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At least 1,135 records · Page 63Linked to original sources
PubMed2000

A lesion of cortical area V2 selectively impairs the perception of the direction of first-order visual motion.

Lesions of area MT/V5 in monkeys and its presumed homologue, the motion area, in humans impair motion perception, including the discrimination of the direction of global motion in random dot kinematograms. Here we report the results of similar tests on patient TF, who has a discrete and very small, unilateral infarct in the medial superior part of the right occipital cortex. Structural MRI, co-registered in software with a standardized human brain atlas, reveals that the lesion involves area V2. The patient was impaired in his retinotopically corresponding left lower quadrant on several motion tasks including discrimination in random dot kinematograms of direction, speed and motion-defined discontinuity. He was also impaired on tasks selectively involving first-order motion based on luminance contrast but not on second-order motion based on texture contrast. The results show that even though area MT/V5 is intact, motion perception is abnormal and, in particular, his perception of first-order motion is impaired.

Cerebral Infarction↗
PubMed2001

Cross-modal integration of auditory and visual motion signals.

Real-world moving objects are usually defined by correlated information in multiple sensory modalities such as vision and hearing. The aim of our study was to assess whether simultaneous auditory supra-threshold motion introduces a bias or affects the sensitivity in a visual motion detection task. We demonstrate a bias in the perceived direction of visual motion that is consistent with the direction of the auditory motion (audio-visual motion capture). This bias effect is robust and occurs even if the auditory and visual motion signals come from different locations or move at different speeds. We also show that visual motion detection thresholds are higher for consistent auditory motion than for inconsistent motion, provided the stimuli move at the same speed and are co-localised.

Acoustic Stimulation↗
PubMed2000

Hinged external fixation of the elbow: optimal axis alignment to minimize motion resistance.

OBJECTIVE: To establish an optimal single hinge axis position for application of hinged external fixation to the elbow joint. DESIGN: Cadaveric biomechanical investigation. SETTING: A customized motion transducer applied passive elbow motion to six cadaveric upper extremities. The instant rotation axis of the humero-ulnar articulation was determined from three-dimensional kinematic data acquired by an electromagnetic motion tracking system. For each specimen, an optimal fixator hinge position was calculated from these motion data. INTERVENTION: A prototype articulated external fixator was applied to the elbow, first with its hinge aligned along the computed optimal position. Then the fixator was mounted in sixteen distinct off-axis positions. MAIN OUTCOME MEASURE: Additional resistance to joint motion (in terms of energy) corresponding to deliberately introduced amounts of relative malalignment between the optimal elbow axis and the actual fixator hinge axis. RESULTS: Aligning the fixator hinge along the optimized axis position resulted in a minimal amount of energy (0.15 joules) needed to rotate the elbow through a prescribed range of motion. Malpositioning the hinge by ten millimeters caused up to ten times that amount of motion resistance. CONCLUSIONS: An optimal fixator hinge position can be determined to minimize the increase in motion resistance due to fixator application. The severely increased motion resistance associated with small amounts of malalignment between the fixator hinge and the anatomic elbow axis suggests the need for highly accurate fixator hinge application.

Cadaver↗
PubMed1994

Spinal motion after cervical fusion. In vivo assessment with roentgen stereophotogrammetry.

