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PubMed2006

Automated lung segmentation of diseased and artifact-corrupted magnetic resonance sections.

Segmentation of the lungs within magnetic resonance (MR) scans is a necessary step in the computer-based analysis of thoracic MR images. This process is often confounded by image acquisition artifacts and disease-induced morphological deformation. We have developed an automated method for lung segmentation that is insensitive to these complications. The automated method was applied to 23 thoracic MR scans (413 sections) obtained from 10 patients. Two radiologists manually outlined the lung regions in a random sample of 101 sections (n=202 lungs), and the extent to which disease or artifact confounded lung border visualization was evaluated. Accuracy of lung regions extracted by the automated segmentation method was quantified by comparison with the radiologist-defined lung regions using an area overlap measure (AOM) that ranged from 0 (disjoint lung regions) to 1 (complete overlap). The AOM between each observer and the automated method was 0.82 when averaged over all lungs. The average AOM in the lung bases, where lung segmentation is most difficult, was 0.73.

Aged↗
PubMed2002

Thoracic aorta: motion artifact reduction with retrospective and prospective electrocardiography-assisted multi-detector row CT.

The authors compared prospective (n = 20) and retrospective (n = 20) electrocardiography (ECG)-assisted multi-detector row computed tomography (CT) with non-ECG-assisted multi-detector row CT (n = 20) of the thoracic aorta with regard to reduction of motion-related artifacts. Image quality was rated for transverse source and sagittal oblique images of the thoracic aorta, including the aortic valve. ECG-assisted multi-detector row CT compared with non-ECG-assisted multi-detector row CT showed a significant reduction in motion artifacts for the entire thoracic aorta.

Adult↗
PubMed1993

Radiographic film fog artifact caused by fluorescent bandage.

Film fog is a common cause of x-ray film artifact. The authors report an unusual source of film fogging in the darkroom--seen in three consecutive radiographs of two different patients--the exposure of film to the low light emission of a fluorescent commercial adhesive bandage worn by the technologist. Heightened awareness of the effects of these bandages will help avoid creation of this film fog artifact.

Artifacts↗
PubMed1998

Unusual artifact with mammography film.

The authors identified the origin of a high-density artifact with mammography film. An acrylic ramp phantom (thickness, 0-7 cm) was used to create a continuously variable radiation exposure. A perturbation in the curve of optical density versus position along the ramp was observed. Development of the film with the emulsion side down eliminated this artifact.

Artifacts↗
PubMed2000

Subclavian MR arteriography: reduction of susceptibility artifact with short echo time and dilute gadopentetate dimeglumine.

At arterial phase gadolinium-enhanced magnetic resonance (MR) angiography, artifactual stenosis of the subclavian artery is sometimes seen adjacent to the subclavian vein on the side of the contrast material injection. Experiments in phantoms and in 19 patients showed increased artifact with longer echo time and higher concentration of injected contrast material. An effective method to substantially decrease this susceptibility artifact was threefold dilution of gadopentetate dimeglumine and use of a short echo time (1 msec).

Adolescent↗
PubMedDate not supplied

AAPM/RSNA physics tutorial for residents: MR artifacts, safety, and quality control.

Artifacts in magnetic resonance (MR) imaging result from the complex interaction of contemporary imager subsystems, including the main magnet, gradient coils, radiofrequency (RF) transmitter and receiver, and reconstruction algorithm used. An understanding of the sources of artifacts enables optimization of the MR imaging system performance. The increasing clinical use of very high magnetic field strengths, high-performance gradients, and multiple RF channels also mandates renewed attention to the biologic effects and physical safety of MR imaging. Radiologists should be aware of the potential physiologic effects of prolonged exposure to magnetic fields, acoustic noise, and RF energy during MR imaging and should use all the available methods for avoiding accidents and adverse effects. Imaging equipment should be regularly tested and monitored to ensure its stability and the uniformity of its functioning. Newly installed or upgraded MR systems should be tested by a physicist or qualified engineer before use. In addition, the authors recommend participation in the MR imaging accreditation program of the American College of Radiology to establish the initial framework for an adequate quality assurance program, which then can be further developed to fulfill local institutional needs.

Artifacts↗
PubMed1992

Are Ranvier's nodes of the central nervous system also artifacts by preparation?

Recent research on peripheral nerves of six species of vertebrates concluded that Ranvier's nodes may be artifacts by preparation. As a consequence, the question as to whether or not Ranvier's nodes of the central nervous system may also be artifacts was logically raised. The ultrastructural data concerning our field of research (the cerebellar cortex) support the notion that Ranvier's nodes are real features in the central nervous system; otherwise, the occurrence of vesicular outpockets establishing, along myelinated axons, well conspicuous en passant nodal synapses cannot be explained.

