Artifactual Appearance Research Articles

Photographic Gel Artifact Simulating International Classification of Retinopathy of Prematurity Notch: Stanford University Network for Diagnosis of Retinopathy of Prematurity (SUNDROP) Report no. 16

To report a series of fundus photographs taken for retinopathy of prematurity (ROP) screening that contain artifacts with imaging characteristics mimicking a notch, a recently refined classification metric in the International Classification of Retinopathy of Prematurity, third edition. Retrospective case series. Infants requiring ROP screening in neonatal intensive care units from the Stanford University Network for Diagnosis of Retinopathy of Prematurity (SUNDROP) and TeleROP telemedicine screening programs. Preterm infants meeting ROP examination criteria were screened with 130° wide-angle imaging systems. The images were taken by a trained nurse in the neonatal intensive care unit and transferred to an ROP specialist using a Health Insurance Portability and Accountability Act-compliant picture archiving and communication system for interpretation. Presence of an artifact that appeared consistent with a notch. We identified a total of 17 cases in ROP screening with artifact findings that had imaging characteristics similar to a notch. The artifactual appearance of the pseudo-notch was created by the camera illumination system within the gel-lens interface when the lens was not well apposed to the cornea. In telemedicine screening for ROP, we present fundus images of eyes with a pseudo-notch appearance; review of overlapping images can help differentiate between notch and artifact. Pediatric retinal specialists need to be aware that artifacts play a confounding role in screening for ROP, that can be mitigated through the use of overlapping and redundant images. Proprietary or commercial disclosure may be found after the references.

The frequency of longitudinally extensive transverse myelitis in MS: A population-based study

BackgroundDetermining the frequency of longitudinally-extensive transverse myelitis (LETM: T2-lesion ≥3 vertebral segments) in multiple sclerosis (MS) is essential to assess its utility in differentiating from aquaporin-4-IgG (AQP4-IgG) positive neuromyelitis optica spectrum disorder (NMOSD) and myelin-oligodendrocyte-glycoprotein-IgG (MOG-IgG) myelitis. We sought to determine the frequency of LETM in MS during a myelitis attack. MethodsWe identified Olmsted County (MN, USA) residents on 12/31/2011 with inflammatory demyelinating disease. Inclusion criteria were: 1) Clinical myelitis episode accompanied by a new spinal magnetic resonance imaging (MRI) lesion (≤6 weeks from onset); 2) MS diagnosis by 2010 McDonald criteria; 3) Seronegative for AQP4-IgG and MOG-IgG. MRI characteristics were determined. ResultsSixty-seven patients (median age at myelitis: 41 years [range, 16–65]; 76% females) with 92 myelitis attacks accompanied by a new MRI spinal cord lesion were identified. The frequency of LETM was 0%. The median T2-hyperintense lesion length in vertebral segments was 1.0 (range, 0.5–2.5) and 82/92 (89%) were peripheral in location on axial sequences; 58% had associated gadolinium enhancement. Two patients (2% of attacks) had multiple short lesions resembling LETM on sagittal images but axial sequences confirmed multiple non-contiguous short lesions. ConclusionLETM is rare in adult MS myelitis and its presence should prompt evaluation for AQP4-IgG, MOG-IgG or other etiologies. Careful scrutiny of axial images is important as coalescence of multiple short lesions may lead to the artifactual appearance of an LETM.

Artifactual Appearance of Thrombosis on Using Metal Artifact Reduction Software Reconstruction in Computed Tomographic Angiography

The authors attempted to use metal artifact reduction software in 2 computed tomographic angiogram studies to decrease beam hardening. Although the beam hardening artifacts were reduced in the postprocessed images, there was an artifactual appearance of thrombosis in the adjacent arteries in the first case and in the inflow cannula of a left ventricular assist device in the second case. Comparison of the reconstructed images with the original images is therefore essential to avoid a misdiagnosis.

Sonographic Appearance of Chromic 2-0 Catgut Sutures in the Parenchyma of a Renal Allograft

A renal transplant recipient had a urinary fistula repaired and a double-pigtail ureteral stent left and later surgically removed. At this same time, an open biopsy was performed and closed with chromic 2-0 catgut sutures. A sonogram revealed an artifactual image that was interpreted as a fragmented piece of the stent that was left in the patient. An exploratory surgery performed, however, was unremarkable, and the renal incision was again closed with chromic 2-0 catgut sutures. A repeated sonogram demonstrated the previous artifact, which raised the suspicion that this appearance should be attributed to the chromic 2-0 catgut sutures. An experiment using a model of coupling gel and chromic 2-0 catgut sutures demonstrated artifacts that matched those seen during sonography of this particular renal allograft. This sonographic artifactual appearance may be seen in hypostenic patients with a high-frequency transducer centered over chromic 2-0 catgut sutures.

