Effects Of Patient Motion Research Articles

How Do Classic (Static) RSA and Patient Motion Artifacts Affect the Assessment of Migration of a TKA Tibial Component? An In Vitro Study.

Classic (static) Roentgen stereophotogrammetric analysis (RSA) is the current gold standard to assess, in vivo, the migration of total joint arthroplasty components. To prevent potential patient motion artifacts during the acquisition of paired radiostereometric images, images must be taken by simultaneously firing both X-ray tubes. However, the influence of nonsynchronized RSA paired images or patient motion artifacts on the precision of RSA and the assessment of implant migration is not well understood. We assessed (1) the effect of possible patient motion on the precision of RSA and (2) apparent differences in implant migration among axes (in-plane and out-of-plane translations and in-plane and out-of-plane rotations) of possible motion artifacts. Radiographs of two tibial knee arthroplasty components, each fixed in two bone-implant models as a customized phantom, were taken in a uniplanar measurement setup. We evaluated both model-based (implant models from reversed engineering) and marker-based (additional attached implant markers) RSA approaches. Between the simulated reference and follow-up examinations, we used one of the bone-implant models to simulate patient motion and the other to simulate no patient motion in parallel. Two defined protocols were followed for each of the bone-implant models: no-motion and simulated motion protocols. RSA image pairs were analyzed using a model-based RSA software package (MBRSA 4.1, RSA core ). Precision was calculated through repeat examinations, and migration of the two components was assessed for comparison of the components with each other. Measurements were taken along the medial-lateral and posterior-anterior axes for translations and around the cranial-caudal axis for rotations. The maximum total point motion was measured for comparison between the two components. The effect of simulated patient motion was generally small, except in the cranial-caudal axis, but the induced imprecision associated with motion was larger in model-based RSA than it was in marker-based RSA. The mean ± standard deviation values of precision in model-based RSA were 0.035 ± 0.015 mm, 0.045 ± 0.014 mm, and 0.049 ± 0.036 mm greater than those in marker-based RSA, in accordance with the simulated motion protocol in translations along the medial-lateral axis (0.018 ± 0.004 mm; p = 0.01), along the posterior-anterior axis (0.018 ± 0.007 mm; p = 0.003), and rotations around the cranial-caudal axis (0.017 ± 0.006 mm; p = 0.02). Apparent differences in implant migration were the greatest for the maximum total point motion. The maximum total point motion increased from 0.038 ± 0.007 mm for the no-motion protocol to 1.684 ± 0.038 mm (p < 0.001) for the simulated motion protocol in marker-based RSA, and from 0.101 ± 0.027 mm for the no-motion protocol to 1.973 ± 0.442 mm (p < 0.001) for the simulated motion protocol in model-based RSA, and was the worst-case scenario regarding patient motion artifacts. Patient motion exceeding 1 mm or 1° on nonsynchronized RSA images affects measurement errors regarding the detection of migration of a tibial component. In clinical RSA studies, the effect of patient motion on the assessment of implant migration should be of particular concern, even if clinical RSA systems have acceptable precision. Specially trained radiographers are crucial for correctly acquiring radiographs, especially when simultaneous radiography exposures are not electronically automated. In general, RSA requires synchronized image acquisition, and this should be the state-of-the-art. In clinical RSA studies, precision assessed by repeat examinations may not be reliable using the current standards that are widely used in radiology departments. When assessing implant migration for reliability, comparison of the maximum total point motion between the tested (simulated motion) implant and baseline (no-motion) implant, as in this study, is advocated because of the accurate detection of patient motion artifacts.

Simple image intensity compensation (SIMIC) method prior to application of distortion correction algorithms in brain diffusion Tensor Magnetic Resonance Imaging: Validation test for two cost functions of distortion correction algorithms

The purpose of this study is to design a simple image intensity compensation SIMIC method prior to the application of a variety of cost functions for distortion correction in diffusion tensor imaging DTI. The synthetic dataset consists of each direction of diffusion weighted imaging DWI made by multiplication of nondiffusion weighted image b = 0 image and tensor matrices. We added the effects of patient motion and eddy current distortion using translation, rotation, scaling and shearing matrices. We calculated the b = 0 image of each direction from original DTI, inversely. A co-registration method was applied to the extracted b = 0 images of each direction based on the original b = 0 image and then, the transformation matrices were generated and the original DTI were transformed using this transformation matrix. For the DTI distortion correction, two kinds of cost functions, normalized mutual information NMI and normalized cross-correlation NCC, were used. Visual assessments and quantitative measurements were used to evaluate the results. When using the NMI as a cost function, the quantitative results showed no significant differences between NMI and NMI with SIMIC method. However, there are significant differences compared with using the NCC as a cost function. Our study showed cost function for image distortion correction with SIMIC method improved the results both quantitatively and in terms of qualitative accuracy. This method may be helpful for DTI analysis and helpful for increasing accuracy. © 2015 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 25, 328-33, 2015

Automatic 3D registration of dynamic stress and rest (82)Rb and flurpiridaz F 18 myocardial perfusion PET data for patient motion detection and correction.

