Purpose:
To allow for a purely image-based motion estimation and compensation in weight-bearing cone-beam computed tomography of the knee joint.
Methods:
Weight-bearing imaging of the knee joint in a ...standing position poses additional requirements for the image reconstruction algorithm. In contrast to supine scans, patient motion needs to be estimated and compensated. The authors propose a method that is based on 2D/3D registration of left and right femur and tibia segmented from a prior, motion-free reconstruction acquired in supine position. Each segmented bone is first roughly aligned to the motion-corrupted reconstruction of a scan in standing or squatting position. Subsequently, a rigid 2D/3D registration is performed for each bone to each of K projection images, estimating 6 × 4 × K motion parameters. The motion of individual bones is combined into global motion fields using thin-plate-spline extrapolation. These can be incorporated into a motion-compensated reconstruction in the backprojection step. The authors performed visual and quantitative comparisons between a state-of-the-art marker-based (MB) method and two variants of the proposed method using gradient correlation (GC) and normalized gradient information (NGI) as similarity measure for the 2D/3D registration.
Results:
The authors evaluated their method on four acquisitions under different squatting positions of the same patient. All methods showed substantial improvement in image quality compared to the uncorrected reconstructions. Compared to NGI and MB, the GC method showed increased streaking artifacts due to misregistrations in lateral projection images. NGI and MB showed comparable image quality at the bone regions. Because the markers are attached to the skin, the MB method performed better at the surface of the legs where the authors observed slight streaking of the NGI and GC methods. For a quantitative evaluation, the authors computed the universal quality index (UQI) for all bone regions with respect to the motion-free reconstruction. The authors quantitative evaluation over regions around the bones yielded a mean UQI of 18.4 for no correction, 53.3 and 56.1 for the proposed method using GC and NGI, respectively, and 53.7 for the MB reference approach. In contrast to the authors registration-based corrections, the MB reference method caused slight nonrigid deformations at bone outlines when compared to a motion-free reference scan.
Conclusions:
The authors showed that their method based on the NGI similarity measure yields reconstruction quality close to the MB reference method. In contrast to the MB method, the proposed method does not require any preparation prior to the examination which will improve the clinical workflow and patient comfort. Further, the authors found that the MB method causes small, nonrigid deformations at the bone outline which indicates that markers may not accurately reflect the internal motion close to the knee joint. Therefore, the authors believe that the proposed method is a promising alternative to MB motion management.
In cone-beam CT, involuntary patient motion and inaccurate or irreproducible scanner motion substantially degrades image quality. To avoid artifacts this motion needs to be estimated and compensated ...during image reconstruction. In previous work we showed that Fourier consistency conditions (FCC) can be used in fan-beam CT to estimate motion in the sinogram domain. This work extends the FCC to 3D cone-beam CT. We derive an efficient cost function to compensate for 3D motion using 2D detector translations. The extended FCC method have been tested with five translational motion patterns, using a challenging numerical phantom. We evaluated the root-mean-square-error and the structural-similarity-index between motion corrected and motion-free reconstructions. Additionally, we computed the mean-absolute-difference (MAD) between the estimated and the ground-truth motion. The practical applicability of the method is demonstrated by application to respiratory motion estimation in rotational angiography, but also to motion correction for weight-bearing imaging of knees. Where the latter makes use of a specifically modified FCC version which is robust to axial truncation. The results show a great reduction of motion artifacts. Accurate estimation results were achieved with a maximum MAD value of 708 μm and 1184 μm for motion along the vertical and horizontal detector direction, respectively. The image quality of reconstructions obtained with the proposed method is close to that of motion corrected reconstructions based on the ground-truth motion. Simulations using noise-free and noisy data demonstrate that FCC are robust to noise. Even high-frequency motion was accurately estimated leading to a considerable reduction of streaking artifacts. The method is purely image-based and therefore independent of any auxiliary data.
Recently, C-arm cone-beam CT systems have been used to acquire knee joints under weight-bearing conditions. For this purpose, the C-arm acquires images on a horizontal trajectory around the standing ...patient, who shows involuntary motion. The current state-of-the-art reconstruction approach estimates motion based on fiducial markers attached to the knee. A drawback is that this method requires calibration prior to each scan, since the horizontal trajectory is not reproducible. In this work, we propose a novel method, which does not need a calibration scan. For comparison, we extended the state-of-the-art method with an iterative scheme and we further introduce a closed-form solution of the compensated projection matrices. For evaluation, a numerical phantom and clinical data are used. The novel approach and the extended state-of-the-art method achieve a reduction of the reprojection error of 94% for the phantom data. The improvement for the clinical data ranged between 10% and 80%, which is followed by the visual impression. Therefore, the novel approach and the extended state-of-the-art method achieve superior results compared to the state-of-the-art method.
