Image Registered Laparoscopic Ultrasound (IRLUS)
The term laparoscopy describes the type of surgery in which a long, tubular instrument with a camera attached to it - called a laparoscope - is used. Such surgeries generally center around the abdominal region, as this is the area where the instrument provides its greatest utility. Although laparoscopic surgery is a fairly new technology, its benefits are well recognized and it has consequently become well established in the medical community. In most cases, only a minimal number of small incisions must be made in order to carry out these surgeries: one for the laparoscope itself, which of course provides the surgeon with a visual of the area of interest, and then others for the instruments. The result is reduced surgical morbidity and faster recovery time for patients.
Since laparoscopy's inception, ultrasound has been added to the technology. The use of ultrasound permits high frequency imaging of organs at close range, which adds many additional benefits to those of the standard laparoscope, such as greater accuracy in checking for the presence of tumors. One difficulty associated with laparoscopic ultrasound (lapus) though is determining exactly what one is viewing with the probe at a given time, as the probe's transducer is not visible during an examination. For those who are less experienced, this problem often negates any of the potential benefits, and consequently the use of laparoscopic ultrasound has not become as mainstream as one might hope and expect.
The laparoscopic ultrasound navigation system is an effort to overcome these disadvantages so that lapus can be used to its fullest potential in all cases where its utilization could prove beneficial. The system design on a basic level is as follows: A tracked electromagnetic sensor is attached to the laparoscopic probe and a CT scan of the patient is performed (see IRGUS page for a picture of the electromagnetic tracker). The laparoscopic probe is calibrated so that the location of the B-scan plane (the area within the transducer's range) is known with respect to the sensor, and the CT scan is loaded into a piece of software called the Slicer. Key elements of the patient's anatomy, visible within the CT, are used to construct a color-coded model of specific parts of the body relevant to the current operation or otherwise useful. For example, the rib cage and aorta are fixed body parts that prove helpful in determining orientation and registering; and, if the surgery were associated with the pancreas, this would also be included in the model. Once the patient has been positioned in the operating room, the visualization within the Slicer software (i.e. the model) and the patient are registered to one another so that movements in both frames correspond to one another. A rendering of the calibrated laparoscopic probe and its b-scan plane within the Slicer software allows the surgeon to see precisely where he/she is looking in realtime.
Because laparoscopic surgery continues to evolve and offshoots from it continue to surface, the navigation system is also continually in development. This is not to mention the mainy issues that still must be overcome, such as the ability to reflect the movement of organs during the course of an operation, due to disturbance or simple breathing, within the Slicer visualization.
Publications
- Ellsmere J, Stoll J, Rattner D, Brooks D, Kane R, Wells III W, Kikinis R, Vosburgh K. A Navigation System for Augmenting Laparoscopic Ultrasound. Int Conf Med Image Comput Comput Assist Interv. 2003;6(Pt 2):184-191.
- Ellsmere J, Stoll J, Wells W, Kikinis R, Vosburgh K, Kane R, Brooks D, Rattner D. A new visualization technique for laparoscopic ultrasonography. Surgery. 2004 Jul;136(1):84-92. PMID: 15232543.