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PubMed1999

Management of biopsy needle artifacts: techniques for RF-refocused MRI.

Several methods were investigated to improve the depiction of biopsy needles in radiofrequency (RF)-refocused magnetic resonance imaging. Distortion correction is performed by the use of view angle tilting (VAT): a gradient is employed on the slice-select axis during readout. Needle conspicuity is increased by offsetting the gradient echo from the spin echo and by inverting the 90 degrees RF pulse slice-select gradient. VAT effectively re-registers in-plane shifts. Since this method changes the projection angle through the slice, some structures appear blurred, while other structures appear sharper. VAT does not correct errors in slice selection. Offsetting the spin echo from the gradient echo increases needle conspicuity but can result in a shift in the apparent location of the needle. Inverting the 90 degrees slice-select gradient effectively increases the needle conspicuity with no shift in the needle location. These methods provide an easy and interactive means to manipulate needle artifacts but should be used cautiously.

Artifacts↗
PubMed1999

Image artifacts due to a time-varying contrast medium concentration in 3D contrast-enhanced MRA.

The purpose of this work was to study image effects due to time-varying contrast medium concentration in contrast-enhanced three dimensional (3D) magnetic resonance angiography (MRA) images. Two different simulation models (1D and 3D) and two different contrast medium variation schemes were used. Phantom measurements were also performed. Experiments were performed for several different bolus timings. Similar sequence and image object parameters were used in both simulations and measurements (TE/TR 2. 1/7.8 mses, flip angle 30 degrees, T1/T2 1200-80/150-40 msec, flow velocity 100 cm/sec). A small variation in bolus timing yielded large variations in the appearance of the image effects, especially if the center of k-space was sampled in the vicinity of rapid contrast medium concentration variation. For a typical bolus injection in a patient, a severe signal loss but only minor ringing and edge artifacts appeared if the bolus injection was poorly timed. Effects of pulsatile flow were minor. The 3D model proved to be a useful tool in these studies. J. Magn. Reson. Imaging 1999;10:919-928.

Aorta↗
PubMed1999

Removal of intravoxel dephasing artifact in gradient-echo images using a field-map based RF refocusing technique.

A technique is proposed to compensate for the slice dephasing artifact and improve the signal-to-noise ratio (SNR) of gradient-echo images. This method is composed of two components: mapping of the internal gradient and design of the slice-selective radiofrequency (RF) pulse. The RF pulse is designed with its phase response as the negative of the product of a chosen echo time and the intravoxel internal gradient profile in a specified region of interest (ROI). The designed RF pulse can refocus the spin phases at a selected echo time and therefore effectively recover the signal loss due to both linear and nonlinear internal gradients. Principles, implementation, and application of the method are described in this note. Magn Reson Med 42:807-812, 1999.

Algorithms↗
PubMed2001

Spectral compensation for flow cytometry: visualization artifacts, limitations, and caveats.

BACKGROUND: In multicolor flow cytometric analysis, compensation for spectral overlap is nearly always necessary. For the most part, such compensation has been relatively simple, producing the desired rectilinear distributions. However, in the realm of multicolor analysis, visualization of compensated often results in unexpected distributions, principally the appearance of a large number of events on the axis, and even more disconcerting, an inability to bring the extent of compensated data down to "autofluorescence" levels. MATERIALS AND METHODS: A mathematical model of detector measurements with variable photon intensities, spillover parameters, measurement errors, and data storage characteristics was used to illustrate sources of apparent error in compensated data. Immunofluorescently stained cells were collected under conditions of limiting light collection and high spillover between detectors to confirm aspects of the model. RESULTS: Photon-counting statistics contribute a nonlinear error to compensated parameters. Measurement errors and log-scale binning error contribute linear errors to compensated parameters. These errors are most apparent with the use of red or far-red fluorochromes (where the emitted light is at low intensity) and with large spillover between detectors. Such errors can lead to data visualization artifacts that can easily lead to incorrect conclusions about data, and account for the apparent "undercompensation" previously described for multicolor staining. CONCLUSIONS: There are inescapable errors arising from imperfect measurements, photon-counting statistics, and even data storage methods that contribute both linearly and nonlinearly to a "spreading" of a properly compensated autofluorescence distribution. This phenomenon precludes the use of "quadrant" statistics or gates to analyze affected data; it also precludes visual adjustment of compensation. Most importantly, it is impossible to properly compensate data using standard visual graphical interfaces (histograms or dot plots). Computer-assisted compensation is required, as well as careful gating and experimental design to determine the distinction between positive and negative events. Finally, the use of special staining controls that employ all reagents except for the one of interest (termed fluorescence minus one, or "FMO" controls) becomes necessary to accurately identify expressing cells in the fully stained sample.

