Tobia Brusa

Medical applications in which patient movements are tracked with 3D surface imaging systems are becoming increasingly popular. The 3D imaging systems used for such applications must be able to cope with controlled and uncontrolled motions of the human body. The key factors for producing a high-quality 3D representation of the moving human body are the spatial resolution, accuracy, and precision of the 3D imaging system. To our knowledge, no international standard yet exists to assess these parameters. In this paper, we propose a phantom model, a method, and parameters for the assessment of spatial resolution, accuracy, and precision to evaluate systems for the 3D imaging of moving objects. The proposed phantom model is an extension of the standard 1951 USAF resolution test chart to 3D and consists of two parallel staircases with varying step heights. The phantom model is actuated with an industrial robot. The application of our method to the Photoneo MotionCam-3D showed that their multishot structured-light mode has a higher accuracy for static and slowly moving objects (accuracy of 0.1 mm) than their single-shot structured-light mode (accuracy of 0.5 mm). However, the single-shot mode can capture fast-moving objects without much loss of accuracy and precision. This provides practical quantifications for the Photoneo MotionCam-3D. Furthermore, this confirms that the proposed phantom model, method, and parameters can be used as part of a standard to assess the spatial resolution, accuracy, and precision of systems for the 3D imaging of moving objects.

Optical 3D scanning applications are increasingly used in various medical fields. Setups involving multiple adjustable systems require repeated extrinsic calibration between patients. Existing calibration solutions are either not applicable to the medical field or require a time-consuming process with multiple captures and target poses. Here, we present an application with a 3D checkerboard (3Dcb) for extrinsic calibration with a single capture. The 3Dcb application can register captures with a reference to validate measurement quality. Furthermore, it can register captures from camera pairs for point-cloud stitching of static and dynamic scenes. Registering static captures from TIDA-00254 to its reference from a Photoneo MotionCam-3D resulted in an error (root mean square error ± standard deviation) of 0.02 mm ± 2.9 mm. Registering a pair of Photoneo MotionCam-3D cameras for dynamic captures resulted in an error of 2.2 mm ± 1.4 mm. These results show that our 3Dcb implementation provides registration for static and dynamic captures that is sufficiently accurate for clinical use. The implementation is also robust and can be used with cameras with comparatively low accuracy. In addition, we provide an extended overview of extrinsic calibration approaches and the application’s code for completeness and service to fellow researchers.

Adolescent idiopathic scoliosis (AIS) is a prevalent musculoskeletal disorder that causes abnormal spinal deformities. The early screening of children and adolescents is crucial to identify and prevent the further progression of AIS. In clinical examinations, scoliometers are often used to noninvasively estimate the primary Cobb angle, and optical 3D scanning systems have also emerged as alternative noninvasive approaches for this purpose. The recent advances in low-cost 3D scanners have led to their use in several studies to estimate the primary Cobb angle or even internal spinal alignment. However, none of these studies demonstrate whether such a low-cost scanner satisfies the minimal requirements for capturing the relevant deformities of the human back. To practically quantify the minimal required spatial resolution and camera resolution to capture the geometry and shape of the deformities of the human back, we used multiple 3D scanning methodologies and systems. The results from an evaluation of 30 captures of AIS patients and 76 captures of healthy subjects showed that the minimal required spatial resolution is between 2 mm and 5 mm, depending on the chosen error tolerance. Therefore, a minimal camera resolution of 640 × 480 pixels is recommended for use in future studies.

Background: A large proportion of age‐related fecal incontinence is attributed to weakness or degeneration of the muscles composing the anal continence organ. However, the individual role of these muscles and their functional interplay remain poorly understood.Methods: This study employs a novel technique based on the combination of MR imaging and FLIP measurements (MR‐FLIP) to obtain anatomical and mechanical information simultaneously. Unlike previous methods used to assess the mechanics of the continence organ, MR‐FLIP allows inter‐individual comparisons and statistical analysis of the sphincter morpho‐mechanical parameters. The anatomy as well as voluntary and involuntary mechanical properties of the anal continence organ were characterized in 20 healthy senior volunteers.Results: Results showed that the external anal sphincter (EAS) forms a funnel‐like shape with wall thickness increasing by a factor of 2.5 from distal (6 ± 0 mm) to proximal (15 ± 3 mm). Both voluntary and involuntary mechanical properties in this region correlate strongly with the thickness of the muscle. The positions of least compliance and maximal orifice closing were both located toward the proximal EAS end. In addition, maximal contraction during squeeze maneuvers was reached after 2 s, but high muscle fatigue was measured during a 7 s holding phase, corresponding to about 60% loss of the energy produced by the muscles during the contraction phase.Conclusions: This work reports baseline parameters describing the morpho‐mechanical condition of the sphincter muscle of healthy elderly volunteers. New parameters were also proposed to quantify the active properties of the muscles based on the mechanical energy associated with muscle contraction and fatigue. This information could be used to assess patients suffering from AI or for the design of novel implants.