concentration measurement may be useful for analyzing the distribution and kinetics of contrast agents or labeled pharmaceuticals. Copyright © 2009 John Wiley & Sons, Ltd.     

Cell layers and neuropil: contrast‐enhanced MRI of mouse brain in vivo

Contrast‐enhanced T₁‐ and T₂‐weighted MRI at 9.4 T and in‐plane resolutions of 25 and 30 µm has been demonstrated to differentiate between neural tissues in mouse brain in vivo, including granule cell layers, principal cell layers, general neuropil, specialized neuropil and white matter. In T₁‐weighted MRI of the olfactory bulb, hippocampus and cerebellum, contrast obtained by the intracranial administration of gadopentetate dimeglumine (Gd‐DTPA) reflects the extra‐ and intracellular spaces of gray matter in agreement with histological data. General neuropil areas are highlighted, whereas other tissues present with lower signal intensities. The induced contrast is similar to that in plain T₂‐weighted MRI, but offers a 16–30‐fold higher contrast‐to‐noise ratio. Systemic administration of manganese chloride increases the signal‐to‐noise ratio in T₁‐weighted MRI to a significantly greater extent in principal cell layers and specialized neuropil than in granule cell layers, whereas gadolinium‐enhanced MRI indicates no larger intracellular spaces in these tissues. Granule cell layers are enhanced no more than general neuropil by manganese, whereas gadolinium‐enhanced MRI indicates significantly larger intracellular spaces in the cell layers. These discrepancies suggest that the signal increase after manganese administration reflects cellular activity which is disproportionate to the intracellular space. As a result, principal cell layers and specialized neuropil become highlighted, whereas granule cell layers, general neuropil and white matter present with lower signal intensities. Copyright © 2013 John Wiley & Sons, Ltd.     

Manganese‐enhanced MRI detection of impaired calcium regulation in a mouse model of cardiac hypertrophy

The aim of this study was to use manganese (Mn)‐enhanced MRI (MEMRI) to detect changes in calcium handling associated with cardiac hypertrophy in a mouse model, and to determine whether the impact of creatine kinase ablation is detectable using this method. Male C57BL/6 (C57, n = 11) and male creatine kinase double‐knockout (CK‐M/Mito^–/–, DBKO, n = 12) mice were imaged using the saturation recovery Look–Locker T₁ mapping sequence before and after the development of cardiac hypertrophy. Hypertrophy was induced via subcutaneous continuous 3‐day infusion of isoproterenol, and sham mice not subjected to cardiac hypertrophy were also imaged. During each scan, the contrast agent Mn was administered and the resulting change in R₁ (=1/T₁) was calculated. Two anatomical regions of interest (ROIs) were considered, the left‐ventricular free wall (LVFW) and the septum, and one ROI in an Mn‐containing standard placed next to the mouse. We found statistically significant (p < 0.05) decreases in the uptake of Mn in both the LVFW and septum following the induction of cardiac hypertrophy. No statistically significant decreases were detected in the standard, and no statistically significant differences were found among the sham mice. Using a murine model, we successfully demonstrated that changes in Mn uptake as a result of cardiac hypertrophy are detectable using the functional contrast agent and calcium mimetic Mn. Our measurements showed a decrease in the relaxivity (R₁) of the myocardium following cardiac hypertrophy compared with normal control mice. Copyright © 2014 John Wiley & Sons, Ltd.     

Iron oxide/manganese oxide co-loaded hybrid nanogels as pH-responsive magnetic resonance contrast agents

This work described a proof of concept study of hybrid nanogel-based magnetic resonance contrast agents, SPIO@GCS/acryl/biotin@Mn-gel, abb. as SGM, for highly efficient, pH-responsive T₁ and T₂ dual-mode magnetic resonance imaging (MRI). SGM have been synthesized by assembling superparamagnetic iron oxide particles into polysaccharide nanoclusters, followed by in-situ reduction of the manganese species on the clusters and a final mild polymerization. The dual-mode SGM showed an interesting pH-responsiveness in in vitro MRI, with both T₁ and T₂ relaxivities turned “ON” in the acidic environment, along with an increase in the r₁ and r₂ relaxivity values by 1.7-fold (from 8.9 to 15.3 mM⁻¹ S⁻¹) and 4.9-fold (from 45.7 to 226 mM⁻¹ S⁻¹), due to desirable silencing and de-silencing effects. This interesting acidic-responsiveness was further verified in vivo with both significantly brightened signal of tumor tissue in T₁-weighted MR images and a darkened signal in T₂-weighted MR images 50 min post-injection of SGM. This smart hybrid nanogel may serve as a promising candidate for further studies of dual-mode (T₁ and T₂) contrast agents in MRI, due to its high stability, interesting pH-response mechanism and indicative imaging of tumors.     

