Journal of X-Ray Science and Technology - Volume 10, issue 1-2

Authors: Qian, Wei | Sun, Xuejun | Clark, Robert

Article Type: Research Article

Abstract: In this paper a novel hybrid filter architecture is presented that incorporates an adaptive multistage nonlinear filter (AMNF) and Multiresolution/Multiorientation Wavelet Transform (MMWT) specifically designed for image enhancement in medical imaging. The MMWT is used for multiresolution and/or multiorientation decomposition and reconstruction of the mammograms where selective reconstruction of subimages is used to perform further enhancement of the MCCs and masses. The specific clinical application is enhancement of microcalcification clusters (MCCs) and …masses in digitized mammograms and the AMNF is used for noise suppression and image enhancement. This novel filter was evaluated using diagnostic images from two databases: (a) and (b). Database (a) has 100 single view mammograms at a resolution of 105 micron and 12 bits gray level. It contains 50 cases of normal mammograms and 50 cases of biopsy proven malignant MCCs. Database (b) has 100 single view mammograms at a resolution of 180 micron and 12 bits gray value. It contains 50 normal and 50 biopsy proven abnormal masses. Visual inspection of the enhanced images demonstrated improved visualization of MCCs/masses and the morphology of the individual subtle microcalcifications and masses compared with unprocessed images. The performance of the enhancement method was quantitatively evaluated using a Kalman Filtering Neural Network for MCCs and mass detection and applied to the digital mammograms of the database (a) and (b). The sensitivities (True Positive (TP) detection rate) of MCC cluster detection were 93% images respectively, and the average false positive (FP) detection rate was 1.35 FP and 1.47 MCCs/image respectively. The sensitivities of mass detection were 85% unprocessed images respectively and the average FP rates were 1.81 and 2.75 masses/image respectively. The Research results in this article demonstrate the importance of the hybrid filter architecture for enhancement in the computerized detection of MCCs and mass. Show more

Citation: Journal of X-Ray Science and Technology, vol. 10, no. 1-2, pp. 1-15, 2002

Authors: Lee, Denny L.Y. | Golden, Kelly P. | Yorker, Jeffrey G. | Davis, Jim | Rodricks, Brian G. | Cheung, Lawrence K. | Jeromin, Lothar S.

Article Type: Research Article

Abstract: Direct conversion of x-ray energy into electrical charge has been extensively developed into imaging products in the past few years. Applications include general radiography, mammography, x-ray crystallography, portal imaging, and non-destructive testing. Direct methods avoid intermediate conversion of x-rays into light prior to generating a measurable electrical charge. This eliminates light scattering effects on image sharpness, allowing detectors to be designed to the limit of the theoretical modulation transfer function for a …discrete-pixel sensor. Working exposure range can be customized by adjusting bias and thickness of sensor layers in coordination with readout-electronics specifications. Mature amorphous selenium technology and recent progress on high-quality Thin-Film Transistor (TFT) arrays for computer displays have allowed development of practical large-area high-resolution flat-panel x-ray imaging systems. A variety of design optimizations enable direct-conversion technology to satisfy a wide range of applications including dynamic imaging. Show more

Citation: Journal of X-Ray Science and Technology, vol. 10, no. 1-2, pp. 17-36, 2002

Authors: Shi, Minyan | Tao, Gang | Liu, Hong

Article Type: Research Article

Abstract: In this paper, an adaptive control technology is presented, which has certain application potential to teleoperation of X -ray machines. The focus of this technology is on transparency which is an important concept for teleoperation systems. In a transparent teleoperation, the human operator feels as if to manipulate the slave environment directly. When a teleoperation system is known, a fixed controller can be designed to ensure a teleoperation control system stable and transparent. In this …case, system transparency is achieved in terms of impedance matching. However, when the parameters of a teleoperation system are unknown, exact impedance matching is impossible and new concepts of transparency are needed. Several suitable adaptive control schemes are developed for control of a teleoperation system with unknown parameters of different types: those with constant values, those with jumping values, and those with smooth but large time-varying values. Associated with different situations of adaptive control systems, different new transparency concepts are introduced and verified by analysis and simulation results. Show more

