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.

Evaluation of an ultrasonic echo-tracking method for measurements of arterial wall movements in two dimensions

Abstract: The longitudinal movement of blood vessel walls has so far gained little or no attention, as it has been presumed that these movements are of a negligible magnitude. However, modern high-resolution ultrasound scanners can demonstrate that the inner layers of the arterial wall exhibit considerable movements in the longitudinal direction. This paper evaluates a new, noninvasive, echo-tracking technique, which simultaneously can track both the radial and the longitudinal movements of the arterial wall with high resolution in vivo. Initially, the method is evaluated in vitro using a specially designed ultrasound phantom, which is attached to and moved by an X-Y system, the movement of which was compared with two high-resolution triangulation lasers. The results show an inaccuracy of 2.5% full scale deflection (fsd), reproducibility of 12 /spl mu/m and a resolution of 5 /spl mu/m, which should be more than sufficient for in vivo studies. The ability of the method is also demonstrated in a limited in vivo study in which a preselected part of the inner vessel wall of the right common carotid artery of a healthy volunteer is tracked in two dimensions over many cardiac cycles. The results show well reproducible x-y movement loops in which the recorded radial and longitudinal movements both are of the magnitude millimetre.

Dual-source spiral CT with pitch up to 3.2 and 75 ms temporal resolution: image reconstruction and assessment of image quality.

Abstract: Purpose: To present the theory for image reconstruction of a high-pitch, high-temporal-resolution spiral scan mode for dual-source CT (DSCT) and evaluate its image quality and dose Methods: With the use of two x-ray sources and two data acquisition systems, spiral CT exams having a nominal temporal resolution per image of up to one-quarter of the gantry rotation time can be acquired using pitch values up to 32 The scan field of view (SFOV) for this mode, however, is limited to the SFOV of the second detector as a maximum, depending on the pitch Spatial and low contrast resolution, image uniformity and noise, CT number accuracy and linearity, and radiation dose were assessed using the ACR CT accreditation phantom, a 30 cm diameter cylindrical water phantom or a 32 cm diameter cylindrical PMMA CTDI phantom Slice sensitivity profiles (SSPs) were measured for different nominal slice thicknesses, and an anthropomorphic phantom was used to assess image artifacts Results were compared between single-source scans at pitch=10 and dual-source scans at pitch=32 In addition, image quality and temporal resolution of an ECG-triggered version of the DSCT high-pitch spiral scan mode were evaluated with a moving coronary artery phantom, and radiation dose was assessed inmore » comparison with other existing cardiac scan techniques Results: No significant differences in quantitative measures of image quality were found between single-source scans at pitch=10 and dual-source scans at pitch=32 for spatial and low contrast resolution, CT number accuracy and linearity, SSPs, image uniformity, and noise The pitch value (16{<=}pitch{<=}32) had only a minor impact on radiation dose and image noise when the effective tube current time product (mA s/pitch) was kept constant However, while not severe, artifacts were found to be more prevalent for the dual-source pitch=32 scan mode when structures varied markedly along the z axis, particularly for head scans Images of the moving coronary artery phantom acquired with the ECG-triggered high-pitch scan mode were visually free from motion artifacts at heart rates of 60 and 70 bpm However, image quality started to deteriorate for higher heart rates At equivalent image quality, the ECG-triggered high-pitch scan mode demonstrated lower radiation dose than other cardiac scan techniques on the same DSCT equipment (25% and 60% dose reduction compared to ECG-triggered sequential step-and-shoot and ECG-gated spiral with x-ray pulsing) Conclusions: A high-pitch (up to pitch=32), high-temporal-resolution (up to 75 ms) dual-source CT scan mode produced equivalent image quality relative to single-source scans using a more typical pitch value (pitch=10) The resultant reduction in the overall acquisition time may offer clinical advantage for cardiovascular, trauma, and pediatric CT applications In addition, ECG-triggered high-pitch scanning may be useful as an alternative to ECG-triggered sequential scanning for patients with low to moderate heart rates up to 70 bpm, with the potential to scan the heart within one heart beat at reduced radiation dose« less

Multisection fat-water imaging with chemical shift selective presaturation.

Abstract: Proton chemical shift imaging yielding separate water and lipid images was performed in a multisection mode on a clinical 1.5-T whole-body magnetic resonance imaging unit. Imaging was performed with a minor modification of the standard multisection spin-warp technique: that is, the addition of a sinc pulse or a soft square pulse and a homospoil gradient at the beginning of the pulse sequence. Phantom and human anatomic images are presented.

Image quality vs radiation dose of four cone beam computed tomography scanners

Abstract: Objectives: To evaluate image quality by examining segmentation accuracy and assess radiation dose for cone beam CT (CBCT) scanners. Methods: A skull phantom, scanned by a laser scanner, and a contrast phantom were used to evaluate segmentation accuracy. The contrast phantom consisted of a polymethyl methacrylate (PMMA) cylinder with cylindrical inserts of air, bone and PMMA. The phantoms were scanned on the (1) Accuitomo 3D, (2) MercuRay, (3) NewTom 3G, (4) i-CAT and (5) Sensation 16. The structures were segmented with an optimal threshold. Thicknesses of the bone of the mandible and the diameter of the cylinders in the contrast phantom were measured across lines at corresponding places in the CT image vs a ground truth. The accuracy was in the 95th percentile of the difference between corresponding measurements. The correlation between accuracy in skull and contrast phantom was calculated. The radiation dose was assessed by DPI100,c (dose profile integral 100,c) at the central hole of a CT dose index (C...

A method for simultaneous correction of spectrum hardening artifacts in CT images containing both bone and iodine

Abstract: A method is described capable of correcting artifacts in x-ray computer tomography (CT) images due to beam hardening in an arbitrary number of substances. The method works with reconstructed image data and does not require the original raw data. It is necessary to have an estimate of the spectrum of the incident x-ray beam. The method is similar to previously described iterative methods that correct artifacts induced by bones. Our implementation was designed to correct for hardening in both bone and iodine contrast agent. It is necessary to identify those regions of the image which contain bone and iodine. A central concept is that of effective density, which is the ratio of CT number of the substance to that of water. It is necessary to establish by a preliminary experiment the relationship between CT number and mass density of iodine or bone. From these data one estimates path integrals through soft tissue (water equivalent), bone, and iodine using a reprojection algorithm applied to the given image. Given this input, a key equation is solved numerically which provides a correction term to be subtracted from the reprojected data. This can be shown to eliminate the nonlinear terms in the projections due to beam hardening, assuming that the original density estimates were correct. In principle, the method can be repeated iteratively to improve the accuracy. However, in our experience using an image of a phantom containing iothalamate meglumine and K2HPO4, scanned using the Siemens Evolution electron beam tomography scanner, the quality of the corrected image was excellent and no further iteration is needed for the phantoms studied. More research is needed to implement the method on clinical scans.