Gadolinium-based contrast agents aggravate mechanical and thermal hyperalgesia in a nitroglycerine-induced migraine model in male mice

In the diagnosis of migraine, which is a neurovascular disease, gadolinium-based contrast agents (GBCAs) are used to rule out more serious conditions. On the other hand, it remains unclear as a scientific gap whether GBCAs may trigger migraine-related pain. The aim of this study was to investigate the effect of GBCAs on mechanical and thermal pain behaviour in a nitroglycerin (NTG)-induced migraine model in mice. NTG (10 mg/kg) was administered intraperitoneally to adult (6-8weeks old) BALB/c mice 2 h before behavioral tests 5 times every other day on days 1st, 3rd, 5th and 9th to induce migraine model (N = 50). As GBCAs, gadobenate dimeglumine (linear-ionic), Gadodiamide (linear-nonionic), and gadobutrol (macrocyclic-nonionic) were delivered intravenously through the tail vein of mice for 5 days on test days. Mechanical pain threshold (plantar and facial withdrawal threshold) was evaluated by plantar von Frey and periorbital von Frey tests on days 1st, 5th, and 9th, and thermal pain threshold (latency) was evaluated by hot plate and cold plate tests on days 3rd and 7th. There was a statistically significant increase in mechanical and thermal hyperalgesia in NTG administered groups compared to the control group. Gadodiamide, gadobutrol and gadobenate dimeglumine administration significantly decreased latency, paw and facial withdrawal threshold (0.18 ± 0.05, 0.17 ± 0.07, 0.16 ± 0.09; 9th day values respectively) compared to NTG group (0.27 ± 0.05). The results of this in vivo study show that GBCAs produce effects that may trigger migraine attacks in migraine. It is recommended that these effects be further investigated and supported by further clinical studies.

Recent advances in nanomaterial-driven strategies for diagnosis and therapy of vascular anomalies

Nanotechnology has demonstrated immense potential in various fields, especially in biomedical field. Among these domains, the development of nanotechnology for diagnosing and treating vascular anomalies has garnered significant attention. Vascular anomalies refer to structural and functional anomalies within the vascular system, which can result in conditions such as vascular malformations and tumors. These anomalies can significantly impact the quality of life of patients and pose significant health concerns. Nanoscale contrast agents have been developed for targeted imaging of blood vessels, enabling more precise identification and characterization of vascular anomalies. These contrast agents can be designed to bind specifically to abnormal blood vessels, providing healthcare professionals with a clearer view of the affected areas. More importantly, nanotechnology also offers promising solutions for targeted therapeutic interventions. Nanoparticles can be engineered to deliver drugs directly to the site of vascular anomalies, maximizing therapeutic effects while minimizing side effects on healthy tissues. Meanwhile, by incorporating functional components into nanoparticles, such as photosensitizers, nanotechnology enables innovative treatment modalities such as photothermal therapy and photodynamic therapy. This review focuses on the applications and potential of nanotechnology in the imaging and therapy of vascular anomalies, as well as discusses the present challenges and future directions.

Spontaneous occlusion of a pial arteriovenous fistula after angiography: The role of iodinated contrast media

Intracranial non-galenic pial arteriovenous fistula (PAVF) is an extremely rare vascular malformation, where one or more pial arteries feeds directly into a cortical vein without any intervening nidus. Though occasionally they can be asymptomatic, neurological symptoms such as headache, seizure, or focal neurological deficit are more common presenting features. Life threatening or fatal hemorrhage is not uncommon, hence needed to be treated more often than not. Spontaneous occlusion of PAVF is reported only four times before. We report a 49-year-old gentleman, who was diagnosed to have a PAVF, possibly secondary to trauma. He presented 5 months and 22 days from initial digital subtraction angiography (DSA) for treatment, and follow-up angiogram showed complete obliteration. He denied any significant event, medication or alternate treatment during this period. His clinical symptoms were stable as well. We postulate iodinated contrast medium induced vasculopathy as a possible cause, which has been described for other vascular pathologies, but never for PAVF.

Metallic artifacts-free spectral computed tomography angiography based on renal clearable bismuth chelate

Computed tomography angiography (CTA) is one of the most important diagnosis techniques for various vascular diseases in clinic. However, metallic artifacts caused by metal implants and calcified plaques in more and more patients severely hinder its wide applications. Herein, we propose an improved metallic artifacts-free spectral CTA technique based on renal clearable bismuth chelate (Bi-DTPA dimeglumine) for the first time. Bi-DTPA dimeglumine owns the merits of ultra-simple synthetic process, approximately 100% of yield, large-scale production capability, good biocompatibility, and favorable renal clearable ability. More importantly, Bi-DTPA dimeglumine shows superior contrast-enhanced effect in CTA compared with clinical iohexol at a wide range of X-ray energies especially in higher X-ray energy. In rabbits' model with metallic transplants, Bi-DTPA dimeglumine assisted-spectral CTA can not only effectively mitigate metallic artifacts by reducing beam hardening effect under high X-ray energy, but also enables accurate delineation of vascular structure. Our proposed strategy opens a revolutionary way to solve the bottleneck problem of metallic artifacts in CTA examinations.

Vesicoureteral reflux by contrast ultrasound, comparison with voiding and retrograde urethrocystography: A prospective accuracy study

INTRODUCTION

Diagnosis of vesicoureteral reflux (VUR) plays an important role in the management and follow-up of children presenting with urinary tract infection. This study compared voiding uronosography (VUS) as a diagnostic method for the diagnosis of VUR with the "gold standard", voiding or micturating cystourethrography (MCU). The objective of the study is not only to compare the effectiveness of both methods, but also to assess the feasibility of implementing VUS technically and economically in a large tertiary radiology center in South America.

MATERIALS AND METHOD

This was a prospective accuracy study that include 41 patients (a total of 85 ureteral units) aged between 1 month and 16 years. VUS was performed in an alternative form as regular MCU, by injecting microbubble contrast solution (SonoVue©) into the bladder through an intermittent catheter and evaluating the presence of reflux with ultrasound. MCU was always performed immediately after VUS. One pediatric radiologist evaluated all VUS exams, while a second independent pediatric radiologist evaluated all MCU exams, with both blinded to each other's assessments.

RESULTS

Comparing VUS with MCU in the diagnosis of VUR, we observed a sensitivity of 92.3 % (95 % CI 74.9-99.1 %), specificity of 98.3 % (95 % CI 90.9-100 %), positive predictive value of 96.0 % (95 % CI 79.6-99.9 %), negative predictive value of 96.7 % (95 % CI 88.5-99.6 %) and a Kappa of 0.916 (0.822-1.000). When comparing the VUR grading between VUS and MCU the agreement between the two methods was high with a Kendall's Tau-b > 0.9. VUS failed to diagnose two grade 1 VUR reflux cases in teenagers while diagnosing one grade 4 VUR in a very dilated kidney-ureter unit, which was missed on MCU. VUS and MCU had similar costs when considering the price of the ultrasound contrast agent.

DISCUSSION

VUS is a reliable alternative method to MCU for the diagnosis of VUR with the advantages of not exposing the child to ionizing radiation and potentially being more accessible due to the greater availability of ultrasound equipment. Limitations to this study include the usage of a single ultrasound equipment, which limits its generalizability and not evaluating the interobserver variability.

CONCLUSION

Consideration should be given to implementing VUS for the diagnosis of VUR, particularly in centers without fluoroscopy equipment available, since the exam's performance and cost are comparable to those of the MCU.

Advances in nanotechnology-based targeted-contrast agents for computed tomography and magnetic resonance

X-ray computed tomography (CT) and magnetic resonance (MR) imaging are essential tools in modern medical diagnosis and treatment. However, traditional contrast agents are inadequate in the diagnosis of various health conditions. Consequently, the development of targeted nano-contrast agents has become a crucial area of focus in the development of medical image-enhancing contrast agents. To fully understand the current development of nano-contrast agents, this review provides an overview of the preparation methods and research advancements in CT nano-contrast agents, MR nano-contrast agents, and CT/MR multimodal nano-contrast agents described in previous publications. Due to the physicochemical properties of nanomaterials, such as self-assembly and surface modifiability, these specific nano-contrast agents can greatly improve the targeting of lesions through various preparation methods and clearly highlight the distinction between lesions and normal tissues in both CT and MR. As a result, they have the potential to be used in the early stages of disease to improve diagnostic capacity and level in medical imaging.

Unique portal venous phase imaging discordance between CEUS and MRI: a valuable predictor of intrahepatic cholangiocarcinoma?

PURPOSE

We have long noted unique portal venous phase (PVP) imaging discordance of focal liver masses between CEUS, showing rapid marked washout, and MRI, showing progressive or sustained enhancement. We postulate association of this unique discordance with intrahepatic cholangiocarcinoma (ICC) and causal relationship to different contrast agent behavior. We investigate this unique discordance, propose its clinical significance for ICC diagnosis, and confirm further histologic associations.

