A handheld fluorescence molecular tomography system for intraoperative optical imaging of tumor margins

Quantitative tumor depth determination using dual wavelength excitation fluorescence

Quantifying solid tumor margins with fluorescence-guided surgery approaches is a challenge, particularly when using near infrared (NIR) wavelengths due to increased penetration depths. An NIR dual wavelength excitation fluorescence (DWEF) approach was developed that capitalizes on the wavelength-dependent attenuation of light in tissue to determine fluorophore depth. A portable dual wavelength excitation fluorescence imaging system was built and tested in parallel with an NIR tumor-targeting fluorophore in tissue mimicking phantoms, chicken tissue, and in vivo mouse models of breast cancer. The system showed high accuracy in all experiments. The low cost and simplicity of this approach make it ideal for clinical use.

Advanced iron oxide nanotheranostics for multimodal and precision treatment of pancreatic ductal adenocarcinoma

Despite current advances in new approaches for cancer detection and treatment, pancreatic cancer remains one of the most lethal cancer types. Difficult to detect early, aggressive tumor biology, and resistance to chemotherapy, radiotherapy, and immunotherapy result in a poor prognosis of pancreatic cancer patients with a 5-year survival of 10%. With advances in cancer nanotechnology, new imaging and drug delivery approaches that allow the development of multifunctional nanotheranostic agents offer opportunities for improving pancreatic cancer treatment using precision oncology. In this review, we will introduce potential applications of innovative theranostic strategies to address major challenges in the treatment of pancreatic cancer at different disease stages. Several important issues concerning targeted delivery of theranostic nanoparticles and tumor stromal barriers are discussed. We then focus on the development of a magnetic iron oxide nanoparticle platform for multimodal therapy of pancreatic cancer, including MRI monitoring targeted nanoparticle/drug delivery, therapeutic response, and tumor re-staging, activation of tumor immune response by immunoactivating nanoparticle and magnetic hyperthermia therapy, and intraoperative interventions for improving the outcome of targeted therapy. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Diagnostic Tools > In Vivo Nanodiagnostics and Imaging.

In Vivo Evaluation of a Miniaturized Fluorescence Molecular Tomography (FMT) Endoscope for Breast Cancer Detection Using Targeted Nanoprobes

In this study, in vivo animal experiments with 12 nude mice bearing breast-cancer-patient-tissue-derived xenograft (PDX) tumors were performed aiming to verify the imaging capability of a novel miniaturized fluorescence molecular tomography (FMT) endoscope, in combination with targeted nanoparticle–near-infrared (NIR) dye conjugates. Tumor-bearing mice were divided into two groups by systematic injection with urokinase plasminogen activator receptor-targeted (n = 7) and nontargeted (n = 5) imaging nanoprobes as a contrast agent, respectively. Each mouse was imaged at 6, 24, and 48 h following the injection of nanoprobes using the FMT endoscope. The results show that systemic delivery of targeted nanoprobes produced a 4-fold enhancement in fluorescence signals from tumors, compared with tumors that received nontargeted nanoprobes. This study indicates that our miniaturized FMT endoscope, coupled with the targeted nanoparticle–NIR dye conjugates as a contrast agent, has high sensitivity and specificity, and thus great potential to be used for image-guided detection and removal of a primary tumor and local metastatic tumors during surgery.

Full density fluorescence molecular tomography (FD-FMT) based on a dichroic mirror

We present a novel method called full density fluorescence molecular tomography (FD-FMT) that can considerably improve the performance of conventional FMT. By converting each source (or detector) to a detector (or source) through the use of a dichroic mirror, FD-FMT not only increases the amount of optical projections by more than fourfold (compared to conventional FMT) to achieve high-resolution image reconstruction, but also offers the possibility to realize miniaturized FMT systems.

