Hybrid integration of real-time US and freehand SPECT: proof of concept in patients with thyroid diseases

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.

Feasibility and Performance of Free-Hand Single-Photon Computed Tomography/Ultrasonography for Preoperative Parathyroid Adenoma Localization: A Pilot Study

The aim of this prospective pilot study was to evaluate the feasibility of a new hybrid imaging modality, free-hand single-photon computed tomography/ultrasonography (fhSPECT/US), for preoperative localization of parathyroid adenomas and to compare its performance with conventional ultrasonography and SPECT/CT. Twelve patients diagnosed with primary hyperparathyroidism underwent sequentially US and parathyroid scintigraphy, including SPECT/CT, followed by fhSPECT/US, allowing for real-time fusion between US and freehand-generated gamma-camera images. The fhSPECT/US detection rates were correlated with histopathology, when available, or with the imaging modality showing the most lesions. Based on a per patient analysis, the detection rate was significantly different when comparing SPECT/CT to fhSPECT/US (p = 0.03), and not significantly different when comparing SPECT/CT to US (p = 0.16) and US to fhSPECT/US (p = 0.08). Based on a per-lesion analysis, the detection rate of SPECT/CT was significantly higher than that of US (p = 0.01) and fhSEPCT/US (p = 0.003), and there was no significant difference in detection rate when comparing US to fhSPECT/US (p = 0.08). The main perceived limitations of fhSPECT/US in lesion detection were: (i) lesions localized at a depth ≥4.5 cm; (ii) imperfect image fusion due to tissue compression; (iii) limited spatial manipulation ability of the SPECT mobile camera handheld probe; and (iv) a wide spread of detected activity. In conclusion, clinical use of fhSPECT/US for localization of parathyroid adenomas is feasible, but shows lower sensitivity than conventional modalities and requires technical improvements.

Intraoperative Gamma Cameras: A Review of Development in the Last Decade and Future Outlook

Portable gamma cameras suitable for intraoperative imaging are in active development and testing. These cameras utilise a range of collimation, detection, and readout architectures, each of which can have significant and interacting impacts on the performance of the system as a whole. In this review, we provide an analysis of intraoperative gamma camera development over the past decade. The designs and performance of 17 imaging systems are compared in depth. We discuss where recent technological developments have had the greatest impact, identify emerging technological and scientific requirements, and predict future research directions. This is a comprehensive review of the current and emerging state-of-the-art as more devices enter clinical practice.

Progress in large field-of-view interventional planar scintigraphy and SPECT imaging

INTRODUCTION

Handheld gamma cameras and gamma probes have been successfully implemented for enabling nuclear image or radio-guidance in minimally-invasive procedures. There is an opportunity for large field-of-view interventional planar scintigraphy and SPECT imaging to complement these small field-of-view devices for two reasons. First, a large field-of-view camera enables imaging of relatively larger organs and activity accumulations that are not close to the patient's skin. And second, more precise corrections can be implemented in the SPECT reconstruction algorithm, improving its quality.

AREAS COVERED

This review article discusses the progress that has been made in the field of large field-of-view interventional planar scintigraphy and SPECT imaging. First, an overview of planar scintigraphy and SPECT is provided. Second, an exploration is given of the potential applications where large field-of-view interventional planar scintigraphy and SPECT imaging may be employed. And third, the requirements for scanner hardware are discussed and an overview of the possible system configurations is provided.

EXPERT OPINION

We believe that there is an opportunity for large field-of-view interventional planar scintigraphy and SPECT imaging to assist clinical workflows. A major effort is now required to evaluate the prototype systems in clinical studies so that valuable practical experience can be obtained.

How molecular imaging will enable robotic precision surgery : The role of artificial intelligence, augmented reality, and navigation

Molecular imaging is one of the pillars of precision surgery. Its applications range from early diagnostics to therapy planning, execution, and the accurate assessment of outcomes. In particular, molecular imaging solutions are in high demand in minimally invasive surgical strategies, such as the substantially increasing field of robotic surgery. This review aims at connecting the molecular imaging and nuclear medicine community to the rapidly expanding armory of surgical medical devices. Such devices entail technologies ranging from artificial intelligence and computer-aided visualization technologies (software) to innovative molecular imaging modalities and surgical navigation (hardware). We discuss technologies based on their role at different steps of the surgical workflow, i.e., from surgical decision and planning, over to target localization and excision guidance, all the way to (back table) surgical verification. This provides a glimpse of how innovations from the technology fields can realize an exciting future for the molecular imaging and surgery communities.

