Four-dimensional ultrasonographic guidance for invasive obstetric procedures.

OBJECTIVE: This pilot study evaluated the use of 4-dimensional (4D) real-time ultrasonographic needle guidance for amniocentesis, chorionic villus sampling (CVS), cordocentesis, and intrauterine transfusions. METHODS: Ninety-nine consecutive procedures were performed with 4D (real-time) multiplanar ultrasonographic imaging. Amniocentesis was done freehand in 3 orthogonal planes of view. Chorionic villus sampling, cordocentesis, and intrauterine transfusions were accomplished with a needle guide and 2 projected orthogonal planes. RESULTS: Needle tip visualization in the A, B, and C orthogonal planes during amniocentesis was noted in 93%, 63%, and 69% of cases, respectively. When a needle guide was used during CVS and cordocentesis, the needle tip was always seen in the 2 projected orthogonal planes, and no lateralization occurred. Four intrauterine transfusions were done with the 4D technique. The only procedural complication in any patient was bradycardia from vessel spasm during an intrauterine transfusion, requiring a cesarean delivery. There were no statistical differences (P > .05) between the numbers of needle insertions required in the 4D group compared with a historical control group in which 2-dimensional ultrasonographic needle guidance was used. CONCLUSIONS: In this feasibility study, a real-time 4D needle guidance technique was successfully used to perform amniocentesis, CVS, cordocentesis, and intrauterine transfusion. This appeared to contribute to the accuracy of needle placement by eliminating the lateralization phenomenon when a fixed needle guide attachment was used (for CVS and cordocentesis). Needle tip visualization was seen in each orthogonal plane in most freehand 4D amniocentesis cases. Future developments in 4D ultrasonographic technology may refine the utility of this technique for invasive obstetric procedures.     

Teaching ultrasound-guided invasive procedures in fetal medicine: learning curves with and without an electronic guidance system.

OBJECTIVE: To compare the learning curves of inexperienced junior obstetrics/gynecology registrars for ultrasound-guided invasive procedures on a training model, with and without an electronic guidance system. STUDY DESIGN: Four junior registrars performed their first 100 procedures on a training model with a new electronic guidance system, and four other junior registrars performed their first 100 procedures on the same training model without using the guidance system. All procedures were performed using a free-hand technique. We evaluated the quality of the procedure, which we defined as the time spent with the entire needle clearly visualized on the screen over the total duration of the procedure. We constructed learning curves for the eight junior registrars for comparative analysis. RESULTS: Quality of the procedure increased over time for all trainees. The learning curves were significantly steeper for trainees using the electronic guidance system. Trainees using the electronic guidance system performed better in the middle of their learning curve (procedures 25-75). All trainees reached the same level of quality by the end of their 100 procedures. CONCLUSIONS: The automated electronic guidance system helps faster learning but, after 100 procedures on a training model, both groups reached the same level of quality.     

A proposed new system for valuing dental procedures. The relative time-cost unit

The relative time cost unit (RTCU) is a proposed new system for valuing dental procedures that provides an alternative to traditional relative value units in fee-setting and reimbursement allowances. It incorporates personnel costs, task mixes, and task times into relative weights for dental procedures. The frequently performed procedure, "2-surface amalgam restoration," is used to illustrate how the RTCU values are derived from hospital task analysis data. The RTCU, as a data-based construct, holds appeal for restructuring fee schedules and has been used for almost a decade by insurance companies to value dental services, construct fee schedules, and evaluate reimbursement to providers.     

A new system for 3D ultrasound-guided placement of cerebral ventricle catheters

Purpose  

We present a new system for 3D ultrasound-guided placement of cerebral ventricle catheters. The system has been developed with the aim to provide accurate ultrasound-based guidance with only minimal changes to the current surgical technique and workflow.     

Puncture procedures utilizing transvaginal ultrasonic guidance.

The introduction of transvaginal sonography has enabled the use of this scanning method for guided puncture procedures. A total of 102 puncture procedures are described: 63 fetal reductions, eight punctures of ectopic pregnancies, 19 drainages of pelvic contents, seven punctures of ovarian cysts, four diagnostic culdocenteses and one injection of a cervical pregnancy.Every procedure is discussed in detail. There was only one procedure-related complication. The advantages of the ultrasound-guided vaginal puncture procedure are its performance under real-time imaging, a low complication rate, a better pregnancy outcome when considering the reduction of multifetal gestations, and, most importantly, the fact that abdominal surgery can be avoided in several cases.     

