Biplane X-ray Imaging Research Articles

Accuracy of biplane x-ray imaging combined with model-based tracking for measuring in-vivo patellofemoral joint motion

BackgroundAccurately measuring in-vivo motion of the knee's patellofemoral (PF) joint is challenging. Conventional measurement techniques have largely been unable to accurately measure three-dimensional, in-vivo motion of the patella during dynamic activities. The purpose of this study was to assess the accuracy of a new model-based technique for measuring PF joint motion.MethodsTo assess the accuracy of this technique, we implanted tantalum beads into the femur and patella of three cadaveric knee specimens and then recorded dynamic biplane radiographic images while manually flexing and extending the specimen. The position of the femur and patella were measured from the biplane images using both the model-based tracking system and a validated dynamic radiostereometric analysis (RSA) technique. Model-based tracking was compared to dynamic RSA by computing measures of bias, precision, and overall dynamic accuracy of four clinically-relevant kinematic parameters (patellar shift, flexion, tilt, and rotation).ResultsThe model-based tracking technique results were in excellent agreement with the RSA technique. Overall dynamic accuracy indicated errors of less than 0.395 mm for patellar shift, 0.875° for flexion, 0.863° for tilt, and 0.877° for rotation.ConclusionThis model-based tracking technique is a non-invasive method for accurately measuring dynamic PF joint motion under in-vivo conditions. The technique is sufficiently accurate in measuring clinically relevant changes in PF joint motion following conservative or surgical treatment.

Measuring dynamic in-vivo glenohumeral joint kinematics: Technique and preliminary results

Rotator cuff tears are a common injury that affect a significant percentage of the population over age 60. Although it is widely believed that the rotator cuff's primary function is to stabilize the humerus against the glenoid during shoulder motion, accurately measuring the three-dimensional (3D) motion of the shoulder's glenohumeral joint under in-vivo conditions has been a challenging endeavor. In particular, conventional motion measurement techniques have frequently been limited to static or two-dimensional (2D) analyses, and have suffered from limited or unknown in-vivo accuracy. We have recently developed and validated a new model-based tracking technique that is capable of accurately measuring the 3D position and orientation of the scapula and humerus from biplane X-ray images. Herein we demonstrate the in-vivo application of this technique for accurately measuring glenohumeral joint translations during shoulder motion in the repaired and contralateral shoulders of patients following rotator cuff repair. Five male subjects were tested at 3–4 months following arthroscopic rotator cuff repair. Superior–inferior humeral translation was measured during elevation, and anterior–posterior humeral translation was measured during external rotation in both the repaired and contralateral shoulders. The data failed to detect statistically significant differences between the repaired and contralateral shoulders in superior–inferior translation ( p=0.74) or anterior–posterior translation ( p=0.77). The measurement technique overcomes the limitations of conventional motion measurement techniques by providing accurate, 3D, in-vivo measures of glenohumeral joint motion during dynamic activities. On-going research is using this technique to assess the effects of conservative and surgical treatment of rotator cuff tears.

DEVELOPMENT OF A COMPUTER-AIDED TRAINING SYSTEM FOR PEDICLE SCREW IMPLANTATION

In this research, we developed an intelligent, computer-assisted training system for pedicle screw implantation in spinal surgery. Base on the biplane X-ray imaging of a pre-drilled saw bone of lumbosacral spine, spatial coordinate correlations between the physical saw bone and the 3D digitizer built an off-line training environment. A senior spine surgeon prepares the pre-drilled position as a standard and the trainee uses the 3D digitizer to approach the referential standard. The techniques developed in this system involve X-ray imaging rectification, registration, image processing, imaging dilation and erosion, bi-plane calibration, and spatial geometric transformation, which will be a pioneer study of further clinical applications. The position accuracy of the guiding system is within 1 mm, and angular accuracy is within 1.5°, which may meet the basic surgical requirements for lumbosacral spine. Eventually, the developed training device was applied to several orthopedics surgeons to collect and analyze the angulation test results.