Amphibians↗
PubMed2000

Epithelial desquamation in asthma: artifact or pathology?

To determine whether the denudation of the bronchial epithelium observed in endobronchial biopsies from asthmatic subjects is a true pathologic feature or an artifact of tissue sampling, we analyzed epithelial integrity in bronchial biopsies from 14 subjects with mild and moderate asthma and 12 healthy subjects. In each subject, 4 to 8 bronchial biopsies were taken from large airways during bronchoscopy, fixed in 4% paraformaldehyde, embedded in glycomethacrylate, cut into 2-microM sections, and stained with toluidine blue. A x4 image of each biopsy was copied to a computer file using a video camera, and lines were drawn and measured along the basement membrane underlying areas completely denuded of overlying epithelium, areas covered by a single layer of basal cells, and areas of intact epithelium. We found that the percentage of basement membrane that was denuded of epithelium was similar in the healthy and asthmatic subjects (14.8 +/- 11.8 versus 11.4 +/- 9.8% respectively, p = 0.38); the percentage of basement membrane that was covered by a single layer of basal cells was also similar in the two groups (46.4 +/- 11.0 versus 54.5 +/- 9.8%, respectively, p = 0. 11). In the asthmatic subjects, we found no significant correlation between the percentage of basement membrane covered by denuded epithelium or by a single layer of basal cells and the FEV(1) percentage of predicted or the PC(20) methacholine. We conclude that denudation of bronchial epithelium in endobronchial biopsies from asthmatic subjects with stable mild and moderate disease is an artifact of tissue sampling and is not a true pathologic feature of the disease, and that the extent of airway epithelial denudation is not correlated with the severity of airway narrowing or the severity of bronchial hyperresponsiveness.

Adult↗
PubMed1998

How a regression artifact makes ICFs/MR look ineffective.

Based on a simple matched-control group quasi-experiment, Conroy (1996) concluded that small ICFs for persons with mental retardation have negative quality-of-life impacts. Our analysis of Conroy's design suggests, in contrast, that the reported effect is a pure regression artifact. The flaw in Conroy's design is selecting a control group on the basis of pretest matching. Although selecting a subsample of controls by matching on static characteristics such as age or gender can reduce the confounding influence of these variables, selection on the basis of pretest scores leads invariably to a large, spurious effect. The literature on this issue dates back a century, with warnings against pretest matching by Galton, Thorndike, McNemar, Stanley, Campbell, Cronbach, and Cook. We reviewed this historical literature and then used a Monte Carlo experiment to estimate the spurious effect that Conroy would observe from pretest matching alone. The magnitude of the artifact is as large as the quality-of-life reduction that Conroy attributed to the effects of living in an ICF. We discussed the methodological logic involved in matching and the broader policy issues raised by this evaluation.

Artifacts↗
PubMed2002

Method for reducing background artifacts from images in single-photon emission computed tomography with a uniformly redundant array coded aperture.

Uniformly redundant array coded apertures have proven to be useful in the design of collimators for x-ray astronomy. They were initially expected to be equally successful in single-photon emission computed tomography (SPECT). Unfortunately, the SPECT images produced by this collimator contain artifacts, which mask the true picture and can lead to false diagnosis. Monte Carlo simulation has shown that the formation of a composite image will significantly reduce these artifacts. A simulation of a tumor in a compressed breast phantom has produced a composite image, which clearly indicates the presence of a 5 mm x 5 mm x 5 mm tumor with a 6:1 intensity ratio relative to the background tissue.

Artifacts↗
PubMed2006

Artifact removal in complex frequency domain optical coherence tomography with an iterative least-squares phase-shifting algorithm.

We present what we believe to be a new computational algorithm for complex frequency domain optical coherence tomography that can effectively suppress artifacts that are caused by uncertainty in phase shift due to sample motion and errors in reference phases. The algorithm treats the phase-shifting values as additional unknowns, and we can determine their exact values by analyzing interference fringes using the numerical least-squares technique. A series of simulations and experiments prove that this algorithm can effectively remove strong mirror-image artifacts because it is unaffected by random phase fluctuation.

Algorithms↗
PubMed2005

Development of a universal ellipsoidal mirror device for fluorescence detected circular dichroism: elimination of polarization artifacts.

