Imaging Sentinel Lymph Nodes

Dual-radionuclide in vivo imaging of micro-metastasis and lymph tract with submillimetre resolution

Multi-radionuclide in vivo imaging with submillimetre resolution can be a potent tool for biomedical research. While high-resolution radionuclide imaging faces challenges in sensitivity, multi-radionuclide imaging encounters difficulty due to radiation contamination, stemming from crosstalk between radionuclides and Compton scattering. Addressing these challenges simultaneously is imperative for multi-radionuclide high-resolution imaging. To tackle this, we developed a high-spatial-resolution and high-energy-resolution small animal single-photon emission computed tomography (SPECT) scanner, named CdTe-DSD SPECT-I. We first assessed the feasibility of multi-tracer SPECT imaging of submillimetre targets. Using the CdTe-DSD SPECT-I, we performed SPECT imaging of submillimetre zeolite spheres absorbed with 125I- and subsequently imaged 125I-accumulated spheroids of 200-400 µm in size within an hour, achieving clear and quantitative images. Furthermore, dual-radionuclide phantom imaging revealed a distinct image of the submillimetre sphere absorbed with 125I- immersed in a 99mTc-pertechnetate solution, and provided a fair quantification of each radionuclide. Lastly, in vivo imaging was conducted on a cancer-bearing mouse with lymph node micro-metastasis using dual-tracers. The results displayed dual-tracer images of lymph tract by 99mTc-phytic acid and the submillimetre metastatic lesion by 125I-, shown to align with the immunofluorescence image.

Oncologic Imaging of the Lymphatic System: Current Perspective with Multi-Modality Imaging and New Horizon

The lymphatic system is an anatomically complex vascular network that is responsible for interstitial fluid homeostasis, transport of large interstitial particles and cells, immunity, and lipid absorption in the gastrointestinal tract. This network of specially adapted vessels and lymphoid tissue provides a major pathway for metastatic spread. Many malignancies produce vascular endothelial factors that induce tumoral and peritumoral lymphangiogenesis, increasing the likelihood for lymphatic spread. Radiologic evaluation for disease staging is the cornerstone of oncologic patient treatment and management. Multiple imaging modalities are available to access both local and distant metastasis. In this manuscript, we review the anatomy, physiology, and imaging of the lymphatic system.

Preoperative planar lymphoscintigraphy allows for sentinel lymph node detection in 51 dogs improving staging accuracy: Feasibility and pitfalls

Sentinel lymph node (SLN) mapping is the current gold standard for the oncological staging of solid malignancies in humans. This prospective observational study describes the feasibility and the limits of preoperative lymphoscintigraphy for SLN detection in dogs with spontaneous malignancies and the improvements in staging accuracy. Client‐owned dogs with confirmed malignant neoplasia and absence of distant metastasis were prospectively enrolled. Lymphoscintigraphy was performed after the peritumoral injection of Technetium‐99m labeled nanocolloids. Regional dynamic and static images were acquired, with and without masking of the injection site with a lead shield. The dogs were then subjected to surgery for tumor excision and SLN extirpation. Intraoperative SLN detection was performed by combining methylene blue dye and a dedicated gamma probe. Overall, 51 dogs with a total of 60 solid malignant tumors were enrolled. Lymphoscintigraphy identified at least one SLN in 57 of 60 cases (95%). The SLN did not always correspond to the regional lymph node (35/57, 61.4%). The use of a lead shield, masking the injection site, markedly improved the SLN visibility. The median time of SLN appearance was 11.4 ± 9.3 min. No side effects were observed. Preoperative lymphoscintigraphy allows for SLN detection in dogs and can improve staging accuracy by either identifying the SLN in a different lymphosome than clinically expected or discriminating the draining node in uncertain cases. The combined use of preoperative and intraoperative techniques is recommended to increase the SLN detection rate.

Design and Challenges of Radiopharmaceuticals

This review describes general concepts with regard to radiopharmaceuticals for diagnostic or therapeutic applications that help to understand the specific challenges encountered during the design, (radio)synthesis, in vitro and in vivo evaluation and clinical translation of novel radiopharmaceuticals. The design of a radiopharmaceutical requires upfront decisions with regard to combining a suitable vector molecule with an appropriate radionuclide, considering the type and location of the molecular target, the desired application, and the time constraints imposed by the relatively short half-life of radionuclides. Well-designed in vitro and in vivo experiments allow nonclinical validation of radiotracers. Ultimately, in combination with a limited toxicology package, the radiotracer becomes a radiopharmaceutical for clinical evaluation, produced in compliance with regulatory requirements for medicines for intravenous (IV) injection.

Evaluation of lymph node metastasis in a rabbit tumor model: correlations between contrast-enhanced ultrasound and pathologic findings

Purpose

The purpose of this study was to evaluate the ability of contrast-enhanced ultrasonography (CEUS) with microbubbles to detect metastatic lymph nodes (LNs) for treatment planning and prognosis.

