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.

Nonlinear sinogram smoothing for low-dose X-ray CT

Abstract: When excessive quantum noise is present in extremely low dose X-ray CT imaging, statistical properties of the data has to be considered to achieve a satisfactory image reconstruction. Statistical iterative reconstruction with accurate modeling of the noise, rather than a filtered back-projection (FBP) with low-pass filtering, is one way to deal with the problem. Estimating a noise-free sinogram to satisfy the FBP reconstruction for the Radon transform is another way. The benefits of the latter include a higher computation efficiency, more uniform spatial resolution in the reconstructed image, and less modification of the current machine configurations. In a clinic X-ray CT system, the acquired raw data must be calibrated, in addition to the logarithmic transform, to achieve the high diagnostic image quality. The calibrated projection data or sinogram no longer follow a compound Poisson distribution in general, but are close to a Gaussian distribution with signal-dependent variance. In this paper, we first investigated a relatively accurate statistical model for the sinogram data, based on several phantom experiments. Then we developed a penalized likelihood method to smooth the sinogram, which led to a set of nonlinear equations that can be solved by iterated conditional mode (ICM) algorithm within a reasonable computing time. The method was applied to several experimental datasets acquired at 120 kVp, 10 mA/20 mA/50 mA protocols with a GE HiSpeed multi-slice detector CT scanner and demonstrated a significant noise suppression without noticeable sacrifice of the spatial resolution.

Depth-resolved model-based reconstruction of attenuation coefficients in optical coherence tomography

Abstract: We present a method, based on a single scattering model, to calculate the attenuation coefficient of each pixel in optical coherence tomography (OCT) depth profiles. Numerical simulations were used to determine the model’s response to different depths and attenuation coefficients. Experiments were performed on uniform and layered phantoms with varying attenuation coefficients. They were measured by a 1300 nm OCT system and their attenuation coefficients were evaluated by our proposed method and by fitting the OCT slope as the gold standard. Both methods showed largely consistent results for the uniform phantoms. On the layered phantom, only our proposed method accurately estimated the attenuation coefficients. For all phantoms, the proposed method largely reduced the variability of the estimated attenuation coefficients. The method was illustrated on an in-vivo retinal OCT scan, effectively removing common imaging artifacts such as shadowing. By providing localized, per-pixel attenuation coefficients, this method enables tissue characterization based on attenuation coefficient estimates from OCT data.

Morphological segmentation and partial volume analysis for volumetry of solid pulmonary lesions in thoracic CT scans

Abstract: Volumetric growth assessment of pulmonary lesions is crucial to both lung cancer screening and oncological therapy monitoring. While several methods for small pulmonary nodules have previously been presented, the segmentation of larger tumors that appear frequently in oncological patients and are more likely to be complexly interconnected with lung morphology has not yet received much attention. We present a fast, automated segmentation method that is based on morphological processing and is suitable for both small and large lesions. In addition, the proposed approach addresses clinical challenges to volume assessment such as variations in imaging protocol or inspiration state by introducing a method of segmentation-based partial volume analysis (SPVA) that follows on the segmentation procedure. Accuracy and reproducibility studies were performed to evaluate the new algorithms. In vivo interobserver and interscan studies on low-dose data from eight clinical metastasis patients revealed that clinically significant volume change can be detected reliably and with negligible computation time by the presented methods. In addition, phantom studies were conducted. Based on the segmentation performed with the proposed method, the performance of the SPVA volumetry method was compared with the conventional technique on a phantom that was scanned with different dosages and reconstructed with varying parameters. Both systematic and absolute errors were shown to be reduced substantially by the SPVA method. The method was especially successful in accounting for slice thickness and reconstruction kernel variations, where the median error was more than halved in comparison to the conventional approach.

Evaluation of specific absorption rate as a dosimeter of MRI-related implant heating.

Abstract: Purpose To compare the magnetic resonance imaging (MRI)-related heating per unit of whole body averaged specific absorption rate (SAR) of a conductive implant exposed to two different 1.5-Tesla/64 MHz MR systems. Materials and Methods Temperature changes at the electrode contacts of a deep brain stimulation lead were measured using fluoroptic thermometry. The leads were placed in a typical surgical implant configuration within a gel-filled phantom of the human head and torso. MRI was performed using two different transmit/receive body coils on two different generation 1.5-Tesla MR systems from the same manufacturer. Temperature changes were normalized to whole body averaged SAR values and compared between the two scanners. Results Depending on the landmark location, the normalized temperature change for the implant was significantly higher on one MR system compared to the other (P < 0.001). Conclusion The findings revealed marked differences across two MR systems in the level of radiofrequency (RF)-induced temperature changes per unit of whole body SAR for a conductive implant. Thus, these data suggest that using SAR to guide MR safety recommendations for neurostimulation systems or other similar implants across different MR systems is unreliable and, therefore, potentially dangerous. Better, more universal, measures are required in order to ensure patient safety. J. Magn. Reson. Imaging 2004;20:315–320. © 2004 Wiley-Liss, Inc.

ECAT: a new computerized tomographic imaging system for positron-emitting radiopharmaceuticals.

Abstract: The ECAT was designed and developed as a positron imaging system capable of providing high contrast, high resolution, quantitative images in two-dimensional (2-D) and tomographic formats. The flexibility in its variety of imaging problems. High (HR), medium (MR), and low (LR) tomographic resolutions are 0.95 +/- 0.1, 1.3 +/- 0.1, and 1.7 +/- 0.1 cm FWHM; high, medium, and low resolutions in 2-D images are 0.85 +/- 0.1, 1.3 +/- 0.1 and 1.7 +/- 0.1, depending on resolution mode employed. ECT system efficiency is 30,100, 15,900, and 9,200 c/sec/muCi/cc with a 20-cm diameter phantom at LR, MR, and HR. Because of the geometric, detector, electronic and shielding design of the system, count-rate capability and linearity are high, with minimum detection of scattered radiation and random coincidence. Measured error agrees well with theoretical statistical predictions down to a level of 1.4% standard deviation. The redundant sampling scheme of this system significantly reduces errors caused by motion and detector instability. Scan times are variable from 10 sec to several min/slice and multiple levels are automatically performed by computer control of patient bed. A variety of human studies illustrate image quality, resolution, and efficiency of both ECT and 2-D imaging mode. Examples of the noninvasive study method have been made possible through development of ECT.