Intensity Of Artifacts Research Articles

Weakly- and Semisupervised Probabilistic Segmentation and Quantification of Reverberation Artifacts.

Objective and Impact Statement. We propose a weakly- and semisupervised, probabilistic needle-and-reverberation-artifact segmentation algorithm to separate the desired tissue-based pixel values from the superimposed artifacts. Our method models the intensity decay of artifact intensities and is designed to minimize the human labeling error. Introduction. Ultrasound image quality has continually been improving. However, when needles or other metallic objects are operating inside the tissue, the resulting reverberation artifacts can severely corrupt the surrounding image quality. Such effects are challenging for existing computer vision algorithms for medical image analysis. Needle reverberation artifacts can be hard to identify at times and affect various pixel values to different degrees. The boundaries of such artifacts are ambiguous, leading to disagreement among human experts labeling the artifacts. Methods. Our learning-based framework consists of three parts. The first part is a probabilistic segmentation network to generate the soft labels based on the human labels. These soft labels are input into the second part which is the transform function, where the training labels for the third part are generated. The third part outputs the final masks which quantifies the reverberation artifacts. Results. We demonstrate the applicability of the approach and compare it against other segmentation algorithms. Our method is capable of both differentiating between the reverberations from artifact-free patches and modeling the intensity fall-off in the artifacts. Conclusion. Our method matches state-of-the-art artifact segmentation performance and sets a new standard in estimating the per-pixel contributions of artifact vs underlying anatomy, especially in the immediately adjacent regions between reverberation lines. Our algorithm is also able to improve the performance of downstream image analysis algorithms.

Simple Experimental Models for Elucidating the Mechanism Underlying Vertical Artifacts in Lung Ultrasound: Tools for Revisiting B-Lines.

Using simple experimental models, we evaluated the generation, configuration and echo intensity of vertical artifacts by varying the point or plane of contact and height of objects that correspond to sources of vertical artifacts in the subpleural space. We used an ultrasound gel spot to imitate the source and a block of bacon as a chest wall phantom. As the size of the point of contact between the gel spot on the polypropylene sheet and the phantom decreased by peeling the sheet, a vertical artifact measuring ≤1 cm was generated and/or extended deeper, finally reaching 10 cm in depth. Next, objects of different shapes made using gel balls were used to observe the generation of artifacts and measure and compare the echo intensity. For a given shape, the intensity was markedly higher in one model with the point of contact than in the other model with the plane of contact. With the same point or plane of contact, the echo intensity was higher in the taller model. The size of the point or plane of contact and height of the source were observed to be key factors in the generation, length and echo intensity of the artifacts.

A real-time narcissus correction algorithm based on Gaussian mixture models

Cooled infrared optical systems often suffer from narcissus artifacts, which can severely degrade their imaging quality. Although the narcissus effects on image quality can be reduced using appropriate optical designs, the narcissus artifacts cannot be fully eliminated by this approach alone. Other approaches use image processing schemes to treat these artifacts as nonuniform noise and apply nonuniformity correction techniques to eliminate the artifacts. However, as the intensity and form of the narcissus artifacts depend on external factors, such as ambient temperature and focal length of the infrared imaging equipment, target-based nonuniformity correction techniques must frequently be calibrated against a standard blackbody radiation source. Moreover, scene-based nonuniformity corrections often produce ghosting artifacts owing to their overreliance on scene motions. In the present work, narcissus artifacts are treated as a type of additive low-frequency noise. Based on the characteristics of these artifacts and the requirements for real-time performance, we propose a new fitting method and a modified two-dimensional Gaussian mixture model (2D-GMM) for the low-frequency noise associated with narcissus artifacts. This allows the model parameters to be calculated rapidly without an iterative process. The resulting estimates of the narcissus signal can then be directly subtracted from the raw image to eliminate the narcissus artifact. The proposed correction algorithm was experimentally demonstrated to be capable of eliminating narcissus artifacts; furthermore, the fitting and correction processes of the algorithm are sufficiently fast to satisfy the requirements of real-time applications.

Assessment of the efficiency of a pre- versus post-acquisition metal artifact reduction algorithm in the presence of 3 different dental implant materials using multiple CBCT settings: An in vitro study.

