Photoacoustic imaging as a highly efficient and precise imaging strategy for the evaluation of brain diseases

Near-Infrared Absorbing Aza-BODIPY Dyes for Optoelectronic Applications

Organic dyes that absorb light in the visible to near-infrared region have garnered significant interest, owing to their extensive utility in organic photovoltaics and various biomedical applications. Aza-boron-dipyrromethene (Aza-BODIPY) dyes are a class of chromophores with impressive photophysical properties such as tunable absorption from the visible region towards near infrared (NIR) region, high molar absorptivity, and fluorescence quantum yield. In this review, we discuss the developments in the aza-BODIPYs, related to their synthetic routes, photophysical properties and their applications. Their design strategies, modifications in chemical structures, mode/position of attachment, and their impact on photo-physical properties are reviewed. The potential applications of aza-BODIPY derivatives such as organic solar cells, photodynamic therapy, boron-neutron capture therapy, fluorescence sensors, photo-redox catalysis, photoacoustic probes and optoelectronic devices are explained.

Achieving Gross Total Resection in Neurosurgery: A Review of Intraoperative Techniques and Their Influence on Surgical Goals

The definition of complete resection in neurosurgery depends on tumor type, surgical aims, and postoperative investigations, directly guiding the choice of intraoperative tools. Most common tumor types present challenges in achieving complete resection due to their infiltrative nature and anatomical constraints. The development of adjuvant treatments has altered the balance between oncological aims and surgical risks. We review local recurrence associated with incomplete resection based on different definitions and emphasize the importance of achieving maximal safe resection in all tumor types. Intraoperative techniques that aid surgeons in identifying tumor boundaries are used in practice and in preclinical or clinical research settings. They encompass both conservative and invasive techniques. Among them, morphological tools include imaging modalities such as intraoperative magnetic resonance imaging, ultrasound, and optical coherence tomography. Fluorescence-guided surgery, mainly using 5-aminolevulinic acid, enhances gross total resection in glioblastomas. Nuclear methods, including positron emission tomography probes, provide tumor detection based on beta or gamma emission after a radiotracer injection. Mass spectrometry- and spectroscopy-based methods offer molecular insights. The adoption of these techniques depends on their relevance, effectiveness, and feasibility. With the emergence of positron emission tomography imaging for use in recurrence benchmarking, positron emission tomography probes raise particular interest among those tools. While all such tools provide valuable insights, their clinical benefits need further evaluation.

Simultaneous photoacoustic and ultrasound imaging: A review

Photoacoustic imaging (PAI) is an emerging biomedical imaging technique that combines the advantages of optical and ultrasound imaging, enabling the generation of images with both optical resolution and acoustic penetration depth. By leveraging similar signal acquisition and processing methods, the integration of photoacoustic and ultrasound imaging has introduced a novel hybrid imaging modality suitable for clinical applications. Photoacoustic-ultrasound imaging allows for non-invasive, high-resolution, and deep-penetrating imaging, providing a wealth of image information. In recent years, with the deepening research and the expanding biomedical application scenarios of photoacoustic-ultrasound bimodal systems, the immense potential of photoacoustic-ultrasound bimodal imaging in basic research and clinical applications has been demonstrated, with some research achievements already commercialized. In this review, we introduce the principles, technical advantages, and biomedical applications of photoacoustic-ultrasound bimodal imaging techniques, specifically focusing on tomographic, microscopic, and endoscopic imaging modalities. Furthermore, we discuss the future directions of photoacoustic-ultrasound bimodal imaging technology.

Second Near-Infrared Macrophage-Biomimetic Nanoprobes for Photoacoustic Imaging of Neuroinflammation

Neuroinflammation is a significant pathological event involving the neurodegenerative process associated with many neurological disorders. Diagnosis and treatment of neuroinflammation in its early stage are essential for the prevention and management of neurological diseases. Herein, we designed macrophage membrane-coated photoacoustic (PA) probes (MSINPs), with targeting specificities based on naturally existing target-ligand interactions for the early diagnosis of neuroinflammation. The second near-infrared dye, IR1061, was doped into silica as the core and was encapsulated with a macrophage membrane. In vitro as well as in vivo, the MSINPs could target inflammatory cells via the inflammation chemotactic effect. PA imaging was used to trace the MSINPs in a neuroinflammation mouse model and showed a great targeted effect of MSINPs in the prefrontal cortex. Therefore, the biomimetic nanoprobe prepared in this study offers a new strategy for PA molecular imaging of neuroinflammation, which can enhance our understanding of the evolution of neuroinflammation in specific brain regions.