Normalization of transposon-mutant library sequencing datasets to improve identification of conditionally essential genes.

Sequencing of transposon-mutant libraries using next-generation sequencing (TnSeq) has become a popular method for determining which genes and non-coding regions are essential for growth under various conditions in bacteria. For methods that rely on quantitative comparison of counts of reads at transposon insertion sites, proper normalization of TnSeq datasets is vitally important. Real TnSeq datasets are often noisy and exhibit a significant skew that can be dominated by high counts at a small number of sites (often for non-biological reasons). If two datasets that are not appropriately normalized are compared, it might cause the artifactual appearance of Differentially Essential (DE) genes in a statistical test, constituting type I errors (false positives). In this paper, we propose a novel method for normalization of TnSeq datasets that corrects for the skew of read-count distributions by fitting them to a Beta-Geometric distribution. We show that this read-count correction procedure reduces the number of false positives when comparing replicate datasets grown under the same conditions (for which no genuine differences in essentiality are expected). We compare these results to results obtained with other normalization procedures, and show that it results in greater reduction in the number of false positives. In addition we investigate the effects of normalization on the detection of DE genes.

Application of Chang's attenuation correction technique for single-photon emission computed tomography partial angle acquisition of Jaszczak phantom.

The acquisition and processing of the Jaszczak phantom is a recommended test by the American College of Radiology for evaluation of gamma camera system performance. To produce the reconstructed phantom image for quality evaluation, attenuation correction is applied. The attenuation of counts originating from the center of the phantom is greater than that originating from the periphery of the phantom causing an artifactual appearance of inhomogeneity in the reconstructed image and complicating phantom evaluation. Chang's mathematical formulation is a common method of attenuation correction applied on most gamma cameras that do not require an external transmission source such as computed tomography, radionuclide sources installed within the gantry of the camera or a flood source. Tomographic acquisition can be obtained in two different acquisition modes for dual-detector gamma camera; one where the two detectors are at 180° configuration and acquire projection images for a full 360°, and the other where the two detectors are positioned at a 90° configuration and acquire projections for only 180°. Though Chang's attenuation correction method has been used for 360° angle acquisition, its applicability for 180° angle acquisition remains a question with one vendor's camera software producing artifacts in the images. This work investigates whether Chang's attenuation correction technique can be applied to both acquisition modes by the development of a Chang's formulation-based algorithm that is applicable to both modes. Assessment of attenuation correction performance by phantom uniformity analysis illustrates improved uniformity with the proposed algorithm (22.6%) compared to the camera software (57.6%).

Influence of Off-resonance in myocardial T1-mapping using SSFP based MOLLI method.

BackgroundMyocardial T1-mapping methods such as MOLLI use SSFP readout and are prone to frequency-dependent error in T1-measurement. A significant error in T1 may result at relatively small off-resonance frequencies that are well within the region without banding artifacts.MethodsThe sensitivity of T1-estimates based on the SSFP based MOLLI sequence to errors in center frequency are calculated by means of a Bloch simulation and validated by phantom measurements. Typical off-resonance errors following local cardiac shimming are determined by field mapping at both 1.5 and 3.0T. In vivo examples demonstrate the artifactual appearance of T1-maps in the presence of off-resonance variation.ResultsOff-resonance varied 61.8 ± 15.5 Hz (mean ± SD, n = 18) across the heart at 1.5T and 125.0 ± 40.6 Hz (mean ± SD, n = 18) at 3.0T. For T1 = 1000 ms, the variation in T1 due to off-resonance variation was approximately 20 ms at 62 Hz, and > 50 ms at 125 Hz.ConclusionsRegional variations due to the inability to completely shim the B0-field variation around the heart appear as regional variation in T1, which is artifactual.

Photomultiplier Tube Artifacts on 67Ga-Citrate Imaging Caused by Loss of Correction Floods Due to an Off-Peak Status of One Head of a Dual-Head -Camera

γ-cameras use flood-field corrections to ensure image uniformity during clinical imaging. A loss or corruption of the correction data of one head of a dual-head camera can result in an off-peak artifactual appearance. We present our experience with the occurrence of such an incident on a (67)Ga scan. A patient was referred for a whole-body (67)Ga scan to evaluate for causes of neutropenic fever. Whole-body planar and static images of the head, chest, abdomen, pelvis, and lower extremities in multiple projections were obtained. Whole-body images showed decreased image quality on the anterior view obtained with detector 1 and an unremarkable posterior image obtained with detector 2. A problem with detector 2 was suspected, and additional static images were obtained after rotation of the detector heads. The posterior images taken with detector 1 showed photomultiplier tube outlines. The anterior images taken with detector 2 showed improved count and image quality. It was later found that the uniformity map for detector 2 had been lost and that this software malfunction led to the resulting imaging problem. When artifacts with an off-peak appearance are seen on scintigraphic images, evaluation of possible causes should include not only isotope window settings but also an incorrect or corrupted uniformity map.

