Small Animal Imaging Research Articles

Electroacupuncture-driven endogenous circulating serum exosomes as a potential therapeutic strategy for sepsis

BackgroundSepsis poses a serious threat to human life and health, with limited options for current clinical treatments. Acupuncture plays an active role in treating sepsis. However, previous studies have focused on the neuromodulatory effect of acupuncture, neglecting its network modulatory effect. Exosomes, as a new way of intercellular communication, may play an important role in transmitting acupuncture information. This paper explores the possibility of electroacupuncture-driven endogenous circulating serum exosomes and their carried miRNAs as a potential treatment for sepsis.MethodsThe sepsis mouse model was established by intraperitoneal injection of lipopolysaccharide (LPS) (12 mg/kg, 24 mg/kg), and EA (continuous wave, 10 Hz, intensity 5) or intraperitoneal injection of Acupuncture Exosomes (Acu-exo) were performed before the model establishment. The therapeutic effect was evaluated by survival rate, ELISA, H&E staining and lung wet/dry weight ration (W/D). In vivo imaging of small animals was used to observe the accumulation of Acu-exo in various organs of sepsis mice. LPS was used to induce macrophages in cell experiments, and the effect of Acu-exo on macrophage inflammatory cytokines was observed. In addition, The miRNA sequencing method was further used to detect the serum exosomes of normal and EA-treated mice, and combined with network biology analysis methods to screen possible key targets.ResultsEA and Acu-exo reduced the W/D and lung tissue damage in sepsis mice, down-regulated the expression of serum inflammatory cytokines TNF-α and IL-6, and increased the survival rate of sepsis mice. In vivo imaging of small animals found that Acu-exo were accumulated in the lungs of sepsis mice. Cell experiments proved that Acu-exo down-regulated the expression of inflammatory cytokines TNF-α, IL-6 and IL-1β to alleviate the inflammatory response induced by LPS in macrophages. MiRNA sequencing revealed 53 differentially expressed miRNAs, and network biology analysis revealed the key targets of Acu-exo in sepsis treatment.ConclusionElectroacupuncture-driven endogenous circulating serum exosomes and their carried miRNAs may be a potential treatment for sepsis.

Broadband transparent ultrasound transducer with polymethyl methacrylate as matching layer for in vivo photoacoustic microscopy

Photoacoustic imaging (PAI) uniquely combines optics and ultrasound, presenting a promising role in biomedical imaging as a non-invasive and label-free imaging technology. As the traditional opaque ultrasound (US) transducers could hinder the transportation of the excitation light and limit the performance of PAI system, piezoelectric transparent ultrasonic transducers (TUTs) with indium tin oxide (ITO) electrodes have been developed to allow light transmission through the transducer and illuminate the sample directly. Nevertheless, without having transparent matching materials with appropriate properties, the bandwidth of those TUTs was generally narrow. In this work, we propose to employ polymethyl methacrylate (PMMA) as the matching layer material to improve the bandwidth of lithium niobate (LN)-based TUTs. The effects of PMMA matching layer on the performance of TUTs have been systematically studied. With the optimized PMMA matching layer, the very wide bandwidth of > 50 % could be achieved for the TUTs even with different transducer frequencies, leading to the great enhancement of axial resolution when compared to the similar reported work. In addition, the imaging performance of the developed TUT prototype has been evaluated in a PAI system and demonstrated by both phantom and in vivo small animal imaging.

Long-circulating doxorubicin and Schizandrin A liposome with drug-resistant liver cancer activity: in vitro and in vivo evaluation

Co-loading doxorubicin (DOX) and Schizandrin A (SchA) long-circulating liposome (SchA-DOX-Lip) have been confirmed to have good antitumor activity in vitro. However, in vivo pharmacodynamics, targeting, safety, and mechanism of action of SchA-DOX-Lip still need to be further verified. We investigated the tumor inhibition effect, targeting, safety evaluation, and regulation of tumor apoptosis-related proteins of the SchA-DOX-Lip. MTT assay was used to investigate the inhibitory effect of SchA-DOX-Lip on CBRH7919 cells. The drug uptake of CBRH7919 cells was observed by inverted fluorescence microscope. The tumor-bearing nude mice models of CBRH7919 were established, and the anti-tumor effect of SchA-DOX-Lip in vivo was evaluated by tumor biological observation, H&E staining, and TUNEL staining. The distribution and targeting of SchA-DOX-Lip in nude mice models were investigated by small animal imaging and tissue distribution experiment of CBRH7919. The biosafety of SchA-DOX-Lip was evaluated by blood routine parameters, biochemical indexes, and H&E staining. The expression of tumor-associated apoptotic proteins (Bcl-2, Bax, and Caspase-3) was detected by immunohistochemistry anvd western blotting. The results showed that SchA-DOX-Lip had cytotoxicity to CBRH7919 cells which effectively inhibited the proliferation of CBRH7919 cells, improved the uptake of drugs by CBRH7919 cells and the targeting effect of drugs on tumor site. H&E staining and biochemical detection results showed that SchA-DOX-Lip had high biosafety and did not cause serious damage to normal tissues. Western-blotting and TUNEL staining results showed that SchA-DOX-Lip could improve the regulatory effect of drugs on tumor apoptosis proteins. It was demonstrated that SchA-DOX-Lip had high safety and strong tumor inhibition effects, providing a new method for the clinical treatment of hepatocellular carcinoma (HCC).

