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1.

Purpose

The success of total knee arthroplasty (TKA) depends on many factors. The position of a prosthesis is vitally important. The purpose of the present study was to evaluate the value of a computer-aided establishing lower extremity mechanical axis in TKA using digital technology.

Methods

A total of 36 cases of patients with TKA were randomly divided into the computer-aided design of navigation template group (NT) and conventional intramedullary positioning group (CIP). Three-dimensional (3D) CT scanning images of the hip, knee, and ankle were obtained in NT group. X-ray images and CT scans were transferred into the 3D reconstruction software. A 3D bone model of the hip, knee, ankle, as well as the modified loading, was reconstructed and saved in a stereolithographic format. In the 3D reconstruction model, the mechanical axis of the lower limb was determined, and the navigational templates produced an accurate model using a rapid prototyping technique. The THA in CIP group was performed according to a routine operation. CT scans were performed postoperatively to evaluate the accuracy of the two TKA methods.

Results

The averaged operative time of the NT group procedures was \(46.8\pm 9.1\) min shorter than those of the conventional procedures (\(57.5\pm 12.3\)  min). The coronal femoral angle, coronal tibial angle, posterior tibial slope were \(89.4^{\circ }\pm 1.5^{\circ }\), \(89.3^{\circ }\pm 1.4^{\circ }\), \(6.8^{\circ }\pm 1.6^{\circ }\) in NT group and \(87.3^{\circ }\pm 3.8^{\circ }\), \(88.1^{\circ }\pm 1.9^{\circ }\), \(10.9^{\circ }\pm 4.6^{\circ }\) in CIP group, respectively. Statistically significant group differences were found.

Conclusions

The navigation template produced through mechanical axis of lower extremity may provide a relative accurate and simple method for TKA.
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2.

Purpose

We present a fully image-based visual servoing framework for neurosurgical navigation and needle guidance. The proposed servo-control scheme allows for compensation of target anatomy movements, maintaining high navigational accuracy over time, and automatic needle guide alignment for accurate manual insertions.

Method

Our system comprises a motorized 3D ultrasound (US) transducer mounted on a robotic arm and equipped with a needle guide. It continuously registers US sweeps in real time with a pre-interventional plan based on CT or MR images and annotations. While a visual control law maintains anatomy visibility and alignment of the needle guide, a force controller is employed for acoustic coupling and tissue pressure. We validate the servoing capabilities of our method on a geometric gel phantom and real human anatomy, and the needle targeting accuracy using CT images on a lumbar spine gel phantom under neurosurgery conditions.

Results

Despite the varying resolution of the acquired 3D sweeps, we achieved direction-independent positioning errors of \(0.35\pm 0.19\) mm and \(0.61^\circ \pm 0.45^\circ \), respectively. Our method is capable of compensating movements of around 25 mm/s and works reliably on human anatomy with errors of \(1.45\pm 0.78\) mm. In all four manual insertions by an expert surgeon, a needle could be successfully inserted into the facet joint, with an estimated targeting accuracy of \(1.33\pm 0.33\) mm, superior to the gold standard.

Conclusion

The experiments demonstrated the feasibility of robotic ultrasound-based navigation and needle guidance for neurosurgical applications such as lumbar spine injections.
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3.

Purpose

During a standard fracture reduction and fixation procedure of the distal radius, only fluoroscopic images are available for planning of the screw placement and monitoring of the drill bit trajectory. Our prototype intra-operative framework integrates planning and drill guidance for a simplified and improved planning transfer.

Methods

Guidance information is extracted using a video camera mounted onto a surgical drill. Real-time feedback of the drill bit position is provided using an augmented view of the planning X-rays. We evaluate the accuracy of the placed screws on plastic bones and on healthy and fractured forearm specimens. We also investigate the difference in accuracy between guided screw placement versus freehand. Moreover, the accuracy of the real-time position feedback of the drill bit is evaluated.