METHODS

Cases were collected within our CEUS department and from pathology records over a ten-year interval. This retrospective review includes 99 patients, 73 with confirmed ICC and 26 other diagnoses, showing unique PVP discordance. The CEUS and MRI enhancement characteristics were compared for all patients.

RESULTS

Unique discordance is identified in 67/73 (92%) ICC and difference between the PVP appearance on MRI and CEUS is statistically significant (p <  0.0001). Arterial phase enhancement did not show statistically significant difference between CEUS and MRI, p >  0.05. Other diagnoses showing unique discordance include especially lymphoma (n = 7), sclerosed hemangioma (n = 6), HCC (n = 4), metastases (n = 2), and other rare entities.

CONCLUSION

ICC shows this discrepant intermodality enhancement pattern in a statistically significant number of cases and should be considered along with other LR-M features in at-risk patients. Discordance is also rarely seen in a number of other liver lesions.

Analytical interference of intravascular contrast agents with clinical laboratory tests: a joint guideline by the ESUR Contrast Media Safety Committee and the Preanalytical Phase Working Group of the EFLM Science Committee

The Contrast Media Safety Committee of the European Society of Urogenital Radiology has, together with the Preanalytical Phase Working Group of the EFLM Science Committee, reviewed the literature and updated its recommendations to increase awareness and provide insight into these interferences. CLINICAL RELEVANCE STATEMENT: Contrast Media may interfere with clinical laboratory tests. Awareness of potential interference may prevent unwanted misdiagnosis. KEY POINTS: • Contrast Media may interfere with clinical laboratory tests; therefore awareness of potential interference may prevent unwanted misdiagnosis. • Clinical Laboratory tests should be performed prior to radiological imaging with contrast media or alternatively, blood or urine collection should be delayed, depending on kidney function.

Ultrasound-Induced Microbubble Cavitation for Targeted Delivery of MiR-29b Mimic to Treat Cardiac Fibrosis

OBJECTIVE

Cardiac fibrosis contributes to adverse ventricular remodeling and is associated with loss of miR-29b. Overexpression of miR-29b via plasmid or intravenous injection of microRNA mimic has blunted fibrosis, but these are inefficient and non-targeted delivery strategies. In this study, we tested the hypothesis that delivery of microRNA-29b (miR-29b) using ultrasound-targeted microbubble cavitation (UTMC) of miR-29b-loaded microbubbles would attenuate cardiac fibrosis and preserve left ventricular (LV) function.

METHODS

Lipid microbubbles were loaded with miR-29b mimic (miR-29b-MB) or negative control (NC) mimic (NC-MB), placed with cardiac fibroblasts (CFs) and treated with pulsed ultrasound. Cells were harvested to measure downstream fibrotic mediators. Mice received angiotensin II (ANG II) infusion causing afterload increase and direct ANG II-induced cardiac fibrosis. UTMC of miRNA-loaded microbubbles was administered to the heart at days 0, 3 and 7. Serial echocardiography was performed, and hearts were harvested on day 10.

RESULTS

UTMC treatment of CFs with miR-29b-MB increased miR-29b and decreased fibrotic transcripts compared with NC-MB treatment. In vivo UTMC + NC-MB led to increased LV mass, reduction in cardiac function and increase in fibrotic markers, demonstrating ANGI II-induced adverse cardiac remodeling. Mice treated with UTMC + miR-29b-MB had preservation of cardiac function, downregulation of cardiac fibrillin and trends of lower COL1A1, COL1A2 and COL3 mRNA and decreased cardiac α-smooth muscle protein.

CONCLUSION

UTMC-mediated delivery of miR-29b mimic blunts expression of fibrosis markers and preserves LV function in ANG II-induced cardiac fibrosis.

Assessment of arterial-phase hyperenhancement and late-phase washout of hepatocellular carcinoma-a meta-analysis of contrast-enhanced ultrasound (CEUS) with SonoVue® and Sonazoid®

OBJECTIVES

The recognition of arterial phase hyperenhancement (APHE) and washout during the late phase is key for correct diagnosis of hepatocellular carcinoma (HCC) with contrast-enhanced ultrasound (CEUS). This meta-analysis was conducted to compare SonoVue®-enhanced and Sonazoid®-enhanced ultrasound in the assessment of HCC enhancement and diagnosis.

METHODS

Studies were included in the analysis if they reported data for HCC enhancement in the arterial phase and late phase for SonoVue® or in the arterial phase and Kupffer phase (KP) for Sonazoid®. Forty-two studies (7502 patients) with use of SonoVue® and 30 studies (2391 patients) with use of Sonazoid® were identified. In a pooled analysis, the comparison between SonoVue® and Sonazoid® CEUS was performed using chi-square test. An inverse variance weighted random-effect model was used to estimate proportion, sensitivity, and specificity along with 95% confidence interval (CI).

RESULTS

In the meta-analysis, the proportion of HCC showing APHE with SonoVue®, 93% (95% CI 91-95%), was significantly higher than the proportion of HCC showing APHE with Sonazoid®, 77% (71-83%) (p < 0.0001); similarly, the proportion of HCC showing washout at late phase/KP was significantly higher with SonoVue®, 86% (83-89%), than with Sonazoid®, 76% (70-82%) (p < 0.0001). The sensitivity and specificity for the detection of APHE plus late-phase/KP washout detection in HCC were also higher with SonoVue® than with Sonazoid® (sensitivity 80% vs 52%; specificity 80% vs 73% in studies within unselected patient populations).

CONCLUSION

APHE and late washout in HCC are more frequently observed with SonoVue® than with Sonazoid®. This may affect the diagnostic performance of CEUS in the diagnosis of HCCs.

CLINICAL RELEVANCE STATEMENT

Meta-analysis data show the presence of key enhancement features for diagnosis of hepatocellular carcinoma is different between ultrasound contrast agents, and arterial hyperenhancement and late washout are more frequently observed at contrast-enhanced ultrasound with SonoVue® than with Sonazoid®.

KEY POINTS

• Dynamic enhancement features are key for imaging-based diagnosis of HCC. • Arterial hyperenhancement and late washout are more often observed in HCCs using SonoVue®-enhanced US than with Sonazoid®. • The existing evidence for contrast-enhanced US may need to be considered being specific to the individual contrast agent.

Safety of Magnetic Resonance Imaging in Pregnancy

Magnetic resonance imaging is being increasingly used to diagnose and follow up a variety of medical conditions in pregnancy, both for maternal and fetal indications. However, limited data regarding its safe use in pregnancy may be a source of anxiety and avoidance for both patients and their healthcare providers. In this review, we critically discuss the main safety concerns of Magnetic Resonance Imaging (MRI) in pregnancy including energy deposition, acoustic noise, and use of contrast agents, supported by data from animal and human studies. Use of maternal sedatives and concerns related to occupational exposure in pregnant personnel are also addressed. Exposure to gadolinium-based contrast agents and sedation for MRI during pregnancy should be avoided whenever feasible.

Preparation, characterization, and magnetic resonance imaging of Fe nanowires

A facile template method was employed to synthesize Fe nanowires of different sizes, dimensions. Comprehensive analyses were conducted to explore their morphology, structure, composition, and magnetic properties. The surface of as-prepared Fe nanowires was modified with SiO2 by sol-gel method to improve the dispersion of as-prepared Fe nanowires in aqueous solution. Furthermore, the relaxation properties, biocompatibility and in vivo imaging abilities of the Fe@SiO2 nanowires were evaluated. The study revealed that the SiO2-coated Fe nanowires functioned effectively as transverse relaxation time (T2) contrast agents (CAs). Notably, as the length of the Fe@SiO2 nanowires increased, their diameter decreased, leading to a higher the transverse relaxivity (r2) value. Our study identified that among the Fe nanowires synthesized, the Fe3@SiO2 nanowires, characterized by a diameter of around 30 nm and a length of approximately 500 nm, exhibited the highest r2 value of 59.3 mM-1 s-1. These nanowires demonstrated good biocompatibility and non-toxicity. Notably, upon conducting small animal imaging a 1.5 T with Sprague-Dawley rats, we observed a discernible negative enhancement effect in the liver. These findings indicate the promising potential of Fe@SiO2 nanowires as T2 CAs, with the possibility of tuning their size for optimized results.

Assembly of fluorophore J-aggregates with nanospacer onto mesoporous nanoparticles for enhanced photoacoustic imaging

Many fluorophores, such as indocyanine green (ICG), have poor photostability and low photothermal efficiency hindering their wide application in photoacoustic (PA) tomography. In the present study, a supramolecular assembly approach was used to develop the hybrid nanoparticles (Hy NPs) of ICG and porous silicon (PSi) as a novel contrast agent for PA tomography. ICG was assembled on the PSi NPs to form J-aggregates within 30 min. The Hy NPs presented a red-shifted absorption, improved photothermal stability, and enhanced PA performance. Furthermore, 1-dodecene (DOC) was assembled into the NPs as a 'nanospacer', which enhanced non-radiative decay for increased thermal release. Compared to the Hy NPs, adding DOC into the Hy NPs (DOC-Hy) increased the PA signal by 83%. Finally, the DOC-Hy was detectable in PA tomography at 1.5 cm depth in tissue phantom even though its concentration was as low as 6.25 µg/mL, indicating the potential for deep tissue PA imaging.

