Search

Recent developments in detectors and electronics enable both positron emission tomography (PET) and X-ray computed tomography (CT) data to be acquired concurrently using the same detection front-end for dual-modality PET/CT imaging. Moreover, it would potentially allow substantial reduction of cost and housing size, in addition to facilitating image fusion. However, the lower energy signals (~ 60 keV versus 511 keV) and higher photon flux per pixel (> 1 Mcps versus 10 kcps) in CT relative to PET cause significant pile-up and dead-time in CT data acquired in photon counting mode. A digital signal processing method was developed and implemented to improve processing of detector signals sampled at low frequency (~ 45 MHz) in presence of pile-up. The method consists in digitally subtracting the detector impulse response at the output of the preamplifier to restore the signal baseline for more accurate energy estimation. When compared to a fixed threshold counting technique, the proposed method features better noise immunity, higher energy resolution and 50% higher rates measured at an estimated true rate of 2.75 Mcps, making CT integration within modern digital PET hardware feasible. Index Terms--Computed tomography, photon-counting, positron emission tomography/computed tomography (PET/CT).

We report the case of a 12-year-old girl presenting with multiple episodes of left upper-quadrant pain caused by torsion of an accessory spleen. We present the CT findings of progression of accessory spleen infarction over the course of 7 days. Keywords Accessory spleen * Torsion * Infarction * CT * Children

A scanner that combines CT scanning and PET scanning may be more effective in detecting non-small-cell lung cancer than either scan alone, according to a study of 50 patients. CT scans can locate a tumor, but cannot tell whether it is benign or malignant. PET scans can distinguish between benign and malignant tumors, but it also highlights inflammation not caused by cancer. The integrated CT-PET scanner combines the best features of both techniques and eliminates the drawbacks.

Optical coherence tomography (OCT) may be very useful for imaging teeth. This technique is similar to CT imaging except that it uses light rays instead of X-rays. It creates a two-dimensional image of a structure without all the surrounding structures to distort the view. One advantage of OCT over dental X-rays is that OCT can image soft tissues, which most X-rays cannot do.

Virtual colonoscopy may be an effective and low-cost method of diagnosing colorectal cancer. During this procedure, helical computed tomography (CT) is used to create two-dimensional images which are then converted into three-dimensional images. The traditional way of examining the colon is to stick an endoscope up the rectum, which can be uncomfortable for the patient and expensive. In a study of 100 patients who received both procedures, virtual colonoscopy detected all the cancers and 90% of the adenomatous polyps larger than 6 millimeters. There were no false-positive findings of cancer.

Electron-beam CT imaging is a noninvasive technique that can measure the amount of fatty plaque inside coronary arteries. Researchers used this technique to study changes in the amount of plaque in 149 patients, 70% of whom were taking cholesterol-lowering drugs called HMG-CoA reductase inhibitors. The amount of plaque decreased only in treated patients whose LDL cholesterol levels had dropped below 120 milligrams per deciliter. In all other patients, including some treated patients, the amount of plaque increased.

Electron-beam CT imaging may be able to noninvasively detect severe coronary artery disease. Usually, most patients must have angiography, during which a dye is injected into the patient's bloodstream. Researchers used electron-bream CT scans to detect coronary artery disease in 125 patients. Because of problems with image quality, only 78 patients had adequate scans. However, the technique accurately detected 92% of the arteries with severe blockage and also detected 94% of the patients who did not have severe coronary artery disease.

Computed tomography (CT) images have been widely used for liver disease diagnosis. Designing and developing computer-assisted image processing techniques to help doctors improve their diagnosis has received considerable interests over the past years. In this paper, a CT liver image diagnostic classification system is presented which will automatically find, extract the CT liver boundary and further classify liver diseases. The system comprises a detect-before-extract (DBE) system which automatically finds the liver boundary and a neural network liver classifier which uses specially designed feature descriptors to distinguish normal liver, two types of liver tumors, hepatoma and hemageoma. The DBE system applies the concept of the normalized fractional Brownian motion model to find an initial liver boundary and then uses a deformable contour model to precisely delineate the liver boundary. The neural network is included to classify liver tumors into hepatoma and hemageoma. It is implemented by a modified probabilistic neural network (PNN) [MPNN] in conjunction with feature descriptors which are generated by fractal feature information and the gray-level co-occurrence matrix. The proposed system was evaluated by 30 liver cases and shown to be efficient and very effective. Index Terms - Fractal, liver boundary, probabilistic neural network, segmentation.