Effect of PVP Molecular Weights on the Synthesis of Ultrasmall Cus Nanoflakes: Synthesis, Properties, and Potential Application for Phototheranostics

Copper sulfide nanoparticles (CuS) hold tremendous potential for applications in photothermal therapy (PTT) and photoacoustic imaging (PAI). However, the conventional chemical coprecipitation method often leads to particle agglomeration issues. To overcome this challenge, we utilized polyvinylpyrrolidone (PVP) as a stabilizing agent, resulting in the synthesis of small PVP-CuS nanoparticles named PC10, PCK30, and PC40. Our study aimed to investigate how different molecular weights of PVP influence the nanoparticles' crystalline characteristics and essential properties, especially their photoacoustic and photothermal responses. While prior research on PVP-assisted CuS nanoparticles has been conducted, our study delves deeper into this area, providing insights into optical properties. Remarkably, all synthesized nanoparticles exhibited a crystalline structure, were smaller than 10 nm, and featured an absorbance peak at 1020 nm, indicating their robust photoacoustic and photothermal capabilities. Among these nanoparticles, PC10 emerged as the standout performer, displaying superior photoacoustic properties. Our photothermal experiments demonstrated significant temperature increases in all cases, with PC10 achieving an impressive efficiency of 51%. Moreover, cytotoxicity assays revealed the nanoparticles' compatibility with cells, coupled with an enhanced incidence of apoptosis compared to necrosis. These findings underscore the promising potential of PVP-stabilized CuS nanoparticles for advanced cancer theranostics.

Theranostic Phthalocyanine and Naphthalocyanine Nanoparticles for Photoacoustic Imaging and Photothermal Therapy of Tumors

Background: Phthalocyanine (PC) and naphthalocyanine (NC) dyes have long garnered interest as theranostic agents for optical imaging and phototherapy due to their near-infrared absorbance, photostability, imaging contrast, and proven safety in clinical trials. Yet, only a small fraction of these dyes has been evaluated as photothermal therapy (PTT) agents for cancer treatment. Methods: Nearly 40 distinct NC and PC dyes were encapsulated within polymeric PEG-PCL micelles via oil-in-water emulsions. The optimal NC/PC-loaded micelle formulations for PTT and photoacoustic (PA) imaging were identified through in vivo and in vitro studies. Results: The most promising candidate, CuNC(Octa)-loaded micelles, demonstrated a strong PA signal with a peak absorbance at ~870 nm, high photothermal efficiency, and photostability. The CuNC(Octa)-loaded micelles exhibited heat generation as good or better than gold nanorods/nanoshells and >10-fold higher photoacoustic signals. Micelle preparation was reproducible/scalable, and the CuNC(Octa)-loaded micelles are highly stable under physiological conditions. The CuNC(Octa)-loaded micelles localize within tumors via enhanced permeability and retention and are readily detectable by PA imaging. In a syngeneic murine tumor model of triple-negative breast cancer, CuNC(Octa)-loaded micelles demonstrate efficient heat generation with PTT, leading to the complete eradication of tumors. Conclusions: CuNC(Octa)-loaded micelles represent a promising theranostic agent for PA imaging and PTT. The ability to utilize conventional ultrasound in combination with PA imaging enables the simultaneous acquisition of information about tumor morphology and micelle accumulation. PTT with CuNC(Octa)-loaded micelles can lead to the complete eradication of highly invasive tumors.

