Abstract. We introduce a new method of rotational image acquisition for four-dimensional (4D) optical coherence tomography (OCT) of beating embryonic chick hearts. The rotational axis and the central A-scan of the OCT are identical. An out-of-phase image sequence covering multiple heartbeats is acquired at every angle of an incremental rotation of the deflection mirrors of the OCT system. Image acquisition is accomplished after a rotation of 180• . Comparison of a displayed live M-mode of the central A-scan with a reference M-mode allows instant detection of translational movements of the embryo. For calculation of 4D data sets, we apply an imagebased retrospective gating algorithm using the phase information of the common central A-scan present in all acquired images. This leads to cylindrical three-dimensional data sets for every time step of the cardiac cycle that can be used for 4D visualization. We demonstrate this approach and provide a video of a beating Hamburger and Hamilton stage 16 embryonic chick heart generated from a 4D OCT data set using rotational image acquisition. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).

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Optical techniques are utilized in robot aided surgery as navigation tools to guide surgical instruments. The advantages are a reduction of severe damage during surgery and of post-surgical trauma. A common approach is to place spherical markers inside the operating field, which can be detected by a 3D imaging device, in order to determine the position of the patient with respect to the instrument. Optical coherence tomography (OCT) is not only capable of detecting these kind of artificial landmarks, but also natural features within the operating field and the bone. For example, during insertion of artificial cochlear implants channels have to be drilled inside the temporal bone [1]. Air inclusions in the surrounding bone, known as mastoid cells, can be used as natural landmarks and their position has to determined with high precision (see figure 1 (left)). However, when using optical devices as navigation tool, the optical properties of biological tissue distort the three dimensional data set due to refractive index changes which have to be corrected for navigation. This has been performed in ophthalmology but has not been done so far for bone and similar materials [2]. Fig. 1 Two dimensional scan of a human temporal bone (left), two dimensional OCT scan of a water droplet on a microscope cover slide (middle), detected boundaries of droplet and slide corrected for refractive index distortion (right).,In this contribution, we present a strategy to correct OCT data for refractive index changes in bone. The correction was carried out with in vitro measurements of porcine temporal bone which were obtained by using a swept source OCT (OCS1300SS) of Thorlabs, Inc. To gain information on the optical properties of the specimen, we prepared a 1 mm thick bone sample with planar and parallel surfaces. The refractive index was determined from OCT scans normal to the bone boundaries according to [3] and was found to be 1.51 ± 0.02. In this work, it was assumed that the bone is a homogeneous material which is a valid assumption in a statistical average. Before refractive index correction, we carried out a geometrical calibration of the OCT, as described in [4], which provides information about the optical path of the OCT's scanning beam in free space. For correction, we determined the incidence angle of the scanning beam with respect to the air-bone boundary and performed the refractive correction by applying Snell's law and linear scaling of the optical path with the refractive index. The performance of the correction was tested first at OCT scans of a water droplet on a microscope cover slide (see figure 1 (middle)) and afterwards at a porcine bone sample with marker holes on the upper and lower surface. We found that the image distortion which accounts for more than 100 μm can be significantly reduced by our correction algorithm. References

External pacemakers (PM) via temporary epicardial leads are routinely applied to infants and children during heart surgery, which usually, after an uneventful post surgical course, can be removed without complications. We report about two infants with complex congenital heart defects after cardiac surgery (arterial switch and Mustard operation for Transposition of the great arteries). Intraoperative these patients received temporary epicardial PM wires. Thirteen and 18 days post surgery, respectively, the PM wires were removed under electrocardiogram (ECG) monitoring. The patients showed acute ECG changes in terms of significant ST elevation during and after removing their pacing wires. Clinically, patients were stable and subsequent echocardiographic examination showed no evidence of myocardial dysfunction or pericardial effusion. In the course of time, patients showed no signs of arrhythmia or abnormal ECG changes. The decision to place temporary pacing wires during the cardiac surgery in patients with congenital heart defects should be considered carefully and their removal should occur under ECG monitoring as soon as the situation of the patient allows. It should be taken into consideration that a complication like this case may be related to delayed removal of temporary PM's leads.