Cortical surface shift estimation using stereovision and optical flow motion tracking via projection image registration

Stereovision is an important intraoperative imaging technique that captures the exposed parenchymal surface noninvasively during open cranial surgery. Estimating cortical surface shift efficiently and accurately is critical to compensate for brain deformation in the operating room (OR). In this study, we present an automatic and robust registration technique based on optical flow (OF) motion tracking to compensate for cortical surface displacement throughout surgery. Stereo images of the cortical surface were acquired at multiple time points after dural opening to reconstruct three-dimensional (3D) texture intensity-encoded cortical surfaces. A local coordinate system was established with its z-axis parallel to the average surface normal direction of the reconstructed cortical surface immediately after dural opening in order to produce two-dimensional (2D) projection images. A dense displacement field between the two projection images was determined directly from OF motion tracking without the need for feature identification or tracking. The starting and end points of the displacement vectors on the two cortical surfaces were then obtained following spatial mapping inversion to produce the full 3D displacement of the exposed cortical surface. We evaluated the technique with images obtained from digital phantoms and 18 surgical cases – 10 of which involved independent measurements of feature locations acquired with a tracked stylus for accuracy comparisons, and 8 others of which 4 involved stereo image acquisitions at three or more time points during surgery to illustrate utility throughout a procedure. Results from the digital phantom images were very accurate (0.05 pixels). In the 10 surgical cases with independently digitized point locations, the average agreement between feature coordinates derived from the cortical surface reconstructions was 1.7–2.1 mm relative to those determined with the tracked stylus probe. The agreement in feature displacement tracking was also comparable to tracked probe data (difference in displacement magnitude was <1 mm on average). The average magnitude of cortical surface displacement was 7.9 ± 5.7 mm (range 0.3–24.4 mm) in all patient cases with the displacement components along gravity being 5.2 ± 6.0 mm relative to the lateral movement of 2.4 ± 1.6 mm. Thus, our technique appears to be sufficiently accurate and computationally efficiency (typically ∼15 s), for applications in the OR.     

3D flash lag illusion

Objective of this research is to study the presence of 3D flash lag illusion created by a moving object that has a motion-in-depth and a flash object. An object consisting of two thin sticks was simulated to approach the subject who observed it with a stereoscope. In the process of approaching, another stick was briefly presented in the middle of the moving sticks. Five human subjects took part in our experiments and all perceived 3D flash lag illusion. The perceived depth created by 3D flash lag illusion was measured by two different psychophysical experiments, by use of a vernier caliper and by a method of nulling with another depth cue. We studied relation between the perceived depth and the presentation distance. The experimental results indicate that the perceived gap by 3D flash lag illusion is independent from the presentation distance.     

Solving da Vinci stereopsis with depth-edge-selective V2 cells

We propose a new model for da Vinci stereopsis based on a coarse-to-fine disparity energy computation in V1 and disparity-boundary-selective units in V2. Unlike previous work, our model contains only binocular cells, relies on distributed representations of disparity, and has a simple V1-to-V2 feedforward structure. We demonstrate with random-dot stereograms that the V2 stage of our model is able to determine the location and the eye-of-origin of monocularly occluded regions, and improve disparity map computation. We also examine a few related issues. First, we argue that since monocular regions are binocularly defined, they cannot generally be detected by monocular cells. Second, we show that our coarse-to-fine V1 model for conventional stereopsis explains double matching in Panum’s limiting case. This provides computational support to the notion that the perceived depth of a monocular bar next to a binocular rectangle may not be da Vinci stereopsis per se [Gillam, B., Cook, M., & Blackburn, S. (2003). Monocular discs in the occlusion zones of binocular surfaces do not have quantitative depth—a comparison with Panum’s limiting case. Perception 32, 1009-1019.]. Third, we demonstrate that some stimuli previously deemed invalid have simple, valid geometric interpretations. Our work suggests that studies of da Vinci stereopsis should focus on stimuli more general than the bar-and-rectangle type and that disparity-boundary-selective V2 cells may provide a simple physiological mechanism for da Vinci stereopsis.     