Artifacts↗
PubMed2000

Heavily T1-weighted images without respiratory artifacts: partial angle inversion recovery fast spin-echo imaging (PAIR-FSE).

We obtained T1-weighted images in the abdominal region using the partial angle inversion recovery fast spin echo (PAIR-FSE) with the respiratory triggering (RT) method and compared the image quality with that of conventional SE (TR/TE 500/10 msec) with the partial angle inversion recovery (PEAR) method. The signal difference to noise ratio of the PAIR-FSE was 1.6 times higher (6.94 +/- 3.08) than that of SE (4.30 +/- 1.88). Respiratory motion-induced ghost artifacts were reduced by half in PAIR-FSE with RT (1.01 +/- 0.47) in comparison with SE with PEAR (2.24 +/- 0.70). J. Magn. Reson. Imaging 2000;12:960-964.

Artifacts↗
PubMed2000

Three-dimensional tailored RF pulses for the reduction of susceptibility artifacts in T(*)(2)-weighted functional MRI.

A three-dimensional tailored RF pulse method for reducing intravoxel dephasing artifacts in T *(2)-weighted functional MRI is presented. A stack of spirals k-space trajectory is employed to excite a disk of magnetization for small tip angles. Smaller disks with a linear through-plane phase are inserted into the disk to locally refocus regions which are normally dephased due to susceptibility variations. Numerical simulations and imaging experiments which use the tailored RF pulses are presented. Limitations of the method and improvements are also discussed.

Artifacts↗
PubMed1995

Interventional physiology. Part XVI: normal coronary flow velocity patterns: considerations of artifacts, arrhythmias, and anomalies.

During normal flow velocity recording, various physiologic or technical problems may appear which can produce confusing flow signals. This section of Interventional Physiology reviews the patterns of normal coronary flow velocity and examines several artifacts and other features encountered in clinical practice. Recognition of these variations will help the interventional cardiologist to differentiate between physiologic and pathologic events.

Arrhythmias, Cardiac↗
PubMed2003

Oral contraceptive pills are associated with artifacts in ThinPrep Pap smears that mimic low-grade squamous intraepithelial lesions.

BACKGROUND: The authors noted a significant increase in the diagnosis of atypical squamous cells of undetermined significance (ASCUS) in premenopausal women using oral contraceptive pills (OCP) (9%) versus women not on OCP (4%) using ThinPrep Pap smears (P = 0.02). The purpose of this study was to correlate these morphologic changes with human papillomavirus (HPV) DNA detection by in situ hybridization and clinical follow-up. METHODS: Eighty-four ThinPrep Pap smears diagnosed as ASCUS or ASCUS favor low-grade squamous intraepithelial lesions (LGSIL) in young women receiving OCP were studied by HPV in situ hybridization. This information was correlated with colposcopic follow-up and AutoCyte Pap smear results. The authors also studied 80 ThinPreps from young women with a Pap smear diagnosis of unequivocal LGSIL where there was a corresponding biopsy (positive controls) and 40 ThinPreps diagnosed as within normal limits and that rescreened as such (negative controls). RESULTS: The detection rate of HPV DNA by in situ hybridization was 33% (28 of 84) in ASCUS cases versus 90% (72 of 80) for cases of unequivocal LGSIL. A blinded review of the 29 ASCUS Pap smears performed by AutoCyte showed that 66% (19 of 29) were diagnosed as within normal limits. The majority of the cervical biopsies in the women with ASCUS by ThinPrep Pap smears were negative for dysplasia (29 of 39 [74%]) whereas 71 of 80 biopsies (88%) showed dysplasia in women with Pap smears diagnosed as unequivocal LGSIL. The periodic acid-Schiff (PAS) stain demonstrated that many of the cells with halos in the ThinPrep Pap smears that mimicked LGSIL contained glycogen. CONCLUSION: The ThinPrep induces changes that mimic LGSIL in young women on OCP. These artifacts may reflect pressure-induced alteration of glycogen. PAS analysis and, more directly, HPV testing by in situ hybridization can help differentiate this mimicking from actual LGSILs.

Adolescent↗
PubMed2001

Cytologic artifacts and pitfalls of thyroid fine-needle aspiration using ThinPrep: a comparative retrospective review.

