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.

Prospects and challenges of rendering tissue density in Hounsfield units for cone beam computed tomography.

Abstract: Objectives Limitations in rendering of tissue density in Hounsfield units (HUs) for cone beam computed tomography (CBCT) are described and illustrated using a phantom and two CBCT systems to demonstrate grayscale measurement variability. Materials and methods The basis of the HU scale, its correlation with measured computed tomography (CT) numbers, and the limitations in the accuracy of such correlation due to artifacts are discussed. Rendering of tissue densities based on HU values of two CBCT systems [NewTom VGi and Hyperion X9, respectively large and small field of view (FOV)] are measured using a phantom. Results Data produced from small FOV CBCT acquisition are generally less affected by artifacts compared with large FOV CBCT. Conclusions Artifacts challenge the accurate conversion of density values into HUs. Care should be taken when interpreting quantitative density measurements obtained with CBCT. With more advanced software and methods, it may be possible to improve the consistency and accuracy of density measurements.

APD-based PET detector for simultaneous PET/MR imaging

Abstract: Two, APD-based, PET modules have been evaluated for use in combined PET/MR imaging. Each module consists of 4 independent, optically isolated detectors. Each detector consists of an 8×8 array of 2×2×20 mm LSO crystals read out by a 2×2 array of 5×5 mm Hamamatsu S8664-55 APDs. The average crystal energy resolution and time resolution (against a plastic scintillator on a PMT) of the detectors was 17% and 1.8 ns, respectively. The modules were positioned in the tunnel of a 1.5 T Siemens Symphony MR scanner. The presence of the PET modules decreased the MR signal-to-noise ratio by about 15% but no image interference was observed. The gradient and RF pulse sequences of the MR produced adverse effects on the PET event signals. These high-frequency pulses did not affect the true PET events but did increase the dead time of the PET system. Simultaneous, artifact-free, images were acquired with the PET and MR system using a small Derenzo phantom. These results show that APD-based PET detectors can be used for a high-resolution and cost-effective integrated PET/MR system.

Dosimetric characterization of a cone-beam O-arm™ imaging system

Abstract: This study compared patient dose and image quality of a mobile O-arm cone beam imaging system in the 3D scan acquisition mode to those of a 64 slice Computed Tomography (CT) imaging system The investigation included patient dose, scattered radiation, and image quality measurements The patient dose was measured using a 06 cc Farmer ion chamber and 30 cm long Computed Tomography (CT) head and body polymethylmethacrylate (PMMA) phantoms The results show that under identical radiographic techniques (kVp, mAs, etc) and with the same scan length, the O-arm in 3D scan acquisition mode delivers approximately half the radiation dose of a 64 slice CT scanner Scattered radiation was measured at several locations around the O-arm, at 1 m, 2 m and 3 m distances in 3D CT scan acquisition mode with a RadCal 10 x 5-180 pancake ion chamber using a 30 cm long CT body phantom as the source of scatter Similar measurements were made in a 64 slice CT scanner The data demonstrate that scattered radiation from the O-arm to personnel involved in a clinical procedure is comparable to that from a 64 slice CT scanner Image quality was compared by exposing a CATPHAN phantom to comparable doses in both the O-arm and the CT scanner The resultant images were then evaluated for modulation transfer function (MTF), high-contrast spatial resolution, and low contrast sensitivity for clinical application purpose The O-arm shows comparable high contrast to the CT (7 lp/cm vs 8 lp/cm) The low contrast in the O-arm is not visible due to fixed pattern noise For image guided surgery applications where the location of a structure is emphasized over a survey of all image details, the O-arm has some advantages due to wide radiation beam coverage and lower patient dose The image quality of the O-arm needs significant improvement for other clinical applications where high image quality is desired

Monte carlo simulations of dose from microCT imaging procedures in a realistic mouse phantom.

Abstract: The purpose of this work was to calculate radiation dose and its organ distribution in a realistic mouse phantom from micro-computed tomography (microCT) imaging protocols. CT dose was calculated using GATE and a voxelized, realistic phantom. The x-ray photon energy spectra used in simulations were precalculated with GATE and validated against previously published data. The number of photons required per simulated experiments was determined by direct exposure measurements. Simulated experiments were performed for three types of beams and two types of mouse beds. Dose-volume histograms and dose percentiles were calculated for each organ. For a typical microCT screening examination with a reconstruction voxel size of 200 microm, the average whole body dose varied from 80 mGy (at 80 kVp) to 160 mGy (at 50 kVp), showing a strong dependence on beam hardness. The average dose to the bone marrow is close to the soft tissue average. However, due to dose nonuniformity and higher radiation sensitivity, 5% of the marrow would receive an effective dose about four times higher than the average. If CT is performed longitudinally, a significant radiation dose can be given. The total absorbed radiation dose is a function of milliamperes-second, beam hardness, and desired image quality (resolution, noise and contrast). To reduce dose, it would be advisable to use the hardest beam possible while maintaining an acceptable contrast in the image.

Calibration of three-dimensional ultrasound images for image-guided radiation therapy

Abstract: A new technique of patient positioning for radiotherapy/radiosurgery of extracranial tumours using three-dimensional (3D) ultrasound images has been developed. The ultrasound probe position is tracked within the treatment room via infrared light emitting diodes (IRLEDs) attached to the probe. In order to retrieve the corresponding room position of the ultrasound image, we developed an initial ultrasound probe calibration technique for both 2D and 3D ultrasound systems. This technique is based on knowledge of points in both room and image coordinates. We first tested the performance of three algorithms in retrieving geometrical transformations using synthetic data with different noise levels. Closed form solution algorithms (singular value decomposition and Horn's quaternion algorithms) were shown to outperform the Hooke and Jeeves iterative algorithm in both speed and accuracy. Furthermore, these simulations show that for a random noise level of 2.5, 5, 7.5 and 10 mm, the number of points required for a transformation accuracy better than 1 mm is 25, 100, 200 and 500 points respectively. Finally, we verified the tracking accuracy of this system using a specially designed ultrasound phantom. Since ultrasound images have a high noise level, we designed an ultrasound phantom that provides a large number of points for the calibration. This tissue equivalent phantom is made of nylon wires, and its room position is optically tracked using IRLEDs. By obtaining multiple images through the nylon wires, the calibration technique uses an average of 300 points for 3D ultrasound volumes and 200 for 2D ultrasound images, and its stability is very good for both rotation (standard deviation: 0.4°) and translation (standard deviation: 0.3 mm) transformations. After this initial calibration procedure, the position of any voxel in the ultrasound image volume can be determined in world space, thereby allowing real-time image guidance of therapeutic procedures. Finally, the overall tracking accuracy of our 3D ultrasound image-guided positioning system was measured to be on average 0.2 mm, 0.9 mm and 0.6 mm for the AP, lateral and axial directions respectively.