Comparison of Similarity Measures for Rigid-body CT/Dual X-ray Image Registrations

A set of experiments were conducted to evaluate six similarity measures for intensity-based rigid-body 3D/2D image registration. Similarity measure is an index that measures the similarity between a digitally reconstructed radiograph (DRR) and an x-ray planar image. The registration is accomplished by maximizing the sum of the similarity measures between biplane x-ray images and the corresponding DRRs in an iterative fashion. We have evaluated the accuracy and attraction ranges of the registrations using six different similarity measures on phantom experiments for head, thorax, and pelvis. The images were acquired using Varian Medial System On-Board Imager. Our results indicated that normalized cross correlation and entropy of difference showed a wide attraction range (62 deg and 83 mm mean attraction range, omega(mean)), but the worst accuracy (4.2 mm maximum error, e(max)). The gradient-based similarity measures, gradient correlation and gradient difference, and the pattern intensity showed sub-millimeter accuracy, but narrow attraction ranges (omega(mean)=29 deg, 31 mm). Mutual information was in-between of these two groups (e(max)=2.5 mm, omega(mean)= 48 deg, 52 mm). On the data of 120 x-ray pairs from eight IRB approved prostate patients, the gradient difference showed the best accuracy. In the clinical applications, registrations starting with the mutual information followed by the gradient difference may provide the best accuracy and the most robustness.

A Novel System for the 3-D Reconstruction of the Human Spine and Rib Cage From Biplanar X-Ray Images

The main objective of this study was to develop a 3-D X-ray reconstruction system of the spine and rib cage for an accurate 3-D clinical assessment of spinal deformities. The system currently used at Sainte-Justine Hospital in Montreal is based on an implicit calibration technique based on a direct linear transform (DLT), using a sufficiently large rigid object incorporated in the positioning apparatus to locate any anatomical structure to be reconstructed within its bounds. During the time lapse between the two successive X-ray acquisitions required for the 3-D reconstruction, involuntary patient motion introduce errors due to the incorrect epipolar geometry inferred from the stationary object. An approach using a new calibration jacket and explicit calibration algorithm is proposed in this paper. This approach yields accurate results and compensates for involuntary motion occurring between X-ray exposures.

Three-Dimensional Reconstruction of the Scoliotic Spine and Pelvis From Uncalibrated Biplanar x-Ray Images

Current three-dimensional (3D) reconstruction methods based on explicit or implicit calibration procedure require a calibration object to generate calibrated x-rays for the 3D reconstruction of the human spine and the pelvis. However, to conduct retrospective studies where no 3D technology is available, 3D reconstruction must be performed from x-ray images where no calibration object was used. The current state of the art offers a variety of methods to obtain a personalized 3D model of a patient's spine, however, none have presented a clinically proven method which allows a 3D reconstruction using uncalibrated x-rays. The main objective of this study was to propose a self-calibration method using only the anatomic content of the x-ray images and evaluate its clinical feasibility on uncalibrated x-ray images for the 3D reconstruction of the scoliotic spine and pelvis. The rationale for proposing a 3D reconstruction method from uncalibrated x-rays is to allow access to 3D evaluation of spinal deformities in any standard clinical setup and to enable the conduct of retrospective studies of any kind. To assess the validity of the 3D reconstructions yielded by the proposed algorithm, a clinical study using 60 pairs of digitized x-rays of children was conducted. The mean age for this group of 60 patients was of 14+/-3 (range 8 to 18) years old. All the children in the study group had scoliosis, with an average Cobb angle on the frontal plane of 25 degrees (range 3 to 70 degrees). For each case, a 3D reconstruction of the spine and pelvis was obtained using both explicit and self-calibration methods, from calibrated and uncalibrated x-rays, respectively. Results show that 3D reconstructions obtained with the proposed method from uncalibrated x-ray images yield- geometrical models that exhibit insignificant differences for 2D and 3D clinical indices commonly used in the evaluation of spinal deformities. This allows a 3D clinical assessment of scoliotic deformities from standard x-rays without the need for calibration, and providing access to this technology in any clinical setup and allowing to perform retrospective studies, which were previously impossible.

Dose distribution of modified heyman packing

Introduction. One of the treatment modalities of brachytherapy of endometrial carcinomas is the modified Heyman packing technique.The aim of the study is to assess the dose distributions of regular arrangements of modified Heyman packings. Materials and Methods. We reconstructed the catheters with biplane X-ray images and optimised the dose distribution with defining‘dose points’ the uterine wall thickness apart from the outermost left and right catheters. We fitted the reconstructed catheters with the diagnostic sagittal MR scan obtained prior to the first insertion. We checked the dose distribution defining ‘patients points’ on sagittal contour of the uterus. Results and Conclusions. The treatment plans optimised ‘on dose points and geometry’ resulted in a satisfactory dose distribution, however systematic overdosed and under-dosed regions have been experienced.

