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Biomedical subjects

Guang Zhong Yang

Publications and source records attributed to Guang Zhong Yang.

10 recordsLinked to original sources
PubMed2006

Elimination of residual blood flow-related signal in 3D volume-selective TSE arterial wall imaging using velocity-sensitive phase reconstruction.

PURPOSE: To improve 3D volume-selective turbo spin-echo (TSE) arterial wall imaging by introducing velocity phase sensitivity to the sequence. MATERIALS AND METHODS: Slow or recirculating blood may give incomplete nulling in 3D vessel wall imaging, hindering differentiation between arterial wall and lumen. Reconstructed phase images are used to reduce the residual blood signal with postprocessing. A volume-selective 3D TSE (1) sequence with increased velocity sensitivity perpendicular to the slab was developed. Sensitivity was introduced by modifying the gradient waveforms such that residual signal from slow or recirculating blood is distinguished from the wall by the phase shift introduced. This was tested on a pulsatile flow phantom and the carotid artery wall of six healthy volunteers and 17 patients. Images were acquired on a Siemens Magnetom Sonata 1.5T scanner. A quantitative comparison of the lumen/wall contrast was made using images acquired with and without modification. RESULTS: Velocity sensitivity produces significantly reduced residual signal by intravoxel dephasing. Phantom "lumen/tissue" contrast improved by 0.10 (P < 0.01), with a similar change in vivo (0.69-0.73, P < 0.01). Postprocessing removal of the blood signal using phase signal provided further improvement. CONCLUSION: Introducing velocity sensitivity reduces unwanted, potentially misleading residual blood in 3D volume-selective vessel wall imaging.

Adult↗
PubMed2006

Evaluation of carotid artery wall volume measurement using novel semiautomated analysis software.

PURPOSE: To evaluate semiautomated analysis software for measuring the total carotid arterial wall volume (TWV) as a measure of atheroma burden. MATERIALS AND METHODS: Semiautomated-software and manual analyses of TWV measured by cardiovascular magnetic resonance (CMR) were compared in two phantom models, 10 subjects with no known carotid artery disease, and eight subjects with known carotid disease. The subjects were scanned twice for reproducibility. RESULTS: In subjects with no known carotid disease, semiautomated analysis of 98% of slices showed an improved interstudy coefficient of variation (COV) compared to manual analysis of 50% of slices (4.0% vs. 6.2%, P = 0.02). The proportion of matched cross-sectional slices usable for TWV measurement was superior (99% vs. 49%, P = 0.005) and the median analysis time was shorter (31 minutes vs. 90 minutes, P < 0.001) using the semiautomated software. In subjects with known carotid disease, semiautomated (99% of slices) and manual (56% of slices) analyses had comparable interstudy COVs (4.1% vs. 3.9%, P = 0.01). However, the proportion of matched cross-sectional slices usable for TWV measurement was greater using semiautomated contouring (96% vs. 56%, P = 0.01). CONCLUSION: Carotid CMR measurement of TWV using novel semiautomated analysis software shows good reproducibility, enables greater coverage of arterial vessel wall length, and is considerably faster compared to manual contouring.

Adult↗
PubMed2006

Gaze-contingent control for minimally invasive robotic surgery.

OBJECTIVE: Recovering tissue depth and deformation during robotically assisted minimally invasive procedures is an important step towards motion compensation, stabilization and co-registration with preoperative data. This work demonstrates that eye gaze derived from binocular eye tracking can be effectively used to recover 3D motion and deformation of the soft tissue. METHODS: A binocular eye-tracking device was integrated into the stereoscopic surgical console. After calibration, the 3D fixation point of the participating subjects could be accurately resolved in real time. A CT-scanned phantom heart model was used to demonstrate the accuracy of gaze-contingent depth extraction and motion stabilization of the soft tissue. The dynamic response of the oculomotor system was assessed with the proposed framework by using autoregressive modeling techniques. In vivo data were also used to perform gaze-contingent decoupling of cardiac and respiratory motion. RESULTS: Depth reconstruction, deformation tracking, and motion stabilization of the soft tissue were possible with binocular eye tracking. The dynamic response of the oculomotor system was able to cope with frequencies likely to occur under most routine minimally invasive surgical operations. CONCLUSION: The proposed framework presents a novel approach towards the tight integration of a human and a surgical robot where interaction in response to sensing is required to be under the control of the operating surgeon.

