Mesh-based method for measuring intracranial volume in patients with craniosynostosis

Purpose

   Craniosynostosis may lead to reduced intracranial volume (ICV) and disturb normal brain growth and development. Thus, ICV is an important parameter with respect to the surgical outcome. Current methods for ICV determination from computed tomography (CT) images have drawbacks. The aim of this study was to investigate the performance of the novel mesh-based method (MBM) for ICV determination with craniosynostosis patients.

Methods

   Twenty-two patients operated on for scaphocephaly were included in this study. ICVs from preoperative, one-week postoperative, and one-year postoperative CT images were measured with MBM. The level of agreement with the manual segmentation method (MSM) was determined for the measurements of preoperative and one-year postoperative datasets. Repeatability was determined with re-measurements of six datasets. Measurement time was recorded for MBM.

Results

   Mean $(\pm \text{ SD})$ preoperative ICV values were 895.0 $\pm $ 153.1 $\text{ cm}^{3}$ and 896.4 $\pm $ 147.2 $\text{ cm}^{3}$ as measured with MBM and MSM, respectively. Corresponding one-year postoperative values were 1,238.3 $\pm $ 118.7 $\text{ cm}^{3}$ and 1,250.1 $\pm $ 117.5 $\text{ cm}^{3}$ . The MBM allowed ICV determination from one-week postoperative datasets. Measurement time with MBM was 4

Conclusions

   MBM is an efficient method for determining the ICV of craniosynostosis patients, allowing the measurement of skulls with bony defects. The repeatability and short measurement time of MBM are attributable to the user interference and assessment of the measurement process.     

A two-stage rule-constrained seedless region growing approach for mandibular body segmentation in MRI

Purpose Extraction of the mandible from 3D volumetric images is frequently required for surgical planning and evaluation. Image segmentation from MRI is more complex than CT due to lower bony signal-to-noise. An automated method to extract the human mandible body shape from magnetic resonance (MR) images of the head was developed and tested. Methods Anonymous MR images data sets of the head from 12 subjects were subjected to a two-stage rule-constrained region growing approach to derive the shape of the body of the human mandible. An initial thresholding technique was applied followed by a 3D seedless region growing algorithm to detect a large portion of the trabecular bone (TB) regions of the mandible. This stage is followed with a rule-constrained 2D segmentation of each MR axial slice to merge the remaining portions of the TB regions with lower intensity levels. The two-stage approach was replicated to detect the cortical bone (CB) regions of the mandibular body. The TB and CB regions detected from the preceding steps were merged and subjected to a series of morphological processes for completion of the mandibular body region definition. Comparisons of the accuracy of segmentation between the two-stage approach, conventional region growing method, 3D level set method, and manual segmentation were made with Jaccard index, Dice index, and mean surface distance (MSD). Results The mean accuracy of the proposed method is $0.958 \,\pm \, 0.020$ for Jaccard index, $0.979 \,\pm \, 0.011$ for Dice index, and $0.204 \,\pm \, 0.127$  mm for MSD. The mean accuracy of CRG is $0.782 \,\pm \, 0.080$ for Jaccard index, $0.876 \,\pm \, 0.053$ for Dice index, and $0.417 \,\pm \, 0.073$  mm for MSD. The mean accuracy of the 3D level set method is $0.874 \,\pm \, 0.0.051$ for Jaccard index, $0.645 \pm 0.306$ for Dice index, and $0.645 \pm 0.306$  mm for MSD. The proposed method shows improvement in accuracy over CRG and 3D level set. Conclusion Accurate segmentation of the body of the human mandible from MR images is achieved with the proposed two-stage rule-constrained seedless region growing approach. The accuracy achieved with the two-stage approach is higher than CRG and 3D level set.     

E-Health and telemedicine

Purpose

To compare the accuracy of a navigation system for oral implantology using either a head-mounted display (HMD) or a monitor as a device for visualization.

