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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: A method has been developed to accurately monitor the motion of the head during a neurological PET acquisition, and correct for this motion prior to image reconstruction and does not add significantly to either the acquisition or the subsequent data processing.
Abstract: A method is described to monitor the motion of the head during neurological positron emission tomography (PET) acquisitions and to correct the data post acquisition for the recorded motion prior to image reconstruction. The technique uses an optical tracking system, Polaris™, to accurately monitor the position of the head during the PET acquisition. The PET data are acquired in list mode where the events are written directly to disk during acquisition. The motion tracking information is aligned to the PET data using a sequence of pseudo-random numbers, which are inserted into the time tags in the list mode event stream through the gating input interface on the tomograph. The position of the head is monitored during the transmission acquisition, and it is assumed that there is minimal head motion during this measurement. Each event, prompt and delayed, in the list mode event stream is corrected for motion and transformed into the transmission space. For a given line of response, normalization, including corrections for detector efficiency, geometry and crystal interference and dead time are applied prior to motion correction and rebinning in the sinogram. A series of phantom experiments were performed to confirm the accuracy of the method: (a) a point source located in three discrete axial positions in the tomograph field of view, 0 mm, 10 mm and 20 mm from a reference point, (b) a multi-line source phantom rotated in both discrete and gradual rotations through ±5° and ±15°, including a vertical and horizontal movement in the plane. For both phantom experiments images were reconstructed for both the fixed and motion corrected data. Measurements for resolution, full width at half maximum (FWHM) and full width at tenth maximum (FWTM), were calculated from these images and a comparison made between the fixed and motion corrected datasets. From the point source measurements, the FWHM at each axial position was 7.1 mm in the horizontal direction, and increasing from 4.7 mm at the 0 mm position, to 4.8 mm, 20 mm offset, in the vertical direction. The results from the multi-line source phantom with ±5° rotations showed a maximum degradation in FWHM, when compared with the stationary phantom, of 0.6 mm, in the horizontal direction, and 0.3 mm in the vertical direction. The corresponding values for the larger rotation, ±15°, were 0.7 mm and 1.1 mm, respectively. The performance of the method was confirmed with a Hoffman brain phantom moved continuously, and a clinical acquisition using [11C]raclopride (normal volunteer). A visual comparison of both the motion and non-motion corrected images of the Hoffman brain phantom clearly demonstrated the efficacy of the method. A sample time-activity curve extracted from the clinical study showed irregularities prior to motion correction, which were removed after correction. A method has been developed to accurately monitor the motion of the head during a neurological PET acquisition, and correct for this motion prior to image reconstruction. The method has been demonstrated to be accurate and does not add significantly to either the acquisition or the subsequent data processing.

227 citations

Journal ArticleDOI
TL;DR: This work presents a novel design approach, regarding coil array elements as antennas, which is characterized by comparison with three other, more conventional designs using finite difference time domain (FDTD) simulations and B +1 measurements on a phantom.
Abstract: Ultra high field MR imaging (≥7 T) of deeply located targets in the body is facing some radiofrequency-field related challenges: interference patterns, reduced penetration depth, and higher Specific Absorbtion Ratio (SAR) levels. These can be alleviated by redesigning the elements of the transmit or transceive array. This is because at these high excitation field (B1) frequencies, conventional array element designs may have become suboptimal. In this work, an alternative design approach is presented, regarding coil array elements as antennas. Following this approach, the Poynting vector of the element should be oriented towards the imaging target region. The single-side adapted dipole antenna is a novel design that fulfills this requirement. The performance of this design as a transmit coil array element has been characterized by comparison with three other, more conventional designs using finite difference time domain (FDTD) simulations and B measurements on a phantom. Results show that the B level at the deeper regions is higher while maintaining relatively low SAR levels. Also, the B field distribution is more symmetrical and more uniform, promising better image homogeneity. Eight radiative antennas have been combined into a belt-like surface array for prostate imaging. T1-weighted (T1W) and T2-weighted (T2W) volunteer images are presented along with B measurements to demonstrate the improved efficiency. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.