PET- and SPECT-based navigation strategies to advance procedural accuracy in interventional radiology and image-guided surgery

INTRODUCTION

Nuclear medicine has a crucial role in interventional strategies where a combination between the increasing use of targeted radiotracers and intraprocedural detection modalities enable novel, but often complex, targeted procedures in both the fields of interventional radiology and surgery. 3D navigation approaches could assist the interventional radiologist or surgeon in such complex procedures.

EVIDENCE ACQUISITION

This review aimed to provide a comprehensive overview of the current application of computer-assisted navigation strategies based on nuclear imaging to assist in interventional radiology and image-guided surgery. This work starts with a brief overview of the typical navigation workflow from a technical perspective, which is followed by the different clinical applications organized based on their anatomical organ of interest.

EVIDENCE SYNTHESIS

Although many studies have proven the feasibility of PET- and SPECT-based navigation strategies for various clinical applications in both interventional radiology and surgery, the strategies are spread widely in both navigation workflows and clinical indications, evaluated in small patient groups. Hence, no golden standard has yet been established.

CONCLUSIONS

Despite that the clinical outcome is yet to be determined in large patient cohorts, navigation seems to be a promising technology to translate nuclear medicine findings, provided by PET- and SPECT-based molecular imaging, to the intervention and operating room. Interventional Nuclear Medicine (iNM) has an exciting future to come using both PET- and SPECT-based navigation.

Interventional nuclear medicine: a focus on radioguided intervention and surgery

Within interventional nuclear medicine (iNM) a prominent role is allocated for the sub-discipline of radioguided surgery. Unique for this discipline is the fact that an increasing number of clinical indications (e.g. lymphatic mapping, local tumor demarcation and/or tumor receptor targeted applications) have been adopted into routine care. The clinical integration is further strengthened by technical innovations in chemistry and engineering that enhance the translational potential of radioguided procedures in iNM. Together, these features not only ensure ongoing expansion of iNM but also warrant a lasting clinical impact for the sub-discipline of radioguided surgery.

Recent advances in nuclear and hybrid detection modalities for image-guided surgery

Introduction: Radioguided surgery is an ever-evolving part of nuclear medicine. In fact, this nuclear medicine sub-discipline actively bridges non-invasive molecular imaging with surgical care. Next to relying on the availability of radio- and bimodal-tracers, the success of radioguided surgery is for a large part dependent on the imaging modalities and imaging concepts available for the surgical setting. With this review, we have aimed to provide a comprehensive update of the most recent advances in the field. Areas covered: We have made an attempt to cover all aspects of radioguided surgery: 1) the use of radioisotopes that emit γ, β⁺, and/or β^- radiation, 2) hardware developments ranging from probes to 2D cameras and even the use of advanced 3D interventional imaging solutions, and 3) multiplexing solutions such as dual-isotope detection or combined radionuclear and optical detection. Expert opinion: Technical refinements in the field of radioguided surgery should continue to focus on supporting its implementation in the increasingly complex minimally invasive surgical setting, e.g. by accommodating robot-assisted laparoscopic surgery. In addition, hybrid concepts that integrate the use of radioisotopes with other image-guided surgery modalities such as fluorescence or ultrasound are likely to expand in the future.

Technetium-99m SPECT/US Hybrid Imaging Compared with Conventional Diagnostic Thyroid Imaging with Scintigraphy and Ultrasound

Side-by-side evaluation of thyroid ultrasound (US) and ^99mTcO₄ scintigraphy can lead to uncertainties in the correct topographic assignment of thyroid nodules. The aim of this study was to evaluate ^99mTcO₄ single-photon emission computed tomography/ultrasound (SPECT/US) fusion imaging. Seventy-nine patients were prospectively investigated. If conventional diagnostics of the thyroid gland (B-mode-US, scintigraphy) produced unclear findings, SPECT was performed and transferred to a US device for real-time sensor-navigated 3-D fusion US investigation. The data sets were manually matched according to their contours. Finally, SPECT/US versus conventional diagnostics was rated using an ordinal 4-point scale (SPECT/US >> conventional diagnostics, SPECT/US > conventional diagnostics, SPECT/US = conventional diagnostics, SPECT/US < conventional diagnostics). SPECT/US was superior (>>, >) in 84% and equivalent (=) in 16% of the cases, respectively. No statistically significant differences were observed for uni-, bi- and multinodular goiters (p ≥ 0.3). In 67%, the respective problem that arose after conventional diagnostics was clarified by SPECT/US. SPECT/US was feasible and was helpful for the clarification of uncertain functionality assessments of thyroid nodules.