Short-wave infrared fluorescence imaging of near-infrared dyes with robust end-tail emission using a small-animal imaging device.

Commercially available near-infrared (NIR) dyes, including indocyanine green (ICG), display an end-tail of the fluorescence emission spectrum detectable in the short-wave infrared (SWIR) window. Imaging methods based on the second NIR spectral region (1,000-1,700 nm) are gaining interest within the biomedical imaging community due to minimal autofluorescence and scattering, allowing higher spatial resolution and depth sensitivity. Using a SWIR fluorescence imaging device, the properties of ICG vs. heptamethine cyanine dyes with emission >800 nm were evaluated using tissue-simulating phantoms and animal experiments. In this study, we tested the hypothesis that an increased rigidity of the heptamethine chain may increase the SWIR imaging performance due to the bathochromic shift of the emission spectrum. Fluorescence SWIR imaging of capillary plastic tubes filled with dyes was followed by experiments on healthy animals in which a time series of fluorescence hindlimb images were analyzed. Our findings suggest that higher spatial resolution can be achieved even at greater depths (>5 mm) or longer wavelengths (>1,100 nm), in both tissue phantoms and animals, opening the possibility to translate the SWIR prototype toward clinical application.

Whole mount of adult ear skin as a model to study vascular malformations.

Genetic analysis in human patients has linked mutations in PIK3CA, the catalytic subunit of PI-3'Kinase, to sporadic incidences of vascular malformations. We have developed a mouse model with inducible and endothelial-specific expression of PIK3CAH1047R , resulting in the development of vascular malformations. Systemic induction of this mutation in adult mice results in rapid lethality, limiting our ability to track and study these lesions; therefore, we developed a topical and local induction protocol using the active metabolite of tamoxifen, 4OH-T, on the ear skin of adults. This approach allows us to successfully model the human disease in a mature and established vascular bed and track the development of vascular malformations. To validate the utility of this model, we applied a topical rapamycin ointment, as rapamycin is therapeutically beneficial to patients in clinical trials. We found that the induced ear lesions showed significant attenuation after treatment, which was easily quantified. These data collectively provide evidence of a new model to study vascular malformations in adult tissues, which should be particularly useful in environments lacking specialized small-animal imaging facilities.

Learning spatially variant degradation for unsupervised blind photoacoustic tomography image restoration

Photoacoustic tomography (PAT) images contain inherent distortions due to the imaging system and heterogeneous tissue properties. Improving image quality requires the removal of these system distortions. While model-based approaches and data-driven techniques have been proposed for PAT image restoration, achieving accurate and robust image recovery remains challenging. Recently, deep-learning-based image deconvolution approaches have shown promise for image recovery. However, PAT imaging presents unique challenges, including spatially varying resolution and the absence of ground truth data. Consequently, there is a pressing need for a novel learning strategy specifically tailored for PAT imaging. Herein, we propose a configurable network model named Deep hybrid Image-PSF Prior (DIPP) that builds upon the physical image degradation model of PAT. DIPP is an unsupervised and deeply learned network model that aims to extract the ideal PAT image from complex system degradation. Our DIPP framework captures the degraded information solely from the acquired PAT image, without relying on ground truth or labeled data for network training. Additionally, we can incorporate the experimentally measured Point Spread Functions (PSFs) of the specific PAT system as a reference to further enhance performance. To evaluate the algorithm’s effectiveness in addressing multiple degradations in PAT, we conduct extensive experiments using simulation images, publicly available datasets, phantom images, and in vivo small animal imaging data. Comparative analyses with classical analytical methods and state-of-the-art deep learning models demonstrate that our DIPP approach achieves significantly improved restoration results in terms of image details and contrast.

Automated Synthesis and Preclinical Evaluation of Optimized Integrin α6-Targeted Positron Emission Tomography Imaging of Pancreatic Cancer.

