Julian J. H. Leong

HMM assessment of quality of movement trajectory in laparoscopic surgery

Laparoscopic surgery poses many different constraints for the operating surgeon, resulting in a slow uptake of advanced laparoscopic procedures. Traditional approaches to the assessment of surgical performance rely on prior classification of a cohort of surgeons’ technical skills for validation, which may introduce subjective bias to the outcome. In this study, Hidden Markov Models (HMMs) are used to learn surgical maneuvers from 11 subjects with mixed abilities. By using the leave-one-out method, the HMMs are trained without prior clustering of subjects into different skill levels, and the output likelihood indicates the similarity of a particular subjects motion trajectories to those of the group. The results show that after a short period of training, the novices become more similar to the group when compared to the initial pre-training assessment. The study demonstrates the strength of the proposed method in ranking the quality of trajectories of the subjects, highlighting its value in minimizing the subjective bias in skills assessment for minimally invasive surgery.

Energy expenditure prediction using a miniaturized ear-worn sensor.

PURPOSE This study aimed to predict human energy expenditure and activity type using a miniature lightweight ear-worn inertia sensor and a novel pattern recognition algorithm for activity detection. METHODS This study used a protocol of 11 activities of daily living: lying down, standing, computer work, vacuuming, stairs, slow walking, brisk walking, slow running, fast running, cycling, and rowing. Subjects included 25 healthy randomized subjects (18 males and 7 females). Each participant wore the ear sensor to record posture and linear acceleration, as well as the Cosmed K4b system for indirect calorimetry. The main outcome measure was the continuous energy expenditure per minute prediction for both task-known and task-blind estimation. RESULTS The values for METs predicted using the proposed algorithm and the measured METs using the K4b showed good agreement with low values for the systematic bias (lying down=0.01, standing=-0.02, computer work=-0.04, vacuuming=-0.17, stairs=-0.02, slow walking=0.01, fast walking=0.04, slow running=0.14, fast running=-0.35, cycling=0.32, and rowing=0.10). For task-blind prediction, the agreement between predicted and measured METs is also good with low values of the systematic bias (lying down=0.11, standing=0.14, computer work=-0.06, vacuuming=0.47, stairs=-0.47, slow walking=0.53, fast walking=-0.11, slow running=0.83, fast running=-1.18, cycling=0.31, and rowing=-0.67). Activity is also well predicted (for task-blind prediction) with an overall success rate of 88.99% and individual correct classification rates of lying down=89.62%, standing/computer work=99.10%, vacuuming=76.60%, stairs=89.13%, walking=85.11%, running=98.96%, and cycling=79.79%. CONCLUSIONS The ear-worn sensor presented in this work is a novel lightweight device that can be used to predict energy expenditure for a range of activities without behavior interference or modification.

Functional prefrontal reorganization accompanies learning-associated refinements in surgery: a manifold embedding approach.

The prefrontal cortex (PFC) is known to be vital for acquisition of visuomotor skills, but its role in the attainment of complex technical skills which comprise both perceptual and motor components, such as those associated with surgery, remains poorly understood. We hypothesized that the prefrontal response to a surgical knot-tying task would be highly dependent on technical expertise, and that activation would wane in the context of learning success following extended practice. The present series of experiments investigated this issue, using functional Near Infrared Spectroscopy (fNIRS) and dexterity analysis to compare the PFC responses and technical skill of expert and novice surgeons performing a surgical knot-tying task in a block design experiment. Applying a data-embedding technique known as Isomap and Earth Movers Distance (EMD) analysis, marked differences in cortical hemodynamic responses between expert and novice surgeons have been found. To determine whether refinement in technical skill was associated with reduced PFC demands, a second experiment assessed the impact of pre- and post-training on the PFC responses in novices. Significant improvements (p < 0.01) were observed in all performance parameters following training. Smaller EMD distances were observed between expert surgeons and novices following training, suggesting an evolving pattern of cortical responses. A random effect model demonstrated a statistically significant decrease in relative changes of total hemoglobin (ΔHbT) [coefficient = −3.825, standard error (s.e.) = 0.8353, z = −4.58, p < 0.001] and oxygenated hemoglobin (ΔHbO2) [coefficient = −4.6815, s.e = 0.6781, z = −6.90, p < 0.001] and a significant increase in deoxygenated hemoglobin (ΔHHb) [coefficient = 0.8192, s.e = 0.3034, z = 2.66, p < 0.01] across training. The results indicate that learning-related refinements in technical performance are mediated by temporal reductions in prefrontal activation.

