Gulab H. Bhatia

Facial surface scanner

An optical noncontact 3-D digitizing system developed to acquire, process, display, and replicate the surface of the human head is described. The modification of the digitizer to help plan and evaluate facial plastic surgery is discussed. The quality and accuracy of the images produced are examined, and some medically relevant results are considered.<<ETX>>

Quantification of facial surface change using a structured light scanner.

Three-dimensional surface changes that accompany facial surgical procedures were measured noninvasively and evaluated quantitatively. An optical three-dimensional surface scanner with 360-degree surface coverage of a subjects head and a subsecond data acquisition was used. The scanner employs six pairs of “white light” pattern projectors and digital TV cameras. A noncontact optical method to quantify facial surface morphology and objectively assess change resulting from reconstructive or cosmetic plastic surgery has been developed. This quantification technique was implemented and tested with the three-dimensional range scanner. This technique defines the entire surface of the head and face, as opposed to the conventional manual method of measuring surface points or facial landmarks. The method allows facial volume change assessment. The method was tested by repeatedly scanning a volunteer who was injected subcutaneously with known volumes of anesthetic solution. The measured and injected volumes were compared and showed little difference.

Anthropometric optical surface imaging system repeatability, precision, and validation

Disciplines using human body surface dimensions require accurate, repeatable measurements. This study presents a design for the analysis of repeatability, precision, and validation of a new anthropometric device. This model enables estimation of the proportion of the total variation attributable to each level of data collection. This model is applied to an analysis of repeatability, precision, and validation of the Cencit Imaging System, a new optical surface scanner. Twenty-seven facial landmarks were marked on 10 men and 10 women at two measurement sessions. Two images were scanned during each session, and each image was digitized twice. The Cencit Imaging System results were compared with a previously validated digitizer. The Cencit Imaging System was found to produce accurate, highly repeatable images. Much of the error in this study is attributable to human error in marking landmarks on the subjects. The new imaging system will prove useful in a variety of anthropometric applications.

Quantitative three-dimensional assessment of face-lift with an optical facial surface scanner.

Three-dimensional computed tomographic scan images of facial deformities provide information that has been useful in planning and evaluating therapy. However, the benefits of computed tomographic imaging in cosmetic plastic surgery are often insufficient to justify exposing the patient to radiation. This report describes application of an optical, noncontact, threedimensional surface digitizer with subsecond scanning time for 360-degree examination of the human head. The resultant threedimensional surface data are suitable for computer graphics display and manipulation, and for noncontact skin surface measurement. The scanner provides accurate and complete coverage of complex facial surfaces. This system was applied to digitization of the human head in the planning and evaluation of facial plastic surgery. The results indicate that the resulting image is accurate enough to detect subtle dimensional changes resulting from surgery, including postoperative edema and surface changes due to face-lift. This type of scanning can assist in a number of tasks performed by plastic surgeons, including collecting anthropomorphic measurements, preoperative and postoperative assessment, volume monitoring, customizing of implants, and interactive planning.

Visualization and quantitative analysis of talocrural joint kinematics

The three dimensional (3D) in vivo kinematic behavior of the ankle joint was evaluated using spiral volumetric CT scanning of a normal adult foot. The CT data were reconstructed and interpolated to create an isotropic 3D data volume. These data were rendered, visualized, segmented into their bony elements, labeled, and exported to disk using Mayo Analyze software. The labeled 3D CT datasets were analyzed to determine relative orientation, translation, and rotation of the tibia-talus, tibia-calcaneus and calcaneus-talus. Using these results, the 3D motion characteristics during normal adult foot flexion/extension were described quantitatively.

Geometric design of a multisensor structured light range digitizer

An optical noncontact 3-D range digitizer based on projection of 2-D structured light patterns and multiplexed charge injection device (CID) camera sensors has been developed. The system acquires digitized data in 0.75 5 and allows 360-deg examination of the subjects head and facial surface features in less than 1 s, making it suitable for digitizing children as well as adults. The resultant 3-D surface data is suitable for computer graphics display and manipulation, numerically controlled replication, and further processing such as surface measurement extraction. The digitizer uses a set of six stationary sensors positioned about the subject. A sensor consists of a pattern projector and a solid state video camera. This device allows quantitative volume measurements and employs no harmful ionizing radiation. The cost of a scan with this technology is substantially less than that of alternative means of collecting 3-D surface data sets, such as by stereometric, moire fringe, and single-point digitization. This system was geometrically designed such that any surlace of the head or facial area was independently digitized by a minimum of two sensors and to capture areas normally occluded with other techniques. The dimensions of the structure were derived to satisfy physical constraints placed on its overall size. The camera and projector orientations in space, the distance from the lens centers to the center of the digitizing volume, and the lens focal lengths were determined analytically. To reduce cost, a standard lens nearest the analytical value was used. Based on the standard size lens, the field of view was calculated.

