Tumor bracketing and safety margin estimation using multimodal marker seeds: a proof of concept

The realization of medical devices for precision surgery - development and implementation of 'stop-and-go' imaging technologies

INTRODUCTION

Surgery and biomedical imaging encompass a big share of the medical-device market. The ever-mounting demand for precision surgery has driven the integration of these two into the field of image-guided surgery. A key-question herein is how imaging modalities can guide the surgical decision-making process. Through performance-based design, chemists, engineers, and doctors need to build a bridge between imaging technologies and surgical challenges.

AREAS-COVERED

This perspective article highlights the complementary nature between the technological design of an image-guidance modality and the type of procedure performed. The specific roles of the involved professionals, imaging technologies, and surgical indications are addressed.

EXPERT-OPINION

Molecular-image-guided surgery has the potential to advance pre-, intra- and post-operative tissue characterization. To achieve this, surgeons need the access to well-designed indication-specific chemical-agents and detection modalities. Hereby, some technologies stimulate exploration ('go'), while others stimulate caution ('stop'). However, failing to adequately address the indication-specific needs rises the risk of incorrect tool employment and sub-optimal surgical performance. Therefore, besides the availability of new technologies, market growth is highly dependent on the practical nature and impact on real-life clinical care. While urology currently takes the lead in the widespread implementation of image-guidance technologies, the topic is generic and its popularity spreads rapidly within surgical oncology.

Synthesis and In Vitro Evaluation of a HER2-Specific ImmunoSCIFI Probe

Secondary Cerenkov-induced fluorescence imaging (SCIFI) is an emerging biomedical optical imaging modality that leverages Cerenkov luminescence, primarily generated by β-emitting radioisotopes, to excite fluorophores that offer near-infrared emissions with optimal tissue penetrance. Dual-functionalized immunoconjugates composed of an antibody, a near-infrared fluorophore, and a β-emitting radioisotope have potential utility as novel SCIFI constructs with high specificity for molecular biomarkers of disease. Here, we report the synthesis and characterization of [89Zr]Zr-DFO-trastuzumab-BOD665, a self-excitatory HER2-specific "immunoSCIFI" probe capable of yielding near-infrared fluorescence in situ without external excitation. The penetration depth of the SCIFI signal was measured in hemoglobin-infused optical tissue phantoms that indicated a 2.05-fold increase compared to 89Zr-generated Cerenkov luminescence. Additionally, the binding specificity of the immunoSCIFI probe for HER2 was evaluated in a cellular assay that showed significantly higher binding to SKBR3 (high HER2 expression) relative to MDA-MB-468 (low HER2) breast cancer cells based on measurements of total flux in the near-infrared region with external excitation blocked. Taken together, the results of this study indicate the potential utility of immunoSCIFI constructs for interrogation of molecular biomarkers of disease.

Solitary pulmonary nodule imaging approaches and the role of optical fibre-based technologies

Solitary pulmonary nodules (SPNs) are a clinical challenge, given there is no single clinical sign or radiological feature that definitively identifies a benign from a malignant SPN. The early detection of lung cancer has a huge impact on survival outcome. Consequently, there is great interest in the prompt diagnosis, and treatment of malignant SPNs. Current diagnostic pathways involve endobronchial/transthoracic tissue biopsies or radiological surveillance, which can be associated with suboptimal diagnostic yield, healthcare costs and patient anxiety. Cutting-edge technologies are needed to disrupt and improve, existing care pathways. Optical fibre-based techniques, which can be delivered via the working channel of a bronchoscope or via transthoracic needle, may deliver advanced diagnostic capabilities in patients with SPNs. Optical endomicroscopy, an autofluorescence-based imaging technique, demonstrates abnormal alveolar structure in SPNs in vivo Alternative optical fingerprinting approaches, such as time-resolved fluorescence spectroscopy and fluorescence-lifetime imaging microscopy, have shown promise in discriminating lung cancer from surrounding healthy tissue. Whilst fibre-based Raman spectroscopy has enabled real-time characterisation of SPNs in vivo Fibre-based technologies have the potential to enable in situ characterisation and real-time microscopic imaging of SPNs, which could aid immediate treatment decisions in patients with SPNs. This review discusses advances in current imaging modalities for evaluating SPNs, including computed tomography (CT) and positron emission tomography-CT. It explores the emergence of optical fibre-based technologies, and discusses their potential role in patients with SPNs and suspected lung cancer.