随机点光栅板的立体视觉检测分析与应用评估

目的应用随机点光栅板对正常人进行立体视觉检测分析。方法选取150名双眼视力正常、无眼疾的成人作为受试者,应用随机点光栅板、数字化立体视觉检查图、Titmus立体视检查图作为对照,检查受试者的立体视锐度,比较3种检查结果的差异。结果 3种方法检测所得立体视觉正常者（立体视锐度≤60″）所占百分比分别为：随机点光栅板95.3%,数字化立体视觉检查图（颜氏图）94.0%,Titmus 96.7%,3种检查结果比较差异无统计学意义（P〉0.05）。结论随机点光栅板是在直观的自然状态下检测立体视锐度,无需佩戴红蓝分视眼镜,使用快捷方便,结果准确可靠,对正常人群及相关职业的筛选有重要的实用价值。     

Visual action control does not rely on strangers--effects of pictorial cues under monocular and binocular vision

Fast goal-directed actions are supposed to be controlled almost exclusively by bottom-up visual control. This mode of processing has been identified with the so-called dorsal visual stream. It is generally accepted that object recognition, mediated by the ventral stream, must be important for deciding what action to execute depending on the specific object to be grasped and the particular purpose. In contrast, the kinematic parameters of the actual movement itself are supposed to be unaffected by recognition processes. This view was recently challenged by the demonstration of a significant impact of object familiarity on grasping kinematics under binocular visual control (McIntosh & Lashley, 2008). This effect was observed for very well known everyday objects. However, it remained unclear whether the effect was really due to long-term, everyday familiarity of the target objects or whether it was simply mediated by short-term learning during the experiment. Therefore, we examined whether the same effect could also be found with objects that were geometrically identical to the ones used by McIntosh and Lashley (2008) and could be distinguished by a pictorial cue but were not associated with long-term, everyday experience. We only found an effect of familiarity under monocular but not under binocular control. Our observation suggests that indeed familiarity exerts an effect on movements under binocular control only if explicit knowledge about the objects is very stable and salient, e.g. after long-term experience.     

Measuring abutment convergence angles using stereovision dental image processing system

PURPOSE

The purpose of this study was to develop a dental image processing system using a three-dimensional (3D) camera and stereovision technology. The reliability of the system for measuring axial wall convergence angles was evaluated.

MATERIALS AND METHODS

The new system predicted 3D coordinate points from 2D images and calculated distances and angles between points. Two examiners measured axial wall convergence angles for seven artificial abutments using a traditional tracing-based method (TBM) and the stereovision-based method (SVBM). Five wax abutment models of simplified abutment forms were made and axial wall convergence angles of wax models were measured by both methods. The data were statistically analyzed at the level of significance, 0.05.

RESULTS

Intraclass correlation coefficients showed excellent intra-examiner and inter-examiner reliabilities for both methods. Bland-Altman plots and paired t-tests showed significant differences between measurements and true values using TBM; differences were not significant with SVBM.

CONCLUSION

This study found that the SVBM reflected true angle values more accurately than a TMB and illustrated an example of 3D computer science applied to clinical dentistry.     

散光对远立体视觉的影响

目的 探讨散光对患者远立体视觉的影响,为散光的临床矫治提供参考依据。方法 随机抽取准分子激光门诊的近视散光患者222例,分别检查其矫正球镜和矫正球柱镜后的立体视觉,研究散光大小、轴向及双眼柱镜差值等因素对其远立体视造成的影响。结果 柱镜矫正后186例(83.8％)患者远立体视锐度显著提高;双眼柱镜差值较小者及双眼呈对称散光者的立体视觉较好。结论 散光度数的大小不影响成年人屈光不正矫正后的立体视觉;双眼散光度数差值越小、双眼散光轴向越趋于对称,立体视功能形成就越好。     

Persistent and automatic intraoperative 3D digitization of surfaces under dynamic magnifications of an operating microscope