Integrin α6 has been considered a promising biomarker, is overexpressed in many tumors, and plays a vital role in tumor formation, recurrence, and metastasis. In this study, we identified a novel high-affinity integrin α6-targeted peptide named RD2 (Arg-Trp-Tyr-Asp-PEG4)2-Lys-Lys and developed a 18F-radiolabeled peptide tracer ([18F]-AlF-NOTA-RD2) and evaluated its potential application in positron emission tomography (PET) imaging of pancreatic cancer. [18F]-AlF-NOTA-RD2 was produced using GMP (Good Manufacturing Practice of Medical Products)-compliant automatic radiosynthesis on a single GE FASTLab2 cassette-type synthesis module. The stability of [18F]-AlF-NOTA-RD2 was analyzed in phosphate-buffered saline (PBS) and fetal bovine serum (FBS). The cell uptake assay of the tracer was assessed using PANC-1 cells. In addition, small-animal PET imaging and biodistribution studies of [18F]-AlF-NOTA-RD2 were performed in pancreatic cancer subcutaneous tumor-bearing mice. The PET tracer [18F]-AlF-NOTA-RD2 was obtained with a radiochemical yield of 23.7 ± 4.7%, radiochemical purity of >99%, and molar activity of 165.7 ± 59.1 GBq/μmol. [18F]-AlF-NOTA-RD2 exhibited good in vitro stability in PBS and FBS. LogP octanol water value for the tracer was -2.28 ± 0.05 (n = 3). The binding affinity of RD2 to the integrin α6 protein (Kd = 0.13 ± 3.65 μM, n = 3) was significantly higher than that of the RWY (CRWYDENAC) (Kd = 6.97 ± 1.44 μM, n = 3). Small-animal PET imaging and biodistribution also revealed that [18F]-AlF-NOTA-RD2 displayed rapid and good tumor uptake and lower liver background uptake in PANC-1 tumor-bearing mice. [18F]-AlF-NOTA-RD2 showed significant radioactivity accumulation in tumors and was successfully blocked by NOTA-RD2. Compared with [18F]-FDG, [18F]-AlF-NOTA-RD2 PET imaging and biodistribution studies in PANC-1 xenograft tumor-bearing mice confirmed a good tumor-to-muscle ratio (8.69 ± 2.03 vs 1.41 ± 0.23, respectively) at 0.5 h and (2.99 ± 3.02 vs 1.43 ± 0.17, respectively) at 1 h post injection. Autoradiography of human pancreatic cancer tumor tissues further confirmed high accumulation of [18F]-AlF-NOTA-RD2. In summary, we developed an optimized integrin α6-targeted imaging tracer and obtained high radioactivity products with a cassette-type synthesis module; moreover, the tracer exhibited good binding affinity with integrin α6 and good target specificity for PANC-1 cells in xenograft pancreatic tumor-bearing mice, demonstrating its promising application as a noninvasive PET radiotracer of integrin α6 expression in pancreatic cancer.

PH/enzyme dual sensitive Gegenqinlian pellets coated with Bletilla striata polysaccharide membranes for the treatment of ulcerative colitis

Gegen Qinlian Decoction, derived from Zhang Zhongjing's Treatise on Typhoid Fever, has been widely used in the treatment of various common diseases, frequently-occurring diseases and difficult and complicated diseases, such as ulcerative colitis. In this study, Bletilla striata polysaccharide (BSP) was innovatively used as a film coating material to prepare Gegen Qinlian pellets with dual sensitivity of pH enzyme for the treatment of ulcerative colitis. BSP has the ability to repair the inflamed colon mucosa and can produce synergistic effects, while avoiding the adverse therapeutic effects caused by the early release of drugs from a single pH-sensitive pellets in the small intestine. The prepared pellets have a uniform particle size, good roundness, a particle size range from 0.8 mm to 1.0 mm, and a particle yield is 85.6 %. The results of in vitro release showed that ES-BSP pellets hardly released drugs in the pH range of 1.2–6.8. However, in the colon mimic fluid containing specific enzymes, the drug release was significantly accelerated, demonstrating the sensitivity of the pellets to pH enzymes. In vivo and ex vivo fluorescence imaging of small animals showed that Gegen Qinlian pellets with dual sensitivity of pH enzyme remained longer in the colon compared with pH-sensitive pellets. In vivo pharmacodynamics study showed that the Gegen Qinlian pellets with dual sensitivity of pH enzyme had a better therapeutic effect in the rat model of the ulcerative colon than the commercially available Gegenqinlian pellets in the control group.

Coating 3D-printed bioceramics with histatin promotes adhesion and osteogenesis of stem cells.

