Takaharu Yamazaki

Estimating a Shooting Angle in Ear Recognition

To improve on our earlier work on single-view-based ear biometrics, an estimation method is presented for the shooting angle of an ear image based on the summation of similarity scores over a threshold within a database of known shooting angles. Experimental results indicate that the estimation method can improve the robustness of ear recognition in varied poses.

Basic Study for 3D Kinematic Measurement of Patella from Single-Plane Fluoroscopic Image Using Intensity-Based 2D/3D Registration

The 3D measurement of dynamic knee kinematics under in vivo conditions is highly valuable for understanding the effects of joint diseases, dysfunction and for evaluating the outcome of surgical procedures. For artificial knee implants, to achieve 3D measurement of the dynamic kinematics, 2D/3D registration techniques which use X-ray fluoroscopic images and computer-aided design model of the implants have been applied to clinical cases. These fluoroscopic techniques have also been applied for motion measurement in joints without implants in recent years, where 3D bone models created from CT or MRI images are utilized. In previous studies, however, the pose estimation accuracy for patella was not sufficient for analyzing 3D knee kinematics, particularly out-of-plane rotation error was relatively large because of small shape and poor geometrical feature of patella. Therefore, this study presents a method to determine 3D kinematics of patella using single-plane fluoroscopic image. The 3D pose of patella is estimated using an intensity-based 2D/3D registration technique, which uses a digitally reconstructed radiography (DRR) image created from 3D bone volume model. The 3D bone volume model for patella was created using CT scan data from a single subject. The 3D pose of the patella model is estimating by maximizing similarity measures between the DRR and fluoroscopic images iteratively with an optimization technique. In order to validate the pose estimation accuracy of patella including femur and tibia/fibura using the intensity-based 2D/3D registration, computer simulation test was performed. A set of synthetic silhouette images was created for each knee model in known typical orientations, and the test was carried out using three similarity measure methods. The result of computer simulation test showed that the root mean square errors were around 1.0 mm, 1.0° except for out-of-plane translation, and the reliability and feasibility of present method was demonstrated.

In vivo three-dimensional kinematics of normal knees during different high-flexion activities

Aims In Asia and the Middle‐East, people often flex their knees deeply in order to perform activities of daily living. The purpose of this study was to investigate the 3D kinematics of normal knees during high‐flexion activities. Our hypothesis was that the femorotibial rotation, varus‐valgus angle, translations, and kinematic pathway of normal knees during high‐flexion activities, varied according to activity. Materials and Methods We investigated the in vivo kinematics of eight normal knees in four male volunteers (mean age 41.8 years; 37 to 53) using 2D and 3D registration technique, and modelled the knees with a computer aided design program. Each subject squatted, kneeled, and sat crosslegged. We evaluated the femoral rotation and varus‐valgus angle relative to the tibia and anteroposterior translation of the medial and lateral side, using the transepicodylar axis as our femoral reference relative to the perpendicular projection on to the tibial plateau. This method evaluates the femur medially from what has elsewhere been described as the extension facet centre, and differs from the method classically applied. Results During squatting and kneeling, the knees displayed femoral external rotation. When sitting cross‐legged, femurs displayed internal rotation from 10° to 100°. From 100°, femoral external rotation was observed. No significant difference in varus‐valgus angle was seen between squatting and kneeling, whereas a varus position was observed from 140° when sitting cross‐legged. The measure kinematic pathway using our methodology found during squatting a medial pivoting pattern from 0° to 40° and bicondylar rollback from 40° to 150°. During kneeling, a medial pivot pattern was evident. When sitting cross‐legged, a lateral pivot pattern was seen from 0° to 100°, and a medial pivot pattern beyond 100°. Conclusion The kinematics of normal knees during high flexion are variable according to activity. Nevertheless, our study was limited to a small number of male patients using a different technique to report the kinematics than previous publications. Accordingly, caution should be observed in generalizing our findings.