Operative ultrasound guidance for various surgical procedures

Although percutaneous ultrasound-guided technique is currently a common practice, the use of ultrasound for the purpose of guidance during surgery has not been widely practiced. Over a period of 10 years, we performed operative ultrasonography in 2,314 operations. In 321 of these operations, operative ultrasound guidance was performed for direct assistance of various surgical procedures, particularly during operations on the brain and spinal cord, liver, pancreas, and kidney. Procedures guided by operative ultrasound were classified into the following categories: intraoperative needle placement for fluid aspiration (n = 38), agent injection (n = 14), catheter introduction (n = 27), biopsy (n = 57), surgical tissue dissection for incision (n = 48), resection (n = 82) of organs, and extraction (n = 55) of stones or foreign bodies. Operative ultrasound guidance facilitates various surgical procedures and is considered a useful modality for reducing operative complications, shortening operating time, performing otherwise impossible procedures, and, at times, developing new surgical operations.     

Four-dimensional ultrasound guidance of prenatal invasive procedures.

OBJECTIVE: Technological advances in ultrasonography have revolutionized prenatal diagnosis and treatment. Here we evaluate the effectiveness of using four-dimensional (4D) ultrasonography to guide prenatal invasive procedures. PATIENTS AND METHODS: Prenatal invasive procedures using 4D ultrasound were recorded prospectively in 93 cases: 10 amnioinfusions, 50 amniocenteses, 8 chorionic villus samplings (CVS) and 25 cordocenteses. The needle target site was first identified using the two-dimensional (2D) mode, and was then confirmed using the three-dimensional (3D) mode. The needle was inserted under 4D ultrasound guidance. After selecting the needle target site, the true position of the needle was determined in three planes ('real-time 3D targeting'). RESULTS: Using 4D ultrasound guidance, most procedures were performed within 5 min and with a 100% success rate, even in cases involving severe oligohydramnios (amniocentesis), thin placentas (CVS) or narrow umbilical veins (cordocentesis). Moreover, there were no serious complications during or after any procedure. CONCLUSIONS: 4D ultrasonography can be used to guide various prenatal invasive procedures offering clear information in all three planes. It is likely that such imaging will reduce the time taken to complete the procedures and reduce the risks associated with them. Copyright (c) 2005 ISUOG. Published by John Wiley & Sons, Ltd.     

A freehand elastographic imaging approach for clinical breast imaging: system development and performance evaluation.

A prototype freehand elastographic imaging system has been developed for clinical breast imaging. The system consists of a fast data acquisition system, which is able to capture sequences of intermediate frequency echo frames at full frame rate from a commercial ultrasound scanner whilst the breast is deformed using hand-induced transducer motion. Two-dimensional echo tracking was used in combination with global distortion compensation and multi-compression averaging to minimise decorrelation noise incurred when stress is applied using hand-induced transducer motion. Experiments were conducted on gelatine phantoms to evaluate the quality of elastograms produced using the prototype system relative to those produced using mechanically induced transducer motion. The strain sensitivity and contrast-to-noise ratio of freehand elastograms compared favourably with elastograms produced using mechanically induced transducer motion. However, better dynamic range and signal-to-noise ratio was achieved when elastograms were created using mechanically induced transducer motion. Despite the loss in performance incurred when stress is applied using hand-induced transducer motion, it was concluded that the prototype system performed sufficiently well to warrant clinical evaluation.     

A probabilistic framework for freehand 3D ultrasound reconstruction applied to catheter ablation guidance in the left atrium

Introduction  The catheter ablation procedure is a minimally invasive surgery used to treat atrial fibrillation. Difficulty visualizing the catheter inside the left atrium anatomy has led to lengthy procedure times and limited success rates. In this paper, we present a set of algorithms for reconstructing 3D ultrasound data of the left atrium in real-time, with an emphasis on automatic tissue classification for improved clarity surrounding regions of interest. Methods  Using an intracardiac echo (ICE) ultrasound catheter, we collect 2D-ICE images of a left atrium phantom from multiple configurations and iteratively compound the acquired data into a 3D-ICE volume. We introduce two new methods for compounding overlapping US data—occupancy-likelihood and response-grid compounding—which automatically classify voxels as “occupied” or “clear,” and mitigate reconstruction artifacts caused by signal dropout. Finally, we use the results of an ICE-to-CT registration algorithm to devise a response-likelihood weighting scheme, which assigns weights to US signals based on the likelihood that they correspond to tissue-reflections. Results  Our algorithms successfully reconstruct a 3D-ICE volume of the left atrium with voxels classified as “occupied” or “clear,” even within difficult-to-image regions like the pulmonary vein openings. We are robust to dropout artifact that plagues a subset of the 2D-ICE images, and our weighting scheme assists in filtering out spurious data attributed to ghost-signals from multi-path reflections. By automatically classifying tissue, our algorithm precludes the need for thresholding, a process that is difficult to automate without subjective input. Our hope is to use this result towards developing 3D ultrasound segmentation algorithms in the future.     

