Surgical navigation for guidewire placement from intraoperative fluoroscopy in orthopaedic surgery.

Objective. Surgical guidewires are commonly used in placing fixation implants to stabilize fractures. Accurate positioning of these instruments is challenged by difficulties in 3D reckoning from 2D fluoroscopy. This work aims to enhance the accuracy and reduce exposure times by providing 3D navigation for guidewire placement from as little as two fluoroscopic images.Approach. Our approach combines machine learning-based segmentation with the geometric model of the imager to determine the 3D poses of guidewires. Instrument tips are encoded as individual keypoints, and the segmentation masks are processed to estimate the trajectory. Correspondence between detections in multiple views is established using the pre-calibrated system geometry, and the corresponding features are backprojected to obtain the 3D pose. Guidewire 3D directions were computed using both an analytical and an optimization-based method. The complete approach was evaluated in cadaveric specimens with respect to potential confounding effects from the imaging geometry and radiographic scene clutter due to other instruments.Main results. The detection network identified the guidewire tips within 2.2 mm and guidewire directions within 1.1°, in 2D detector coordinates. Feature correspondence rejected false detections, particularly in images with other instruments, to achieve 83% precision and 90% recall. Estimating the 3D direction via numerical optimization showed added robustness to guidewires aligned with the gantry rotation plane. Guidewire tips and directions were localized in 3D world coordinates with a median accuracy of 1.8 mm and 2.7°, respectively.Significance. The paper reports a new method for automatic 2D detection and 3D localization of guidewires from pairs of fluoroscopic images. Localized guidewires can be virtually overlaid on the patient's pre-operative 3D scan during the intervention. Accurate pose determination for multiple guidewires from two images offers to reduce radiation dose by minimizing the need for repeated imaging and provides quantitative feedback prior to implant placement.

C-arm orbits for metal artifact avoidance (MAA) in cone-beam CT.

Metal artifacts present a challenge to cone-beam CT (CBCT) image-guided surgery, obscuring visualization of metal instruments and adjacent anatomy-often in the very region of interest pertinent to the imaging/surgical tasks. We present a method to reduce the influence of metal artifacts by prospectively defining an image acquisition protocol-viz., the C-arm source-detector orbit-that mitigates metal-induced biases in the projection data. The metal artifact avoidance (MAA) method is compatible with simple mobile C-arms, does not require exact prior information on the patient or metal implants, and is consistent with 3D filtered backprojection (FBP), more advanced (e.g. polyenergetic) model-based image reconstruction (MBIR), and metal artifact reduction (MAR) post-processing methods. The MAA method consists of: (i) coarse localization of metal objects in the field-of-view (FOV) via two or more low-dose scout projection views and segmentation (e.g. a simple U-Net) in coarse backprojection; (ii) model-based prediction of metal-induced x-ray spectral shift for all source-detector vertices accessible by the imaging system (e.g. gantry rotation and tilt angles); and (iii) identification of a circular or non-circular orbit that reduces the variation in spectral shift. The method was developed, tested, and evaluated in a series of studies presenting increasing levels of complexity and realism, including digital simulations, phantom experiment, and cadaver experiment in the context of image-guided spine surgery (pedicle screw implants). The MAA method accurately predicted tilted circular and non-circular orbits that reduced the magnitude of metal artifacts in CBCT reconstructions. Realistic distributions of metal instrumentation were successfully localized (0.71 median Dice coefficient) from 2-6 low-dose scout views even in complex anatomical scenes. The MAA-predicted tilted circular orbits reduced root-mean-square error (RMSE) in 3D image reconstructions by 46%-70% and 'blooming' artifacts (apparent width of the screw shaft) by 20-45%. Non-circular orbits defined by MAA achieved a further ∼46% reduction in RMSE compared to the best (tilted) circular orbit. The MAA method presents a practical means to predict C-arm orbits that minimize spectral bias from metal instrumentation. Resulting orbits-either simple tilted circular orbits or more complex non-circular orbits that can be executed with a motorized multi-axis C-arm-exhibited substantial reduction of metal artifacts in raw CBCT reconstructions by virtue of higher fidelity projection data, which are in turn compatible with subsequent MAR post-processing and/or polyenergetic MBIR to further reduce artifacts.

