Lars Aurdal

Early recognition of regional cardiac ischemia using a 3-axis accelerometer sensor.

Perioperative mortality in coronary artery bypass grafting is usually caused by reduced left ventricular function due to regional myocardial ischemia or infarction. Post-operative graft occlusion is a well-known problem in coronary surgery. A sensitive tool to detect graft occlusion and monitor myocardial function may give the opportunity to revise malfunctioning grafts before departure from the hospital. This paper describes how a new method can detect cardiac ischemia using a 3-axis piezoelectric accelerometer. In three anesthetized pigs, a 3-axis piezoelectric accelerometer was sutured on the lateral free wall of the left ventricle. The left anterior descending (LAD) was occluded for different time periods and the accelerometer data were sampled with a PC. Short-time Fourier transform was calculated based on the accelerometer time series. The results were visualized using a 2D color-coded time-frequency plot. In the area of occlusion, a change to stronger power of higher harmonics was observed. Consequently, a difference value between the instant frequency pattern and a reference frequency pattern showed a rise in absolute value during the occlusion period. The preliminary results indicate that early recognition of regional cardiac ischemia is possible by analyzing accelerometer data acquired from the three animal trials using the prototype 3-axis accelerometer sensor.

Liver tumor cryoablation: a commentary on the need of improved procedural monitoring.

Cryoablation is a method used for in situ destruction of liver tumors not eligible for surgical resection. Local recurrences following such treatment have been reported at rates of 5–44%. Insufficient procedural monitoring of the ablation is one plausible explanation for these recurrences. The cryoablative procedure is usually monitored by ultrasonography, but acoustic shadowing and loss of signals, compromise visualisation of the cryolesion circumference. Other monitoring modalities such as computer tomography and invasive methods like the use of thermocouples and impedance measurements have also been studied, but are not in common clinical use as single monitoring modalities. Thermodynamic conditions assumed adequate for tumor eradication are likely to occur only in parts of the cryolesion. This tumoricidal part of the cryolesion is not adequately depicted using any of these modalities. Magnetic resonance imaging (MRI) provides a clear delineation of the cryolesion circumference. Noninvasive temperature measurements assisted by MRI indicate which parts of the cryolesion that may be subject to complete necrosis. In this article MRI monitored cryoablation of liver tumors is discussed. Improved peroperative monitoring as offered by MRI may reduce the rates of local recurrences after treatment, but further technological improvements are required.

Intraoperative contrast-enhanced MR-imaging as predictor of tissue damage during cryoablation of porcine liver

This study evaluate intraoperative Magnetic Resonance Imaging (MRI) as predictor of tissue damage following cryoablation of porcine liver with and without concomitant hepatic vascular inflow occlusion. Inflow occlusion was used during freezing in 6 of 12 pigs included. The volumes of the procedural ice-balls were estimated from MR images. Immediately after thawing contrast (MnDPDP) enhanced MRI was performed to estimate the volume of the cryolesion. Four days after ablation MRI was repeated of the in-vivo and the ex-vivo liver. Photography was performed of the sliced liver specimens to estimate the volumes of the lesions. The intraoperative volume of the cryolesion as shown by contrast enhanced MRI corresponded well to the ice-ball volume for lesions made without vascular occlusion (difference 0.3 +/- 0.9 cm(3), p = 0.239). For lesions made during occlusion the volume of the intraoperative cryolesion was larger than the corresponding ice-ball (difference 7.5 +/- 3.3 cm(3), p = 0.003). The volume of the cryolesions as estimated from histopathology four days after freezing and contrast enhanced MRI immediately after freezing corresponded well for lesions made with (difference -2.6 +/- 4.5 cm(3), p = 0.110) and without vascular occlusion (difference -0.5 +/- 2.3 cm(3), p = 0.695). Intraoperative MnDPDP-enhanced MRI of the cryolesion is predictive of the tissue damage induced during cryoablation of porcine liver. The procedural ice-ball is not, if induced during inflow occlusion.

An interactive augmented reality 3D visualization system for destroying liver tumor using cryoablation

Abstract Cryoablation is one of many local destruction techniques used to remove liver tumors. The procedure is cumbersome and time-consuming if there is no real-time access to intra-operative images as well as navigation information of instruments. In this paper, we propose a software-based solution that addresses issues like interactive, real-time navigation and visualization of cryoprobes, segmented tumor, intra-operative MR images, temperature maps, and isotherm surfaces. The system has an intuitive graphical user interface that provides access to a variety of functionalities. It enables the surgeon to perform the procedure safely, accurately, and rapidly by providing visual decision support mechanism.

Augmented reality for safer coronary artery bypass

Abstract The standard procedure for left anterior descending (LAD) coronary artery bypass requires a sternum split. The internal mammary artery (IMA), most typically the left one (LIMA), is dissected free from behind the sternum and is then anastomosed onto the heart below the occlusion of the LAD. Totally endoscopic coronary artery bypass (TECAB) is a less invasive alternative to the standard procedure. This procedure results in heavily reduced invasiveness, but also leads to loss of precision, reduced force feedback and loss of overview. The purpose of this work is to alleviate the problems related to loss of overview by generating an augmented reality for the surgeons in which they are given the impression of ‘seeing through’ the tissues surrounding the LIMA thus making localization of the LIMA a simple matter. Using preoperative CT or MR data, the LIMA is located with respect to the sternum and the tissues surrounding it. Intraoperatively, the sternum is located and the tissues surrounding the LIMA are tracked using a stereo videoscope held by a robotic arm. Knowing the position of the videoscope relative to the sternum now makes it possible to calculate where in the videoscopic images the LIMA is located. This information is then used to generate an augmented reality showing the tissues surrounding the LIMA as transparent, thus revealing the position of the LIMA within them.

Head tracking of a surgical robotic scopeholder - a user involvement test of the system

This paper addresses the concept, development and testing of a new head-tracking system and a user involvement test for comparison between the proposed system and two other control techniques to control the scope — either voice control of Aesop from ComputerMotion (ComputerMotion Inc., Goleta, California) or HeadControl of EndoAssist from Armstrong (Armstrong Healthcare Limited, High Wycombe, England). The average time to complete the task using HeadTracking in both 3D and 2D -mode was shorter than the times for the two other control modes. The average task time using HeadTracking were 39,9% shorter, using 3D with head-mounted display (HMD) and 54,1% using 2D screen compared to HeadControl with EndoAssist. These results were found to be statistical significant (p<0.05). In order for robotic devices to be introduced successfully into surgical practice, the development of transparent surgeon/machine interface is critical. This user involvement test showed that our HeadTracking system with it’s ability to follow the head movements in an intuitive manner, is transparent in functionality to the surgeons which found the system to be the best suited to control the scope in laparoscopic surgery.

Using distance transformations to determine safe needle/probe paths during interventional procedures

This article reports on a method for planning probe placement in the liver during interventional procedures so as to avoid large hepatic vessels.