Evaluation and Comparison of Target Registration Error in Active and Passive Optical Tracking Systems

Optical tracking systems combined with imaging modalities such as computed tomography and magnetic reso-nance imaging are important parts of image guided surgery systems. By determining the location and orientation of sur-gical tools relative to a patient's reference system, tracking systems assist surgeons during the planning and execution of image guided procedures. Therefore, knowledge of the tracking system-induced error is of great importance. To this end, this study compared one passive and two active optical tracking systems in terms of their Target Registration Error. Two experiments were performed to measure the systems' accuracy, testing the impact of factors such as the size of the measuring volume, length of surgical instruments and environmental conditions with orthopedic procedures in mind. According to the performed experiments, the active systems achieved significantly higher accuracy than the tested passive system, reporting an overall accuracy of 0.063 mm (SD = 0.025) and 0.259 mm (SD = 0.152), respectively.

Mixed reality as a novel tool for diagnostic and surgical navigation in orthopaedics

Purpose

This study presents a novel surgical navigation tool developed in mixed reality environment for orthopaedic surgery. Joint and skeletal deformities affect all age groups and greatly reduce the range of motion of the joints. These deformities are notoriously difficult to diagnose and to correct through surgery.

Method

We have developed a surgical tool which integrates surgical instrument tracking and augmented reality through a head mounted display. This allows the surgeon to visualise bones with the illusion of possessing “X-ray” vision. The studies presented below aim to assess the accuracy of the surgical navigation tool in tracking a location at the tip of the surgical instrument in holographic space.

Results

Results show that the average accuracy provided by the navigation tool is around 8 mm, and qualitative assessment by the orthopaedic surgeons provided positive feedback in terms of the capabilities for diagnostic use.

Conclusions

More improvements are necessary for the navigation tool to be accurate enough for surgical applications, however, this new tool has the potential to improve diagnostic accuracy and allow for safer and more precise surgeries, as well as provide for better learning conditions for orthopaedic surgeons in training.

Evaluation of a novel navigation platform for laparoscopic liver surgery with organ deformation compensation using injected fiducials

In laparoscopic liver resection, surgeons conventionally rely on anatomical landmarks detected through a laparoscope, preoperative volumetric images and laparoscopic ultrasound to compensate for the challenges of minimally invasive access. Image guidance using optical tracking and registration procedures is a promising tool, although often undermined by its inaccuracy. This study evaluates a novel surgical navigation solution that can compensate for liver deformations using an accurate and effective registration method. The proposed solution relies on a robotic C-arm to perform registration to preoperative CT/MRI image data and allows for intraoperative updates during resection using fluoroscopic images. Navigation is offered both as a 3D liver model with real-time instrument visualization, as well as an augmented reality overlay on the laparoscope camera view. Testing was conducted through a pre-clinical trial which included four porcine models. Accuracy of the navigation system was measured through two evaluation methods: liver surface fiducials reprojection and a comparison between planned and navigated resection margins. Target Registration Error with the fiducials evaluation shows that the accuracy in the vicinity of the lesion was 3.78±1.89 mm. Resection margin evaluations resulted in an overall median accuracy of 4.44 mm with a maximum error of 9.75 mm over the four subjects. The presented solution is accurate enough to be potentially clinically beneficial for surgical guidance in laparoscopic liver surgery.

Accelerating B-spline interpolation on GPUs: Application to medical image registration

BACKGROUND AND OBJECTIVE

B-spline interpolation (BSI) is a popular technique in the context of medical imaging due to its adaptability and robustness in 3D object modeling. A field that utilizes BSI is Image Guided Surgery (IGS). IGS provides navigation using medical images, which can be segmented and reconstructed into 3D models, often through BSI. Image registration tasks also use BSI to transform medical imaging data collected before the surgery and intra-operative data collected during the surgery into a common coordinate space. However, such IGS tasks are computationally demanding, especially when applied to 3D medical images, due to the complexity and amount of data involved. Therefore, optimization of IGS algorithms is greatly desirable, for example, to perform image registration tasks intra-operatively and to enable real-time applications. A traditional CPU does not have sufficient computing power to achieve these goals and, thus, it is preferable to rely on GPUs. In this paper, we introduce a novel GPU implementation of BSI to accelerate the calculation of the deformation field in non-rigid image registration algorithms.