Methods

Drilling experiments in plastic mandibles were performed by seven investigators supported by a navigation system using an HMD. A set of drilling experiments was carried out using a traditional monitor setup as standard of reference. Prior to the experiments, CT scans of the mandibles were performed. Positions of the boreholes were determined with the planning software Mimics $^{\circledR }$ . In order to find the correct positions of the boreholes, individuals had to match two pairs of crosshairs. By an infrared tracking device, the navigation system was able to spot the artificial jaw and the angular piece of the drill allowing for the navigation. After the experiments, a second CT scan was acquired: (i) to identify the beginning and the end of the boreholes, (ii) to compare the positions of the planned implant and the boreholes and (iii) to calculate the deviations.

Results

Overall deviation of the starting point of the borehole was $1.24 \pm 0.84\,\mathrm{mm}$ for the HMD and $1.12 \pm 0.68\,\mathrm{mm}$ for the monitor, $2.68 \pm 1.65\,\mathrm{mm}$ of the end point of the borehole for the HMD and $2.46 \pm 1.34\,\mathrm{mm}$ for the monitor. The mean deviation of the axis was $4.68^{\circ }\pm 3.7^{\circ }$ for the HMD and $4.53^{\circ }\pm 4.17^{\circ }$ for the monitor.

Conclusions

As overall accuracies do not differ significantly, the two methods seem to be equal. Personal skills seem to be crucial as the results show remarkable differences among the test persons. The results of our study demonstrate that the use of an HMD has no major drawbacks compared to the monitor setting. The striking advantage is that the surgeon is no longer obliged to turn his head away from the operation site during navigation, as all data relevant for the procedure are superimposed on the image of the real world in his field of view.     

Optimal setting of image bounding box can improve registration accuracy of diffusion tensor tractography

Purpose

When we register diffusion tensor tractography (DTT) to anatomical images such as fast imaging employing steady-state acquisition (FIESTA), we register the B0 image to FIESTA. Precise registration of the DTT B0 image to FIESTA is possible with non-rigid registration compared to rigid registration, although the non-rigid methods lack convenience. We report the effect of image data bounding box settings on registration accuracy using a normalized mutual information (NMI) method

Methods

MRI scans of 10 patients were used in this study. Registration was performed without modification of the bounding box in the control group, and the results were compared with groups re-registered using multiple bounding boxes limited to the region of interest (ROI). The distance of misalignment after registration at 3 anatomical characteristic points that are common to both FIESTA and B0 images was used as an index of accuracy.

Results

Mean ( $\pm $ SD) misalignment at the 3 anatomical points decreased significantly from $5.99\pm 1.58$ to $2.21\pm 1.24$  mm, $p<0.0001$ ), $4.36\pm 1.58$ to $1.48\pm 0.58$  mm, ( $p<0.0001)$ , and $5.21\pm 1.76$ to $1.20\pm 0.74$  mm, ( $p<0.0001)$ , each showing improvement compared to the control group

Conclusion

Narrowing the image data bounding box to the ROI improves the accuracy of registering B0 images to FIESTA by NMI method. With our proposed methodology, accuracy can be improved in extremely easy steps, and this methodology may prove useful for DTT registration to anatomical image     

Correlation of thermodilution-derived extravascular lung water and ventilation/perfusion-compartments in a porcine model

Purpose

This study examines the correlation between the transpulmonary thermodilution derived extravascular lung water content (EVLW) and the ventilation/perfusion-distribution ( $ \dot{V}/\dot{Q} $ ) measured by multiple inert gas elimination (MIGET) in a porcine model.

Methods

$ \dot{V}/\dot{Q} $ measured by micropore membrane inlet mass spectrometry-MIGET (MMIMS-MIGET) and EVLW were simultaneously measured in twelve pigs in the heathy state, with impaired gas exchange from repetitive lung lavage and after 3 h of ventilation. The relationship between $ \dot{V}/\dot{Q} $ compartments and EVLW was analysed by linear correlation and regression.

Results

Considerable increases in EVLW and $ \dot{V}/\dot{Q} $ mismatching were induced through the lavage procedure. Significant correlations between the EVLW and the $ \dot{V}/\dot{Q} $ fractions representing pulmonary shunt and low $ \dot{V}/\dot{Q} $ were found. Perfusion to the normal $ \dot{V}/\dot{Q} $ regions was inversely correlated to the EVLW.