Automated lower limb prosthesis design

The design of lower limb prostheses requires definitive geometric data to customize socket shape. Optical surface imaging and spiral x-ray computed tomography were applied to geometric analysis of limb residua in below knee (BK) amputees. Residua (limb remnants after amputation) of BK amputees were digitized and measured. Surface (optical) and volumetric (CT) data of the residuum were used to generate solid models and specify socket shape in (SDRC I-DEAS) CAD software. Volume measurements on the solid models were found to correspond within 2% of surface models and direct determinations made using Archimedean weighing. Anatomic 3D reconstruction of the residuum by optical surface and spiral x-ray computed tomography imaging are feasible modalities for prosthesis design.

Assessment of mass properties of human head using various three-dimensional imaging modalities

Better methods are needed to analyse personal protective devices, such as helmets or facemasks, before they are used in practice. Software tools to quantify three-dimensional craniofacial mass properties are developed to improve our understanding of craniofacial impact biomechanics, supplement existing knowledge of osseous structure and provide a comprehensive description of human head morphology. The application of state-of-the-art imaging systems, solid modelling and other software tools are studied to determine the associated errors in mass property estimation by spiral computed tomography, three-dimensional magnetic resonance and optical surface scanning using phantoms and cadaver head studies. Volume, centre of gravity and principal moments of inertia are determined from solid mathematical models for each scanning modality. Landmark-based registration is used to register scans of the same object obtained from the three imaging modalities to a common reference co-ordinate system. Physically and analytically determined mass properties are used as the standard for truth. Although this comparative study does not lend itself to statistical analysis owing to the small sample size, results indicate that any of the three imaging modalities can be used to predict mass properties within the uncertainty of existing methods. Applying these techniques in vivo is practical and feasible.

Surface imaging of the human body

An optical surface scanner was used to digitize and model the torso of an adult female. This 3D surface scanner employs structured light and has an acquisition time of less than one second for a 0.4 X 0.4 X 0.4 meter sample volume. A female volunteer was digitized in three parts using this surface scanner: head, upper torso, and lower torso. External fiducials were used to aid in registration of the three data sets to create a complete body surface model. The fiducial point loci were sampled and entered in a least squares optimization scheme to rigidly transform (rotate and translate) the three data sets into alignment. The digitized data of each scan was converted into spline surfaces and imported into a computer graphics surface modeling package (Studio, Alias Research, Inc. Toronto, Canada). The results demonstrate whole body surface modeling with an optical surface scanner to achieve rapid complex 3D surface coverage.

Design of a multisensor optical surface scanner

A reconfigurable, optical, 3D scanning system with sub-second acquisition of human body surface data was designed and simulated. Sensor elements (digital cameras/light beam projectors) that meet resolution, accuracy, and speed requirements are included in the system design. The sensors are interfaced to video frame grabber(s) under computer control resulting in a modular, low cost system. System operation and data processing are performed using a desktop graphics workstation. Surface data collected with this system can be oversampled to improve resolution and accuracy (viewed by overlapping camera/projector pairs). Multi- resolution data can be collected for different surfaces simultaneously or separately. Modeling and calibration of this reconfigurable system are achieved via a robust optimal estimation technique. Reconstruction software that allows seamless merging of a range data from multiple sensors has been implemented. Laser scanners that acquire body surface range data using one or two sensors require several seconds for data collection. Surface digitization of inaminate objects is feasible with such devices, but their use in human surface metrology is limited due to motion artifacts and occluded surfaces. Use of multiple, independent active sensors providing rapid collection and multi-resolution data enable sampling of complex human surface morphology not otherwise practical. 3D facial surface data has provided accurate measurements used in facial/craniofacial plastic surgery and modern personal protective equipment systems. Whole body data obtained with this new system is applicable to human factors research, medical diagnosis/treatment, and industrial design.