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At least 1,099 records · Page 61Linked to original sources
PubMed2003

Can PET provide the 3D extent of tumor motion for individualized internal target volumes? A phantom study of the limitations of CT and the promise of PET.

PURPOSE: To characterize the limitations of fast, spiral computed tomography (CT) when imaging a moving object and to investigate whether positron emission tomography (PET) can predict the internal target volume (ITV) and ultimately improve the planning target volume (PTV) for moving tumors. METHODS AND MATERIALS: To mimic tumors, three fillable spheres were imaged while both stationary and during periodic motion using spiral CT and PET. CT- and PET-imaged volumes were defined quantitatively using voxel values. Ideal PTVs for each scenario were calculated. CT-based PTVs were generated using margins of 7.5, 10, and 15 mm to account for both organ motion and setup uncertainties. PET-based PTVs were derived with the assumption that motion was captured in the PET images and only a margin (7.5 mm) for setup errors was necessary. Comparisons between CT-based and PET-based PTVs with ideal PTVs were performed. RESULTS: CT imaging of moving spheres resulted in significant distortions in the three-dimensional (3D) image-based representations, and did not, in general, result in images well representative of either moving or stationary spheres. PET images were similar to the ideal capsular shape encompassing the sphere and its motion. In all cases, CT-imaged volumes were larger than that for the stationary sphere (range of excess volume from 0.4 to 29 cm(3) for stationary volumes of 2.14 to 172 cm(3)), but smaller than that for the true motion volume. PET-imaged volumes were larger than the true motion volume (difference from ideal ranged from 3 to 94 cm(3) for motion volumes of 1.2 to 243 cm(3)) and much larger than the stationary volume. Using CT data, geographic miss of some part of the ideal PTV occurred for 0 of 24 cases, 11 of 24 cases, and 18 of 24 cases using a 15-mm, 10-mm, and 7.5-mm margin, respectively. Geographic miss did not occur in any case for the PET-based PTV. The amount of "normal tissue" included in CT-based PTVs was dramatically greater than that included in PET-based PTVs. CONCLUSION: Fast CT imaging of a moving tumor can result in poor representation of the time-averaged position and shape of the tumor. PET imaging can provide a more accurate representation of the 3D volume encompassing motion of model tumors and has potential to provide patient-specific motion volumes for an individualized ITV.

Artifacts↗
PubMed1998

Continuous passive motion following metacarpophalangeal joint arthroplasty.

To determine whether a postoperative rehabilitation protocol incorporating continuous passive motion would increase the total range of motion obtained 6 months following silicone interposition arthroplasty of the metacarpophalangeal joints in patients with rheumatoid arthritis, a prospective trial randomizing patients to receive either continuous passive motion or the standard dynamic splint protocol (modified Madden protocol) was undertaken. Fifteen hands (60 joints) were treated with the modified Madden protocol and 10 hands (40 joints) had continuous passive motion. The mean 6-month postoperative range of motion was 7 degrees in the modified Madden cohort compared with 39 degrees in the continuous passive motion cohort, representing an improvement of 22 degrees in the modified Madden cohort compared with an improvement of only 5 degrees in the continuous passive motion cohort. Residual ulnar deviation 8 degrees vs 12 degrees and grip strength (2.3 kgf v 3.7 kgf) were both lower in the continuous passive motion cohort. Incorporation of the continuous passive motion machine in the postoperative rehabilitation protocol does not offer sufficient advantages to justify the added costs.

Adult↗
PubMed2003

Disorders of motion and depth.

Damage to the human homologue of area MT produces a motion perception deficit similar to that found in the monkey with MT lesions. Even temporary disruption of MT processing with transcranial magnetic stimulation can produce a temporary akinetopsia [127]. Motion perception deficits, however, also are found with a variety of subcortical lesions and other neurologic disorders that can best be described as causing a disconnection within the motion processing stream. The precise role of these subcortical structures, such as the cerebellum, remains to be determined. Simple motion perception, moreover, is only a part of MT function. It undoubtedly has an important role in the perception of depth from motion and stereopsis [112]. Psychophysical studies using aftereffects in normal observers suggest a link between stereo mechanisms and the perception of depth from motion [9-11]. There is even a simple correlation between stereo acuity and the perception of depth from motion [128]. Future studies of patients with cortical lesions will take a closer look at depth perception in association with motion perception and should provide a better understanding of how motion and depth are processed together.

