TECHNICAL NOTE: SOME VIEWS ON THE TREATMENT OF "ARTIFACTS" IN PSYCHOPHYSIOLOGICAL RECORDINGS

The treatment of artifactual responses in psychophysiology is rarely discussed or made explicit in research reports. The rationales and procedures of five approaches are presented: excluding the data; averaging other epochs; subjective estimation; straight-line connecting; and following the pen. Each approach is based on a somewhat different theoretical orientation, and the choice of each will depend on the researcher's theoretical preference and also the relative “costs” of losing data vs programming special instructions. Other considerations such as objectivity, consistency, and replicability are discussed.     

Correction of EOG Artifacts in Event-Related Potentials of the EEG: Aspects of Reliability and Validity

Correction of EOG artifacts using a regression approach is evaluated in terms of reliability and validity. Transmission rates are estimated for eight EEG channels in 67 subjects. The trimmed group means of these rates are shown to provide reliable measures. Eye artifact correction based on these group means is superior to the conventional rejection in terms of reducing correlation between EOG and EEG.     

Extraction of artefactual MRS patterns from a large database using non-negative matrix factorization

Despite the success of automated pattern recognition methods in problems of human brain tumor diagnostic classification, limited attention has been paid to the issue of automated data quality assessment in the field of MRS for neuro-oncology. Beyond some early attempts to address this issue, the current standard in practice is MRS quality control through human (expert-based) assessment. One aspect of automatic quality control is the problem of detecting artefacts in MRS data. Artefacts, whose variety has already been reviewed in some detail and some of which may even escape human quality control, have a negative influence in pattern recognition methods attempting to assist tumor characterization. The automatic detection of MRS artefacts should be beneficial for radiology as it guarantees more reliable tumor characterizations, as well as the development of more robust pattern recognition-based tumor classifiers and more trustable MRS data processing and analysis pipelines. Feature extraction methods have previously been used to help distinguishing between good and bad quality spectra to apply subsequent supervised pattern recognition techniques. In this study, we apply feature extraction differently and use a variant of a method for blind source separation, namely Convex Non-Negative Matrix Factorization, to unveil MRS signal sources in a completely unsupervised way. We hypothesize that, while most sources will correspond to the different tumor patterns, some of them will reflect signal artefacts. The experimental work reported in this paper, analyzing a combined short and long echo time ¹H-MRS database of more than 2000 spectra acquired at 1.5T and corresponding to different tumor types and other anomalous masses, provides a first proof of concept that points to the possible validity of this approach.     

Ultrastructure of the Ewing's Sarcoma Family of Tumors

The transmission electron microscope is a valuable diagnostic and research tool that is presently underappreciated. In the area of human immunodeficiency virus research alone, it has provided critical information about viral pathogenesis and opportunistic infections and malignancies. However, because it has not always been used with care, the literature contains misinterpretations, especially as to what is a virus and what is actually a cell organelle, e.g., lysosome and Golgi vesicles. It is important to review the subject periodically to maintain its quality.     

Efficacy and limitations of the histological diagnosis of type 1 autoimmune pancreatitis with endoscopic ultrasound-guided fine needle biopsy with large tissue amounts

ObjectivesWe examined the efficacy and limitations of acquiring large specimens by endoscopic ultrasound-guided fine needle biopsy (EUS-FNB) for diagnosing type 1 autoimmune pancreatitis (AIP).MethodsPatients from 12 institutions with non-neoplastic diseases or pancreatic ductal adenocarcinoma (PDAC) with large EUS-FNB specimens were investigated. Slides stained with hematoxylin-eosin, elastic, IgG4, and IgG stains were evaluated. The IgG4- and IgG-positive cell numbers were counted in three foci. The diagnoses were based on the Japan Pancreas Society 2011 (JPS 2011) criteria and the International Consensus Diagnostic Criteria (ICDC).ResultsWe analyzed 85 non-neoplastic (definite type 1 AIP in 73/85 based on the ICDC) cases and 64 PDAC cases. IgG4-positive cells were numerous (>10 in 85.9%), and the IgG4/IgG ratios were high (>40% in 81.2%). Plasma cell crushing by an artifact caused unsuccessful immunostaining, notably in smaller samples. Tissue lengths were an important factor for the presence of storiform fibrosis and obliterative phlebitis, but storiform fibrosis was equivocal even in large tissues. A definite or possible histological diagnosis was achieved in 45.9% (39/85) and 41.2% (35/85), respectively, and contributed to the definite final diagnosis of type 1 AIP in 33.3% (ICDC) and 55.6% (JPS 2011) in cases with segmental/focal lesions. In the PDAC group, >10 IgG4-positive cells was rare (2/58), but elastic stains revealed fibrous venous occlusions in 10.3% (6/58).ConclusionsEUS-FNB with large tissue amounts was useful for diagnosing type 1 AIP, notably by facilitating successful IgG4 immunostaining, but definite diagnosis may not be achieved even in cases with large specimens.     

Comparison of coronary artery calcium screening image quality between C-150 and e-Speed electron beam scanners

RATIONALE AND OBJECTIVE: The newest generation of electron beam tomographic scanner (e-Speed) has increased spatial and temporal resolution compared with the C-150 XP scanner. The aim of this study was to evaluate coronary artery calcium screening image quality between the e-Speed and C-150 scanners (GE Imatron, San Francisco, CA). MATERIALS AND METHODS: Studies from 41 patients (14 women and 27 men) who underwent serial coronary artery calcium screening with the C-150 (first study) and the e-Speed (second study) were analyzed. Individual computed tomography (CT) slices were assessed for coronary artery motion artifacts, and CT Hounsfield units (HU) and noise values (CT HU standard deviation) at 16 discrete cardiac sites were measured and averaged. RESULTS: With the e-Speed scanner, there were significant decreases in right coronary artery motion artifacts compared with the C-150 scanner (0.3% versus 1.8%, P < .001) as well as decreased noise values (24.3 versus 32.0 HU, P < .001). CONCLUSION: Image quality is significantly improved with use of the e-Speed scanner, due to its improved temporal and spatial resolution, compared with the C-150 scanner.     

Magnetic resonance artifact induced by the electrode Activa 3389: an in vitro and in vivo study

Summary Background. The electrode Activa 3389 is widely implanted for deep brain stimulation (DBS) and MRI is often used to control the position of the electrode. However, induced distorsion artifacts may result in imprecise localization and may lead to misinterpretations of the clinical effects and mechanisms of DBS.Methods. In vitro 3D MR study: the proximal and distal contacts of one electrode were spotted by two localizers. The maximal artifact height (MAH) and width (MAW: measured on distal contact), and the distances between the artifact and the localizers (proximal, distal and lateral) were measured on 2 transverse and sagittal MR sequences with 90 degrees rotation of frequency-encoded gradient and phase direction.In vivo 3D MR study: coronal and sagittal reconstructions along the main axis of the electrode were performed on 10 postoperative MR (20 electrodes) to measure MAH and MAW.A Student t test was used to compare in vitro and in vivo measurements.Findings. In vitro study: A MAH of 10.35mm (±0.23) and MAW of 3.6mm (±0.2) were found. We measured symmetrical extensions of the artifact over the distal contact.In vivo study: A MAH of 10.36mm (±0.44) and MAW of 3.56mm (±0.30) were obtained. No significant different artifact dimensions were measured between in vitro and in vivo studies (p<0.0001).Interpretation. Precise 3D localization of the electrode in implanted patients is provided by MR identification of the limits of the distal contact artifact. The position of the other contacts is deduced given the size of the contacts and the intercontact distance.