Christopher Allen Nafis

Enhancing reality in the operating room

Three dimensional computer models of the anatomy generated from volume acquisitions of computed tomography and magnetic resonance imaging are useful adjuncts to 2D images. This paper describes a system that merges the computer generated 3D models with live video to enhance the surgeons understanding of the anatomy beneath the surface. The system can be used as a planning aid before the operation and provide additional information during an operation. The application of the system to a brain operation is described.<<ETX>>

Method for evaluating compatibility of commercial electromagnetic (EM) microsensor tracking systems with surgical and imaging tables

Electromagnetic (EM) tracking systems have been successfully used for Surgical Navigation in ENT, cranial, and spine applications for several years. Catheter sized micro EM sensors have also been used in tightly controlled cardiac mapping and pulmonary applications. EM systems have the benefit over optical navigation systems of not requiring a line-of-sight between devices. Ferrous metals or conductive materials that are transient within the EM working volume may impact tracking performance. Effective methods for detecting and reporting EM field distortions are generally well known. Distortion compensation can be achieved for objects that have a static spatial relationship to a tracking sensor. New commercially available micro EM tracking systems offer opportunities for expanded image-guided navigation procedures. It is important to know and understand how well these systems perform with different surgical tables and ancillary equipment. By their design and intended use, micro EM sensors will be located at the distal tip of tracked devices and therefore be in closer proximity to the tables. Our goal was to define a simple and portable process that could be used to estimate the EM tracker accuracy, and to vet a large number of popular general surgery and imaging tables that are used in the United States and abroad.

A hardware and software protocol for the evaluation of electromagnetic tracker accuracy in the clinical environment: a multi-center study

This paper proposes an assessment protocol that incorporates both hardware and analysis methods for evaluation of electromagnetic tracker accuracy in different clinical environments. The susceptibility of electromagnetic tracker measurement accuracy is both highly dependent on nearby ferromagnetic interference sources and non-isotropic. These inherent limitations combined with the various hardware components and assessment techniques used within different studies makes the direct comparison of measurement accuracy between studies difficult. This paper presents a multicenter study to evaluate electromagnetic devices in different clinical environments using a common hardware phantom and assessment techniques so that results are directly comparable. Measurement accuracy has been shown to be in the range of 0.79-6.67mm within a 180mm3 sub-volume of the Aurora measurement space in five different clinical environments.

Method for estimating dynamic EM tracking accuracy of surgical navigation tools

Optical tracking systems have been used for several years in image guided medical procedures. Vendors often state static accuracies of a single retro-reflective sphere or LED. Expensive coordinate measurement machines (CMM) are used to validate the positional accuracy over the specified working volume. Users are interested in the dynamic accuracy of their tools. The configuration of individual sensors into a unique tool, the calibration of the tool tip, and the motion of the tool contribute additional errors. Electromagnetic (EM) tracking systems are considered an enabling technology for many image guided procedures because they are not limited by line-of-sight restrictions, take minimum space in the operating room, and the sensors can be very small. It is often difficult to quantify the accuracy of EM trackers because they can be affected by field distortion from certain metal objects. Many high-accuracy measurement devices can affect the EM measurements being validated. EM Tracker accuracy tends to vary over the working volume and orientation of the sensors. We present several simple methods for estimating the dynamic accuracy of EM tracked tools. We discuss the characteristics of the EM Tracker used in the GE Healthcare family of surgical navigation systems. Results for other tracking systems are included.

Mobile, contactless, single-shot, fingerprint capture system

In some applications such as field stations, disaster situations or similar conditions, it is desirable to have a contactless, rugged means to collect fingerprint information. The approach described in this paper enables acceleration of the capture process by eliminating an otherwise system and finger cleanup procedure, minimizes the chance of the spread of disease or contaminations, and uses an innovative optical system able to provide rolled equivalent fingerprint information desirable for reliable 2D matching against existing databases. The approach described captures highresolution fingerprints and 3D information simultaneously using a single camera. Liquid crystal polarization rotators combined with birefringent elements provides the focus shift and a depth from focus algorithm extracts the 3D data. This imaging technique does not involve any moving parts, thus reducing cost and complexity of the system as well as increasing its robustness. Data collection is expected to take less than 100 milliseconds, capturing all four-finger images simultaneously to avoid sequencing errors. This paper describes the various options considered for contactless fingerprint capture, and why the particular approach was ultimately chosen.