Alzheimer Disease↗
PubMed2002

Brain Areas Active during Visual Perception of Biological Motion.

Theories of vision posit that form and motion are represented by neural mechanisms segregated into functionally and anatomically distinct pathways. Using point-light animations of biological motion, we examine the extent to which form and motion pathways are mutually involved in perceiving figures depicted by the spatio-temporal integration of local motion components. Previous work discloses that viewing biological motion selectively activates a region on the posterior superior temporal sulcus (STSp). Here we report that the occipital and fusiform face areas (OFA and FFA) also contain neural signals capable of differentiating biological from nonbiological motion. EBA and LOC, although involved in perception of human form, do not contain neural signals selective for biological motion. Our results suggest that a network of distributed neural areas in the form and motion pathways underlie the perception of biological motion.

Brain Mapping↗
PubMed2000

Coherent global motion in the absence of coherent velocity signals.

It is widely believed that form and motion are analysed separately in mammalian visual systems. Form is confined within a stream that projects ventrally from V1 to the inferotemporal cortex, and motion within a stream that projects more dorsally, to the posterior parietal cortex [1] [2] [3] [4] [5] [6] [7]. Current descriptions suggest that there is little contact between the two streams until the products of their separate analyses are bound together at a late (and still unidentified) stage in perception [3] [8] [9] [10]. There are, however, indications that form and motion signals may interact [11], and that form signals, streaks derived from motion, may assist in the analysis of its direction [12]. Lennie [13] proposes that all image attributes, form and motion included, remain intimately coupled within the same retinotopic map at all stages of visual analysis. Here we show that form, independent of motion, can give coherence to incoherent motion. Sequences of Glass patterns [14] built to a common global rule are devoid of coherent motion signals, but they produce motion consistent with the global rule for form, not with the random velocity components of the pattern sequence.

Animals↗
PubMed1997

Phantom motion after effects--evidence of detectors for the analysis of optic flow.

BACKGROUND: Electrophysiological recording from the extrastriate cortex of non-human primates has revealed neurons that have large receptive fields and are sensitive to various components of object or self movement, such as translations, rotations and expansion/contractions. If these mechanisms exist in human vision, they might be susceptible to adaptation that generates motion aftereffects (MAEs). Indeed, it might be possible to adapt the mechanism in one part of the visual field and reveal what we term a 'phantom MAE' in another part. RESULTS: The existence of phantom MAEs was probed by adapting to a pattern that contained motion in only two non-adjacent 'quarter' segments and then testing using patterns that had elements in only the other two segments. We also tested for the more conventional 'concrete' MAE by testing in the same two segments that had adapted. The strength of each MAE was quantified by measuring the percentage of dots that had to be moved in the opposite direction to the MAE in order to nullify it. Four experiments tested rotational motion, expansion/contraction motion, translational motion and a 'rotation' that consisted simply of the two segments that contained only translational motions of opposing direction. Compared to a baseline measurement where no adaptation took place, all subjects in all experiments exhibited both concrete and phantom MAEs, with the size of the latter approximately half that of the former. CONCLUSIONS: Adaptation to two segments that contained upward and downward motion induced the perception of leftward and rightward motion in another part of the visual field. This strongly suggests there are mechanisms in human vision that are sensitive to complex motions such as rotations.

Afterimage↗
PubMed1998

Temporal precision of the encoding of motion information by visual interneurons.

BACKGROUND: There is much controversy about the timescale on which neurons process and transmit information. On the one hand, a vast amount of information can be processed by the nervous system if the precise timing of individual spikes on a millisecond timescale is important. On the other hand, neuronal responses to identical stimuli often vary considerably and stochastic response fluctuations can exceed the mean response amplitude. Here, we examined the timescale on which neural responses could be locked to visual motion stimuli. RESULTS: Spikes of motion-sensitive neurons in the visual system of the blowfly are time-locked to visual motion with a precision in the range of several tens of milliseconds. Nevertheless, different motion-sensitive neurons with largely overlapping receptive fields generate a large proportion of spikes almost synchronously. This precision is brought about by stochastic rather than by motion-induced membrane-potential fluctuations elicited by the common peripheral input. The stochastic membrane-potential fluctuations contain more power at frequencies above 30-40 Hz than the motion-induced potential changes. A model of spike generation indicates that such fast membrane-potential changes are a major determinant of the precise timing of spikes. CONCLUSIONS: The timing of spikes in neurons of the motion pathway of the blowfly is controlled on a millisecond timescale by fast membrane-potential fluctuations. Despite this precision, spikes do not lock to motion stimuli on this timescale because visual motion does not induce sufficiently rapid changes in the membrane potential.