STUDY DESIGN: A roentgen stereophotogrammetric (RS) technique using metallic markers was used to determine in vivo three-dimensional (3-D) motion data in the post-operative cervical spine. Two patients were examined with RS following fusion for up to 12 months at scheduled intervals. OBJECTIVES: The study was designed to develop a technique and provide an in vivo assessment of the fusion process following surgery. Besides the researchers and surgeons, this type of information is of particular interest to the FDA and implant manufacturers. SUMMARY OF BACKGROUND DATA: The high accuracy of the roentgen stereophotogrammetric (RS) technique using metallic markers to predict displacements across body joints, including spinal joints, has been well established in the literature. Its applications in the lumbar region to assess the fusion process as a function of time following surgery have also been reported. Similar in vivo applications (and results) dealing with the cervical region are lacking. METHODS: A roentgen stereophotogrammetric (RS) technique using metallic markers was developed. Appropriate in vitro studies were undertaken to assess its accuracy for in vivo applications in the cervical spine region. Following this, three Vitallium beads were surgically implanted in anatomically appropriate positions in of each the exposed vertebrae of two patients at the time of surgery. The patients were followed with RS serially for 12 months after surgery at scheduled intervals. At each RS session, roentgen stereo pairs of the cervical spine in neutral, maximum voluntary flexion, and maximum voluntary extension were obtained using a biplanar radiographic system. The metallic beads on the radiographs were digitized using an in-house software package to determine vertebral motions across the fused segments. RESULTS: In patient 1 (atlantoaxial fusion), the flexion-extension range of rotational motion decreased with time while the corresponding AP translation at the fusion level increased from 6 mm at 3 months post-op to 13 mm at 6 and 12 months postoperatively. The abnormal AP translation at 6 months and beyond was evident on extension/extension lateral radiographs, but the AP translation at 3 months was not visually evident. In patient 2 (anterior discectomy and interbody fusion), motions of small magnitude were observed at the fused level in all three axes. These motions actually increased over the one year observation period, but were never large enough to be visually detectable on lateral extension/extension radiographs. Patient 2 had a good clinical result despite these small motions. CONCLUSIONS: Roentgen stereophotogrammetry may detect motion in the in vivo cervical spine with a sensitivity heretofore unavailable. In patient 1, we were able to detect motion before it was visually manifest. In patient 2, small motions were detected at the level of a successful anterior cervical fusion, the significance of which remain uncertain.

Atlanto-Axial Joint↗
PubMed1999

Motion analysis of cervical vertebrae during whiplash loading.

STUDY DESIGN: The motion of each cervical vertebra during simulated rear-end car collisions was analyzed. OBJECTIVES: To clarify the mechanism of zygapophysial joint injury during whiplash loading. SUMMARY OF BACKGROUND DATA: The zygapophysial joint is the suspected origin of neck pain after rear-end car collision. However, no studies have been conducted on the mechanisms of zygapophysial joint injuries. METHODS: Ten healthy male volunteers participated in this study. Subjects sat on a sled that glided backward on inclined rails and crashed into a damper at 4 km/kr. The motion of the cervical spine was recorded using cineradiography. Each vertebra's rotational angle and the instantaneous axes of rotation of the C5-C6 motion segments were quantified. These measurements implemented the template method. RESULTS: There were three distinct patterns of cervical spine motion after impact. In the flexion-extension group, C6 rotated backward before the upper vertebrae in the early phase; thus, the cervical spine showed a flexion position (initial flexion). After C6 reached its maximum rotational angle, C5 was induced to extend. As upper motion segments went into flexion, and the lower segments into extension, the cervical spine took an S-shaped position. In this position, the C5-C6 motion segments showed an open-book motion with an upward-shifted instantaneous axis of rotation. CONCLUSIONS: The cervical spine is forced to move from the lower vertebrae during rear-end collisions. This motion completely differs from normal extension motion and is probably related to the injury mechanism.

Accidents, Traffic↗
PubMed2001

Range of motion and lordosis of the lumbar spine: reliability of measurement and normative values.

STUDY DESIGN: Repeated measures for intratester reliability were performed. OBJECTIVES: To investigate the intratester reliability of a new measurement technique that evaluates lumbar range of motion in three planes using a pelvic restraint device, and to examine the reliability of lumbar lordosis measurement by inclinometer technique. Preliminary normative data on lumbar range of motion and lumbar lordosis were collected for comparison with the findings of previous studies. SUMMARY OF BACKGROUND DATA: Various noninvasive measurement methods have been developed for recording lumbar range of motion. However, pelvic movement was not effectively restricted during the use of these measurement techniques. The use of the pelvic restraint device to measure lumbar range of motion has not been investigated previously. Very few studies have investigated the reliability of quantifying lumbar lordosis by the inclinometer technique. METHODS: Normative values were measured in 35 healthy men, and 12 of these subjects were included for the reliability study. Pelvic motion was limited by the pelvic restraint device during lumbar range of motion measurement in standing. An inclinometer was used for evaluation of lumbar flexion, extension, lateral flexion, and lumbar lordosis, whereas a lumbar rotameter was used to measure axial rotation. RESULTS: Good intratester reliability was shown in the lumbar range of motion and lordosis measurement. Most of the intraclass correlation coefficient and Pearson's r values (accompanied with nonsignificant paired t tests) were greater than 0.9, and most of the intrasubject coefficients of variation were less than 10%. The values of lumbar range of motion in three planes and lumbar lordosis found in the current study were comparable with those from most of the previous studies on these measurements in the normal population. CONCLUSIONS: Inclinometer and lumbar rotameter measurements with the use of a pelvic restraint device are reliable for measuring lumbar spine range of motion. Use of the inclinometer technique to record lumbar lordosis also is a reliable measure.