We have developed an uncollimated sheet line source with a fluoroplastic tube for gamma ray transmission CT (TCT). This source filled with Tc-99m was attached to the collimator face on one head of a dual head single photon emission computed tomography (SPECT) system. In simultaneous SPECT/TCT scans using Tl-201 as the SPECT source and Tc-99m as the TCT source, scatter and spilldown contamination in the Tc-99m (141 keV) data and the Tl-201 (75 keV) data can be removed with the triple energy window (TEW) method. However, lead X-ray contamination in the Tl-201 data cannot be removed with the TEW method. We have developed an estimation method of the lead X-ray contamination in the Tl-201 data, This method depends on the hypothesis that the lead X-ray is proportional to the amount of attenuating media and primary photons along each projection path. The amount of attenuating media is given by a transmission image and that of primary photons is estimated by the TEW method. The coefficients needed for this estimation are experimentally determined by only Tc-99m TCT scan data. The feasibility of the proposed method was demonstrated by a chest phantom study and a myocardial clinical study.

The improvement of the X-ray computed tomography (CT), used in the field of earth science and geology, is discussed. Its spatial resolution is enhanced for greater density discrimination and flexibility in imaging. High resolution CT together with the use of computer software are powerful application tools in relation to the geological research on fossils. The first high-resolution CT scanner was established in the Departments of Geological Sciences and Anthropology of the University of Texas in Austin.

This paper presents an innovative technology called 3D virtual colonoscopy, which incorporates several advanced visualization techniques to enable the physician to virtually examine the inner surface of the entire colon for identifying and inspecting colonic polyps. We first describe our unique process of acquiring and reconstructing a patient's colon model, followed by the novel visualization algorithms that we have developed to provide automatic planned navigations as well as interactive guided navigations inside the colon. Finally, we present our experimental results on a simulated pipe phantom, the Visible Human data set, and patient data.

Reconstructive matching (RM) is a novel approach to multidimensional object matching, using cross-correlation in the Radon projection domain. The scheme which is invariant to shift, rotation, and scale change is effective in computerized tomography object matching before reconstruction. RM decomposes the matching into processes of decreased dimensionality. The computation price of RM is competitive, and is useful in MD objects.

Numerical simulations of the transmission of a light impulse through strongly scattering and weakly absorbing slab media and of fan-beam-type optical computed-tomography imaging for cylindrical media are presented. A hybrid calculation scheme of scattering by the Monte Carlo method is employed to obtain the temporal variation of transmittance of the light impulse through the media. A set of projection data is provided by temporally extrapolating the difference in the optical density between the absorbing object and the nonabsorbing reference to the shortest time of flight. For the case of identical scattering between the object and reference, the reconstructed image of the difference in the absorption coefficient has better accuracy and spatial resolution than those images by the time-gating method.

We have developed a unique laser fabrication system that uses an ultraviolet laser beam and liquid photopolymer. The system can easily be used to fabricate physical models without milling tools in only one process by using digital data obtained from medical computed tomography (CT) scanners or computer-aided design systems. We describe the fabrication of a smooth physical model such as a cerebrum, using the laser fabrication system, with the help of CT and magnetic resonance images that are made with coarse slices. Each sandwiched area between adjoining images is interpolated by using third-order spline curves in the cylindrical coordinate system. This modeling technique can play a major role in personal prosthesis, surgical planning, and implant design.

Virtual colonoscopy is a promising diagnostic tool but some problems remain to be resolved. This technique involves using helical CT imaging to create two-dimensional images of the colon, which are then converted into three-dimensional images. It is meant to replace colonoscopy, which involves inserting an endoscope up the rectum, an expensive and often painful procedure. Faster scanners are needed that can detect small intestinal polyps. Software must be improved to shorten the time it takes to create the final image. If these problems can be solved, the technique could be a noninvasive way of detecting colorectal cancer.

Electron-beam CT imaging should be tested in clinical trials before it is made widely available to the public. This is a noninvasive technique for measuring the amount of plaque in the coronary arteries. As of Dec, 1998, there were 50 electron-beam scanners in the US, and the technique is actively marketed to consumers. However, many patients with minimal coronary artery disease can have a heart attack. Thus the technique could lead to a false sense of security. It could also lead to further testing, some of which may be unnecessary.

