Variations in Microwave Ablation Zones as a Function of Probe Spacing, Angulation and Geometry.

Despite advancements in precision and efficacy of microwave ablation for tumor management, accurately predicting ablation zone geometry and minimum ablation margin remains a major challenge. This pilot study seeks to elucidate the influence of probe configuration on the morphometry of resulting ablation zones using tissue mimicking thermochromic phantoms. In-vitro results from 12 ablations were analyzed: a single probe ablation (n=1) and dual probe ablations (n=11). Angles and separations greatly influenced ablation zone morphometry. In dual-probe ablations, probe tip separation and angle of offset were positively correlated with ablation zone volume, length, and cross-sectional circularity. IR ablation planning is currently suboptimal, as it often relies upon cognitive registration. Even treatment planning software creates virtual composite ablation volumes based upon data from theoretical ablations in single, idealized configurations and settings. These findings draw attention to a need for improved ablation zone prediction and planning, which might impact efficiency, safety, cost, and outcomes.

Endobronchial Navigation Guided by Cone-Beam CT-Based Augmented Fluoroscopy without a Bronchoscope: Feasibility Study in Phantom and Swine.

PURPOSE: To evaluate the accuracy of cone-beam computed tomography (CT)-based augmented fluoroscopy (AF) image guidance for endobronchial navigation to peripheral lung targets. METHODS: Prototypic endobronchial navigation AF software that superimposed segmented airways, targets, and pathways based on cone-beam CT onto fluoroscopy images was evaluated ex vivo in fixed swine lungs and in vivo in healthy swine (n = 4) without a bronchoscope. Ex vivo and in vivo (n = 3) phase 1 experiments used guide catheters and AF software version 1, whereas in vivo phase 2 (n = 1) experiments also used an endovascular steerable guiding sheath, upgraded AF software version 2, and lung-specific low-radiation-dose protocols. First-pass navigation success was defined as catheter delivery into a targeted airway segment solely using AF, with second-pass success defined as reaching the targeted segment by using updated AF image guidance based on confirmatory cone-beam CT. Secondary outcomes were navigation error, navigation time, radiation exposure, and preliminary safety. RESULTS: First-pass success was 100% (10/10) ex vivo and 19/24 (79%) and 11/15 (73%) for in vivo phases 1 and 2, respectively. Phase 2 second-pass success was 4/4 (100%). Navigation errors were 2.2 ± 1.2 mm ex vivo and 4.9 ± 3.2 mm and 4.0 ± 2.6 mm for in vivo phases 1 and 2, respectively. No major device-related complications were observed in the in vivo experiments. CONCLUSIONS: Endobronchial navigation is feasible and accurate with cone-beam CT-based AF image guidance. AF can guide endobronchial navigation with endovascular catheters and steerable guiding sheaths to peripheral lung targets, potentially overcoming limitations associated with bronchoscopy.

In Vivo Characterization of the Swine Airway Morphometry and Motion Based on Computed Tomographic Imaging During Respiration.

Swine are a commonly used model in translational pulmonary research. However, in vivo airway morphometry during respiration has not been studied in extensive detail using modern imaging tools. Chest computed tomographic was performed in swine (n = 3) at multiple stages of respiration. Morphometric parameters of each airway segment at end-expiration and end-inspiration were compared as well as among matched anatomical regions (proximal and distal; ventral, lateral, and dorsal). Analysis included segment diameter, length, ellipticity, and the bifurcation angle between daughter branches. Deformation of the airway during respiration was qualitatively visualized using a point-to-point deformation map. Comparison of airway generation showed airway diameter and length were larger at end-inspiration in the fourth and seventh generations compared to end-expiration. Bifurcation angle was larger at end-inspiration compared to end-expiration. Analysis by anatomical region showed that length and bifurcation angle were larger at inspiration in the distal airway regions only. Regardless of respiratory phase, the lateral regions had larger diameters and lengths compared to the ventral and dorsal regions at similar generations and proximal regions had larger bifurcation angles. The findings that morphological changes were more prevalent in distal airways during respiration was confirmed by analysis of a deformation map. Compared to human airway models, the relative diameter may be smaller and length may be greater in swine in similar airway generations. This morphometric description of the swine airways during respiration may guide conduct of preclinical translational studies, revealing advantages and limitations of swine models for specific evaluations. Such morphometric parameters may directly determine the suitability of the swine model for the study of lung interventions, in terms of recapitulation of human morphometry dynamics.

Methodology for Computational Fluid Dynamic Validation for Medical Use: Application to Intracranial Aneurysm.

