Pharmaceutical and medical technology companies accessing real-world medical data are not interested in personally identifiable data but rather in cohort data such as statistical aggregates, patterns, and trends. These companies cooperate with medical institutions that collect medical data and want to share it but they need to protect the privacy of individuals on the shared data. We present PyDPLib, a Python Differential Privacy library for private medical data analytics. We illustrate an application of differential privacy using PyDPLib in our platform for visualizing private statistics on a database of prostate cancer patients. Our experimental results show that PyDPLib allows creating statistical data plots without compromising patients’ privacy while preserving underlying data distributions. Even though PyDPLib has been developed to be used in our platform for reporting the radiological examinations and procedures, it is general enough to be used to provide differential privacy on data in any data analytics and visualization platform, service or application.

Background Assessment of lymphatic status via sentinel lymph node (SLN) biopsy is an integral and crucial part of melanoma surgical oncology. The most common technique for sentinel node mapping is preoperative planar scintigraphy of an injected gamma-emitting lymphatic tracer followed by intraoperative node localization using a non-imaging gamma probe with auditory feedback. In recent years, intraoperative visualization of SLNs in 3-D has become possible by coupling the probe to an external system capable of tracking its location and orientation as it is read out, thereby enabling computation of the 3D distribution of the tracer (freehand SPECT). In this project, the non-imaging probe of the fhSPECT system was replaced by a unique handheld gamma camera containing an array of sodium iodide crystals optically coupled to an array of silicon photomultipliers (SiPMs). A feasibility study was performed in which preoperative SLN mapping was performed using camera fhSPECT and the number of detected nodes was compared to that visualized by lymphoscintigraphy, probe fhSPECT, and to the number ultimately excised under non-imaging probe guidance.Results Among five subjects, SLNs were detected in nine lymphatic basins, with one to five SLNs detected per basin. A basin-by-basin comparison showed that the number of SLNs detected using camera fhSPECT exceeded that using lymphoscintigraphy and probe fhSPECT in seven of nine basins and five of five basins, respectively (probe fhSPECT scans were not performed for four basins). It exceeded the number excised under non-imaging probe guidance for seven of nine basins, and equaled the number excised for the other two basins. Conclusions Freehand SPECT using a prototype SiPM-based gamma camera demonstrates high sensitivity for detection of SLNs in a preoperative setting. Camera fhSPECT is a potential means for efficiently obtaining real-time 3D activity distribution maps in applications such as image-guided percutaneous biopsy, and surgical SLN biopsy or radioguided tumor excision.

Selective internal radiotherapy (SIRT) is a treatment modality in advanced liver cancer. A careful treatment planning including an angiographic evaluation of the hepatic blood supply and determination of liver and tumor volume by imaging (e.g. contrast-enhanced MRI) is part of the pre-therapeutic workflow. Treatment is performed by an intra-arterial angiographic application of 90Y-labeled microspheres. Particularly, the segmentation of the liver and calculation of tumor burden are time-consuming activities, but they are a prerequisite of state-of-the-art dosimetry models. In this study, we validated an interactive software tool, which provides a semi-automatic segmentation of co-registered image data (e.g. contrast-enhanced abdominal CT, SPECT/CT, and MRI). A reader experienced in manual liver segmentation for SIRT work-up employed dosimetry software to segment abdominal CT and MRI scans and documented the completion time. A first database contains ten cases (contrast-enhanced CT data) from the Liver Tumor Segmentation (LiTS) Challenge. Results from software-guided semi-automatic segmentation were compared to the published ground truth using Sørensen-Dice coefficient (mean score = 92.9 ± 1.5%). The average time for semi-automatic liver segmentation was 3.8 times faster compared to the manual slice-by-slice delineation. Main deviations between both approaches were observed in the areas of the gall bladder, vena cava inferior and hepatic vascular network. Furthermore, a second analyzed database consists of SPECT/CT and MRI datasets (or CT in case of contraindication for MRI) from pre-therapeutic imaging in 20 patients scheduled for SIRT. All 20 datasets were segmented manually and by using the semi-automatic algorithm of the analyzed software. The examination of the second database does not show any significant difference between both applied methodologies. Using the present tool, segmentations of the liver can be achieved with high accuracy while speeding up the physician’s workflow.