Action Potentials↗
PubMed1996

Effects of tomographic motion, slice thickness, and object thickness on film density.

The experiment used the computer-aided CommCat model IS 2000 tomographic machine (Imaging Sciences International, Roebling, N.J.). The objective of the experiment was to study the influence of tomographic tube motion, tomographic slice thickness, and object thickness on film density. The experiment was conducted by x-radiating an aluminum step-wedge placed along the x-axis. Exposures were made for different tube motions and for different slice thicknesses. In linear horizontal and linear vertical motions, an increased slice thickness decreased film density. Slice thickness had a stronger effect on film density when the object to be x-radiated was thinner. In circular, elliptical, spiral, and hypocycloidal motions, changes in slice thickness had no noticeable effect on film density because the manufacturer had programmed the machine to produce approximately similar exposure times by increasing the x-ray tube velocity thickness had a greater effect on film density for circular, elliptical, spiral, and hypocycloidal tube motions than for linear horizontal and linear vertical tube motions. Clinical observation showed that except for the linear vertical motion (motion that was oriented in the same direction as that of the tube travel) all other motions produced a zone of diffusion along the edges of the steps of the step-wedge. An increase in slice thickness had an effect on film density. Slice thickness had a noticeable effect on film density in linear but not in multidirectional tomography. Object thickness had a greater effect on film density in multidirectional than in linear tomography.

Absorptiometry, Photon↗
PubMedDate not supplied

Direction repulsion in motion transparency.

A series of experiments investigated perceived direction of motion and depth segregation in motion transparency displays consisting of two planes of dots moving in different directions. Direction and depth judgments were obtained from human observers viewing these "bi-directional" animation sequences with and without explicit stereoscopic depth information. We found that (1) misperception of motion direction ("direction repulsion") occurs when two spatially intermingled directions of motion are within 60 deg of each other; (2) direction repulsion is minimal at cardinal directions; (3) perception of two directions of motion always results in separate motion planes segregated in depth; and (4) stereoscopic depth information has no effect on the magnitude of direction repulsion, but it does disambiguate the depth relations between motion directions. These results are developed within the context of a two-stage model of motion transparency. On this model, motion directions are registered within units subject to inhibitory interactions that cause direction repulsion, with the outputs of these units pooled within units selective for direction and disparity.

Adaptation, Ocular↗
PubMed1977

Relation of split apparent motion to metacontrast.

The apparent suppression of the target in metacontrast is often accompanied by "split" apparent motion. In Experiments 1, 4, 5, and 6 "neighboring stimuli" (similar to and flanking the mask stimuli) were added to the display, and subjects rated both metacontrast and split motion. Under some conditions, both split motion and metacontrast were completely eliminated (Experiment 1), supporting the assumption that apparent motion is necessary for metacontrast. However, under other conditions, neighboring stimuli caused a much stronger depression of metacontrast than of split motion (Experiments 4 and 5), sometimes even enhancing the latter (Experiment 6), supporting the assumption that the mechanisms underlying the two phenomena are essentially independent. Further, peripheral presentation and close spacing of target and mask with no neighboring stimuli (Experiments 2 and 3) gave strong metacontrast while completely eliminating split motion, showing clearly that apparent motion is not necessary for metacontrast. Results are interpreted in terms of a "fusion" process underlying metacontrast and a "direction-sensitive unit" underlying apparent motion. Interactions between these two processes that might account for the common co-occurrence of motion and metacontrast are proposed.

Fixation, Ocular↗
PubMed1992

Neural correlates of perceptual motion coherence.

