Medical image analysis

The status of augmented reality in laparoscopic surgery as of 2016.

Introduction. The development augmented reality devices allow physicians to incorporate data visualization into diagnostic and treatment procedures to improve work efficiency, safety, and cost and to enhance surgical training. However, the awareness of possibilities of augmented reality is generally low. This review evaluates whether augmented reality can presently improve the results of surgical procedures. Methods. We performed a review of available literature dating from 2010 to November 2016 by searching PubMed and Scopus using the terms “augmented reality” and “surgery.” Results. The initial search yielded 808 studies. After removing duplicates and including only journal articles, a total of 417 studies were identified. By reading of abstracts, 91 relevant studies were chosen to be included. 11 references were gathered by cross-referencing. A total of 102 studies were included in this review. Conclusions. The present literature suggest an increasing interest of surgeons regarding employing augmented reality into surgery leading to improved safety and efficacy of surgical procedures. Many studies showed that the performance of newly devised augmented reality systems is comparable to traditional techniques. However, several problems need to be addressed before augmented reality is implemented into the routine practice.

https://downloads.hindawi.com/journals/jhe/2017/4574172.pdf

Recent Development of Augmented Reality in Surgery: A Review

Percutaneous Microwave versus Radiofrequency Ablation of Colorectal Liver Metastases: Ablation with Clear Margins (A0) Provides the Best Local Tumor Control.

The state of the art of visualization in mixed reality image guided surgery.

Purpose
Augmented reality (AR) obtains increasing acceptance in the operating room. However, a meaningful augmentation of the surgical view with a 3D visualization of planning data which allows reliable comparisons of distances and spatial relations is still an open request.

Illustrative visualization of 3D planning models for augmented reality in liver surgery.

Percutaneous radiofrequency ablation (RFA) is becoming a standard minimally invasive clinical procedure for the treatment of liver tumors. However, planning the applicator placement such that the malignant tissue is completely destroyed, is a demanding task that requires considerable experience. In this work, we present a fast GPU-based real-time approximation of the ablation zone incorporating the cooling effect of liver vessels. Weighted distance fields of varying RF applicator types are derived from complex numerical simulations to allow a fast estimation of the ablation zone. Furthermore, the heat-sink effect of the cooling blood flow close to the applicator's electrode is estimated by means of a preprocessed thermal equilibrium representation of the liver parenchyma and blood vessels. Utilizing the graphics card, the weighted distance field incorporating the cooling blood flow is calculated using a modular shader framework, which facilitates the real-time visualization of the ablation zone in projected slice views and in volume rendering. The proposed methods are integrated in our software assistant prototype for planning RFA therapy. The software allows the physician to interactively place virtual RF applicator models. The real-time visualization of the corresponding approximated ablation zone facilitates interactive evaluation of the tumor coverage in order to optimize the applicator's placement such that all cancer cells are destroyed by the ablation.

GPU-based Real-Time Approximation of the Ablation Zone for Radiofrequency Ablation

Purpose 
To demonstrate and quantify the heat sink effect in hepatic microwave ablation (MWA) in a standardized ex vivo model, and to analyze the influence of vessel distance and blood flow on lesion volume and shape.


Materials and Methods 
108 ex vivo MWA procedures were performed in freshly harvested pig livers. Antennas were inserted parallel to non-perfused and perfused (700,1400 ml/min) glass tubes (diameter 5mm) at different distances (10, 15, 20mm). Ablation zones (radius, area) were analyzed and compared (Kruskal-Wallis Test, Dunn’s multiple comparison Test). Temperature changes adjacent to the tubes were measured throughout the ablation cycle.


Results 
Maximum temperature decreased significantly with increasing flow and distance (p<0.05). Compared to non-perfused tubes, ablation zones were significantly deformed by perfused tubes within 15mm distance to the antenna (p<0.05). At a flow rate of 700ml/min ablation zone radius was reduced to 37.2% and 80.1% at 10 and 15mm tube distance, respectively; ablation zone area was reduced to 50.5% and 89.7%, respectively.


Conclusion 
Significant changes of ablation zones were demonstrated in a pig liver model. Considerable heat sink effect was observed within a diameter of 15mm around simulated vessels, dependent on flow rate. This has to be taken into account when ablating liver lesions close to vessels.

/pdf/experimental-evaluation-of-the-heat-sink-effect-in-hepatic-3wuvhj8lsj.pdf

Experimental Evaluation of the Heat Sink Effect in Hepatic Microwave Ablation

To quantify the cooling effect of hepatic vessels on liver radiofrequency (RF) ablation ex situ. Bipolar RF applicators (diameter = 1.8 mm, electrode length = 30 mm) were inserted parallel to perfused glass tubes (diameter = 5 and 10 mm; flow = 250–1,800 ml/min) at distances of 5 and 10 mm in porcine livers ex vivo. RF ablation was performed at 30 W/15 kJ. RF lesions were analyzed by measuring the maximum (r
 max) and minimum radius (r
 min) and the lesion area. Glass tubes without flow showed no influence on RF lesions, whereas perfused glass tubes had a significant cooling effect on lesions. r
 min was reduced to 50% at 5 mm applicator-to-vessel distance and the lesion area was reduced from 407 to 321 mm2 (p < 0.001). There was no significant influence of glass tube diameter or flow volume on any of the analyzed parameters. Cooling effects of intrahepatic vessels could be simulated in an ex situ model. Cooling effects should be taken into account in RF ablation within 10 mm distance to major liver vessels regardless of blood flow volume or vessel diameter. Surgical RF ablation with temporary blood flow occlusion should be considered in such constellations.

Ex situ quantification of the cooling effect of liver vessels on radiofrequency ablation

Image-guided radiofrequency ablation (RFA) is a broadly used minimally invasive method for the thermal destruction of focal liver malignancies using needle-shaped instruments. The established planning workflow is based on examination of 2D slices and manual definition of the access path. During that process, multiple criteria for all possible trajectories have to be taken into account. Hence, it demands considerable experience and constitutes a significant mental task. An access path determination method based on image processing and numerical optimization is proposed. Fast GPU-based simulation approximation is utilized to incorporate the heat distribution including realistic cooling effects from nearby blood vessels. A user interface for intuitive exploration of the optimization results is introduced. The proposed methods are integrated into a clinical software assistant. To evaluate the suitability of the interactive optimization approach for the identification of meaningful therapy strategies, a retrospective study has been carried out. The system is able to propose clinically relevant trajectories to the target by incorporating multiple criteria. A novel method for planning of image-guided radiofrequency ablation by means of interactive access path determination based on optimization is presented. A first retrospective study indicates that the method is suited to improve the classical planning of RFA.

Christian Rieder

Papers

Illustrative visualization of 3D planning models for augmented reality in liver surgery.

GPU-based Real-Time Approximation of the Ablation Zone for Radiofrequency Ablation

Experimental Evaluation of the Heat Sink Effect in Hepatic Microwave Ablation

Ex situ quantification of the cooling effect of liver vessels on radiofrequency ablation

Interactive multi-criteria planning for radiofrequency ablation