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Biomedical subjects

K S Nayak

Publications and source records attributed to K S Nayak.

9 recordsLinked to original sources
PubMed2001

Rapid ventricular assessment using real-time interactive multislice MRI.

A multislice real-time imaging technique is described which can provide continuous visualization of the entire left ventricle under resting and stress conditions. Three dynamically adjustable slices containing apical, mid, and base short axis views are imaged 16 times/sec (48 images/sec), with each image providing 3.12 mm resolution over a 20 cm field of view. Initial studies indicate that this technique is useful for the assessment of LV function by providing simultaneous real-time visualization of all 16 wall segments. This technique may also be used for stress LV function and, when used in conjunction with contrast agents, myocardial perfusion imaging. Magn Reson Med 45:371-375, 2001.

Coronary Circulation↗
PubMed2001

Efficient off-resonance correction for spiral imaging.

A new spiral imaging technique incorporates the acquisition of a field map into imaging interleaves. Variable density spiral trajectories are designed to oversample the central region of k-space, and interleaves are acquired at two different echo times. A field map is extracted from this data and multifrequency reconstruction is used to form an off-resonance corrected image using the entire dataset. Simulation, phantom, and in vivo results indicate that this technique can be used to achieve higher image and/or field map spatial resolution compared to conventional techniques. Magn Reson Med 45:521-524, 2001.

Artifacts↗
PubMed2001

Real-time black-blood MRI using spatial presaturation.

A real-time interactive black-blood imaging system is described. Rapid blood suppression is achieved by exciting and dephasing slabs outside the imaging slice before each imaging excitation. Sharp-profiled radio frequency saturation pulses placed close to the imaging slice provide good blood suppression, even in views containing slow through-plane flow. In vivo results indicate that this technique improves endocardial border definition during systole in real-time cardiac wall-motion studies. Phantom and animal results indicate that this technique nearly eliminates flow artifacts in real-time intravascular studies. J. Magn. Reson. Imaging 2001;13:807-812.

Algorithms↗
PubMed2001

Real-time interactive coronary MRA.

An interactive real-time imaging system capable of rapid coronary artery imaging is described. High-resolution spiral and circular echo planar trajectories were used to achieve 0.8 x 1.6 mm2 resolution in 135 ms (CEPI) or 1.13 x 1.13 mm2 resolution in 189 ms (spirals), over a 20-cm FOV. Using a sliding window reconstruction, display rates of up to 37 images/sec were achieved. Initial results indicate this technique can perform as a high-quality 2D coronary localizer and with SNR improvement may enable rapid screening of the coronary tree.

CD-I↗
PubMed2001

Leiomyoma of the kidney--report of two cases.

Renal leimyoma is an uncommon benign tumour, which pose a challenging diagnostic and therapeutic problem. When multiple (leiomyomatosis) they are preoperatively mistaken for malignant tumors. We herein-present one case of renal leiomyomatois developing in a 50 year old male, which was clinically diagnosed as renal cell carcinoma and one case of renal leiomyoma in a 37 year old male.

Adult↗
PubMed2000

Automatic field map generation and off-resonance correction for projection reconstruction imaging.

A new projection reconstruction technique utilizes the oversampling of low spatial frequencies to estimate and correct for off-resonance effects. Interleaved spokes are acquired at one of two different echo times. From separated early-TE and late-TE raw data, two one-quarter resolution images are reconstructed and a one-quarter resolution field map is computed. Multifrequency reconstruction with all the data is then used to simultaneously correct for off-resonance and compensate for the difference in echo times. Resulting images obtained on phantoms and in vivo demonstrate significantly reduced off-resonance artifact without the acquisition of a separate field map.

Humans↗
PubMed2000

Real-time color flow MRI.

A real-time interactive color flow MRI system capable of rapidly visualizing cardiac and vascular flow is described. Interleaved spiral phase contrast datasets are acquired continuously, while real-time gridding and phase differencing is used to compute density and velocity maps. These maps are then displayed using a color overlay similar to what is used by ultrasound. For cardiac applications, 6 independent images/sec are acquired with in-plane resolution of 2.4 mm over a 20 cm field of view (FOV). Sliding window reconstruction achieves display rates up to 18 images/sec. Appropriate tradeoffs are made for other applications. Flow phantom studies indicate this technique accurately measures velocities up to 2 m/sec, and accurately captures real-time velocity waveforms (comparable to continuous wave ultrasound). In vivo studies indicate this technique is useful for imaging cardiac and vascular flow, particularly valvular regurgitation. Arbitrary scan planes can be quickly localized, and flow measured in any direction.

Aortic Valve↗