Adult↗
PubMed2002

Neural space integrity of the lower cervical spine: effect of normal range of motion.

STUDY DESIGN: An experimental investigation of intervertebral foramen and spinal canal neural space integrity was performed throughout physiologic range of motion of the lower cervical spine in intact human cadaver specimens. OBJECTIVE: To investigate cervical positions that might place the neural tissues of the spine in heightened risk of injury. To meet this objective the following hypotheses were tested: 1) spinal canal integrity varies with specific normal range of motion positions of the lower cervical spine, and 2) intervertebral foramen integrity is dependent on and unique for different physiologic positions of the lower cervical spine. SUMMARY OF BACKGROUND DATA: Cervical spine injuries are frequently associated with compressive damage to neurologic tissues and consequently poor clinical outcomes. Neurologic injury typically occurs from disc, ligamentous, or bony occlusion of the spinal canal and intervertebral foraminal spaces dynamically during an injury event or with abnormal alignment and position after the injury event. Prior studies have shown pressure and geometric changes in cervical spine neural spaces in certain cervical spine positions. However, to the authors' knowledge, this is the first research effort aimed at elucidating the integrity of the cervical spine neural spaces throughout the normal physiologic range of motion. METHODS: The authors instrumented 17 fresh-frozen unembalmed cadaveric human cervical spines (C3-C7) with specially designed intervertebral foramen occlusion transducers and a spinal canal occlusion transducer. The specimens were loaded with pure bending moments to produce simulated physiologic motions of the lower cervical spine. The resulting occlusion profiles for the intervertebral foramen and spinal canal were recorded along with the 6-degree of freedom position of the cervical spine. Because these occlusion measurements describe the ability of the spine to preserve the space for the neural structures, the authors define this neuroprotective role of the vertebral column as neural space integrity. RESULTS: The range of motion developed experimentally in this study compared well with published reports of normal cervical motion. Thus, subsequent changes in neural space integrity may be regarded as resulting from normal human cervical spine motion. No significant change in the spinal canal space was detected for any physiologic motion; however, intervertebral foramen integrity was significantly altered in extension, ipsilateral bending, combined ipsilateral bending and extension, and combined contralateral bending with extension when compared with intact upright neutral position. CONCLUSIONS: This study defines the range of neural space integrity associated with simulated physiologic motion of the lower cervical spine in an experimental setting. This information may be useful in comparing neural space changes in pathologic conditions and may enhance refinement of neurologic injury prevention strategies.

Biomechanical Phenomena↗
PubMed2005

Intervertebral motion after incremental damage to the posterior structures of the cervical spine.

STUDY DESIGN: Compare intervertebral motion after incremental damage to posterior cervical structures in whole cadavers to motion in asymptomatic subjects. OBJECTIVE: Determine if damage to the posterior structures of the cervical spine can be detected by quantitative analysis of flexion-extension radiographs. SUMMARY OF BACKGROUND DATA: Simulated damage to the posterior structures of the cervical spine can change intervertebral motion, if intervertebral motion before damage is known. It is not known if intervertebral motion measured from flexion-extension radiographs can be used to detect damage to the posterior structures if motion before damage is not known. METHODS: Incremental injury to posterior ligaments and facet joints was simulated in 12 whole cadavers. Intervertebral motion was measured from flexion-extension images using validated and clinically applicable software. Measurements were compared to previously published measurements for asymptomatic subjects. RESULTS: Extensive damage could be simulated in all the cervical spines without intervertebral motion exceeding the 95% confidence limits for asymptomatic subjects. After sectioning all posterior ligaments, destroying both facet joints, and then sectioning the posterior longitudinal ligaments, intervertebral motion exceeded the 95% confidence intervals in 69% of the cadavers. Intervertebral shear decreased with incremental damage to posterior structures. CONCLUSIONS: Radiographic assessment of the cervical spine may not be sufficient to exclude even extensive damage to the posterior structures of the cervical spine.

