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Imaging phantom

About: Imaging phantom is a research topic. Over the lifetime, 28170 publications have been published within this topic receiving 510003 citations. The topic is also known as: phantom.


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Journal ArticleDOI
TL;DR: The mechanical design and validation of the prototype system using an in vitro prostate phantom are described, which shows that prostate motion is small with an in-plane displacement of less than 1 mm during the biopsy procedure.
Abstract: There are currently limitations associated with the prostate biopsy procedure, which is the most commonly used method for a definitive diagnosis of prostate cancer. With the use of two-dimensional (2D) transrectal ultrasound (TRUS) for needle-guidance in this procedure, the physician has restricted anatomical reference points for guiding the needle to target sites. Further, any motion of the physician's hand during the procedure may cause the prostate to move or deform to a prohibitive extent. These variations make it difficult to establish a consistent reference frame for guiding a needle. We have developed a 3D navigation system for prostate biopsy, which addresses these shortcomings. This system is composed of a 3D US imaging subsystem and a passive mechanical arm to minimize prostate motion. To validate our prototype, a series of experiments were performed on prostate phantoms. The 3D scan of the string phantom produced minimal geometric distortions, and the geometric error of the 3D imaging subsystem was 0.37 mm. The accuracy of 3D prostate segmentation was determined by comparing the known volume in a certified phantom to a reconstructed volume generated by our system and was shown to estimate the volume with less then 5% error. Biopsy needle guidance accuracy tests in agar prostate phantoms showed that the mean error was 2.1 mm and the 3D location of the biopsy core was recorded with a mean error of 1.8 mm. In this paper, we describe the mechanical design and validation of the prototype system using an in vitro prostate phantom. Preliminary results from an ongoing clinical trial show that prostate motion is small with an in-plane displacement of less than 1 mm during the biopsy procedure.

137 citations

Journal ArticleDOI
TL;DR: L2‐regularized reconstruction algorithms with closed‐form solutions that achieve dramatic computational speed‐up relative to state of the art L1‐ and L2‐based iterative algorithms while maintaining similar image quality for various applications in MRI reconstruction are introduced.
Abstract: Purpose: We introduce L2-regularized reconstruction algorithms with closed-form solutions that achieve dramatic computational speed-up relative to state of the art L1- and L2-based iterative algorithms while maintaining similar image quality for various applications in MRI reconstruction. Materials and Methods: We compare fast L2-based methods to state of the art algorithms employing iterative L1- and L2-regularization in numerical phantom and in vivo data in three applications; (i) Fast Quantitative Susceptibility Mapping (QSM), (ii) Lipid artifact suppression in Magnetic Resonance Spectroscopic Imaging (MRSI), and (iii) Diffusion Spectrum Imaging (DSI). In all cases, proposed L2-based methods are compared with the state of the art algorithms, and two to three orders of magnitude speed up is demonstrated with similar reconstruction quality. Results: The closed-form solution developed for regularized QSM allows processing of a three-dimensional volume under 5 s, the proposed lipid suppression algorithm takes under 1 s to reconstruct single-slice MRSI data, while the PCA based DSI algorithm estimates diffusion propagators from undersampled q-space for a single slice under 30 s, all running in Matlab using a standard workstation. Conclusion: For the applications considered herein, closed-form L2-regularization can be a faster alternative to its iterative counterpart or L1-based iterative algorithms, without compromising image quality.