Within image-guided surgery, ‘hybrid’ guidance technologies have been used to integrate the complementary features of radioactive guidance and fluorescence guidance. Here, we explore how the generation of a novel freehand fluorescence (fhFluo) imaging approach complements freehand SPECT (fhSPECT) in a hybrid setup. Near-infrared optical tracking was used to register the position and the orientation of a hybrid opto-nuclear detection probe while recording its readings. Dedicated look-up table models were used for 3D reconstruction. In phantom and excised tissue settings (i.e., flat-surface human skin explants), fhSPECT and fhFluo were investigated for image resolution and in-tissue signal penetration. Finally, the combined potential of these freehand technologies was evaluated on prostate and lymph node specimens of prostate cancer patients receiving prostatectomy and sentinel lymph node dissection (tracers: indocyanine green (ICG) +99m Tc-nanocolloid or ICG-99mTc-nanocolloid). After hardware and software integration, the hybrid setup created 3D nuclear and fluorescence tomography scans. The imaging resolution of fhFluo (1 mm) was superior to that of fhSPECT (6 mm). Fluorescence modalities were confined to a maximum depth of 0.5 cm, while nuclear modalities were usable at all evaluated depths (<2 cm). Both fhSPECT and fhFluo enabled augmented- and virtual-reality navigation toward segmented image hotspots, including relative hotspot quantification with an accuracy of 3.9% and 4.1%. Imaging in surgical specimens confirmed these trends (fhSPECT: in-depth detectability, low resolution, and fhFluo: superior resolution, superficial detectability). Overall, when radioactive and fluorescent tracer signatures are used, fhFluo has complementary value to fhSPECT. Combined the freehand technologies render a unique hybrid imaging and navigation modality.

INTRODUCTION:Clinical Bremsstrahlung imaging with gamma cameras or SPECT scanners, for example used in selective internal radiation therapy (SIRT) [1], suffers from low contrast due to a continuous spectrum and a high amount of scatter. Information about the scattering of the radionuclide within the patient's body can be obtained from Monte-Carlo simulations and subsequently being used to improve image quality.METHODS:An MAA-acquisition (CT+SPECT) of a HCC patient with a unifocal uptake in the right liver lobe is segmented (lesion) and loaded into the MC simulation framework GATE [2]. The voxelized lesion is used as Y90 source (1.5 GBq, 'fastY90' [3] is used yielding a speedup of 2.3×), the CT dataset is used for attenuation by converting HUs into corresponding materials. A mini gamma camera (Crystal Photonics, Germany) with a LEHR collimator and 4 × 4 cm2 detector size is positioned close to liver on the patient's skin, pointing towards the lesion. A simulation (60 s acquisition time) is performed on a cluster with 512 cores (2.2-2.5 Ghz each). The total number of counts, the energy spectrum and the order of scattered particles within each geometric volume are obtained from the ROOT output. Particles that have not scattered at all are defined as primary events. Scattering is only calculated within the phantom.RESULTS:The simulation took 172 min on the cluster with input data voxel size of 1 × 1 × 3.75 mm3. The number of emitted particles is 7.6 M with 600 k detected counts (∼8% ratio). 13.3% of the detected particles are primary events. Additionally, scatter of multiple orders has been observed (41%, 24% and 13% and 8% for the first four orders).CONCLUSION:The energy-spectrum of the simulated 2D gamma camera image can be analyzed and used to correct the actual image acquired of that specific patient to achieve improved image quality and subsequently also dosimetry.