A computer-aided training system for pedicle screw implantation

In this research, we propose an intelligent, computer-assisted training system for pedicle screw implantation in spine surgery. Based on the biplane X-ray imaging of a pre-drilled saw bone, spatial coordinate correlations between the physical saw bone and the 3D digitizer built an off-line training environment. A senior spine surgeon prepares the pre-drill position as a standard and the trainee used the 3D digitizer to approach the referential standard. The techniques developed in this system involve X-ray imaging rectification, registration, image processing, imaging dilation and erosion, biplane calibration, and spatial geometric transformation, which will be a pioneer study of further clinical application. The position accuracy of the guiding system is within 1 mm, and angular accuracy is within 1.5°, which may meet the basic surgical requirements for lumbar, thoracic and even cervical spine.

Accurate 3D reconstruction of complex blood vessel geometries from intravascular ultrasound images: in vitro study

We present a technique that accurately reconstructs complex three dimensional blood vessel geometry from 2D intravascular ultrasound (IVUS) images. Biplane x-ray fluoroscopy is used to imagethe ultrasound catheter tip at a few key points along its path as the catheter is pulled through the blood vessel. An interpolating spline describes the continuous catheterpath. The IVUS images are located orthogonal to the path, resulting in a non-uniform structured scalar volume of echo densities. Isocontour surfaces are used to view the vessel geometry, while transparency and clipping enable interactive exploration of interior structures. The two geometries studied are a bovine artery vascular graft having U-shapeand a constriction, and a canine carotid artery having multiple branches and a constriction. Accuracy of the reconstructions is established by comparing the reconstructions to (1) silicone moulds of the vessel interior, (2) biplane x-ray images, and (3) the original echo images. Excellent shape and geometry correspondence was observed in both geometries. Quantitative measurements made at key locations of the 3D reconstructions also were in good agreement with those made in silicone moulds. The proposed technique is easily adoptable in clinical practice, since it uses x-rays with minimal exposure and existing IVUS technology.

Self-calibration of a biplane X-ray imaging system for an optimal three dimensional reconstruction

The purpose of this paper is to elaborate a three dimensional (3D) reconstruction method, using biplane X-ray angiograms acquired daily by the clinician, without any special calibration procedure during the X-ray examination. The absolute geometry of the X-ray imaging system is determined by an iterative procedure based on the minimization of the mean square distance between observed and analytical projections of a set of reference points identified by the clinician on the simultaneous pair of images. Once the geometry of the imaging system is found the 3D structure of interest is retrieved from classical methods of binocular stereovision. This 3D information is a prerequisite for an accurate evaluation of the degree of severity of a vascular structure or motion anomaly and therefore, for establishing an appropriate diagnosis. The proposed 3D reconstruction method is validated on synthetic and real data and is shown to perform robustly and accurately in the presence of noise. The method should be particularly useful in clinical applications as it needs very little intervention from the clinician.

Recognition and storage of metal heart marker position from biplane X-ray images at video rates.

We have developed a semiautomatic microcomputer-based instrument for recording the three-dimensional positions of metal heart markers from biplane X-ray images at 60 frames/s. This instrument eliminates the need for film processing and tedious digitizing by human operators. Markers are recognized electronically on each video line using criteria of density changes (edge detection), size, and location. Only the X-Y or Z-Y location of each marker is stored. This transformation of the gray scale image into a list of coordinates achieves a data compression of 250 fold. A small fast memory and a second large one provide an effective slowing of the high peak rates of the marker location data. This buffering allows the marker coordinates to be permanently stored on a floppy disk for later analysis. Four s of data can be stored in one burst when 20 markers are used. The instrument was designed to measure the pumping action of the heart through the calculation of instantaneous local strain, wall thickness, and chamber volume. This paper compares alternate recognition strategies and storage methods.

Calculation of right and left cardiac ventricular volumes. Method using standard computer equipment and biplane angiocardiograms.

A method has been described for the digital computer calculation of intracardiac ventricular volumes from orthogonal biplane x-ray images. It is directly applicable to both left and right ventricles and uses equipment commonly found in medium size computer centers. Validation of the method is presented using data from geometrical shapes and casts of human ventricular cavities.