Mesenchymal stem cell and 3D printing-based bone tissue engineering present a promising technique to repair large-volume bone defects. Its success is highly dependent on cell attachment, spreading, osteogenic differentiation and in-vivo survival of stem cells on 3D printed scaffolds. In this study, we adopted a human salivary histatin-1 (Hst1) as a cell-targeting strategy to enhance the interactions of human adipose-derived stem cells (hASCs) on 3D printed β-tricalcium phosphate (β-TCP) scaffolds. Fluorescent images showed that Hst1 significantly enhanced the total numbers and surface area of hASCs on both bio-inert glass and 3D printed β-TCP scaffold. In addition, Hst1 was associated with significantly higher proliferation, alkaline phosphate staining on 3D printed β-TCP scaffolds than the control. Subsequently, the small animal imaging showed that the fluorescent densities of the Hst1-treated hASC/3D printed TCP constructs were always significantly higher than those of the control. The specific inhibitors of ERK and p38 but not JNK signaling significantly inhibited the adhesion of hASCs. Hst1 promoted total fluorescent intensities of talin, vinculin and paxillin per cell. In conclusion, Hst1 could significantly promote the adhesion, spreading, osteogenic differentiation and in-vivo survival of hASCs on 3D printed β-TCP scaffolds, bearing a promising application potential in stem cell/3D printing-based bone tissue engineering.

A Lipid Droplet-Specific NIR Fluorescent Probe with a Large Stokes Shift for In Vivo Visualization of Polarity in Contrast-Induced Acute Kidney Injury.

The research on lipid droplets (LDs) has attracted great attention in the field of biomedical science in recent years. LD malfunction is found to be associated with the development of acute kidney injury (AKI). To monitor this biological process and explain related pathological behavior, the development of excellent LD fluorescent probes with a polarity-sensitive character would provide a desirable strategy. Herein, we designed a new polarity-susceptible fluorescent probe named LD-B with LD targetability, which exhibits very weak fluorescence in highly polar solvents based on the twisted intramolecular charge transfer effect but enhanced fluorescence in low polar environments, enabling us to visualize polarity alteration. The probe LD-B also possesses the merits of intense near-infrared (NIR) emission, good photostability, large Stokes shift, low toxicity, faster metabolic rate, and wash-free ability; thereby, it would contribute to efficient LD fluorescence visualization application. Using LD-B via confocal laser scanning fluorescence imaging and a small-animal imaging system in vivo, we first manifested a prominent rise of LD polarity in contrast-induced AKI (CI-AKI), not only at the cellular level but also in animals in vivo. Furthermore, the in vivo studies suggest that LD-B could accumulate in the kidney. In addition, the normal cell lines (including kidney cells) exhibiting a greater polarity of LDs than the cancer cells have been demonstrated systemically. Altogether, our work presents an effective approach for the medical diagnosis of LDs related to CI-AKI and identification of potential therapeutic markers.

Pharmacokinetics and pharmacodynamic evaluation of hyaluronic acid-modified imatinib-loaded PEGylated liposomes in CD44-positive Gist882 tumor-bearing mice

To develop a PEGylated and CD44-targeted liposomes, enabled by surface coating with hyaluronic acid (HA) via amide bond to improve the efficacy of imatinib mesylate (IM), for tumor-targeted cytoplasmic drug delivery. HA was covalently grafted on DSPE-PEG2000-NH2 polymer. HA-modified or unmodified PEGylated liposomes were prepared with ethanol injection method, and the stability, drug release, and cytotoxicity of these liposomes were studied. Meanwhile, intracellular drug delivery efficiency, antitumor efficacy, and pharmacokinetics were also investigated. Ex vivo fluorescence biodistribution was also detected by small animal imaging. In addition, endocytosis mechanism was also explored HA-coated PEGylated liposomes (137.5 nm ± 10.24) had a negative zeta potential (−29.3 mV ± 5.44) and high drug loading (27.8%, w/w). The liposomes were stable with cumulative drug leakage (<60%) under physiological conditions. Blank liposomes were nontoxic to Gist882 cells, and IM-loaded liposomes had higher cytotoxicity to Gist882 cells. HA-modified PEGylated liposomes were internalized more effectively than non-HA coating via CD44-mediated endocytosis. Besides, the cellular uptake of HA-modified liposomes also partly depends on caveolin-medicated endocytosis and micropinocytosis. In rats, both liposomes produced a prolonged half-life of IM (HA/Lp/IM: 14.97h; Lp/IM: 11.15h) by 3- to 4.5-folds compared with the IM solution (3.61h). HA-decorated PEGylated liposomes encapsulated IM exhibited strong inhibitory effect on tumor growth in Gist882 cell-bearing nude mice and formation of 2D/3D tumor spheroids. The Ki67 immunohistochemistry result was consistent with the above results. IM-loaded PEGylated liposomes modified with HA exerted the excellent anti-tumor effect on tumor-bearing mice and more drugs accumulated into the tumor site.