Computational fluid dynamics (CFD) is a promising tool to aid in clinical diagnoses of cardiovascular diseases. However, it uses assumptions that simplify the complexities of the real cardiovascular flow. Due to high-stakes in the clinical setting, it is critical to calculate the effect of these assumptions in the CFD simulation results. However, existing CFD validation approaches do not quantify error in the simulation results due to the CFD solver's modeling assumptions. Instead, they directly compare CFD simulation results against validation data. Thus, to quantify the accuracy of a CFD solver, we developed a validation methodology that calculates the CFD model error (arising from modeling assumptions). Our methodology identifies independent error sources in CFD and validation experiments, and calculates the model error by parsing out other sources of error inherent in simulation and experiments. To demonstrate the method, we simulated the flow field of a patient-specific intracranial aneurysm (IA) in the commercial CFD software star-ccm+. Particle image velocimetry (PIV) provided validation datasets for the flow field on two orthogonal planes. The average model error in the star-ccm+ solver was 5.63 ± 5.49% along the intersecting validation line of the orthogonal planes. Furthermore, we demonstrated that our validation method is superior to existing validation approaches by applying three representative existing validation techniques to our CFD and experimental dataset, and comparing the validation results. Our validation methodology offers a streamlined workflow to extract the "true" accuracy of a CFD solver.

Smart goggles augmented reality CT-US fusion compared to conventional fusion navigation for percutaneous needle insertion.

PURPOSE: Targeting accuracy determines outcomes for percutaneous needle interventions. Augmented reality (AR) in IR may improve procedural guidance and facilitate access to complex locations. This study aimed to evaluate percutaneous needle placement accuracy using a goggle-based AR system compared to an ultrasound (US)-based fusion navigation system. METHODS: Six interventional radiologists performed 24 independent needle placements in an anthropomorphic phantom (CIRS 057A) in four needle guidance cohorts (n = 6 each): (1) US-based fusion, (2) goggle-based AR with stereoscopically projected anatomy (AR-overlay), (3) goggle AR without the projection (AR-plain), and (4) CT-guided freehand. US-based fusion included US/CT registration with electromagnetic (EM) needle, transducer, and patient tracking. For AR-overlay, US, EM-tracked needle, stereoscopic anatomical structures and targets were superimposed over the phantom. Needle placement accuracy (distance from needle tip to target center), placement time (from skin puncture to final position), and procedure time (time to completion) were measured. RESULTS: Mean needle placement accuracy using US-based fusion, AR-overlay, AR-plain, and freehand was 4.5 ± 1.7 mm, 7.0 ± 4.7 mm, 4.7 ± 1.7 mm, and 9.2 ± 5.8 mm, respectively. AR-plain demonstrated comparable accuracy to US-based fusion (p = 0.7) and AR-overlay (p = 0.06). Excluding two outliers, AR-overlay accuracy became 5.9 ± 2.6 mm. US-based fusion had the highest mean placement time (44.3 ± 27.7 s) compared to all navigation cohorts (p < 0.001). Longest procedure times were recorded with AR-overlay (34 ± 10.2 min) compared to AR-plain (22.7 ± 8.6 min, p = 0.09), US-based fusion (19.5 ± 5.6 min, p = 0.02), and freehand (14.8 ± 1.6 min, p = 0.002). CONCLUSION: Goggle-based AR showed no difference in needle placement accuracy compared to the commercially available US-based fusion navigation platform. Differences in accuracy and procedure times were apparent with different display modes (with/without stereoscopic projections). The AR-based projection of the US and needle trajectory over the body may be a helpful tool to enhance visuospatial orientation. Thus, this study refines the potential role of AR for needle placements, which may serve as a catalyst for informed implementation of AR techniques in IR.

Ultrasound and x-ray imageable poloxamer-based hydrogel for loco-regional therapy delivery in the liver.

Intratumoral injections have the potential for enhanced cancer treatment efficacy while reducing costs and systemic exposure. However, intratumoral drug injections can result in substantial off-target leakage and are invisible under standard imaging modalities like ultrasound (US) and x-ray. A thermosensitive poloxamer-based gel for drug delivery was developed that is visible using x-ray imaging (computed tomography (CT), cone beam CT, fluoroscopy), as well as using US by means of integrating perfluorobutane-filled microbubbles (MBs). MBs content was optimized using tissue mimicking phantoms and ex vivo bovine livers. Gel formulations less than 1% MBs provided gel depositions that were clearly identifiable on US and distinguishable from tissue background and with minimal acoustic artifacts. The cross-sectional areas of gel depositions obtained with US and CT imaging were similar in studies using ex vivo bovine liver and postmortem in situ swine liver. The gel formulation enhanced multimodal image-guided navigation, enabling fusion of ultrasound and x-ray/CT imaging, which may enhance targeting, definition of spatial delivery, and overlap of tumor and gel. Although speculative, such a paradigm for intratumoral drug delivery might streamline clinical workflows, reduce radiation exposure by reliance on US, and boost the precision and accuracy of drug delivery targeting during procedures. Imageable gels may also provide enhanced temporal and spatial control of intratumoral conformal drug delivery.