Survey of Transfer Learning Approaches in the Machine Learning of Digital Health Sensing Data

Machine learning and digital health sensing data have led to numerous research achievements aimed at improving digital health technology. However, using machine learning in digital health poses challenges related to data availability, such as incomplete, unstructured, and fragmented data, as well as issues related to data privacy, security, and data format standardization. Furthermore, there is a risk of bias and discrimination in machine learning models. Thus, developing an accurate prediction model from scratch can be an expensive and complicated task that often requires extensive experiments and complex computations. Transfer learning methods have emerged as a feasible solution to address these issues by transferring knowledge from a previously trained task to develop high-performance prediction models for a new task. This survey paper provides a comprehensive study of the effectiveness of transfer learning for digital health applications to enhance the accuracy and efficiency of diagnoses and prognoses, as well as to improve healthcare services. The first part of this survey paper presents and discusses the most common digital health sensing technologies as valuable data resources for machine learning applications, including transfer learning. The second part discusses the meaning of transfer learning, clarifying the categories and types of knowledge transfer. It also explains transfer learning methods and strategies, and their role in addressing the challenges in developing accurate machine learning models, specifically on digital health sensing data. These methods include feature extraction, fine-tuning, domain adaptation, multitask learning, federated learning, and few-/single-/zero-shot learning. This survey paper highlights the key features of each transfer learning method and strategy, and discusses the limitations and challenges of using transfer learning for digital health applications. Overall, this paper is a comprehensive survey of transfer learning methods on digital health sensing data which aims to inspire researchers to gain knowledge of transfer learning approaches and their applications in digital health, enhance the current transfer learning approaches in digital health, develop new transfer learning strategies to overcome the current limitations, and apply them to a variety of digital health technologies.

Unleashing novel horizons in advanced prostate cancer treatment: investigating the potential of prostate specific membrane antigen-targeted nanomedicine-based combination therapy

Prostate cancer (PCa) is a prevalent malignancy with increasing incidence in middle-aged and older men. Despite various treatment options, advanced metastatic PCa remains challenging with poor prognosis and limited effective therapies. Nanomedicine, with its targeted drug delivery capabilities, has emerged as a promising approach to enhance treatment efficacy and reduce adverse effects. Prostate-specific membrane antigen (PSMA) stands as one of the most distinctive and highly selective biomarkers for PCa, exhibiting robust expression in PCa cells. In this review, we explore the applications of PSMA-targeted nanomedicines in advanced PCa management. Our primary objective is to bridge the gap between cutting-edge nanomedicine research and clinical practice, making it accessible to the medical community. We discuss mainstream treatment strategies for advanced PCa, including chemotherapy, radiotherapy, and immunotherapy, in the context of PSMA-targeted nanomedicines. Additionally, we elucidate novel treatment concepts such as photodynamic and photothermal therapies, along with nano-theragnostics. We present the content in a clear and accessible manner, appealing to general physicians, including those with limited backgrounds in biochemistry and bioengineering. The review emphasizes the potential benefits of PSMA-targeted nanomedicines in enhancing treatment efficiency and improving patient outcomes. While the use of PSMA-targeted nano-drug delivery has demonstrated promising results, further investigation is required to comprehend the precise mechanisms of action, pharmacotoxicity, and long-term outcomes. By meticulous optimization of the combination of nanomedicines and PSMA ligands, a novel horizon of PSMA-targeted nanomedicine-based combination therapy could bring renewed hope for patients with advanced PCa.

Optimizing Axial and Peripheral Substitutions in Si-Centered Naphthalocyanine Dyes for Enhancing Aqueous Solubility and Photoacoustic Signal Intensity

Photoacoustic imaging using external contrast agents is emerging as a powerful modality for real-time molecular imaging of deep-seated tumors. There are several chromophores, such as indocyanine green and IRDye800, that can potentially be used for photoacoustic imaging; however, their use is limited due to several drawbacks, particularly photostability. There is, therefore, an urgent need to design agents to enhance contrast in photoacoustic imaging. Naphthalocyanine dyes have been demonstrated for their use as photoacoustic contrast agents; however, their low solubility in aqueous solvents and high aggregation propensity limit their application. In this study, we report the synthesis and characterization of silicon-centered naphthalocyanine dyes with high aqueous solubility and near infra-red (NIR) absorption in the range of 850-920 nm which make them ideal candidates for photoacoustic imaging. A series of Silicon-centered naphthalocyanine dyes were developed with varying axial and peripheral substitutions, all in an attempt to enhance their aqueous solubility and improve photophysical properties. We demonstrate that axial incorporation of charged ammonium mesylate group enhances water solubility. Moreover, the incorporation of peripheral 2-methoxyethoxy groups at the α-position modulates the electronic properties by altering the π-electron delocalization and enhancing photoacoustic signal amplitude. In addition, all the dyes were synthesized to incorporate an N-hydroxysuccinimidyl group to enable further bioconjugation. In summary, we report the synthesis of water-soluble silicon-centered naphthalocyanine dyes with a high photoacoustic signal amplitude that can potentially be used as contrast agents for molecular photoacoustic imaging.