Manganese‐enhanced MRI visualizes V1 in the non‐human primate visual cortex

MRI at 7 Tesla has been used to investigate the accumulation of manganese in the occipital cortex of common marmoset monkeys (Callithrix jacchus) after administering four fractionated injections of 30 mg/kg MnCl₂ · 4H₂O in the tail vein. We found a statistically significant decrease in T₁ in the primary (V1) and secondary (V2) areas of the visual cortex caused by an accumulation of manganese. The larger T₁ shortening in V1 (ΔT₁ = 640 ms) relative to V2 (ΔT₁ = 490 ms) allowed us to robustly detect the V1/V2 border in vivo using heavily T₁‐weighted MRI. Furthermore, the dorso‐medial (DM) and middle‐temporal (MT) areas of the visual pathway could be identified by their T₁‐weighted enhancement. We showed by comparison to histological sections stained for cytochrome oxidase (CO) activity that the extent of V1 is accurately identified throughout the visual cortex by manganese‐enhanced MRI (MEMRI). This provides a means of visualizing functional cortical regions in vivo and could be used in longitudinal studies of phenomena such as cortical plasticity, and for non‐destructive localization of cortical regions to guide in the implementation of functional techniques. Published in 2009 by John Wiley & Sons, Ltd.     

Sensitive MRI detection of internalized T1 contrast agents using magnetization transfer contrast

This work addresses the possibility of using Magnetization Transfer Contrast (MTC) for an improved MRI detection of T₁ relaxation agents. The need to improve the detection threshold of MRI agents is particularly stringent when the contrast agents failed to accumulate to the proper extent in targeting procedures. The herein reported approach is based on the T₁ dependence of MT contrast. It has been assessed that MT contrast can allow the detection of a Gd‐containing agent at a lower detection threshold than the one accessible by acquiring T_1W images. Measurements have been carried out either in TS/A cells or in vivo in a syngeneic murine breast cancer model. The reported data showed that in cellular experiments the MTC method displays a better sensitivity with respect to the common T_1W experiments. In particular, the reached detection threshold allowed the visualization of samples containing only 2% of Gd‐labeled cells diluted in unlabeled cells. In vivo experiments displayed a more diversified scheme. In particular, the tumor region showed two distinct behaviors accordingly with the localization of the imaging probe. The probe located in the tumor core could be detected to the same extent either by T_1w or MTC contrast. Conversely, the agent located in the tumor rim was detected with a larger sensitivity by the MTC method herein described. Copyright © 2015 John Wiley & Sons, Ltd.     

Orotracheal manganese‐enhanced MRI (MEMRI): An effective approach for lung tumor detection

Lung cancer is a primary cause of cancer deaths worldwide. Timely detection of this pathology is necessary to delay or interrupt lung cancer progression, ultimately resulting in a possible better prognosis for the patient. In this context, magnetic resonance imaging (MRI) is especially promising. Ultra‐short echo time (UTE) MRI sequences, in combination with gadolinium‐based contrast agents, have indeed shown to be especially adapted to the detection of lung neoplastic lesions at submillimeter precision. Manganese‐enhanced MRI (MEMRI) increasingly appears to be a possible effective alternative to gadolinium‐enhanced MRI. In this work, we investigated whether low‐dose MEMRI can effectively target non‐small‐cell lung cancer in rodents, whilst minimizing the potential toxic effect of manganese. Both systemic and orotracheal administration modalities allowed the identification of tumors of submillimeter size, as confirmed by bioluminescence imaging and histology. Equivalent tumor signal enhancements and contrast‐to‐noise ratios were observed with orotracheal administration using 20 times lower doses compared with the more conventional systemic route. This finding is of crucial importance as it supports the observation that higher performances of contrast agents can be obtained using an orotracheal administration route when targeting lung diseases. As a consequence, lower concentrations of contrast media can be employed, reducing the dose and potential safety issues. The non‐detectable accumulation of ionic manganese in the brain and liver following orotracheal administration observed in vivo is extremely encouraging with regard to the safety of the orotracheal protocol with low‐dose Mn²⁺ administration. To our knowledge, this is the first time that a study has clearly allowed the high‐precision detection of lung tumor and its contours via the synergic employment of a strongly T₁‐weighted MRI UTE sequence and ionic manganese, an inexpensive contrast agent. Overall, these results support the growing interest in drug and contrast agent delivery via the airways to target and diagnose several diseases of the lungs.     