Conclusions

Increased EVLW is associated with increased low $ \dot{V}/\dot{Q} $ and shunt, but not equal to pulmonary shunt alone. Beneath true shunt EVLW can also be associated with low $ \dot{V}/\dot{Q} $ regions.     

C-arm angle measurement with accelerometer for brachytherapy: an accuracy study

Purpose

 X-ray fluoroscopy guidance is frequently used in medical interventions. Image-guided interventional procedures that employ localization for registration require accurate information about the C-arm’s rotation angle that provides the data externally in real time. Optical, electromagnetic, and image-based pose tracking systems have limited convenience and accuracy. An alternative method to recover C-arm orientation was developed using an accelerometer as tilt sensor.

Methods

    The fluoroscopic C-arm’s orientation was estimated using a tri-axial acceleration sensor mounted on the X-ray detector as a tilt sensor. When the C-arm is stationary, the measured acceleration direction corresponds to the gravitational force direction. The accelerometer was calibrated with respect to the C-arm’s rotation along its two axes, using a high-accuracy optical tracker as a reference. The scaling and offset error of the sensor was compensated using polynomial fitting. The system was evaluated on a GE OEC 9800 C-arm. Results obtained by accelerometer, built-in sensor, and image-based tracking were compared, using optical tracking as ground truth data.

Results

The accelerometer-based orientation measurement error for primary angle rotation was $-0.1\pm 0.0^{\circ }$ and for secondary angle rotation it was $0.1\pm 0.0^{\circ }$ . The built-in sensor orientation measurement error for primary angle rotation was $-0.1\pm 0.2^{\circ }$ , and for secondary angle rotation it was $0.1\pm 0.2^{\circ }$ . The image-based orientation measurement error for primary angle rotation was $-0.1\pm 1.3^{\circ }$ , and for secondary angle rotation it was $-1.3\pm 0.3^{\circ }$ .

Conclusion

The accelerometer provided better results than the built-in sensor and image-based tracking. The accelerometer sensor is small, inexpensive, covers the full rotation range of the C-arm, does not require line of sight, and can be easily installed to any mobile X-ray machine. Therefore, accelerometer tilt sensing is a very promising applicant for orientation angle tracking of C-arm fluoroscopes.     

Simultaneous extraction of carotid artery intima-media interfaces in ultrasound images: assessment of wall thickness temporal variation during the cardiac cycle

Objectives

   The aim of this work is to present and evaluate a novel segmentation method for localizing the contours of the intima-media complex in the carotid artery wall through longitudinal ultrasound B-mode imaging. The method is used to investigate the association between atherosclerosis risk factors and the cyclic variation of the intima-media thickness during the heart beat.

Methods

   The framework introduced is based on two main features. The first is a simultaneous extraction of both the lumen-intima and the media-adventitia interfaces, using the combination of an original shape-adapted filter bank and a specific dynamic programming scheme. The second is an innovative spatial transformation that eases the extraction of skewed and curved contours, and exploits the result from the previous image as a priori information, when processing the current image. The intima-media thickness is automatically derived from the estimated contours for each time step during the cardiac cycle. Our method was evaluated in vivo on 57 healthy volunteers and 25 patients at high cardiovascular risk. Reference contours were generated for each subject by averaging the tracings performed by three experienced observers.

Results

   Segmentation errors were \(29 \pm 27\,\upmu \hbox {m}\) for the lumen-intima interface, \(42 \pm 38\,\upmu \hbox {m}\) for the media-adventitia interface, and \(22 \pm 16\,\upmu \hbox {m}\) for the intima-media thickness. This uncertainty was similar to inter- and intra-observer variability. Furthermore, the amplitude of the temporal variation in thickness of the intima-media layers during the cardiac cycle was significantly higher in at-risk patients compared to healthy volunteers \((79 \pm 36\) vs. \(64 \pm 26\,\upmu \hbox {m},\, p=0.032)\) .

Conclusion

   The method proposed may provide a relevant diagnostic aid for atherosclerosis screening in clinical studies.     

Early intermittent noninvasive ventilation for acute chest syndrome in adults with sickle cell disease: a pilot study

Purpose

Alveolar hypoxia and hypoxic vasoconstriction lead to trapping of sickle cells within the pulmonary vasculature. Improving alveolar ventilation and oxygenation may improve the outcome of acute chest syndrome (ACS).