Recent Trend of Ultrasound-Mediated Nanoparticle Delivery for Brain Imaging and Treatment

In view of the fact that the blood-brain barrier (BBB) prevents the transport of imaging probes and therapeutic agents to the brain and thus hinders the diagnosis and treatment of brain-related disorders, methods of circumventing this problem (e.g., ultrasound-mediated nanoparticle delivery) have drawn much attention. Among the related techniques, focused ultrasound (FUS) is a favorite means of enhancing drug delivery via transient BBB opening. Photoacoustic brain imaging relies on the conversion of light into heat and the detection of ultrasound signals from contrast agents, offering the benefits of high resolution and large penetration depth. The extensive versatility and adjustable physicochemical properties of nanoparticles make them promising therapeutic agents and imaging probes, allowing for successful brain imaging and treatment through the combined action of ultrasound and nanoparticulate agents. FUS-induced BBB opening enables nanoparticle-based drug delivery systems to efficiently access the brain. Moreover, photoacoustic brain imaging using nanoparticle-based contrast agents effectively visualizes brain morphologies or diseases. Herein, we review the progress in the simultaneous use of nanoparticles and ultrasound in brain research, revealing the potential of ultrasound-mediated nanoparticle delivery for the effective diagnosis and treatment of brain disorders.

Organic Small Molecule Contrast Agent for Targeted Photoacoustic Imaging of Patient-Derived Brain Tumors

Traditional glioblastoma (GBM) cell lines do not maintain the heterogeneity of the original tumor, cell interactions, and therapy response, thus limiting their investigation in GBM theranostics. Herein, a kind of GBM tumor-targeting nanoparticles (NPs) TCFNP@iRGD are designed and constructed, which are generated by photoacoustic (PA) contrast agent 2-(3-cyano-4,5,5-trimethylfuran-2(5H)-ylidene) malononitrile (TCF)-OH through facile nanoprecipitation and decorated with an active targeting ligand iRGD. Their potential in GBM detection via PA imaging on glioma patient-derived cells intracranial xenograft models is evaluated for the first time. Excellent tumor-specific PA mapping performance of GBM is realized by TCFNP@iRGD, demonstrating its promising potential in the clinical diagnosis of GBM.

Optical fiber-based handheld polarized photoacoustic computed tomography for detecting anisotropy of tissues

BACKGROUND

Photoacoustic computed tomography (PACT) is a fast-developing biomedical imaging modality and has immense potential for clinical translation. It utilizes laser excitation and acoustic detection to achieve high spatial resolution and considerable imaging depth in biological tissues. Current PACT primarily treats the absorption coefficient of tissues as a scalar variable while reconstructing the image, which limits its use for anisotropic evaluation of the tissues. Thus, by incorporating polarized imaging methods to evaluate anisotropy, applications of PACT can be further enhanced. So far, dichroism-sensitive PACT has been suggested for polarization detection of biological tissues. However, this approach is unsuitable for intraoperative imaging, since high-power spatial light is needed for excitation, which is dangerous and inconvenient to operate. Thus, there is a need to develop a polarized PACT system suitable for clinical use.

METHODS

Herein, we have proposed a specially designed handheld polarized PACT (HP-PACT) system, which was designed to promote intraoperative anisotropy detection of biological tissues. Excitation light was delivered by an optical fiber and reshaped by a compact set of lenses at the output end of the optical fiber. A polarizer was applied to generate linearly polarized light, and the polarization direction was adjusted by simply rotating the half-wave plate. Photoacoustic imaging (PAI) using excitation with several different polarization directions was carried out. Optical axes and the structure of the anisotropic objects were obtained using the principle of polarization detection with the PAI.

RESULTS

We experimentally demonstrated the performance of HP-PACT by imaging both the polarized and unpolarized plastic films. The results showed that HP-PACT can successfully detect the direction of the optical axes of polarized plastic films and has the ability to image at different depths. When linearly polarized light with different polarization directions was used as excitation, PAI studies on a highly anisotropic bovine tendon and relatively low anisotropic mouse leg showed the structural differences between the 2 tissues. The quantified degrees of anisotropy of the bovine tendon and mouse legs were 0.6 and 0.3, respectively.