Results

A total of 166 screws were placed. On 37 plastic bones, our obtained accuracy was \(1.01\,\pm \,0.56\) mm, \(3.74^\circ \,\pm \,4.39^\circ \) and \(1.70^\circ \,\pm \,1.35^\circ \) in tip position and orientation (azimuth and elevation), respectively. On the three healthy forearm specimens, our obtained accuracy was \(1.63 \pm 0.91\) mm, \(5.85^\circ \pm 4.93^\circ \) and \(3.48^\circ \pm 3.07^\circ \). On the two fractured specimens, we attained: \(1.39 \pm 0.47\) mm, \(2.93^\circ \pm 1.83^\circ \) and \(2.14^\circ \pm 1.84^\circ \). When screw plans were applied freehand (without our guidance system), the achieved accuracy was \(1.73 \pm 0.82\) mm, \(6.01^\circ \pm 4.94^\circ \,\mathrm{{and}}\, 3.52^\circ \pm 2.48^\circ \), while when they were transferred under guidance, we obtained \(0.89 \pm 0.37\) mm, \(2.85^\circ \pm 2.57^\circ \,\mathrm{{and}}\, 1.49^\circ \pm 1.17^\circ \).

Conclusions

Our results show that our framework is expected to increase the accuracy in screw positioning and to improve robustness w.r.t. freehand placement.
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4.

Purpose

To investigate the feasibility of differential geometry features in the detection of anatomical feature points on a patient surface in infrared-ray-based range images in image-guided radiation therapy.

Methods

The key technology was to reconstruct the patient surface in the range image, i.e., point distribution with three-dimensional coordinates, and characterize the geometrical shape at every point based on curvature features. The region of interest on the range image was extracted by using a template matching technique, and the range image was processed for reducing temporal and spatial noise. Next, a mathematical smooth surface of the patient was reconstructed from the range image by using a non-uniform rational B-splines model. The feature points were detected based on curvature features computed on the reconstructed surface. The framework was tested on range images acquired by a time-of-flight (TOF) camera and a Kinect sensor for two surface (texture) types of head phantoms A and B that had different anatomical geometries. The detection accuracy was evaluated by measuring the residual error, i.e., the mean of minimum Euclidean distances (MMED) between reference (ground truth) and detected feature points on convex and concave regions.

Results

The MMEDs obtained using convex feature points for range images of the translated and rotated phantom A were \(1.79 \pm 0.53\) and \(1.97\pm 0.21\,\hbox {mm}\), respectively, using the TOF camera. For the phantom B, the MMEDs of the convex and concave feature points were \(0.26\pm 0.09\) and \(0.52\pm 0.12\) mm, respectively, using the Kinect sensor. There was a statistically significant difference in the decreased MMED for convex feature points compared with concave feature points \((P<0.001)\).

Conclusions

The proposed framework has demonstrated the feasibility of differential geometry features for the detection of anatomical feature points on a patient surface in range image-guided radiation therapy.
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5.

Purpose

To describe an algorithm for the accurate segmentation of the main pulmonary artery (MPA) and determining its length, mid-cross-sectional area and mid-circumferential perimeter. This will help with accurate, rapid and reproducible MPA measurements which can be used to detect diseases that cause raised pulmonary arterial pressure, and allow standardized serial measurements to assess progression or response to treatment.

Method

We perform MPA segmentation using a novel approach based on erosion and dilation. A centerline is then determined by skeletonization, graph construction and spline fitting. MPA cross sections perpendicular to the centerline are analyzed in order to determine MPA length, and mid-cross-sectional area and perimeter. The technique was developed using four normal chest CT data sets and then tested on twenty normal post-contrast chest CT studies. Results are compared to manual segmentation and measurement by a thoracic radiologist.