MRI Contrasting Agent Based on Mn-MOF-74 Nanoparticles with Coordinatively Unsaturated Sites

PURPOSE

The development of magnetic resonance imaging (MRI) contrasting agents (CAs) that are safer and have a higher relaxivity than Gd(III)-based agents is a significant research topic. Herein, we propose the use of a Mn-based metal organic framework (MOF), Mn-MOF-74, characterized by a safe paramagnetic center, a coordinatively unsaturated site (CUS) for aquation, and a long rotational correlation time, endowing high relaxivity. Furthermore, biocompatibility and delivery to the tumor are generally expected for MOFs that are obtainable in the nanometer size range.

PROCEDURE

Drop-wise mixing of 2,5-dihydroxyterephthalic acid (DHTP) and Mn(II) acetate yielded Mn-MOF-74 with a diameter of < 150 nm, which was then modified with 1-fivefold higher amounts of poly(ethylene glycol) (M.W. = 5000) to afford MOFs stably dispersed in water for at least 24 h.

RESULTS

The longitudinal and transverse relaxivity of the PEG-modified MOF was in the range of r1 = 8.08-13.5 and r2 = 32.7-46.8 mM-1 s-1, respectively (1.0 T, 23.7-23.9 °C), being larger than those of typical Gd(III)- and Mn(II)-based CAs of single-nuclear metal complexes. The in vivo imaging of a tumor-bearing mouse clearly showed that the tumor could be readily recognized due to signal enhancement (117%) in T1-weighted images, whereas other tissues showed small signal changes.

CONCLUSIONS

These results suggest that PEG-Mn-MOF-74 can be passively delivered to tumors and can act as a high-relaxivity T1 agent.

Large-scale in situ self-assembly and doping engineering of zinc ferrite nanoclusters for high performance bioimaging

Iron oxide nanomaterials has good biocompatibility and safety, and has been used as contrast agents for magnetic resonance imaging (MRI). However, its clinical usefulness is hampered by its difficult preparation on large scale, its rapid clearance in vivo and low target tissue enrichment efficiency. Here, we report the synthesis of water-soluble, biocompatible, superparamagnetic non-stoichiometric zinc ferrite nanoclusters (nZFNCs) of approximately 50 g in a single batch using a one-pot synthesis technique. nZFNCs is a secondary cluster structure with a size of about 40 nm composed of zinc-doped iron oxide nanoparticles with a size of about 6 nm. The surface of nZFNCS is endowed with a large number of carboxyl groups as active sites. By simply controlling the synthesis process and adjusting the proportion of metal precursors, the amount of zinc doping can be controlled, while maintaining the same size to ensure similar pharmacokinetics. Compared with undoped, the magnetic responsiveness and relaxation efficiency of nZFNCs are significantly improved, and the transverse relaxation efficiency (r2) can reach 425.5 mM-1 s-1 (doping amount x = 0.25), which is 7 times higher than that of commercial Resovist and 10 times higher than that of Feridex. In vivo imaging results also further confirmed the excellent contrast enhancement performance of the nanoclusters, which can achieve high contrast for more than 2 h in the liver. The advantage of this platform over comparable systems is that the contrast enhancement features are derived from simple techniques that do not require complex physical and chemical methods.

Treatment-Induced Bone Marrow Enhancement at MRI in Breast Cancer Patients Receiving Granulocyte-Colony Stimulating Factor Adjunct to Chemotherapy

RATIONALE AND OBJECTIVES

Granulocyte-colony stimulating factor (G-CSF) induces the reconversion of fatty bone marrow to hematopoietic bone marrow. The bone marrow changes are detectable as signal intensity changes at MRI. The aim of this study was to evaluate sternal bone marrow enhancement following G-CSF and chemotherapy treatment in women with breast cancer.

MATERIALS AND METHODS

This retrospective study included breast cancer patients who received neoadjuvant chemotherapy with adjunct G-CSF. The signal intensity of sternal bone marrow at MRI on T1-weighted contrast-enhanced subtracted images was measured before treatment, at the end of treatment, and at 1-year follow-up. The bone marrow signal intensity (BM SI) index was calculated by dividing the signal intensity of sternal marrow by the signal intensity of the chest wall muscle. Data were collected between 2012 and 2017, with follow-up until August 2022. Mean BM SI indices were compared before and after treatment, and at 1-year follow-up. Differences in bone marrow enhancement between time points were analyzed using a one-way repeated measures ANOVA.

RESULTS

A total of 109 breast cancer patients (mean age 46.1 ± 10.4 years) were included in our study. None of the women had distal metastases at presentation. A repeated-measures ANOVA determined that mean BM SI index scores differed significantly across the three time points (F[1.62, 100.67] = 44.57, p < .001). At post hoc pairwise comparison using the Bonferroni correction BM SI index significantly increased between initial assessment and following treatment (2.15 vs 3.33, p < .001), and significantly decreased at 1-year follow-up (3.33 vs 1.45, p < .001). In a subgroup analysis, while women younger than 50 years had a significant increase in marrow enhancement after G-CSF treatment, in women aged 50 years and older, the difference was not statistically significant.

CONCLUSION

Treatment with G-CSF as an adjunct to chemotherapy can result in increased sternal bone marrow enhancement due to marrow reconversion. Radiologists should be aware of this effect in order to avoid misinterpretation as false marrow metastases.

Contrast-induced anaphylaxis: does it occur in the medical environment and is it being responded to appropriately?

PURPOSE

To analyze the appropriateness of primary response for anaphylaxis due to iodinated contrast media (ICM) or gadolinium-based contrast agents (GBCA).

MATERIALS AND METHODS

This retrospective study included all patients in whom intravenous contrast agents (five types of ICMs and four types of GBCAs) were administered at our hospital between April 2016 and September 2021. For the patients who developed anaphylaxis, we obtained data on the time records of contrast injection, anaphylaxis onset, and intramuscular adrenaline (epinephrine) administration.

RESULTS

Of the 76,555 ICM and 30,731 GBCA administrations, anaphylaxis occurred in 49 cases (0.05%), and in 48 cases (98.0%) the onset was within 30 min after administration with widely distributed times (median, 7.5 min; interquartile range, 4.5-10.8 min; max, 26 min). Intramuscular adrenaline administration was performed in 43 cases (87.8%), and this was done within five minutes after the onset in 37 cases (75.5%). Only in 24 cases (49.0%), there were time records of both the onset and adrenaline administration (if performed).

CONCLUSION

Anaphylaxis occurred within 30 min after contrast injection in the majority of the cases, but times were widely distributed. Only in 75.5% of cases, appropriate primary treatment was performed, and the importance of keeping exact time records in patients' charts should be re-emphasized.

Spectral computed tomography-guided radiotherapy of osteosarcoma utilizing BiOI nanosheets

As an aggressive malignant bone tumor, osteosarcoma (OS) is usually found in children and adolescents. Computed tomography (CT) is an important tool for the clinical evaluation of osteosarcoma, but limits to low diagnostic specificity due to single parameters of traditional CT and modest signal-to-noise ratio of clinical iodinated contrast agents. As one kind of spectral CT, dual-energy CT (DECT), with the advantage of a provision of multi-parameter information, makes it possible to acquire the best signal-to-noise ratio image, accurate detection, as well as imaging-guided therapy of bone tumors. Hereby, we synthesized BiOI nanosheets (BiOI NSs) as a DECT contrast agent with superior imaging capability compared to iodine agents for clinical detection of OS. Meanwhile, the synthesized BiOI NSs with great biocompatibility is able to achieve effective radiotherapy (RT) by enhancing X-ray dose deposition at the tumor site, leading to DNA damage, which in turn inhibits tumor growth. This study offers a promising new avenue for DECT imaging-guided treatment of OS. STATEMENT OF SIGNIFICANCE: Osteosarcoma (OS) is a common primary malignant bone tumor. Traditional surgical procedures and conventional CT scans are often used for the treatment and monitoring of OS, but the effects are generally unsatisfactory. In this work, BiOI nanosheets (NSs) was reported for dual-energy CT (DECT) imaging-guided OS radiotherapy. The powerful and constant X-ray absorption of BiOI NSs at any energy guarantees excellent enhanced DECT imaging performance, allowing detailed visualization of OS through images with a better signal-to-noise ratio and guiding radiotherapy process. The deposition of X-rays could be greatly enhanced by Bi atoms to induce serious DNA damage in radiotherapy. Taken together, the BiOI NSs for DECT-guided radiotherapy will greatly improve the current treatment status of OS.