Could variations in technical skills acquisition in surgery be explained by differences in cortical plasticity

Variations in technical performance in surgery are known to exist but are poorly understood. Gaining an appreciation of these differences may have implications for technical skills training, assessment, and selection. Investigators attempting to correlate technical skill with visuospatial or perceptual tests have failed to identify surrogate markers of surgical aptitude. Evidence from unrelated fields suggests that studying brain function may advance our understanding of disparate technical performance in surgery. Methods:A literature search was conducted to identify relevant studies assessing both motor skills learning and changes in brain function. Results:The brain is dynamic and patterns of activation vary with experience and training, a property referred to as “neuroplasticity.” Functional neuroimaging studies of complex nonsurgical skills have demonstrated smaller, more refined neuronal networks in experts compared with novices. Novel unrefined performance places a significant burden on generic areas of attention and control such as the anterior cingulate cortex and the prefrontal cortex (PFC). These regions are recruited less as skills are performed with increasing automaticity. Persistent PFC activation has been shown to herald poor bimanual coordination learning in studies involving nonsurgical tasks. Concluding Hypothesis:It is suspected that alterations in brain activation foci accompany a transition through phases of surgical skills learning and that those patterns of activation may vary according to technical ability. Validating this hypothesis is challenging because it requires studying brain function in ambulant subjects performing complex motor skills. In a surgical knot-tying study involving over 60 subjects of varying expertise, PFC activation was identified in novices but not in trained surgeons. Further work should aim to determine whether PFC activation attenuates in the context of learning success in surgery.

Optical mapping of the frontal cortex during a surgical knot-tying task, a feasibility study

Functional neuroimaging technologies have transformed cognitive neuroscience by enhancing our understanding of the functional sub-classification of brain regions. Whilst a number of studies have explored brain activation associated with complex motor skills, few of the tasks investigated have had direct occupational relevance. To date there have been no functional studies involving surgeons or motor paradigms with relevance to surgery. This study reports on the feasibility of Near Infrared Spectroscopy (NIRS) for studying subjects performing realistic surgical tasks in a laboratory setting. We observed a recognisable haemodynamic response to brain activation, which was reliable and repeatable in subjects despite days without practice on the task. A wide range of prefrontal activation was observed, thought to reflect considerable variation in the cognitive resources allocated to complete a highly attention demanding surgical task.

The effect of depth perception on visual-motor compensation in minimal invasive surgery

Despite technological advances in minimally invasive surgery (MIS) in recent years, 3D visualization of the operative field still remains one of greatest challenges. In this paper, the effect of three visualization techniques including conventional 2D, 2D with enhanced depth cue based on shadow, and active 3D displays for novices with no prior adaptation to laparoscopic visualization techniques has been analyzed. A wavelet based paradigm is proposed which offer important insights into the effect of depth perception and visual-motor compensation when performing MIS instrument maneuvers. The proposed method has shown to be advantageous over conventional end-point methods of laparoscopic performance assessment as important supplementary information can be derived from the same trajectories where conventional measures fail to show significant differences.