Immuno-PET of colorectal cancer with a CEA-targeted [68Ga]Ga-nanobody: from bench to bedside.

An accurate diagnosis of colorectal carcinoma (CRC) can assist physicians in developing reasonable therapeutic regimens, thereby significantly improving the patient's prognosis. Carcinoembryonic antigen (CEA)-targeted PET imaging shows great potential for this purpose. Despite showing remarkable abilities to detect primary and metastatic CRC, previously reported CEA-specific antibody radiotracers or pretargeted imaging are not suitable for clinical use due to poor pharmacokinetics and complicated imaging procedures. In contrast, radiolabeled nanobodies exhibit ideal characteristics for PET imaging, for instance, rapid clearance rates and excellent distribution profiles, allowing same-day imaging with sufficient contrast. In this study, we developed a novel CEA-targeted nanobody radiotracer, [68Ga]Ga-HNI01, and assessed its tumor imaging ability and biodistribution profile in preclinical xenografts and patients with primary and metastatic CRC. The novel nanobody HNI01 was acquired by immunizing the llama with CEA proteins. [68Ga]Ga-HNI01 was synthesized by site-specifically conjugating [68Ga]Ga with tris(hydroxypyridinone) (THP). Small-animal PET imaging and biodistribution studies were performed in CEA-overexpressed LS174T and CEA-low-expressed HT-29 tumor models. Following successful preclinical assessment, a phase I study was conducted on 9 patients with primary and metastatic CRC. Study participants received 151.21 ± 25.25MBq of intravenous [68Ga]Ga-HNI01 and underwent PET/CT scans at 1h and 2h post injection. Patients 01-03 also underwent whole-body dynamic PET imaging within 0-40min p.i. All patients underwent [18F]F-FDG PET/CT imaging within 1week after [68Ga]Ga-HNI01 imaging. Tracer distribution, pharmacokinetics, and radiation dosimetry were calculated. [68Ga]Ga-HNI01 was successfully synthesized within 10min under mild conditions, and the radiochemical purity was more than 98% without purification. Micro-PET imaging with [68Ga]Ga-HNI01 revealed clear visualization of LS174T tumors, while signals from HT-29 tumors were significantly lower. Biodistribution studies indicated that uptake of [68Ga]Ga-HNI01 in LS174T and HT-29 was 8.83 ± 3.02%ID/g and 1.81 ± 0.87%ID/g, respectively, at 2h p.i. No adverse events occurred in all clinical participants after the injection of [68Ga]Ga-HNI01. A fast blood clearance and low background uptake were observed, and CRC lesions could be visualized with high contrast as early as 30min after injection. [68Ga]Ga-HNI01 PET could clearly detect metastatic lesions in the liver, lung, and pancreas and showed superior ability in detecting small metastases. A significant accumulation of radioactivity was observed in the kidney, and normal tissues physiologically expressing CEA receptors showed slight uptakes of [68Ga]Ga-HNI01. An interesting finding was that strong uptake of [68Ga]Ga-HNI01 was found in non-malignant colorectal tissues adjacent to the primary tumor in some patients, suggesting abnormal CEA expression in these healthy tissues. [68Ga]Ga-HNI01 is a novel CEA-targeted PET imaging radiotracer with excellent pharmacokinetics and favorable dosimetry profiles. [68Ga]Ga-HNI01 PET is an effective and convenient imaging tool for detecting CRC lesions, particularly for identifying small metastases. Furthermore, its high specificity for CEA in vivo makes it an ideal tool for selecting patients for anti-CEA therapy.

