23,202 research outputs found
Extracting respiratory signals from thoracic cone beam CT projections
Patient respiratory signal associated with the cone beam CT (CBCT)
projections is important for lung cancer radiotherapy. In contrast to
monitoring an external surrogate of respiration, such signal can be extracted
directly from the CBCT projections. In this paper, we propose a novel local
principle component analysis (LPCA) method to extract the respiratory signal by
distinguishing the respiration motion-induced content change from the gantry
rotation-induced content change in the CBCT projections. The LPCA method is
evaluated by comparing with three state-of-the-art projection-based methods,
namely, the Amsterdam Shroud (AS) method, the intensity analysis (IA) method,
and the Fourier-transform based phase analysis (FT-p) method. The clinical CBCT
projection data of eight patients, acquired under various clinical scenarios,
were used to investigate the performance of each method. We found that the
proposed LPCA method has demonstrated the best overall performance for cases
tested and thus is a promising technique for extracting respiratory signal. We
also identified the applicability of each existing method.Comment: 21 pages, 11 figures, submitted to Phys. Med. Bio
A novel ultrasonic strain gauge for single-sided measurement of a local 3D strain field
A novel method is introduced for the measurement of a 3D strain field by exploiting the interaction between ultrasound waves and geometrical characteristics of the insonified specimen. First, the response of obliquely incident harmonic waves to a deterministic surface roughness is utilized. Analysis of backscattered amplitudes in Bragg diffraction geometry then yields a measure for the in-plane strain field by mapping any shift in angular dependency. Secondly, the analysis of the reflection characteristics of normal incident pulsed waves in frequency domain provides a measure of the out-of-plane normal strain field component, simply by tracking any change in the stimulation condition for a thickness resonance. As such, the developed ultrasonic strain gauge yields an absolute, contactless and single-sided mapping of a local 3D strain field, in which both sample preparation and alignment procedure are needless. Results are presented for cold-rolled DC06 steel samples onto which skin passing of the work rolls is applied. The samples have been mechanically loaded, introducing plastic strain levels ranging from 2% up to 35%. The ultrasonically measured strains have been validated with various other strain measurement techniques, including manual micrometer, longitudinal and transverse mechanical extensometer and optical mono- and stereovision digital image correlation. Good agreement has been obtained between the ultrasonically determined strain values and the results of the conventional methods. As the ultrasonic strain gauge provides all three normal strain field components, it has been employed for the extraction of Lankford ratios at different applied longitudinal plastic strain levels, revealing a strain dependent plastic anisotropy of the investigated DC06 steel sheet
Respiratory organ motion in interventional MRI : tracking, guiding and modeling
Respiratory organ motion is one of the major challenges in interventional MRI, particularly in interventions with therapeutic ultrasound in the abdominal region. High-intensity focused ultrasound found an application in interventional MRI for noninvasive treatments of different abnormalities. In order to guide surgical and treatment interventions, organ motion imaging and modeling is commonly required before a treatment start. Accurate tracking of organ motion during various interventional MRI procedures is prerequisite for a successful outcome and safe therapy.
In this thesis, an attempt has been made to develop approaches using focused ultrasound which could be used in future clinically for the treatment of abdominal organs, such as the liver and the kidney. Two distinct methods have been presented with its ex vivo and in vivo treatment results. In the first method, an MR-based pencil-beam navigator has been used to track organ motion and provide the motion information for acoustic focal point steering, while in the second approach a hybrid imaging using both ultrasound and magnetic resonance imaging was combined for advanced guiding capabilities.
Organ motion modeling and four-dimensional imaging of organ motion is increasingly required before the surgical interventions. However, due to the current safety limitations and hardware restrictions, the MR acquisition of a time-resolved sequence of volumetric images is not possible with high temporal and spatial resolution. A novel multislice acquisition scheme that is based on a two-dimensional navigator, instead of a commonly used pencil-beam navigator, was devised to acquire the data slices and the corresponding navigator simultaneously using a CAIPIRINHA parallel imaging method. The acquisition duration for four-dimensional dataset sampling is reduced compared to the existing approaches, while the image contrast and quality are improved as well.
Tracking respiratory organ motion is required in interventional procedures and during MR imaging of moving organs. An MR-based navigator is commonly used, however, it is usually associated with image artifacts, such as signal voids. Spectrally selective navigators can come in handy in cases where the imaging organ is surrounding with an adipose tissue, because it can provide an indirect measure of organ motion. A novel spectrally selective navigator based on a crossed-pair navigator has been developed. Experiments show the advantages of the application of this novel navigator for the volumetric imaging of the liver in vivo, where this navigator was used to gate the gradient-recalled echo sequence
320-Channel Dual Phase Lock-in Optical Spectrometer
The development of a multiple-channel lock-in optical spectrometer (LIOS) is
presented, which enables parallel phase-sensitive detection at the output of an
optical spectrometer. The light intensity from a spectrally broad source is
modulated at the reference frequency, and focused into a high-resolution
imaging spectrometer. The height at which the light enters the spectrometer is
controlled by an acousto-optic deflector, and the height information is
preserved at the output focal plane. A two-dimensional InGaAs focal plane array
collects light that has been dispersed in wavelength along the horizontal
direction, and in time along the vertical direction. The data is demodulated
using a high performance computer-based digital signal processor. This parallel
approach greatly enhances (by more than 100x) the speed at which spectrally
resolved lock-in data can be acquired. The noise performance of a working
system optimized for the 1300 nm wavelength range is analyzed using a laser
diode light source. Time-resolved absorption traces are obtained for InAs
quantum dots embedded in a GaAs matrix, and for dispersed films of PbSe
nanocrystals.Comment: 27 pages, 11 figures, submitted to the journal "Review of Scientific
Instruments
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