The motions of overlapping contours in a visual scene may arise from the physical motion(s) of either a single or multiple surface(s). A central problem facing the visual motion system is that of assigning the most likely interpretation. The rules underlying this perceptual decision can be explored using a visual stimulus formed by superimposing two moving gratings. The resultant percept is either that of a single coherently moving 'plaid pattern' (coherent motion) or of the two component gratings sliding noncoherently across one another (noncoherent motion). When plaid patterns are configured to mimic one transparent grating overlying another, the percept of noncoherent motion dominates. We now report that neurons in the visual cortex of rhesus monkeys exhibit changes in direction tuning that parallel this perceptual phenomenon: sensitivity to the motions of the component gratings is enhanced under conditions that favour the perception of noncoherent motion. These results challenge models of cortical visual processing that fail to take into account the contribution of figural image segmentation cues to the analysis of visual motion.

Animals↗
PubMed1995

Two stages of visual processing for radial and circular motion.

As we move through our environment, the flow of the deforming images on our retinae provides rich information about ego motion and about the three-dimensional structure of the external world. Flow-fields comprise five independent components, including radial and circular motion. Here we provide psychophysical evidence for the existence of neural mechanisms in human vision that integrate motion signals along these complex trajectories. Signal-to-noise sensitivity for discriminating the direction of radial, circular and translational motion increased predictably with the number of exposed sectors, implying the existence of specialized detectors that integrate motion signals of different directions from different locations. However, contrast sensitivity for complex motion did not increase greatly with sector number, implying that the specialized detectors are preceded by a first stage of local-motion mechanisms that impose a contrast threshold. These findings fit well with recent electrophysiological evidence in monkey showing that whereas motion-sensitive neurons in primary visual cortex respond best to local translation, many neurons in the medial superior temporal cortex have large receptive fields tuned to radial, circular or spiral motion.

Contrast Sensitivity↗
PubMed1998

Visual search for motion-in-depth: stereomotion does not 'pop out' from disparity noise.

In a visual search task, targets defined by motion or binocular disparity stand out effortlessly from stationary distractors ('pop-out'), suggesting that target and distractors are processed by different neural mechanisms. We used pop-out to explore whether motion directly toward or away from the observer (z-motion) is detected using binocular motion cues. A target moving laterally (x-motion) popped out amid stationary distractors with binocular disparity, but z-motion did not pop out. However, a small x-motion added to the target's z-motion caused it to pop out. We therefore suggest that the visual system may not be specifically sensitive to binocular motion differences.

Artifacts↗
PubMed2002

Pattern-motion responses in human visual cortex.

Physiological models of visual motion processing posit that 'pattern-motion cells' represent the direction of moving objects independent of their particular spatial pattern. We performed fMRI experiments to identify neuronal activity in the human brain selective for pattern motion. A protocol using adaptation to moving 'plaid' stimuli allowed us to separate pattern-motion responses from other types of motion-related activity within the same brain structures, and revealed strong pattern-motion selectivity in human visual area MT+. Reducing the perceptual coherence of the plaids yielded a corresponding decrease in pattern-motion responsivity, providing evidence that percepts of coherent motion are closely linked to the activity of pattern-motion cells in human MT+.

Adult↗
PubMed2001

Pattern and component motion selectivity in cortical area PMLS of the cat.

Visual motion perception is one of the most prominent functions performed by the mammalian cerebral cortex. The moving images are commonly considered to be processed in two stages. The first-stage neurons are sensitive to the motion of one-dimensional orientated components, and their outputs are combined at the second stage to perceive the global motion of the whole pattern. Alternatively, the pattern motion may be signalled by monitoring a distinctive feature of the image, such as a line-end or a corner. In the present study, a series of 'random-line' patterns were used to measure the direction-tuning responses of 138 neurons in the posteromedial lateral suprasylvian area of the cat. The novel stimuli comprised identical thin line segments, with a length : width ratio no less than 10 : 1, which were moved perpendicularly or obliquely to their common orientation during the recordings. When the component lines were much shorter than the size of receptive field, the majority of cells were selective to the direction of pattern motion while only a small subset was sensitive to the direction of component motion. However, the response profiles of most cells became more component-motion selective with the increment of orientation element in stimulus by elongating the component lines in the patterns. These findings imply that the two-stage theory might be incomplete for modelling the visual motion analysis. Even at relatively low levels of the visual system, some kind of nonorientation-based processing may coexist with the orientation-sensitive processing in a dynamic competition, where one rises as the other falls depending upon the strength of the orientation element in the stimulus, so that under some circumstances it becomes possible to signal the veridical direction of pattern motion.