Keywords: adaptive control, human operator, performance robustness, slave environment, stability, system uncertainties, teleoperation systems, tracking, transparency

Citation: Journal of X-Ray Science and Technology, vol. 10, no. 1-2, pp. 37-57, 2002

Authors: Ye, Yangbo | Wang, Ge | Zhu, Jiehua

Article Type: Research Article

Abstract: In this report, we present a number-theory-based approach for discrete tomography (DT),which is based on parallel projections of rational slopes. Using a well-controlled geometry of X-ray beams, we obtain a system of linear equations with integer coefficients. Assuming that the range of pixel values is a(i,j)=0,1<FORMULA>, &mldr;, <FORMULA>M-1<FORMULA>, with <FORMULA>M being a prime number, we reduce the equations modulo M . To invert the linear system, each algorithmic step only …needs log^2_2 M bit operations. In the case of a small M , we have a greatly reduced computational complexity, relative to the conventional DT algorithms, which require log^2_2 N bit operations for a real number solution with a precision of 1/N . We also report computer simulation results to support our analytic conclusions. Show more

Keywords: computed tomography (CT), discrete tomography (DT), number theory, Diophantine equations, computational complexity

Citation: Journal of X-Ray Science and Technology, vol. 10, no. 1-2, pp. 59-66, 2001

Authors: Zhao, Shiying | Bae, Kyongtae T. | Whiting, Bruce | Wang, Ge

Article Type: Research Article

Abstract: Image artifacts induced by multiple metallic objects pose a persistent problem in X-ray computed tomography (CT). Among existing CT methods for metal artifact reduction, the wavelet-based approach we recently developed is very promising in practice. In this paper, we report a major refinement to our earlier work [1]. The key component of this refinement is a novel weighting scheme for wavelet multiresolution interpolation. This weighting scheme is designed specifically to take into account multiple metallic implants …in the field of view. In contrast to commonly used noniterative algorithms, our algorithm identifies and corrects most seriously corrupted projection data based on wavelet multiresolution analysis. Experimental results indicate that the proposed algorithm significantly improves the image quality, and clearly reveals anatomic details in the immediate vicinity of multiple metallic implants. Show more

Keywords: X-ray computed tomography (CT), metal artifact reduction (MAR), image quality, wavelet, multiresolution

Citation: Journal of X-Ray Science and Technology, vol. 10, no. 1-2, pp. 67-76, 2002

Authors: Jiang, Ming | Wang, Ge

Article Type: Research Article

Abstract: The iterative approach is important for computed tomography (CT) and attracting more and more attention with the rapid evolution of computer technology. In this paper, classic results and recent advances on iterative algorithms for image reconstruction are reviewed, with an emphasis on the ART-like and EM-like algorithms in both of their simultaneous and ordered-subset formats. The following issues are discussed: what the computational structures are, under what conditions the algorithms converge, what …the final limits are, what the relaxation strategies we have, how the final limits depend on the initial guesses, and so on. In addition, heuristic arguments are given for the SART and EM algorithms for understanding the algorithms. Finally, future research directions are discussed, along with guidelines for practical applications of iterative algorithms. Show more

Citation: Journal of X-Ray Science and Technology, vol. 10, no. 1-2, pp. 77-86, 2002

Authors: Baydush, Alan H. | Floyd Jr., Carey E.