We have developed an ellipsoidal mirror fluorescence detected circular dichroism (FDCD) device with enhanced detection sensitivity that eliminates the polarization artifact; this is applicable to samples with strongly polarized fluorescence. The device, JASCO FDCD465, has an ellipsoidal mirror structure with a framework consisting of three mirrors (one elliptical and two plane mirrors) that maximally collects light in the FDCD. All assemblies on the device including the ellipsoidal mirror, cylindrical cell, and photomultiplier tube (PMT) are aligned on the chamber-fitting sample mount as an attachment compatible with a standard CD spectropolarimeter. The new FDCD465 device eliminates the polarization artifact caused by anisotropic distribution of the emitted light. It represents a convenient, reliable, and sensitive FDCD attachment to the JASCO J-800 CD spectrometer series that can be used under both isotropic and photoselected conditions.

Artifacts↗
PubMed1992

An artifact induced by negative pressure ventilation.

This report draws attention to an artifact that influences the qualitative information gained from respiratory inductance plethysmography during negative pressure ventilation with a cuirass. This artifact may prevent identification of upper airway obstruction, a manageable complication of this mode of ventilation.

Artifacts↗
PubMed1993

[Possibilities for recognizing and suppressing artifacts in EMG signals].

Two methods are introduced to suppress artifacts in the EMG signal, as can occur with EMG detection. These methods are based upon an adaptive threshold, which depends on the muscle activity measured just before. Even small artifacts are identified and suppressed in a small EMG, so if they are not too long in duration they do not noticeably falsify the muscle activity detection. These methods are quite effective, simple and thus easily realizable.

Artifacts↗
PubMed2000

[Artifact detection and signal reconstruction in the pupillogram].

Just as the EEG reflects different wake and sleep stages, changes in pupil dynamics reflecting different levels of vigilance are also to be found. The literature contains numerous reports on experimental set-ups for the recording of the pupillogram. Interesting methods of signal processing are to be found in [7] and [5]. Currently, such recordings are being used to check the success of sleep therapy. A problem that still needs solving is the optimal handling of artifacts caused by blinking. The present article proposes a procedure for artifact detection by back-propagation networks, and subsequent reconstruction of the signal by an AR model. Estimation of the signal is first demonstrated by a test signal, and then by a corrupted pupillogram.

Arousal↗
PubMed2000

Artifact-tolerant controllers for automatic drug delivery in anesthesia.

This article presents a method for treating measurement artifacts in model-based control systems. A nonlinear modification to the usual observer structure is introduced to prevent the measurement artifacts from winding up the controller states. It is shown how stability of the closed loop system can be analyzed and an example of a successful application in a clinical study is provided.

Algorithms↗
PubMed1994

MR imaging of the liver at 1.5 T: value of signal averaging in suppressing motion artifacts.

OBJECTIVE: Prior reports have suggested that signal averaging is not as effective as phase reordering for suppressing motion-related artifacts on T1-weighted spin-echo MR imaging of the liver at high field strengths. We hypothesized that with shorter TEs, signal averaging could be effective, and therefore undertook this study to compare signal averaging with phase reordering at 1.5T. SUBJECTS AND METHODS: Thirty consecutive patients underwent MR imaging of the liver at 1.5 T with two T1-weighted spin-echo pulse sequences. In one sequence we used signal averaging and in the other we used phase reordering as the primary motion suppression techniques. For each patient, the order in which these sequences were performed was randomized; TR (400-500 msec), TE (11-12 msec), and field of view (32-34 cm) remained constant. Images were analyzed quantitatively for liver signal-to-noise ratio (SNR), liver-spleen contrast-to-noise ratio (CNR), and liver-lesion CNR (in 16 patients with focal liver lesions), as well as qualitatively (three observers, blinded to technique) for overall image quality. RESULTS: Signal averaging resulted in images with significantly greater liver SNR, liver-spleen CNR, and liver-lesion CNR than did phase reordering (p = .0001, .002, and .02, respectively). All observers showed a preference for the signal-averaged images. For one observer, this preference was statistically significant; for the others, it was not. CONCLUSION: Signal averaging can be an effective means of suppressing motion-related artifacts on T1-weighted MR images of the liver obtained at 1.5 T.

Artifacts↗
PubMed1996

Artifacts in chest radiographs with a third-generation computed radiography system.

Photostimulable phosphor computed radiography (CR) is a developing and increasingly widespread technology. The purpose of this pictorial essay is to familiarize readers with the appearance and cause of image artifacts that can occur in a third-generation computed radiographic system. Artifacts are described that relate to imaging plates, image readers, image processing, and film processing.

Adult↗