Methods

Prospective randomized single-center open study from November 1998 to February 2002 to test whether noninvasive ventilation (NIV) was more effective than oxygen alone in improving oxygenation on day 3 in adults with ACS and to evaluate the effects on pain, transfusion requirements, and length of stay.

Results

Seventy-one consecutive ACS episodes in 67 patients were randomly allocated to oxygen (n = 36) or NIV (n = 35) for 3 days in a medical step-down unit. Baseline respiratory rate and pain score were higher in the NIV group. NIV promptly lowered the respiratory rate, raised $ {\text{Pa}}_{{\text{O}_{2}}} $ , and decreased alveolar–arterial oxygen gradient $ (({\text{A}} - {\text{a}})_{{{\text{O}}_{ 2} }} ) $ , which remained unchanged with oxygen alone. $ {\text{Pa}}_{{{\text{CO}}_{ 2} }} $ significantly worsened only in the oxygen group. On day 3, the groups did not differ regarding the proportion of episodes with normal $ {\text{Pa}}_{{{\text{O}}_{ 2} }} $ (35% with NIV and 25% with oxygen; P = 0.5) or $ (({\text{A}} - {\text{a}})_{{{\text{O}}_{ 2} }} ) $ . Patient satisfaction and compliance were lower with NIV. No differences were noted in pain relief, transfusions, or length of stay. In the subgroup of patients with severe hypoxemia $ ( {\text{Pa}}_{{{\text{O}}_{ 2} }} \le 6 5\,{\text{mmHg)}} $ , physiological variables also improved faster with NIV, the differences being slightly more pronounced.

Conclusions

Respiratory rate and gas exchange improved faster with NIV. However, NIV failed to significantly reduce the number of patients remaining hypoxemic at day 3, and was associated with greater patient discomfort.     

A low-cost tracked C-arm (TC-arm) upgrade system for versatile quantitative intraoperative imaging

Purpose

   C-arm fluoroscopy is frequently used in clinical applications as a low-cost and mobile real-time qualitative assessment tool. C-arms, however, are not widely accepted for applications involving quantitative assessments, mainly due to the lack of reliable and low-cost position tracking methods, as well as adequate calibration and registration techniques. The solution suggested in this work is a tracked C-arm (TC-arm) which employs a low-cost sensor tracking module that can be retrofitted to any conventional C-arm for tracking the individual joints of the device.

Methods

   Registration and offline calibration methods were developed that allow accurate tracking of the gantry and determination of the exact intrinsic and extrinsic parameters of the imaging system for any acquired fluoroscopic image. The performance of the system was evaluated in comparison to an Optotrak \(^\mathrm{TM}\) motion tracking system and by a series of experiments on accurately built ball-bearing phantoms. Accuracies of the system were determined for 2D–3D registration, three-dimensional landmark localization, and for generating panoramic stitched views in simulated intraoperative applications.

Results

   The system was able to track the center point of the gantry with an accuracy of \(1.5 \pm 1.2\)  mm or better. Accuracies of 2D–3D registrations were \(2.3 \pm 1.1\)  mm and \(0.2 \pm 0.2^{\circ }\) . Three-dimensional landmark localization had an accuracy of \(3.1 \pm 1.3\%\) of the length (or \(4.4 \pm 1.9\)  mm) on average, depending on whether the landmarks were located along, above, or across the table. The overall accuracies of the two-dimensional measurements conducted on stitched panoramic images of the femur and lumbar spine were 2.5 \(\pm \) 2.0 % \((3.1 \pm 2.5 \hbox { mm})\) and \(0.3 \pm 0.2^{\circ }\) , respectively.

Conclusion

   The TC-arm system has the potential to achieve sophisticated quantitative fluoroscopy assessment capabilities using an existing C-arm imaging system. This technology may be useful to improve the quality of orthopedic surgery and interventional radiology.     

Feasibility of respiratory motion-compensated stereoscopic X-ray tracking for bronchoscopy

Purpose

   Precise localization in bronchoscopy is challenging, particularly for peripheral lesions that cannot be reached by conventional bronchoscopes with a large working channel. Existing navigation methods are hampered by respiratory motion, e.g., in the lower lobes. We present an image-guided approach that considers respiratory motion and can localize instruments.