Reconstruction method for fluorescence molecular tomography based on L1-norm primal accelerated proximal gradient

Fluorescence molecular tomography (FMT) has been widely used in preclinical tumor imaging, which enables three-dimensional imaging of the distribution of fluorescent probes in small animal bodies via image reconstruction method. However, the reconstruction results are usually unsatisfactory in the term of robustness and efficiency because of the ill-posed and ill-conditioned of FMT problem. In this study, an FMT reconstruction method based on primal accelerated proximal gradient (PAPG) descent and L1-norm regularized projection (L1RP) is proposed. The proposed method utilizes the current and previous iterations to obtain a search point at each iteration. To achieve fast convergence, the PAPG method is applied to efficiently solve the search point, and then L1RP is performed to obtain the robust and accurate reconstruction. To verify the performance of the proposed method, simulation experiments are conducted. The comparative results revealed that it held advantages of robustness, accuracy, and efficiency in FMT reconstructions. Furthermore, a phantom experiment and an in vivo mouse experiment were also performed, which proved the potential and feasibility of the proposed method for practical applications.

Fluorescence-guided surgery and intervention - An AAPM emerging technology blue paper

Fluorescence-guided surgery (FGS) and other interventions are rapidly evolving as a class of technologically driven interventional approaches in which many surgical specialties visualize fluorescent molecular tracers or biomarkers through associated cameras or oculars to guide clinical decisions on pathological lesion detection and excision/ablation. The technology has been commercialized for some specific applications, but also presents technical challenges unique to optical imaging that could confound the utility of some interventional procedures where real-time decisions must be made. Accordingly, the AAPM has initiated the publication of this Blue Paper of The Emerging Technology Working Group (TETAWG) and the creation of a Task Group from the Therapy Physics Committee within the Treatment Delivery Subcommittee. In describing the relevant issues, this document outlines the key parameters, stakeholders, impacts, and outcomes of clinical FGS technology and its applications. The presentation is not intended to be conclusive, but rather to inform the field of medical physics and stimulate the discussions needed in the field with respect to a seemingly low-risk imaging technology that has high potential for significant therapeutic impact. This AAPM Task Group is working toward consensus around guidelines and standards for advancing the field safely and effectively.

Tailoring Adjuvant Radiation Therapy by Intraoperative Imaging to Detect Residual Cancer

For many solid cancers, radiation therapy is offered as an adjuvant to surgical resection to lower rates of local recurrence and improve survival. However, a subset of patients treated with surgery alone will not have a local recurrence. Currently, there is no way to accurately determine which patients have microscopic residual disease in the tumor bed after surgery and therefore are most likely to benefit from adjuvant radiation therapy. To address this problem, a number of technologies have been developed to try to improve margin assessment of resected tissue and to detect residual cancer in the tumor bed. Moreover, some of these approaches have been translated from the preclinical arena into clinical trials. Here, we review different types of intraoperative molecular imaging systems for cancer. Optical imaging techniques like epi-illumination, fluorescence molecular tomography and optoacoustic imaging can be coupled with exogenous fluorescent imaging probes that accumulate in tumors passively via the enhanced permeability and retention effect or are targeted to tumor tissues based on affinity or enzyme activity. In these approaches, detection of fluorescence in the tumor bed may indicate residual disease. Protease activated probes have generated great interest because of their potential for leading to high tumor to normal contrast. Recently, the first Phase I clinical trial to assess the safety and activation of a protease activated probe was conducted. Spectroscopic methods like radiofrequency spectroscopy and Raman spectroscopy, which are based on energy absorption and scattering, respectively, have also been tested in humans and are able to distinguish between normal and tumors tissues intraoperatively. Most recently, multimodal contrast agents have been developed that target tumors and contain both fluorescent dyes and magnetic resonance imaging contrast agents, allowing for preoperative planning and intraoperative margin assessment with a single contrast agent. Further clinical testing of these various intraoperative imaging approaches may lead to more accurate methods for margin assessment and the intraoperative detection of microscopic residual disease, which could guide further resection and the use of adjuvant radiation therapy.

