Fiducial-based fusion of 3D dental models with magnetic resonance imaging

Purpose

Magnetic resonance imaging (MRI) is widely used in study of maxillofacial structures. While MRI is the modality of choice for soft tissues, it fails to capture hard tissues such as bone and teeth. Virtual dental models, acquired by optical 3D scanners, are becoming more accessible for dental practice and are starting to replace the conventional dental impressions. The goal of this research is to fuse the high-resolution 3D dental models with MRI to enhance the value of imaging for applications where detailed analysis of maxillofacial structures are needed such as patient examination, surgical planning, and modeling.

Methods

A subject-specific dental attachment was digitally designed and 3D printed based on the subject’s face width and dental anatomy. The attachment contained 19 semi-ellipsoidal concavities in predetermined positions where oil-based ellipsoidal fiducial markers were later placed. The MRI was acquired while the subject bit on the dental attachment. The spatial position of the center of mass of each fiducial in the resultant MR Image was calculated by averaging its voxels’ spatial coordinates. The rigid transformation to fuse dental models to MRI was calculated based on the least squares mapping of corresponding fiducials and solved via singular-value decomposition.

Results

The target registration error (TRE) of the proposed fusion process, calculated in a leave-one-fiducial-out fashion, was estimated at 0.49 mm. The results suggest that 6–9 fiducials suffice to achieve a TRE of equal to half the MRI voxel size.

Conclusion

Ellipsoidal oil-based fiducials produce distinguishable intensities in MRI and can be used as registration fiducials. The achieved accuracy of the proposed approach is sufficient to leverage the merged 3D dental models with the MRI data for a finer analysis of the maxillofacial structures where complete geometry models are needed.

     

Sequential surgical signatures in micro-suturing task

Purpose

Surgical processes are generally only studied by identifying differences in populations such as participants or level of expertise. But the similarity between this population is also important in understanding the process. We therefore proposed to study these two aspects.

Methods

In this article, we show how similarities in process workflow within a population can be identified as sequential surgical signatures. To this purpose, we have proposed a pattern mining approach to identify these signatures.

Validation

We validated our method with a data set composed of seventeen micro-surgical suturing tasks performed by four participants with two levels of expertise.

Results

We identified sequential surgical signatures specific to each participant, shared between participants with and without the same level of expertise. These signatures are also able to perfectly define the level of expertise of the participant who performed a new micro-surgical suturing task. However, it is more complicated to determine who the participant is, and the method correctly determines this information in only 64% of cases.

Conclusion

We show for the first time the concept of sequential surgical signature. This new concept has the potential to further help to understand surgical procedures and provide useful knowledge to define future CAS systems.

     

Psychometric properties of the Zephyr bioharness device: a systematic review

Background

Technological development and improvements in Wearable Physiological Monitoring devices, have facilitated the wireless and continuous field-based monitoring/capturing of physiologic measures in healthy, clinical or athletic populations. These devices have many applications for prevention and rehabilitation of musculoskeletal disorders, assuming reliable and valid data is collected. The purpose of this study was to appraise the quality and synthesize findings from published studies on psychometric properties of heart rate measurements taken with the Zephyr Bioharness device.

Methods

We searched the Embase, Medline, PsycInfo, PuMed and Google Scholar databases to identify articles. Articles were appraised for quality using a structured clinical measurement specific appraisal tool. Two raters evaluated the quality and conducted data extraction. We extracted data on the reliability (intra-class correlation coefficients and standard error of measurement) and validity measures (Pearson/Spearman’s correlation coefficients) along with mean differences. Agreement parameters were summarised by the average biases and 95% limits of agreement.

Results

A total of ten studies were included: quality ratings ranged from 54 to 92%. The intra-class correlation coefficients reported ranged from 0.85–0.98. The construct validity coefficients compared against gold standard calibrations or other commercially used devices, ranged from 0.74–0.99 and 0.67–0.98 respectively. Zephyr Bioharness agreement error ranged from ??4.81 (under-estimation) to 3.00 (over-estimation) beats per minute, with varying 95% limits of agreement, when compared with gold standard measures.

Conclusion

Good to excellent quality evidence from ten studies suggested that the Zephyr Bioharness device can provide reliable and valid measurements of heart rate across multiple contexts, and that it displayed good agreements vs. gold standard comparators – supporting criterion validity.

     

Improving pediatric emergency department physicians’ adherence to clinical practice guidelines on the diagnosis and management of group A beta-hemolytic streptococcal pharyngitis—a cross-sectional study

Introduction

Pharyngitis is one of the major and commonly seen presentations in pediatric emergency departments. While it could be caused by both bacterial and viral pathogens, antibiotics are improperly prescribed regardless of the pathogen. Inappropriate usage of antibiotics has risen the concern of microbial resistance and the need for stricter guidelines. Many guidelines have been validated for this reason, and the Centor score (Modified/McIsaac) is most commonly implemented. This study aims to assess the adherence and enumerate the reasons behind the suboptimal adherence to guidelines (Centor/McIsaac score) of pediatric emergency department physicians in the diagnosis and management of GABHS pharyngitis to lay the groundwork for future actions and to employ educational programs and implement local guidelines for the prevention of the development of multi-drug resistant microorganisms.