Multi-Wavelength Fluorescence in Image-Guided Surgery, Clinical Feasibility and Future Perspectives

With the rise of fluorescence-guided surgery, it has become evident that different types of fluorescence signals can provide value in the surgical setting. Hereby a different range of targets have been pursued in a great variety of surgical indications. One of the future challenges lies in combining complementary fluorescent readouts during one and the same surgical procedure, so-called multi-wavelength fluorescence guidance. In this review we summarize the current clinical state-of-the-art in multi-wavelength fluorescence guidance, basic technical concepts, possible future extensions of existing clinical indications and impact that the technology can bring to clinical care.

Toward (Hybrid) Navigation of a Fluorescence Camera in an Open Surgery Setting

With the introduction of the hybrid tracer indocyanine green (ICG)-^99mTc-nanocolloid, a direct relation between preoperative imaging and intraoperative fluorescence guidance was established. However, fluorescence guidance remains limited by its superficial nature. This study evaluated the feasibility of a nuclear medicine-based navigation concept that allowed intraoperative positioning of a fluorescence camera (FC) in the vicinity of preoperatively defined ICG-^99mTc-nanocolloid containing sentinel nodes (SNs).

METHODS

Five patients with penile cancer scheduled for SN biopsy were injected with ICG-^99mTc-nanocolloid followed by preoperative SPECT/CT imaging. The navigation device was used to provide a real-time augmented reality overlay of the SPECT/CT images and video output of the FC. This overlay was then used for FC navigation.

RESULTS

SPECT/CT identified 13 SNs in 9 groins. FC navigation was successful for all 12 intraoperatively evaluated SNs (average error, 8.8 mm; range, 0-20 mm).

CONCLUSION

This study reveals the potential benefits of FC navigation during open surgery procedures.

U-SPECT-BioFluo: an integrated radionuclide, bioluminescence, and fluorescence imaging platform

Background

In vivo bioluminescence, fluorescence, and single-photon emission computed tomography (SPECT) imaging provide complementary information about biological processes. However, to date these signatures are evaluated separately on individual preclinical systems. In this paper, we introduce a fully integrated bioluminescence-fluorescence-SPECT platform. Next to an optimization in logistics and image fusion, this integration can help improve understanding of the optical imaging (OI) results.

Methods

An OI module was developed for a preclinical SPECT system (U-SPECT, MILabs, Utrecht, the Netherlands). The applicability of the module for bioluminescence and fluorescence imaging was evaluated in both a phantom and in an in vivo setting using mice implanted with a 4 T1-luc + tumor. A combination of a fluorescent dye and radioactive moiety was used to directly relate the optical images of the module to the SPECT findings. Bioluminescence imaging (BLI) was compared to the localization of the fluorescence signal in the tumors.

Results

Both the phantom and in vivo mouse studies showed that superficial fluorescence signals could be imaged accurately. The SPECT and bioluminescence images could be used to place the fluorescence findings in perspective, e.g. by showing tracer accumulation in non-target organs such as the liver and kidneys (SPECT) and giving a semi-quantitative read-out for tumor spread (bioluminescence).

Conclusions

We developed a fully integrated multimodal platform that provides complementary registered imaging of bioluminescent, fluorescent, and SPECT signatures in a single scanning session with a single dose of anesthesia. In our view, integration of these modalities helps to improve data interpretation of optical findings in relation to radionuclide images.

