Presence Of Image Motion Research Articles

Particle Tracking Facilitates Real Time Capable Motion Correction in 2D or 3D Two-Photon Imaging of Neuronal Activity.

The application of 2-photon laser scanning microscopy (TPLSM) techniques to measure the dynamics of cellular calcium signals in populations of neurons is an extremely powerful technique for characterizing neural activity within the central nervous system. The use of TPLSM on awake and behaving subjects promises new insights into how neural circuit elements cooperatively interact to form sensory perceptions and generate behavior. A major challenge in imaging such preparations is unavoidable animal and tissue movement, which leads to shifts in the imaging location (jitter). The presence of image motion can lead to artifacts, especially since quantification of TPLSM images involves analysis of fluctuations in fluorescence intensities for each neuron, determined from small regions of interest (ROIs). Here, we validate a new motion correction approach to compensate for motion of TPLSM images in the superficial layers of auditory cortex of awake mice. We use a nominally uniform fluorescent signal as a secondary signal to complement the dynamic signals from genetically encoded calcium indicators. We tested motion correction for single plane time lapse imaging as well as multiplane (i.e., volume) time lapse imaging of cortical tissue. Our procedure of motion correction relies on locating the brightest neurons and tracking their positions over time using established techniques of particle finding and tracking. We show that our tracking based approach provides subpixel resolution without compromising speed. Unlike most established methods, our algorithm also captures deformations of the field of view and thus can compensate e.g., for rotations. Object tracking based motion correction thus offers an alternative approach for motion correction, one that is well suited for real time spike inference analysis and feedback control, and for correcting for tissue distortions.

SU‐E‐I‐70: Use of Blade Sequences to Eliminate Motion and Pulsation Artifacts in Knee MR Imaging

Purpose: The purpose of this study is to evaluate the ability of Proton Density (PD)‐BLADE sequences in reducing or even eliminating motion and pulsatile flow artifacts in knee MRI examinations. Methods: Eighty consecutive patients, who had been routinely scanned for knee examination, participated in the study. The following pairs of sequences with and without BLADE were compared: a) PD Turbo Spin Echo (TSE) Sagittal (SAG) Fat Saturation (FS) in thirty five patients, b) PD TSE Coronal (COR) FS in nineteen patients, c) T2 TSE AXIAL in thirteen patients and d) PD TSE SAG in thirteen patients. Both qualitative and quantitative analyses were performed based on the signal‐to‐noise ratio (SNR), contrast‐to‐noise ratio (CNR), and relative contrast (ReCon) measures of normal anatomic structures. The qualitative analysis was performed by experienced radiologists. Also, the presence of image motion and pulsation artifacts was evaluated. Results: Based on the results of the SNR, CRN and ReCon for the different sequences and anatomical structures, the BLADE sequences were significantly superior in nineteen cases, whereas the corresponding conventional sequences were significantly superior in six only cases. The BLADE sequences eliminated motion artifacts in all the cases. However, motion artifacts were shown in: a) six PD TSE SAG FS, b) three PD TSE COR FS, c) three PD TSE SAG, and d) two T2 TSE AXIAL conventional sequences. In our results, it was found that in PD FS sequences (Sagittal and Coronal) the differences between the BLADE and conventional sequences regarding the elimination of motion and pulsatile flow artifacts were statistically significant. In all the comparisons, the PD FS BLADE sequences (coronal and sagittal) were significantly superior to the corresponding conventional sequences regarding the classification of their image quality. Conclusion: This technique appears to be capable to potentially eliminate motion and pulsatile flow artifacts in knee MR images.

Elimination of motion, pulsatile flow and cross-talk artifacts using blade sequences in lumbar spine MR imaging

The purpose of this study is to evaluate the ability of T2 turbo spin echo (TSE) axial and sagittal BLADE sequences in reducing or even eliminating motion, pulsatile flow and cross-talk artifacts in lumbar spine MRI examinations. Forty four patients, who had routinely undergone a lumbar spine examination, participated in the study. The following pairs of sequences with and without BLADE were compared: a) T2 TSE Sagittal (SAG) in thirty two cases, and b) T2 TSE Axial (AX) also in thirty two cases. Both quantitative and qualitative analyses were performed based on measurements in different normal anatomical structures and examination of seven characteristics, respectively. The qualitative analysis was performed by experienced radiologists. Also, the presence of image motion, pulsatile flow and cross-talk artifacts was evaluated. Based on the results of the qualitative analysis for the different sequences and anatomical structures, the BLADE sequences were found to be significantly superior to the conventional ones in all the cases. The BLADE sequences eliminated the motion artifacts in all the cases. In our results, it was found that in the examined sequences (sagittal and axial) the differences between the BLADE and conventional sequences regarding the elimination of motion, pulsatile flow and cross-talk artifacts were statistically significant. In all the comparisons, the T2 TSE BLADE sequences were significantly superior to the corresponding conventional sequences regarding the classification of their image quality. In conclusion, this technique appears to be capable of potentially eliminating motion, pulsatile flow and cross-talk artifacts in lumbar spine MR images and producing high quality images in collaborative and non-collaborative patients.

