We present preliminary investigations that examine the feasibility of incorporating volumetric images generated using
digital tomosynthesis into brachytherapy treatment planning. The Integrated Brachytherapy Unit (IBU) at our facility
consists of an L-arm, C-arm isocentric motion system with an x-ray tube and fluoroscopic imager attached. Clinically,
this unit is used to generate oblique, anterior-posterior, and lateral images for simple treatment planning and dose
prescriptions. Oncologists would strongly prefer to have volumetric data to better determine three dimensional dose
distributions (dose-volume histograms) to the target area and organs at risk. Moving the patient back and forth to CT
causes undo stress on the patient, allows extensive motion of organs and treatment applicators, and adds additional time
to patient treatment. We propose to use the IBU imaging system with digital tomosynthesis to generate volumetric
patient data, which can be used for improving treatment planning and overall reducing treatment time. Initial image data
sets will be acquired over a limited arc of a human-like phantom composed of real bones and tissue equivalent material.
A brachytherapy applicator will be incorporated into one of the phantoms for visualization purposes. Digital
tomosynthesis will be used to generate a volumetric image of this phantom setup. This volumetric image set will be
visually inspected to determine the feasibility of future incorporation of these types of images into brachytherapy
treatment planning. We conclude that initial images using the tomosynthesis reconstruction technique show much
promise and bode well for future work.
We present preliminary investigations that examine the feasibility of incorporating digital tomosynthesis into radiation oncology practice with the use of kilovoltage on-board imagers (OBI). Modern radiation oncology linear accelerators now include hardware options for the addition of OBI for on-line patient setup verification. These systems include an x-ray tube and detector mounted directly on the accelerator gantry that rotate with the same isocenter. Applications include cone beam computed tomography (CBCT), fluoroscopy, and radiographs to examine daily patient positioning to determine if the patient is in the same location as the treatment plan. While CBCT provides the greatest anatomical detail, this approach is limited by long acquisition and reconstruction times and higher patient dose. We propose to examine the use of tomosynthesis reconstructed volumetric data from limited angle projection images for short imaging time and reduced patient dose. Initial data uses 61 projection images acquired over an isocentric arc of twenty degrees with the detector approximately fifty-four centimeters from isocenter. A modified filtered back projection technique, which included a mathematical correction for isocentric motion, was used to reconstruct volume images. These images will be visually and mathematically compared to volumetric computed tomography images to determine efficacy of this system for daily patient positioning verification. Initial images using the tomosynthesis reconstruction technique show much promise and bode well for effective daily patient positioning verification with reduced patient dose and imaging time. Additionally, the fast image acquisition may allow for a single breath hold imaging sequence, which will have no breath motion.
Digital tomosynthesis is a method that enables the retroactive reconstruction of arbitrary tomographic planes in an object from a finite series of digital projection radiographs, acquired with limited angle tube movement. Conventional tomosynthesis suffers from the presence of blurring artifacts, created by objects located outside of each reconstructed plane. Matrix inversion tomosynthesis (MITS) utilizes known acquisition geometry to solve directly for the unwanted out-of-plane blur artifacts, thus enabling their removal. This paper examines practical strategies for the implementation of MITS in a clinical setting, on a flat-panel fast-readout detector, with the aim of minimizing procedure time and image reconstruction artifacts concurrently. Topics include a comparison of continuous vs. incremental tube motion, the presence of reconstruction artifacts due to error in computing the x-ray tube location, the effect of scrubbing the detector between projections to reduce image retention, and a method for accounting for data that gets projected off the detector. We conclude that MITS is robust enough to be clinically applicable, even under less-than-ideal conditions. Rapid image acquisition with continuous tube movement and no detector scrubbing is clinically desirable for MITS imaging of the chest, where patient motion is a concern. Knowledge of the source-detector geometry can be satisfactorily determined via either a lead fiducial marker placed on the patient, or a tube motion device with sufficient precision and accuracy. Extrapolation of data at the top and bottom of projection images provides excellent amelioration of image truncation artifacts.
Digital tomosynthesis is a method for reconstructing arbitrary planes in an object from a series of projection radiographs, acquired with limited angle tube movement. Conventional 'shift and add' tomosynthesis suffers from the presence of blurring artifacts, created by objects located outside of each reconstructed plane. Matrix inversion tomosynthesis (MITS) uses known geometry, and a set of coupled linear algebra equations to solve for the blurring function in each reconstructed plane, enabling removal of the unwanted out-of-plane blur artifacts. For this paper, both MITS and conventional tomosynthesis reconstructions were generated for a simulated impulse located at varying distance from the detector, and also an anthropomorphic chest phantom. Exploration of the effects of total angular tube movement, number of projection radiographs acquired, and number of planes reconstructed via matrix inversion tomosynthesis, on residual out-of-plane blur ensued. We conclude that optimization of image acquisition and plane reconstruction parameters can improve slice image quality. In all examined scenarios, the MITS algorithm outperforms conventional tomosynthesis in removing out-of-plane blur.
The improved image quality and characteristics of new flat- panel x-ray detectors have renewed interest in advanced algorithms such as tomosynthesis. Digital tomosynthesis is a method of acquiring and reconstructing a three-dimensional data set with limited-angle tube movement. Historically, conventional tomosynthesis reconstruction has suffered contamination of the planes of interest by blurred out-of- plane structures. This paper focuses on a Matrix Inversion Tomosynthesis (MITS) algorithm to remove unwanted blur from adjacent planes. The algorithm uses a set of coupled equations to solve for the blurring function in each reconstructed plane. This paper demonstrates the use of the MITS algorithm in three imaging applications: small animal microscopy, chest radiography, and orthopedics. The results of the MITS reconstruction process demonstrate an improved reduction of blur from out-of-plane structures when compared to conventional tomosynthesis. We conclude that the MITS algorithm holds potential in a variety of applications to improve three-dimensional image reconstruction.
We show that the optical properties of a sample with moderate scatter can be obtained by performing frequency domain measurements in a reflection geometry. In experiments and Monte Carlo simulations we show that absorption and scatter produce opposing trends in the amplitude signal and common trends in the phase signal. Therefore a measured amplitude and phase signal correspond to a unique combination of optical properties for a given phase function.
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