Methods

   We developed a rigid chest marker containing steel balls visible in X-ray images and a pattern for passive tracking with an optical camera system. An experimental setup to evaluate stereoscopic localization and to mimic chest motion was established in our interventional suite. The marker motion was recorded, and X-ray images were acquired from different angles using a standard C-arm. All coordinates were expressed with respect to the stationary tracking camera. The feasibility of motion-compensated stereoscopic localization was assessed.

Results

   The orientation of the C-arm could be established with a mean error of less than $1^{\circ }$ . Triangulation based on two different X-ray images from different angles resulted in a mean error of 1.8 ( $\pm $ 0.7) mm. A similar result was obtained when the marker was moved between X-ray acquisitions, and the mean error was 1.6 ( $\pm $ 1.4) mm. The latencies were approximately 80 and 380 ms for tracking camera and X-ray imaging, respectively. Stereoscopic localization of a moving target was feasible.

Conclusions

   The system presents a flexible alternative for precise stereoscopic localization of a bronchoscope or instruments using a standard C-arm. We demonstrated the ability to track multiple moving markers and to compensate for respiratory motion.     

A morphological study of anatomical plates for acetabular posterior column

Purposes

   The objective of this work is to explore the morphological characteristics of the acetabular posterior column using digital technology, in order to develop anatomical plates for internal fixation of acetabular posterior column fractures.

Materials and methods

   Three-dimensional reconstruction models of the pelvis were developed from computed tomography scan data of 111 adult patients. From them, the diameter (D) of the femoral head, three approximate arcs along the acetabular posterior column plate path with corresponding radius of curvature \(\hbox {R}_{1}, \hbox {R}_{2}\) and \(\hbox {R}_{3}\) , as well as an angle \(\alpha \) were measured. A statistical analysis was used to determine the most feasible method of designing anatomical plates according to the data.

Results

   The statistical analysis results showed that \(\hbox {R}_{1}, \hbox {R}_{2}\) and \(\hbox {R}_{3}\) had no correlations with D, and they also exhibited no statistically significant differences between genders. By examining the correlations between four morphological parameters of the acetabular posterior column, the results showed \(\hbox {R}_{2}\) increased along with \(\hbox {R}_{1}, \alpha \) was inversely proportional to \(\hbox {R}_{1}\) and \(\hbox {R}_{2}\) , and \(\hbox {R}_{3}\) was independent with little variation. Taking \(\hbox {R}_{1}\) as the reference, the data were divided into three groups and three types of anatomical plates were designed according to the three groups of data.

Conclusion

   The anatomical structure of the acetabular posterior column exhibits great individual differences. Anatomical plates designed in this study have higher accuracy than those conventional ones, which is helpful to the quality of fracture reduction and reduce the operation difficult. Meanwhile, they also can be conveniently used in clinic.     

Experimental evaluation of ultrasound-guided 3D needle steering in biological tissue

Purpose

In this paper, we present a system capable of automatically steering bevel tip flexible needles under ultrasound guidance toward stationary and moving targets in gelatin phantoms and biological tissue while avoiding stationary and moving obstacles. We use three-dimensional (3D) ultrasound to track the needle tip during the procedure.

Methods

Our system uses a fast sampling-based path planner to compute and periodically update a feasible path to the target that avoids obstacles. We then use a novel control algorithm to steer the needle along the path in a manner that reduces the number of needle rotations, thus reducing tissue damage. We present experimental results for needle insertion procedures for both stationary and moving targets and obstacles for up to 90 mm of needle insertion.

Results

We obtained a mean targeting error of \(0.32\pm 0.10\) and \(0.38\,\pm \,0.19\)  mm in gelatin-based phantom and biological tissue, respectively.

Conclusions

The achieved submillimeter accuracy suggests that our approach is sufficient to target the smallest lesions ( \(\phi \)  2 mm) that can be detected using state-of-the-art ultrasound imaging systems.     