Algorithms↗
PubMed2005

Interstudy reproducibility of three-dimensional volume-selective fast spin echo magnetic resonance for quantifying carotid artery wall volume.

PURPOSE: To assess the interstudy reproducibility of a three-dimensional volume-selective, fast spin echo (FSE) magnetic resonance technique for the assessment of carotid artery wall volume, which is a marker for total carotid plaque volume. MATERIALS AND METHODS: Interstudy reproducibility was evaluated in 10 subjects with evidence of carotid artery atherosclerotic disease on carotid Doppler ultrasonography. Subjects were scanned twice with an interscan time of one hour to four days. The carotid artery was imaged in cross-section, and the total carotid arterial wall volume (TWV) was calculated by subtraction of the total carotid lumen volume from the total outer carotid vessel volume. RESULTS: The mean carotid TWV for the scans was 741 and 734 mm3, respectively, with no significant difference (mean difference 7 mm3; P = 0.5). The time for each study was approximately 20 minutes. The standard deviation of the differences between the measurements was 33 mm3, yielding an interstudy coefficient of variation of 4.4%. Sample size calculations showed that 16 patients would enable this difference in plaque volume over time to be detected with 80% power at a P value of 0.05. CONCLUSION: Volumetric analysis with CMR of carotid artery plaques using a three-dimensional volume-selective FSE is efficient with good interstudy reproducibility, and is well suited for longitudinal studies of progression of carotid atheroma with reasonable sample sizes.

Aged↗
PubMed2005

Comparison between three-dimensional volume-selective turbo spin-echo imaging and two-dimensional ultrasound for assessing carotid artery structure and function.

PURPOSE: To compare a volume-selective three-dimensional turbo spin echo (TSE) technique with ultrasound (US) for assessing carotid artery wall structure and function. MATERIALS AND METHODS: A three-dimensional volume-selective TSE technique was used to image the carotid artery in 10 healthy subjects and five hypertensive subjects (each of whom were scanned three times while they received different hypertension treatments). Lumen and wall area were measured on MR images. Two-dimensional US measurements of the intima-media thickness (IMT) and lumen diameter were taken in three orientations through a single cross section. The lumen area change over the cardiac cycle was used to determine distension. For validation, a Bland-Altman analysis was used to compare the vessel wall and lumen areas measured by three-dimensional MRI volumes with those obtained by US scans. RESULTS: Agreement between the two methods was found. The mean difference in distension between US and MRI was 1.2% (+/-5.1%). For the wall area measurements, good agreement was shown, but there was a systematic difference due to the visualization of the adventitia by MRI. Both techniques offer an easy way to objectively measure lumen indices. MRI can provide the complete circumference over the length of a vessel, while US is flexible and relatively inexpensive. The application of US is limited, however, when subjects are poorly echogenic. A difference between hypertensive and healthy subjects was found. CONCLUSION: There was a good agreement between MRI and the clinically established two-dimensional US method. The MRI method has the advantage of providing increased vessel coverage, which permits one to assess localized abnormalities without assuming vessel uniformity.

Adult↗
PubMed2005

3D volume-selective turbo spin echo for carotid artery wall imaging with navigator detection of swallowing.

PURPOSE: To improve 3D volume-selective turbo spin echo (TSE) carotid artery wall imaging by incorporating navigators to reduce artifacts caused by swallowing. MATERIALS AND METHODS: Images were acquired on a Siemens Magnetom Sonata 1.5T scanner. 3D volume-selective TSE scans of the carotid arteries were acquired in six healthy volunteers. A cross-pair navigator placed on the back of the tongue was used to detect swallowing and movement. Two swallowing patterns were tested: 1) a single swallow approximately halfway through the scan time, at the center of k(z), and 2) repeated swallowing as often as possible throughout the scan period. Images were acquired with and without navigators for comparison. Signal intensity in the lumen was quantified for the quality of blood suppression, and the clarity of the vessel wall in the common carotid was ranked by four independent blinded observers. RESULTS: In general, lower signal intensity was recorded in the lumen, and decreased blurring and ghosting were observed on scans with navigator control. This reduction in lumen signal intensity signifies an improvement in the black-blood imaging technique. The differences likely reflect the improved double inversion/blood suppression efficiency due to cycles being rejected when the heart rate changed at the point of swallowing, or decreased motional blurring/ghosting of tissue when the navigator is used, or a combination of these two effects. A statistical analysis of image quality showed a significant difference between navigated and non-navigated scans as scored by four independent, blinded observers. For both swallowing patterns, the mean score for the navigator images was on average 0.6 greater than that of non-navigator images (on a scoring scale of 0-5, where 0 = no vessel visible, and 5 = good delineation and blood suppression) and P-values for all observers were less than 0.01. Overall, the central swallow scans were scored higher than the repeated swallow scans. One reason for this may be the fact that the heart rate increased on swallowing, and this often lasted for one or two cardiac cycles after the navigator returned to the normal acceptance position. The effect of the increased heart rate after swallowing is likely to have an effect on double inversion blood suppression efficiency. Therefore, the increased amount of heart rate changes with repeated swallowing may have a greater adverse effect, even if the navigator rejects data views during the swallowing motion. CONCLUSION: The clarity of vessel wall delineation and the apparent efficiency of blood suppression are reduced by swallowing during acquisition. Both motion blurring and quality of blood suppression are factors that can be improved with the use of a navigator accept/reject method.