Reconstruction of fluorescence molecular tomography via a nonmonotone spectral projected gradient pursuit method

Fluorescence molecular tomography (FMT) is a promising imaging technique in preclinical research, enabling three-dimensional location of the specific tumor position for small animal imaging. However, FMT presents a challenging inverse problem that is quite ill-posed and ill-conditioned. Thus, the reconstruction of FMT faces various challenges in its robustness and efficiency. We present an FMT reconstruction method based on nonmonotone spectral projected gradient pursuit (NSPGP) with /₁-norm optimization. At each iteration, a spectral gradient-projection method approximately minimizes a least-squares problem with an explicit one-norm constraint. A nonmonotone line search strategy is utilized to get the appropriate updating direction, which guarantees global convergence. Additionally, the Barzilai-Borwein step length is applied to build the optimal step length, further improving the convergence speed of the proposed method. Several numerical simulation studies, including multisource cases as well as comparative analyses, have been performed to evaluate the performance of the proposed method. The results indicate that the proposed NSPGP method is able to ensure the accuracy, robustness, and efficiency of FMT reconstruction. Furthermore, an in vivo experiment based on a heterogeneous mouse model was conducted, and the results demonstrated that the proposed method held the potential for practical applications of FMT.

Basic science research in pediatric radiology - how to empower the leading edge of our field

Basic science research aims to explore, understand and predict phenomena in the natural world. It spurs the discovery of fundamentally new principles and leads to new knowledge and new concepts. By comparison, applied research employs basic science knowledge toward practical applications. In the clinical realm, basic science research and applied research should be closely connected. Basic science discoveries can build the foundation for a broad range of practical applications and thereby bring major benefits to human health, education, environment and economy. This article explains how basic science research impacts our field, it describes examples of new research directions in pediatric imaging and it outlines current challenges that we need to overcome in order to enable the next groundbreaking discovery.

uPAR-targeted optical imaging contrasts as theranostic agents for tumor margin detection

Complete removal of tumors by surgery is the most important prognostic factor for cancer patients with the early stage cancers. The ability to identify invasive tumor edges of the primary tumor, locally invaded small tumor lesions, and drug resistant residual tumors following neoadjuvant therapy during surgery should significantly reduce the incidence of local tumor recurrence and improve survival of cancer patients. In this study, we report that urokinase plasminogen activator (uPA) and its receptor (uPAR) are the ligand/cell surface target pair for the development of targeted optical imaging probes for enhancing imaging contrasts in the tumor border. Recombinant peptides of the amino terminal fragment (ATF) of the receptor binding domain of uPA were labeled with near infrared fluorescence (NIR) dye molecules either as peptide-imaging or peptide-conjugated nanoparticle imaging probes. Systemic delivery of the uPAR-targeted imaging probes in mice bearing orthotopic human breast or pancreatic tumor xenografts or mouse mammary tumors led to the accumulation of the probes in the tumor and stromal cells, resulting in strong signals for optical imaging of tumors and identification of tumor margins. Histological analysis showed that a high level of uPAR-targeted nanoparticles was present in the tumor edge or active tumor stroma immediately adjacent to the tumor cells. Furthermore, following targeted therapy using uPAR-targeted theranostic nanoparticles, residual tumors were detectable by optical imaging through the imaging contrasts produced by NIR-dye-labeled theranostic nanoparticles in drug resistant tumor cells. Therefore, results of our study support the potential of the development of uPAR-targeted imaging and theranostic agents for image-guided surgery.

