Biomedical subjects

Yudong Zhu

Publications and source records attributed to Yudong Zhu.

7 recordsLinked to original sources

PubMed2006

Toward single breath-hold whole-heart coverage coronary MRA using highly accelerated parallel imaging with a 32-channel MR system.

Coronary MR angiography (CMRA) is generally confined to the acquisition of multiple targeted slabs with coverage dictated by the competing constraints of signal-to-noise ratio (SNR), physiological motion, and scan time. This work addresses these obstacles by demonstrating the technical feasibility of using a 32-channel coil array and receiver system for highly accelerated volumetric breath-hold CMRA. The use of the 32-element array in unaccelerated CMRA studies provided a baseline SNR increase of as much as 40% over conventional cardiac-optimized phased array coils, which resulted in substantially enhanced image quality and improved delineation of the coronary arteries. Modest accelerations were used to reduce breath-hold durations for tailored coverage of the coronary arteries using targeted multi-oblique slabs to as little as 10 s. Finally, high net accelerations were combined with the SNR advantages of a 3D steady-state free precession (SSFP) technique to achieve previously unattainable comprehensive volumetric coverage of the coronary arteries in a single breath-hold. The merits and limitations of this simplified volumetric imaging approach are discussed and its implications for coronary MRA are considered.

Coronary Angiography↗

PubMed2005

Rapid volumetric MRI using parallel imaging with order-of-magnitude accelerations and a 32-element RF coil array: feasibility and implications.

RATIONALE AND OBJECTIVES: Many clinical applications of Magnetic Resonance Imaging are constrained by basic limits on imaging speed. Parallel MRI relaxes these limits by using the sensitivity patterns of arrays of radiofrequency receiver coils to encode spatial information in a manner complementary to traditional encoding with magnetic field gradients. Until now, parallel MRI has been used to achieve modest improvements in imaging speed; order-of-magnitude improvements have been elusive given fundamental losses in signal-to-noise ratio. The goal of this work was to demonstrate that, with appropriate hardware and careful SNR management, rapid volumetric imaging at high accelerations is in fact feasible. MATERIALS AND METHODS: Contrast-enhanced MRI with an axial 3D spoiled gradient echo imaging sequence was performed in healthy adult subjects using a 32-element RF coil array and a prototype 32-channel MR imaging system. Large imaging volumes were prescribed, in place of traditional limited slabs targeted only to suspect regions. RESULTS: As much as 16-fold net accelerations of imaging were achieved repeatably using this approach. The use of large 3D volumes allowed comprehensive anatomical coverage at clinically useful spatial and/or temporal resolution. The need for careful, time-consuming, and subject-specific scan prescription was also eliminated. CONCLUSION: The highly parallel imaging approach presented here allows previously inaccessible volumetric coverage for time-sensitive MRI examinations such as contrast-enhanced MRA, and simultaneously provides a substantially simplified imaging paradigm. The resulting capability for rapid volumetric imaging promises to combine the strengths of MRI with some of the advantages of alternative imaging modalities such as multidetector CT.

Adult↗

PubMed2004

Parallel excitation with an array of transmit coils.

Theoretical and experimental results are presented that establish the value of parallel excitation with a transmit coil array in accelerating excitation and managing RF power deposition. While a 2D or 3D excitation pulse can be used to induce a multidimensional transverse magnetization pattern for a variety of applications (e.g., a 2D localized pattern for accelerating spatial encoding during signal acquisition), it often involves the use of prolonged RF and gradient pulses. Given a parallel system that is composed of multiple transmit coils with corresponding RF pulse synthesizers and amplifiers, the results suggest that by exploiting the localization characteristics of the coils, an orchestrated play of shorter RF pulses can achieve desired excitation profiles faster without adding strains to gradients. A closed-form design for accelerated multidimensional excitations is described for the small-tip-angle regime, and its suppression of interfering aliasing lobes from coarse excitation k-space sampling is interpreted based on an analogy to sensitivity encoding (SENSE). With or without acceleration, the results also suggest that by taking advantage of the extra degrees of freedom inherent in a parallel system, parallel excitation provides better management of RF power deposition while facilitating the faithful production of desired excitation profiles. Sample accelerated and specific absorption rate (SAR)-reduced excitation pulses were designed in this study, and evaluated in experiments.