Ultrasound localization microscopy

Ultrasound Localization Microscopy (ULM) is an emerging technique that provides impressive super-resolved images of microvasculature, i.e., images with much better resolution than the conventional diffraction-limited ultrasound techniques and is already taking its first steps from preclinical to clinical applications. In comparison to the established perfusion or flow measurement methods, namely contrast-enhanced ultrasound (CEUS) and Doppler techniques, ULM allows imaging and flow measurements even down to the capillary level. As ULM can be realized as a post-processing method, conventional ultrasound systems can be used for. ULM relies on the localization of single microbubbles (MB) of commercial, clinically approved contrast agents. In general, these very small and strong scatterers with typical radii of 1-3 µm are imaged much larger in ultrasound images than they actually are due to the point spread function of the imaging system. However, by applying appropriate methods, these MBs can be localized with sub-pixel precision. Then, by tracking MBs over successive frames of image sequences, not only the morphology of vascular trees but also functional information such as flow velocities or directions can be obtained and visualized. In addition, quantitative parameters can be derived to describe pathological and physiological changes in the microvasculature. In this review, the general concept of ULM and conditions for its applicability to microvessel imaging are explained. Based on this, various aspects of the different processing steps for a concrete implementation are discussed. The trade-off between complete reconstruction of the microvasculature and the necessary measurement time as well as the implementation in 3D are reviewed in more detail, as they are the focus of current research. Through an overview of potential or already realized preclinical and clinical applications - pathologic angiogenesis or degeneration of vessels, physiological angiogenesis, or the general understanding of organ or tissue function - the great potential of ULM is demonstrated.

Abdominal Ultrasonography After Transrectal Filling With Contrast Agents in Colorectal Cancer With Severely Stenotic Lesions

OBJECTIVE

Abdominal ultrasonography after transrectal filling with contrast agent (AU-TFCA) was retrospectively evaluated with respect to determination of T stage and lesion length in patients with colorectal cancer (CRC) who had previously failed colonoscopy because of severe intestinal stenosis.

METHODS

The population comprised 83 patients with CRC with intestinal stenosis and previously failed colonoscopy who underwent AU-TFCA, and in addition contrast-enhanced computed tomography (CECT) and/or magnetic resonance imaging (MRI), 2 wk before surgery. The diagnostic performance of AU-TFCA and CECT/MRI was evaluated relative to the post-operative pathological results (PPRs) by paired sample t-test, receiver operator characteristic (ROC) curve, Pearson's χ²-test and κ and intraclass correlation coefficients.

RESULTS

The T staging identified via AU-TFCA, but not CECT/MRI, was relatively consistent with that of the PPRs (linearly weighted κ coefficient: 0.558, p < 0.001, and linearly weighted κ coefficient: 0.237, p < 0.001, respectively). The overall diagnostic accuracy of T staging based on AU-TFCA (83.1%) was significantly higher than that based on CECT/MRI (50.6%). Regarding lesion length, the results of AU-TFCA and PPRs were comparable (t = 1.852, p = 0.068), but those of CECT/MRI and PPRs were significantly different (t = 8.450, p < 0.001).

CONCLUSION

AU-TFCA is effective in evaluation of lesion length and T stage in patients with severely stenotic CRC lesions who previously failed colonoscopy. The diagnostic accuracy of AU-TFCA is significantly better compared with that of CECT/MRI.

Current Status of Sub-micron Cavitation-Enhancing Agents for Sonothrombolysis

Thrombosis in cardiovascular disease is an urgent global issue, but treatment progress is limited by the risks of current antithrombotic approaches. The cavitation effect in ultrasound-mediated thrombolysis offers a promising mechanical alternative for clot lysis. Further addition of microbubble contrast agents introduces artificial cavitation nuclei that can enhance the mechanical disruption induced by ultrasound. Recent studies have proposed sub-micron particles as novel sonothrombolysis agents with increased spatial specificity, safety and stability for thrombus disruption. In this article, the applications of different sub-micron particles for sonothrombolysis are discussed. Also reviewed are in vitro and in vivo studies that apply these particles as cavitation agents and as adjuvants to thrombolytic drugs. Finally, perspectives on future developments in sub-micron agents for cavitation-enhanced sonothrombolysis are shared.

Unilateral contrast-induced encephalopathy with contrast medium exudation: A case report

BACKGROUND

Contrast-induced encephalopathy (CIE) is a rare transient, reversible abnormality in the structure or function of the nervous system caused by the intravascular use of contrast agents. CIE can present with a range of neurological manifestations, including focal neurological deficits (hemiplegia, hemianopia, cortical blindness, aphasia, and parkinsonism) and systemic symptoms (confusion, seizures, and coma). However, if not accurately diagnosed and treated in a timely manner, CIE can cause irreversible damage to patients, especially critically ill patients.

CASE SUMMARY

A male in his 50 s, 2 h after digital subtraction angiography, had a progressive disorder of consciousness, mixed aphasia, bilateral pupillary sluggish light reflex, and right limb weakness. Seven hours after the procedure, he developed unconsciousness, high fever (39.5 °C), seizures, hemiplegia, neck stiffness (+), and right Babinski signs (+). computed tomography (CT) findings 2 h postprocedure were very confusing and led us to misdiagnose the patient with subarachnoid hemorrhage. Brain CT was performed again 7 h after the procedure. Compared with the CT 2 h after the procedure, the CT 7 h after the procedure showed that the manifestations of subarachnoid hemorrhage in the left cerebral hemisphere had disappeared and were replaced by brain tissue swelling, and the cerebral sulci had disappeared. Combined with the clinical manifestations of the patient and after the exclusion of subarachnoid hemorrhage and cerebrovascular embolism, we diagnosed the patient with CIE, and intravenous fluids were given for adequate hydration, as well as mannitol, albumin dehydration, furosemide and the glucocorticoid methylprednisolone. After 17 d of active treatment, the patient was discharged with no sequelae.

CONCLUSION

CIE should be taken seriously, but it is easily misdiagnosed, and once CIE is diagnosed, rapid, accurate diagnosis and treatment are critical steps. Whether a follow-up examination using a contrast agent can be performed should be closely evaluated, and the patient should be fully informed of the associated risks.

Generalized mathematical framework for contrast-enhanced ultrasound imaging with pulse inversion spectral deconvolution

A generalized mathematical framework for performing contrast-enhanced ultrasound (CEUS) imaging is introduced. Termed pulse inversion spectral deconvolution (PISD), this CEUS approach is founded on Gaussian derivative functions (GDFs). PISD pulses are used to form two inverted pulse sequences, which are then used to filter backscattered ultrasound (US) data for isolation of the nonlinear (NL) microbubble (MB) signal component. An US scanner equipped with a linear array transducer was used for data acquisition. With a vascular flow phantom perfused with MBs, data was collected using PISD and NL-based CEUS imaging. The role of wide-beam transmit aperture size (32 or 64 elements) was also evaluated using an US pulse frequency of 6.25 MHz. Image enhancement was quantified by a contrast-to-noise ratio (CNR). Preliminary in vivo data was collected in the hindlimb and kidney of healthy rats. Overall, in vitro wide-beam CEUS imaging using an aperture size of 64 elements yielded improved CNR values. Specifically, PISD-based CEUS imaging produced CNR values of 37.3 dB. For comparison, CNR values obtained using B-mode US or NL approaches were 2.1 and 12.1 dB, respectively. In vivo results demonstrated that PISD-based CEUS imaging improved vascular visualization compared to the NL imaging strategy.

Specific nanoarchitecture of silica nanoparticles codoped with the oppositely charged Mn2+ and Ru2+ complexes for dual paramagnetic-luminescent contrasting effects

The silica nanoparticles (SNs) co-doped with paramagnetic ([Mn(HL)]^n-,) and luminescent ([Ru(dipy)₃]²⁺) complexes are represented. The specific distribution of [Mn(HL)]^n- within the SNs allows to achieve about ten-fold enhancing in magnetic relaxivities in comparison with those of [Mn(HL)]^n- in solutions. The leaching of [Mn(HL)]^n- from the shell can be minimized through the co-doping of [Ru(dipy)₃]²⁺ into the core of the SNs. The co-doped SNs exhibit colloid stability in aqueous solutions, including those modeling a blood serum. The surface of the co-doped SNs was also decorated by amino- and carboxy-groups. The cytotoxicity, hemoagglutination and hemolytic activities of the co-doped SNs are on the levels convenient for "in vivo" studies, although the amino-decorated SNs cause more noticeable agglutination and suppression of cell viability. The co-doped SNs being intravenously injected into mice allows to reveal their biodistribution in both ex vivo and in vivo conditions through confocal microscopy and magnetic resonance imaging correspondingly.