RADIATION EXPOSURE OF THE INVESTIGATOR DURING NAVIGATED FUSION OF 124IODINE PET IMAGING AND ULTRASOUND

To assess the radiation exposure of the investigator during navigated fusion of nuclear medicine images with ultrasound after application of I-124. Dosimetry with two different types of thermoluminescent detectors (TLD) was performed in 25 patients. The dose rate at the patient's neck was measured with a calibrated dose rate meter (DRM) and served as the standard of reference. The average exposure per investigation at the patient's neck measured by LiF:Mg,Cu,P TLDs (cumulative: 212 μSv), LiF:Mg,Ti TLDs (cumulative: 112 μSv) and DRM (cumulative: 150.3 μSv). The radiation exposure of the hand during navigated fusion of nuclear medicine imaging with 124I and ultrasound with a mean duration of 13 min is low and comparable between different methods. Yearly examinations are not expected to add a relevant cumulative risk.

99mTc-Pertechnetate-SPECT/US Hybrid Imaging Enhances Diagnostic Certainty Compared With Conventional Thyroid Imaging With Scintigraphy and Ultrasound

Evaluation of thyroid ultrasound and Tc-pertechnetate scintigraphy side by side frequently produces ambiguous results regarding the correct assignment of anatomy and functionality of a nodule. We describe the usefulness of Tc-pertechnetate-SPECT/US-fusion imaging. A 75-year-old woman was referred for exclusion of cold nodules. After conventional diagnostics (in vitro thyroid parameters, B mode-US, planar Tc-pertechnetate-thyroid scintigraphy), a SPECT was performed using a conventional gamma camera. The SPECT data set was transferred to an ultrasound device (LOGIQ E9), and sensor-navigated 3D ultrasound was performed. Both data sets (SPECT/US) were fused in real time, revealing the exact functional state of multiple nodules.

Localization of Parathyroid Adenoma With Real-Time Ultrasound: Freehand SPECT Fusion

Preoperative localization of parathyroid adenoma in primary hyperparathyroidism gains in importance as there is a trend toward minimally invasive parathyroid surgery. Besides MRI, 4-dimensional CT, PET/CT, invasive-selective venous sampling, or angiography, both ultrasound and scintigraphy are standard of care for lesion localization. Here we report on a 53-year-old woman with suspicion of primary hyperparathyroidism using real-time fusion of scintigraphic (freehand SPECT) and ultrasound imaging for adenoma localization. Real-time fusion of ultrasound and freehand SPECT allowed noninvasive dedicated metabolic and anatomic adenoma localization and treatment planning.

Fusion of freehand SPECT and ultrasound: First experience in preoperative localization of sentinel lymph nodes

PURPOSE

Radioguided sentinel lymph node biopsy (SLNB) is the standard of care in breast cancer and melanoma. Additional preoperative Single-photon emission computed tomography (SPECT/CT) for improved anatomical co-registration of the SLNs causes additional radiation exposure and is time-consuming and expensive. The aim of this prospective study was to evaluate a novel approach involving real-time fusion of freehand SPECT (fhSPECT) and ultrasound (US) for anatomical co-registration of SLNs.

METHODS

From February 2015 to February 2016, 153 patients were included in this prospective study. All patients underwent lymphoscintigraphy according to practical guidelines and 151 (118 cases of breast cancer, 30 cutaneous malignancies, and three cases of vulvar cancer) of the 153 patients were additionally investigated with fhSPECT-US. FhSPECT connected to a hand-held gamma detector generates three-dimensional images of the radioactivity distribution in the scanned area. For co-registration and real-time fusion of fhSPECT and subsequently performed US, an infrared stereo tracking system was used.