Methods

For the metastatic LN model, ground VX₂ tumor tissues were injected subcutaneously in 12 rabbits, just below the right hind limb. The rabbits were classified into three groups based on the LN area: group A (n=4, >1.9 cm² ), group B (n=4, 1-1.9 cm² ), and group C (n=4, <1 cm² ). The LNs were monitored on CEUS for 10 seconds after injecting 2.5 mL of microbubbles. The percent area of metastatic LNs was calculated on pathologic images and compared with CEUS images.

Results

In group A, the mean percent area of metastasis was 40.7%±19.4%. In all cases of metastasis, round-shaped perfusion defects were clearly observed in CEUS images. The metastatic areas were strongly correlated with pathologic findings. The mean percent area in group B was 21.5%±14.4%. The CEUS findings showed multiple nodular perfusion defects, clearly revealing the metastatic areas. In group B, the CEUS and pathologic findings were concordant for three of the four cases. The mean percent area in group C was 9.1%±6.4%. However, in this group, CEUS only detected a small perfusion defect in one case.

Conclusion

CEUS has the potential to depict characteristic imaging features of metastatic LNs but still has limitations in early detection.

Axillary sentinel node biopsy in prone position for melanomas on the upper back or nape

In patients with melanomas on the upper back or nape, axillary sentinel lymph node (SLN) biopsy (SLNB), when performed in the traditional supine position, is often disturbed by scattered radiation emitted from the primary tumor site. The results from the present study suggestthat axillary SLNB performed in the prone position can solve this problem. We compared two consecutive groups of patients with melanomas of the dorsal trunk or nape who received axillary SLNB performed either in the supine (n = 119) or in the prone position (n = 130). The number of SLNs detected and excised was significantly higher in prone position group (2.4 ± 1.5 SLNs versus 1.9 ± 0.95 SLNs, p = 0.002). Using the prone position, intra-operative repositioning of the patient for excision of a primary site of the upper back or neck was not necessary. The SLN identification rates and the SLN-positivity rates did not differ significantly between the two types of intraoperative patient positioning. There were no significant differences in survival outcomes or false-negative rates. In conclusion, axillary SLNB in prone position yields a higher number of excised SLNs in patients with melanomas of the upper back or nape. Axillary SLNB in prone position is easy to perform and reliable. Intraoperative repositioning of the patient is not necessary, which saves time and resources.

Melanoma patient imaging in the era of effective systemic therapies

Imaging plays a critical role in the current multi-disciplinary management of patients with melanoma. It is used for primary disease staging, surgical planning, and surveillance in high-risk patients, and for monitoring the effects of systemic or loco-regional therapies. Several different imaging modalities have been utilised in the past. Contemporary imaging practises vary geographically depending on clinical guidelines, physician preferences, availability and cost. Targeted therapies and immunotherapies have revolutionised the treatment of patients with metastatic melanoma over the last few years. With this have come new patterns of disease that were not observed after conventional therapies, and new criteria to assess therapeutic responses. In this article we review the role of imaging for patients with melanoma in the era of effective systemic therapies and discuss likely future developments.

Sentinel Lymph Node Biopsy in Cutaneous Melanoma: Standard and New Technical Procedures and Clinical Advances. A Systematic Review of the Literature

Melanoma is an important public health problem, and its incidence is increasing worldwide. The disease status of regional lymph nodes is the most important prognostic factor in early-stage melanoma patients. Sentinel lymph node biopsy (SLNB) was introduced in the early 1990s as a less invasive procedure than complete lymph node dissection to allow histopathologic evaluation of the "sentinel lymph node" (SLN), which is the first node along the lymphatic pathway from a primary tumor. Sentinel lymph node biopsy has minimal complication risks compared with standard complete lymph node dissection. Currently, SLNB is the accepted method for staging patients with clinically node-negative cutaneous melanoma and provides the most powerful prognostic information by evaluating the nodal basin status. The current practice of SLNB consists of the injection of Tc-labeled radiopharmaceutical, preoperative lymphoscintigraphy with the possibility of using the SPECT/CT hybrid imaging, and intraoperative SLN localization using a handheld gamma probe with or without the use of blue dye. Recently, the SLN localization and detection have been enhanced with the use of new tracers and new intraoperative devices, which have demonstrated to be particularly useful in melanomas of the head and neck region and in area of complex anatomy. Despite these important advances in the technology and the increasing experience in SLN mapping, major research centers have reported a false-negative rate higher than 15%. This relatively high false-negative rate, greater than those reported in the initial validation studies, points out the importance for the nuclear medicine community to continuously improve their knowledge on the biological behavior of melanoma and to improve the technical aspects that may allow more precise staging. For the SLNB procedure to be accurate, it is of critical importance that all "true" SLNs are identified and removed for examination. The aim of this article is to provide general information about the SLNB procedure in clinical practice highlighting the importance of standardization and accuracy of SLN identification in the light of the most recent technical innovations.