Detection of magnetomotive ultrasound signals from human tissue

Rectal cancer is a common cancer, with presently a 5-year survival of 67 %. Treatment is based on tumor stage, but current staging methods, such as magnetic resonance imaging (MRI) or ultrasound, are limited in the ability to correctly stage the disease. Magnetomotive ultrasound is a developing modality that has a potential to improve rectal cancer staging. Magnetic nanoparticles are set in motion by an external magnetic field, and the resulting motion signature is detected by ultrasound. Here, we report on magnetomotive images of magnetic nanoparticles in human tissue, using a prototype system where a rotating permanent magnet provides the varying magnetic field, and an ultrasound transducer array encircling the magnet, detects the induced motion. Prior to surgery, a patient with a low rectal tumor was injected at three sites close to the tumor with magnetic nanoparticles. Postsurgical magnetomotive ultrasound scanning revealed the three injection sites, with no obvious artefactual signals. A phantom study showed detection of nanoparticles beyond 40 mm, where 30 mm is the expected maximum distance to mesorectal lymph nodes. Magnetomotive ultrasound image of iron oxide nanoparticles in human tissue. Prior to surgery a patient was injected with nanoparticles, and the excised tissue specimen was imaged with a prototype magnetomotive ultrasound system. The three colored areas overlaid on the standard B-mode greyscale image, correspond to the three injection sites.

Use of metal-based contrast agents for in vivo MR and CT imaging of phagocytic cells in neurological pathologies

The activation of phagocytic cells is a hallmark of many neurological diseases. Imaging them in their 3-dimensional cerebral environment over time is crucial to better understand their role in disease pathogenesis and to monitor their potential therapeutic effects. Phagocytic cells have the ability to internalize metal-based contrast agents both in vitro and in vivo and can thus be tracked by magnetic resonance imaging (MRI) or computed tomography (CT). In this review article, we summarize the different labelling strategies, contrast agents, and in vivo imaging modalities that can be used to monitor cells with phagocytic activity in the central nervous system using MRI and CT, with a focus on clinical applications. Metal-based nanoparticle contrast agents such as gadolinium, gold and iron are ideal candidates for these applications as they have favourable magnetic and/or radiopaque properties and can be fine-tuned for optimal uptake by phagocytic cells. However, they also come with downsides due to their potential toxicity, especially in the brain where they might accumulate. We therefore conclude our review by discussing the pitfalls, safety and potential for clinical translation of these metal-based neuroimaging techniques. Early results in patients with neuropathologies such as multiple sclerosis, stroke, trauma, cerebral aneurysm and glioblastoma are promising. If the challenges represented by safety issues are overcome, phagocytic cells imaging will be a very valuable tool for studying and understanding the inflammatory response and evaluating treatments that aim at mitigating this response in patients with neurological diseases.

Current advancement in the development of manganese complexes as magnetic resonance imaging probes

Emerging non-invasive molecular imaging modalities can detect a pathophysiological state at the molecular level before any anatomic changes are observed. Magnetic resonance imaging (MRI) is preferred over other nuclear imaging techniques owing to its radiation-free approach. Conventionally, most MRI contrast agents employed predominantly involve lanthanide metal: Gadolinium (Gd) until the discovery of associated severe nephrogenic toxicity issues. This limitation led a way to the development of manganese-based contrast agents which offer similar positive contrast enhancement capability. A vast quantity of experimental data has been accumulated over the last decade to define the physicochemical characteristics of manganese chelates with various ligand scaffolds. One can now observe how the ligand configurations, rigidity, and donor-acceptor characteristics impact the stability of the complex. This review covers the current trends in the development of manganese-based MRI contrast agents, the mechanisms they are based on and design considerations for newer manganese-based contrast agents with higher diagnostic strength along with better safety profiles.

Spectral computed tomography with inorganic nanomaterials: State-of-the-art

Recently, spectral computed tomography (CT) technology has received great interest in the field of radiology. Spectral CT imaging utilizes the distinct, energy-dependent X-ray absorption properties of substances in order to provide additional imaging information. Dual-energy CT and multi-energy CT (Spectral CT) are capable of constructing monochromatic energy images, material separation images, energy spectrum curves, constructing effective atomic number maps, and more. However, poor contrast, due to neighboring X-ray attenuation of organs and tissues, is still a challenge to spectral CT. Hence, contrast agents (CAs) are applied for better differentiation of a given region of interest (ROI). Currently, many different kinds of inorganic nanoparticulate CAs for spectral CT have been developed due to the limitations of clinical iodine (I)-based contrast media, leading to the conclusion that inorganic nanomedicine applied to spectral CT will be a powerful collaboration both in basic research and in clinics. In this review, the underlying principles and types of spectral CT techniques are discussed, and some evolving clinical diagnosis applications of spectral CT techniques are introduced. In particular, recent developments in inorganic CAs used for spectral CT are summarized. Finally, the challenges and future developments of inorganic nanomedicine in spectral CT are briefly discussed.

Contrast-enhanced ultrasound of solid pancreatic head lesions: a prospective study

OBJECTIVE

To evaluate the role of contrast-enhanced ultrasound (CEUS) in the differential diagnosis of solid pancreatic head lesions (SPHL).

METHODS

This prospective study comprised consecutive patients with SPHL who underwent CEUS evaluation of the pancreas. Findings recorded at CEUS were enhancement patterns (degree, completeness, centripetal enhancement, and percentage enhancement) and presence of central vessels. In addition, time to peak (TTP) and washout time (WT) were recorded. The final diagnosis was based on histopathology or cytology. Multivariate analysis was performed to identify parameters that were significantly associated with pancreatic ductal adenocarcinoma (PDAC).

RESULTS

Ninety-eight patients (median age 53.8 years, 59 males) were evaluated. The final diagnosis was PDAC (n = 64, 65.3%), inflammatory mass (n = 16, 16.3%), neuroendocrine tumor (NET, n = 14, 14.3%), and other tumors (n = 4, 4.1%). Hypoenhancement, incomplete enhancement, and centripetal enhancement were significantly more common in PDAC than non-PDAC lesions (p = 0.001, p = 0.031, and p = 0.002, respectively). Central vessels were present in a significantly greater number of non-PDAC lesions (p = 0.0001). Hypoenhancement with < 30% enhancement at CEUS had sensitivity and specificity of 80.6% and 67.7%, respectively, for PDAC. There was no significant difference in the TTP and WT between PDAC and non - PDAC lesions. However, the WT was significantly shorter in PDAC compared to NET (p = 0.011). In multivariate analysis, lack of central vessels was significantly associated with a PDAC diagnosis.

CONCLUSION

CEUS is a useful tool for the evaluation of SPHL. CEUS can be incorporated into the diagnostic algorithm to differentiate PDAC from non-PDAC lesions.

KEY POINTS

• Hypoenhancement and incomplete enhancement at CEUS were significantly more common in PDAC than in non-PDAC. • Central vessels at CEUS were significantly associated with PDAC. • There was no difference in TTP and WT between PDAC and non-PDAC lesions.

Age differential response to bevacizumab therapy in choroidal neovascularization in rabbits

Choroidal neovascularization (CNV) in young rabbits has been shown to have a rapid, robust response after treatment with bevacizumab, an anti-vascular endothelial growth factor (VEGF) medication. This investigation evaluates an age differential response to bevacizumab in older populations of rabbits using multimodal high resolution molecular imaging. Young (4 months old) and life span (14 months old) rabbits were given subretinal injections of Matrigel and VEGF to produce CNV. All CNV rabbit models were then treated with a bevacizumab intravitreal injection. Rabbits were then monitored longitudinally using photoacoustic microscopy (PAM), optical coherence tomography (OCT), color photography, and fluorescence imaging. Chain-like gold nanoparticle clusters (CGNP) conjugated with tripeptide arginylglycylaspartic acid (RGD) was injected intravenously for molecular imaging. Robust CNV developed in both young and old rabbits. After intravitreal bevacizumab injection, fluorescence signals were markedly decreased 90.13% in the young group. In contrast, old rabbit CNV area decreased by only 10.56% post-bevacizumab treatment. OCT images confirmed a rapid decrease of CNV in the young group. CGNPs demonstrated high PAM signal in old rabbits and minimal PAM signal in young rabbits after bevacizumab, indicating CNV regression. There is a significant difference in response to intravitreal bevacizumab treatment between young and old rabbits with CNV which can be monitored with multimodal molecular imaging. Old rabbits demonstrate significant persistent disease activity. This represents the first large eye model of persistent disease activity of CNV and could serve as the foundation for future investigations into the mechanism of persistent disease activity and the development of novel therapies.

Naturally grown duckweeds as quasi-hyperaccumulators of rare earth elements and yttrium in aquatic systems and the biounavailability of gadolinium-based MRI contrast agents

The use of rare earths and yttrium (REY) in high-technology products is accompanied by their increasing release into the environment. Concerns regarding the (eco-)toxicity and bioaccumulation of these emerging contaminants highlight the need for research on REY uptake by (aquatic) plants. Duckweeds are widespread macrophytes in lentic waters and receive increasing attention as a potential protein-rich food additive. We here provide a baseline dataset for the complete set of REY in naturally grown duckweed assemblages and ambient freshwater and coastal brackish seawater. Our results show that duckweeds strongly bioaccumulate REY and incorporate them at the μg/kg level (dry matter basis). Their shale-normalised (_SN) REY patterns are mildly fractionated relative to upper continental crust, regardless of sampling location and season. In contrast, the patterns of ambient waters increase from light to heavy REY (LREY and HREY, resp.) and may show prominent positive anthropogenic Gd_SN anomalies due to the presence of Gd-based contrast agents (Gd-CAs) applied for magnetic resonance imaging (MRI). The lack of Gd_SN anomalies in the duckweed assemblages reveals discrimination against the uptake of Gd-CAs by the macrophytes, providing further evidence for the conservative behaviour of these xenobiotics in the environment. High REY concentrations and apparent bulk distribution coefficients between duckweeds and ambient waters of up to 10⁵ show that duckweeds are quasi-hyperaccumulators of REY. Uptake of LREY is up to two orders of magnitude higher than of HREY, possibly due to stronger complexation of HREY with dissolved ligands. The REY closely correlate with Mn but not with Ca, suggesting that uptake of REY and Mn occurs via the same pathway and revealing the negligible role of calcium oxalates. Our study demonstrates that while duckweeds are quasi-hyperaccumulators of REY, there is currently no risk that anthropogenic Gd from MRI contrast agents may enter the food chain via consumption of duckweeds.