Arthrography↗
PubMed2006

The effect of scoliosis fusion on spinal motion: a comparison of fused and nonfused patients with idiopathic scoliosis.

STUDY DESIGN: Movement analysis of spinal motion. OBJECTIVE: To compare spinal motion among females with normal spines, those with idiopathic scoliosis who had not had spinal fusion, and those who had undergone fusion for idiopathic scoliosis. SUMMARY OF BACKGROUND DATA: Previous reports have documented loss of spinal motion following fusion for idiopathic scoliosis in adolescents and adults. To our knowledge, comparison to control groups both with and without scoliosis that have not had spinal fusions has not been performed to date. METHODS: A total of 91 females between the ages of 15 and 28 years underwent computerized movement analysis. There were 34 fused patients, 32 unfused patients, and 25 healthy controls. The fused patients were divided into 3 groups: (1) 21 patients who had thoracic fusions that extended distally to T11, T12, or L1; (2) 6 patients with thoracic fusions ending at L2; and (3) 7 patients with thoracolumbar or lumbar fusions extending to L3 or L4. Marker triads were placed at C7-T1, T12-L1, and on the pelvis. Forward bend, extension, and left and right lateral bend were measured and divided into thoracic and lumbar motion. RESULTS: There was no difference in any motion between the control and unfused groups. There was overall 25% less total spinal motion in the surgical groups compared to the unfused group. Patients who had thoracic fusions had diminished thoracic motion, especially lateral bending, whereas those who had lumbar fusions had the least lumbar motion, particularly on forward bend and lateral bend maneuvers. There was no compensatory hypermobility of the unfused segments in the surgical group. CONCLUSIONS: Diminished spinal motion can be measured in patients who have had spinal fusions. Although stiffness in the operated curves should be expected, compensatory hypermobility in the unfused segments does not occur, resulting in a net loss of flexibility compared to controls.

Adolescent↗
PubMed2006

The effects of optical blur on motion and texture perception.

PURPOSE: The purpose of this study is to determine how decreased visual acuity affects performance on tasks of motion and texture perception. METHODS: Positive diopter lenses were used to match three subjects at five levels of decimal visual acuity (DVA) ranging from an uncorrected DVA of 1.6 to the lowest DVA of 0.2. Performance thresholds were determined at each acuity level for five different psychophysical tasks. The tasks assessed the perception of motion-defined form, global motion, maximum motion displacement (Dmax), texture-defined form, and global texture. RESULTS: Reducing visual acuity decreased performance on the tasks of motion-defined form identification, texture-defined form identification, and global texture integration. Performance on the Dmax task improved with a reduction in visual acuity. Performance on the global motion task was unaffected by changes in visual acuity. CONCLUSIONS: Visual acuity should be considered when interpreting the results of developmental or clinical studies of motion and texture perception. The only exception to this is global motion perception, at least when DVA is better than 0.2. The effect of blur on tasks of motion and texture perception may reflect the extent to which high spatial frequency information is required for performance on these tasks.

Humans↗
PubMedDate not supplied

Sixteen-slice multidetector computed tomography pulmonary angiography: evaluation of cardiogenic motion artifacts and influence of rotation time on image quality.