One of the major challenges impeding advancement in image-guided surgical (IGS) systems is the soft-tissue deformation during surgical procedures. These deformations reduce the utility of the patient’s preoperative images and may produce inaccuracies in the application of preoperative surgical plans. Solutions to compensate for the tissue deformations include the acquisition of intraoperative tomographic images of the whole organ for direct displacement measurement and techniques that combines intraoperative organ surface measurements with computational biomechanical models to predict subsurface displacements. The later solution has the advantage of being less expensive and amenable to surgical workflow. Several modalities such as textured laser scanners, conoscopic holography, and stereo-pair cameras have been proposed for the intraoperative 3D estimation of organ surfaces to drive patient-specific biomechanical models for the intraoperative update of preoperative images. Though each modality has its respective advantages and disadvantages, stereo-pair camera approaches used within a standard operating microscope is the focus of this article. A new method that permits the automatic and near real-time estimation of 3D surfaces (at 1 Hz) under varying magnifications of the operating microscope is proposed. This method has been evaluated on a CAD phantom object and on full-length neurosurgery video sequences (∼1 h) acquired intraoperatively by the proposed stereovision system. To the best of our knowledge, this type of validation study on full-length brain tumor surgery videos has not been done before. The method for estimating the unknown magnification factor of the operating microscope achieves accuracy within 0.02 of the theoretical value on a CAD phantom and within 0.06 on 4 clinical videos of the entire brain tumor surgery. When compared to a laser range scanner, the proposed method for reconstructing 3D surfaces intraoperatively achieves root mean square errors (surface-to-surface distance) in the 0.28–0.81 mm range on the phantom object and in the 0.54–1.35 mm range on 4 clinical cases. The digitization accuracy of the presented stereovision methods indicate that the operating microscope can be used to deliver the persistent intraoperative input required by computational biomechanical models to update the patient’s preoperative images and facilitate active surgical guidance.     

ReSTOR多焦点人工晶状体植入术后全程立体视觉质量分析

目的 比较双眼植入ReSTOR＋3D多焦点人工晶状体（MIOL）与单焦点人工晶状体（SIOL）术后的近、中、远视力和立体视觉质量.方法 前瞻性对照研究.选择接受白内障超声乳化吸除联合人工晶状体植入术的患者共46例（92眼）,年龄45～67岁.按植入人工晶状体的不同分为两组：ReSTOR＋3D（AcrySof ReSTOR SN6AD1）MIOL组23例（46眼）,AcrySof IQ（AcrySof IQ SN60WF）SIOL组23例（46眼）,均非同期手术.患者分别于第二只眼术后3个月时检查裸眼及配戴最佳远距离矫正眼镜时的近、中、远视力和立体视锐度,并对术后患者主观立体视觉质量进行问卷调查.样本均数的比较采用配对t检验,样本率之间比较采用x2检验.结果 术后3个月,裸眼近、中视力及最佳矫正近、中距离视力比较,MIOL组明显优于SIOL组,差异均有统计学意义（x2分别为26.2、23.7、29.3、25.0,P均＜0.05） 裸眼远视力及最佳矫正远视力比较,两组差异均无统计学意义（P＞0.05）.裸眼及最佳矫正下的立体视锐度比较：MIOL组的近立体视锐度明显优于SIOL组,差异均有统计学意义（x2分别为26.3和23.5,P均＜0.05） MIOL组的中距离立体视锐度亦优于SIOL组,差异有统计学意义（x2分别为15.2和12.6,P均＜0.05） 而两组的远立体视锐度比较,差异均无统计学意义（P＞0.05）.MIOL组对近、中距离立体视觉质量的满意度为4.05±0.25和4.25±0.25,均高于SIOL组,差异有统计学意义（t分别为5.4和5.1,P均＜0.05） 而两组对远距离立体视觉质量的满意度差异无统计学意义（P＞0.05）.结论 ReSTOR＋3D MIOL的近、中距离视力和立体视锐度明显优于SIOL,可为患者提供更好的立体视觉质量,患者术后对近、中距离立体视觉质量的满意度更高.