Elimination of motion and pulsation artifacts using BLADE sequences in knee MR imaging

The purpose of this study is to evaluate the ability of proton density (PD)-BLADE sequences in reducing or even eliminating motion and pulsatile flow artifacts in knee magnetic resonance imaging examinations. Eighty consecutive patients, who had been routinely scanned for knee examination, participated in the study. The following pairs of sequences with and without BLADE were compared: (a) PD turbo spin echo (TSE) sagittal (SAG) fat saturation (FS) in 35 patients, (b) PD TSE coronal (COR) FS in 19 patients, (c) T2 TSE axial in 13 patients and (d) PD TSE SAG in 13 patients. Both qualitative and quantitative analyses were performed based on the signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and relative contrast (ReCon) measures of normal anatomic structures. The qualitative analysis was performed by experienced radiologists. Also, the presence of image motion and pulsation artifacts was evaluated. Based on the results of the SNR, CRN and ReCon for the different sequences and anatomical structures, the BLADE sequences were significantly superior in 19 cases, whereas the corresponding conventional sequences were significantly superior in only 6 cases. BLADE sequences eliminated motion artifacts in all the cases. However, motion artifacts were shown in (a) six PD TSE SAG FS, (b) three PD TSE COR FS, (c) three PD TSE SAG and (d) two T2 TSE axial conventional sequences. In our results, it was found that, in PD FS sequences (sagittal and coronal), the differences between the BLADE and conventional sequences regarding the elimination of motion and pulsatile flow artifacts were statistically significant. In all the comparisons, the PD FS BLADE sequences (coronal and sagittal) were significantly superior to the corresponding conventional sequences regarding the classification of their image quality. In conclusion, this technique appears to be capable to potentially eliminate motion and pulsatile flow artifacts in MR images.

Velocity dependence of Vernier and letter acuity for band-pass filtered moving stimuli

The ability to see fine detail diminishes when the target of interest moves at a speed greater than a few deg/s. The purpose of this study was to identify fundamental limitations on spatial acuity that result from image motion. Discrimination of Vernier offset was measured for a pair of vertical abutting lines and letter resolution was measured using a four-orientation letter ‘T’. These stimuli were digitally filtered using one of five band-pass (bandwidth=1.5 octaves) filters with a center frequency between 0.83 and 13.2 c/deg, and presented at velocities that ranged from 0 to 12 deg/s. Filtered and unfiltered stimuli were presented for 150 ms at a constant multiple (4× or 2×) of the contrast-detection threshold at each velocity. For stimuli of low to middle spatial frequency (up to 3.3 c/deg), Vernier and letter acuity for equally detectable targets are essentially unaffected by velocity up to 12 deg/s, i.e., for temporal frequencies of motion (velocity × spatial frequency) up to approximately 50 Hz. For stimuli of higher spatial frequency, acuity remains essentially constant until the velocity corresponds to a temporal frequency of about 30 Hz, and increases thereafter. Both Vernier and letter acuities worsen by approximately a factor of two for each one-octave decrease in filter spatial frequency. Both types of acuities worsen also as the contrast of the stimulus is reduced, but Vernier discrimination exhibits a stronger contrast-dependence than letter resolution. Our results support previous suggestions that a shift in the spatial scale used by the visual system to analyze spatial stimuli is principally responsible for the degradation of acuity in the presence of image motion. The results are consistent with a spatio-temporal-frequency limitation on spatial thresholds for moving stimuli, and not with a temporal-frequency limitation per se.

Vernier in motion: what accounts for the threshold elevation?

Vernier acuity is susceptible to degradation by image motion. The purpose of this study was to determine to what extent vernier thresholds are elevated in the presence of image motion because of reduced stimulus visibility, due to contrast smearing, or to a shift in the spatial scale of analysis. To test the visibility hypothesis, we measured vernier thresholds as a function of stimulus velocity (0-6 deg/sec), for various levels of stimulus visibility, each normalized to the detection threshold at the respective velocity. Contrary to the prediction of the visibility hypothesis, vernier thresholds worsen as the velocity increases, even when the stimuli are equally visible. To test the shift in spatial scale hypothesis, we determined spatial frequency tuning functions for vernier discrimination and line detection tasks, using a masking paradigm. We measured vernier and line detection thresholds as a function of spatial frequency of a sine-wave mask (0.5-32 c/deg), and for stimulus and mask velocities ranging from 0 to 4 deg/sec. Peak masking for both vernier discrimination and line detection, which indicates the most sensitive band of spatial frequencies for each task, shifts systematically toward lower spatial frequencies as the velocity increases. The progressive increase in spatial scale largely accounts for the worsening of vernier thresholds for moving stimuli. Differences between peak masking for vernier discrimination and line detection were found at 0 and 1 deg/sec, suggesting that different mechanisms mediate the two tasks, at least at low velocities. The masking results are consistent with previous findings that directionally selective motion detectors mediate detection of moving stimuli, but suggest that these detectors do not analyze vernier offsets. We conclude that the elevation of vernier threshold for a moving stimulus is accounted for primarily by a shift of sensitivity to mechanisms of lower spatial frequency, and not by decreased stimulus visibility.

Partially coherent diffraction by a defocused slit aperture in the presence of image motion and transverse vibrations

This paper presents an analysis of the far-field diffraction pattern of partially spatially coherent light by an optical system with a defocused slit aperture in the presence of linear image motion and sinusoidal transverse vibrations. For partially coherent light sinc and gaussian forms of correlations in the two points over the diffracting aperture are employed. The results for the irradiance distribution have been presented graphically for typical values of the coherence, defocusing and vibrational parameters.