Methodology

We surveyed pediatric emergency department physicians of ten teaching hospitals of Riyadh, Saudi Arabia. We used convenient sampling and estimated a sample size of 170 physicians, and interns and medical centers without pediatric emergency department were excluded from the study. Elements of the Centor score (Modified/McIsaac) were used as a part of the assessment of physicians’ knowledge of the guidelines. Adherence was assessed by requiring the participants to answer questions regarding their usage of diagnostic means when they suspect a bacterial cause of pharyngitis, as recommended by the guidelines.

Results

A total of 243 physicians answered the questionnaire, 43 consultants (17.6%) and 200 non-consultants (82.4%). On the knowledge score, 9.1% scored 0, and the majority of both groups, 46.5%, earned a score of 1. The remainder 44.4%, earned a score of 2. Adherence to guidelines was defined as when diagnostic tests (throat culture or rapid antigen detection test) were always requested prior to prescribing antibiotics when acute bacterial pharyngitis was suspected. Only 27.3% (n?=?67) of our sample are adherent to guidelines, whereas the majority, 72.7% (n?=?175), are non-adherent. Several factors were assessed as reasons for lack of adherence.

Conclusion

Lack of knowledge and adherence to guidelines is prevalent in our setting, with awareness, knowledge, and behavior of physicians playing as major factors behind this low adherence. Studies should aim towards the assessment of adherence towards locally developed guidelines.

     

Using needle orientation sensing as surrogate signal for respiratory motion estimation in percutaneous interventions

Purpose

To develop and evaluate an approach to estimate the respiratory-induced motion of lesions in the chest and abdomen.

Materials and methods

The proposed approach uses the motion of an initial reference needle inserted into a moving organ to estimate the lesion (target) displacement that is caused by respiration. The needles position is measured using an inertial measurement unit (IMU) sensor externally attached to the hub of an initially placed reference needle. Data obtained from the IMU sensor and the target motion are used to train a learning-based approach to estimate the position of the moving target. An experimental platform was designed to mimic respiratory motion of the liver. Liver motion profiles of human subjects provided inputs to the experimental platform. Variables including the insertion angle, target depth, target motion velocity and target proximity to the reference needle were evaluated by measuring the error of the estimated target position and processing time.

Results

The mean error of estimation of the target position ranged between 0.86 and 1.29 mm. The processing maximum training and testing time was 5 ms which is suitable for real-time target motion estimation using the needle position sensor.

Conclusion

The external motion of an initially placed reference needle inserted into a moving organ can be used as a surrogate, measurable and accessible signal to estimate in real-time the position of a moving target caused by respiration; this technique could then be used to guide the placement of subsequently inserted needles directly into the target.

     

Simulation of facial expressions using person-specific sEMG signals controlling a biomechanical face model

Purpose

Functional inoperability in advanced oral cancer is difficult to assess preoperatively. To assess functions of lips and tongue, biomechanical models are required. Apart from adjusting generic models to individual anatomy, muscle activation patterns (MAPs) driving patient-specific functional movements are necessary to predict remaining functional outcome. We aim to evaluate how volunteer-specific MAPs derived from surface electromyographic (sEMG) signals control a biomechanical face model.

Methods

Muscle activity of seven facial muscles in six volunteers was measured bilaterally with sEMG. A triple camera set-up recorded 3D lip movement. The generic face model in ArtiSynth was adapted to our needs. We controlled the model using the volunteer-specific MAPs. Three activation strategies were tested: activating all muscles \((\hbox {act}_\mathrm{all})\), selecting the three muscles showing highest muscle activity bilaterally \((\hbox {act}_3)\)—this was calculated by taking the mean of left and right muscles and then selecting the three with highest variance—and activating the muscles considered most relevant per instruction \((\hbox {act}_\mathrm{rel})\), bilaterally. The model’s lip movement was compared to the actual lip movement performed by the volunteers, using 3D correlation coefficients \((\rho )\).

Results

The correlation coefficient between simulations and measurements with \(\hbox {act}_\mathrm{rel}\) resulted in a median \(\rho \) of 0.77. \(\hbox {act}_3\) had a median \(\rho \) of 0.78, whereas with \(\hbox {act}_\mathrm{all}\) the median \(\rho \) decreased to 0.45.

Conclusion

We demonstrated that MAPs derived from noninvasive sEMG measurements can control movement of the lips in a generic finite element face model with a median \(\rho \) of 0.78. Ultimately, this is important to show the patient-specific residual movement using the patient’s own MAPs. When the required treatment tools and personalisation techniques for geometry and anatomy become available, this may enable surgeons to test the functional results of wedge excisions for lip cancer in a virtual environment and to weigh surgery versus organ-sparing radiotherapy or photodynamic therapy.