PurposeThe aim of this study was to assess artifacts generated in cone-beam computed tomography (CBCT) of 3 types of dental implants using 3 metal artifact reduction (MAR) algorithm conditions (pre-acquisition MAR, postacquisition MAR, and no MAR), and 2 peak kilovoltage (kVp) settings.Materials and MethodsTitanium-zirconium, titanium, and zirconium alloy implants were placed in a dry mandible. CBCT images were acquired using 84 and 90 kVp and at normal resolution for all 3 MAR conditions. The images were analyzed using ImageJ software (National Institutes of Health, Bethesda, MD) to calculate the intensity of artifacts for each combination of material and settings. A 3-factor analysis of variance model with up to 3-way interactions was used to determine whether there was a statistically significant difference in the mean intensity of artifacts associated with each factor.ResultsThe analysis of all 3 MAR conditions showed that using no MAR resulted in substantially more severe artifacts than either of the 2 MAR algorithms for the 3 implant materials; however, there were no significant differences between pre- and post-acquisition MAR. The 90 kVp setting generated less intense artifacts on average than the 84 kVp setting. The titanium-zirconium alloy generated significantly less intense artifacts than zirconium. Titanium generated artifacts at an intermediate level relative to the other 2 implant materials, but was not statistically significantly different from either.ConclusionThis in vitro study suggests that artifacts can be minimized by using a titanium-zirconium alloy at the 90 kVp setting, with either MAR setting.

Carbon fiber\u2013reinforced PEEK versus titanium implants: an in vitro comparison of susceptibility artifacts in CT and MR imaging

Artifacts in computed tomography (CT) and magnetic resonance imaging (MRI) due to titanium implants in spine surgery are known to cause difficulties in follow-up imaging, radiation planning, and precise dose delivery in patients with spinal tumors. Carbon fiber–reinforced polyetheretherketon (CFRP) implants aim to reduce these artifacts. Our aim was to analyze susceptibility artifacts of these implants using a standardized in vitro model. Titanium and CFRP screw-rod phantoms were embedded in 3% agarose gel. Phantoms were scanned with Siemens Somatom AS Open and 3.0-T Siemens Skyra scanners. Regions of interest (ROIs) were plotted and analyzed for CT and MRI at clinically relevant localizations. CT voxel–based imaging analysis showed a significant difference of artifact intensity and central overlay between titanium and CFRP phantoms. For the virtual regions of the spinal canal, titanium implants (ti) presented − 30.7 HU vs. 33.4 HU mean for CFRP (p < 0.001), at the posterior margin of the vertebral body 68.9 HU (ti) vs. 59.8 HU (CFRP) (p < 0.001) and at the anterior part of the vertebral body 201.2 HU (ti) vs. 70.4 HU (CFRP) (p < 0.001), respectively. MRI data was only visually interpreted due to the low sample size and lack of an objective measuring system as Hounsfield units in CT. CT imaging of the phantom with typical implant configuration for thoracic stabilization could demonstrate a significant artifact reduction in CFRP implants compared with titanium implants for evaluation of index structures. Radiolucency with less artifacts provides a better interpretation of follow-up imaging, radiation planning, and more precise dose delivery.

Microscopic Structure of Swollen Hydrogels by Scanning Electron and Light Microscopies: Artifacts and Reality.

The exact knowledge of hydrogel microstructure, mainly its pore topology, is a key issue in hydrogel engineering. For visualization of the swollen hydrogels, the cryogenic or high vacuum scanning electron microscopies (cryo-SEM or HVSEM) are frequently used while the possibility of artifact-biased images is frequently underestimated. The major cause of artifacts is the formation of ice crystals upon freezing of the hydrated gel. Some porous hydrogels can be visualized with SEM without the danger of artifacts because the growing crystals are accommodated within already existing primary pores of the gel. In some non-porous hydrogels the secondary pores will also not be formed due to rigid network structure of gels that counteracts the crystal nucleation and growth. We have tested the limits of true reproduction of the hydrogel morphology imposed by the swelling degree and mechanical strength of gels by investigating a series of methacrylate hydrogels made by crosslinking polymerization of glycerol monomethacrylate and 2-hydroxyethyl methacrylate including their interpenetrating networks. The hydrogel morphology was studied using cryo-SEM, HVSEM, environmental scanning electron microscopy (ESEM), laser scanning confocal microscopy (LSCM) and classical wide-field light microscopy (LM). The cryo-SEM and HVSEM yielded artifact-free micrographs for limited range of non-porous hydrogels and for macroporous gels. A true non-porous structure was observed free of artifacts only for hydrogels exhibiting relatively low swelling and high elastic modulus above 0.5 MPa, whereas for highly swollen and/or mechanically weak hydrogels the cryo-SEM/HVSEM experiments resulted in secondary porosity. In this contribution we present several cases of severe artifact formation in PHEMA and PGMA hydrogels during their visualization by cryo-SEM and HVSEM. We also put forward empirical correlation between hydrogel morphological and mechanical parameters and the occurrence and intensity of artifacts.