OBJECTIVE: To describe the site and severity of cardiogenic motion artifacts on 16-slice multidetector computed tomography (CT) angiograms of the pulmonary circulation and to determine the impact of the gantry rotation time on image quality. METHODS: Sixty-nine patients underwent nonelectrocardiographically gated 16-slice multidetector CT angiography of the pulmonary circulation with a rotation time of 0.5 second (group 1, n = 37) or 0.375 second (group 2, n = 32). All scans were prospectively analyzed for the presence of cardiogenic motion artifacts in the pulmonary arteries, defined as a blurring of the edges of the pulmonary arteries on lung window settings with or without an artifactual loss of enhancement in the arterial lumen on soft tissue windows ("pseudofilling defect"). In addition, the severity of pulmonary arterial blurring was recorded using a 4-point scale. RESULTS: Fifty-six patients (81%) had at least 1 pulmonary artery affected by cardiogenic motion artifacts. At the level of the central pulmonary arteries, movement artifacts responsible for a blurring of the arterial wall were present in 35 patients (51%), mainly observed at the level of the pulmonary trunk (n = 28, 41% of patients) and right main pulmonary artery (n = 23, 33% of patients); in 2 patients, motion artifact was responsible for a pseudoflap appearance within the arterial lumen (n = 2, 4% of patients). Motion artifacts at the level of lobar pulmonary arteries were noted only in the lower divisions of the lingula (n = 1, 1.5% of patients) and in the left lower lobe (n = 2, 3% of patients). At the level of the segmental pulmonary arteries, motion artifacts were most frequently found in the lower divisions of the left upper lobe (lingula) (n = 19, 27.5% of patients) and left lower lobe (n = 29, 42% of patients). At the subsegmental level, motion artifacts were most common in the lower divisions of the left upper lobe (lingula) (n = 30, 43.5% of patients) and left lower lobe (n = 35, 51% of patients). Pseudofilling defects were depicted at the segmental and subsegmental levels in 28 patients (41% of the study group), almost exclusively located in the lingula and left lower lobe. Cardiogenic motion artifacts were observed with a significantly lower frequency in group 2 (22 of 32 patients, 69%) than in group 1 (34 of 37 patients, 92%) (P = 0.0142), with a concurrent reduction in the frequency of pseudofilling defects identified in 20 patients (54%) in group 1 and in 8 patients (25%) in group 2 (P = 0.0142). CONCLUSION: The use of a 0.375-second rotation time enables significant reduction in the frequency of cardiogenic motion artifacts on 16-slice multidetector CT angiograms of the pulmonary circulation.

Adult↗
PubMed1996

On the elementary mechanism underlying secondary motion processing.

The movement of luminance-defined targets can be easily extracted by elementary motion detectors (EMDs) of the correlation type which often are referred to as Reichardt-detectors. In contrast to such 'primary motion', in 'secondary motion' the moving target is defined by more complex features, like changes in texture, flicker, or local contrast. Such stimulus attributes have to be extracted from the retinal intensity distribution by some nonlinear preprocessing, before they are fed into motion detectors. An intriguing case is the perception of the movement of the motion signal, as is present in theta motion, where an object moves in a different direction than the texture on its surface. A two-layer model of hierarchically organised EMDs has been postulated to account for such motion extraction. Other than for the first layer, the computational nature of the mechanism underlying motion processing in the second layer so far is a matter of speculation, and is therefore characterized here by means of computer simulations and psychophysical experiments. Random dot kinematograms were generated in which sinusoidally modulated vertical dot motion defined gratings, and coherence thresholds were measured for the direction discrimination of a horizontally travelling modulation function. This was done for a variety of spatial frequencies and speeds of the modulation sinusoid. Thresholds turn out to be lowest not for a particular speed, but for a fixed temporal frequency of the modulation function (about 1 cycle per second), when various combinations of fine and coarse, and fast and slow secondary gratings are tested. This result favours a correlation-type mechanism over a gradient-type scheme which should lead to a speed-optimum independent of spatial frequency.

Adult↗
PubMed2005

Neuromagnetic correlates of visual motion coherence.

In order to characterize cortical responses to coherent motion we use magnetoencephalography (MEG) to measure human brain activity that is modulated by the degree of global coherence in a visual motion stimulus. Five subjects passively viewed two-phase motion sequences of sparse random dot fields. In the first (incoherent) phase the dots moved in random directions; in the second (coherent) phase a variable percentage of dots moved uniformly in one direction while the others moved randomly. We show that: (i) visual-motion-evoked magnetic fields, measured with a whole-scalp neuromagnetometer, reveal two transient events, within which we identify two significant peaks--the 'ON-M220' peak approximately 220 ms after the onset of incoherent motion and the 'TR-M230' peak, approximately 230 ms after the transition from incoherent to coherent motion; (ii) in lateral occipital channels, the TR-M230 peak amplitude varies with the percentage of motion coherence; (iii) two main sources are active in response to the transition from incoherent to coherent motion, the human medial temporal area complex/V3 accessory area (hMT+/V3A) and the superior temporal sulcus (STS), and (iv) these distinct areas show a similar, significant dependence of response strength and latency on motion coherence.

