Minimally invasive holographic surface scanning for soft-tissue image registration

Abstract

Recent advances in registration have extended intrasurgical image guidance from its origins in bone-based procedures to new applications in soft tissues, thus enabling visualization of spatial relationships between surgical instruments and subsurface structures before incisions begin. Preoperative images are generally registered to soft tissues through aligning segmented volumetric image data with an intraoperatively sensed cloud of organ surface points. However, there is currently no viable noncontact minimally invasive scanning technology that can collect these points through a single laparoscopic port, which limits wider adoption of soft-tissue image guidance. In this paper, we describe a system based on conoscopic holography that is capable of minimally invasive surface scanning. We present the results of several validation experiments scanning ex vivo biological and phantom tissues with a system consisting of a tracked, off-the-shelf, relatively inexpensive conoscopic holography unit. These experiments indicate that conoscopic holography is suitable for use with biological tissues, and can provide surface scans of comparable quality to existing clinically used laser range scanning systems that require open surgery. We demonstrate experimentally that conoscopic holography can be used to guide a surgical needle to desired subsurface targets with an average tip error of less than 3 mm.

Fig. 1

Conceptual drawing of organ surface scanning using conoscopic holog-raphy. The tracked Conoprobe returns distance measurements, which are converted to a point cloud that defines the shape of the tissue surface.

Fig. 2

Experimental setup for surface scanning using the tracked Conoprobe. Optical and magnetic origins are indicated. The black and white optical tracking fiducials can be seen on the Conoprobe and needle assembly.

Fig. 3

Photograph of the Optimet Conoprobe Mark 3.0, the off-the-shelf conoscopic holography system used in our experiments, which collects high-precision distance measurements. Superimposed is a conceptual diagram of the basic components generally used in conoscopic holography to process returning light. The end product is an interference fringe pattern on the CCD sensing array at the back of the device, from which distances are computed.

Fig. 4

Baseline Conoprobe measurements were collected using a manually actuated precision linear slide. Tick marks on the actuation handle (visible at the left-hand end side of the slide) can resolve 10 μm of linear sample motion. One full-handle revolution produces 2 mm of sample travel.

Fig. 5

Standard deviations of repeated measurements taken with various tissue and control samples over the Conoprobe’s measurement range. Each point represents the standard deviation of ten repeated measurements taken at the beginning, middle, and end of the Conoprobe’s measurement range.

Fig. 6

Experimental Conoprobe measurement error versus distance for biological tissues. Each data point above shows the difference from 10 mm recorded by the Conoprobe when the sample was physically transported 10.00 mm.

Fig. 7

Experimental setup for mirror deflection experiments (left) rotating mirror experiment and (right) fixed mirror, translating sample experiment.

Fig. 8

Experimental data for the fixed mirror, moving target experiment. Each data point above shows the difference from 10 mm recorded by the Conoprobe when the target was physically transported 10.00 mm. Comparing these data to the data shown in Fig. 6 reveals no discernible measurement accuracy effects from using a mirror to aim the Conoprobe beam.

Fig. 9

Deviation from a perfect line traced on the target plane as the mirror rotates, sweeping the Conoprobe measurement point across it.

Fig. 10

Liver tissue supported by spherical plastic ball creates a liver sphere.

Fig. 11

Liver sphere scan data with fitting parametric surface superimposed.

Fig. 12

Scanned Conoprobe points displayed on meshed phantom surface taken from a CT scan. An ICP algorithm was used to register the datasets.

Fig. 13

First prototype of a laparoscopic tube attached to the Conoprobe. A small CCD camera is attached to the tip of the tube, enabling the physician to view the position of the laser measurement spot on a handheld display screen. (Inset, lower left) Display screen and the tip of the tube seen end-on. This first prototype illustrates the basic concept, but is not yet airtight.