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.

Variance analysis of x-ray CT sinograms in the presence of electronic noise background.

Abstract: Purpose: Low-dose x-ray computed tomography (CT) is clinically desired Accurate noise modeling is a fundamental issue for low-dose CT image reconstruction via statistics-based sinogram restoration or statistical iterative image reconstruction In this paper, the authors analyzed the statistical moments of low-dose CT data in the presence of electronic noise background Methods: The authors first studied the statistical moment properties of detected signals in CT transmission domain, where the noise of detected signals is considered as quanta fluctuation upon electronic noise background Then the authors derived, via the Taylor expansion, a new formula for the mean–variance relationship of the detected signals in CT sinogram domain, wherein the image formation becomes a linear operation between the sinogram data and the unknown image, rather than a nonlinear operation in the CT transmission domain To get insight into the derived new formula by experiments, an anthropomorphic torso phantom was scanned repeatedly by a commercial CT scanner at five different mAs levels from 100 down to 17 Results: The results demonstrated that the electronic noise background is significant when low-mAs (or low-dose) scan is performed Conclusions: The influence of the electronic noise background should be considered in low-dose CT imaging

Technical performance evaluation of a human brain PET/MRI system

Abstract: Technical performance evaluation of a human brain PET/MRI system. The magnetic field compatible positron emission tomography (PET) insert is based on avalanche photodiode (APD) arrays coupled with lutetium oxyorthosilicate (LSO) crystals and slip-fits into a slightly modified clinical 3-T MRI system. The mutual interference between the two imaging techniques was minimised by the careful design of the hardware to maintain the quality of the B 0 and B 1 field homogeneity. The signal-to-noise ratio (SNR) and the homogeneity of the MR images were minimally influenced by the presence of the PET. Measurements according to the Function Biomedical Informatics Research Network (FBIRN) protocol proved the combined system’s ability to perform functional MRI (fMRI). The performance of the PET insert was evaluated according to the National Electrical Manufacturers Association (NEMA) standard. The noise equivalent count rate (NEC) peaked at 30.7 × 103 counts/s at 7.3 kBq/mL. The point source sensitivity was greater than 7 %. The spatial resolution in the centre field of view was less than 3 mm. Patient data sets clearly revealed a noticeably good PET and MR image quality. PET and MRI phantom tests and first patient data exhibit the device’s potential for simultaneous multiparametric imaging. • Combination of PET and MRI is a new emerging imaging technology. • Evaluated brain PET/MRI enables uncompromised imaging performance. • PET/MRI aims to provide multiparametric imaging allowing acquisition of morphology and metabolism.

Respiratory Motion Correction in Oncologic PET Using T1-Weighted MR Imaging on a Simultaneous Whole-Body PET/MR System

Abstract: Hybrid PET/MR combines the exceptional molecular sensitivity of PET with the high resolution and versatility of MR imaging. Simultaneous data acquisition additionally promises the use of MR to enhance the quality of PET images, for example, by respiratory motion correction. This advantage is especially relevant in thoracic and abdominal areas to improve the visibility of small lesions with low radiotracer uptake and to enhance uptake quantification. In this work, the applicability and performance of an MR-based method of respiratory motion correction for PET tumor imaging was evaluated in phantom and patient studies. Methods: PET list-mode data from a motion phantom with 22Na point sources and 5 patients with tumor manifestations in the thorax and upper abdomen were acquired on a simultaneous hybrid PET/MR system. During the first 3 min of a 5-min PET scan, the respiration-induced tissue deformation in the PET field of view was recorded using a sagittal 2-dimensional multislice gradient echo MR sequence. MR navigator data to measure the location of the diaphragm were acquired throughout the PET scan. Respiration-gated PET data were coregistered using the MR-derived motion fields to obtain a single motion-corrected PET dataset. The effect of motion correction on tumor visibility, delineation, and radiotracer uptake quantification was analyzed with respect to uncorrected and gated images. Results: Image quality in terms of lesion delineation and uptake quantification was significantly improved compared with uncorrected images for both phantom and patient data. In patients, in head–feet line profiles of 14 manifestations, the slope became steeper by 66.7% (P = 0.001) and full width at half maximum was reduced by 20.6% (P = 0.001). The mean increase in maximum standardized uptake value, lesion-to-background ratio (contrast), and signal-to-noise ratio was 28.1% (P = 0.001), 24.7% (P = 0.001), and 27.3% (P = 0.003), respectively. Lesion volume was reduced by an average of 26.5% (P = 0.002). As opposed to the gated images, no increase in background noise was observed. However, motion correction performed worse than gating in terms of contrast (−11.3%, P = 0.002), maximum standardized uptake value (−10.7%, P = 0.003), and slope steepness (−19.3%, P = 0.001). Conclusion: The proposed method for MR-based respiratory motion correction of PET data proved feasible and effective. The short examination time and convenience (no additional equipment required) of the method allow for easy integration into clinical routine imaging. Performance compared with gating procedures can be further improved using list-mode–based motion correction.

Calculation of backscatter factors for diagnostic radiology using Monte Carlo methods.

Abstract: Backscatter factors were determined for x-ray beams relevant to diagnostic radiology using Monte Carlo methods. The phantom size considered most suitable for calibration of dosimeters is a cuboid of 30 x 30 cm2 front surface and 15 cm depth. This phantom size also provides a good approximation to adult patients. Three different media were studied: water, PMMA and ICRU tissue; the source geometry was a point source with varying field size and source-to-phantom distance. The variations of the backscatter factor with phantom medium and field geometry were examined. From the obtained data, a set of backscatter factors was selected and proposed for adoption as a standard set for the calibration of dosimeters to be used to measure diagnostic reference doses.

Proton dose monitoring with PET: quantitative studies in Lucite.

Abstract: The feasibility of using PET for proton dose monitoring is examined here in detail. First experimental studies in a Lucite phantom have been performed at the medical TRIUMF proton beamline for proton energies of 62 MeV and 110 MeV. The proton dose delivered to the phantom ranged from 16 Gy up to 317 Gy. The induced activity was analysed 20-40 min after the irradiation with a PET scanner. The obtained depth activity profiles were compared to our calculation based on a model using available isotope production cross-section data. Both the observed absolute count rates and the activity profiles were found to agree very well with this model. Effects such as proton range straggling, inelastic nuclear interactions and the energy spectrum of the emitted positrons were studied in detail and found to change the activities by 5-10%. The lateral deposition of dose in the phantom could be very well localized by the induced activity. However, the spatial correlation between dose depth profiles and depth activity profiles was found to be poor, hence the extraction of isodose profiles from activity profiles seems to be very difficult.