RESULTS

In all patients an SLN was found on lymphoscintigraphy, and the fhSPECT detected corresponding hotspots in all but one patient. In 72 % of patients and 73 % of lymph node basins, real-time anatomical co-registration with US was feasible. The rate of success in achieving good co-registration increased from 60 to 75 % after training by a radiologist specialized in breast imaging. A higher co-registration rate (78 %) was observed in patients with only one SLN than in those with two SLNs (68 %) or three or more SLNs (0 %).

CONCLUSIONS

Real-time fusion of fhSPECT and US for preoperative anatomical co-registration of SLNs is feasible. However, before this approach can completely replace preoperative lymphatic imaging, further technical developments are needed.

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.

Radiation exposure of the investigator's hand during fusion imaging of the thyroid with 99mTcO4-free-hand SPECT and ultrasound

The objective of this study was to assess the radiation exposure of the investigators' hand during free-hand single photon emission tomography/ultrasound ((99m)TcO4-fhSPECT/US) of the thyroid. Conventional dosimetry by rings with thermoluminescent detectors (TLDs) was performed in 32 patients (Group A), followed by TLD-chipstrate dosimetry in further 20 patients (Group B). In both the groups, the ambient dose rate was measured by dose rate meter (DRM). The applied activity was in the range of 60-80 MBq (99m)TcO4. In Group A, the exposure per investigation was 7.53 µSv (calculated average) by ring dosimetry and 9.02±5.64 µSv by DRM; in Group B, 10.93 and 9.51 ± 1.76 µSv, respectively. Based on estimated 1224 yearly thyroid investigations per nuclear medicine specialist in Germany, the estimated cumulative yearly exposure of the hand was 11.32 mSv. The hand exposure during a thyroid (99m)TcO4-fhSPECT/US of 20-min duration proved modest and comparable with different methods. Yearly examinations in excess of 1000 per investigator are not expected to add a relevant cumulative risk.

Clinical Usefulness of a Novel Freehand 3D Imaging Device for Radio-Guided Intraoperative Sentinel Lymph Node Detection in Malignant Melanoma

INTRODUCTION

Patients with invasive malignant melanoma are commonly referred for sentinel lymph node (SLN) detection. A recently proposed 3D tomographic imaging modality is freehand SPECT (declipseSPECT). This "bedside system" was originally developed to enable minimal-invasive image-guided surgery. The aim of this retrospective analysis was to assess the clinical use of this freehand detector device for image-guided lymphatic mapping in melanoma patients.

MATERIALS AND METHODS

Thirty-nine patients (12 female and 27 male subjects) were included (age, 30-79 years). All of them had at least one location of melanoma with tumoral stage pT1b or greater in 37 and pTx in 2 patients in different sites of the body (abdomen in 4, back in 14, head and neck in 5, lower extremity in 6, and upper extremity in 10 patients). Lymphoscintigraphy was performed with 65 to 127 MBq Tc-nanocolloid. A 2-day protocol was applied with SPECT-CT acquisition (Brightview XCT, Philips) at day 1 and surgery using radio-guided freehand SPECT at day 2. SPECT-CT data were integrated into the 3D navigation system to enable fast and direct localization of the SLN by displaying the depth of the node from the skin surface and lateral margins in relation to the gamma probe.

RESULTS

Comparable preoperative imaging and intraoperative localization was observed in 18 patients. In 14 cases, more lymph nodes were resected than detected by SPECT-CT including 1 patient without evidence of an SLN because this node was located close to the primary right ear tumor. In 10 of these patients, intraoperative freehand SPECT revealed additional sites of lymph nodes. In 7 cases, more findings were detected by SPECT-CT than surgically removed. The procedure was safe and easy to perform, and the time of surgical intervention using freehand SPECT was in the range of 36 to 133 minutes (mean time, 66.56 minutes).

CONCLUSIONS

Freehand SPECT detected more SLN compared with SPECT-CT, and the tracking system provided precise anatomical localization of the radioactive-labeled SLNs.

Fusion of Freehand SPECT and Ultrasound to Perform Ultrasound-Guided Fine-Needle Aspiration Cytology of Sentinel Nodes in Head and Neck Cancer

BACKGROUND AND PURPOSE

Criteria for ultrasound-guided fine-needle aspiration cytology (USgFNAC) for the detection of occult lymph node metastasis in patients with clinically negative head and neck cancer are based on the morphology of cervical lymph nodes. To improve the selection of lymph nodes for USgFNAC, we examined the feasibility of fused freehand single-photon emission tomography ultrasound-guided fine-needle cytology (freehand SPECT-USgFNAC) of sentinel nodes in patients with early stage oral and head and neck skin cancer.

