Image Guided Interventional Treatment of Coronary Chronic Total Occlusion
In the field on cardiovascular interventions, the chronic total occlusion (CTO) is a subset of lesion types that is the most challenging to treat, evidenced by the low procedural success (55%–80%) depending on the techniques and experience of the physician. In comparison, the procedural success rate of non-occluded lesions is approximately 90%. The most important reason for this lower success rate is the fact that the lesion cannot be crossed by the guidewire. Different techniques with extra equipment and additional guidewires are used to increase the rate of success. E.g. a support catheter can provide extra column strength, supporting the guidewire advancement through the occlusion while maintaining its flexibility. Consequences are an increase of complications such as false lumen creation or vessel dissection. Furthermore, these procedures may take hours leading to highirradiation exposure of patient andthe physician and use of large volumes of nefrotoxic contrast dye.
We will develop a support catheter with triple functionality: (1) imaging with an ultrasound transducer that does not only look sideways, but also in front, so that the CTO lesion can be visualized and information from the signal can be used to uncover the better accessible areas for crossing the CTO and avoid a dissection of the arterial wall or the creation of a false lumen; (2) accurate steering of the device based on the optimal use of the information already given by the location of the device, and the situation in front and around the device; (3) 3D visualization of the catheter without the use of X-ray by integrating a specially designed optical fiber into the support catheter.
WP3.2.1: Forward looking (Erasmus MC)
We will develop forward-looking ultrasound transducers, miniaturized to fit into the limited space available in a catheter. The transducers will have a frequency of 15–40 MHz, balancing between resolution and penetration. Data processing strategies will be developed to distinguish between the densities of different types of tissue that are present in the lesion, as the lesser dense tissues are promising entry points for the guidewire. Candidates are echogenicity, elasticity (possibly imaged by means of acoustic radiation force impulse (ARFI) imaging), and signal parameters like penetration depth. This classification scheme will be developed on phantoms with known properties, as well as on autopsy materials. Different soft tissues are notoriously difficult to distinguish in ultrasound images. If the ultrasound-accessible parameters provide insufficient specificity to assist in determining the suitable entry point, we will exploit the optical fibre in the catheter and explore the use of photo-acoustic imaging or OCT.
WP3.2.2: Steering (TUD)
Only the most distal part will be able to steer, since it leads the rest of the catheter. With a minimum angle of 20o of the distal part, the catheter has sufficient maneuverability to steer the catheter. Various methods of steering will be investigated. These include mechanical, electrical, or shape memory materials. A requirement is to leverage the limited space available in the catheter, especially since a part of the space is being used for ultrasound transducers.
WP3.2.3: Position and shape sensing (Philips)
The position of the catheter tip will be sensed by optical shape sensing (OSS). An accuracy of 1 mm is required for the support catheter with OSS to be useful. Accuracy of the shape sensing can be influenced by the design of the fiber, but also with the reconstruction of the shape by the software. The shape sensing of the fiber will be real time (10 Hz), and the hardware & software have to be sufficiently fast to process the data and reconstruct the shape. For an optimal use of the 3D shape of the fiber and thus the catheter, it must be placed in a 3D environment of the arteries that can be pre-recorded with CT or MRI. The overlay of the pre-recorded image and the OSS image must overlay exactly to obtain an accuracy of 1 mm. By using a fixed reference point in space that is taken up with the calibration of the fluoroscopy used, an overlap of both images can be realized.