At the advent of multislice computed tomography (CT) a variety of approximate cone-beam algorithms have been proposed suited for reconstruction of small cone-angle CT data in a spiral mode of operation. The goal of this study is to identify a practical and efficient approximate cone-beam method, extend its potential for medical use, and demonstrate its performance at medium cone-angles required for area detector CT. We will investigate two different approximate single-slice rebinning algorithms for cone-beam CT: the multirow Fourier reconstruction (MFR) [1] and an extension of the advanced single-slice rebinning method (ASSR) [2], [3], which combines the idea of ASSR with a z-filtering approach. Thus, both algorithms, MFR and ASSR, are formulated in the framework of z-filtering using optimized spiral interpolation algorithms. In each view, X-ray samples to be used for reconstruction are identified, which describe an approximation to a virtual reconstruction plane. The performance of approximate reconstruction should improve as the virtual reconstruction plane better fits the spiral focus path. The image quality of the respective reconstruction will be assessed with respect to image artifacts, spatial resolution, contrast resolution, and image noise. It turns out that the ASSR method using tilted reconstruction planes is a practical and efficient algorithm, providing image quality comparable to that of a single-row scanning system even with a 46-row detector at a table feed of 64 mm. Both algorithms tolerate any table feed below the maximum value associated to the detector height. Due to the z-filter approach, all detector data sampled can be used for image reconstruction. Index Terms--Cone artifact, cone-beam CT, contrast resoltion, image noise, single-slice reconstruction, spatial resolution, spiral CT, spiral interpolation,

The new spiral multislice computed tomography (CT) scanners and the significant increase in rotation speed offer great potential for cardiac imaging with X-ray CT. We have therefore developed the dedicated cardiac reconstruction algorithms 180 [degrees] multislice cardio interpolation (MCI) and 180 [degrees] multislice cardio delta (MCD) and here offer further details and validation. The algorithm 180 [degrees] MCI is an electrocardiogram (ECG)-correlated filtering (or weighting) algorithm in both the cardiac phase and in the z-position. Effective scan times (absolute temporal resolution) of as low as [t.sub.eff] = 56 ms are possible, assuming M = 4 simultaneously measured slices at a rotation time of [t.sub.rot] = 0.5 s and S [is less than or equal to] d [is less than or equal to] 3S tier the table feed d per rotation, where S denotes the collimated slice thickness. The relative temporal resolution w (fraction of the heart cycle depicted in the image), which is the more important parameter in cardiac imaging, will then be as low as w = 12.5% of the heart cycle. The second approach, 180 [degrees] MCD, is an ECG-correlated partial scan reconstruction of 180 [degrees] + [Delta] data with [Delta] [much less than] [Phi] (fan-angle). Its absolute temporal resolution lies in the order of 250 ms (for the central ray, i.e., for the center of rotation), and the relative temporal resolution w increases with increasing heart rate, e.g., from typically w, = 25% at [f.sub.H] = 60 [min.sup.-1] to w = 50% at [f.sub.H] = 120 [min.sup.-1], assuming again [t.sub.rot] = 0.5 s. For validation purposes, we have done simulations of a virtual cardiac motion phantom, measurements of a dedicated cardiac calibration and motion phantom, and we have reconstructed patient data with simultaneously acquired ECG. Both algorithms significantly improve the image quality compared with the standard reconstruction algorithms 180 [degrees] multislice linear interpolation (MLI) and 180 [degrees] multislice filtered interpolation (MFI). However, 180 [degrees] MCI is clearly superior to 180 [degrees] MCD for all heart rates. This is best illustrated by multiplanar reformations (MPR) or other three-dimensional (3-D) displays of the volume. 180 [degrees] MCI, due to its higher temporal resolution, is best for spatial and temporal four-dimensional (4-D) tracking of the anatomy. A tunable scanner rotation time to avoid resonance behavior of the heart rate and the scanner's rotation and shorter rotation times would be of further benefit. Index Terms--Computed tomography (CT), four-dimensional (4-D) reconstruction, heart, multirow detector systems, multislice spiral CT (MSCT).

One of the most recent technical advancements in computed tomography (CT) is the introduction of multislice CT (MCT). Because multiple detector rows are used for data acquisition, MCT offers higher volume coverage, faster scan speed, and reduced: X-ray tube loading. Recognizing its unique data-sampling pattern, several image reconstruction algorithms were developed. These algorithms have been shown to be adequate in producing clinically acceptable images. Recent studies, however, have revealed that the image quality of MCT can be significantly degraded when helical data are acquired with a tilted gantry. The degraded image quality has rendered this feature unacceptable for clinical usage. In this paper, we first: present a detailed investigation on the cause of the image quality degradation. An analytical model is derived to provide a mathematical basis for correction. Several compensation schemes are subsequently presented, and a detailed performance comparison is provided in terms of spatial resolution, noise, computation efficiency, and image artifacts. Index Terms--Computed tomography, helical CT, multislice CT, tilted helical CT.

Doctors and scientists urged the federal government to start a large study of a new way of detecting lung cancer as soon as possible, seizing what they see as a [...]