The authors aimed to develop an image-based registration scheme to detect and correct patient motion in stress and rest cardiac positron emission tomography (PET)/CT images. The patient motion correction was of primary interest and the effects of patient motion with the use of flurpiridaz F 18 and (82)Rb were demonstrated. The authors evaluated stress/rest PET myocardial perfusion imaging datasets in 30 patients (60 datasets in total, 21 male and 9 female) using a new perfusion agent (flurpiridaz F 18) (n = 16) and (82)Rb (n = 14), acquired on a Siemens Biograph-64 scanner in list mode. Stress and rest images were reconstructed into 4 ((82)Rb) or 10 (flurpiridaz F 18) dynamic frames (60 s each) using standard reconstruction (2D attenuation weighted ordered subsets expectation maximization). Patient motion correction was achieved by an image-based registration scheme optimizing a cost function using modified normalized cross-correlation that combined global and local features. For comparison, visual scoring of motion was performed on the scale of 0 to 2 (no motion, moderate motion, and large motion) by two experienced observers. The proposed registration technique had a 93% success rate in removing left ventricular motion, as visually assessed. The maximum detected motion extent for stress and rest were 5.2 mm and 4.9 mm for flurpiridaz F 18 perfusion and 3.0 mm and 4.3 mm for (82)Rb perfusion studies, respectively. Motion extent (maximum frame-to-frame displacement) obtained for stress and rest were (2.2 ± 1.1, 1.4 ± 0.7, 1.9 ± 1.3) mm and (2.0 ± 1.1, 1.2 ±0 .9, 1.9 ± 0.9) mm for flurpiridaz F 18 perfusion studies and (1.9 ± 0.7, 0.7 ± 0.6, 1.3 ± 0.6) mm and (2.0 ± 0.9, 0.6 ± 0.4, 1.2 ± 1.2) mm for (82)Rb perfusion studies, respectively. A visually detectable patient motion threshold was established to be ≥2.2 mm, corresponding to visual user scores of 1 and 2. After motion correction, the average increases in contrast-to-noise ratio (CNR) from all frames for larger than the motion threshold were 16.2% in stress flurpiridaz F 18 and 12.2% in rest flurpiridaz F 18 studies. The average increases in CNR were 4.6% in stress (82)Rb studies and 4.3% in rest (82)Rb studies. Fully automatic motion correction of dynamic PET frames can be performed accurately, potentially allowing improved image quantification of cardiac PET data.

Real-time axial motion detection and correction for single photon emission computed tomography using a linear prediction filter

We have developed an algorithm for real-time detection and complete correction of the patient motion effects during single photon emission computed tomography. The algorithm is based on a linear prediction filter (LPC). The new prediction of projection data algorithm (PPDA) detects most motions-such as those of the head, legs, and hands-using comparison of the predicted and measured frame data. When the data acquisition for a specific frame is completed, the accuracy of the acquired data is evaluated by the PPDA. If patient motion is detected, the scanning procedure is stopped. After the patient rests in his or her true position, data acquisition is repeated only for the corrupted frame and the scanning procedure is continued. Various experimental data were used to validate the motion detection algorithm; on the whole, the proposed method was tested with approximately 100 test cases. The PPDA shows promising results. Using the PPDA enables us to prevent the scanner from collecting disturbed data during the scan and replaces them with motion-free data by real-time rescanning for the corrupted frames. As a result, the effects of patient motion is corrected in real time.

Effects of patient motion during myocardial perfusion SPECT on linogram and sinogram by two iterative and FBP reconstruction methods

Patient motion during myocardial perfusion SPECT (MPS) produces images with artifactual defects. We studied the pattern and extent induced by simulated motion using different kinds of reconstruction methods. Methods: Movements were applied to raw projections with control images and were assessed by a panel of consultants. The motions were applied in 1–3 pixels, in X and Y planes, plus and minus directions in early, middle and late phases of imaging, in non-returning and returning patterns. The simulated images were reconstructed using OSEM and FBP methods. Myoquant Software interpreted all images visually and quantitatively. Using simulated motions, 288 different states were studied plus 2 original images. From 144 images in each method of reconstruction, 64 and 32 images were categorized as definitely abnormal (P<0.001). These were 51 and 45 images in±direction of motion (P=0.602) and 54 and 45 images in X and Y directions (P=0.340). The summed stress score (SSS) was 5.25 and 8.25 using FBP and OSEM (P=0.001), 6.90 and 6.60 in the±direction (P=0.727), and 5.98 and 7.52 in the X and Y directions of motion (P=0.07). OSEM has more profound effect on motion artifacts and this kind of reconstruction should not be used when patient motion is suspected.