Results

The mean MPA length, mid-cross-sectional area and mid-circumferential perimeter of the twenty test data sets, calculated by our algorithm, are 43.6 \(\pm \) 9.2 mm, 552.9 \(\pm \) 132.4\(\hbox { mm}^{2}\) and \(86.0 \pm 10.5\hbox { mm}\), respectively, compared with \(41.3 \pm 5.9\hbox { mm}, 574.1 \pm 124.2\hbox { mm}^{2}\) and \(99.7 \pm 12.1\hbox { mm}\) obtained manually by the radiologist. Our technique shows high correlation with the manually determined parameters for both mid- cross-sectional area (\(R = 0.96\)) and length (\(R = 0.93\)), and good correlation for mid-circumferential perimeter (\(R = 0.87\)).

Conclusion

Our algorithm is a robust accurate automated method for obtaining measurements of the MPA. This allows a more standardized method for determining length, and mid- cross-sectional area/perimeter and therefore allows more accurate comparison of MPA measurements.
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6.

Purpose

To determine a quick and accurate user input method for manipulating tablet personal computers (PCs) in sterile techniques.

Methods

We evaluated three different manipulation methods, (1) Computer mouse and sterile system drape, (2) Fingers and sterile system drape, and (3) Digitizer stylus and sterile ultrasound probe cover with a pinhole, in terms of the central processing unit (CPU) performance, manipulation performance, and contactlessness.

Results

A significant decrease in CPU score (\(p< 0.001\)) and an increase in CPU temperature (\(p< 0.001\)) were observed when a system drape was used. The respective mean times taken to select a target image from an image series (ST) and the mean times for measuring points on an image (MT) were \(5.84 \pm 2.04\) and \(5.65 \pm 1.02\) s for the computer mouse method, \(6.67 \pm 3.12\) and \(3.89 \pm 0.91\) s for the finger method, and \(4.09 \pm 1.41\) and \(3.52 \pm 0.94\) s for the digitizer stylus method, respectively. The ST for the finger method was significantly longer than for the digitizer stylus method (\(p = 0.047\)). The MT for the computer mouse method was significantly longer than for the digitizer stylus method (\(p = 0.001\)). The mean success rate for measuring points on an image was significantly lower for the finger method when the diameter of the target was equal to or smaller than 8 mm than for the other methods. No significant difference in the adenosine triphosphate amount at the surface of the tablet PC was observed before, during, or after manipulation via the digitizer stylus method while wearing starch-powdered sterile gloves (\(p = 0.89\)).

Conclusions

Quick and accurate manipulation of tablet PCs in sterile techniques without CPU load is feasible using a digitizer stylus and sterile ultrasound probe cover with a pinhole.
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7.

Purpose

Joint fractures must be accurately reduced minimising soft tissue damages to avoid negative surgical outcomes. To this regard, we have developed the RAFS surgical system, which allows the percutaneous reduction of intra-articular fractures and provides intra-operative real-time 3D image guidance to the surgeon. Earlier experiments showed the effectiveness of the RAFS system on phantoms, but also key issues which precluded its use in a clinical application. This work proposes a redesign of the RAFS’s navigation system overcoming the earlier version’s issues, aiming to move the RAFS system into a surgical environment.

Methods

The navigation system is improved through an image registration framework allowing the intra-operative registration between pre-operative CT images and intra-operative fluoroscopic images of a fractured bone using a custom-made fiducial marker. The objective of the registration is to estimate the relative pose between a bone fragment and an orthopaedic manipulation pin inserted into it intra-operatively. The actual pose of the bone fragment can be updated in real time using an optical tracker, enabling the image guidance.

Results

Experiments on phantom and cadavers demonstrated the accuracy and reliability of the registration framework, showing a reduction accuracy (sTRE) of about \(0.88~\pm 0.2\,\hbox {mm}\) (phantom) and \(1.15\pm 0.8\,\hbox {mm}\) (cadavers). Four distal femur fractures were successfully reduced in cadaveric specimens using the improved navigation system and the RAFS system following the new clinical workflow (reduction error \(1.2\pm 0.3\,\hbox {mm}\), \(2\pm 1{^{\circ }})\).