METHODS

Our BSI implementation on GPUs minimizes the data that needs to be moved between memory and processing cores during loading of the input grid, and leverages the large on-chip GPU register file for reuse of input values. Moreover, we re-formulate our method as trilinear interpolations to reduce computational complexity and increase accuracy. To provide pre-clinical validation of our method and demonstrate its benefits in medical applications, we integrate our improved BSI into a registration workflow for compensation of liver deformation (caused by pneumoperitoneum, i.e., inflation of the abdomen) and evaluate its performance.

RESULTS

Our approach improves the performance of BSI by an average of 6.5×  and interpolation accuracy by 2×  compared to three state-of-the-art GPU implementations. Through pre-clinical validation, we demonstrate that our optimized interpolation accelerates a non-rigid image registration algorithm, which is based on the Free Form Deformation (FFD) method, by up to 34%.

CONCLUSION

Our study shows that we can achieve significant performance and accuracy gains with our novel parallelization scheme that makes effective use of the GPU resources. We show that our method improves the performance of real medical imaging registration applications used in practice today.

The effect of intraoperative imaging on surgical navigation for laparoscopic liver resection surgery

Conventional surgical navigation systems rely on preoperative imaging to provide guidance. In laparoscopic liver surgery, insufflation of the abdomen (pneumoperitoneum) can cause deformations on the liver, introducing inaccuracies in the correspondence between the preoperative images and the intraoperative reality. This study evaluates the improvements provided by intraoperative imaging for laparoscopic liver surgical navigation, when displayed as augmented reality (AR). Significant differences were found in terms of accuracy of the AR, in favor of intraoperative imaging. In addition, results showed an effect of user-induced error: image-to-patient registration based on annotations performed by clinicians caused 33% more inaccuracy as compared to image-to-patient registration algorithms that do not depend on user annotations. Hence, to achieve accurate surgical navigation for laparoscopic liver surgery, intraoperative imaging is recommendable to compensate for deformation. Moreover, user annotation errors may lead to inaccuracies in registration processes.

Efficacy of external cephalic version performed at term

OBJECTIVE

To evaluate the efficacy and complications of external cephalic version in term (37 or more weeks) gestation.

STUDY DESIGN

A case series from February 1990 until December 1994 studied 160 patients with term singleton breech presentation. External cephalic version (ECV) with prophylactic tocolysis was the method used.

RESULTS

ECV was successful in 67% of the cases (107/160) overall, in 56% of the nulliparous (57/102) and 86% of the multiparous women (50/58). About 90% of those with successful ECV (96/107) had a vaginal delivery with a vertex presentation of the fetus. Emergency Caesarean section due to fetal distress was not required during or immediately after the procedure. No perinatal mortality or babies with an Apgar score less than 7 at 5 min were observed.

CONCLUSIONS

ECV in term pregnancy seems to be useful and it is safe both for the mother and the fetus. It should be performed at term, with close monitoring of the fetus, and in an environment able to provide an emergency Caesarean section.

Prevalence of fetal left ventricular hyperechogenic foci in a low risk population

OBJECTIVE

To ascertain the prevalence and clinical significance of small hyperechogenic foci detected in the fetal left ventricle in routine ultrasound screening of pregnant women attending our hospital.

POPULATION AND METHODS

From April 1994 to April 1995, 1135 consecutive pregnant women examined at the obstetric ultrasound unit of our hospital were studied prospectively. A postnatal cardiologic examination was performed when signs of cardiopathy were observed at the prenatal ultrasound investigation or the neonatal examination.

RESULTS

Congenital heart disease was detected in 10/1148 infants born (0.9%); eight diagnoses were made prenatally (detection rate 80%). The prevalence of left ventricular hyperechogenic foci was 3.2% (37/1148 fetuses). In 35 cases (94.6%) the foci were no longer observed at the routine third trimester examination. Only in two cases (5.4%) did foci persist at the postnatal examination but without clinical signs of cardiopathy or karyotype anomalies. No association was observed between foci and major structural abnormalities. The foci were single in 32 cases (86.5%). Four foci (10.8%) were located at the interventricular septum, five (13.5%) bilaterally at the papillary apparatus of the mitral valve, and the others at the ventricular wall. No focus was associated with incompetence of the affected valve, whereas five (13.5%) were associated with a fetal disorder.

CONCLUSIONS

The prevalence of intracardiac hyperechogenic foci in our general population considered at low risk was more than five times greater than that reported in the literature. Foci were not associated with structural heart defects or chromosomal abnormalities. Persistence during the third trimester and postnatal life was rare and without evident signs of heart disease.