Anthropomorphic liver phantom with flow for multimodal image-guided liver therapy research and training.

PURPOSE: The objective of this study was to develop a multimodal, permanent liver phantom displaying functional vasculature and common pathologies, for teaching, training and equipment development in laparoscopic ultrasound and navigation. METHODS: Molten wax was injected simultaneously into the portal and hepatic veins of a human liver. Upon solidification of the wax, the surrounding liver tissue was dissolved, leaving a cast of the vessels. A connection was established between the two vascular trees by manually manipulating the wax. The cast was placed, along with different multimodal tumor models, in a liver shaped mold, which was subsequently filled with a polymer. After curing, the wax was melted and flushed out of the model, thereby establishing a system of interconnected channels, replicating the major vasculature of the original liver. Thus, a liquid can be circulated through the model in a way that closely mimics the natural blood flow. RESULTS: Both the tumor models, i.e., the metastatic tumors, hepatocellular carcinoma and benign cyst, and the vessels inside the liver model, were clearly visualized by all the three imaging modalities: CT, MR and ultrasound. Doppler ultrasound images of the vessels proved the blood flow functionality of the phantom. CONCLUSION: By a two-step casting procedure, we produced a multimodal liver phantom, with open vascular channels, and tumor models, that is the next best thing to practicing imaging and guidance procedures in animals or humans. The technique is in principle applicable to any organ of the body.

Liver deformation in an animal model due to pneumoperitoneum assessed by a vessel-based deformable registration.

PURPOSE: Surgical navigation based on preoperative images partly overcomes some of the drawbacks of minimally invasive interventions - reduction of free sight, lack of dexterity and tactile feedback. The usefulness of preoperative images is limited in laparoscopic liver surgery, as the liver shifts due to respiration, induction of pneumoperitoneum and surgical manipulation. In this study, we evaluated the shift and deformation in an animal liver caused by respiration and pneumopertioneum using intraoperative cone beam CT. MATERIAL AND METHODS: 3D cone beam CT scans were acquired with arterial contrast. The centerlines of the segmented vessels were extracted from the images taken at different respiration and pressure settings. A non-rigid registration method was used to measure the shift and deformation. The mean Euclidean distance between the annotated landmarks was used for evaluation. RESULTS: A shift and deformation of 44.6 mm on average was introduced due to the combined effect of respiration and pneumoperitoneum. On average 91% of the deformations caused by the respiration and pneumoperitoneum were recovered. CONCLUSION: The results can contribute to the use of intraoperative imaging to correct for anatomic shift so that preoperative data can be used with greater confidence and accuracy during guidance of laparoscopic liver procedures.

Laparoscopic ultrasound for hepatocellular carcinoma and colorectal liver metastasis: an overview.

Laparoscopic ultrasound (LUS) increases patient safety by allowing the surgeon to see beyond surfaces of organs. LUS, however, is not in widespread use due to long learning curve and difficulties in interpreting the ultrasound images. In this paper, we highlight LUS's many advantages and its indispensable nature in laparoscopic liver procedures. The focus is the use of LUS in diagnosis and treatment of hepatocellular carcinoma and colorectal metastasis. The majority of patients have associated liver cirrhosis, and are terminally ill. Therefore, it is important to avoid unnecessary surgical trauma. LUS is sensitive in the detection of small liver lesions that are often missed by other preoperative imaging methods. This makes LUS an excellent tool for diagnostic and therapeutic purposes. Our overview focuses on procedures relating to hepatocellular carcinoma and colorectal metastasis where LUS is used and has been proven to benefit patient survival and potentially improve quality of life.

Navigated laparoscopy--liver shift and deformation due to pneumoperitoneum in an animal model.

BACKGROUND: Precise laparoscopic liver resection requires accurate planning and visualization of important anatomy such as vessels and tumors. Combining laparoscopic ultrasound with navigation technology could provide this. Preoperative images are valuable for planning and overview of the procedure, while intraoperative images provide an updated view of the surgical field. PURPOSE: To validate the accuracy of navigation technology based on preoperative images, we need to understand how much the liver shifts and deforms due to heartbeat, breathing, surgical manipulation and pneumoperitoneum. In this study, we evaluated liver tumor shift and deformation due to pneumoperitoneum in an animal model. METHODS: Tumor models were injected into the liver of the animal, and 3D CT images were acquired before and after insufflation. Tumor shifts and deformation were determined. RESULTS: The results showed significant tumor position shift due to pneumoperitoneum, with a maximum of 28 mm in cranio-caudal direction. No significant tumor deformation was detected. Small standard deviations suggest rigid body transformation of the liver as a whole, but this needs further investigation. CONCLUSION: The findings indicate a need for anatomic shift correction of preoperative images before they are used in combination with LUS guidance during a laparoscopic liver resection procedure.