Investigation of Partial Directed Coherence for Hand-Eye Coordination in Laparoscopic Training

Effective hand-eye coordination is an important aspect of training in laparoscopic surgery. This paper investigates the interdependency of the hand and eye movement along with the variability of their temporal relationships based on Granger-causality. Partial directed coherence is used to reveal the subtle effects of improvement in hand-eye coordination, where the causal relationship between instrument and eye movement gradually reverse during simple laparoscopic tasks. For assessing the practical value of the proposed technique for minimally invasive surgery, two laparoscopic experiments have been conducted to examine the ability of the trainees in handling mental rotation tasks, as well as dissection and manipulation skills in laparoscopic surgery. Detailed experimental results highlight the value of the technique in investigating hand-eye coordination in laparoscopic training, particularly during early motor learning for complex bimanual procedures.

Near-infrared spectroscopy: potential clinical benefits in surgery.

We read with interest the article by Stephen M. Cohn and congratulate the author on a comprehensive overview of the potential clinical roles of near-infrared spectroscopy (NIRS) within surgical practice. The article provides an extremely useful insight into the principles of NIRS technology, and its potential applications for predicting outcomes from hemorrhagic shock, detecting compartment syndrome, assessing peripheral vascular disease (on which topic a systematic review has recently been published), monitoring free flaps, and assisting in diagnosis of necrotizing fasciitis. We share the authors enthusiasm about the future role that NIRS can play in surgery. From our limited experience, we would like to draw attention to two additional surgical applications for NIRS technology, ie, advancing surgical education and as a diagnostic imaging modality. As Cohn describes, NIRS can be used to monitor oxygenation change in the cerebral cortex and has been evaluated in neonates, comatose patients, and those suffering severe brain injury. NIRS has also been used to evaluate variations in cerebral oxygenation during carotid endarterectomy and cardiac surgery. And, providing valuable information on the status of brain oxygenation in response to surgical pathology, NIRS can monitor the hemodynamic response of brain activation in healthy individuals, based on a principle known as “neurovascular coupling” (neuronal activation evokes a temporally offset hemodynamic response). This response comprises a task-induced increase in oxygenated hemoglobin coupled with a decrease in deoxygenated hemoglobin, both of which are detected using NIRS. Our primary research interest in NIRS is aimed at shedding light on cortical excitation patterns in surgical operators themselves, thereby advancing our understanding of technical-skills acquisition at the cortical level. In an analysis of 62 subjects, we observed different prefrontal cortical responses, depending on years of experience and technical skill of the operator. Ongoing work is aimed at understanding how cortical activation patterns change (“neuroplasticity”) in response to learning through deliberate practice. This analysis can assist technical-skills training by helping to track a resident’s progress through the different stages of motor-skills learning. Additionally, brain imaging, together with dexterity analysis, assessment of visual search strategies, and hand-to-eye coordination can provide a more comprehensive understanding of technical surgical skill. The potential of NIRS for monitoring tissue flap oxygenation status, such as in patients undergoing pedicled trans rectus abdominis myocutaneous flap breast reconstruction was briefly discussed by Cohn. The potential of NIRS to image the diseased tumor-bearing breast was not mentioned. NIRS breast-imaging techniques are commonly known as either optical mammography or optical tomography. These techniques use harmless NIR light to provide functional information about breast lesions, such as total hemoglobin content and oxygen saturation, and represent a novel diagnostic arm that could augment traditional imaging modalities. In a recent systematic review of the literature, we found that approximately 85% of breast lesions are detectable using optical mammography. In addition, breast lesions appear to contain at least twice the hemoglobin concentration of background healthy breast tissue. Recent evidence suggests that it might be possible to distinguish cancer from the non cancer-bearing breast, based on hemoglobin concentration and oxygen saturation, although we were unable to find strong evidence to support discrimination between benign and malignant lesions with current NIRS technology. It is likely that combining NIRS with another modality, such as magnetic resonance imaging or ultrasonography, can help to differentiate lesions based on their malignant potential. As Cohn’s comprehensive review demonstrates, there is an increasing list of potential applications for NIRS technology to augment surgical practice. As this technology continues to develop, it is likely that additional promising applications will be found. For promise to be turned into reality, future work must identify which of these applications offers the greatest benefit to patients and which are economically viable options to pursue.