BACKGROUND: The ThinPrep Processor has gained popularity as a collection and preparation technique for fine-needle aspiration biopsy (FNAB). Specific cytologic criteria to evaluate ThinPrep preparation (TP) may differ from those of conventional preparation (CP). The authors retrospectively reviewed the quality, cytologic features, and pitfalls of TP versus CP in thyroid FNABs and addressed the cytomorphologic criteria used to evaluate TP specimens. METHODS: Thyroid FNABs received between January 1996-July 1999 were identified from the computer files of the Department of Pathology, University of Michigan (Ann Arbor, MI). Histologic correlation and clinical follow-up were reviewed. The cytology slides were reevaluated for cellularity, cellular preservation, artifacts, background material, architectural integrity, cytoplasmic details, and nuclear details by two observers. RESULTS: Of the 209 thyroid FNABs performed during the study period, TP and CP prepared 127 and 82 cases respectively. Histologic correlation was available in 68 (33%) cases (32 TP and 36 CP). Overall sensitivity was 80% and specificity was 98%. The sensitivity of CP versus TP was 87% and 70%, respectively. Thyroid FNABs prepared by TP, as compared with CP, were characterized by the following: The TP slide 1) allowed assessment of the overall specimen cellularity but not individual passes of an FNAB, 2) contained only "hard" colloid that appeared dense, markedly fragmented, or in droplets, 3) showed crowded, tight, tissue clusters with loss of cellular preservation, especially in the larger aggregates, 4) demonstrated more cell shrinkage, 5) showed increased disruption of the cytoplasm and numerous naked nuclei, 6) occasionally gave nucleoli a more prominent appearance, and 7) was less likely to show nuclear grooves and "pseudoinclusions" in papillary carcinoma. CONCLUSIONS: This study concluded that cytologic features used to evaluate thyroid FNABs prepared by CP may need to be modified when using TP. Awareness of the above-described findings and further studies to evaluate TP are essential to avoid potential diagnostic pitfalls.

Artifacts↗
PubMed2004

Suppression of photobleaching-induced artifacts in frequency-domain FLIM by permutation of the recording order.

BACKGROUND: Photobleaching can lead to significant errors in frequency-domain fluorescence lifetime imaging microscopy (FLIM). Existing correction methods for photobleaching require additional recordings and processing time and can result in additional noise. A method is introduced that suppresses the effects of photobleaching without the need for extra recordings or processing. METHODS: Existing bleach correction methods and the method introduced in this report whereby the recording order of the phases is permuted were compared using numerical simulations. RESULTS: Certain orders were found to make measurements virtually insensitive to photobleaching. At 12 recordings, errors in measured phase and modulation depth decreased by a factor 512 and 393, respectively, compared to recordings using sequential recording order. The optimal order is independent of modulation depth, phase, and extent of photobleaching. Thus, the same order can be used for practically all situations. Application of the method in FLIM measurements of EYFP-transfected HeLa cells was found effectively to suppress photobleaching induced artifacts. CONCLUSIONS: In view of the ease of implementation, its inherent robustness, and the possibility to still apply existing correction methods afterward, there is no good reason not to use the permuted recording order presented in this report instead of a sequential order.

Artifacts↗
PubMed2006

Worm-like artifacts in exfoliative cytology.

The presence of worms in cytological smears is occasionally reported, although various other structures exist that may be confused with such parasites. We present eight worm-like artifacts observed in routine Papanicolaou smears. Recognition of these structures is important to avoid overvaluation or confusion with true worms.

Animals↗
PubMed2002

Correlation of single-lumen silicone implant integrity with chemical shift artifact on T2-weighted magnetic resonance images.

PURPOSE: To correlate the integrity of single-lumen silicone gel implants with chemical shift artifact (CSA) associated with infolding of the elastomer shell. MATERIALS AND METHODS: The T2-weighted images of presurgical MRI examinations of 54 implants were retrospectively reviewed by two breast radiologists blinded to the operative and pathologic findings. CSA associated with intraluminal membranes was quantified by determining the fraction of membranes with it and categorized as minimal (0-1/3 of membranes involved), moderate (>1/3- <2/3), and marked (2/3 to all). CSA was qualified by noting whether CSA intensity of the membranes was less than or similar to that of blood vessels. The CSA was correlated with the surgical or pathology findings to judge integrity of the implant. RESULTS: Nineteen implants were intact, 35 were dysfunctional (gel leakage or rupture). Twenty-eight of 29 (97%) with a minimal fraction of membranes with CSA were dysfunctional; 17/21 (81%) with CSA associated with a marked fraction of membranes were intact (P < 0.001). All 28 implants with CSA intensity less than vessels were dysfunctional, 19/26 (73%) with CSA equal to vessels were intact (P < 0.001). All 25 implants with minimal CSA and intensity less than vessels were dysfunctional. Seventeen of 19 (89%) implants with CSA associated with a marked fraction of membranes and intensity equal to vessels were intact (P = 0.02). The magnetic resonance imaging (MRI) signs were combined with strong CSA as a predictor of integrity, and 22 of 26 (85%) implants were correctly diagnosed, 4 dysfunctional and 18 intact (P < 0.0001). CONCLUSION: CSA correlates with integrity of silicone gel implants on T2-weighted images and can be used with other MRI signs to improve diagnosis.