Water signal attenuation by D2O infusion as a novel contrast mechanism for 1H perfusion MRI

Deuterium oxide (D₂O), which is commercially available and nonradioactive, was proposed as a perfusion tracer before the clinical usage of conventional gadolinium‐based MRI contrast agents. However, the sensitivity of direct deuterium detection is the major challenge for its application. In this study, we propose a contrast‐enhanced strategy to indirectly trace administered D₂O by monitoring the signal attenuation of ¹H MRI. Experiments on D₂O concentration phantoms and in vivo rat brains were conducted to prove the concept of the proposed contrast mechanism. An average maximum signal drop ratio of 5.25 ± 0.91% was detected on ¹H MR images of rat brains with 2 mL of D₂O administered per 100 g of body weight. As a diffusible tracer for perfusion, D₂O infusion is a practicable method for the assessment of tissue perfusion and has the potential to provide different information from gadolinium‐based contrast agents, which have limited permeability for blood vessels. Furthermore, the observed negative relaxivities of D₂O reveal the ¹H–D exchange effect. Therefore, applications of perfusion MRI with D₂O as a contrast agent are worthy of further investigation. Copyright © 2013 John Wiley & Sons, Ltd.     

In vivo chlorine‐35, sodium‐23 and proton magnetic resonance imaging of the rat brain

In this study we demonstrate the feasibility of combined chlorine‐35, sodium‐23 and proton magnetic resonance imaging (MRI) at 9.4 Tesla, and present the first in vivo chlorine‐35 images obtained by means of MRI. With the experimental setup used in this study all measurements could be done in one session without changing the setup or moving the subject. The multinuclear measurement requires a total measurement time of 2 h and provides morphological (protons) and physiological (sodium‐23, chlorine‐35) information in one scanning session. Chlorine‐35, sodium‐23 and high resolution proton images were acquired from a phantom, a healthy rat and from a rat displaying a focal cerebral infarction. Compared to the healthy tissue a signal enhancement of a factor of 2.2 ± 0.2 in the chlorine‐35 and a factor of 2.9 ± 0.6 in the sodium‐23 images is observed in the areas of infarction. Exemplary unlocalized measurement of the in vivo longitudinal and transversal relaxation time of chlorine‐35 in a healthy rat showed multi‐exponential behaviour. A biexponential fit revealed a fast and a slow relaxing component with T_1,a = (1.7 ± 0.4) ms, T_1,b = (25.1 ± 1.4) ms, amplitudes of A = 0.26 ± 0.02, (1–A) = 0.74 ± 0.02 and T_2,a = (1.3 ± 0.1) ms, T_2,b = (11.8 ± 1.1) ms, A = 0.64 ± 0.02, (1–A) = 0.36 ± 0.02. Combined proton, sodium‐23 and chlorine‐35 MRI may provide a new approach for non‐invasive studies of ionic regulatory processes under physiological and pathological conditions in vivo. Copyright © 2010 John Wiley & Sons, Ltd.     