Modeling the effects of patient motion in MRI data acquisition

Modeling the effects of patient motion in MRI data acquisition

The effect of patient motion on dose uncertainty in charged particle irradiation for lesions encircling the brain stem or spinal cord

A specialized charged-particle radiotherapy technique developed at Lawrence Berkeley Laboratory (LBL) is applied to patients with lesions abutting or surrounding the spinal cord or brain stem. This technique divides the target into two parts, one partially surrounding the critical structure (brain stem or spinal cord) and a second excluding the critical structure and abutting the first portion of the target. Compensators are used to conform the dose distribution to the distal surface of the target. This technique represents a novel approach in treating unresectable or residual tumors surrounding the spinal cord or brain stem. Since the placement of the patient with respect to beam-shaping devices is critical for divided-target treatments, a method for calculating dose distributions reflecting random patient motion is proposed, and the effects of random patient motion are studied for two divided-target patient examples. Dose-volume histograms and a normal-tissue complication probability model are used in this analysis. For the patients considered in this study, the normal-tissue-complication probability model predicts that random patient motion less than or equal to 0.2 cm is tolerable in terms of spinal cord complications.

Adaptive motion compensation in MR imaging without use of navigator echoes.

Retrospective correction of magnetic resonance (MR) image data to eliminate the effects of patient motion is possible with use of adaptive correction techniques. These methods require an accurate record of the motion that occurs during imaging. The authors evaluated whether motion information suitable for adaptive correction could be obtained from phase-encoded image data alone rather than from separate navigator echoes. Once such displacements were estimated from the image data, motion correction proceeded with use of the same algorithm used for the navigator echoes. The results show that image data alone can be used to effectively measure view-to-view displacements in phantoms, but external markers are required for accurate measurement during axial head imaging of patients.

Digital subtraction angiography using a temporal bandpass filter: associated patient motion properties.

A system for performing real-time digital angiography both intraarterially and intravenously is described. A filtering process, rather than mask subtraction produces diagnostic-quality angiograms using existing fluoroscopic x-ray systems operated continuously (30 frames/sec) at less than 70 kVp and 20 mA. The image degradation effects of patient motion (breathing, swallowing, sudden movement) are dealt with differently from a subtraction approach. Certain periodic patient motions can be accommodated without the need for postprocessing. An analysis of experimental and clinical results of intravenous angiographic studies is presented, with emphasis on patient motion properties.

THE SELECTION OF OPTIMUM MAMMOGRAPHY TECHNIC.

To be of utmost value to the radiologist, a roentgenogram of the breast should clearly demonstrate both tiny calcific deposits and fine soft-tissue structures in fat. This requires far greater resolution than most other x-ray examinations, because calcific specks 0.5 mm. and smaller are common, as are soft-tissue fibrils 2 mm. and less in diameter. Roentgenographic images must hence be extremely sharp. In addition, high-contrast technic is required, especially to highlight images of fine soft-tissue structures which are otherwise only marginally detectable. The two technics in widespread use were developed empirically (1, 2). More recently, our previous paper attempted to provide a basis of greater precision for designing and evaluating technics (3). Further investigation, however, has been required to accomplish this goal, along the following lines: (a) More extensive studies below 30 kvp (b) Tests with a beryllium-window tube (c) The effect of patient motion; estimate of permissible amplitude (d) Film development and equipment problems. This communication presents the results of recent studies of these questions, with the object of helping to determine the basis for selecting an optimum technic. Our approach is as follows: Part I. Discussion of the technical factors Part II. Experimental measurements Part III. Discussion and practical conclusions. Part I: Discussion of Technical Factors Table I lists several technical factors important in mammography. Analysis of the effect of each is made difficult by their large number and interdependence. Hence it is convenient to consider them in three separate groups. The first (marked with a dagger in Table I) includes general considerations common to all exposure technics. The second involves geometric considerations. The factors in both of these groups can be treated in a rather straightforward way, and their effects readily evaluated with a minimum of experimental work. They are considered below. The remaining factors relate to beam quality, film choice, and permissible patient motion. They are considered in Part II. General Considerations Common to all Technics 1. Viewing of roentgenograms: Roentgenographic contrast increases roughly in proportion to the density to which the film is exposed (Fig .1). For this reason, mammograms are best overexposed by ordinary standards. This procedure incidentally yields maximum information regarding internal and chest wall areas. The use of an adjustable high-intensity viewbox of the industrial type is advised, to penetrate dark areas on the film. In addition, it is important to mask out glare from the brighter chest wall portion of the roentgenogram. 2. Film Development4: The recommended time is five minutes at 68° F. for no-screen and AA-industrial films, while eight minutes are helpful in speeding up M-industrial film.