Search

Purpose Recent technical advancements in PET imaging have improved sensitivity and spatial resolution. Consequently, clinical nuclear medicine will be confronted with PET images on a previously unfamiliar resolution. To better understand [F-18]FDG distribution at submillimetric scale, a direct correlation of radionuclide-imaging and histopathology is required.Methods A total of five patients diagnosed with a malignancy of the head and neck were injected with a clinical activity of [F-18]FDG before undergoing surgical resection. The resected specimen was imaged using a preclinical high-resolution PET/CT, followed by slicing of the specimen. Multiple slices were rescanned using a micro-PET/CT device, and one of the slices was snap-frozen for frozen sections. Frozen sections were placed on an autoradiographic film, followed by haematoxylin and eosin staining to prepare them for histopathological assessment. The results from both autoradiography and histopathology were co-registered using an iterative co-registration algorithm, and regions of interest were identified to study radiotracer uptake.Results The co-registration between the autoradiographs and their corresponding histopathology was successful in all specimens. The use of this novel methodology allowed direct comparison of autoradiography and histopathology and enabled the visualisation of uncharted heterogeneity in [F-18]FDG uptake in both benign and malignant tissue.Conclusion We here describe a novel methodology enabling the direct co-registration of [F-18]FDG autoradiography with the gold standard of histopathology in human malignant tissue. The future use of the current methodology could further increase our understanding of the distribution of radionuclides in surgically excised malignancies and hence, improve the integration of pathology and molecular imaging in a multiscale perspective.

Introduction Each year, more than two million women worldwide are diagnosed with breast cancer [1]. In the typical surgical treatment of this cancer the primary tumour is removed together with the so called sentinel lymph nodes (SLNs), the lymph nodes that have the highest probability of being invaded by cancer cells. The current clinical standard to detect SLNs makes use of a combination of radioactive 99mTc labelled nanocolloids and blue dyes, but has downsides such as less flexible imaging procedures and long-lasting skin discoloration. There is a need for safer and better methods to perform diagnosis. Methods Here we have developed dual-modality HfO2 nanocrystals (NCs) for the in vivo detection of SLNs using X-ray Computed Tomography (CT) and near-infrared (NIR) fluorescence. To resemble the behavior of the currently used 99mTc labelled nanocolloids, the NCs were synthesized to be approximately the same size after surface functionalization (5-10 nm). Next, strongly binding ligands [2] were designed, synthesised and combined with click chemistry to obtain highly concentrated and stable suspensions of the functionalized dual-modality NCs in PBS. We then performed an in vivo evaluation of the NCs in mice, imaging the lymphatic system using CT and NIR-fluorescence over time and compared their performance to 99mTc-Nanocoll, the most used radiographic compound for SLN identification in Europe. Results/Discussion Custom ligands were successfully synthesized for payload coupling to obtain a stable dual-modality NC formulation. We found that shortly after subcutaneous hind footpad injection of the formulation, containing a dose of 0.28 mg NCs/g bodyweight and 28 µmol/L conjugated fluorophore, the NCs drain to the SLN and provide high in vivo CT contrast enhancement and NIR-fluorescence. The signal for both modalities remains high over several hours, which could make the NCs useable for extended surgical procedures. A longitudinal study on a test group (N = 6) showed that the contrast-to-noise (CNR) ratio of the SLN becomes sufficiently high, CNR > 4-5, for diagnostic purposes starting approximately 15-30 mins post-injection while little to no contrast enhancement was observed in higher echelons. Finally, in the comparison with 99mTc-nanocolloids we found that the NCs show similar drainage behaviour as the clinical standard while allowing for faster scan times at higher spatial resolution. Conclusions Through synthesis and surface chemistry optimization, dual-modality HfO2 NCs were enabled to perform lymphatic imaging. An in vivo proof-of-concept showed that they could be used as alternative for the current clinical standard, opening up diagnostic applications and guided surgery on imaging modalities that are more readily available, with improved probe shelf-life and overall lower radiation exposure.

Aim/Introduction: Over the last decades, the use of 18F-FDG has taken a pivotal role in oncological diagnosis, staging and follow-up. While endless research has shown the clinical importance of 18F-FDG, we remain unaware how 18F-FDG behaves in and around human malignancies on a submillimetric scale. Unfortunately, as glucose metabolism is an active process, pathological assessment of relevant protein markers was found to be inadequate in correctly predicting 18F-FDG-uptake. Technological improvements are resulting in increasing spatial resolution for PET-scanners, therefore an urgent understanding of 18F-FDG-distribution on these higher resolutions is required. Materials and Methods: In the current study, we developed a methodology that enabled direct coregistration of the radioactivity-distribution in a surgically resected specimen with histopathological assessment. Patients were injected with 4 MBq/kg of 18F-FDG prior to the initiation of standard of care surgical oncological resection. After resection of the malignancy, the surgical specimen was imaged using preclinical micro-PET and -CT devices with a spatial resolution of 800µm and 50µm, respectively. After imaging, the specimen was freshly sliced into thin slices of approximately 2mm by a pathologist. One slice was snap-frozen and frozen sections were imaged using an autoradiographic flm overnight. Following the imaging, frozen sections were stained with standard hematoxylin and eosin staining. Pathological results were overlayed with the results of 18F-FDG PET/CT and autoradiography to coregister the histopathological and imaging results. Results: We performed this methodology on a total of four patients with cutaneous squamous cell carcinoma (n=2), angiosarcoma (n=1) and thyroid medullary carcinoma (n=1). While the mean time between injection and autoradiography was 3h49, we were able to image sufcient radioactivity to directly coregister the results with the clinical pathological frozen sections. All regions with identifed malignant tissue displayed increased 18F-FDG-uptake. However, uptake was not limited to these regions, as a similar increased uptake was identifed in adjacent benign sebaceous glands. Interestingly, we also identifed a heterogeneous 18F-FDGuptake in separate clusters of malignant tissue, which could partly be explained by the cluster’s amount of peritumoral infammatory cells. Conclusion: To the best of our knowledge, these results are the frst to describe direct coregistration of 18F-FDG with the gold standard of histopathology in any human malignancy. These heterogeneous results display an important diversity in metabolic activity between diferent tumor and peritumoral tissues. The use of this methodology could increase our understanding of radiotracer distribution in human diseases on a previously unprecedented scale in clinical nuclear medicine.