Characterization of a novel MR‐detectable nanoantioxidant that mitigates the recall immune response

In many human diseases, the presence of inflammation is associated with an increase in the level of reactive oxygen species (ROS). The resulting state of oxidative stress is highly detrimental and can initiate a cascade of events that ultimately lead to cell death. Thus, many therapeutic attempts have been focused on either modulating the immune system to lower inflammation or reducing the damaging caused by ROS. Berlin et al. reported the development of a novel nanoantioxidant known as poly(ethylene glycol)‐functionalized‐hydrophilic carbon clusters (PEG‐HCCs). They showed that PEG‐HCCs could be targeted to cancer cells, utilized as a drug delivery vector, and can even be visualized ex vivo. Our work here furthers this work and characterizes Gd‐DTPA conjugated PEG‐HCCs and explores the potential for in vivo tracking of T cells in live mice. We utilized a mouse model of delayed‐type hypersensitivity (DTH) to assess the immunomodulatory effects of PEG‐HCCs. The T₁‐agent Gd‐DTPA was then conjugated to the PEG‐HCCs and T₁ measurements, and T₁‐weighted MRI of the modified PEG‐HCCs was done to assess their relaxivity. We then assessed if PEG‐HCCs could be visualized both ex vivo and in vivo within the mouse lymph node and spleen. Mice treated with PEG‐HCCs showed significant improvements in the DTH assay as compared to the vehicle (saline)‐treated control. Flow cytometry demonstrated that splenic T cells are capable of internalizing PEG‐HCCs whereas fluorescent immunohistochemistry showed that PEG‐HCCs are detectable within the cortex of lymph nodes. Finally, our nanoantioxidants can be visualized in vivo within the lymph nodes and spleen of a mouse after addition of the Gd‐DTPA. PEG‐HCCs are internalized by T cells in the spleen and can reduce inflammation by suppression of a recall immune response. PEG‐HCCs can be modified to allow for both in vitro and in vivo visualization using MRI. © 2016 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd.     

Simultaneous evaluation of vascular morphology,blood volume and transvascular permeability using SPION‐based,dual‐contrast MRI: imaging optimization and feasibility test

Exploiting ultrashort‐T_E (UTE) MRI, T₁‐weighted positive contrast can be obtained from superparamagnetic iron oxide nanoparticles (SPIONs), which are widely used as a robust T₂‐weighted, negative contrast agent on conventional MR images. Our study was designed (a) to optimize the dual‐contrast MRI method using SPIONs and (b) to validate the feasibility of simultaneously evaluating the vascular morphology, blood volume and transvascular permeability using the dual‐contrast effect of SPIONs. All studies were conducted using 3 T MRI. According to numerical simulation, 0.15 mM was the optimal blood SPION concentration for visualizing the positive contrast effect using UTE MRI (T_E = 0.09 ms), and a flip angle of 40° could provide sufficient SPION‐induced enhancement and acceptable measurement noise for UTE MR angiography. A pharmacokinetic study showed that this concentration can be steadily maintained from 30 to 360 min after the injection of 29 mg/kg of SPIONs. An in vivo study using these settings displayed image quality and CNR of SPION‐enhanced UTE MR angiography (image quality score 3.5; CNR 146) comparable to those of the conventional, Gd‐enhanced method (image quality score 3.8; CNR 148) (p > 0.05). Using dual‐contrast MR images obtained from SPION‐enhanced UTE and conventional spin‐ and gradient‐echo methods, the transvascular permeability (water exchange index 1.76–1.77), cerebral blood volume (2.58–2.60%) and vessel caliber index (3.06–3.10) could be consistently quantified (coefficient of variation less than 9.6%; Bland–Altman 95% limits of agreement 0.886–1.111) and were similar to the literature values. Therefore, using the optimized setting of combined SPION‐based MRI techniques, the vascular morphology, blood volume and transvascular permeability can be comprehensively evaluated during a single session of MR examination. Copyright © 2015 John Wiley & Sons, Ltd.     

Monitoring dynamic alterations in calcium homeostasis by T1‐mapping manganese‐enhanced MRI (MEMRI) in the early stage of small intestinal ischemia–reperfusion injury