Influence of tooth position within the field of view on the intensity of cone-beam computed tomographic imaging artifacts when assessing teeth restored with various intracanal materials.

PurposeThis study aimed to quantify the influence of tooth position within the field-of-view (FOV) on cone-beam computed tomography (CBCT) imaging artifacts' intensity when assessing teeth restored with various intracanal materials.Materials and MethodsSeventy single-rooted teeth were divided into 7 groups (10 teeth per group): NiCr post (NC), AgPd post (AP), metal core fiberglass post (MCFG), fiberglass post (FG), anatomical fiberglass post (AFG), fiberglass post cemented with core build-up cement (FGCo), and anatomical fiberglass post cemented with core build-up cement (AFGCo). All posts were cemented using a regular dual-curing resin cement (Allcem), except FGCo and AFGCo which were cemented with a core build-up dual-curing resin cement (AllcemCore). Each tooth was scanned on a CS9000 in 5 positions within the FOV: a central position, anterior horizontal peripheral, peripheral superior, peripheral inferior, and posterior horizontal peripheral position. Hyperdense, hypodense, remaining teeth areas and ROI areas were quantitatively analyzed using ImageJ software.ResultsPosterior horizontal peripheral position increased the intensity of artifacts on FGCo and AFGCo post groups (P<0.05), and specifically the hypodense artifact intensity on FG and AFG post groups (P<0.05). NC and AP groups presented greater intensity of artifacts than any other post groups (P<0.05).ConclusionArtifact intensity increases in the presence of high atomic number materials and when the object is not centered within the FOV. The impact of positioning within the FOV on artifact was greater for fiberglass posts cemented with core build-up dual-curing cement than for metal posts and fiberglass posts cemented with regular dual-curing cement.

Assessment of the Influence of Different Intracanal Materials on the Detection of Root Fracture in Birooted Teeth by Cone-beam Computed Tomography

IntroductionThe aim of this study was to assess 2 cone-beam computed tomographic systems on the detection of artificially induced vertical root fractures (VRFs) and artifact intensity using birooted teeth restored with different intracanal materials. MethodsThe sample consisted of 20 extracted birooted premolars. Root fracture was induced in half of the sample. Seven intracanal material combinations were used in each tooth, 1 at a time: unrestored, gutta-percha, a buccal root with gutta-percha and a lingual root with a fiberglass post, a buccal root with gutta-percha and a lingual root with a metal core fiberglass post, fiberglass posts, metal core fiberglass posts, and NiCr posts. Cone-beam computed tomographic scans were acquired using CS 9000 3D (Carestream Dental Rochester, NY) and OP300 (Instrumentarium Dental Inc, Tuusula, Finland) units. Exposure parameters were fixed at 90 kV and 8 mA. The voxel size and field of view were set at 0.085 mm and 5 × 5 cm for OP300 and 0.076 mm and 5 × 3.75 cm for CS 9000, respectively. Two observers assessed all images using a 5-point confidence scale for VRF detection and a 4-point score for artifact interference. The sensitivity, specificity, accuracy, and area under the receiver operating characteristic curve were compared using 2-way analysis of variance and the Tukey test (α = 0.05). Artifact interference was evaluated by descriptive statistics and the chi-square test. ResultsThere were significant differences between scanners (P > .05) and among the different intracanal material groups (OP300) (P < .05) for specificity. When a metal post was present in both roots, severe artifact interference was observed in all images. ConclusionsCS 9000 3D presented better performance than OP300 on VRF detection of endodontically treated teeth. Unrestored teeth and teeth filled with fiberglass posts were considered the groups with the lowest artifact interference and the highest VRF detection results.

Efficiency of Iterative Metal Artifact Reduction Algorithm (iMAR) Applied to Brain Volume Perfusion CT in the Follow-up of Patients after Coiling or Clipping of Ruptured Brain Aneurysms