#6744 SELF-ASSEMBLED FISETIN NANOPARTICLES WITH ENHANCED BIOACTIVITIES FOR EFFECTIVE HYPERURICEMIC NEPHROPATHY THERAPY

Abstract Background and Aims The prevalence of hyperuricemia is rising rapidly around the world, and increasing evidence demonstrates that hyperuricemia is the independent risk factor for chronic kidney diseases (CKD) development and progression. Hyperuricemia-induced renal injury, namely hyperuricemic nephropathy (HN), is characterized by urate crystal formation, tubulointerstitial fibrosis and glomerulosclerosis, which would eventually progress into end-stage renal disease (ESRD). Up to now, the mechanism of HN remains unclear and the treatment still needs further exploration. Fisetin is a natural flavanol with potent antioxidative and anti-inflammatory properties and showed therapeutic effects in mice with HN. However, the poor water solubility, rapid metabolism, and low bioavailability of fisetin largely hampered its clinical application. Herein, we reported the simple and efficient preparation of fisetin-EGCG nanoparticles (EG/FIS NPs) based on a solvent-mediated disassembly/reassembly strategy. Method The fisetin nano-formulation (FIS/EG NPs) was prepared based on a general solvent-mediated disassembly/reassembly strategy. The physicochemical properties of FIS/EG NPs including morphology, specific surface area and pore size distribution, drug encapsulation rate and loading rate, intracellular distribution were characterized. The potential toxic effects of FIS/EG NPs on RAW264.7 and TCMK-1 cells were investigated by CCK-8. Meanwhile, the anti-oxidative and anti-inflammatory effects of FIS/EG NPs were detected in vivo and in vitro. In vivo small animal imaging was employed to assess the kidney accumulation of FIS/EG NPs. And finally, HN was induced to measure the effect of FIS/EG NPs in mice and PAS staining, Masson staining, RT-qPCR were used to explore underlying mechanisms. Results EG/FIS NPs with stable water dispersion was prepared by using a general solvent-mediated disassembly/reassembly strategy. EG/FIS NPs contains both features of fisetin and EG NPs, and displayed more potent free radical scavenging ability than fisetin and EG NPs. Meanwhile, it was found that both RAW264.7 and TCMK-1 cells were able to uptake EG/FIS NPs and no proliferation toxicity was observed in these two cell types after incubation with various concentrations of EG/FIS NPs. By in vivo and in vitro experiments, fisetin and EG NPs were shown to have synergistic effects in inhibiting LPS-stimulated NO production after encapsulation. Moreover, fluorescence imaging revealed that EG/FIS NPs preferentially accumulated in the injured kidneys of HN mice. Finally, it was observed that EG/FIS NPs exhibited enhanced therapeutic efficiency against HN due to the combined antioxidative, anti-inflammatory, and antifibrotic activities of fisetin and EG NPs Conclusion Collectively, these results suggested that EGCG-based nanocarriers might be a novel strategy for the development of therapeutic drugs for HN.

Stretchable receive coil for 7T small animal MRI

Receive coils used in small animal MRI are rigid, inflexible surface loops that do not conform to the anatomy being imaged. The recent trend toward design of stretchable coils that are tailored to fit any anatomical curvature has been focused on human imaging. This work demonstrates the application of stretchable coils for small animal imaging at 7T. A stretchable coil measuring 3.5 × 3.5 cm was developed for acquisition of rat brain and spine images. The SNR maps of the stretchable coil were compared with those of a traditional flexible PCB coil and a commercial surface coil. Stretch and conformance testing of the coil was performed. Ex vivo images of rat brain and spine from the stretchable a coil was acquired using T1 FLASH and T2 Turbo RARE sequences. The axial phantom SNR maps showed that the stretchable coil provided 48.5% and 42.8% higher SNR than the commercial coil for T1-w and T2-w images within the defined ROI. A 33% increase in average penetration depth was observed within the ROI using the stretchable coil when compared to the commercial coil. The ex-vivo rat brain and spine images showed distinguishable anatomical details. Stretching the coil reduced the resonant frequency with reduction in SNR, while the conformance to varying sample volumes increased the resonant frequency with decreased SNR. This study also features an open-source plug-and-play system with preamplifiers that can be used to interface surface coils with the 7T Bruker scanner.

Piezoelectric bimorph-driven ultrasound scanner for high frequency ultrasound imaging

Ultrasound imaging commonly uses mechanical or electronic scanning methods. However, the mechanical scanning systems are bulky and susceptible to electromagnetic interference, while electronic scanning systems are complex and expensive. A more affordable and compact solution for high frequency preclinical and clinical imaging is single-element transducer based ultrasound imaging. This method offers high spatial resolution with low cost and low complexity. In this study, a novel single-element high frequency ultrasound imaging scanner was introduced. The scanner is based on piezoelectric bimorph drive and designed to be low-cost, compact, and handheld. Tungsten wire phantom imaging was performed on a dedicated ultrasound imaging system, and the obtained results were analyzed and compared. The results demonstrate that piezoelectric bimorph drive allows for high frequency imaging with a scanning speed of up to 208 frames per second. The image quality was higher than that of electromagnetic motor drive. The versatility of the ultrasound imaging system makes it suitable for preclinical and clinical applications, including small animal imaging, ophthalmic imaging, skin imaging, and intraoperative ultrasound imaging.