Adult↗
PubMed2003

Effects of cardiac motion on right coronary artery hemodynamics.

The purpose of this work was to investigate the effects of physiologically realistic cardiac-induced motion on hemodynamics in human right coronary arteries. The blood flow patterns were numerically simulated in a modeled right coronary artery (RCA) having a uniform circular cross section of 2.48 mm diam. Arterial motion was specified based on biplane cineangiograms, and incorporated physiologically realistic bending and torsion. Simulations were carried out with steady and pulsatile inflow conditions (mean ReD=233, alpha=1.82) in both fixed and moving RCA models, to evaluate the relative importance of RCA motion, flow pulsation, and the interaction between motion and flow pulsation. RCA motion with a steady inlet flow rate caused variations in wall shear stress (WSS) magnitude up to 150% of the inlet Poiseuille value. There was significant spatial variability in the magnitude of this motion-induced WSS variation. However, the time-averaged WSS distribution was similar to that predicted in a static model representing the time-averaged geometry. Furthermore, the effects of flow pulsatility dominated RCA motion-induced effects; specifically, there were only modest differences in the WSS history between simulations conducted in fixed and moving RCA models with pulsatile inflow. RCA motion has little effect on time-averaged WSS patterns. It has a larger effect on the temporal variation of WSS, but even this effect is overshadowed by the variations in WSS due to flow pulsation. The hemodynamic effects of RCA motion can, therefore, be ignored as a first approximation in modeling studies.

Arteries↗
PubMed2003

The effects of tumor motion on planning and delivery of respiratory-gated IMRT.

The purpose of this study is to investigate the effects of object motion on the planning and delivery of IMRT. Two phantoms containing objects were imaged using CT under a variety of motion conditions. The effects of object motion on axial CT acquisition with and without gating were assessed qualitatively and quantitatively. Measurements of effective slice width and position for the CT scans were made. Mutual information image fusion was adapted for use as a quantitative measure of object deformation in CT images. IMRT plans were generated on the CT scans of the moving and gated object images. These plans were delivered with motion, with and without gating, and the delivery error between the moving deliveries and a nonmoving delivery was assessed using a scalable vector-based index. Motion during CT acquisition produces motion artifact, object deformation, and object mispositioning, which can be substantially reduced with gating. Objects that vary in cross section in the direction of motion exhibit the most deformation in CT images. Mutual information provides a useful quantitative estimate of object deformation. The delivery of IMRT in the presence of target motion significantly alters the delivered dose distribution in relation to the planned distribution. The utilization of gating for IMRT treatment, including imaging, planning, and delivery, significantly reduces the errors introduced by object motion.

Artifacts↗
PubMed2005

Motion-encoded dose calculation through fluence/sinogram modification.

Conventional radiotherapy treatment planning systems rely on a static computed tomography (CT) image for planning and evaluation. Intra/inter-fraction patient motions may result in significant differences between the planned and the delivered dose. In this paper, we develop a method to incorporate the knowledge of intra/inter-fraction patient motion directly into the dose calculation. By decomposing the motion into a parallel (to beam direction) component and perpendicular (to beam direction) component, we show that the motion effects can be accounted for by simply modifying the fluence distribution (sinogram). After such modification, dose calculation is the same as those based on a static planning image. This method is superior to the "dose-convolution" method because it is not based on "shift invariant" assumption. Therefore, it deals with material heterogeneity and surface curvature very well. We test our method using extensive simulations, which include four phantoms, four motion patterns, and three plan beams. We compare our method with the "dose-convolution" and the "stochastic simulation" methods (gold standard). As for the homogeneous flat surface phantom, our method has similar accuracy as the "dose-convolution" method. As for all other phantoms, our method outperforms the "dose-convolution." The maximum motion encoded dose calculation error using our method is within 4% of the gold standard. It is shown that a treatment planning system that is based on "motion-encoded dose calculation" can incorporate random and systematic motion errors in a very simple fashion. Under this approximation, in principle, a planning target volume definition is not required, since it already accounts for the intra/inter-fraction motion variations and it automatically optimizes the cumulative dose rather than the single fraction dose.