Conclusion

Experiments showed the feasibility of the image registration framework. It was successfully integrated into the navigation system, allowing the use of the RAFS system in a realistic surgical application.
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8.

Purpose

Accurate lung tumor segmentation is a prerequisite for effective radiation therapy and surgical planning. However, tumor delineation is challenging when the tumor boundaries are indistinct on PET or CT. To address this problem, we developed a segmentation method to improve the delineation of primary lung tumors from PET–CT images.

Methods

We formulated the segmentation problem as a label information propagation process in an iterative manner. Our model incorporates spatial–topological information from PET and local intensity changes from CT. The topological information of the regions was extracted based on the metabolic activity of different tissues. The spatial–topological information moderates the amount of label information that a pixel receives: The label information attenuates as the spatial distance increases and when crossing different topological regions. Thus, the spatial–topological constraint assists accurate tumor delineation and separation. The label information propagation and transition model are solved under a random walk framework.

Results

Our method achieved an average DSC of \(0.848 \pm 0.036\) and HD (mm) of \(8.652 \pm 4.532\) on 40 patients with lung cancer. The t test showed a significant improvement (p value \(<\) 0.05) in segmentation accuracy when compared to eight other methods. Our method was better able to delineate tumors that had heterogeneous FDG uptake and which abutted adjacent structures that had similar densities.

Conclusions

Our method, using a spatial–topological constraint, provided better lung tumor delineation, in particular, when the tumor involved or abutted the chest wall and the mediastinum.
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9.

Purpose

Mitral valve reconstruction is a widespread surgical method to repair incompetent mitral valves, which usually includes implantation of a ring prosthesis. To date, intraoperative analysis of the mitral valve is merely based on visual assessment using simple surgical tools, which might not allow for accurate assessment of the complex anatomy.

Methods

We propose a novel intraoperative computer-based assistance system, which combines passive optical tracking technology with tailored measurement strategies applicable during different phases of the intraoperative workflow. Based on the assessment of the valvular apparatus by customized tracked instruments, the system (1) generates an enhanced three-dimensional visualization, which (2) incorporates accurate quantifications and (3) provides assistance, e.g., in terms of virtual prosthesis selection.

Results

Phantom experiments in a realistic environment revealed a high system accuracy (mean precision \(0.12 \pm 0.09\) mm and mean trueness \(0.77 \pm 0.39\) mm) and a low user error (mean precision \(0.18 \pm 0.10 \) mm and mean trueness \(0.81 \pm 0.36\) mm). The assistance system was successfully applied five times during open and minimally invasive reconstructive surgery in patients having mitral valve insufficiency. The measurement steps integrate well into the traditional workflow, enhancing the surgeon’s three-dimensional perception and generating a suggestion for an appropriate prosthesis.

Conclusion

The proposed assistance system provides a novel, accurate, and reproducible method for assessing the valvular geometry intraoperatively.
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10.

Purpose

Accurate preoperative planning is crucial for the outcome of total hip arthroplasty. Recently, 2D pelvic X-ray radiographs have been replaced by 3D CT. However, CT suffers from relatively high radiation dosage and cost. An alternative is to reconstruct a 3D patient-specific volume data from 2D X-ray images.

Methods

In this paper, based on a fully automatic image segmentation algorithm, we propose a new control point-based 2D–3D registration approach for a deformable registration of a 3D volumetric template to a limited number of 2D calibrated X-ray images and show its application to personalized reconstruction of 3D volumes of the proximal femur. The 2D–3D registration is done with a hierarchical two-stage strategy: the scaled-rigid 2D–3D registration stage followed by a regularized deformable B-spline 2D–3D registration stage. In both stages, a set of control points with uniform spacing are placed over the domain of the 3D volumetric template first. The registration is then driven by computing updated positions of these control points with intensity-based 2D–2D image registrations of the input X-ray images with the associated digitally reconstructed radiographs, which allows computing the associated registration transformation at each stage.