NEMA NU 1-2018 performance characterization and Monte Carlo model validation of the Cubresa Spark SiPM-based preclinical SPECT scanner

BackgroundThe Cubresa Spark is a novel benchtop silicon-photomultiplier (SiPM)-based preclinical SPECT system. SiPMs in SPECT significantly improve resolution and reduce detector size compared to preclinical cameras with photomultiplier tubes requiring highly magnifying collimators. The NEMA NU 1 Standard for Performance Measurements of Gamma Cameras provides methods that can be readily applied or extended to characterize preclinical cameras with minor modifications. The primary objective of this study is to characterize the Spark according to the NEMA NU 1-2018 standard to gain insight into its nuclear medicine imaging capabilities. The secondary objective is to validate a GATE Monte Carlo simulation model of the Spark for use in preclinical SPECT studies.MethodsNEMA NU 1-2018 guidelines were applied to characterize the Spark’s intrinsic, system, and tomographic performance with single- and multi-pinhole collimators. Phantoms were fabricated according to NEMA specifications with deviations involving high-resolution modifications. GATE was utilized to model the detector head with the single-pinhole collimator, and NEMA measurements were employed to tune and validate the model. Single-pinhole and multi-pinhole SPECT data were reconstructed with the Software for Tomographic Image Reconstruction and HiSPECT, respectively.ResultsThe limiting intrinsic resolution was measured as 0.85 mm owing to a high-resolution SiPM array combined with a 3 mm-thick scintillation crystal. The average limiting tomographic resolution was 1.37 mm and 1.19 mm for the single- and multi-pinhole collimators, respectively, which have magnification factors near unity at the center of rotation. The maximum observed count rate was 15,400 cps, and planar sensitivities of 34 cps/MBq and 150 cps/MBq were measured at the center of rotation for the single- and multi-pinhole collimators, respectively. All simulated tests agreed well with measurement, where the most considerable deviations were below 7%.ConclusionsNEMA NU 1-2018 standards determined that a SiPM detector mitigates the need for highly magnifying pinhole collimators while preserving detailed information in projection images. Measured and simulated NEMA results were highly comparable with differences on the order of a few percent, confirming simulation accuracy and validating the GATE model. Of the collimators initially provided with the Spark, the multi-pinhole collimator offers high resolution and sensitivity for organ-specific imaging of small animals, and the single-pinhole collimator enables high-resolution whole-body imaging of small animals.

Multi-stage image registration based on list-mode proton radiographies for small animal proton irradiation: A simulation study

We present a multi-stage and multi-resolution deformable image registration framework for image-guidance at a small animal proton irradiation platform. The framework is based on list-mode proton radiographies acquired at different angles, which are used to deform a 3D treatment planning CT relying on normalized mutual information (NMI) or root mean square error (RMSE) in the projection domain.We utilized a mouse X-ray micro-CT expressed in relative stopping power (RSP), and obtained Monte Carlo simulations of proton images in list-mode for three different treatment sites (brain, head and neck, lung). Rigid transformations and controlled artificial deformation were applied to mimic position misalignments, weight loss and breathing changes. Results were evaluated based on the residual RMSE of RSP in the image domain including the comparison of extracted local features, i.e. between the reference micro-CT and the one transformed taking into account the calculated deformation.The residual RMSE of the RSP showed that the accuracy of the registration framework is promising for compensating rigid (>97% accuracy) and non-rigid (∼95% accuracy) transformations with respect to a conventional 3D-3D registration. Results showed that the registration accuracy is degraded when considering the realistic detector performance and NMI as a metric, whereas the RMSE in projection domain is rather insensitive.This work demonstrates the pre-clinical feasibility of the registration framework on different treatment sites and its use for small animal imaging with a realistic detector. Further computational optimization of the framework is required to enable the use of this tool for online estimation of the deformation.

Realization of NIR-II 3D whole-body contour and tumor blood vessels imaging in small animals using rotational stereo vision technique.

Optical imaging in the second near-infrared (NIR-II, 1000 to 1700nm) region is capable of deep tumor vascular imaging due to low light scattering and low autofluorescence. Non-invasive real-time NIR-II fluorescence imaging is instrumental in monitoring tumor status. Our aim is to develop an NIR-II fluorescence rotational stereo imaging system for 360-deg three-dimensional (3D) imaging of whole-body blood vessels, tumor vessels, and 3D contour of mice. Our study combined an NIR-II camera with a 360-deg rotational stereovision technique for tumor vascular imaging and 3D surface contour for mice. Moreover, self-made NIR-II fluorescent polymer dots were applied in high-contrast NIR-II vascular imaging, along with a 3D blood vessel enhancement algorithm for acquiring high-resolution 3D blood vessel images. The system was validated with a custom-made 3D printing phantom and in vivo experiments of 4T1 tumor-bearing mice. The results showed that the NIR-II 3D 360-deg tumor blood vessels and mice contour could be reconstructed with 0.15mm spatial resolution, 0.3mm depth resolution, and 5mm imaging depth in an ex vivo experiment. The pioneering development of an NIR-II 3D 360-deg rotational stereo imaging system was first applied in small animal tumor blood vessel imaging and 3D surface contour imaging, demonstrating its capability of reconstructing tumor blood vessels and mice contour. Therefore, the 3D imaging system can be instrumental in monitoring tumor therapy effects.

