Registration of a statistical model to intraoperative ultrasound for scaphoid screw fixation

Purpose

Volar percutaneous scaphoid fracture fixation is conventionally performed under fluoroscopy-based guidance, where surgeons need to mentally determine a trajectory for the insertion of the screw and its depth based on a series of 2D projection images. In addition to challenges associated with mapping 2D information to a 3D space, the process involves exposure to ionizing radiation. Three-dimensional ultrasound has been suggested as an alternative imaging tool for this procedure; however, it has not yet been integrated into clinical routine since ultrasound only provides a limited view of the scaphoid and its surrounding anatomy.

Methods

We propose a registration of a statistical wrist shape + scale + pose model to a preoperative CT and intraoperative ultrasound to derive a patient-specific 3D model for guiding scaphoid fracture fixation. The registered model is then used to determine clinically important intervention parameters, including the screw length and the trajectory of screw insertion in the scaphoid bone.

Results

Feasibility experiments are performed using 13 cadaver wrists. In 10 out of 13 cases, the trajectory of screw suggested by the registered model meets all clinically important intervention parameters. Overall, an average 94 % of maximum allowable screw length is obtained based on the measurements from gold standard CT. Also, we obtained an average 92 % successful volar accessibility, which indicates that the trajectory is not obstructed by the surrounding trapezium bone.

Conclusions

These promising results indicate that determining clinically important screw insertion parameters for scaphoid fracture fixation is feasible using 3D ultrasound imaging. This suggests the potential of this technology in replacing fluoroscopic guidance for this procedure in future applications.

     

Sonographic measurement of the fetal femur: factors affecting accuracy

Variations have been observed in the measurement of fetal femoral diaphysis length by ultrasound. This in vitro study examines the effect of depth, the angle of the bone relative to the axis of the sound beam, the machine, and the observer on the precision of measurement. Using analysis of variance techniques, it demonstrates that three of these factors (depth, angle, and machine) have significant effects. Depth-associated variations were less than one millimeter and are probably not of clinical importance. However, the variations due to changes in angle are highly significant (P = less than 0.001) and may be controlled by obtaining the measurement with the femur perpendicular to the sound beam. Errors due to variation between machines were also highly significant (P = less than 0.001). When determining serial growth patterns, the errors due to variations between machines can be controlled by using the same machine for each examination. The variation between machines is also an important factor to consider when choosing a curve for reference purposes.     

Joint registration of ultrasound,CT and a shape+pose statistical model of the lumbar spine for guiding anesthesia

Purpose

Facet joint injections and epidural needle insertions are widely used for spine anesthesia. Accurate needle placement is important for effective therapy delivery and avoiding complications arising from damage of soft tissue and nerves. Needle guidance is usually performed by fluoroscopy or palpation, resulting in radiation exposure and multiple needle re-insertions. Several ultrasound (US)-based approaches have been proposed but have not found wide acceptance in clinical routine. This is mainly due to difficulties in interpretation of the complex spinal anatomy in US, which leads to clinicians’ lack of confidence in relying only on information derived from US for needle guidance.

Methods

We introduce a multimodal joint registration technique that takes advantage of easy-to-interpret preprocedure computed topography (CT) scans of the lumbar spine to concurrently register a shape+pose model to the intraprocedure 3D US. Common shape coefficients are assumed between two modalities, while pose coefficients are specific to each modality.

Results

The joint method was evaluated on patient data consisting of ten pairs of US and CT scans of the lumbar spine. It was successfully applied in all cases and yielded an RMS shape error of 2.1 mm compared to the CT ground truth. The joint registration technique was compared to a previously proposed method of statistical model to US registration Rasoulian et al. (Information processing in computer-assisted interventions. Springer, Berlin, pp 51–60, 2013). The joint framework improved registration accuracy to US in 7 out of 17 visible vertebrae, belonging to four patients. In the remaining cases, the two methods were equally accurate.

Conclusion

The joint registration allows visualization and augmentation of important anatomy in both the US and CT domain and improves the registration accuracy in both modalities. Observing the patient-specific model in the CT domain allows the clinicians to assess the local registration accuracy qualitatively, which is likely to increase their confidence in using the US model for deriving needle guidance decisions.

     

Hearing aid and hearing assistance technology use in Aotearoa/New Zealand

Objective: The purpose of this study was to describe factors that are related to hearing aid and hearing assistance technology ownership and use in Aotearoa/New Zealand. Design: Adults with hearing impairment living in New Zealand were surveyed regarding health-related quality of life and device usage. Audiometric data (hearing sensitivity and speech in noise) were collected. Study sample: Data were obtained from 123 adults with hearing impairment: 73 reported current hearing-aid use, 81 reported current hearing assistance technology use. Results: In both analyses, device users had more difficulty understanding speech in background noise, had poor hearing in both their better and worse hearing ears, and perceived more consequences of hearing impairment in their everyday lives (both emotionally and socially) than non-hearing-aid users. Discriminant analyses showed that the social consequences of hearing impairment and the better ear hearing best classified hearing aid users from non-users but social consequences and worse ear hearing best classified hearing assistance technology users from non-users. Conclusions: Quality of life measurements and speech-in-noise assessments provide useful clinical information. Hearing-impaired adults in New Zealand who use hearing aids also tend to use hearing assistance technology, which has important clinical implications.     