Glutathione-capped gold nanoclusters as near-infrared-emitting efficient contrast agents for confocal fluorescence imaging of tissue-mimicking phantoms

An innovative research has been conducted focused on demonstrating the ability of novel dual-emissive glutathione-stabilized gold nanoclusters (GSH-AuNCs) to perform bright near-infrared (NIR)-emitting contrast agents inside tissue-mimicking agarose-phantoms via two complementary confocal fluorescence imaging techniques. First, using a new and fast microwave-assisted approach, we synthesized photostable dual-emitting GSH-AuNCs with an average size of 3.2 ± 0.4 nm and NIR emission quantum yield of 9.9%. Steady-state fluorescence measurements coupled with fluorescence lifetime imaging microscopy (FLIM) assays performed on lyophilized GSH-AuNCs revealed that the obtained GSH-AuNCs exhibit PL emissions at 610 nm (red PL) and, respectively, 800 nm (NIR PL) in both solution and powder solid-state. Time-resolved fluorescence measurements showed that the two PL components are characterized by average lifetimes of 407 ns (red PL) and 1821 ns (NIR PL), respectively. Additionally, due to a partial overlap between the red PL and the absorption of the NIR PL, an energy transfer between the two coexisting emissive centers was discovered and confirmed via steady-state and time-resolved fluorescence measurements. Furthermore, the FLIM analysis performed on powder GSH-AuNCs under 640 nm, an excitation more suitable for bioimaging applications, revealed a homogeneous and photostable NIR PL signal from GSH-AuNCs. Finally, the ability of GSH-AuNCs to operate as reliable NIR-emitting contrast agents inside tissue-mimicking agarose-phantoms was demonstrated here for the first time via complementary FLIM and re-scan confocal fluorescence imaging techniques. In consequence, GSH-AuNCs show great promise for future in vivo imaging applications via confocal fluorescence microscopy.

Polymer-coated BiOCl nanosheets for safe and regioselective gastrointestinal X-ray imaging

Bismuth-based compounds are considered to be the best candidates for computed tomography (CT) imaging of gastrointestinal (GI) tract due to high X-ray absorption. Here, we report the introduction of polymer-coated bismuth oxychloride (BiOCl) nanosheets for highly efficient CT imaging in healthy mice and animal with colitis. We demonstrate simple, low cost and fast aqueous synthesis protocol which provides gram-quantity yield of chemically stable BiOCl nanosheets. The developed contrast gives 2.55-fold better CT enhancement compared to conventional contrast with negligible in vivo toxicity. As a major finding we report a regioselective CT imaging of GI tract by using nanoparticles coated with differentially charged polymers. Coating of nanoparticles with a positively charged polymer leads to their fast accumulation in small intestine, while the coating with negatively charged polymers stimulates prolonged stomach retention. We propose that this effect may be explained by a pH-controlled aggregation of nanoparticles in stomach. This feature may become the basis for advancement in clinical diagnosis of entire GI tract.

Recent development of contrast agents for magnetic resonance and multimodal imaging of glioblastoma

Glioblastoma (GBM) as the most common primary malignant brain tumor exhibits a high incidence and degree of malignancy as well as poor prognosis. Due to the existence of formidable blood–brain barrier (BBB) and the aggressive growth and infiltrating nature of GBM, timely diagnosis and treatment of GBM is still very challenging. Among different imaging modalities, magnetic resonance imaging (MRI) with merits including high soft tissue resolution, non-invasiveness and non-limited penetration depth has become the preferred tool for GBM diagnosis. Furthermore, multimodal imaging with combination of MRI and other imaging modalities would not only synergistically integrate the pros, but also overcome the certain limitation in each imaging modality, offering more accurate morphological and pathophysiological information of brain tumors. Since contrast agents contribute to amplify imaging signal output for unambiguous pin-pointing of tumors, tremendous efforts have been devoted to advances of contrast agents for MRI and multimodal imaging. Herein, we put special focus on summary of the most recent advances of not only MRI contrast agents including iron oxide-, manganese (Mn)-, gadolinium (Gd)-, ¹⁹F- and copper (Cu)-incorporated nanoplatforms for GBM imaging, but also dual-modal or triple-modal nanoprobes. Furthermore, potential obstacles and perspectives for future research and clinical translation of these contrast agents are discussed. We hope this review provides insights for scientists and students with interest in this area.

Contrast-enhanced ultrasonography to guide diagnostic and therapeutic interventional procedures

Although not necessary for the vast majority of ultrasound-guided procedures, intravenous contrast agents can be useful for procedures aimed at lesions that require contrast enhancement to be seen on ultrasonography. Using contrast-enhanced ultrasonography to guide procedures has two drawbacks: first, because enhancement from ultrasound contrast agents is short lived, it is often necessary to plan several injections; second, because the needle is poorly seen on contrast-enhanced ultrasonography, a dual image display format is necessary. Contrast-enhanced ultrasonography can be used for planning and monitoring diagnostic and therapeutic procedures, for guiding the procedures, and for follow-up. Using contrast-enhanced ultrasonography enables better results in both types of procedures; moreover, it can be used within cavities.

Slow-Flow Ultrasound Localization Microscopy Using Recondensation of Perfluoropentane Nanodroplets

Ultrasound localization microscopy (ULM) is an emerging, super-resolution imaging technique for detailed mapping of the microvascular structure and flow velocity via subwavelength localization and tracking of microbubbles. Because microbubbles rely on blood flow for movement throughout the vascular space, acquisition times can be long in the smallest, low-flow microvessels. In addition, detection of microbubbles in low-flow regions can be difficult because of minimal separation of microbubble signal from tissue. Nanoscale, phase-change contrast agents (PCCAs) have emerged as a switchable, intermittent or persisting contrast agent for ULM via acoustic droplet vaporization (ADV). Here, the focus is on characterizing the spatiotemporal contrast properties of less volatile perfluoropentane (PFP) PCCAs. The results indicate that at physiological temperature, nanoscale PFP PCCAs with diameters less than 100 nm disappear within microseconds after ADV with high-frequency ultrasound (16 MHz, 5- to 6-MPa peak negative pressure) and that nanoscale PFP PCCAs have an inherent deactivation mechanism via immediate recondensation after ADV. This "blinking" on-and-off contrast signal allowed separation of flow in an in vitro flow phantom, regardless of flow conditions, although with a need for some replenishment at very low flow conditions to maintain count rate. This blinking behavior allows for rapid spatial mapping in areas of low or no flow with ULM, but limits velocity tracking because there is no stable bubble formation with nanoscale PFP PCCAs.

The value of preoperative sentinel lymph node contrast-enhanced ultrasound for breast cancer: a large, multicenter trial

Objective

The study conducted a multicenter study in China to explore the learning curve of contrast enhanced ultrasound (CEUS) for sentinel lymph nodes (SLNs), the feasibility of using this technique for the localization of SLNs and lymphatic channels (LCs) and its diagnostic performance for lymph node metastasis.

Method

Nine hundred two patients with early invasive breast cancer from six tertiary class hospitals in China were enrolled between December 2016 and December 2019. Each patient received general ultrasound scanning and SLN-CEUS before surgery. The locations and sizes of LCs and SLNs were marked on the body surface based on observations from SLN-CEUS. These body surface markers were then compared with intraoperative blue staining in terms of their locations. The first 40 patients from each center were included in determining the learning curve of SLN-CEUS across sites. The remaining patients were used to investigate the diagnostic efficacy of this technique in comparison with intraoperative blue staining and pathology respectively.

Result

The ultrasound doctor can master SLN-CEUS after 25 cases, and the mean operating time is 22.5 min. The sensitivity, specificity, negative predictive value, and positive predictive value of SLN-CEUS in diagnosing lymph node metastases were 86.47, 89.81, 74.90, and 94.97% respectively.

Conclusion

Ultrasound doctors can master SLN-CEUS with a suitable learning curve. SLN-CEUS is a feasible and useful approach to locate SLNs and LCs before surgery and it is helpful for diagnosing LN metastases.