A fast slam approach to freehand 3-d ultrasound reconstruction for catheter ablation guidance in the left atrium

We present a method for real-time, freehand 3D ultrasound (3D-US) reconstruction of moving anatomy, with specific application towards guiding the catheter ablation procedure in the left atrium. Using an intracardiac echo (ICE) catheter with a pose (position/orientation) sensor mounted to its tip, we continually mosaic 2D-ICE images of a left atrium phantom model to form a 3D-US volume. Our mosaicing strategy employs a probabilistic framework based on simultaneous localization and mapping (SLAM), a technique commonly used in mobile robotics for creating maps of unexplored environments. The measured ICE catheter tip pose provides an initial estimate for compounding 2D-ICE image data into the 3D-US volume. However, we simultaneously consider the overlap-consistency shared between 2D-ICE images and the 3D-US volume, computing a “corrected” tip pose if need be to ensure spatially-consistent reconstruction. This allows us to compensate for anatomic movement and sensor drift that would otherwise cause motion artifacts in the 3D-US volume. Our approach incorporates 2D-ICE data immediately after acquisition, allowing us to continuously update the registration parameters linking sensor coordinates to 3D-US coordinates. This, in turn, enables real-time localization and display of sensorized therapeutic catheters within the 3D-US volume for facilitating procedural guidance.     

A new method of transvaginal ultrasound-guided polypectomy: a feasibility study.

OBJECTIVES: A new device has been manufactured (Safe T Choice), which allows attachment of a transvaginal ultrasound probe to a specially adapted cervical tenaculum. This affords the capacity to monitor intrauterine surgical procedures without the need for hysteroscopy. The purpose of this study was to investigate the feasibility of endometrial polypectomy using this device combined with saline contrast sonohysterography (SCSH) to monitor the procedure. METHODS: Women diagnosed with an endometrial polyp on routine B-mode two-dimensional transvaginal ultrasound (TVS) were invited to join the study. Transvaginal ultrasound-guided polypectomies were carried out by a single operator. The procedure was timed from application until removal of the tenaculum. The ultrasound views were rated as satisfactory or poor. Success of the procedure was gauged by complete removal of the polyp without recourse to hysteroscopy. Women also attended for postoperative follow-up ultrasound scans to check for residual disease. RESULTS: Thirty-seven women were recruited to the study. The mean operating time was 8 min (95% CI, 5.9-10.4). The procedure was successful in 32/37 (86.5%) cases (95% CI, 75.5-97.5). In three cases (8.1%) the procedure failed because of an inability to obtain satisfactory images of the uterine cavity, and in two further cases (5.4%) the operator was unable to grasp and remove the polyp. Two patients (5.4%) bled from the tenaculum insertion site, necessitating suture for hemostasis. There were no other complications and none of the patients had evidence of residual polyp tissue at the follow-up visit. CONCLUSION: This study showed that transvaginal ultrasound-guided polypectomy is a feasible technique for the removal of endometrial polyps. Further work is required to compare outcomes and cost-effectiveness of this technique with hysteroscopic polypectomy.     

Registration of 3D freehand ultrasound to a bone model for orthopedic procedures of the forearm

Purpose

For guidance of orthopedic surgery, the registration of preoperative images and corresponding surgical plans with the surgical setting can be of great value. Ultrasound (US) is an ideal modality for surgical guidance, as it is non-ionizing, real time, easy to use, and requires minimal (magnetic/radiation) safety limitations. By extracting bone surfaces from 3D freehand US and registering these to preoperative bone models, complementary information from these modalities can be fused and presented in the surgical realm.

Methods

A partial bone surface is extracted from US using phase symmetry and a factor graph-based approach. This is registered to the detailed 3D bone model, conventionally generated for preoperative planning, based on a proposed multi-initialization and surface-based scheme robust to partial surfaces.

Results

36 forearm US volumes acquired using a tracked US probe were independently registered to a 3D model of the radius, manually extracted from MRI. Given intraoperative time restrictions, a computationally efficient algorithm was determined based on a comparison of different approaches. For all 36 registrations, a mean (± SD) point-to-point surface distance of \(0.57\,(\pm \,0.08)\,\hbox {mm}\) was obtained from manual gold standard US bone annotations (not used during the registration) to the 3D bone model.