Fluorescent lectins for local in vivo visualization of peripheral nerves

Damage to peripheral nerves caused during a surgical intervention often results in function loss. Fluorescence imaging has the potential to improve intraoperative identification and preservation of these structures. However, only very few nerve targeting agents are available. This study describes the in vivo nerve staining capabilities of locally administered fluorescent lectin-analogues. To this end WGA, PNA, PHA-L and LEL were functionalized with Cy5 (λex max 640 nm; λem max 680 nm). Transfer of these imaging agents along the sciatic nerve was evaluated in Thy1-YFP mice (n = 12) after intramuscular injection. Migration from the injection site was assessed in vivo using a laboratory fluorescence scanner and ex vivo via fluorescence confocal microscopy. All four lectins showed retrograde movement and staining of the epineurium with a signal-to-muscle ratio of around two. On average, the longest transfer distance was obtained with WGA-Cy5 (0.95 cm). Since WGA also gave minimal uptake in the lymphatic system, this lectin type revealed the highest potential as a migration imaging agent to visualize nerves.

Image navigation as a means to expand the boundaries of fluorescence-guided surgery

Hybrid tracers that are both radioactive and fluorescent help extend the use of fluorescence-guided surgery to deeper structures. Such hybrid tracers facilitate preoperative surgical planning using (3D) scintigraphic images and enable synchronous intraoperative radio- and fluorescence guidance. Nevertheless, we previously found that improved orientation during laparoscopic surgery remains desirable. Here we illustrate how intraoperative navigation based on optical tracking of a fluorescence endoscope may help further improve the accuracy of hybrid surgical guidance. After feeding SPECT/CT images with an optical fiducial as a reference target to the navigation system, optical tracking could be used to position the tip of the fluorescence endoscope relative to the preoperative 3D imaging data. This hybrid navigation approach allowed us to accurately identify marker seeds in a phantom setup. The multispectral nature of the fluorescence endoscope enabled stepwise visualization of the two clinically approved fluorescent dyes, fluorescein and indocyanine green. In addition, the approach was used to navigate toward the prostate in a patient undergoing robot-assisted prostatectomy. Navigation of the tracked fluorescence endoscope toward the target identified on SPECT/CT resulted in real-time gradual visualization of the fluorescent signal in the prostate, thus providing an intraoperative confirmation of the navigation accuracy.

Hybrid peptide dendrimers for imaging of chemokine receptor 4 (CXCR4) expression

The chemokine receptor 4 (CXCR4), which is overexpressed in many types of cancer, is an emerging target in the field of molecular imaging and therapeutics. The CXCR4 binding of several peptides, including the cyclic Ac-TZ14011, has already been validated. In this study mono-, di- and tetrameric Ac-TZ14011-containing dendrimers were prepared and functionalized with a multimodal (hybrid) label, consisting of a Cy5.5-like fluorophore and a DTPA chelate. Confocal microscopy revealed that all three dendrimers were membrane bound at 4 °C, consistent with CXCR4 binding in vitro. The unlabeled dimer and tetramer had a somewhat lower affinity for CXCR4 than the unlabeled monomer. However, when labeled with the multimodal label the CXCR4 affinity of the dimer and tetramer was considerably higher compared to that of the labeled monomer. On top of that, biodistribution studies revealed that the additional peptides in the dimer and tetramer reduced nonspecific muscle uptake. Thus, multimerization of the cyclic Ac-TZ14011 peptide reduces the negative influence of the multimodal label on the receptor affinity and the biodistribution.

Peptide-functionalized luminescent iridium complexes for lifetime imaging of CXCR4 expression

The chemokine receptor 4 (CXCR4) is over-expressed in 23 types of cancer in which it plays a role in, among others, the metastatic spread. For this reason it is a potential biomarker for the field of diagnostic oncology. The antagonistic Ac-TZ14011 peptide, which binds to CXCR4, has been conjugated to luminescent iridium dyes to allow for CXCR4 visualization. The iridium dyes are cyclometalated octahedral iridium(III) 2-phenylpyridine complexes that can be functionalized with one, two or three targeting Ac-TZ14011 peptides. Confocal microscopy and fluorescence lifetime imaging microscopy (FLIM) showed that the peptide-iridium complex conjugates can be used to visualize CXCR4 expression in tumor cells. The CXCR4 receptor affinity and specific cell binding of the mono-, di- and trimeric peptide derivatives were assessed by using flow cytometry. The three derivatives possessed nanomolar receptor affinity and could distinguish between cell lines with different CXCR4 expression levels. This yields the first example of a neutral iridium(III) complex functionalized with peptides for FLIM-based visualization of a cancer associated membrane receptor.