     

Development of a vibration haptic simulator for shoulder arthroplasty

Purpose

Glenoid reaming is a technically challenging step during shoulder arthroplasty that could possibly be learned during simulation training. Creation of a realistic simulation using vibration feedback in this context is innovative. Our study focused on the development and internal validation of a novel glenoid reaming simulator for potential use as a training tool.

Methods

Vibration and force profiles associated with glenoid reaming were quantified during a cadaveric experiment. Subsequently, a simulator was fabricated utilizing a haptic vibration transducer with high- and low-fidelity amplifiers; system calibration was performed matching vibration peak–peak values for both amplifiers. Eight experts performed simulated reaming trials. The experts were asked to identify isolated layer profiles produced by the simulator. Additionally, experts’ efficiency to successfully perform a simulated glenoid ream based solely on vibration feedback was recorded.

Results

Cadaveric experimental cartilage reaming produced lower vibrations compared to subchondral and cancellous bones (\(p\le 0.03\)). Gain calibration of a lower-fidelity (3.5 \({g}_{\mathrm{pk-pk}}, 0.36\,{g}_{\mathrm{rms}})\) and higher-fidelity (3.4 \({g}_{\mathrm{pk-pk}}, 0.33\,{g}_{\mathrm{rms}})\) amplifier resulted in values similar to the cadaveric experimental benchmark (3.5 \({g}_{\mathrm{pk-pk}}, 0.30\,{g}_{\mathrm{rms}})\). When identifying random tissue layer samples, experts were correct \(52\pm 9\%\) of the time and success rate varied with tissue type (\(p=0.003\)). During simulated reaming, the experts stopped at the targeted subchondral bone with a success rate of \(78\pm 24\%\). The fidelity of the simulation did not have an effect on accuracy, applied force, or reaming time (\(p>0.05\)). However, the applied force tended to increase with trial number (\(p=0.047\)).

Conclusions

Development of the glenoid reaming simulator, coupled with expert evaluation furthered our understanding of the role of haptic vibration feedback during glenoid reaming. This study was the first to (1) propose, develop and examine simulated glenoid reaming, and (2) explore the use of haptic vibration feedback in the realm of shoulder arthroplasty.

     

Meaningful Assessment of Robotic Surgical Style using the Wisdom of Crowds

Objective

Quantitative assessment of surgical skills is an important aspect of surgical training; however, the proposed metrics are sometimes difficult to interpret and may not capture the stylistic characteristics that define expertise. This study proposes a methodology for evaluating the surgical skill, based on metrics associated with stylistic adjectives, and evaluates the ability of this method to differentiate expertise levels.

Methods

We recruited subjects from different expertise levels to perform training tasks on a surgical simulator. A lexicon of contrasting adjective pairs, based on important skills for robotic surgery, inspired by the global evaluative assessment of robotic skills tool, was developed. To validate the use of stylistic adjectives for surgical skill assessment, posture videos of the subjects performing the task, as well as videos of the task were rated by crowd-workers. Metrics associated with each adjective were found using kinematic and physiological measurements through correlation with the crowd-sourced adjective assignment ratings. To evaluate the chosen metrics’ ability in distinguishing expertise levels, two classifiers were trained and tested using these metrics.

Results

Crowd-assignment ratings for all adjectives were significantly correlated with expertise levels. The results indicate that naive Bayes classifier performs the best, with an accuracy of \(89\pm 12\), \(94\pm 8\), \(95\pm 7\), and \(100\pm 0\%\) when classifying into four, three, and two levels of expertise, respectively.

Conclusion

The proposed method is effective at mapping understandable adjectives of expertise to the stylistic movements and physiological response of trainees.

     

Ultrasound thermal monitoring with an external ultrasound source for customized bipolar RF ablation shapes

Purpose

Thermotherapy is a clinical procedure which delivers thermal energy to a target, and it has been applied for various medical treatments. Temperature monitoring during thermotherapy is important to achieve precise and reproducible results. Medical ultrasound can be used for thermal monitoring and is an attractive medical imaging modality due to its advantages including non-ionizing radiation, cost-effectiveness and portability. We propose an ultrasound thermal monitoring method using a speed-of-sound tomographic approach coupled with a biophysical heat diffusion model.

Methods

We implement an ultrasound thermometry approach using an external ultrasound source. We reconstruct the speed-of-sound images using time-of-flight information from the external ultrasound source and convert the speed-of-sound information into temperature by using the a priori knowledge brought by a biophysical heat diffusion model.

Results

Customized treatment shapes can be created using switching channels of radio frequency bipolar needle electrodes. Simulations of various ablation lesion shapes in the temperature range of 21–59 \(^\circ \)C are performed to study the feasibility of the proposed method. We also evaluated our method with ex vivo porcine liver experiments, in which we generated temperature images between 22 and 45 \(^\circ \)C.

Conclusion

In this paper, we present a proof of concept showing the feasibility of our ultrasound thermal monitoring method. The proposed method could be applied to various thermotherapy procedures by only adding an ultrasound source.