Results

Evaluated on datasets of 44 patients, our method achieved an overall surface reconstruction accuracy of \(0.9 \pm 0.2\,\hbox {mm}\) and an average Dice coefficient of \(94.4 \pm 1.1\,\%\). We further investigated the cortical bone region reconstruction accuracy, which is important for planning cementless total hip arthroplasty. An average cortical bone region Dice coefficient of \(85.1 \pm 2.9\,\%\) and an inner cortical bone surface reconstruction accuracy of \(0.7 \pm 0.2\,\hbox {mm}\) were found.

Conclusions

In summary, we developed a new approach for reconstruction of 3D personalized volumes of the proximal femur from 2D X-ray images. Comprehensive experiments demonstrated the efficacy of the present approach.
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11.

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.
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12.

Purpose

Objective determination of the orbital volume is important in the diagnostic process and in evaluating the efficacy of medical and/or surgical treatment of orbital diseases. Tools designed to measure orbital volume with computed tomography (CT) often cannot be used with cone beam CT (CBCT) because of inferior tissue representation, although CBCT has the benefit of greater availability and lower patient radiation exposure. Therefore, a model-based segmentation technique is presented as a new method for measuring orbital volume and compared to alternative techniques.

Methods

Both eyes from thirty subjects with no known orbital pathology who had undergone CBCT as a part of routine care were evaluated (\(n = 60\) eyes). Orbital volume was measured with manual, atlas-based, and model-based segmentation methods. Volume measurements, volume determination time, and usability were compared between the three methods. Differences in means were tested for statistical significance using two-tailed Student’s t tests.

Results

Neither atlas-based \((26.63 \pm 3.15\,\hbox {mm}^{3})\) nor model-based \((26.87 \pm 2.99\,\hbox {mm}^{3})\) measurements were significantly different from manual volume measurements \((26.65 \pm 4.0\,\hbox {mm}^{3})\). However, the time required to determine orbital volume was significantly longer for manual measurements (\(10.24 \pm 1.21\) min) than for atlas-based (\(6.96 \pm 2.62\) min, \(p < 0.001\)) or model-based (\(5.73 \pm 1.12\) min, \(p < 0.001\)) measurements.

Conclusion

All three orbital volume measurement methods examined can accurately measure orbital volume, although atlas-based and model-based methods seem to be more user-friendly and less time-consuming. The new model-based technique achieves fully automated segmentation results, whereas all atlas-based segmentations at least required manipulations to the anterior closing. Additionally, model-based segmentation can provide reliable orbital volume measurements when CT image quality is poor.
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13.

Purpose

X-ray imaging is widely used for guiding minimally invasive surgeries. Despite ongoing efforts in particular toward advanced visualization incorporating mixed reality concepts, correct depth perception from X-ray imaging is still hampered due to its projective nature.

Methods

In this paper, we introduce a new concept for predicting depth information from single-view X-ray images. Patient-specific training data for depth and corresponding X-ray attenuation information are constructed using readily available preoperative 3D image information. The corresponding depth model is learned employing a novel label-consistent dictionary learning method incorporating atlas and spatial prior constraints to allow for efficient reconstruction performance.

Results

We have validated our algorithm on patient data acquired for different anatomy focus (abdomen and thorax). Of 100 image pairs per each of 6 experimental instances, 80 images have been used for training and 20 for testing. Depth estimation results have been compared to ground truth depth values.

Conclusion

We have achieved around \(4.40\,\%\,\pm \,2.04\) and \(11.47\,\%\,\pm \,2.27\) mean squared error on abdomen and thorax datasets, respectively, and visual results of our proposed method are very promising. We have therefore presented a new concept for enhancing depth perception for image-guided interventions.
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14.