MATERIALS AND METHODS

Six patients with early-stage head and neck cancer (4 oral and 2 head and neck skin cancers) and a clinically negative neck who were scheduled for transoral or local excision and a sentinel node procedure underwent USgFNAC and freehand SPECT-USgFNAC preoperatively.

RESULTS

All freehand SPECT sonographic examinations were technically successful in terms of identifying sentinel nodes. All aspirates of sentinel nodes obtained by freehand SPECT-USgFNAC contained substantial radioactivity, confirming puncture of the sentinel nodes. USgFNAC evaluated 13 lymph nodes; freehand SPECT-USgFNAC, 19 nodes; and sentinel node biopsy, 13 nodes. Three sentinel nodes were histopathologically positive and were selected for aspiration cytology by freehand SPECT-USgFNAC, but not by conventional ultrasound. The cytologic examination findings of the aspirations were negative or inconclusive.

CONCLUSIONS

Freehand SPECT ultrasound can identify sentinel nodes and could potentially improve USgFNAC in patients with head and neck cancer by better selection of lymph nodes at highest risk of having metastases (sentinel nodes), but its sensitivity is limited by sampling error and insufficient aspirated material for cytology.

Real-time ultrasound and freehand-SPECT. Experiences with sentinel lymph node mapping

Aim of this work is to report first experiences of the feasibility and applicability of a hybrid freehandSPECT/ultrasound (fh-SPECT/US) imaging concept, with regard to SLN imaging, in patients with breast cancer and malignant melanoma.

PATIENTS, METHODS

18 patients with breast cancer or malignant melanoma received standard SLN scintigraphy. Following this, fh-SPECT using declipse®SPECT (SurgicEye, Munich, Germany) was performed, a handheld-gamma camera-based method to visualize activity distribution within a region of interest as a cross-sectional data set. These data were transferred to an ultrasound device and sensor-navigated ultrasound was performed combining fh-SPECT data with ultrasound images, displaying superimposed images. Quality of fh-SPECT and co-registration accuracy was assigned to one of four categories and occurrence of artefacts was assessed.

RESULTS

In 4/18 examinations, there was a no deviation regarding co-registration of both data sets. For 9/18 patients, there was a deviation of <1 cm (mean 0.7±0.3 cm, range 0.3-1.0 cm). For 3/18 patients, a deviation >1 cm was present (mean 1.7±0.3 cm, range 1.5-2.0 cm). In 2/18 examinations no lymph node was found in the region of highest activity. Fh-SPECT reconstruction artifacts occurred in 6/18 examinations.

CONCLUSION

The fusion imaging concept combining SLN information with ultrasound images presented here proves to be feasible and technically successful. However, significant technical limitations were shown in fh-SPECT quality and fusion precision. Subject to technical optimisation of SPECT quality and co-registration, a meaningful contribution to the preoperative planning of lymph node therapy is imaginable. Thus, fundamentally a preoperative histological examination by fh-SPECT/US-guided biopsy is possible.

Current and future intraoperative imaging strategies to increase radical resection rates in pancreatic cancer surgery

Prognosis of patients with pancreatic cancer is poor. Even the small minority that undergoes resection with curative intent has low 5-year survival rates. This may partly be explained by the high number of irradical resections, which results in local recurrence and impaired overall survival. Currently, ultrasonography is used during surgery for resectability assessment and frozen-section analysis is used for assessment of resection margins in order to decrease the number of irradical resections. The introduction of minimal invasive techniques in pancreatic surgery has deprived surgeons from direct tactile information. To improve intraoperative assessment of pancreatic tumor extension, enhanced or novel intraoperative imaging technologies accurately visualizing and delineating cancer cells are necessary. Emerging modalities are intraoperative near-infrared fluorescence imaging and freehand nuclear imaging using tumor-specific targeted contrast agents. In this review, we performed a meta-analysis of the literature on laparoscopic ultrasonography and we summarized and discussed current and future intraoperative imaging modalities and their potential for improved tumor demarcation during pancreatic surgery.