Manganese‐enhanced MRI studies have proven to be useful in monitoring physiological activities associated with calcium ions (Ca²⁺) due to the paramagnetic property of the manganese ion (Mn²⁺), which makes it an excellent probe of Ca²⁺. In this study, we developed a method in which a Mn²⁺‐enhanced T₁‐map MRI could enable the monitoring of Ca²⁺ influx during the early stages of intestinal ischemia–reperfusion (I/R) injury. The Mn²⁺ infusion protocol was optimized by obtaining dose‐dependent and time‐course wash‐out curves using a Mn²⁺‐enhanced T₁‐map MRI of rabbit abdomens following an intravenous infusion of 50 mmol/l MnCl₂ (5–10 nmol/g body weight (BW)). In the rabbit model of intestinal I/R injury, T₁ values were derived from the T₁ maps in the intestinal wall region and revealed a relationship between the dose of the infused MnCl₂ and the intestinal wall relaxation time. Significant Mn²⁺ clearance was also observed over time in control animals after the infusion of Mn²⁺ at a dose of 10 nmol/g BW. This technique was also shown to be sensitive enough to monitor variations in calcium ion homeostasis in vivo after small intestinal I/R injury. The T₁ values of the intestinal I/R group were significantly lower (P < 0.05) than that of the control group at 5, 10, and 15 min after Mn²⁺ infusion. Our data suggest that MnCl₂ has the potential to be an MRI contrast agent that can be effectively used to monitor changes in intracellular Ca²⁺ homeostasis during the early stages of intestinal I/R injury. Copyright © 2015 John Wiley & Sons, Ltd.     

Oxygen‐induced frequency shifts in hyperoxia: a significant component of BOLD signal

In comparison to the well‐documented significance of intravascular deoxyhemoglobin (deoxyHgb), the effects of dissolved oxygen on the blood‐oxygen‐level‐dependent (BOLD) signal have not been widely reported. Based on the fact that the prolonged inspiration of high oxygen fraction gas can result in up to a sixfold increase of the baseline tissue oxygenation, the current study focused on the influence of dissolved oxygen on the BOLD signal during hyperoxia. As results, our in vitro study revealed that the r₁ and r₂ (relaxivities) of the oxygen‐treated serum were 0.22 mM^?1 · s^?1and 0.19 mM^?1 · s^?1_, respectively. In an in vivo experiment, hyperoxic respiration induced negative BOLD contrast (i.e. signal decrease) in 18–42% of measured brain regions, voxels with accompanying significant decreases in both the T₂^* (?12.1% to ?19.4%) and T₁ (?5.8% to ?3.3%) relaxation times. In contrast, the T₂^* relaxation time significantly increased (11.2% to 14.0%) for the voxels displaying positive BOLD contrast (in 41–50% of the measured brain), which reflected a hyperoxygenation‐induced reduction in tissue deoxyHgb concentration. These data imply that hyperoxia‐driven BOLD signal changes are primarily determined by the counteracting effects of extravascular oxygen and intravascular deoxyHgb. Oxygen‐induced magnetic susceptibility was further demonstrated by the study of 1 min hypoxia, which induced BOLD signal changes opposite to those under hyperoxia. Vasoconstriction was more common in voxels with negative BOLD contrast than in voxels with positive contrast (% change of blood volume, ?9.8% to ?12.8% versus 2.0% to 2.2%), which further suggests that negative BOLD contrast is mainly evoked by an increase in extravascular oxygen concentration. Conclusively, frequency shifts, which are induced by the accumulation of oxygen molecules and associated magnetic field inhomogeneity, are a significant source of the negative BOLD contrast during hyperoxia. Copyright © 2014 John Wiley & Sons, Ltd.     

Characterization of a rat orthotopic pancreatic head tumor model using three‐dimensional and quantitative multi‐parametric MRI

The purpose of this study was to investigate the reliability of 3D isotropic MRI and quantitative multi‐parametric MRI characterization on an orthotopic pancreatic head tumor model in rats. 3D isotropic T₂‐weighted MRI was performed as a routine for tumor longitudinal follow‐up and volume estimation. Common bile duct diameter was measured from 3D multiplanar reconstruction. Quantitative multi‐parametric measurements including pixel‐wise T₂, T₁ relaxivity, apparent diffusion coefficient (ADC) and apparent diffusion kurtosis mapping were performed twice throughout tumor growth. Semi‐quantitative and quantitative analyses based on an extended Tofts model were applied to region‐of‐interest‐based dynamic contrast‐enhanced imaging, followed by contrast ratio measurement on standard contrast‐enhanced imaging. Moreover, low‐level texture‐based analysis was inspected for T₂, T₁, ADC and contrast ratio measurements. Results indicated that multi‐parametric MRI showed good reproducibility for tumor characterization; the measurements were not affected by tumor growth. Tumor growth was further confirmed with histology examinations. To conclude, state‐of‐the‐art clinical MRI techniques were translated to this preclinical tumor model with high reliability, and have paved the way for translational oncology studies on this tumor model.     