Secular Trends in Hospitalization for IBD: The Ecological Niche

One of the most common designs in epidemiology research is the ecological study, in which the units of analysis are populations or groups of people, rather than individuals. In addition to their ease and low-cost, these studies can also provide very valuable information when individual-level data are difficult to obtain or when the primary interest is in the ecologic inference, such as in public policy or program legislation. The article by Dr. Sonnenberg and colleagues in this month’s issue adds to a growing body of ecological studies examining the secular trends (trends that are not cyclical or seasonal but exist over a relatively long period of time) of hospitalizations for inflammatory bowel disease (IBD) in this country [1]. Prior studies have demonstrated stable to increasing hospitalization rates for ulcerative colitis (UC) and increasing hospitalization rates for Crohn’s disease (CD) in the US [2, 3]. Dr. Sonnenberg’s work extends this analysis to the US military veteran’s population, increasing the body of data on ageand race-specific results. The authors found rising hospitalization rates until 1989 when rates of hospitalizations decreased overall. However, when examining these trends by race, they found increasing rates of hospitalization in non-whites, most significantly in the oldest (65?) age group, for both UC and CD throughout the study period. Prior studies have shown race-specific differences in utilization of surgery as well as disease manifestations and complications in IBD patients [4–8]. Age-specific changes in hospitalizations were not found in one prior study [2], but were found to peak during earlier years in CD patients in another [3]. Taken together, these ecological studies suggest that inpatient care for IBD may represent an increasingly large proportion of our healthcare resources. There are several reasons why one might observe an increase in IBD hospitalizations over time. The simplest is that there are more people being hospitalized, the same number of people are being hospitalized more often, or a combination of the two. Likewise, if there is an increase in the actual number of patients with IBD, the rate of hospitalization per individual could be less, but the rate of hospitalization could appear to be rising solely because the disease is becoming more common. However, ecological studies are prone to certain biases that can result in an artifactual appearance of long-term trends. Like all studies, the data used to examine secular trends needs to be accurately measured to avoid misclassification bias, in which errors occur in classifying populations exposure or disease status. In this article by Sonnenberg, the investigators have measured incidence of hospitalization in each year relative to the total population of the United States. The potential problem with this design is that the total USA population is not eligible to be hospitalized in Veteran Affairs hospitals. Thus, observed trends could reflect disproportionate changes in the demographics and size of the population eligible to use the Veteran Affairs resources rather than a true change in the rates of hospitalizations among eligible Veterans. To address this, Sonnenberg et al. also used the population of patients hospitalized in the Veteran Affairs healthcare system for any reason as an alternative denominator for defining hospitalization rates. This comes closer to defining the truly eligible population, but remains subject to bias from secular trends in hospitalization for other conditions. Reassuringly, results using this alternative denominator were relatively similar to the primary results in their study. Ecological studies may also suffer from confounding by group, where the apparent association between a group and M. Bewtra (&) J. D. Lewis University of Pennsylvania, Philadelphia, Pennsylvania, USA e-mail: Meenakshi.Bewtra@uphs.upenn.edu

DIGITAL RADIOGRAPHY: IMAGE QUALITY AND RADIATION DOSE

Digital radiography devices, rapidly replacing analog screen-film detectors, are now common in diagnostic radiological imaging, where implementation has been accelerated by the commodity status of electronic imaging and display systems. The shift from narrow latitude, fixed-speed screen-film detectors to wide latitude, variable-speed digital detectors has created a flexible imaging system that can easily result in overexposures to the patient without the knowledge of the operator, thus potentially increasing the radiation burden of the patient population from radiographic examinations. In addition, image processing can be inappropriately applied causing inconsistent or artifactual appearance of anatomy, which can lead to misdiagnosis. On the other hand, many advantages can be obtained from the variable-speed digital detector, such as an ability to lower dose in many examinations, image post-processing for disease-specific conditions, display flexibility to change the appearance of the image and aid the physician in making a differential diagnosis, and easy access to digital images. An understanding of digital radiography is necessary to minimize the possibility of overexposures and inconsistent results, and to achieve the principle of as low as reasonably achievable (ALARA) for the safe and effective care of all patients. Thus many issues must be considered for optimal implementation of digital radiography, as reviewed in this article.

