We consider the problem of automatically tracking the mitral valve in cardiac ultrasound time series and present an unsupervised method for decomposing and segmenting the mitral valve from noisy ultrasound videos. To do so we propose a Robust Nonnegative Matrix Factorization (RNMF) method that naturally decomposes the time series into three separate parts, highlighting the cardiac cycle, mitral valve, and ultrasound noise. The low rank component of RNMF captures the simple motions of the cardiac cycle effectively aside from the sporadic motion of the mitral valve tissue that is captured innately in our RNMF sparse signal term. Using the RNMF representation, we introduce a simple valve object detection algorithm. Our method performs especially well in noisy time series when existing methods fail, differentiating general noise from the subtle and complex motions of the mitral valve. The valve is then segmented using simple thresholding and diffusion. The method presented is highly robust to low quality ultrasound video, and does not require manual preprocessing, prior labeling, or any training data.
We consider the problem of identifying frames in a cardiac ultrasound video associated with left ventricular chamber end-systolic (ES, contraction) and end-diastolic (ED, expansion) phases of the cardiac cycle. Our procedure involves a simple application of non-negative matrix factorization (NMF) to a series of frames of a video from a single patient. Rank-2 NMF is performed to compute two end-members. The end members are shown to be close representations of the actual heart morphology at the end of each phase of the heart function. Moreover, the entire time series can be represented as a linear combination of these two end-member states thus providing a very low dimensional representation of the time dynamics of the heart. Unlike previous work, our methods do not require any electrocardiogram (ECG) information in order to select the end-diastolic frame. Results are presented for a data set of 99 patients including both healthy and diseased examples.
In many in-situ instruments information about the mass of the sample could aid in the interpretation of the data and
portioning instruments might require an accurate sizing of the sample mass before dispensing the sample. In addition,
on potential sample return missions a method to directly assess the captured sample size would be required to determine
if the sampler could return or needs to continue attempting to acquire sample. In an effort to meet these requirements
piezoelectric balances were developed using flextensional actuators which are capable of monitoring the mass using two
methods. A piezoelectric balance could be used to measure mass directly by monitoring the voltage developed across
the piezoelectric which is linear with force, or it could be used in resonance to produce a frequency change proportional
to the mass change. In the case of the latter, the piezoelectric actuator/balance would be swept in frequency through its
fundamental resonance. If a mass is added to the balance the resonance frequency would shift down proportionally to
the mass. By monitoring the frequency shift the mass could be determined. This design would allow for two
independent measurements of the mass. In microgravity environments spacecraft thrusters could be used to provide
acceleration in order to produce the required force for the first technique or to bring the mass into contact with the
balance in the second approach. In addition, the measuring actuators, if driven at higher voltages, could be used to
fluidize the powder to aid sample movement. In this paper, we outline some of our design considerations and present the
results of a few prototype balances that we have developed.
In previous work, we investigated 3-D synthetic aperture imaging with 2-D array designs for real-time rectilinear volumetric imaging of targets near the transducer such as the breast and carotid artery. Here we present results for cylindrical 3-D imaging for 3-D transrectal ultrasound (TRUS). The major benefit of this design is the interconnect where an expensive multilayer flex circuit is no longer required. The interconnect uses a row-column addressing scheme to enable different groups of elements. Over 256 transmissions, this design is capable of synthesizing a 256 x 256 = 65,536 element fully sampled 2-D cylindrical array if desired. In receive, the echoes from individual elements along a row are recorded by the system receive channels. For faster volume acquisition time, we present a design where all elements of the 2-D array transmit simultaneously, and signals are recorded one row at a time. For a depth of 6 cm, a volume rate of 50 volumes/s can be achieved. We have performed computer simulations of a 10 MHz 256 x 256 synthetic cylindrical 2-D array with a radius of curvature of 10 mm to determine the radiation pattern. For an 128 x 128 subaperture, the on-axis case (x,y,z) = (0,0,20) mm showed a narrow beam down to -40 dB. In the transversal direction, on-axis lateral beamwidths at -6, -20, and -40 dB were 0.47 mm, 0.81 mm, and 2.54 mm, respectively. As for the longitudinal direction, the beamwidths are slightly narrower than in transversal direction, giving 0.39 mm, 0.72 mm, and 1.51 mm for the same corresponding dB levels.
Ultrasound imaging is a well established technology for echocardiography on humans. For cardiac imaging in small animals whose hearts beat at a rate higher than 300 beats per minute, the spatial and temporal resolution of current clinical ultrasonic scanners are far from ideal and simply inadequate for such applications. In this research, a real-time high frequency ultrasound imaging system was developed with a frame rate higher than 80 frames per second (fps) for cardiac applications in small animals. The device has a mechanical sector scanner using magnetic drive mechanism to reduce moving parts and ensure longevity. A very lightweight (< 0.28 g) single element transducer was specially designed and constructed for this research to achieve a frame rate of at least 80 fps. The 30-50 MHz transducers swept through an arc at the end of a pendulum for imaging the heart of small animals. The imaging electronics consisted of a low noise pulser/receiver, a high-speed data acquisition board, and digital signal processing algorithms. In vivo results on mouse embryos showed that real time ultrasound imaging at frame rate exceeding 80 fps could demonstrate detailed depiction of cardiac function with a spatial resolution of around 50 microns, which allows researchers to fully examine and monitor small animal cardiac functions.