Noninvasive middle ear imaging using optical coherence tomography (OCT) presents some unique challenges for real-time, clinical use in humans. We present results from a two-dimensional/three-dimensional OCT system built to assess the imaging requirements of clinical middle ear imaging, and the technical challenges associated with them. These include the need to work at a low numerical aperture, the deleterious effects of transtympanic imaging on image quality at the ossicles, sensitivity requirements for clinical fidelity of images at real-time rates, and the high dynamic-range requirements of the ear. We validated the system by imaging cadaveric specimens with simulated disorders to show the clinical applicability of the images. We also provide additional insight into the likely role of OCT in clinical otology.
To date, clinical implementation of high-frequency ultrasound has been limited due to the difficulties in fabricating
sufficiently small micro-array transducers. Specifically, if an array is desired with the ability to beam-steer to large
angles, an inter-element pitch of approximately .5λ is required to avoid grating lobe artifacts. At high-frequencies (30-70MHz), this introduces major fabrication challenges since the required element pitch is between 10 and 25 microns. A
new technique called Phase Coherence Imaging has been introduced in the literature for suppressing grating lobes in
large-pitch arrays by calculating a weighting factor proportional to the instantaneous phase coherence of the received
element echoes. If the reflected echoes in the grating lobe region are relatively broadband, only some of the echoes will
overlap and the resulting weighting factor will be less. Unfortunately, most beamforming techniques result in relatively
narrowband echoes in the grating lobe region, making this technique less effective. We have developed a technique that
splits the N-element transmit aperture into N/K transmit elements and N receive elements in order to better suppress
grating lobes by increasing the bandwidth of the grating lobe echoes. We have also developed a technique that uses a
probing pulse from a virtual point source behind the array in order to pre-calculate weighting factors from broadband
echoes before conventional transmit beamforming is used. Radiation patterns have been simulated and the amount of
grating lobe suppression has been quantified using the proposed techniques. It has been shown that these techniques are
very effective in suppressing grating lobes in large-pitch phased-arrays, potentially simplifying high-frequency array
fabrication.
We describe experiments with photon pairs to evaluate, correct for, and
avoid sources of error in optical quantum information processing.
It is well known that a simple beamsplitter can
non-deterministicially prepare or select entangled polarization
states. We use quantum process tomography (QPT) to fully
characterize this effect, including loss and decoherence. The QPT
results identify errors and indicate how well they can
be corrected. To evade decoherence in a
noisy quantum channel, we identify decoherence-free subspaces
using experimental channel characterization, without need for a
priori knowledge of the decoherence mechanism or simplifying
assumptions. Working with pairs of polarization-encoded photonic
qubits, we use tomographic and adaptive techniques to identify 2-
and 3-state decoherence-free subspaces for encoding
decoherence-free qubits and qutrits within the noisy channel.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.