Metal artifacts resulting from coiling or clipping of a brain aneurysm degrade image quality and reduce diagnostic usefulness of computed tomography perfusion CTP. Our aim was to assess the diagnostic value of the iterative metal artifact reduction algorithm (iMAR) in CTP studies after coiling or clipping of ruptured intracranial aneurysms. Fifty-eight CTP exams performed in 32 patients were analysed. iMAR was applied to the source images from the CT scanner. Perfusion maps were generated from datasets both with and without iMAR, and both datasets were compared qualitatively and quantitatively. Qualitative analysis included evaluation of intensity of artifacts, image quality, presence of new artifacts, and the reader’s confidence in their diagnosis as well as diagnostic impression. Quantitative analysis included evaluation of tissue attenuation curves, evaluation of region of interest (ROI)-based measurement of perfusion values at levels that do and do not contain metal, compared to previously published reference ranges of perfusion values. Our results showed that application of iMAR reduced artifacts and significantly improved image quality. New artifacts were observed adjacent to metallic implants, but did not limit the evaluation of other regions. After correction for artifact readers’ confidence in their diagnosis increased from 41.3% to 87.9%, and the diagnostic impression changed in 31% of the exams. No difference between tissue attenuation curves was found. For slices without metal, no difference was noted between values measured before and after iMAR, and the total number of ROIs in the reference range of perfusion values was unchanged. At the level of the metal implant, 89.85% of ROIs obtained before using iMAR showed calculation errors. After using iMAR, only 1.7% showed errors. Before iMAR 3.1% of values were in the reference range, whereas after iMAR this increased to 33.1%. In conclusion, our results show that iMAR is an excellent tool for reducing artifacts in CTP. It is therefore recommended for use in clinical practice, particularly when severe artifacts are present, or when hypoperfusion is suspected at the level of the coil or clip. After the application of iMAR, the perfusion values at the level of the metal can be better calculated, but may not lie within the reference range; therefore, quantitative analysis at the level of artifacts is not advisable.

3D black-blood 3T-MRI for the diagnosis of abdominal large vessel vasculitis.

To assess the value of a T1-3D black-blood turbo spin echo (TSE) sequence for the diagnosis of abdominal large vessel vasculitis (LVV). The study included 20 patients with abdominal LVV and 17 controls, who underwent a 3T-MRI scan using a modified T1-3D volumetric isotropic TSE acquisition and a segmented T1-3D turbo field echo sequence (T1-mVISTA/T1-eTHRIVE). Two radiologists independently analyzed the aorta for concentric contrast enhancement, concentric wall thickening, image quality, and flow artifact intensity (CCE/CWT/IQ/FAI; 4-point scales). The mean aortic wall thickness (MAWT) in post-contrast T1-mVISTA was compared between patients and controls. IQ of T1-mVISTA was rated good to excellent in 91.5% of 282 evaluated vessel segments with no or minor FAI present in 85.5%. The inter-observer reproducibility for the identification of CCE/CWT on T1-mVISTA was 0.92 and 0.93 (p < 0.001). The distribution of segmental inflammation in T1-mVISTA significantly correlated with T1-eTHRIVE (CCE, κ= 0.768; CWT, κ = 0.715; p < 0.001), resulting in a sensitivity, specificity, and positive predictive value of 100%, 81.3%, and 83.3%. The MAWT significantly differed between patients and controls (3.29 ± 0.81 vs. 2.24 ± 0.45mm; p < 0.001). T1-mVISTA enables the evaluation of the MAWT and allows the detection of abdominal LVV. • 3D T1w-mVISTA accurately depicted the large abdominal vessels. • 3D T1w-mVISTA enables accurate measurements of the abdominal aortic wall thickness. • 3D T1w-mVISTA is useful for the detection of abdominal LVV.

Influence of Artifact Corrections on MRI Signal Intensity Ratios for Assessment of Gadolinium Brain Retention

Differences in brain signal intensity ratios (SIRs) of deep brain nuclei in T1-weighted (T1w) magnetic resonance images were reported as an indicator of gadolinium brain retention. Variable methods of image reconstruction and inhomogeneity correction for T1w images exist, which might affect the accuracy of SIRs. The aim of our prospective study was to investigate the effect of flow artifact compensation (FAC) and intensity inhomogeneity correction (IIC) on the dentate nucleus-to-pons and globus pallidus-to-thalamus SIRs in study participants who had previously received multiple doses of gadobutrol. This study included 76 participants who received five or more gadobutrol-enhanced scans between 2007 and 2017. A control group of 25 participants without gadolinium-based contrast agent application in their patient history was included for comparison. Unenhanced brain magnetic resonance imaging including two T1w spin-echo sequences with and without FAC was performed in all participants. Both sequences were reconstructed with and without IIC. Images were assessed for flow artifacts and SIRs were calculated. Using FAC, a lower proportion of participants had to be excluded from the final analysis of dentate nucleus-to-pons SIR due to flow artifacts (15% versus 46%, p < 0.001). Without IIC, a difference was found between the study and the control group for the dentate nucleus-to-pons ratio (p = 0.004), but not for the same sequence reconstructed with IIC (p = 0.29). For the globus pallidus-to-thalamus ratio, no difference was found between the study and control group. The application of an IIC algorithm has significant impact on brain nuclei SIRs for the assessment of gadolinium brain retention.