CONCLUSIONS

The proposed HP-PACT is able to determine the anisotropic substances' optical axes and distinguish anisotropic substances from isotropic ones. Thus, HP-PACT has the potential for intraoperative diagnosis and treatment of anisotropic tissues, including nerves and tendons.

Oxygen saturation and blood volume analysis by Photoacoustic imaging to identify pre and post-PDT vascular changes

In this study, the blood volume and oxygen saturation of tumors were measured after photoacoustic imaging (PAI) under conditions of pre-photodynamic therapy (PDT), post-PDT, and 4 hrs, and 24 hrs post-PDT. PDTs with aminolevulinic acid (ALA) and low and high doses of benzoporphyrin derivative (BPD) were conducted to observe oxygen saturation changes, and the rapid oxygen consumption in the blood detected due to the action of BPD at the vascular level resulted in the recovery of PDT completion. Likewise, blood volume changes followed by ALA-PDT and BPD-PDT at low and high doses depicted a fast expansion of the blood volume after treatment. The tumor subjected to a high dose of ALA-PDT showed a partial alteration of Hb-pO₂ in the first 24 hrs, as did the tumors treated with two ALA- and BPD-mediated PDTs. The Hb-pO₂ started reducing immediately post-PDT and was less than 30% after 4 hrs until 24 hrs post-PDT. Reduced vascular demand was possibly due to tumor necrosis, as shown by the permanent damage in the cancer cells' bioluminescence signal. The ALA-mediated PDT-subjected tumor showed a 50% drop in BV at 24 hrs post-PDT, which is suggestive of vascular pruning. The studied data of blood volume against BLI showed the blood volume and oxygenation variations validating the cells' metabolic activity, including cell death.

Cerebrovascular imaging in vivo by non-contact photoacoustic microscopy based on photoacoustic remote sensing with a laser diode for interrogation

Photoacoustic microscopy (PAM) is a unique tool for biomedical applications because it can visualize optical absorption contrast in vivo. Recently, non-contact PAM based on non-interferometric photoacoustic remote sensing (PARS), termed PARS microscopy, has shown promise for selected imaging applications. A variety of superluminescent diodes (SLDs) have been employed in the PARS microscopy system as the interrogation light source. Here, we investigate the use of a low-cost laser diode (LD) as the interrogation light source in PARS microscopy, termed PARS-LD. A side-by-side comparison of PARS-LD and a PARS microscopy system using an SLD was conducted that showed comparable performance in terms of resolution and signal-to-noise ratio. More importantly, for the first time to our knowledge, in vivo PAM imaging of mouse brain vessels was conducted in a non-contact manner, and the results show that PARS-LD provides great performance.

Quantitative multilayered assessment of skin lightening by photoacoustic microscopy

BACKGROUND

With the emergence of various new skin-lightening products, there is an urgent need to scientifically evaluate the efficacy and toxicology of these products, and provide scientific guidance for their use based on physiological differences between individuals. Visualized imaging methods and quantitative evaluation criteria play key roles in evaluating the efficacy of skin-lightening products. In order to quantify the changes in the multilayered morphology and endogenous components of human skin before and after the use of lightening products, high-resolution three-dimensional (3D) imaging of human skin is required.

METHODS

In this study, photoacoustic microscopy (PAM; SSPM-532, Guangdong Photoacoustic Medical Technology Co., Ltd.) was used to capture the morphological structures of human skin and reveal skin components quantitatively. The efficacy and safety of skin-lightening products were evaluated by measuring skin melanin concentration and observing skin morphology. The melanin concentration in the epidermis was obtained by examining the linear relationship between photoacoustic (PA) signals. Further, the epidermal thickness and the melanin distribution were obtained in the cross-sectional (x-z) and lateral (x-y) images. Finally, the efficacy of skin-lightening products was evaluated according to the concentration and distribution of melanin in the epidermis, and the safety of cosmetics was assessed by observing the vascular morphology in the dermis.

RESULTS

PAM noninvasively could assess the multilayered morphological structures of human skin, which allowed for quantification of epidermal thickness and melanin concentration of different skin sites. Based on this, the efficacy and safety of skin-lightening products in multilayer structures were quantitatively evaluated.