PURPOSE Hand- and robot-guided mini gamma cameras have been introduced for the acquisition of single-photon emission computed tomography (SPECT) images. Less cumbersome than whole-body scanners, they allow for a fast acquisition of the radioactivity distribution, for example, to differentiate cancerous from hormonally hyperactive lesions inside the thyroid. This work compares acquisition protocols and reconstruction algorithms in an attempt to identify the most suitable approach for fast acquisition and efficient image reconstruction, suitable for localization of extended sources, such as lesions inside the thyroid. METHODS Our setup consists of a mini gamma camera with precise tracking information provided by a robotic arm, which also provides reproducible positioning for our experiments. Based on a realistic phantom of the thyroid including hot and cold nodules as well as background radioactivity, the authors compare "step and shoot" (SAS) and continuous data (CD) acquisition protocols in combination with two different statistical reconstruction methods: maximum-likelihood expectation-maximization (ML-EM) for time-integrated count values and list-mode expectation-maximization (LM-EM) for individually detected gamma rays. In addition, the authors simulate lower uptake values by statistically subsampling the experimental data in order to study the behavior of their approach without changing other aspects of the acquired data. RESULTS All compared methods yield suitable results, resolving the hot nodules and the cold nodule from the background. However, the CD acquisition is twice as fast as the SAS acquisition, while yielding better coverage of the thyroid phantom, resulting in qualitatively more accurate reconstructions of the isthmus between the lobes. For CD acquisitions, the LM-EM reconstruction method is preferable, as it yields comparable image quality to ML-EM at significantly higher speeds, on average by an order of magnitude. CONCLUSIONS This work identifies CD acquisition protocols combined with LM-EM reconstruction as a prime candidate for the wider introduction of SPECT imaging with flexible mini gamma cameras in the clinical practice.

304 Objectives Selective Internal Radiotherapy (SIRT) of the liver requires imaging with 99mTc-labeled MAA prior to the delivery of the therapeutic 90Y-labeled microspheres. Both are injected intra-hepatic following angiographic catheterization. SPECT/CT is used to assess its distribution in the patient. We suggest replacing the current workflow, requiring two individual catheterizations and SPECT/CT acquisitions each in the nuclear medicine clinic, by a one-step procedure, performed entirely in the angiography suite using a hand-held gamma camera system (freehand SPECT). The combination of freehand SPECT with interventional C-arm CT would provide the accumulation pattern of both types of radioactive labeled microspheres to consecutively perform diagnostic and therapeutic procedures in a single interventional procedure. This preliminary study evaluates the feasibility of freehand SPECT on an abdominal phantom. Methods Freehand SPECT imaging was performed with a hand-held gamma-camera using a 40x40mm CZT-detector (declipseSPECT, Surgiceye, Munich, Germany). The 3D-SPECT images were reconstructed (26x26x28cm3 volume of interest, 5mm voxel size, 20 Iterations) from projection data measured with the optically tracked gamma camera. Imaging was performed with a water filled IEC body phantom with spheres (diameter between 10mm and 37mm). Different phantom setups simulated positive contrasts inside the whole phantom using all spheres (scenario A) or the two largest spheres (diameter 28mm and 37mm, scenario B) positioned in a lateral segment of the phantom. For scenario A all spheres were filled with 99mTc (113MBq/mL) without background activity. For scenario B the two largest spheres were filled with activity (99mTc, 100MBq/mL) and with activity inside the background (99mTc, ratio=8:1, B-1). Additionally, scenario B was examined with 90Y in the two largest spheres (2.8MBq/mL) without background activity (B-2). Images were acquired on different realistic (acquisition from the front and sides of the phantom respecting imaging paradigm during the angiographic procedure) and unrealistic (acquisition also from transverse sides and back side of the phantom) trajectories with scanning times below 15 minutes. The image quality is assessed based on the detectability of lesions. Results In scenario A, all 6 99mTc filled spheres were detectable by using unrealistic scanning trajectories only. In imaging scenario B, both spheres can be distinguished with realistic and unrealistic acquisition trajectories using 99mTc (B-1) and 90Y (B-2), respectively. Activity pattern located in a section of the phantom, comparable to the locations of microspheres accumulation inside the liver during radioembolization procedures, were detectable by scanning conditions conform to requirements from angiographic procedure. Conclusions This phantom study demonstrated the feasibility of SPECT imaging in parallel to interventional-angiographic procedure by using a hand-held gamma camera. Ongoing work investigates the image quality with more complex and realistic phantoms. Patient studies are also planned.