In vivo MR guided boiling histotripsy in a mouse tumor model evaluated by MRI and histopathology

Boiling histotripsy (BH) is a new high intensity focused ultrasound (HIFU) ablation technique to mechanically fragmentize soft tissue into submicrometer fragments. So far, ultrasound has been used for BH treatment guidance and evaluation. The in vivo histopathological effects of this treatment are largely unknown. Here, we report on an MR guided BH method to treat subcutaneous tumors in a mouse model. The treatment effects of BH were evaluated one hour and four days later with MRI and histopathology, and compared with the effects of thermal HIFU (T‐HIFU). The lesions caused by BH were easily detected with T₂w imaging as a hyper‐intense signal area with a hypo‐intense rim. Histopathological evaluation showed that the targeted tissue was completely disintegrated and that a narrow transition zone (<200 µm) containing many apoptotic cells was present between disintegrated and vital tumor tissue. A high level of agreement was found between T₂w imaging and H&E stained sections, making T₂w imaging a suitable method for treatment evaluation during or directly after BH. After T‐HIFU, contrast enhanced imaging was required for adequate detection of the ablation zone. On histopathology, an ablation zone with concentric layers was seen after T‐HIFU. In line with histopathology, contrast enhanced MRI revealed that after BH or T‐HIFU perfusion within the lesion was absent, while after BH in the transition zone some micro‐hemorrhaging appeared. Four days after BH, the transition zone with apoptotic cells was histologically no longer detectable, corresponding to the absence of a hypo‐intense rim around the lesion in T₂w images. This study demonstrates the first results of in vivo BH on mouse tumor using MRI for treatment guidance and evaluation and opens the way for more detailed investigation of the in vivo effects of BH. Copyright © 2016 John Wiley & Sons, Ltd.     

MEMRI and tumors: a method for the evaluation of the contribution of Mn(II) ions in the extracellular compartment

The purpose of the work was to set‐up a simple method to evaluate the contribution of Mn²⁺ ions in the intra‐ and extracellular tumor compartments in a MEMRI experiment. This task has been tackled by “silencing” the relaxation enhancement arising from Mn²⁺ ions in the extracellular space. In vitro relaxometric measurements allowed assessment of the sequestering activity of DO2A (1,4,7,10‐tetraazacyclododecane‐1,7‐diacetic acid) towards Mn²⁺ ions, as the addition of Ca‐DO2A to a solution of MnCl₂ causes a drop of relaxivity upon the formation of the highly stable and low‐relaxivity Mn‐DO2A. It has been proved that the sequestering ability of DO2A towards Mn²⁺ ions is also fully effective in the presence of serum albumin. Moreover, it has been shown that Mn‐DO2A does not enter cell membranes, nor does the presence of Ca‐DO2A in the extracellular space prompt migration of Mn ions from the intracellular compartment. On this basis the in vivo, instantaneous, drop in SE% (percent signal enhancement) in T₁‐weighted images is taken as evidence of the sequestration of extracellular Mn²⁺ ions upon addition of Ca‐DO2A. By applying the method to B16F10 tumor bearing mice, T₁ decrease is readily detected in the tumor region, whereas a negligible change in SE% is observed in kidneys, liver and muscle. The relaxometric MRI results have been validated by ICP‐MS measurements. Copyright © 2015 John Wiley & Sons, Ltd.     