Algorithms↗
PubMed2005

The application of the sinusoidal model to lung cancer patient respiratory motion.

Accurate modeling of the respiratory cycle is important to account for the effect of organ motion on dose calculation for lung cancer patients. The aim of this study is to evaluate the accuracy of a respiratory model for lung cancer patients. Lujan et al. [Med. Phys. 26(5), 715-720 (1999)] proposed a model, which became widely used, to describe organ motion due to respiration. This model assumes that the parameters do not vary between and within breathing cycles. In this study, first, the correlation of respiratory motion traces with the model f(t) as a function of the parameter n (n = 1, 2, 3) was undertaken for each breathing cycle from 331 four-minute respiratory traces acquired from 24 lung cancer patients using three breathing types: free breathing, audio instruction, and audio-visual biofeedback. Because cos2 and cos4 had similar correlation coefficients, and cos2 and cos1 have a trigonometric relationship, for simplicity, the cos1 value was consequently used for further analysis in which the variations in mean position (z0), amplitude of motion (b) and period (tau) with and without biofeedback or instructions were investigated. For all breathing types, the parameter values, mean position (z0), amplitude of motion (b), and period (tau) exhibited significant cycle-to-cycle variations. Audio-visual biofeedback showed the least variations for all three parameters (z0, b, and tau). It was found that mean position (z0) could be approximated with a normal distribution, and the amplitude of motion (b) and period (tau) could be approximated with log normal distributions. The overall probability density function (pdf) of f(t) for each of the three breathing types was fitted with three models: normal, bimodal, and the pdf of a simple harmonic oscillator. It was found that the normal and the bimodal models represented the overall respiratory motion pdfs with correlation values from 0.95 to 0.99, whereas the range of the simple harmonic oscillator pdf correlation values was 0.71 to 0.81. This study demonstrates that the pdfs of mean position (z0), amplitude of motion (b), and period (tau) can be used for sampling to obtain more realistic respiratory traces. The overall standard deviations of respiratory motion were 0.48, 0.57, and 0.55 cm for free breathing, audio instruction, and audio-visual biofeedback, respectively.

Algorithms↗
PubMed2001

Elevated visual motion detection thresholds in adults with acquired ophthalmoplegia.

AIMS: To test the hypothesis that in patients with acquired chronic bilateral ophthalmoplegia, abnormal retinal image slippage during head movements would result in abnormal thresholds for visual perception of motion. METHODS: Five patients (two males and three females) with ophthalmoplegia were included in the study. The average age was 44 years (range 30-69 years). The aetiology of ophthalmoplegia was myasthenia gravis (MG; n=2), chronic progressive external ophthalmoplegia (CPEO; n=2), and chronic idiopathic orbital inflammation. Visual motion detection thresholds were assessed using horizontal and vertical gratings (spatial frequency) set at thresholds for visibility. The grating was then accelerated at 0.09 deg/s(2). The subject's task was to detect the drift direction of the stimulus. RESULTS: Visual motion detection thresholds were raised to a mean of 0.434 deg/s (SD 0.09) (mean normal value 0.287 deg/s (SD 0.08)) for horizontal motion; and to a mean of 0.425 deg/s (SD 0.1) (mean normal value 0.252 deg/s (SD 0.08)) for vertical motion. The difference in values for both horizontal and vertical motion detection were statistically significant when compared with age matched controls; p <0.023 for horizontal motion and p<0.07 for vertical motion (two tailed t test). CONCLUSION: Abnormally raised visual motion thresholds were found in patients with ophthalmoplegia. This may represent a centrally mediated adaptive mechanism to ignore excessive retinal slip and thus avoid oscillopsia during head movements.

Adult↗