Artifacts↗
PubMed2005

Soft-tissue motion tracking and structure estimation for robotic assisted MIS procedures.

In robotically assisted laparoscopic surgery, soft-tissue motion tracking and structure recovery are important for intraoperative surgical guidance, motion compensation and delivering active constraints. In this paper, we present a novel method for feature based motion tracking of deformable soft-tissue surfaces in totally endoscopic coronary artery bypass graft (TECAB) surgery. We combine two feature detectors to recover distinct regions on the epicardial surface for which the sparse 3D surface geometry may be computed using a pre-calibrated stereo laparoscope. The movement of the 3D points is then tracked in the stereo images with stereo-temporal constrains by using an iterative registration algorithm. The practical value of the technique is demonstrated on both a deformable phantom model with tomographically derived surface geometry and in vivo robotic assisted minimally invasive surgery (MIS) image sequences.

Algorithms↗
PubMed2005

A practical approach towards accurate dense 3D depth recovery for robotic laparoscopic surgery.

OBJECTIVE: Recovering tissue deformation during robotic-assisted minimally invasive surgery (MIS) is an important step towards motion compensation and stabilization. This article presents a practical strategy for dense 3D depth recovery and temporal motion tracking for deformable surfaces. METHODS: The method combines image rectification with constrained disparity registration for reliable depth estimation. The accuracy and practical value of the technique are validated using a tissue phantom with known 3D geometry and motion characteristics and in vivo data. RESULTS: Results from the phantom model correctly follow the motion trend indicated from the ground truth provided by CT scanning, and regression analysis shows the intrinsic accuracy that can be achieved with the proposed technique. Results applied to in vivo robotic-assisted MIS data are also provided, indicating the practical value of the proposed method. CONCLUSION: The proposed method presents a practical strategy for dense depth recovery of surface structure in robotic-assisted MIS that incorporates stereo vision. Results on phantom and in vivo data indicate the quality of the method and also highlight the importance of further considering the effects of specular highlights.

Algorithms↗
PubMed2003

Volume-selective 3D turbo spin echo imaging for vascular wall imaging and distensibility measurement.

PURPOSE: To use a volume-selective 3D turbo spin echo (TSE) technique to image the carotid artery wall and measure distensibility. MATERIALS AND METHODS: A high-resolution volume-selective 3D TSE sequence has been developed. Volume selection is accomplished by orthogonal gradients for the 90 degrees and 180 degrees excitations and allows a 3D volume of vessel wall to be imaged in a relatively short time. The technique has been developed to allow imaging at any defined phase of the cardiac cycle so that the vascular function and distensibility can be studied. RESULTS: Scan efficiency is increased by the reduced phase encode field of view (FOV) (k(y) steps) by the use of selective volume excitation. Significantly more slices (k(z) phase encode steps) for vessel coverage can be acquired with the same scan time as that of the conventional sequence while maintaining signal-to-noise ratio (SNR) levels. The practical value of the technique was demonstrated on 10 normal subjects with high-resolution vessel distensibility measurements of the carotid arteries. CONCLUSION: A volume-selective TSE method has been used for carotid artery wall imaging and measurement of distensibility in normal subjects. Larger coverage of the vessel, and therefore more information for clinical diagnostics, was achieved with the same overall scan time with an SNR comparable to that of 2D full FOV images.

Adult↗