HER-2/neu targeted delivery of a nanoprobe enables dual photoacoustic and fluorescence tomography of ovarian cancer

Development of sensitive and specific imaging approaches for the detection of ovarian cancer holds great promise for improving survival of ovarian cancer patients. Here we describe a dual-modality photoacoustic and fluorescence molecular tomography (PAT/FMT) approach in combination with a targeted imaging probe for three-dimensional imaging of ovarian tumors in mice. We found that the selective accumulation of the HER-2/neu targeted magnetic iron oxide nanoparticles (IONPs) led to about 5-fold contrast enhancements in the tumor for PAT, while near-infrared (NIR) dye labeled nanoparticles emitted strong optical signals for FMT. Both PAT and FMT were demonstrated to be able to detect ovarian tumors located deep in the peritoneal cavity in mice. The targeted nanoprobes allowed mapping tumors in high resolution via PAT, and high sensitivity and specificity via FMT. This study demonstrated the potential of the application of HER-2/neu-targeted PAT/FMT approach for non-invasive or intraoperative imaging of ovarian cancer.

FROM THE CLINICAL EDITOR

This paper details the development of a dual-modality photoacoustic and fluorescence molecular tomography approach in combination with a targeted imaging probe for three-dimensional imaging of ovarian tumors in a mouse model, demonstrating the application of the HER-2/neu-targeted approach for non-invasive or intraoperative imaging of ovarian cancer.

Assessing breast cancer margins ex vivo using aqueous quantum-dot-molecular probes

Positive margins have been a critical issue that hinders the success of breast- conserving surgery. The incidence of positive margins is estimated to range from 20% to as high as 60%. Currently, there is no effective intraoperative method for margin assessment. It would be desirable if there is a rapid and reliable breast cancer margin assessment tool in the operating room so that further surgery can be continued if necessary to reduce re-excision rate. In this study, we seek to develop a sensitive and specific molecular probe to help surgeons assess if the surgical margin is clean. The molecular probe consists of the unique aqueous quantum dots developed in our laboratory conjugated with antibodies specific to breast cancer markers such as Tn-antigen. Excised tumors from tumor-bearing nude mice were used to demonstrate the method. AQD-Tn mAb probe proved to be sensitive and specific to identify cancer area quantitatively without being affected by the heterogeneity of the tissue. The integrity of the surgical specimen was not affected by the AQD treatment. Furthermore, AQD-Tn mAb method could determine margin status within 30 minutes of tumor excision, indicating its potential as an accurate intraoperative margin assessment method.

Microelectromechanical systems scanning-mirror-based handheld probe for fluorescence molecular tomography

A novel handheld probe based on a microelectromechanical systems (MEMS) scanning mirror for three-dimensional (3D) fluorescence molecular tomography (FMT) is described. The miniaturized probe consists of a MEMS mirror for delivering an excitation light beam to multiple preselected points at the tissue surface and an optical fiber array for collecting the fluorescent emission light from the tissue. Several phantom experiments based on indocyanine green, an FDA approved near-infrared (NIR) fluorescent dye, were conducted to assess the imaging ability of this device. Tumor-bearing mice with systematically injected tumor-targeted NIR fluorescent probes were scanned to further demonstrate the ability of this MEMS-based FMT for imaging small animals.

A NaYbF4: Tm3+ nanoprobe for CT and NIR-to-NIR fluorescent bimodal imaging

Early diagnosis that combines the high-resolutional CT and sensitive NIR-fluorescence bioimaging could provide more accurate information for cancerous tissues, which, however, remain a big challenge. Here we report a simple bimodal imaging platform based on PEGylated NaYbF(4): Tm(3+) nanoparticles (NPs) of less than 20 nm in diameter for both CT and NIR-fluorescence bioimaging. The as-designed nanoprobes showed excellent in vitro and in vivo performances in the dual-bioimaging, very low cytotoxicity and no detectable tissue damage in one month. Remarkably, the Yb(3+) in the lattice of NaYbF(4): Tm(3+) NPs functions not only as a promising CT contrast medium due to its high X-ray absorption coefficiency, but also an excellent sensitizer contributing to the strong NIR-fluorescent emissions for its large NIR absorption cross-section. In addition, these NPs could be easily excreted mainly via feces without detectable remnant in the animal bodies.