Lipoatrophia semicircularis: A compressive lipoatrophy consecutive to persistent mechanical pressure

Lipoatrophia semicircularis is an infrequent condition characterized by semicircular depressions of the anterolateral aspects of the thighs. The origin of this peculiar variant of lipoatrophy is unknown, although repeated mechanical trauma on the affected thighs has been advocated in many cases. A 57-year-old woman presented with a 1-year history of two bilateral, parallel, symmetric, asymptomatic depressions on the anterolateral aspect of her thighs. The patient worked as a cashier, permanently seated and almost always wearing trousers. The localization of lesions and their linear artifactual appearance perfectly matched with the strangling folds formed by trousers while being sat. Echotomographic examination revealed a loss of the normal echogenic pattern in the subcutaneous tissue of the affected areas. We believe that the anatomical adipose constitution of women's thighs predisposes that a persistent mechanical pressure induced by wearing trousers while being sat for long periods of time, originates a relative impaired circulation on a tenuous perfused tissue, and induces the development of lipoatrophia semicircularis.

Computed Tomography Appearance of an Intra-Aortic Balloon Pump

The case of a patient with an indwelling intra-aortic balloon pump (IABP) who underwent computed tomography (CT) to rule out mesenteric ischemia is reported. Three-dimensional reconstruction revealed regularly spaced air-fluid levels within the aorta. Intra-aortic balloon pump function is reviewed, and it is shown that its artifactual appearance on CT results from the phase difference between the cardiac cycle and gantry speed. Recognizing and understanding the appearance of an IABP is important so as not confuse it with intra-aortic air, which suggests ischemia.

PHASE CONTRAST MR ANGIOGRAPHY TECHNIQUES

Phase contrast MR methods encode information from macroscopic motion into the phase of the MR signal. Phase contrast methods can be applied with small and large fields-of-view, can give quantitative measures of velocity, and provide excellent suppression of signals from stationary tissue. Unlike time-of-flight methods, phase contrast methods directly measure flow and thus are not hindered by the artifactual appearance of tissue having short T1. Phase contrast angiograms can be two-dimensional (thin slice or projectile), three-dimensional, and/or time resolved and have applications throughout the body.

Heat shock-induced repression of proteolysis: poly(A)-binding protein degradation patterns can illusorily suggest its specific loss during heat shock.

Poly(A)-binding protein (PABP) is highly susceptible to proteolysis during cell lysis of Drosophila tissue culture cells unless substantial amounts of proteolysis inhibitors are included in the extraction buffer. This intrinsic proteolytic activity is substantially reduced during heat shock. An artifactual appearance that poly(A)-binding protein is specifically degraded by heat shock can result. Several contradictory descriptions of PABP may also be related to its proteolysis. Repression of proteolysis is likely to reflect a physiologically significant regulatory event, based on recent examinations of HSP70 stability during and after heat shock.

Comparison of extraction and precipitation methods for the HPLC determination of furosemide in plasma and urine

Comparisons have been made between an ether extraction method and an acetonitrile precipitation method for the HPLC determination of furosemide (frusemide) in human plasma and urine. Recoveries of furosemide were 81-89% (ether extraction method for plasma), 73-103% (acetonitrile precipitation method for plasma) and 62-89% (ether extraction method for urine) for the concentration ranges studied. Values of correlation coefficients were 0.9998, 0.9991 and 0.9997 for standard curves for the three methods, respectively. Accuracy and precision (RSD) were: 92.4-114% +/- 3.57-20% for ether-extracted plasma; 98.1-103% +/- 3.47-19.9% for acetonitrile-precipitated plasma; and 103-107% +/- 4.03-13.2% for ether-extracted urine. Because of carryover of endogenous urine components, the acetonitrile-precipitation assay was unacceptable for urine. Furosemide was stable in frozen plasma for at least 113 days and in frozen urine for at least 204 days. No artifactual appearance of the hydrolysis product of furosemide, 4-chloro-5-sulfamoylanthranilic acid (CSA), was detected by the ether-extraction method under normal assay conditions.

Separation of transcriptively active and inactive chromatin Agarose gel chromatography

Sheared chromatin fractionated by currently accepted methods of agarose gel exclusion chromatography, undergoes a limited and non-specific aggregation resulting from the high ionic strength and divalent cation concentration of the column elution buffer. Such aggregation causes the artifactual appearance of radioactively labeled, newly synthesized RNA within the column exclusion volume, erroneously suggesting an enrichment for actively transcribed chromatin. Claims for the efficacy of agarose gel exclusion as a method for separating template-active and -inactive chromatin are based largely on assays for active chromatin which rely on localization of specific molecular complexes of chromatin and nascent RNA. Under the conditions employed, the present studies invalidate this assay and thus cast considerable doubt on the agarose gel exclusion method itself.