Purpose

Reduction is a crucial step in the surgical treatment of bone fractures. Finding an optimal path for restoring anatomical alignment is considered technically demanding because collisions as well as high forces caused by surrounding soft tissues can avoid desired reduction movements. The repetition of reduction movements leads to a trial-and-error process which causes a prolonged duration of surgery. By planning an appropriate reduction path—an optimal sequence of target-directed movements—these problems should be overcome. For this purpose, a computer-based method has been developed.

Methods

Using the example of simple femoral shaft fractures, 3D models are generated out of CT images. A reposition algorithm aligns both fragments by reconstructing their broken edges. According to the criteria of a deduced planning strategy, a modified A*-algorithm searches collision-free route of minimal force from the dislocated into the computed target position. Muscular forces are considered using a musculoskeletal reduction model (OpenSim model), and bone collisions are detected by an appropriate method.

Results

Five femoral SYNBONE models were broken into different fracture classification types and were automatically reduced from ten randomly selected displaced positions. Highest mean translational and rotational error for achieving target alignment is \(1.2 \pm 0.9\,\hbox {mm}\) and \(2.6^{\circ } \pm 2.8^{\circ }\). Mean value and standard deviation of occurring forces are \(15.83 \pm 5.05\,\hbox {N}\) for M. tensor fasciae latae and \(3.53 \pm 1.8\,\hbox {N}\) for M. semitendinosus over all trials. These pathways are precise, collision-free, required forces are minimized, and thus regarded as optimal paths.

Conclusions

A novel method for planning reduction paths under consideration of collisions and muscular forces is introduced. The results deliver additional knowledge for an appropriate tactical reduction procedure and can provide a basis for further navigated or robotic-assisted developments.
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15.

Purpose

The purpose of the present study is to apply kinetic analysis to investigate exercise-related changes in the metabolism of the skeletal muscle of the rat hindlimb by [\({}^{11}\hbox {C}\)]acetate positron emission tomography and computed tomography (PET/CT).

Methods

Contractions were induced in Wistar rats’ left hindlimb by electrostimulation of the Vastus Lateralis muscle motor point. After 15 min of muscle contractions, [\({}^{11}\hbox {C}\)]acetate was injected and PET/CT of both hindlimbs was acquired. The resting hindlimb was used as a control reference. The kinetic parameters \(K_1\) and \(k_2\) were calculated for the target muscles (exercised and control) and correlated with the corresponding standardized uptake values (SUVs). The ratio between each kinetic parameter values and the SUV extracted for the exercised muscle and the muscle at rest was computed (\(K_1^{Ex}/K_1^{Re},\, k_2^{Ex}/k_2^{Re}\) and \(\hbox {SUV}^{Ex}/\hbox {SUV}^{Re}\), respectively).

Results

Kinetic analysis quantitatively confirmed that net tracer uptake (\(K_1\)) and washout (\(k_2\)) were significantly higher in exercised muscles (\(K_1: \,0.34 \pm 0.12 \hbox { min}^{-1}\) for exercised muscles vs. \(0.18 \pm 0.09\hbox { min}^{-1}\) for resting muscles, \(P=0.01\); \(k_2:\, 0.22 \pm 0.05\hbox { min}^{-1}\) for exercised muscle vs. \(0.14 \pm 0.04 \hbox { min}^{-1}\) for resting muscle, \(P=0.002\)). On the other hand, SUV was not significantly different between active and inactive muscles (\(0.7 \pm 0.2\) for exercised muscles vs. \(0.6 \pm 0.1\) for resting muscles). Linear regression analysis revealed a good correlation (\(R^2=0.75,\, P=0.005\)) between net tracer uptake ratio (\(K_1^{Ex}/K_1^{Re}\)) and the SUV ratio \((\hbox {SUV}^{Ex}/\hbox {SUV}^{Re}\)). A lower correlation was found between the net tracer washout ratio (\(k_2^{Ex}/k_2^{Re}\)) and the SUV ratio (\(R^2=0.37,\, P=0.1\)).