Action Potentials↗
PubMed1999

Prophylactic ondansetron for post-operative emesis: meta-analysis of its effectiveness in patients with and without a previous history of motion sickness.

The post-operative anti-emetic efficacy of 4 and 8 mg of ondansetron in adult patients with and without a previous history of motion sickness (PHMS) was assessed by meta-analysis. MEDLINE and EMBASE databases were searched for randomized placebo-controlled trials evaluating the anti-emetic effectiveness of ondansetron in a 24-h period. In the 49 studies found, a further selection was with respect to those studies that noted the patient's previous history of motion sickness. Twelve trials involving 2122 patients; 446 previous history of motion sickness(+) patients and 1676 previous history of motion sickness(-) patients met the selection criteria. The dose of 4 mg ondansetron was 71.5% more effective in previous history of motion sickness(+) than in previous history of motion sickness(-) patients. For the 8 mg dose, the odds ratios (95% CI) were: previous history of motion sickness(+) = 3.11 (1.40-6.93) and previous history of motion sickness(-) = 2.08 (1.35-3.21). The calculated number needed to treat was also more favourable in previous history of motion sickness(+) patients for both doses of ondansetron, demonstrating a higher effectiveness in this subgroup of patients.

Antiemetics↗
PubMed2000

Mechanisms of human motion perception: combining evidence from evoked potentials, behavioural performance and computational modelling.

Based on single cell recordings in monkey, it has been suggested that neural activity can be related directly to psychophysically measured threshold behaviour. Here, we investigated in humans whether evoked potentials correlate with behavioural measurements like discrimination thresholds and reaction time. Subjects were asked to report the perceived direction of object motion stimuli which contained variable amounts of coherent motion. Simultaneously, we recorded evoked potentials with a multielectrode array, or measured the reaction time. We show here that motion coherence had a strong influence on both amplitude and latency of the evoked potential. Stronger motion signals evoked stronger and faster cortical responses. The latency reduction of the motion onset response with increasing coherence correlated very well with the concurrent decrease in reaction time. Taken together, these results suggest that temporal integration is an important step in analysing motion signals to generate a reliable behavioural response. We stimulated a two-dimensional array of correlation-type motion detectors with the same motion sequences, and analysed the distribution of local motion signals according to signal detection theory. Performance resembled that of human subjects when the decision strategy was optimized so as to exclude small signals and, in particular, when the ideal observer had some knowledge about a region of interest in which the object was to be expected.

Cerebral Cortex↗
PubMed1999

The effect of thumb metacarpophalangeal ulnar collateral ligament attachment site on joint range of motion: an in vitro study.

Although reconstruction of the torn thumb metacarpophalangeal (MCP) joint ulnar collateral ligament (UCL) has been shown to reduce symptoms, final joint motion may be different from that of the uninjured state. It was hypothesized that nonanatomic repositioning of the UCL might affect joint motion; therefore, the effect of UCL attachment site on MCP range of motion was investigated. The UCL and MCP joint capsule were visualized in each of 8 fresh cadaveric hands without otherwise disrupting the joint. The centers of the ligament attachments were marked with pins and each specimen was mounted on a testing frame capable of applying loads through the flexor and extensor tendons. After measuring the flexion, extension, and radial and ulnar deviation ranges of motion of the intact specimen, the origin of the ligament (on the metacarpal) and an attached bone block were elevated and repositioned 2 mm proximal and 2 mm palmar and range of motion was tested. The origin was reattached in its anatomic location and the insertion of the ligament was similarly elevated and displaced 2 mm in distal, dorsal, and palmar directions. Compared with the intact joint, palmar placement of the UCL origin on the metacarpal increased radial deviation (from a mean of 18 degrees to a mean of 27 degrees); proximal placement of the origin decreased it (from 18 degrees to 10 degrees). Similarly, dorsal placement of the UCL insertion on the phalanx increased radial deviation (from 18 degrees to 25 degrees) and distal positioning of the insertion decreased it (from 18 degrees to 11 degrees). Relative to intact joint flexion range of motion (mean, 57 degrees), distal placement of the UCL phalangeal insertion restricted motion (mean, 47 degrees), as did palmar placement (mean, 48 degrees). Extension and ulnar deviation motions were unaffected by ligament attachment position. This study demonstrates that nonanatomic reconstruction of the UCL alters normal MCP joint range of motion.

Biomechanical Phenomena↗