For the real-time fusion of different modalities, a variety of tracking methods are available including the optical, electromagnetic (EM) and image-based tracking. But as a drawback optical tracking suffers from line of sight issues and EM tracking requires the manual referencing for the fusion procedure and is not usable in Magnetic Resonance Imaging (MRI) environment. To avoid these issues, we propose a real-time setup containing a camera capable of inside-Out tracking using combined circular markers attached to Ultrasound (US) probe and a suitable platform for automatic overlay of MRI and US image using markers. This new approach could help clinicians carry out successful surgical procedures by requiring least system interaction and solving line of sight issues. As a proof-of-concept, we show our first result by mimicking common liver tumor intervention using framed marker fusion technique in a candle gel phantom. We evaluated the tracking error distances using the combination of special markers with Inside-Out approach and conventional optical tracking. The results achieved show comparable performance to the standard Outside-In tracking and manual reference approach, while easing the interventional procedure in terms of hardware and line of sight requirements.

Tracking systems are used in many medical scenarios for the localization of devices or the patient, for example in intra-operative nuclear imaging. The infrared tracking system commonly used for this purpose is outside-in and often suffers from line of sight issues. To alleviate these, we present the combination of an inside-out tracking technique with a hand-held mini gamma camera and an image reconstruction pipeline to provide 3D SPECT-like images in a compact flexible setup suitable for interventions. As a proof-of-concept we show first results on phantoms mimicking common nuclear medicine procedures, sentinel lymph node biopsy in thyroid and breast cancer. Additionally, we show a first clinical result of this procedure on a breast cancer patient. The results achieved show comparable performance to the standard outsidein tracking approach, while easing the interventional procedure in terms of hardware and line of sight requirements.

Freehand SPECT (fhSPECT) is a technology platform for providing 3-dimensional (3D) navigation for radioguided surgical procedures, such as sentinel lymph node (SLN) biopsy (SLNB). In addition to the information provided by conventional handheld gamma detection probes, fhSPECT allows for direct visualization of the distribution of radioactivity in any given region of interest, allowing for improved navigation to radioactive target lesions and providing accurate lesion depth measurements.Herein, we will review the currently available clinical data on the use of fhSPECT: (i) for SLNB of various malignancies, including difficult-to-detect SLNs, and (ii) for radioguided localization of solid tumors. Moreover, the combination of fhSPECT with other technologies (e.g., small field-of-view gamma cameras, and diagnostic ultrasound) is discussed. These technical advances have the potential to greatly expand the clinical application of radioguided surgery in the future.

Thyroid imaging using radioactive tracers is a common task in clinics and is usually performed using 2D gamma cameras (scintigraphy). In this work we present a setup for 3D imaging of the thyroid using a mini gamma camera mounted on a robotic arm. Several images are acquired moving the mini gamma camera along a trajectory around the thyroid. Afterwards, a tomographic reconstruction computes a 3D SPECT-like image of the thyroid. First results are shown of a thyroid phantom using a conventional statistical reconstruction scheme (MLEM) and using a sparse regularization approach based on total variation.

The development of modern robotics and compact imaging detectors allows the transfer of diagnostic imaging modalities to the operating room, supporting surgeons to perform faster and safer procedures. An intervention that currently suffers from a lack of interventional imaging is radioembolization, a treatment for hepatic carcinoma. Currently, this procedure requires moving the patient from an angiography suite for preliminary catheterization and injection to a whole-body SPECT/CT for leakage detection, necessitating a second catheterization back in the angiography suite for the actual radioembolization. We propose an imaging setup that simplifies this procedure using a robotic approach to directly acquire an interventional SPECT/CT in the angiography suite. Using C-arm CT and a co-calibrated gamma camera mounted on a robotic arm, a personalized trajectory of the gamma camera is generated from the C-arm CT, enabling an interventional SPECT reconstruction that is inherently co-registered to the C-arm CT. In this work we demonstrate the feasibility of this personalized interventional SPECT/CT imaging approach in a liver phantom study.