Synthesis and evaluation of a bimodal CXCR4 antagonistic peptide

The antagonistic Ac-TZ14011 peptide, which binds to the chemokine receptor 4, has been labeled with a multifunctional single attachment point reagent that contains a DTPA chelate and a fluorescent dye with Cy5.5 spectral properties. Flow cytometry and confocal microscopy showed that the bimodal labeled peptide gave a specific receptor binding that is similar to monofunctionalized peptide derivatives. Therefore, the newly developed bimodal peptide derivative can be used in multimodal imaging applications.

Intraoperative laparoscopic fluorescence guidance to the sentinel lymph node in prostate cancer patients: clinical proof of concept of an integrated functional imaging approach using a multimodal tracer

BACKGROUND

Integration of molecular imaging and in particular intraoperative image guidance is expected to improve the surgical accuracy of laparoscopic lymph node (LN) dissection.

OBJECTIVE

To show the applicability of combining preoperative, intraoperative, and postoperative sentinel node imaging using an integrated diagnostic approach based on an imaging agent that is both radioactive and fluorescent.

DESIGN, SETTING, AND PARTICIPANTS

Before surgery, multimodal indocyanine green (ICG)-(99m)Tc-NanoColl was injected into the prostate. Subsequent lymphoscintigraphy and single-photon emission computed tomography/computed tomography (SPECT/CT) imaging of pelvic nodes was performed to determine the location of the sentinel lymph nodes (SLNs) preoperatively. During the surgical procedure a fluorescence laparoscope, optimized for detection in the near infrared range, was used to visualize the nodes identified on SPECT/CT. Eleven patients scheduled for robot-assisted laparoscopic prostatectomy (RALP) with an increased risk of nodal metastasis, based on Memorial Sloan-Kettering Cancer Center/Kattan nomogram estimation, participated in a pilot assessment (N09IGF).

SURGICAL PROCEDURE

Patients underwent RALP with LN dissection for prostate cancer.

MEASUREMENTS

Radioactive and fluorescent signals were monitored using different modalities, and the correlation between the two types of signals was studied. The location of preoperatively detected SLNs was documented.

RESULTS AND LIMITATIONS

Preoperatively, SLNs were identified by SPECT/CT, and the multimodal nature of the imaging agent also enabled intraoperative detection via fluorescence imaging. Fluorescence particularly improved surgical guidance in areas with a high radioactive background signal such as the injection site. Ex vivo analysis revealed a strong correlation between the radioactive and fluorescent content in the excised LNs. Fluorescence detection is limited by the severe tissue attenuation of the signal. Therefore, radio guidance to the areas of interest is still desirable.

CONCLUSIONS

Initial data indicate that multimodal ICG-(99m)Tc-NanoColloid, in combination with a laparoscopic fluorescence laparoscope, can be used to facilitate and optimize dissection of SLNs during RALP procedures.

(Non-targeted) radioactive/fluorescent nanoparticles and their potential in combined pre- and intraoperative imaging during sentinel lymph node resection

One clinical precedent for the use of nanosized imaging agents is the localization of the tumor draining sentinel lymph nodes. In this application, radiocolloids such as (99m)Tc-NanoColl are currently used to plan the surgical procedure and to provide acoustic guidance during the intervention. Additional injections of dyes are common to provide optical surgical guidance. Bimodal imaging agents, which are both radioactive and fluorescent, have the potential to be used for both surgical planning and intraoperative fluorescence guidance towards the sentinel lymph nodes. This review provides an overview of the radioactive, fluorescent, and size properties of (non-targeted) bimodal nanoparticles, and their (potential) value in sentinel lymph node detection.