Comparison of Patient Position and Midline Lumbar Neuraxial Access Via Statistical Model Registration to Ultrasound

Patient positioning and needle puncture site are important for lumbar neuraxial anesthesia. We sought to identify optimal patient positioning and puncture sites with a novel ultrasound registration. We registered a statistical model to volumetric ultrasound data acquired from volunteers (n?=?10) in three positions: (i) prone; (ii) seated with thoracic and lumbar flexion; and (iii) seated as in position ii, with a 10° dorsal tilt. We determined injection target size and penetration success by simulating lumbar injections on validated registered models. Injection window and target area sizes in seated positions were significantly larger than those in prone positions by 65% in L2–3 and 130% in L3–4; a 10° tilt had no significant effect on target sizes between seated positions. In agreement with computed tomography studies, simulated L2–3 and L3–4 injections had the highest success at the 50% and 75% midline puncture sites, respectively, measured from superior to inferior spinous process. We conclude that our registration to ultrasound technique is a potential tool for tolerable determination of puncture site success in vivo.     

Single-operator real-time ultrasound-guidance to aim and insert a lumbar epidural needle

Purpose

In conventional practice of epidural needle placement, determining the interspinous level and choosing the puncture site are based on palpation of anatomical landmarks, which can be difficult with some subjects. Thereafter, the correct passage of the needle towards the epidural space is a blind “feel as you go” method. An aim-and-insert single-operator ultrasound-guided epidural needle placement is described and demonstrated.

Method

Nineteen subjects undergoing elective Cesarean delivery consented to undergo both a pre-puncture ultrasound scan and real-time paramedian ultrasound-guidance for needle insertion. Following were the study objectives: to measure the success of a combined spinal-epidural needle insertion under real-time guidance, to compare the locations of the chosen interspinous levels as determined by both ultrasound and palpation, to measure the change in depth of the epidural space from the skin surface as pressure is applied to the ultrasound transducer, and to investigate the geometric limitations of using a fixed needle guide.

Results

One subject did not participate in the study because pre-puncture ultrasound examination showed unrecognizable bony landmarks. In 18 of 19 subjects, the epidural needle entered the epidural space successfully, as defined by a loss-of-resistance. In two subjects, entry into the epidural space was not achieved despite ultrasound guidance. Eighteen of the 19 interspinous spaces that were identified using palpation were consistent with those determined by ultrasound. The transducer pressure changed the depth of the epidural space by 2.8 mm. The measurements of the insertion lengths corresponded with the geometrical model of the needle guide, but the needle required a larger insertion angle than would be needed without the guide.

Conclusion

This small study demonstrates the feasibility of the ultrasound-guidance technique. Areas for further development are identified for both ultrasound software and physical design.     

Utility of prepuncture ultrasound for localization of the thoracic epidural space

Background

Ultrasound has been shown to facilitate accurate identification of the intervertebral level and to predict skin-to-epidural depth in the lumbar epidural space with reliable precision. We hypothesized that we could accurately predict the skin-to-epidural depth and the intervertebral level in the thoracic spine with the use of ultrasound.

Methods

Twenty patients presenting for thoracic surgery were included in a feasibility study. The skin-to-epidural depth was measured using prepuncture ultrasound in the paramedian window, and the predicted depth was compared with the actual needle depth and the depth as measured by computed tomography. In addition, the intervertebral levels were identified by ultrasound using the “counting up” method, and the results were compared with the levels identified by anesthesiologists.

Results

The ultrasound-based depth measurements displayed a bias of 3.21 mm with 95% limits of agreement from ?7.47 to 13.9 mm compared with the clinically determined needle depth. The intervertebral levels identified by the anesthesiologists and the sonographer matched in only 40% of cases.

Conclusion

Ultrasound-based measurements of skin-to-epidural depth show acceptable agreement with the actual depth observed during epidural catheterization; however, the limits of agreement are wide, which restricts the predictive value of ultrasound-based measurements. Further study is required to delineate the role of ultrasound in thoracic epidural catheterizations.     

Adaptive ultrasound imaging of the lumbar spine for guidance of epidural anesthesia

Ultrasound imaging can help in choosing the needle trajectory for epidural anesthesia but anatomical features are not always clear. Spatial compounding can emphasize structures; however, features in the beam-steered images are not aligned due to varying speeds of sound. A non-rigid registration method, called warping, shifts pixels of the beam-steered images to best match the reference image. Linear prediction is used to find the warping vectors and decrease computational cost. An adaptive median-based combination technique for compounding is also investigated. The algorithms are tested on a spine phantom and human subjects. The results show a significant improvement in quality when using warping with adaptive median-based compounding.