One of the most widely used techniques for the water content determination in food is Karl Fischer (KF) titration. The primary advantage with respect to methods based on loss of weight is its high ...selectivity to water. On the other hand, KF titration is only possible when water in food samples is freely available. Thus, a suitable sample preparation to release water completely has to be selected and done prior to the KF titration. Although KF titration itself is a fast method (1–2 min for a single analysis), the sample preparation step is time-consuming, e.g. 1–2 h when performing an external extraction. The use of a high-speed stirrer for internal homogenization, in addition to fast control algorithms in automatic KF titrators, offers a fast, quick and efficient alternative to more traditional sample preparation techniques. Sample preparation and stirring time can be considerably reduced, and auxiliary solvents can be avoided. The whole analysis is completely automated. In this contribution the use of high-speed homogenizers in KF titration will be discussed in detail.
Visual discomfort is a major problem for head-mounted displays and other stereo displays. One effect that is known to reduce visual comfort is double vision, which can occur due to high disparities. ...Previous studies suggest that adding artificial out-of-focus blur increases the fusional limits, where the left and right image can be fused without double vision. We investigate the effect of adding artificial out-of-focus blur on visual discomfort using two different setups. One uses a stereo monitor and an eye tracker to change the depth of focus based on the gaze of the user. The other one uses a video-see through head mounted display. A study involving 18 subjects showed that the viewing comfort when using blur is significantly higher in both setups for virtual scenes. However we can not confirm without doubt that the higher viewing comfort is only related to an increase of the fusional limits, as many subjects reported that double vision did not occur during the experiment. Results for additional photographed images that have been shown to the subjects were less significant. A first prototype of an AR system extracting a depth map from stereo images and adding artificial out-of-focus blur is presented.
► We examine test-retest-reliability, internal consistency and plasticity of tasks measuring inhibition-related functions. ► Most measures yield good test-retest-reliability and internal ...consistencies. ► No systematic within- and between-session changes are present. ► Therefore these measures are able to represent inhibition-related traits. ► Results are relevant for pathophysiological, genetic and pharmacological research.
This study investigated the internal reliability, temporal stability and plasticity of commonly used measures of inhibition-related functions. Stop-signal, go/no-go, antisaccade, Simon, Eriksen flanker, Stroop and Continuous Performance tasks were administered twice to 23 healthy participants over a period of approximately 11weeks in order to assess test–retest correlations, internal consistency (Cronbach’s alpha), and systematic between as well as within session performance changes. Most of the inhibition-related measures showed good test–retest reliabilities and internal consistencies, with the exception of the stop-signal reaction time measure, which showed poor reliability. Generally no systematic performance changes were observed across the two assessments with the exception of four variables of the Eriksen flanker, Simon and Stroop task which showed reduced variability of reaction time and an improvement in the response time for incongruent trials at second assessment. Predominantly stable performance within one test session was shown for most measures. Overall, these results are informative for studies with designs requiring temporally stable parameters e.g. genetic or longitudinal treatment studies.
This study addresses the relationship between trait impulsivity and inhibitory control, two features known to be impaired in a number of psychiatric conditions. While impulsivity is often measured ...using psychometric self-report questionnaires, the inhibition of inappropriate, impulsive motor responses is typically measured using experimental laboratory tasks. It remains unclear, however, whether psychometrically assessed impulsivity and experimentally operationalized inhibitory performance are related to each other. Therefore, we investigated the relationship between these two traits in a large sample using correlative and latent variable analysis. A total of 504 healthy individuals completed the Barratt Impulsiveness Scale (BIS-11) and a battery of four prepotent response inhibition paradigms: the antisaccade, Stroop, stop-signal, and go/no-go tasks. We found significant associations of BIS impulsivity with commission errors on the go/no-go task and directional errors on the antisaccade task, over and above effects of age, gender, and intelligence. Latent variable analysis (a) supported the idea that all four inhibitory measures load on the same underlying construct termed "prepotent response inhibition" and (b) revealed that 12% of variance of the prepotent response inhibition construct could be explained by BIS impulsivity. Overall, the magnitude of associations observed was small, indicating that while a portion of variance in prepotent response inhibition can be explained by psychometric trait impulsivity, the majority of variance remains unexplained. Thus, these findings suggest that prepotent response inhibition paradigms can account for psychometric trait impulsivity only to a limited extent. Implications for studies of patient populations with symptoms of impulsivity are discussed.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Purpose
Rotational coronary angiography enables 3D reconstruction but suffers from intra‐scan cardiac and respiratory motion. While gating handles cardiac motion, respiratory motion requires ...compensation. State‐of‐the‐art algorithms rely on 3D‐2D registration that depends on initial reconstructions of sufficient quality. We propose a compensation method that is applied directly in projection domain. It overcomes the need for reconstruction and thus complements the state‐of‐the‐art.