Statistical model-based segmentation of the proximal femur in digital antero-posterior (AP) pelvic radiographs

Purpose

   Segmentation of the proximal femur in digital antero-posterior (AP) pelvic radiographs is required to create a three-dimensional model of the hip joint for use in planning and treatment. However, manually extracting the femoral contour is tedious and prone to subjective bias, while automatic segmentation must accommodate poor image quality, anatomical structure overlap, and femur deformity. A new method was developed for femur segmentation in AP pelvic radiographs.

Methods

   Using manual annotations on 100 AP pelvic radiographs, a statistical shape model (SSM) and a statistical appearance model (SAM) of the femur contour were constructed. The SSM and SAM were used to segment new AP pelvic radiographs with a three-stage approach. At initialization, the mean SSM model is coarsely registered to the femur in the AP radiograph through a scaled rigid registration. Mahalanobis distance defined on the SAM is employed as the search criteria for each annotated suggested landmark location. Dynamic programming was used to eliminate ambiguities. After all landmarks are assigned, a regularized non-rigid registration method deforms the current mean shape of SSM to produce a new segmentation of proximal femur. The second and third stages are iteratively executed to convergence.

Results

   A set of 100 clinical AP pelvic radiographs (not used for training) were evaluated. The mean segmentation error was $0.96\,\hbox {mm} \pm 0.35\,\hbox {mm}$ , requiring $<\!5$  s per case when implemented with Matlab. The influence of the initialization on segmentation results was tested by six clinicians, demonstrating no significance difference.

Conclusions

   A fast, robust and accurate method for femur segmentation in digital AP pelvic radiographs was developed by combining SSM and SAM with dynamic programming. This method can be extended to segmentation of other bony structures such as the pelvis.     

Warning navigation system using real-time safe region monitoring for otologic surgery

Purpose We developed a surgical navigation system that warns the surgeon with auditory and visual feedback to protect the facial nerve with real-time monitoring of the safe region during drilling. Methods Warning navigation modules were developed and integrated into a free open source software platform. To obtain high registration accuracy, we used a high-precision laser-sintered template of the patient’s bone surface to register the computed tomography (CT) images. We calculated the closest distance between the drill tip and the surface of the facial nerve during drilling. When the drill tip entered the safe regions, the navigation system provided an auditory and visual signal which differed in each safe region. To evaluate the effectiveness of the system, we performed phantom experiments for maintaining a given safe margin from the facial nerve when drilling bone models, with and without the navigation system. The error of the safe margin was measured on postoperative CT images. In real surgery, we evaluated the feasibility of the system in comparison with conventional facial nerve monitoring. Results The navigation accuracy was submillimeter for the target registration error. In the phantom study, the task with navigation ( $0.7 \pm 0.25$ mm) was more successful with smaller error, than the task without navigation ( $1.37 \pm 0.39$ mm, $P<0.05$ ). The clinical feasibility of the system was confirmed in three real surgeries. Conclusions This system could assist surgeons in preserving the facial nerve and potentially contribute to enhanced patient safety in the surgery.     

Using the low-pass monogenic signal framework for cell/background classification on multiple cell lines in bright-field microscope images

Purpose

   Several cell detection approaches which deal with bright-field microscope images utilize defocusing to increase image contrast. The latter is related to the physical light phase through the transport of intensity equation (TIE). Recently, it was shown that it is possible to approximate the solution of the TIE using a low-pass monogenic signal framework. The purpose of this paper is to show that using the local phase of the aforementioned monogenic signal instead of the defocused image improves the cell/background classification accuracy.

Materials and methods

   The paper statement was tested on an image database composed of three cell lines: adherent CHO, adherent L929, and Sf21 in suspension. Local phase and local energy images were generated using the low-pass monogenic signal framework with axial derivative images as input. Machine learning was then employed to investigate the discriminative power of the local phase. Three classifier models were utilized: random forest (RF), support vector machine (SVM) with a linear kernel, and SVM with a radial basis function (RBF) kernel.

Results

   The improvement, averaged over cell lines, of classifying $5 \times 5$ sized patches extracted from the local phase image instead of the defocused image was $7.3$  % using the RF, $11.6$  % using the linear SVM, and $10.2$  % when a RBF kernel was employed instead of the linear one. Furthermore, the feature images can be sorted by increasing discriminative power as follows: at-focus signal, local energy, defocused signal, local phase. The only exception to this order was the superiority of local energy over defocused signal for suspended cells.