Conclusion

The present study showed that kinetic modelling can detect changes between active and inactive skeletal muscles with a higher sensitivity with respect to the SUV, when performed with [\({}^{11}\hbox {C}\)]acetate PET/CT.
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16.

Objective

To develop a hybrid augmented marker-based navigation system for acetabular reorientation during peri-acetabular osteotomy (PAO).

Methods

The system consists of a tracking unit attached to the patient’s pelvis, augmented marker attached to the acetabular fragment and a host computer to do all the computations and visualization. The augmented marker is comprised of an external planar Aruco marker facing toward the tracking unit and an internal inertial measurement unit (IMU) to measure its orientation. The orientation output from the IMU is sent to the host computer. The tracking unit streams a live video of the augmented marker to the host computer, where the planar marker is detected and its pose is estimated. A Kalman filter-based sensor fusion combines the output from marker tracking and the IMU. We validated the proposed system using a plastic bone study and a cadaver study. Every time, we compared the inclination and anteversion values measured by the proposed system to those from a previously developed optical tracking-based navigation system.

Results

Mean absolute differences for inclination and anteversion were 1.34 (\(\pm \,1.50\)) and 1.21 (\(\pm \, 1.07\))\(^\circ \), respectively, for the cadaver study. Mean absolute differences were 1.63 (\(\pm \,1.48\)) and 1.55 (\(\pm \,1.49\))\(^\circ \) for inclination and anteversion for the plastic bone study. In both validation studies, very strong correlations were observed.

Conclusion

We successfully demonstrated the feasibility of our system to measure the acetabular orientation during PAO.
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17.

Purpose

To develop a novel automated method for segmentation of the injured spleen using morphological properties following abdominal trauma. Average attenuation of a normal spleen in computed tomography (CT) does not vary significantly between subjects. However, in the case of solid organ injury, the shape and attenuation of the spleen on CT may vary depending on the time and severity of the injury. Timely assessment of the severity and extent of the injury is of vital importance in the setting of trauma.

Methods

We developed an automated computer-aided method for segmenting the injured spleen from CT scans of patients who had splenectomy due to abdominal trauma. We used ten subjects to train our computer-aided diagnosis (CAD) method. To validate the CAD method, we used twenty subjects in our testing group. Probabilistic atlases of the spleens were created using manually segmented data from ten CT scans. The organ location was modeled based on the position of the spleen with respect to the left side of the spine followed by the extraction of shape features. We performed the spleen segmentation in three steps. First, we created a mask of the spleen, and then we used this mask to segment the spleen. The third and final step was the estimation of the spleen edges in the presence of an injury such as laceration or hematoma.

Results

The traumatized spleens were segmented with a high degree of agreement with the radiologist-drawn contours. The spleen quantification led to \(86\pm 5\,\%\) volume overlap, \(92.5\pm 3.11\,\%\) Dice similarity index, \(89.05\pm 5.29\,\%/96.42\pm 2.55\) precision/sensitivity, \(8\pm 5\,\%\) volume estimation error rate, \(1.09\pm 0.62/1.91\pm 1.45\,\hbox {mm}\) average surface distance/root-mean-squared error.

Conclusions

Our CAD method robustly segments the spleen in the presence of morphological changes such as laceration, contusion, pseudoaneurysm, active bleeding, periorgan and parenchymal hematoma, including subcapsular hematoma due to abdominal trauma. CAD of the splenic injury due to abdominal trauma can assist in rapid diagnosis and assessment and guide clinical management. Our segmentation method is a general framework that can be adapted to segment other injured solid abdominal organs.
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18.

Purpose

Percutaneous screw fixation is an effective technique in addressing minimally displaced anterior column acetabular fractures. The aim of this study is to evaluate the ease of percutaneous screw insertion for acetabular anterior column fracture, as it pertains to anterograde versus retrograde insertion techniques.