Manganese complexes and manganese-based metal-organic frameworks as contrast agents in MRI and chemotherapeutics agents: Applications and prospects

Manganese-based Metal-organic Frameworks (Mn-MOFs) represents a unique sub-class of MOFs with low toxicity, oxidative ability, and biocompatibility, which plays vital role in the application of this class of MOFs in medical field. Mn-MOFs show great potential in biomedical applications, and has been extensively studied as compared to other MOFs in transition metal series. They are important in medical applications because Mn(II) possess large electron spin number and longer electron relaxation time. They display fast water exchange rate and could be employed as a potential MRI contrast agent because of their strong targeting ability. Manganese complexes with different ligands also display prospective applications in area such as carrier for drug targeting in anti-tumor and antimicrobial therapy. In the review presented herewith, the application of Mn-based complexes and Mn-MOFs have been emphasized in the area such as imaging viz. MRI, multimodal imaging, antitumor activities such as chemodynamic therapy, photodynamic therapy, sonodynamic therapy and antimicrobial applications. Also, how rational designing and syntheses of targeted Mn-based complexes and Mn-MOFs can engender desired applications.

Effects of iron oxide nanoparticles as T2-MRI contrast agents on reproductive system in male mice

Iron oxide nanoparticles (IONPs)-based contrast agents are widely used for T₂-weighted magnetic resonance imaging (MRI) in clinical diagnosis, highlighting the necessity and importance to evaluate their potential systematic toxicities. Although a few previous studies have documented the toxicity concerns of IONPs to major organs, limited data are available on the potential reproductive toxicity caused by IONPs, especially when administrated via intravenous injection to mimic clinical use of MRI contrast agents. Our study aimed to determine whether exposure to IONPs would affect male reproductive system and cause other related health concerns in ICR mice. The mice were intravenously injected with different concentrations IONPs once followed by routine toxicity tests of major organs and a series of reproductive function-related analyses at different timepoints. As a result, most of the contrast agents were captured by reticuloendothelial system (RES) organs such as liver and spleen, while IONPs have not presented adverse effects on the normal function of these major organs. In contrast, although IONPs were not able to enter testis through the blood testicular barrier (BTB), and they have not obviously impaired the overall testicular function or altered the serum sex hormones levels, IONPs exposure could damage Sertoli cells in BTB especially at a relative high concentration. Moreover, IONPs administration led to a short-term reduction in the quantity and quality of sperms in a dose-dependent manner, which might be attributed to the increase of oxidative stress and apoptotic activity in epididymis. However, the semen parameters have gradually returned to the normal range within 14 days after the initial injection of IONPs. Collectively, these results demonstrated that IONPs could cause reversible damage to the reproductive system of male mice without affecting the main organs, providing new guidance for the clinical application of IONPs as T₂-MRI contrast agents.

A Human-derived Dual MRI/PET Reporter Gene System with High Translational Potential for Cell Tracking

PURPOSE

Reporter gene imaging has been extensively used to longitudinally report on whole-body distribution and viability of transplanted engineered cells. Multi-modal cell tracking can provide complementary information on cell fate. Typical multi-modal reporter gene systems often combine clinical and preclinical modalities. A multi-modal reporter gene system for magnetic resonance imaging (MRI) and positron emission tomography (PET), two clinical modalities, would be advantageous by combining the sensitivity of PET with the high-resolution morphology and non-ionizing nature of MRI.

PROCEDURES

We developed and evaluated a dual MRI/PET reporter gene system composed of two human-derived reporter genes that utilize clinical reporter probes for engineered cell detection. As a proof-of-concept, breast cancer cells were engineered to co-express the human organic anion transporter polypeptide 1B3 (OATP1B3) that uptakes the clinical MRI contrast agent gadolinium ethoxybenzyl-diethylenetriaminepentaacetic acid (Gd-EOB-DTPA), and the human sodium iodide symporter (NIS) which uptakes the PET tracer, [¹⁸F] tetrafluoroborate ([¹⁸F] TFB).

RESULTS

T₁-weighted MRI results in mice exhibited significantly higher MRI signals in reporter-gene-engineered mammary fat pad tumors versus contralateral naïve tumors (p < 0.05). No differences in contrast enhancement were observed at 5 h after Gd-EOB-DTPA administration using either intravenous or intraperitoneal injection. We also found significantly higher standard uptake values (SUV) in engineered tumors in comparison to the naïve tumors in [¹⁸F]TFB PET images (p < 0.001). Intratumoral heterogeneity in signal enhancement was more conspicuous in relatively higher resolution MR images compared to PET images.

CONCLUSIONS

Our study demonstrates the ability to noninvasively track cells engineered with our human-derived dual MRI/PET reporter system, enabling a more comprehensive evaluation of transplanted cells. Future work is focused on applying this tool to track therapeutic cells, which may one day enable the broader application of cell tracking within the healthcare system.

Developing a Microbubble-Based Contrast Agent for Synchrotron Multiple-Image Radiography

PURPOSE

Multiple-image radiography (MIR) is an analyzer-based synchrotron X-ray imaging approach capable of dissociating absorption, refraction, and scattering components of X-ray interaction with the material. It generates additional image contrast mechanisms (besides absorption), especially in the case of soft tissues, while minimizing absorbed radiation dose. Our goal is to develop a contrast agent for MIR using ultrasound microbubbles by carrying out a systematic assessment of size, shell material, and concentration.

PROCEDURES

Microbubbles were synthesized with two different shell materials: phospholipid and polyvinyl-alcohol. Polydisperse perfluorobutane-filled lipid microbubbles were divided into five size groups using centrifugation. Two distributions of air-filled polymer microbubbles were generated: 2-3 µm and 3-4 µm. A subset of polymer microbubbles 3-4 µm had iron oxide nanoparticles incorporated into their shell or coated on their surface. Microbubbles were immobilized in agar with different concentrations: 5 × 10⁷, 5 × 10⁶, and 5 × 10⁵ MBs/ml. MIR was conducted on the BioMedical Imaging and Therapy beamline at the Canadian Light Source. Three images were generated: Gaussian amplitude, refraction, and ultra-small-angle X-ray scattering (USAXS). The contrast signal was quantified by measuring mean pixel values and comparing them with agar.

RESULTS

No difference was detected in absorption or refraction images of all tested microbubbles. Using USAXS, a significant signal increase was observed with lipid microbubbles 6-10 µm at the highest concentration (p = 0.02), but no signal was observed at lower concentrations.

CONCLUSIONS

These data indicate that lipid microbubbles 6-10 µm are candidates as contrast agents for MIR, specifically for USAXS. A minimum concentration of 5 × 10⁷ microbubbles (lipid-shell 6-10 µm) per milliliter was needed to generate a detectable signal.

Evidence of high bioaccessibility of gadolinium-contrast agents in natural waters after human oral uptake

Considering the large occurrence of anthropogenic Gd concentrations in natural waters, its continuous usage increase in technology developments and products and the lack of data on potential Gd human exposure due to ingestion of contaminated waters, it is urgently needed to understand how gadolinium contrast agents (Gd-CAs) reacts in the human digestive system. Here, we aimed to identify through in vitro bioaccessibility tests whether Gd-CAs can be potentially assimilated by humans after oral uptake and if there is a significant difference between contrast agents. We also roughly estimated the potential bioaccessibility of anthropogenic Gd for tap waters worldwide. Gd-CAs are highly bioaccessible (77 to 112%). The macrocyclic complexes pose the highest potential risk, because there are more stable than linear complexes in the gastrointestinal tract and, as such, tend to remain in solution and thus might bring Gd at the intestinal barrier making it potentially bioavailable. The estimated range of potential intake of Gd varied from 13 to 4839 μg in a lifespan of 70 years. The high bioaccessibility of anthropogenic Gd in tap waters calls for appropriate actions to develop better practices to treat wastewater contaminated by Gd-CAs in order to safeguard population and ecosystem health.

Starting a pediatric contrast ultrasound service: made simple!

The addition of contrast US to an existing pediatric US service requires several preparatory steps. This overview provides a guide to simplify the process. Initially, it is important to communicate to all stakeholders the justifications for pediatric contrast US, including (1) its comparable or better diagnostic results relative to other modalities; (2) its reduction in procedural sedation or anesthesia by avoiding MRI or CT; (3) its reduction or elimination of radiation exposure by not having to perform fluoroscopy or CT; (4) the higher safety profile of US contrast agents (UCA) compared to other contrast agents; (5) the improved exam comfort and ease inherent to US, leading to better patient and family experience, including bedside US exams for children who cannot be transported; (6) the need for another diagnostic option in light of increasing demand by parents and providers; and (7) its status as an approved and reimbursable exam. It is necessary to have an UCA incorporated into the pharmacy formulary noting that only SonoVue/Lumason is currently approved for pediatric use. In the United States this UCA is approved for intravenous administration for cardiac and liver imaging and for vesicoureteric reflux detection with intravesical application. In Europe and China it is only approved for the intravesical use in children. All other applications are off-label. The US scanner needs to be equipped with contrast-specific software. The UCA has to be prepared just before the exam and it is important to strictly follow the steps as outlined in the packaging inserts in order to prevent premature destruction of the microbubbles. The initial training in contrast US is best focused on the frontline staff actually performing the US studies; these might be sonographers, pediatric or interventional radiologists, or trainees. It is important from the outset to educate the referring physicians about contrast US. It is helpful to participate in existing contrast US courses, particularly those with hands-on components.