Navigated laparoscopic ultrasound in abdominal soft tissue surgery: technological overview and perspectives.

PURPOSE: Two-dimensinal laparoscopic ultrasound (LUS) is commonly used for many laparoscopic procedures, but 3D LUS and navigation technology are not conventional tools in the clinic. Navigated LUS can help the user understand and interpret the ultrasound images in relation to the laparoscopic view and preoperative images. When combined with information from MRI or CT, navigated LUS has the potential to provide information about anatomic shifts during the procedure. In this paper, we present an overview of the ongoing technological research and development related to LUS combined with navigation technology, The purpose of this overview is threefold: (1) an introduction for those new to the field of navigated LUS; (2) an overview for those working in the field and; and (3) as a reference for those searching for literature on technological developments related to navigation in ultrasound-guided laparoscopic surgery. METHODS: Databases were searched to identify relevant publications from the last 10 years. RESULTS: We were able to identify 18 key papers in the area of navigated LUS for the abdomen, originating from about 10-11 groups. We present the literature overview, including descriptions of our own experience in the field, and a discussion of the important clinical and technological aspects related to navigated LUS. CONCLUSIONS: LUS integrated with miniaturized tracking technology is likely to play an important role in guiding future laparoscopic surgery.

Development of a multimodal tumor model for porcine liver.

In our efforts to develop a guidance system for laparoscopic liver surgery, we are working towards a live animal tumor model. The objective of this study was to establish the tumor model for live porcine liver, visible on both computed tomography (CT) and ultrasound images. The tumor model was created by injecting a mixture of agarose, sephadex, and glycerol. Together with water, the mixture was heated to bring its components into solution. Once heating was complete, methylthionine chloride and CT contrast were added. Using laparoscopic ultrasound guidance, the tumor model mixture was injected into in vivo porcine liver. The resulting model tumors were radiolucent, visible on both CT and conventional X-ray. They appeared as hyperechoic lesions on ultrasound images. Compared to the CT images, the model tumors in the ultrasound images showed good correspondence in size. We conclude that our tumor model, due to its clearly identifiable nature on multiple imaging modalities, is a valuable tool for further studies on laparoscopic ultrasound (2D and 3D) and navigated ultrasound in laparoscopic surgery of the liver and other organs in a pre-clinical set-up.

Laparoscopic ultrasound: a survey of its current and future use, requirements, and integration with navigation technology.

BACKGROUND: Laparoscopic ultrasound (LUS) increases surgical safety by allowing the surgeon to see beyond the organ surface, by visualizing vascular structures and by improving surgical precision of tumor resection. A questionnaire-based survey was used to investigate the current use and future expectations of LUS technology. METHODS: A questionnaire consisting of 26 questions was distributed manually at four different conferences (60% at the European Association for Endoscopic Surgery (EAES) conference, Stockholm 2008). The answers were summarized with descriptive statistics and nonparametric tests at a significance level of 0.05. RESULTS: The questionnaire was answered by 177 surgeons from 40 different countries (85% from Europe). Of these surgeons, 43% use ultrasound during laparoscopic procedures. Generally, more LUS users are found at university hospitals than at general community hospitals. Surgeons use LUS primarily in procedures related to the liver (67% of the surgeons who use LUS), but LUS also is used in other procedures related to the pancreas, biliary tract, and colon. In a 5-year perspective, 82% of surgeons believe in an increased use of LUS, and 79% of surgeons also think that the use of LUS combined with navigation technology will increase and that the most important requirements for such a system are good image quality, easy interpretation, and a high degree of precision. CONCLUSIONS: Although the surgeons believe LUS has advantages, only 43% of the respondents reported using it. The surveyed surgeons were largely positive toward an increased use of LUS in a 5-year perspective and believe that LUS combined with navigation technology will contribute to improving the surgical precision of tumor resection.