Conclusions

   Local phase computed using the low-pass monogenic signal framework considerably outperforms the defocused image for the purpose of pixel-patch cell/background classification in bright-field microscopy.     

Automated implant segmentation in cone-beam CT using edge detection and particle counting

Purpose

To develop a fully automated, accurate and robust segmentation technique for dental implants on cone-beam CT (CBCT) images.

Methods

A head-size cylindrical polymethyl methacrylate phantom was used, containing titanium rods of 5.15 mm diameter. The phantom was scanned on 17 CBCT devices, using a total of 39 exposure protocols. Images were manually thresholded to verify the applicability of adaptive thresholding and to determine a minimum threshold value \(({T}_{\mathrm{min}})\) . A three-step automatic segmentation technique was developed. Firstly, images were pre-thresholded using \({T}_{\mathrm{min}}\) . Next, edge enhancement was performed by filtering the image with a Sobel operator. The filtered image was thresholded using an iteratively determined fixed threshold \(({T}_{\mathrm{edge}})\) and converted to binary. Finally, a particle counting method was used to delineate the rods. The segmented area of the titanium rods was compared to the actual area, which was corrected for phantom tilting.

Results

Manual thresholding resulted in large variation in threshold values between CBCTs. After applying the edge-enhancing filter, a stable \({T}_{\mathrm{edge}}\) value of 7.5 % was found. Particle counting successfully detected the rods for all but one device. Deviations between the segmented and real area ranged between \(-\) 2.7 and + \(14.4\,\hbox {mm}^{2}\) with an average absolute error of \(2.8\,\hbox {mm}^{2}\) . Considering the diameter of the segmented area, submillimeter accuracy was seen for all but two data sets.

Conclusion

A segmentation technique was defined which can be applied to CBCT data for an accurate and fully automatic delineation of titanium rods. The technique was validated in vitro and will be further tested and refined on patient data.     

Three-dimensional prediction of free-flap volume in autologous breast reconstruction by CT angiography imaging

Purpose

   The diagnostic use of computer tomography angiography (CTA) to identify perforating blood vessels for abdominal free-flap breast reconstruction was extended to estimate the three-dimensional (3D) preoperative flap volume and to compare it with the real intraoperative flap weights in order to (1) evaluate the accuracy of CTA-based 3D flap volume prediction, and (2) to analyze abdominal tissue estimation for required breast volume reconstruction.

Methods

   Preoperative CTA was performed in 54 patients undergoing unilateral breast reconstruction with a free, deep, inferior epigastric artery perforator flap. 3D flap volumes ( \(\hbox {cm}^{3}\) ) based on CTA data were calculated and compared with the actual intraoperative flap weight (g). In addition, a breast volume to flap volume ratio was calculated to analyze whether the estimated 3D abdominal flap volume would match that of the breast to be removed.

Results

   40 CTA data sets (74.1 %) fulfilled the technical requirements for a reliable determination of flap volume. 3D CTA flap volume prediction showed no relevant differences to the actual flap weight (p = 0.44) and high correlations (r = 0.998, \(p < 0.001\) ), allowing a prediction accuracy within 0.29 \(\pm \) 3.0 % (range: from \(-\) 8.77 to 5.67 %) of the real flap weight. Significantly larger flap volumes were harvested compared with the actually required breast volumes ( \(p < 0.001\) ), leading to an average of 21 % of the remnant flap tissue potentially being discarded.

Conclusions

   CTA-based 3D flap volume prediction provides accurate preoperative guidelines concerning the needed amount of abdominal tissue that can be harvested to achieve acceptable symmetry.     

An automated insertion tool for cochlear implants with integrated force sensing capability

Purpose

Minimally invasive cochlear implantation and residual hearing preservation require both the surgical approach to the cochlea as well as the implant insertion to be performed in an atraumatic fashion. Considering the geometric limitations of this approach, specialized instrumentation is required to insert the electrode while preserving intracochlear membranes carrying the sensory hair cells.