Visualization of calcium phosphate cement in teeth by zero echo time 1H MRI at high field

¹H magnetic resonance imaging (MRI) by a zero echo time (ZTE) sequence is an excellent method to image teeth. Calcium phosphate cement (CPC) materials are applied in the restoration of tooth lesions, but it has not yet been investigated whether they can be detected by computed tomography (CT) or MRI. The aim of this study was to optimize high‐field ZTE imaging to enable the visualization of a new CPC formulation implanted in teeth and to apply this in the assessment of its decomposition in vivo. CPC was implanted in three human and three goat teeth ex vivo and in three goat teeth in vivo. An ultrashort echo time (UTE) sequence with multiple flip angles and echo times was applied at 11.7 T to measure T₁ and T₂* values of CPC, enamel and dentin. Teeth with CPC were imaged with an optimized ZTE sequence. Goat teeth implanted with CPC in vivo were imaged after 7 weeks ex vivo. T₂* relaxation of implanted CPC, dentin and enamel was better fitted by a model assuming a Gaussian rather than a Lorentzian distribution. For CPC and human enamel and dentin, the average T₂* values were 273 ± 19, 562 ± 221 and 476 ± 147 μs, respectively, the average T₂ values were 1234 ± 27, 963 ± 151 and 577 ± 41 μs, respectively, and the average T₁ values were 1065 ± 45, 972 ± 40 and 903 ± 7 ms, respectively. In ZTE images, CPC had a higher signal‐to‐noise‐ratio than dentin and enamel because of the higher water content. Seven weeks after in vivo implantation, the CPC‐filled lesions showed less homogeneous structures, a lower T₁ value and T₂* separated into two components. MRI by ZTE provides excellent contrast for CPC in teeth and allows its decomposition to be followed.     

Imaging and quantification of metastatic melanoma cells in lymph nodes with a ferritin MR reporter in living mice

Cellular MRI with a reporter gene offers the opportunity to track small numbers of tumor cells and to study metastatic processes in their earliest developmental stages in the target organs of interest. This study demonstrates the feasibility of using the MR reporter ferritin for the noninvasive imaging and quantification of metastatic melanoma cells in the lymph nodes (LNs) of living mice. A B16F10 murine melanoma cell line expressing human ferritin heavy chain (hFTH) and green fluorescent protein (GFP) was constructed to allow the detection of cells by MRI and fluorescence imaging. Stable overexpression of hFTH and GFP in B16F10 murine melanoma cells was feasible and showed no cellular toxicity. In addition, hFTH cells were detectable by 9.4‐T MRI in vitro and in vivo, yielding significant changes in T₂* relative to control cells. In BALB/c nude mice, the presence of hFTH‐ and GFP‐expressing metastatic melanoma cells in deep‐seated axillary LNs was demonstrated as areas of low T₂* on MRI, but the same LNs were not visible by fluorescence imaging because the light was unable to penetrate the tissue. Furthermore, the metastatic volume of each LN, which was assessed by cumulative histogram analysis of the T₂* MRI data, correlated well with tumor burden, which was determined by histology (r = ?0.8773, p = 0.0001). This study is the first to use MRI and an MR reporter gene for both the visualization and quantification of metastatic cancer cells in LNs. Copyright © 2011 John Wiley & Sons, Ltd.     

Preclinical MR fingerprinting (MRF) at 7 T: effective quantitative imaging for rodent disease models

High‐field preclinical MRI scanners are now commonly used to quantitatively assess disease status and the efficacy of novel therapies in a wide variety of rodent models. Unfortunately, conventional MRI methods are highly susceptible to respiratory and cardiac motion artifacts resulting in potentially inaccurate and misleading data. We have developed an initial preclinical 7.0‐T MRI implementation of the highly novel MR fingerprinting (MRF) methodology which has been described previously for clinical imaging applications. The MRF technology combines a priori variation in the MRI acquisition parameters with dictionary‐based matching of acquired signal evolution profiles to simultaneously generate quantitative maps of T₁ and T₂ relaxation times and proton density. This preclinical MRF acquisition was constructed from a fast imaging with steady‐state free precession (FISP) MRI pulse sequence to acquire 600 MRF images with both evolving T₁ and T₂ weighting in approximately 30 min. This initial high‐field preclinical MRF investigation demonstrated reproducible and differentiated estimates of in vitro phantoms with different relaxation times. In vivo preclinical MRF results in mouse kidneys and brain tumor models demonstrated an inherent resistance to respiratory motion artifacts as well as sensitivity to known pathology. These results suggest that MRF methodology may offer the opportunity for the quantification of numerous MRI parameters for a wide variety of preclinical imaging applications. Copyright © 2015 John Wiley & Sons, Ltd.