227 citations

Journal ArticleDOI
TL;DR: An alternative approach to correct for flip angle inaccuracies in the driven equilibrium single pulse observation of T1 (DESPOT1) T1 mapping method is investigated.
Abstract: Purpose To investigate an alternative approach to correct for flip angle inaccuracies in the driven equilibrium single pulse observation of T1 (DESPOT1) T1 mapping method. Materials and Methods While DESPOT1 is a robust method for rapid whole-brain voxelwise mapping of the longitudinal relaxation time, the approach is inherently sensitive to inaccuracies in the transmitted flip angle, defined by the B1 field, which become more severe with increased field. Here we propose an extension of the DESPOT1 technique, involving the additional acquisition of an inversion-prepared SPGR image alongside the conventional multiangle DESPOT1 data. From these combined data both B1 and T1 may be determined with high accuracy and precision. The method is evaluated at 3T with phantom and in vivo imaging experiments, with derived T1 estimates compared with values calculated from multiple inversion time inversion recovery data. Results The method provides robust correction of flip angle variations, with less than 5% error compared with reference values for T1 between 300 msec and 2500 msec. Conclusions The described approach, dubbed DESPOT1-HIFI, permits whole-brain T1 mapping at 3T, with 1 mm3 isotropic voxels, in a clinically feasible time (≈10 minutes) with T1 accuracy greater than 5% and with high precision. J. Magn. Reson. Imaging 2007;26:1106–1111. © 2007 Wiley-Liss, Inc.

227 citations

Journal ArticleDOI
Tianfang Li1, B. Thorndyke1, Eduard Schreibmann1, Yong Yang1, Lei Xing1 
TL;DR: A method to enhance the performance of 4D PET by developing a new technique of4D PET reconstruction with incorporation of an organ motion model derived from 4D-CT images based on the well-known maximum-likelihood expectation-maximization (ML-EM) algorithm is proposed.
Abstract: Positron emission tonography (PET) is useful in diagnosis and radiation treatment planning for a variety of cancers. For patients with cancers in thoracic or upper abdominal region, the respiratory motion produces large distortions in the tumor shape and size, affecting the accuracy in both diagnosis and treatment. Four-dimensional (4D) (gated) PET aims to reduce the motion artifacts and to provide accurate measurement of the tumor volume and the tracer concentration. A major issue in 4D PET is the lack of statistics. Since the collected photons are divided into several frames in the 4D PET scan, the quality of each reconstructed frame degrades as the number of frames increases. The increased noise in each frame heavily degrades the quantitative accuracy of the PET imaging. In this work, we propose a method to enhance the performance of 4D PET by developing a new technique of 4D PET reconstruction with incorporation of an organ motion model derived from 4D-CT images. The method is based on the well-known maximum-likelihood expectation-maximization (ML-EM) algorithm. During the processes of forward- and backward-projection in the ML-EM iterations, all projection data acquired at different phases are combined together to update the emission map with the aid of deformable model, the statistics is therefore greatly improved. The proposed algorithm was first evaluated with computer simulations using a mathematical dynamic phantom. Experiment with a moving physical phantom was then carried out to demonstrate the accuracy of the proposed method and the increase of signal-to-noise ratio over three-dimensional PET. Finally, the 4D PET reconstruction was applied to a patient case.

226 citations

Journal ArticleDOI
TL;DR: Despite limitations of the system when compared with a state of the art CT scanner, the transmission anatomical maps allow for precise anatomical localisation and for attenuation correction of the emission images.
Abstract: Scintigraphic diagnosis, based on functional image interpretation, becomes more accurate and meaningful when supported by corresponding anatomical data. In order to produce anatomical images that are inherently registered with images of emission computerised tomography acquired with a gamma camera, an X-ray transmission system was mounted on the slip-ring gantry of a GEMS Millennium VG gamma camera. The X-ray imaging system is composed of an X-ray tube and a set of detectors located on opposite sides of the gantry rotor that moves around the patient along with the nuclear detectors. A cross-sectional anatomical transmission map is acquired as the system rotates around the patient in a manner similar to a third-generation computerised tomography (CT) system. Following transmission, single-photon emission tomography (SPET) or positron emission tomography (PET) coincidence detection images are acquired and the resultant emission images are thus inherently registered to the anatomical maps. Attenuation correction of the emission images is performed with the same anatomical maps to generate transmission maps. Phantom experiments of system performance and examples of first SPET and coincidence detection patient images are presented. Despite limitations of the system when compared with a state of the art CT scanner, the transmission anatomical maps allow for precise anatomical localisation and for attenuation correction of the emission images.

225 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