Article Type: Research Article

Abstract: {\it Purpose:} The effect of Bayesian image estimation (BIE), which reduces image scatter and improves contrast-to-noise ratios (CNR), on reduced dose digital mammography is studied. {\it Methods/Materials:} Standard dose digital mammographic images of the ACR breast phantom were acquired with and without a grid. Additional images were acquired without the grid at reduced exposures and were processed by BIE. CNR values were computed for visible masses before and after processing for each exposure and …compared to using a grid. {\it Results:} With no change in exposure, BIE applied to the image acquired without the grid improves CNR from 209 to 520% over that provided by the grid. While these results were not as good at reduced exposures, BIE processing still improved CNR from 236 to 465% over a grid. {\it Conclusions:} BIE processing of reduced exposure level images offers increased CNR and subjective visualization compared to images acquired with a grid at standard exposure. Show more

Keywords: scatter, image processing, statistical estimation, Bayesian, digital mammography

Citation: Journal of X-Ray Science and Technology, vol. 10, no. 1-2, pp. 87-93, 2002

Authors: Lin, Yao | Tian, Jie | He, Huiguang

Article Type: Research Article

Abstract: A new interactive segmentation method that combines fuzzy connected object extraction and edge detection is proposed. Fuzzy connectedness is a global fuzzy relation, which effectively captures fuzzy "hanging togetherness" of image elements. First, by selecting the seed point, fuzzy connectedness value between each image element and the seed point is computed via dynamic programming. Then, through adjusting the parameter, the different fuzzy connected object could be extracted. Finally, an edge detection method is …adopted to detect the object boundary. The algorithm is demonstrated on some medical images: segmentation of knee tissues in CT image and segmentation of brain tissues in MR image. The results show that this method works well for some CT and MR images. Show more

Citation: Journal of X-Ray Science and Technology, vol. 10, no. 1-2, pp. 95-106, 2002

Authors: Tsai, J.-S. | Mahajan, A. | Borden, J. | Rivard, M.J. | Engler, M.J.

Article Type: Research Article

Abstract: A GK plan (GKP) is dosimetrically reproduced following GK Frame (GKF) system failure. A humanoid head Phantom embedded with seven targets was used for the simulation. GKF was attached to the Phantom by 4 pin screws. GKP using CT images solely assigned a single shot to each target for dose coverage. The shots treatment times were based on dose prescription and the skull geometric data (SGD). Afterwards, GKF was adjusted and CT, SGD were repeated. A …new GKP was reconstructed by transforming the shots coordinates and treatment times from the original GKF/SGD systems to the new ones. TLDs were inserted into the target sites for dose verifications achieving mutual agreement within 2% clinical cases forced us to do GKF reinstallation: pin loosened in the midway of patient treatment; treatment encountered a helpless GKF collision with the helmet. Each case, a new GKP reproduced by the aforementioned transformations was adopted to keep GK SRS ongoing. In conclusion, if GK SRS was forced to stop due to either a pin attachment failure or GKF collision with helmet, then GKF readjustment and rescan images will not compromise the outcome of a GK SRS treatment. Show more

Keywords: gamma Knife stereotactic radiosurgery, humanoid phantom, CT, MRI, TLD, Pin screw, Localizer Frame, Frame re-installation, Shot center coordinates, Coordinates transformation, Skull geometry data, Scout plan

Citation: Journal of X-Ray Science and Technology, vol. 10, no. 1-2, pp. 107-126, 2002

Authors: Haller, John W. | Westerman, Bryan | Vannier, Michael W.

Article Type: Research Article

Abstract: Multirow CT detectors coupled with 2, 4, 8 and 16 or more simultaneous data acquisition channels are now used in clinical imaging. Furthermore, multirow CT detectors are used with conventional or flat-panel image intensifiers mounted on c-arms that allow 3D CT scanning in rotational angiography or orthopedic interventions. These multirow, multichannel CT systems provide increased speed that translates into the ability to scan larger segments of anatomy more quickly. The principal drawback of …multislice/multidector/multichannel CT scanners are increased computational burden, faster data rates, more voluminous data sets, and most importantly, the requirement to use cone beam rather than slice-by-slice reconstruction algorithms. The future of multichannel CT in clinical applications demands improved radiation dose efficiency, isotropic imaging, tailored cone beam reconstruction algorithms, and post-processing visualization of volume image data. Show more

Keywords: X-ray, spiral, computed tomography, imaging

Citation: Journal of X-Ray Science and Technology, vol. 10, no. 1-2, pp. 127-138, 2002