CONCLUSIONS

As a quantitative imaging method, PAM, has the potential to accurately evaluate the use of skin-lightening products. The method can also be extended to assessments within the larger field of aesthetic medicine.

Sulourea-coordinated Pd nanocubes for NIR-responsive photothermal/H2S therapy of cancer

BACKGROUND

Photothermal therapy (PTT) frequently cause thermal resistance in tumor cells by inducing the heat shock response, limiting its therapeutic effect. Hydrogen sulfide (H2S) with appropriate concentration can reverse the Warburg effect in cancer cells. The combination of PTT with H2S gas therapy is expected to achieve synergistic tumor treatment.

METHODS

Here, sulourea (Su) is developed as a thermosensitive/hydrolysable H2S donor to be loaded into Pd nanocubes through in-depth coordination for construction of the Pd-Su nanomedicine for the first time to achieve photo-controlled H2S release, realizing the effective combination of photothermal therapy and H2S gas therapy.

RESULTS

The Pd-Su nanomedicine shows a high Su loading capacity (85 mg g-1), a high near-infrared (NIR) photothermal conversion efficiency (69.4%), and NIR-controlled H2S release by the photothermal-triggered hydrolysis of Su. The combination of photothermal heating and H2S produces a strong synergetic effect by H2S-induced inhibition of heat shock response, thereby effectively inhibiting tumor growth. Moreover, high intratumoral accumulation of the Pd-Su nanomedicine after intravenous injection also enables photothermal/photoacoustic dual-mode imaging-guided tumor treatment.

CONCLUSIONS

The proposed NIR-responsive heat/H2S release strategy provides a new approach for effective cancer therapy.

Second near-infrared (NIR-II) imaging: a novel diagnostic technique for brain diseases

Imaging in the second near-infrared II (NIR-II) window, a kind of biomedical imaging technology with characteristics of high sensitivity, high resolution, and real-time imaging, is commonly used in the diagnosis of brain diseases. Compared with the conventional visible light (400-750 nm) and NIR-I (750-900 nm) imaging, the NIR-II has a longer wavelength of 1000-1700 nm. Notably, the superiorities of NIR-II can minimize the light scattering and autofluorescence of biological tissue with the depth of brain tissue penetration up to 7.4 mm. Herein, we summarized the main principles of NIR-II in animal models of traumatic brain injury, cerebrovascular visualization, brain tumor, inflammation, and stroke. Simultaneously, we encapsulated the in vivo process of NIR-II probes and their in vivo and in vitro toxic effects. We further dissected its limitations and following optimization measures.

In vivo Multi-scale Photoacoustic Imaging Guided Photothermal Therapy of Cervical Cancer based on Customized Laser System and Targeted Nanoparticles

BACKGROUND

Effective treatment strategy for cervical carcinoma is subject to the limitation of its anatomical location and histological characteristics. Comprehensive imaging before cervical carcinoma treatment is of great significance for the patients. Current imaging methods cannot meet the requirements of high resolution, deep imaging depth and non-invasive imaging at the same time. Fortunately, Photoacoustic imaging (PAI) is a novel imaging method that combines rich optical contrast, high ultrasonic spatial resolution, and deep penetration depth in a single modality. Moreover, PAI-guided photothermal therapy (PTT) by aid of targeting nanoparticles is an emerging and effective cancer treatment in recent years.

METHODS

Here, strong near-infrared region (NIR) absorption-conjugated polymer PIIGDTS (PD) nanoparticles with folic acid (FA) modification (namely, PD-FA) that targeted at Hela cell were specifically designed as cervical tumor imaging contrast agents and photothermal agents.

RESULTS

The obtained PD-FA nanoparticles exhibited admirable photoacoustic contrast-enhancing ability and desirable PTT behavior with the photothermal conversion efficiency as high as 62.6% in vitro. Furthermore, the PAI performance and PTT efficiency were tested in HeLa tumor-bearing nude mice after injection of PD-FA nanoparticles. In vivo multi-scale, PAI provided B-san and 3D dimension imaging for intuitive and comprehensive information of Hela tumor. Moreover, the Hela tumor can be completely eliminated within 18 days after PTT, with no toxicity and side effects.

CONCLUSION

In summary, PD-FA injection combined with PAI and PTT systems provides a novel powerful tool for early diagnosis and precise treatment of cervical cancer.