Topic
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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TL;DR: The use of the kVP-dependent scaling procedure leads to a significant improvement in reconstructed PET activity levels in phantom measurements, resolving errors of almost 40% otherwise seen for the case of dense bone phantoms at 80 kVp.
Abstract: A tube-voltage-dependent scheme is presented for transforming Hounsfield units (HU) measured by different computed tomography (CT) scanners at different x-ray tube voltages (kVp) to 511 keV linear attenuation values for attenuation correction in positron emission tomography (PET) data reconstruction A Gammex 467 electron density CT phantom was imaged using a Siemens Sensation 16-slice CT, a Siemens Emotion 6-slice CT, a GE Lightspeed 16-slice CT, a Hitachi CXR 4-slice CT, and a Toshiba Aquilion 16-slice CT at kVp ranging from 80 to 140 kVp All of these CT scanners are also available in combination with a PET scanner as a PET/CT tomograph HU obtained for various reference tissue substitutes in the phantom were compared with the known linear attenuation values at 511 keV The transformation, appropriate for lung, soft tissue, and bone, yields the function 96 x 10(-5) (HU+ 1000) below a threshold of approximately 50 HU and a (HU+ 1000)+b above the threshold, where a and b are fixed parameters that depend on the kVp setting The use of the kVp-dependent scaling procedure leads to a significant improvement in reconstructed PET activity levels in phantom measurements, resolving errors of almost 40% otherwise seen for the case of dense bone phantoms at 80 kVp Results are also presented for patient studies involving multiple CT scans at different kVp settings, which should all lead to the same 511 keV linear attenuation values A linear fit to values obtained from 140 kVp CT images using the kVp-dependent scaling plotted as a function of the corresponding values obtained from 80 kVp CT images yielded y = 1003 x -0001 with an R2 value of 0999, indicating that the same values are obtained to a high degree of accuracy
239 citations
TL;DR: An optically transparent phantom was developed for use in high-intensity focused ultrasound (US), or HIFU, dosimetry studies and characterized as a function of BSA concentration and temperature.
Abstract: An optically transparent phantom was developed for use in high-intensity focused ultrasound (US), or HIFU, dosimetry studies. The phantom is composed of polyacrylamide hydrogel, embedded with bovine serum albumin (BSA) that becomes optically opaque when denatured. Acoustic and optical properties of the phantom were characterized as a function of BSA concentration and temperature. The speed of sound (1544 m/s) and acoustic impedance (1.6 MRayls) were similar to the values in soft tissue. The attenuation coefficient was approximately 8 times lower than that of soft tissues (0.02 Np/cm/MHz for 9% BSA). The nonlinear (B/A) coefficient was similar to the value in water. HIFU lesions were readily seen during formation in the phantom. In US B-mode images, the HIFU lesions were observed as hyperechoic regions only if the cavitation activity was present. The phantom can be used for fast characterization and calibration of US-image guided HIFU devices before animal or clinical studies.
239 citations
TL;DR: The findings suggest that there is a wide range of CT numbers observed for a given tissue type as a result of scanner performance alone, and that if absolute CT numbers are to be used for diagnosis the user must document that these machine-related variations are less than the differences thought to be significant.
Abstract: The use of CT numbers as absolute values was examined by scanning a standard phantom on five CT scanners under a variety of conditions simulating those encountered in routine body CT scanning. The results show that: (1) There are significant differences in absolute CT numbers between most scanners (only one scanner produced CT numbers that were equal to zero for water); (2) There are significant differences in absolute CT numbers between two scanners of the same manufacturer and model that were examined; (3) There is a significant difference in CT numbers in a single phantom scan, dependent on location in the scan, and the format of this variability is not constant from one scanner to another; and (4) There may be a significant difference in absolute CT numbers depending on various physical factors (e.g., kilovoltage, phantom orientation in scan aperture, and position of the phantom in the scan aperture). The findings suggest that there is a wide range of CT numbers observed for a given tissue type as a r...
239 citations
TL;DR: The accuracy of computed tomography measurements in assessing cortical bone is analysed to determine the dependency of thickness and density measurements on the true width and density of the cortex and on the spatial resolution in the CT images using two optimized segmentation methods.
Abstract: In this study we analysed the accuracy of computed tomography (CT) measurements in assessing cortical bone. We determined the dependency of thickness and density measurements on the true width and density of the cortex and on the spatial resolution in the CT images using two optimized segmentation methods. As a secondary goal, we assessed the ability of CT to reflect small changes in cortical thickness. Two different bone-mimicking phantoms with varying cortical thickness were scanned with single-slice CT on a Somatom Plus 4 scanner. Images were reconstructed with both a standard and a high-resolution convolution kernel. Two special operator-independent segmentation methods were used to automatically detect the edges of the cortical shell. We measured cortical thickness and density and compared the phantom measurements with theoretical computations by simulating a cross-sectional shape of the cortical shell. Based on the simulations, we calculated CT's power to detect small changes in cortical thickness. Simulations and phantom measurements were in very good agreement. Cortical thickness could be measured with an error of less than 10% if the true thickness was larger than 0.9 (0.7) mm for the standard (high-resolution) kernel which is close to the full width at half maximum (FWHM) of the point spread functions for these kernels and our scanner. Density measurements yielded errors of less than 10% for true cortical thickness values above two to three times the FWHM corresponding to 2.5 (2) mm in our case. The simulations showed that a 10% change in cortical width would not be detected with satisfying probability in bones with a cortical shell thinner than 1.2 mm. An accurate determination of the cortical thickness is limited to bones with a thickness higher than the FWHM of the scanner's point spread function. Therefore, the use of a high-resolution reconstruction kernel is crucial. Cortical bone mineral density can only be measured accurately in bones two to three times thicker than this number. In thinner bones, the measured density becomes dependent on the thickness. Changes in cortical thickness can only be assessed if the change is rather large or if the measured bone has sufficient thickness. Therefore, assessing density or thickness of the vertebral shell by CT should be treated with caution.
239 citations