Particle Tracing Based on 4D Flow Magnetic Resonance Imaging: A Systematic Review into Methods, Applications, and Current Developments.

BACKGROUND: Particle tracing based on 4D Flow MRI has been applied as a quantitative and qualitative postprocessing technique to study temporally evolving blood flow patterns. PURPOSE: To systematically review the various methods to perform 4D Flow MRI-based particle tracing, as well as the clinical value, clinical applications, and current developments of the technique. STUDY TYPE: The study type is systematic review. SUBJECTS: Patients with cardiovascular disease (such as Marfan, Fontan, Tetralogy of Fallot), healthy controls, and cardiovascular phantoms that received 4D Flow MRI with particle tracing. FIELD STRENGTH/SEQUENCE: Three-dimensional three-directional cine phase-contrast MRI, at 1.5 T and 3 T. ASSESSMENT: Two systematic searches were performed on the PubMed database using Boolean operators and the relevant key terms covering 4D Flow MRI and particle tracing. One systematic search was focused on particle tracing methods, whereas the other on applications. Additional articles from other sources were sought out and included after a similar inspection. Particle tracing methods, clinical applications, clinical value, and current developments were extracted. STATISTICAL TESTS: The main results of the included studies are summarized, without additional statistical analysis. RESULTS: Of 127 unique articles retrieved from the initial search, 56 were included (28 for methods and 54 for applications). Most articles that described particle tracing methods used an adaptive timestep, a fourth order Runge-Kutta integration method, and linear interpolation in the time dimension. Particle tracing was applied in heart chambers, aorta, venae cavae, Fontan circulation, pulmonary arteries, abdominal vasculature, peripheral arteries, carotid arteries, and cerebral vasculature. Applications were grouped as intravascular, intracardiac, flow stasis, and research. DATA CONCLUSIONS: Particle tracing based on 4D Flow MRI gives unique insight into blood flow in several cardiovascular diseases, but the quality depends heavily on the MRI data quality. Further studies are required to evaluate the clinical value of the technique for different cardiovascular diseases. EVIDENCE LEVEL: 5. TECHNICAL EFFICACY: Stage 1.

Optical Navigation of the Drop-In γ-Probe as a Means to Strengthen the Connection Between Robot-Assisted and Radioguided Surgery.

With translation of the Drop-In γ-probe, radioguidance has advanced into laparoscopic robot-assisted surgery. Global-positioning-system-like navigation can further enhance the symbiosis between nuclear medicine and surgery. Therefore, we developed a fluorescence-video-based tracking method that integrates the Drop-In with navigated robotic surgery. Methods: Fluorescent markers, integrated into the Drop-In, were automatically detected using a daVinci Firefly laparoscope. Subsequently, a declipseSPECT-navigation platform calculated the Drop-In location within the surgical field. Using a phantom (n = 3), we pursued robotic navigation on SPECT/CT, whereas intraoperative feasibility was validated during porcine surgery (n = 4). Results: Video-based tracking allowed for navigation of the Drop-In toward all lesions detected on SPECT/CT (external iliac and common iliac artery regions). Augmented-reality visualization in the surgical console indicated the distance to these lesions in real time, confirmed by the Drop-In readout. Porcine surgery underlined the feasibility of the concept. Conclusion: Optical navigation of the Drop-In probe provides a next step toward connecting nuclear medicine with robotic surgery.