Absorption↗

PubMed2004

Highly parallel volumetric imaging with a 32-element RF coil array.

The improvement of MRI speed with parallel acquisition is ultimately an SNR-limited process. To offset acquisition- and reconstruction-related SNR losses, practical parallel imaging at high accelerations should include the use of a many-element array with a high intrinsic signal-to-noise ratio (SNR) and spatial-encoding capability, and an advantageous imaging paradigm. We present a 32-element receive-coil array and a volumetric paradigm that address the SNR challenge at high accelerations by maximally exploiting multidimensional acceleration in conjunction with noise averaging. Geometric details beyond an initial design concept for the array were determined with the guidance of simulations. Imaging with the support of 32-channel data acquisition systems produced in vivo results with up to 16-fold acceleration, including images from rapid abdominal and MRA studies.

Equipment Design↗

PubMed2004

Large field-of-view real-time MRI with a 32-channel system.

The emergence of parallel MRI techniques and new applications for real-time interactive MRI underscores the need to evaluate performance gained by increasing the capability of MRI phased-array systems beyond the standard four to eight high-bandwidth channels. Therefore, to explore the advantages of highly parallel MRI a 32-channel 1.5 T MRI system and 32-element torso phased arrays were designed and constructed for real-time interactive MRI. The system was assembled from multiple synchronized scanner-receiver subsystems. Software was developed to coordinate across subsystems the real-time acquisition, reconstruction, and display of 32-channel images. Real-time, large field-of-view (FOV) body-survey imaging was performed using interleaved echo-planar and single-shot fast-spin-echo pulse sequences. A new method is demonstrated for augmenting parallel image acquisition by independently offsetting the frequency of different array elements (FASSET) to variably shift their FOV. When combined with conventional parallel imaging techniques, image acceleration factors of up to 4 were investigated. The use of a large number of coils allowed the FOV to be doubled in two dimensions during rapid imaging, with no degradation of imaging time or spatial resolution. The system provides a platform for evaluating the applications of many-channel real-time MRI, and for understanding the factors that optimize the choice of array size.

Abdomen↗

PubMed2003

Extended field-of-view imaging with table translation and frequency sweeping.

A new method for MRI of an extended field of view (FOV) has been developed and validated. The method employs concurrent MR data acquisition and patient table motion. Table motion-induced image artifacts are minimized by sweeping the frequency of the receiver at a rate matching the table's speed. Multiple regional images are collected and combined to reconstruct the full FOV. The imaging parameters and table speed are chosen to ensure that each regional image of the subject is collected while the corresponding anatomy is in the useable imaging volume of the scanner. Additional strategies are applied to further reduce field inhomogeneity-induced artifacts, especially distortions due to gradient field nonlinearity. The method is robust and can be easily incorporated into most multislice 2D and volumetric 3D imaging pulse sequences. It is anticipated that this technique will be useful for a variety of applications, including angiographic runoffs, whole-body screening, and short-magnet imaging.

Algorithms↗

PubMed2003

[Application of endolaser in vitrectomy for retinal vascular disease].

PURPOSE: To discuss the usage and effectiveness of endolaser in vitrectomy for retinal vascular disease. METHODS: Twenty-four cases (28 eyes) of vitrectomy for retinal vascular disease were treated with endolaser. The methods of endolaser: 21 eyes were treated with panretinal scatter therapy; 2 eyes with endolaser ring-intercepting around retinal and sealing retinal breaks; 5 eye with focal therapy. RESULTS: After follow-up for 1-24 months (mean 9 months), retinal hemorrhage recurred in 3 eyes; the other 25 eyes, retinas were totally reattached, retinal breaks were sealed, and vision had considerable recovery, no hemorrhage. The ratio of recovery is up to 89.2%. CONCLUSIONS: Endolaser is an important adjuvant in vitreous operation nowadays and an effective procedure in vitrectomy for the cases of retinal hemorrhage.

Adolescent↗