137 citations

Journal ArticleDOI
TL;DR: In this article, an implantable planar inverted-F antennas, designed for intracranial pressure (ICP) monitoring at 2.45 GHz, is presented, incorporating a scalp phantom emulating the implant environment and an absorbing chamber, for characterizing the antennas, in terms of their reflection coefficient (S 11), resonance frequency (fr), and transmission coefficient through the phantom (S 21), and is reported for the first time.
Abstract: Characterization of implantable planar inverted-F antennas, designed for intracranial pressure (ICP) monitoring at 2.45 GHz, is presented. A setup, incorporating a scalp phantom emulating the implant environment and an absorbing chamber, was implemented for characterizing the antennas, in terms of their reflection coefficient (S 11), resonance frequency (fr), and transmission coefficient through the phantom (S 21) , and is reported for the first time. As a result of our observations that even a very slight change of the biocompatible (silicone) thickness can drastically change the characteristics of such antennas, several antenna prototypes with various silicone thicknesses were tested for a better understanding of the change in their performance with thickness. The main contributions of this paper rest in the evaluation of the antenna characteristics with respect to time, temperature, and far-field radiation, in an emulated biological environment. In this regard, the impact of the coating thickness on fr, drift of fr, S 11, and S 21 over time, and the effective radiated power (ERP) from the transmission (S 21) measurements were evaluated through careful measurements. A decrease in S 11 of 1.2-2.3 dB and an increase in S 21 of 2.2-2.4 dB, over a period of two days, were observed at 2.45 GHz. A decrease of 8-18 MHz for fr was also observed over the same period of time. This drift was due to the absorption of saline by the silicone, leading to a change in its effective dielectric property. An fr increase of approximately 14.5 MHz was also observed by raising the temperature from 20 degC to 37 degC, mainly because of the negative temperature coefficient of the phantom permittivity. Transmission measurements performed using both S 21 and the received power measurement (for an ICP device mimic) yielded a maximum ERP of approximately 2 mW per 1 W of power delivered to the antennas at 2.45 GHz.

136 citations

Journal ArticleDOI
TL;DR: Results show that three‐dimensional chemical exchange saturation trasfer MRI using gradient‐ and spin‐echo acquisition is feasible for whole‐brainchemical exchange saturation transfer studies at 3T in a clinical time frame.
Abstract: Chemical exchange saturation transfer magnetic resonance imaging can detect low-concentration compounds with exchangeable protons through saturation transfer to water. This technique is generally slow, as it requires acquisition of saturation images at multiple frequencies. In addition, multislice imaging is complicated by saturation effects differing from slice to slice because of relaxation losses. In this study, a fast three-dimensional chemical exchange saturation transfer imaging sequence is presented that allows whole-brain coverage for a frequency-dependent saturation spectrum (z-spectrum, 26 frequencies) in less than 10 min. The approach employs a three-dimensional gradient- and spin-echo readout using a prototype 32-channel phased-array coil, combined with two-dimensional sensitivity encoding accelerations. Results from a homogenous protein-containing phantom at 3T show that the sequence produced a uniform contrast across all slices. To show translational feasibility, scans were also performed on five healthy human subjects. Results for chemical exchange saturation transfer images at 3.5 ppm downfield of the water resonance, so-called amide proton transfer images, show that lipid signals are sufficiently suppressed and artifacts caused by B(0) inhomogeneity can be removed in postprocessing. The scan time and image quality of these in vivo results show that three-dimensional chemical exchange saturation transfer MRI using gradient- and spin-echo acquisition is feasible for whole-brain chemical exchange saturation transfer studies at 3T in a clinical time frame.

136 citations

Journal ArticleDOI
TL;DR: The phantom length and integration range for dosimetry of cone-beam CT needed to be more than 300 mm to represent more than 90% of the DPI for the body phantom with the beamwidth of more than 20 mm, and this conclusion may be applied to other multislice CT-scanners as well.
Abstract: In order to examine phantom length necessary to assess radiation dose delivered to patients in cone-beam CT with an enlarged beamwidth, we measured dose profiles in cylindrical phantoms of sufficient length using a prototype 256-slice CT-scanner developed at our institute. Dose profiles parallel to the rotation axis were measured at the central and peripheral positions in PMMA (polymethylmethacrylate) phantoms of 160 or 320 mm diameter and 900 mm length. For practical application, we joined unit cylinders (150 mm long) together to provide phantoms of 900 mm length. Dose profiles were measured with a pin photodiode sensor having a sensitive region of approximately 2.8 x 2.8 mm2 and 2.7 mm thickness. Beamwidths of the scanner were varied from 20 to 138 mm. Dose profile integrals (DPI) were calculated using the measured dose profiles for various beamwidths and integration ranges. For the body phantom (320-mm-diam phantom), 76% of the DPI was represented for a 20 mm beamwidth and 60% was represented for a 138 mm beamwidth if dose profiles were integrated over a 100 mm range, while more than 90% of the DPI was represented for beamwidths between 20 and 138 mm if integration was carried out over a 300 mm range. The phantom length and integration range for dosimetry of cone-beam CT needed to be more than 300 mm to represent more than 90% of the DPI for the body phantom with the beamwidth of more than 20 mm. Although we reached this conclusion using the prototype 256-slice CT-scanner, it may be applied to other multislice CT-scanners as well.

136 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,623
20223,476
20211,221
20201,482
20191,568
20181,503