A novel fluoroscopic method for multidimensional evaluation of swallowing function

OBJECTIVE Dynamic videofluoroscopic swallow study (VFSS) is used to investigate swallowing movements. However, it requires prolonged radiation exposure and mainly provides qualitative information. Herein, we present a multi-dimensional method for analyzing swallowing based on a pulsed, low-dose fluoroscopy technique that uses serial-shot images and evaluates the size, position, and temporal profile of the bolus to obtain a more comprehensive and realistic analysis of swallowing movements. METHODS Fifteen healthy adults drank two liquids: 20mL of pure water followed by 20mL of contrast medium mixture in a fluoroscopic study. Data were recorded in serial-shot images (7.5 frames/second, 1024×1024-pixel resolution, DICOM format). The images from the water and contrast swallows were inverted, synchronized, and subtracted to visualize the bolus in each frame. The pathway of the bolus was divided into 15 parts traversing the oropharynx, hypopharynx, and upper esophagus, and the total gray value was measured in each section. The results were presented as contour graphs. RESULTS The contour graphs allowed for information on the size, anatomical location, and temporal location of the bolus during swallowing to be displayed simultaneously. Two distinct swallowing patterns were observed in the subjects. The bolus showed two peaks-one in the hypopharynx and one in the upper esophagus-in all subjects. However, in nine of the 15 subjects, the two peaks were in different frames, whereas in six of the subjects, the two peaks were in the same frame. CONCLUSION We developed a new method for quantitatively evaluating swallowing. The technique allows for multidimensional assessment of the size, position, and temporal profile of the movement of the bolus across the pharynx. This method evaluates the swallowing movements using sharp, high-resolution images obtained by serial-shot, pulsed fluoroscopy with low radiation exposure. Additional studies are required to further clarify the variability of swallowing patterns and their clinical relevance in the evaluation of swallowing movements in healthy subjects and in patients with swallowing disorders.

Can intraoperative kinematic analysis predict postoperative kinematics following total knee arthroplasty? A preliminary

The preliminary study analyzed the relationship between intraoperative navigation-based kinematics and postoperative 2-dimensional/3-dimensional (2D/3D) image registration-based kinematics in total knee arthroplasty (TKA). Six knees in 5 patients were analyzed. All TKA procedures were performed using an image-free knee navigation system. Tibial internal rotation was assessed by intraoperative knee kinematics. At 1 year after surgery, tibial internal rotation was evaluated using a 2D/3D image registration technique under loaded and unloaded conditions. The correlation between intraoperative and postoperative data for the tibial internal rotation angle at 10 increments of knee flexion was then assessed. Difference in the knee flexion angle between the intraoperative and postoperative evaluations was adjusted to account for the sagittal cutting angle of the distal femur and proximal tibia. A correlation was found between the intraoperative and postoperative data for loaded knee flexion with this adjustment (Pearsons r = 0.725, p = 0.012). However, intraoperative kinematics was not significantly correlated with postoperative kinematics in the absence of loading. Larger adequately powered prospective studies are now needed to confirm our preliminary finding that postoperative loaded kinematics can be predicted by intraoperative evaluation. J. Med. Invest. 65:21-26, February, 2018.

Strain measurements of the tibial insert of a knee prosthesis using a knee motion simulator

OBJECTIVE The longevity of a knee prosthesis is influenced by the wear of the tibial insert due to its posture and movement. In this study, we assumed that the strain on the tibial insert is one of the main reasons for its wear and investigated the influence of the knee varus-valgus angles on the mechanical stress of the tibial insert. METHODS Knee prosthesis motion was simulated using a knee motion simulator based on a parallel-link six degrees-of-freedom actuator and the principal strain and pressure distribution of the tibial insert were measured. In particular, the early stance phase obtained from in vivo X-ray images was examined because the knee is applied to the largest load during extension/flexion movement. The knee varus-valgus angles were 0° (neutral alignment), 3°, and 5° malalignment. RESULTS Under a neutral orientation, the pressure was higher at the middle and posterior condyles. The first and second principal strains were larger at the high and low pressure areas, respectively. Even for a 3° malalignment, the load was concentrated at one condyle and the positive first principal strain increased dramatically at the high pressure area. The negative second principal strain was large at the low pressure area on the other condyle. The maximum equivalent strain was 1.3-2.1 times larger at the high pressure area. For a 5° malalignment, the maximum equivalent strain increased slightly. CONCLUSION These strain and pressure measurements can provide the mechanical stress of the tibial insert in detail for determining the longevity of an artificial knee joint.