Artifacts↗
PubMed2002

Correction of slab boundary artifact using histogram matching.

PURPOSE: To improve the imaging efficiency of multi-slab three-dimensional acquisitions by decreasing slab overlap and the number of blanked slices. MATERIALS AND METHODS: Application of the histogram matching technique for correction of the slab boundary artifact (SBA) due to non-ideal radiofrequency pulse profiles has been proposed. The technique was validated by studying its effectiveness in reducing the SBA in phantom images, as well as in proton density- and T2-weighted brain images. RESULTS: The correction algorithm considerably decreases the disruption of image volume continuity due to the SBA, and improves slice-to-slice intensity continuity. CONCLUSION: The proposed technique can greatly reduce the SBA when the SBA can be described as a global intensity variation along the slab. The technique may be used to improve imaging efficiency of the multi-slab three-dimensional fast spin-echo sequences by decreasing the amount of required slab overlap.

Algorithms↗
PubMedDate not supplied

Motion artifact reduction with three-point ghost phase cancellation.

A novel method for "ghost" artifact suppression is introduced. It suppresses ghosts induced by motion in any direction, as well as other types of quasi-periodic signal modulation. Because it requires neither special hardware nor intensive data processing, it can be easily implemented on conventional magnetic resonance (MR) imagers. The method is based on the concept of decomposition of a ghosted complex image into a ghost mask and ideal image. A set of deliberately designed acquisitions are used to generate a set of ghosted complex images in which the ghost components are related in a simple manner. With use of equations describing image decomposition and ghost correlation, the ideal image can be calculated pixel by pixel. The ideal image obtained (representing the time-averaged spin-density distribution) is shown to be a truer representation of physical reality than the ghost-free image obtained with ordered phase encoding. In this technique, both interview and intraview effects are taken into account. The technique is also useful in simultaneously suppressing ghosts from multifrequency signal modulations such as respiratory and cardiac motions. The method was successfully tested with three time-interleaved, phase-encoding-order-shifted acquisitions. Experimental results have shown that it is a simple but effective technique.

Abdomen↗
PubMedDate not supplied

MR imaging and metallic implants for anterior cruciate ligament reconstruction: assessment of ferromagnetism and artifact.

Magnetic resonance (MR) imaging is contraindicated for patients with certain ferromagnetic implants, primarily because of potential risks related to movement or dislodgment of the devices. An additional problem with metallic implants is the potential image distortion that may affect the interpretation of the MR study. Since MR imaging is frequently useful for the evaluation of postoperative anterior cruciate ligament (ACL) reconstruction, the ferromagnetic qualities and artifacts associated with MR imaging were determined for five metallic orthopedic implants commonly used for this surgery. Only the Perfix interference screw displayed a substantial deflection force and caused extensive signal loss. Images of the knee of one patient with two Perfix screws in place were not interpretable because of the image distortion caused by these implants. Therefore, alternative nonferromagnetic implants should be considered for reconstruction of the ACL.

Anterior Cruciate Ligament Injuries↗
PubMedDate not supplied

Chemical shift artifact along the section-select axis.

Chemical shift artifact (CSA), familiar to radiologists along the frequency-encoding axis, also occurs along the section-select axis. The authors observed a case in which CSA mimicked a renal mass. Subsequent retrospective analysis of 50 abdominal magnetic resonance (MR) imaging studies was performed to assess occurrence of CSA adjacent to the upper and lower renal poles. CSA along the section-select axis was observed in 76% of cases and adjacent to 39% of all renal poles imaged. CSA along the section-select axis is common in abdominal MR imaging and may occasionally mimic disease.

Abdomen↗
PubMedDate not supplied

Phase-correction method for reduction of B0 instability artifacts.

View-to-view phase shifts due to B0 instability are corrected by applying a phase correction to the low-spatial-frequency views. The algorithm described herein assumes that the signal intensity in the space outside of an object represents only noise. A set of phases for the low-spatial-frequency views are calculated by minimizing, in the image, the intensity of the induced artifacts in the space outside of the object.

Algorithms↗