Nuclear imaging modalities like PET or SPECT are in extensive use in medical diagnostics. In a move towards personalized therapy, we present a flexible nuclear tomographic imaging system to enable intra-operative SPECT-like 3D imaging. The system consists of a miniaturized gamma camera mounted on a robot arm for flexible positioning, while spatio-temporal localization is provided by an optical tracking system. To facilitate statistical tomographic reconstruction of the radiotracer distribution using a maximum likelihood approach, a precise model of the mini gamma camera is generated by measurements. The entire system is evaluated in a series of experiments using a hot spot phantom, with a focus on criteria relevant for the intra-operative workflow, namely the number of required imaging positions as well as the required imaging time. The results show that high quality reconstructed images of simple hot spot configurations with positional errors of less than one millimeter are possible within acquisition times as short as 15s.

Nowadays for clinical applications such as sentinel lymph node biopsy in breast or prostate cancer, only pre-operative image data is used for navigation, i.e. CT, SPECT/CT or PET/CT. Freehand SPECT and freehand PET provide intra-operative functional imaging techniques that can be complemented with pre- and intra-operative MR imaging to allow for better planning, navigation and guidance. In this paper we propose a method to enable navigation based on pre- or intra-operatively acquired MR images. A fully MR compatible phantom and a dedicated MR compatible optical tracking target with MR markers is built for this study. PET/MR, SPECT/CT and freehand SPECT scans of the phantom are performed. Registration is done using point based registration of the known marker and target geometries and a ground truth is obtained from a SPECT/CT and an MR image that are directly registered. The RMS errors was 0.31mm for the ground truth and 3.29mm when using segmentation of the MR markers and their spatial relationship with the optical tracking spheres of the dedicated target. Thus, the freehand SPECT can be registered easily by this approach without the need of any additional CT scans and therefore without any additional radiation dose for the patient. This enables intra-operative fusion of the pre- or intra-operatively acquired MR data, which could provide valuable additional information for intra-operative applications such as guidance based on accurate anatomy or verifying exact tumor location in combination with detailed morphological patient data.

Different types of nuclear imaging systems have been used in the past, starting with pre-operative gantry-based SPECT systems and gamma cameras for 2D imaging of radioactive distributions. The main applications are concentrated on diagnostic imaging, since traditional SPECT systems and gamma cameras are bulky and heavy. With the development of compact gamma cameras with good resolution and high sensitivity, it is now possible to use them without a fixed imaging gantry. Mounting the camera onto a robot arm solves the weight issue, while also providing a highly repeatable and reliable acquisition platform. In this work we introduce a novel robotic setup performing scans with a mini gamma camera, along with the required calibration steps, and show the first SPECT reconstructions. The results are extremely promising, both in terms of image quality as well as reproducibility. In our experiments, the novel setup outperformed a commercial fhSPECT system, reaching accuracies comparable to state-of-the-art SPECT systems.

Systems allowing freehand SPECT imaging inside the operating room have been introduced previously. In this work, we aim to take one step further and enable 3D freehand imaging using positron emitting radio-traces such as [18F]FDG. Our system combines a high-energy gamma probe with an optical tracking system. Detection of the 511 keV annihilation gammas from positron-emitting radio-tracers is modeled analytically. The algorithm iteratively reconstructs the radioactivity distribution within a localized volume of interest. Based on the PET/CT data of 7 patients with tumors and lymph node metastases in the head and neck region, we build a neck phantom with [18F]FDG-filled reservoirs representing tumors and lymph nodes. Using this phantom, we investigate the limitations and capabilities of our method. Finally, we discuss possible improvements and requirements needed so that our approach becomes clinically applicable.

We present a novel approach for intra-operative localization of lymph nodes and metastases in the head and neck region using the radio-tracer [18F]FDG. By combining an optical tracking system with a high-energy gamma probe to detect 511keV annihilation gammas, we enable intra-operative PET to visualize activity distributions. Detection of these gammas is modeled ad-hoc analytically, taking into account several factors affecting the detection process. This allows us to iteratively reconstruct the radio-tracer distribution within a localized volume of interest. As a feasibility study we analyze clinical data of 7 patients with tumors in the head and neck region, and derive a realistic neck phantom configuration with [18F]FDG-filled lesions mimicking tumors and lymph nodes. We demonstrate the capabilities and limitations of our approach using that neck phantom. We also outline possible improvements to make our method clinically viable towards less invasive surgeries.