Contrast agents for photoacoustic imaging: a review of stem cell tracking

With the advent of stem cell therapy for spinal cord injuries, stroke, burns, macular degeneration, heart diseases, diabetes, rheumatoid arthritis and osteoarthritis; the need to track the survival, migration pathways, spatial destination and differentiation of transplanted stem cells in a clinical setting has gained increased relevance. Indeed, getting regulatory approval to use these therapies in the clinic depends on biodistribution studies. Although optoacoustic imaging (OAI) or photoacoustic imaging can detect functional information of cell activities in real-time, the selection and application of suitable contrast agents is essential to achieve optimal sensitivity and contrast for sensing at clinically relevant depths and can even provide information about molecular activity. This review explores OAI methodologies in conjunction with the specific application of exogenous contrast agents in comparison to other imaging modalities and describes the properties of exogenous contrast agents for quantitative and qualitative monitoring of stem cells. Specific characteristics such as biocompatibility, the absorption coefficient, and surface functionalization are compared and how the labelling efficiency translates to both short and long-term visualization of mesenchymal stem cells is explored. An overview of novel properties of recently developed optoacoustic contrast agents and their capability to detect disease and recovery progression in clinical settings is provided which includes newly developed exogenous contrast agents to monitor stem cells in real-time for multimodal sensing.

Optothermal properties of plasmonic inorganic nanoparticles for photoacoustic applications

Plasmonic systems are becoming a favourable alternative to dye molecules in the generation of photoacoustic signals for spectroscopy and imaging. In particular, inorganic nanoparticles are appealing because of their versatility. In fact, as the shape, size and chemical composition of nanoparticles are directly correlated with their plasmonic properties, the excitation wavelength can be tuned to their plasmon resonance by adjusting such traits. This feature enables an extensive spectral range to be covered. In addition, surface chemical modifications can be performed to provide the nanoparticles with designed functionalities, e.g., selective affinity for specific macromolecules. The efficiency of the conversion of absorbed photon energy into heat, which is the physical basis of the photoacoustic signal, can be accurately determined by photoacoustic methods. This review contrasts studies that evaluate photoconversion in various kinds of nanomaterials by different methods, with the objective of facilitating the researchers' choice of suitable plasmonic nanoparticles for photoacoustic applications.

Safety and efficacy of citric acid-upconverting nanoparticles for multimodal biological imaging in BALB/c mice

There has been significant progress with rare-earth coated upconversion nanoparticles (UCNPs) representing a promising new generation of contrast agents for biomedical applications. However, in vivo biological safety remains poorly investigated. This work examined citric acid-UCNP (NaYF4:Yb³⁺/Gd³⁺, ∼ 5 nm, Cit-UCNP) generated as contrast agents for multimodal imaging with concurrent magnetic resonance (MRI) and X-ray computed tomography (CT). We first examined the in vitro cytotoxicity and efficacy of Cit-UCNPs as a contrast agent. We then performed a systematic investigation of their in vivo biodistribution and biocompatibility. Our results noted that Cit-UCNPs have minimal toxicity and demonstrated significant potential as contrast agents for multimodal biomedical imaging. This study indicates Cit-UCNPs could be a valuable addition to enhance long-term targeted diagnostic and prognostic multimodal clinical imaging approaches.

Facile Fabrication of BiF3: Ln (Ln = Gd, Yb, Er)@PVP Nanoparticles for High-Efficiency Computed Tomography Imaging

X-ray computed tomography (CT) has been widely used in clinical practice, and contrast agents such as Iohexol are often used to enhance the contrast of CT imaging between normal and diseased tissue. However, such contrast agents can have some toxicity. Thus, new CT contrast agents are urgently needed. Owing to the high atomic number (Z = 83), low cost, good biological safety, and great X-ray attenuation property (5.74 cm² kg^-1 at 100 keV), bismuth has gained great interest from researchers in the field of nano-sized CT contrast agents. Here, we synthesized BiF₃: Ln@PVP nanoparticles (NPs) with an average particle size of about 380 nm. After coating them with polyvinylpyrrolidone (PVP), the BiF₃: Ln@PVP NPs possessed good stability and great biocompatibility. Meanwhile, compared with the clinical contrast agent Iohexol, BiF₃: Ln@PVP NPs showed superior in vitro CT imaging contrast. Subsequently, after in situ injection with BiF₃: Ln@PVP NPs, the CT value of the tumor site after the injection was significantly higher than that before the injection (the CT value of the pre-injection and post-injection was 48.9 HU and 194.58 HU, respectively). The morphology of the gastrointestinal (GI) tract can be clearly observed over time after oral administration of BiF₃: Ln@PVP NPs. Finally, the BiF₃: Ln@PVP NPs were completely discharged from the GI tract of mice within 48 h of oral administration with no obvious damage to the GI tract. In summary, our easily synthesized BiF₃: Ln@PVP NPs can be used as a potential clinical contrast agent and may have broad application prospects in CT imaging.

Advances in micro-CT imaging of small animals

PURPOSE

Micron-scale computed tomography (micro-CT) imaging is a ubiquitous, cost-effective, and non-invasive three-dimensional imaging modality. We review recent developments and applications of micro-CT for preclinical research.

METHODS

Based on a comprehensive review of recent micro-CT literature, we summarize features of state-of-the-art hardware and ongoing challenges and promising research directions in the field.

RESULTS

Representative features of commercially available micro-CT scanners and some new applications for both in vivo and ex vivo imaging are described. New advancements include spectral scanning using dual-energy micro-CT based on energy-integrating detectors or a new generation of photon-counting x-ray detectors (PCDs). Beyond two-material discrimination, PCDs enable quantitative differentiation of intrinsic tissues from one or more extrinsic contrast agents. When these extrinsic contrast agents are incorporated into a nanoparticle platform (e.g. liposomes), novel micro-CT imaging applications are possible such as combined therapy and diagnostic imaging in the field of cancer theranostics. Another major area of research in micro-CT is in x-ray phase contrast (XPC) imaging. XPC imaging opens CT to many new imaging applications because phase changes are more sensitive to density variations in soft tissues than standard absorption imaging. We further review the impact of deep learning on micro-CT. We feature several recent works which have successfully applied deep learning to micro-CT data, and we outline several challenges specific to micro-CT.

CONCLUSIONS

All of these advancements establish micro-CT imaging at the forefront of preclinical research, able to provide anatomical, functional, and even molecular information while serving as a testbench for translational research.

Super-Resolution Ultrasound Localization Microscopy on a Rabbit Liver VX2 Tumor Model: An Initial Feasibility Study

Ultrasound localization microscopy can image microvasculature in vivo without sacrificing imaging penetration depth. However, the reliance on super-resolution inference limits the applicability of the technique because subpixel tissue motion can corrupt microvascular reconstruction. Consequently, the majority of previous pre-clinical research on this super-resolution procedure has been restricted to low-motion experimental models with ample motion correction or data rejection, which precludes the imaging of organ sites that exhibit a high degree of respiratory and other motion. In this article, we present a novel anesthesia protocol in rabbits that induces safe, controllable periods of apnea to enable the long image-acquisition times required for ultrasound localization microscopy. We apply this protocol to a VX2 liver tumor model undergoing sorafenib therapy and compare the results to super-resolution images from conventional high-dose isoflurane anesthesia. We find that the apneic protocol was necessary to correctly identify the poorly vascularized tumor cores, as verified by immunohistochemistry, and to reveal the tumoral microvascular architecture.

Functionalized contrast agents for multimodality photoacoustic microscopy, optical coherence tomography, and fluorescence microscopy molecular retinal imaging

Near-infrared (NIR) targeting contrast agents have been investigated as great photoabsorbers to improve photoacoustic microscopy (PAM), OCT, and fluorescence imaging contrast for visualization of various diseases. In ophthalmology, a limited number of NIR contrast agents have been approved for clinical use. Recently, gold nanoparticles with different size and shapes have been developed for molecular imaging. This chapter provides the principles of multimodality PAM, OCT, and fluorescence imaging as well as a brief overview of contrast agents for optical imaging. A detailed protocol for the fabrication of discrete colloidal gold nanoparticles (GNPs), synthesis of functionalized RGD-conjugated chain-like GNP (CGNP) clusters labeled with indocyanine green (ICG) fluorescence dye (ICG@CGNP clusters-RGD), and validation of the synthesized nanoparticles to evaluate newly developed blood vessels in the retina, named choroidal neovascularization (CNV), is described. Using RGD peptide, ICG@CGNPs clusters-RGD can bind integrin which is expressed on activated endothelial cells and newly developed CNV. The targeting efficiency of nanoparticles is monitored by multimodality PAM, OCT, and fluorescence imaging longitudinally.