Conclusions

A registration framework based on the bone surface extraction from 3D freehand US and a subsequent fast, automatic surface alignment robust to single-sided view and large false-positive rates from US was shown to achieve registration accuracy feasible for practical orthopedic scenarios and a qualitative outcome indicating good visual image alignment.

     

A new scanning approach for limb extremities using a water bag in freehand 3-D ultrasound

3-D ultrasound (US) can significantly improve the visualization of musculoskeletal tissues, such as residual limbs, feet and hands. Traditionally, mechanical scanning is normally required to obtain the entire volume of these limb extremities. In this paper, a new scanning approach using a water bag was described to collect the complete volume of various tissues surrounding bones. The water bag was used to contain the limb extremity and the scanning was conducted on its external surface from different directions. The recorded 2-D US images containing complete anatomic information surrounding the bones from different directions were used to form full 3-D volumes of the limb extremities. A plastic auxiliary apparatus was designed to hold the water bag and support the subject's limb part with an armrest. A corresponding algorithm was proposed to remove invalid image information within each sweep by a separating plane defined semiautomatically. Two phantoms were used to test the repeatability and accuracy of the imaging. The distance between two plastic bands attached to a plastic tube filled with US gel measured by a micrometer and from the four reconstructed volumes were 39.03 +/- 0.36 mm and 39.2 +/- 0.5 mm, respectively. The diameter, height and volume of a silicone cylinder phantom measured for the 10 reconstructed volumes were 40.2 +/- 1.4 mm, 12.9 +/- 1.0 mm and 16400 +/- 1600 mm(3), respectively. They agreed with the corresponding results obtained by the micrometer, which were 41.29 +/- 0.13 mm, 12.98 +/- 0.17 mm and 17370 +/- 140 mm(3), respectively. The reconstructed volumes of the two phantoms, a chicken leg in vitro, and human fingers in vivo were also reported. The preliminary results obtained in this study demonstrated that this new scanning approach should have potential for the 3-D US imaging of musculoskeletal extremities using freehand scanning.     

A real-time freehand ultrasound calibration system with automatic accuracy feedback and control

This article describes a fully automatic, real-time, freehand ultrasound calibration system. The system was designed to be simple and sterilizable, intended for operating-room usage. The calibration system employed an automatic-error-retrieval and accuracy-control mechanism based on a set of ground-truth data. Extensive validations were conducted on a data set of 10,000 images in 50 independent calibration trials to thoroughly investigate the accuracy, robustness, and performance of the calibration system. On average, the calibration accuracy (measured in three-dimensional reconstruction error against a known ground truth) of all 50 trials was 0.66 mm. In addition, the calibration errors converged to submillimeter in 98% of all trials within 12.5 s on average. Overall, the calibration system was able to consistently, efficiently and robustly achieve high calibration accuracy with real-time performance.     

超声引导消融治疗子宫肌瘤导航系统的设计

目的:如何将消融装置精确的放置到预期的位置,是射频消融治疗子宫肌瘤中的难点,因此研究应用于超声引导下消融治疗子宫肌瘤的导航系统。方法:①设计超声引导下消融治疗子宫肌瘤的导航系统,该系统的关键是同时跟踪超声探头和射频消融针的空间位置,从而准确的将射频消融针放到准确的位置,并缩短手术时间及使手术的创伤更小。②系统主要由三维超声导航和空间定位装置组成。使用以下设备:B型超声仪(ULTRAMARK-9,ATL公司,美国);磁跟踪器(pciBirds,model6DFOB,Ascension Technology公司,美国);射频电极;图形工作站,用于采集超声图像、记录磁跟踪器提供的位置信息、导航图像显示等。利用磁定位器实时跟踪超声探头和穿刺针,构建三维超声,穿刺操作中实时显示二维超声图像平面在三维超声中的位置及与穿刺针的空间位置关系。③为了测试系统的精度和稳定性,设计了水槽模型。以30g/L的琼脂糖经水浴加热后,注入模具中,冷却凝固后取出,制成球形穿刺目标,将球体圆心和射频电极针尖到达的实际位置之间的差值作为系统误差进行对该系统进行评价。结果:利用水槽模型进行了30次实验,最大穿刺角度为60°,实验中采集的数字图像均为768*576像素的8位灰度图像。所有实验均顺利完成穿刺操作,实验的系统误差范围在3mm内。结论:利用超声引导下消融治疗子宫肌瘤导航系统可以实现三维空间的准确定位,实现灵活准确的穿刺操作。