Morphometric characterization and temporal temperature measurements during hepatic microwave ablation in swine.

PURPOSE: Heat-induced destruction of cancer cells via microwave ablation (MWA) is emerging as a viable treatment of primary and metastatic liver cancer. Prediction of the impacted zone where cell death occurs, especially in the presence of vasculature, is challenging but may be achieved via biophysical modeling. To advance and characterize thermal MWA for focal cancer treatment, an in vivo method and experimental dataset were created for assessment of biophysical models designed to dynamically predict ablation zone parameters, given the delivery device, power, location, and proximity to vessels. MATERIALS AND METHODS: MWA zone size, shape, and temperature were characterized and monitored in the absence of perfusion in ex vivo liver and a tissue-mimicking thermochromic phantom (TMTCP) at two power settings. Temperature was monitored over time using implanted thermocouples with their locations defined by CT. TMTCPs were used to identify the location of the ablation zone relative to the probe. In 6 swine, contrast-enhanced CTs were additionally acquired to visualize vasculature and absence of perfusion along with corresponding post-mortem gross pathology. RESULTS: Bench studies demonstrated average ablation zone sizes of 4.13±1.56cm2 and 8.51±3.92cm2, solidity of 0.96±0.06 and 0.99±0.01, ablations centered 3.75cm and 3.5cm proximal to the probe tip, and temperatures of 50 ºC at 14.5±13.4s and 2.5±2.1s for 40W and 90W ablations, respectively. In vivo imaging showed average volumes of 9.8±4.8cm3 and 33.2±28.4cm3 and 3D solidity of 0.87±0.02 and 0.75±0.15, and gross pathology showed a hemorrhagic halo area of 3.1±1.2cm2 and 9.1±3.0cm2 for 40W and 90W ablations, respectfully. Temperatures reached 50ºC at 19.5±9.2s and 13.0±8.3s for 40W and 90W ablations, respectively. CONCLUSION: MWA results are challenging to predict and are more variable than manufacturer-provided and bench predictions due to vascular stasis, heat-induced tissue changes, and probe operating conditions. Accurate prediction of MWA zones and temperature in vivo requires comprehensive thermal validation sets.

Endovascular steerable and endobronchial precurved guiding sheaths for transbronchial needle delivery under augmented fluoroscopy and cone beam CT image guidance.

BACKGROUND: Endobronchial navigation is performed in a variety of ways, none of which are meeting all the clinicians' needs required to reach diagnostic success in every patient. We sought to characterize precurved and steerable guiding sheaths (GS) in endobronchial targeting for lung biopsy using cone beam computed tomography (CBCT) based augmented fluoroscopy (AF) image guidance. METHODS: Four precurved GS (EdgeTM 45, 90, 180, 180EW, Medtronic) and two steerable GS [6.5 F Destino Twist (DT), Oscor; 6 F Morph, BioCardia] were evaluated alone and in combination with an electromagnetic tracking (EM) guide and biopsy needles in three experimental phases: (I) bench model to assess GS deflection and perform biopsy simulations; (II) ex vivo swine lung comparing 2 steerable and 2 precurved GS; and (III) in vivo male swine lung to deliver a needle (n=2 swine) or to deliver a fiducial marker (n=2 swine) using 2 steerable GS. Ex vivo and in vivo image guidance was performed with either commercial or prototype AF image guidance software (Philips) based on either prior CT or procedural CBCT. Primary outcomes were GS delivery angle (θGS) and needle delivery angle (θN) in bench evaluation and needle delivery error (mm) (mean ± se) for ex vivo and in vivo studies. RESULTS: The steerable DT had the largest range of GS delivery angles (θN: 0-114°) with either the 21 G or 19 G biopsy needle in the bench model. In ex vivo swine lung, needle delivery errors were 8.7±0.9 mm (precurved Edge 90), 5.4±1.9 mm (precurved Edge 180), 4.7±1.2 mm (steerable DT), and 5.6±2.4 mm (steerable Morph). In vivo, the needle delivery errors for the steerable GS were 6.0±1.0 mm (DT) and 15±7.0 mm (Morph). In vivo marker coil delivery was successful for both the steerable DT and morph GS. A case report demonstrated successful needle biopsy with the steerable DT. CONCLUSIONS: Endobronchial needle delivery with AF guidance is feasible without a bronchoscope with steerable GS providing comparable or improved accuracy compared to precurved GS.