Solving inverse problems for biological models using the collage method for differential equations.

In the first part of this paper we show how inverse problems for differential equations can be solved using the so-called collage method. Inverse problems can be solved by minimizing the collage distance in an appropriate metric space. We then provide several numerical examples in mathematical biology. We consider applications of this approach to the following areas: population dynamics, mRNA and protein concentration, bacteria and amoeba cells interaction, tumor growth.

Rayleigh scattering and redistribution of radiation in He I plasmas: measurements and calculations.

Conditions for which Rayleigh scattering and redistribution of radiation can be observed are examined. The competition between the relaxation processes and spontaneous emission is shown to determine the conditions for partial redistribution. We investigate specific cases in the singlet and triplet He I atomic system for plasma parameters reachable experimentally in a well diagnosed magnetic multipole source. Partial redistribution on the 2 1S-4 1P at 396.5 nm, 2 1P-5 1D at 438.8 nm, 2 3P-5 3D at 402.6 nm, 2 3P-4 3D at 447.2 nm and 2 3P-4 3S at 471.3 nm fine structure transitions is observed employing a dye laser pumping the He I plasma. We make use of a previously developed two-photon formalism based on the frequency fluctuation model to calculate radiative redistribution functions. Results of the partial redistribution measurements are presented, augmented by a comparison with calculations. This allows us to confirm available electron-atom elastic collision rates to within 20%.

Implication of acid cholesteryl ester hydrolase in the regulation of steroid biosynthesis in rat Leydig cells.

Cholesteryl ester hydrolase (CEH) activities with different pH optima, i.e. at about pH 4.0 and pH 7.0, were found in Leydig cells isolated from rat testis. Highly purified intact Leydig cells responded to human chorionic gonadotropin treatment with increased intracellular cAMP levels, increased testosterone release, and a 1.5-fold stimulation of the acid CEH activity. Treatment of non-stimulated homogenised cells with cAMP-dependent proteinkinase, cAMP and ATP lead to a 3.0-fold stimulation of the acid CEH activity. These findings suggest that interconvertible CEH with an acidic pH optimum--presumably of lysosomal location--contributes to the regulation of steroidogenesis in Leydig cells.

Protease inhibitors reduce lysosomal acid phospholipase A1 activity in cultured rat hepatocytes.

When rat hepatocytes were cultured in the presence of various specific protease inhibitors, lysosomal acid phospholipase A1 activity decreased progressively. Exposure of the cultured cells to 0.1 micrograms/ml of pepstatin, E 64, leupeptin or chymostatin also reduced the catalytic activities of several lysosomal marker enzymes. Irrespective of the protease inhibitor type employed, acid phospholipase A1 activity reacted most sensitively, followed by acid phosphatase, acid beta-N-acetyl-D-hexosaminidase and acid beta-glucuronidase. Of the protease inhibitors studied, pepstatin appeared to be most potent in reducing lysosomal enzyme activities in cultured hepatocytes. These findings suggest that proteolytic processes at as yet unknown, possibly extralysosomal sites play an important role in the turnover rates of lysosomal enzymes.

Functioning lipoadenoma of the parathyroid gland.

A lipoadenoma of the parathyroid gland was discovered at autopsy as the result of a search for the cause of terminally detected hyperparathyroidism in an elderly man who had suffered cerebral infarction. It is the only case known to the authors in which this uncommon cause of hyperparathyroidism was found at post-mortem examination after hypercalcemia and raised levels of serum immunoreactive parathormone were documented during life.

[Upper gastrointestinal hemorrhage as a rare complication of stomach catheterization]. / Eine obere gastrointestinale Blutung als seltene Komplikation einer Magensonde.

An episode of acute gastrointestinal bleeding following the insertion of a feeding tube is reported. The various possible complications of feeding tube insertion and the prevention of such complications are discussed.