Methods
Virtual single‐frame background subtraction based on vessel segmentation and spectral deconvolution yields non‐truncated images of the contrasted lumen. This allows motion compensation based on data consistency conditions. We compensate craniocaudal shifts by optimizing epipolar consistency to (a) devise an image‐based surrogate for cardiac motion and (b) compensate for respiratory motion. We validate our approach in two numerical phantom studies and three clinical cases.
Results
Correlation of the image‐based surrogate for cardiac motion with the ECG‐based ground truth was excellent yielding a Pearson correlation of 0.93 ± 0.04. Considering motion compensation, the target error measure decreased by 98% and 69%, respectively, for the phantom experiments while for the clinical cases the same figure of merit improved by 46 ± 21%.
Conclusions
The proposed method is entirely image‐based and accurately estimates craniocaudal shifts due to respiration and cardiac contraction. Future work will investigate experimental trajectories and possibilities for simplification of the single‐frame subtraction pipeline.
According to intuitive concepts, ‘ease of articulation’ is influenced by factors like word length or the presence of consonant clusters in an utterance. Imaging studies of speech motor control use ...these factors to systematically tax the speech motor system. Evidence from apraxia of speech, a disorder supposed to result from speech motor planning impairment after lesions to speech motor centers in the left hemisphere, supports the relevance of these and other factors in disordered speech planning and the genesis of apraxic speech errors. Yet, there is no unified account of the structural properties rendering a word easy or difficult to pronounce.
To model the motor planning demands of word articulation by a nonlinear regression model trained to predict the likelihood of accurate word production in apraxia of speech.
We used a tree-structure model in which vocal tract gestures are embedded in hierarchically nested prosodic domains to derive a recursive set of terms for the computation of the likelihood of accurate word production. The model was trained with accuracy data from a set of 136 words averaged over 66 samples from apraxic speakers. In a second step, the model coefficients were used to predict a test dataset of accuracy values for 96 new words, averaged over 120 samples produced by a different group of apraxic speakers.
Accurate modeling of the first dataset was achieved in the training study (R2adj = .71). In the cross-validation, the test dataset was predicted with a high accuracy as well (R2adj = .67). The model shape, as reflected by the coefficient estimates, was consistent with current phonetic theories and with clinical evidence. In accordance with phonetic and psycholinguistic work, a strong influence of word stress on articulation errors was found.
The proposed model provides a unified and transparent account of the motor planning requirements of word articulation.
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Recent research using individual task settings suggests that a major problem in schizophrenia is a dysfunctional theory of mind system leading to false mental state attributions. However, if a more ...low-level deficit to integrate own and other's actions (action blindness) is present in schizophrenia is still unknown. Using a Social Simon task, we tested if schizophrenia patients have a deficit in self-other integration. Further, we tested for a possible genetic bias of this dysfunction by studying clinically unaffected first-degree relatives of schizophrenia patients. While schizophrenia patients showed no Social Simon effect, we found a reliable Social Simon effect in healthy participants and first-degree relatives of schizophrenia patients. Joint task performance differed statistically between patients and healthy controls. We did not find any differences in the size of the Social Simon effects of relatives and healthy controls. The present findings suggest that schizophrenia patients have severe problems with self-other integration, which may lead to problems in social interactions. Since first-degree relatives of schizophrenia patients showed a reliable Social Simon effect, the evidence for a genetic bias of this social dysfunction in schizophrenia however is weak.
► Social Simon task in schizophrenia patients. ► Test for a genetic bias. ► Defective self-other integration may explain problems with mentalizing.
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