Destructive interference from phase fluctuations caused by motion during 1 H magnetic resonance spectroscopy (MRS) stimulated-echo acquisition mode (STEAM) and point-resolved spectroscopy (PRESS) acquisitions can significantly diminish the traditional ͌N-gain in signal-to-noise ratio (SNR) afforded by averaging N signals, especially in the torso. The SNR loss is highly variable among individuals, even when identical acquisition protocols are used. This paper presents a theory for the SNR loss, assuming that the phase fluctuates randomly. It is shown that SNR in conventional averaging is reduced by the factor sinc( ͌3/), where is the standard deviation (SD) of the phase. "Constructive averaging," whereby each individual acquisition is phase-corrected using the phase of a high-SNR peak before averaging, reverses the SNR loss from motioninduced dephasing, resulting in a {1/sinc( ͌3/)}-fold SNR improvement. It is also shown that basing phase corrections on an average of ͌N adjacent points both improves correction accuracy and effectively eliminates false signal artifacts when corrections are based on low-SNR peaks. The theory is validated over a sevenfold range of variation in signal loss due to motion observed in

Magnetic resonance imaging (MRI) is traditionally performed with fixed externally applied gradient magnetic fields and is hence intrinsically locked to the laboratory frame of reference (FoR). Here a method for high-resolution MRI that employs active, catheter-based, tiny internal probes that utilize the spatial properties of the probe itself for localization is proposed and demonstrated at 3 T. Because these properties are intrinsic to the probe, they move with it, transforming MRI from the laboratory FoR to the FoR of the device itself, analogous to an endoscope. The "MRI endoscope" can utilize loop coils and loopless antennas with modified sensitivity, in combination with adiabatic excitation by the device itself, to restrict the MRI sensitivity to a disk-shaped plane a few mm thick. Excitation with the MRI endoscope limits the eddy currents induced in the sample to an excited volume whose size is orders of magnitude below that excited by a conventional body MRI coil. Heat testing shows maximum local temperature increases of <1 degrees C during MRI, within regulatory guidelines. The method is demonstrated in a kiwifruit, in intact porcine and rabbit aortas, and in an atherosclerotic human iliac artery specimen, with in-plane resolution as small as 80 microm and 1.5-5 mm slice thickness.

Fast, minimally invasive, high-resolution intravascular imaging is essential for identifying vascular pathological features and for developing novel diagnostic tools and treatments. Intravascular magnetic resonance imaging (MRI) with active internal probes offers high sensitivity to pathological features without ionizing radiation or the limited luminal views of conventional X-rays, but has been unable to provide a high-speed, high-resolution, endoscopic view. Herein, real-time MRI endoscopy is introduced for performing MRI from a viewpoint intrinsically locked to a miniature active, internal transmitter–receiver in a clinical 3.0-TMRI scanner. Real-time MRI endoscopy at up to 2 frames/s depicts vascular wall morphological features, atherosclerosis, and calcification at 80 to 300 μm resolution during probe advancement through diseased human iliac artery specimens and atherosclerotic rabbit aortas in vivo. MRI endoscopy offers the potential for fast, minimally invasive, transluminal, high-resolution imaging of vascular disease on a common clinical platform suitable for evaluating and targeting atherosclerosis in both experimental and clinical settings.

Purpose: To determine and track the planar orientation of active interventional devices without using localizing RF microcoils. Materials and Methods:An image-based tracking method that determines a device's orientation using projection images was developed. An automated and a manual detection scheme were implemented. The method was demonstrated in an in vivo mesocaval puncture procedure in swine, which required accurate orientation of an active transvascular needle catheter. Results:The plane of the catheter was determined using two projection images. The scan plane was adjusted automatically to follow the catheter plane, and its orientation with respect to a previously acquired target plane was displayed. The algorithm facilitated navigation for a fast and accurate puncture. Conclusion:Using image-based techniques, with no mechanical design changes, the orientation of an active intravascular probe could be tracked.

A real-time acoustical source location system implemented at the CAIP Center at Rutgers University presently tracks all sounds within a room. The system aims a video camera and audio sensors at the determined sound source for transmission of video and audio information to a remote teleconferencing location. It is desired to only direct attention to speech and to ignore nonspeech such as the shuffling of feet or the moving of papers. Speech detection is implemented to allow the system to aim sensors only at talkers. Present detection methods depend upon energy levels and the pitch present in voiced sounds to detect speech. In a reverberant environment the accuracy of speech detection degrades. Speech detection accuracy in reverberation is tested. Measures of false acceptance of nonspeech signals and false rejection of speech signals are used to determine which speech detection methods are optimal in different reverberant rooms. Speech and nonspeech in reverberant rooms are simulated using impulse responses generated by CATT-Acoustic. The test environments range from anechoic to heavily reverberant. A look-back buffer and adaptive tracking of energy and zero-crossing levels are used to allow speech detection to work optimally with the current source location system.