Three-dimensional embedded defect detection and localization in a semi-transparent medium

The fabrication of new optical materials has many challenges that suggest the need for new metrology tools. To this purpose, the authors designed a system for localizing 10 micron embedded defects in a 10-millimeter thick semitransparent medium. The system, comprising a single camera and a motion system, uses a combination of brightfield and darkfield illumination. This paper describes the optical design and algorithm tradeoffs used to reach the desired detection and measurement characteristics using stereo photogrammetry and parallel-camera stereoscopic matching. Initial experiment results concerning defect detection and positioning, as well as analysis of computational complexity of a complete wafer inspection are presented. We concluded that parallel camera stereoscopic matching combined with darkfield illumination provides the most compatible solution to the 3D defect detection and positioning requirement, detecting 10 micron defects at a positioning accuracy of better than +/- 0.5 millimeters and at a speed of less than 3 minutes per part.

Navigation and imaging system sychronized with respiratory and/or cardiac activity

An imaging and navigation system is disclosed herein. The imaging and navigation system includes a computer and an ultrasonic imaging device disposed at least partially within an ultrasound catheter. The ultrasonic imaging device is connected to the computer and is adapted to obtain a generally real time three-dimensional image. The imaging and navigation system also includes a tracking system connected to the computer. The tracking system is adapted to estimate a position of a medical instrument. The imaging and navigation system also includes a display connected to the computer. The display is adapted to depict the generally real time three-dimensional image from the ultrasonic imaging device and to graphically convey the estimated position of the medical instrument.

Real-time 3D part metrology using polarization rotation

This paper describes a real time, low cost part metrology method for capturing and extracting 3D part data using a single camera and no moving elements. 3D capture in machine vision is typically done using stereo photogrammetry, phase shifting using structured light, or autofocus mechanism for depth capture. These methods rely on expensive and often slow components such as multiple cameras, specialized lighting, or motion components such as motors or piezoelectric actuators. We demonstrated a method for 3D capture using only a single camera, birefringent lenses and ultra-fast electronic polarization switches. Using multiple images acquired at different polarization states and thus different focal distances, a high-resolution 3D point cloud of a test part was extracted with a good match to the ground truth data. This paper will describe the operation of the method and discuss the practical limitations.

Automated 3D IR defect mapping system for CZT wafer and tile inspection and characterization

In this paper, the design and evaluation of a 3D stereo, near infrared (IR), defect mapping system for CZT inspection is described. This system provides rapid acquisition and data analysis that result in detailed mapping of CZT crystal defects across the area of wafers up to 100 millimeter diameter and through thicknesses of up to 20 millimeter. In this paper, system characterization has been performed including a close evaluation of the bright field and dark field illumination configurations for both wafer-scale and tile-scale inspection. A comparison of microscope image and IR image for the same sample is performed. As a result, the IR inspection system has successfully demonstrated the capability of detecting and localizing inclusions within minutes for a whole CZT wafer. Important information is provided for selecting defect free areas out of a wafer and thereby ensuring the quality of the tile. This system would support the CZT wafer dicing and assembly techniques that enable the economical production of CZT detectors. This capability can improve the yield and reduce the cost of the thick detector devices that are rarely produced today.

Dual-illumination NIR system for wafer level defect inspection

CdZnTe is a high efficiency, room temperature radiation detection material that has attracted great interesting in medical and security applications. CZT crystals can be grown by various methods. Particularly, CZT grown with the Transfer Heater Method (THM) method have been shown to have fewer defects and greater material uniformity. In this work, we developed a proof-of-concept dual lighting NIR imaging system that can be implemented to quickly and nondestructively screen CZT boule and wafers during the manufacturing process. The system works by imaging the defects inside CZT at a shallow depth of focus, taking a stack of images step by step at different depths through the sample. The images are then processed with in-house software, which can locate the defects at different depths, construct the 3D mapping of the defects, and provide statistical defect information. This can help with screening materials for use in detector manufacturing at an early stage, which can significantly reduce the downstream cost of detector fabrication. This inspection method can also be used to help the manufacturer understand the cause of the defect formation and ultimately improve the manufacturing process.