Method

From 2009 to 2013, CT imaging from 30 adult volunteers (15 males, 15 females) without history of pelvic disruption and/or morphologic abnormalities were evaluated. From these images, virtual 3D pelvic models were generated. The differences area of screw starting points, limitation position of anterior column screws, and range of screw directions were analyzed.

Conclusion

We found in our analysis that anterograde and retrograde had not only variations in their starting points, but differences in areas of insertion. Typically, anterograde portals have a larger area for insertion. Additionally, given the limitations we noted in screw position and the severity of the acetabular fractures, this will allow the treating surgeon to determine the most optimal technique for percutaneous anterior column screw fixation.

Results

In our analysis, we found two areas for effective percutaneous anterograde insertion and one area for effective retrograde insertion. They both possess geometries with different shapes. Additionally, the area of anterograde insertion is larger than the retrograde area of insertion. The limitations in screw positions were shown in the AP, inlet, outlet, iliac oblique, obturator oblique, and lateral views. The direction range between superior and inferior and between medial and lateral were measured and recorded. In area of anterograde, the angle between the superior and inferior limits was \(29.2^{\circ }\pm 2.7^{\circ }\), while the angle limit between medial and lateral was \(18.5^{\circ }\pm 1.8^{\circ }\). In area of retrograde, the angle between the superior and inferior limits was \(8.32^{\circ }\pm 1.3^{\circ }\), while the angle limit between medial and lateral was \(7.5^{\circ }\pm 0.8^{\circ }\)
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19.

Purpose

A fully automatic multiatlas-based method for segmentation of the spine and pelvis in a torso CT volume is proposed. A novel landmark-guided diffeomorphic demons algorithm is used to register a given CT image to multiple atlas volumes. This algorithm can utilize both grayscale image information and given landmark coordinate information optimally.

Methods

The segmentation has four steps. Firstly, 170 bony landmarks are detected in the given volume. Using these landmark positions, an atlas selection procedure is performed to reduce the computational cost of the following registration. Then the chosen atlas volumes are registered to the given CT image. Finally, voxelwise label voting is performed to determine the final segmentation result.

Results

The proposed method was evaluated using 50 torso CT datasets as well as the public SpineWeb dataset. As a result, a mean distance error of \(0.59\pm 0.14\hbox { mm}\) and a mean Dice coefficient of \(0.90\pm 0.02\) were achieved for the whole spine and the pelvic bones, which are competitive with other state-of-the-art methods.

Conclusion

From the experimental results, the usefulness of the proposed segmentation method was validated.
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20.

Purpose

Metallic foreign bodies (MFBs) retained in soft tissue may pose potential threats to patient health. Interventional procedures using conventional navigation systems are associated with high rate of radiation exposure. We postulated that the surgical approach visualization and navigation system would offer precise percutaneous localization and linear guidance with reduced radiation dosage and system complexity.

Methods

In total, 76 patients underwent percutaneous MFB extraction with the technique, which consists of: (A) displaying the target spot (here the MFB) on the screen; (B) projecting the laser beam onto the skin surface; (C) indicating the optimal direction and angle of the needle; and (D) guiding the surgical approach until the MFB was extracted.

Results

A total of 76 MFBs were successfully extracted with a single operation. No systemic complications were observed. The procedure took between 2 and 11 min, with an average of \(5.55\pm 2.21\) min, demonstrating the characteristics of a normal distribution. The mean size of wound was \(12.01\pm 4.16\) mm. The mean amount of bleeding was \(6.12\pm 3.56\) ml. The number of times the intra-operative fluoroscopy was used ranged from one to four times for a single procedure, with an average of 1.89 ± 0.74.

Conclusion

The proposed navigation system which combines the laser positioning and navigation techniques seems to be a novel surgical approach of high accuracy and efficiency.
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