Methods

An automated insertion tool for cochlear implants, which is capable of sensing insertion forces with a theoretical resolution of $30\,\upmu \mathrm{N}$ , is presented. In contrast to previous designs, the custom force sensor is integrated in the insertion mechanism. Moreover, a test bench for insertion studies under constant and reproducible boundary conditions is proposed. It is used to experimentally validate the force sensing insertion tool, which is achieved by comparing the acquired forces to a ground truth measurement. The results of insertion studies on both an acrylic cochlear phantom and temporal bone specimen are given and discussed.

Results

Results reveal that friction, occurring between the electrode carrier and the inside of the insertion tool guide tube, is likely to affect the force output of the proposed sensor. An appropriate method to compensate for these disturbances is presented and experimentally validated. Using the proposed approach to friction identification, a mean accuracy of $(4.0\pm 3.2)\, \hbox {mN}$ is observed.

Conclusions

The force information provided by the proposed, automated insertion tool can be used to detect complications during electrode insertion. However, in order to obtain accurate results, an identification of frictional forces prior to insertion is mandatory. The insertion tool is capable of automatically executing the appropriate trajectories.     

Intraoperative detection and localization of cylindrical implants in cone-beam CT image data

Purpose

Orthopedic fractures are often fixed using metal implants. The correct positioning of cylindrical implants such as surgical screws, rods and guide wires is highly important. Intraoperative 3D imaging is often used to ensure proper implant placement. However, 3D image interaction is time-consuming and requires experience. We developed an automatic method that simplifies and accelerates location assessment of cylindrical implants in 3D images.

Methods

Our approach is composed of three major steps. At first, cylindrical characteristics are detected by analyzing image gradients in small image regions. Next, these characteristics are grouped in a cluster analysis. The clusters represent cylindrical implants and are used to initialize a cylinder-to-image registration. Finally, the two end points are optimized regarding image contrast along the cylinder axis.

Results

A total of 67 images containing 420 cylindrical implants were used for testing. Different anatomical regions (calcaneus, spine) and various image sources (two mobile devices, three reconstruction methods) were investigated. Depending on the evaluation set, the detection performance was between 91.7 and 96.1 % true- positive rate with a false-positive rate between 2.0 and 3.2 %. The end point distance errors ranged from \(1.0 \pm 1.2\) to \(4.3 \pm 2.9\)  mm and the orientation errors from \(1.6 \pm 2.2\) to \(2.3 \pm 2.2\) degrees. The average computation time was less than 5 seconds.

Conclusions

An automatic method was developed and tested that obviates the need for 3D image interaction during intraoperative assessment of cylindrical orthopedic implants. The required time for working with the viewing software of cone-beam CT device is drastically reduced and leads to a shorter time under anesthesia for the patient.     

Stent graft visualization and planning tool for endovascular surgery using finite element analysis

Purpose

A new approach to optimize stent graft selection for endovascular aortic repair is the use of finite element analysis. Once the finite element model is created and solved, a software module is needed to view the simulation results in the clinical work environment. A new tool for interpretation of simulation results, named Medical Postprocessor, that enables comparison of different stent graft configurations and products was designed, implemented and tested.

Methods

 Aortic endovascular stent graft ring forces and sealing states in the vessel landing zone of three different configurations were provided in a surgical planning software using the Medical Imaging Interaction Tool Kit (MITK) software system. For data interpretation, software modules for 2D and 3D presentations were implemented. Ten surgeons evaluated the software features of the Medical Postprocessor. These surgeons performed usability tests and answered questionnaires based on their experience with the system.

Results

The Medical Postprocessor visualization system enabled vascular surgeons to determine the configuration with the highest overall fixation force in \(16 \pm 6\)  s, best proximal sealing in \(56 \pm 24\)  s and highest proximal fixation force in \(38\pm 12\)  s. The majority considered the multiformat data provided helpful and found the Medical Postprocessor to be an efficient decision support system for stent graft selection. The evaluation of the user interface results in an ISONORM-conform user interface (113.5 points).

Conclusion

The Medical Postprocessor visualization software tool for analyzing stent graft properties was evaluated by vascular surgeons. The results show that the software can assist the interpretation of simulation results to optimize stent graft configuration and sizing.