Functional ultrasound detects frequency-specific acute and delayed S-ketamine effects in the healthy mouse brain.

S-ketamine has received great interest due to both its antidepressant effects and its potential to induce psychosis when administered subchronically. However, no studies have investigated both its acute and delayed effects using in vivo small-animal imaging. Recently, functional ultrasound (fUS) has emerged as a powerful alternative to functional magnetic resonance imaging (fMRI), outperforming it in sensitivity and in spatiotemporal resolution. In this study, we employed fUS to thoroughly characterize acute and delayed S-ketamine effects on functional connectivity (FC) within the same cohort at slow frequency bands ranging from 0.01 to 1.25 Hz, previously reported to exhibit FC. We acquired fUS in a total of 16 healthy C57/Bl6 mice split in two cohorts (n = 8 received saline, n = 8 S-ketamine). One day after the first scans, performed at rest, the mice received the first dose of S-ketamine during the second measurement, followed by four further doses administered every 2 days. First, we assessed FC reproducibility and reliability at baseline in six frequency bands. Then, we investigated the acute and delayed effects at day 1 after the first dose and at day 9, 1 day after the last dose, for all bands, resulting in a total of four fUS measurements for every mouse. We found reproducible (r > 0.9) and reliable (r > 0.9) group-average readouts in all frequency bands, only the 0.01-0.27 Hz band performing slightly worse. Acutely, S-ketamine induced strong FC increases in five of the six bands, peaking in the 0.073-0.2 Hz band. These increases comprised both cortical and subcortical brain areas, yet were of a transient nature, FC almost returning to baseline levels towards the end of the scan. Intriguingly, we observed robust corticostriatal FC decreases in the fastest band acquired (0.75 Hz-1.25 Hz). These changes persisted to a weaker extent after 1 day and at this timepoint they were accompanied by decreases in the other five bands as well. After 9 days, the decreases in the 0.75-1.25 Hz band were maintained, however no changes between cohorts could be detected in any other bands. In summary, the study reports that acute and delayed ketamine effects in mice are not only dissimilar but have different directionalities in most frequency bands. The complementary readouts of the employed frequency bands recommend the use of fUS for frequency-specific investigation of pharmacological effects on FC.

High Acoustic Impedance and Attenuation Backing for High-Frequency Focused P(VDF-TrFE)-Based Transducers.

Backing materials with tailored acoustic properties are beneficial for miniaturized ultrasonic transducer design. Whereas piezoelectric P(VDF-TrFE) films are common elements in high-frequency (>20 MHz) transducer design, their low coupling coefficient limits their sensitivity. Defining a suitable sensitivity-bandwidth trade-off for miniaturized high-frequency applications requires backings with impedances of >25 MRayl and strongly attenuating to account for miniaturized requirements. The motivation of this work is related to several medical applications such as small animal, skin or eye imaging. Simulations showed that increasing the acoustic impedance of the backing from 4.5 to 25 MRayl increases transducer sensitivity by 5 dB but decreases the bandwidth, which nevertheless remains high enough for the targeted applications. In this paper, porous sintered bronze material with spherically shaped grains, size-adapted for 25-30 MHz frequency, was impregnated with tin or epoxy resin to create multiphasic metallic backings. Microstructural characterizations of these new multiphasic composites showed that impregnation was incomplete and that a third air phase was present. The selected composites, sintered bronze-tin-air and sintered bronze-epoxy-air, at 5-35 MHz characterization, produced attenuation coefficients of 1.2 and >4 dB/mm/MHz and impedances of 32.4 and 26.4 MRayl, respectively. High-impedance composites were adopted as backing (thickness = 2 mm) to fabricate focused single-element P(VDF-TrFE)-based transducers (focal distance = 14 mm). The center frequency was 27 MHz, while the bandwidth at -6 dB was 65% for the sintered-bronze-tin-air-based transducer. We evaluated imaging performance using a pulse-echo system on a tungsten wire (diameter = 25 μm) phantom. Images confirmed the viability of integrating these backings in miniaturized transducers for imaging applications.