Metal Artifact Reduction in Routine Chest and Abdominal Examinations Using Virtual Monoenergetic Images From Spectral Detector Computed Tomography.

The objective of this study was to investigate the quantitative and qualitative effects of virtual monoenergetic images (VMIs) by spectral detector computed tomography (SDCT) on metal artifacts in routine examinations. Fifty-nine patients with metal artifacts (caused by pacemakers, ports, screws, or prosthetic joints) affecting muscular tissue in the chest and/or abdomen were scanned using SDCT. Attenuation values around the metallic device were compared with contralateral unaffected values, for conventional images and 80 to 200 keV VMIs. In addition, general image quality and artifact intensity were rated by 2 readers. The VMIs significantly decreased metal artifact intensity in all patients (P < 0.05). In 39 patients (66.1%), the attenuation values of the artifact and the unaffected area on the optimal keV level were very similar (≤5 Hounsfield unit difference). Qualitative analysis showed that high VMIs significantly improved artifact intensity, with best scores at 140 keV. High monoenergetic images of SDCT significantly reduce metal artifacts, with optimal assessment at 140 keV.

Frequency and Diagnostic Implications of Image Artifacts by Eye-Lens Shielding in Head CT.

The eye lens is one of the most radiosensitive organs, and medical radiation is one of the main causes of cataracts. To protect the lens during head CT examinations, protectors have been developed; however, they can lead to image artifacts, which is a major disadvantage of their use. This study retrospectively evaluates the frequency and extent of artifacts caused by these protectors related to three anatomic regions (eye, brain, and bone) and their dependence on protector positioning. Datasets from 261 consecutive head CT examinations obtained during 3.5 months of routine clinical imaging were assessed. Diagnostic quality of the images was evaluated by objective measuring and subjective scoring on a 5-point Likert scale. Furthermore, the position of the lens protector in correlation to the eye lens and the intensity and frequency of artifacts were analyzed. Only 4.6% of all analyzed examinations were completely free from artifacts; 95.4% showed artifacts at least in the orbital cavity. Although the brain was affected in 27.8% of cases, in only 5.8% of cases was there a risk of misinterpretation, such as suspected intracranial bleeding. In 24.9% of cases, the lens was not properly covered by the protector. A too cranial position of the protector was identified as the main risk factor for cerebral artifacts. Eye shielding for brain CT examinations often leads to artifacts. However, in only a small percentage of cases do these artifacts affect tissue depiction in regions beyond the eye (i.e., brain or bones). Correct positioning is mandatory to minimize artifacts.

Wideband myocardial perfusion pulse sequence for imaging patients with a cardiac implantable electronic device.

To develop a wideband cardiac perfusion pulse sequence and test whether it is capable of suppressing image artifacts in patients with a cardiac implantable electronic device (CIED), while not exceeding the specific absorption rate (SAR) limit (2.0 W/kg). A wideband perfusion pulse sequence was developed by incorporating a wideband saturation pulse to achieve a good balance between saturation of magnetization and SAR. Clinical standard and wideband perfusion MRI scans were performed back-to-back in a randomized order on 16 patients with a CIED undergoing clinical cardiac MRI. Two expert readers graded the artifact intensity and extent on a segmental basis using a 5-point Likert scale, where significant artifact was defined by a composite score. The variance in myocardial signal prior to tissue-enhancement was analyzed to quantify artifact-intensity. Whole-body SAR values computed by the MR scanner were read from the DICOM header. Either a paired t-test or Wilcoxon signed-rank test was performed to compare two groups. While the mean whole-body SAR for a single-slice wideband perfusion scan (0.38 ± 0.08W/kg) was significantly (p < 0.05) higher than for a single-slice standard perfusion scan (0.11 ± 0.03W/kg), it was 81% below 2.0 W/kg. The mean variance in myocardial signal prior to tissue-enhancement was significantly (p < 0.001) higher for standard (422.6 ± 306.6 a.u.) than wideband (107.0 ± 60.9 a.u.). Among 105 myocardial segments, standard produced 19 segments (18%) that were deemed to have significant artifacts, whereas wideband produced only 3 segments (3%). A wideband perfusion pulse sequence is capable of suppressing image artifacts induced by a CIED while not exceeding SAR at 2.0 W/kg.

Intensity of artefacts in cone beam CT examinations caused by titanium and glass fibre-reinforced composite implants.

The aim was to compare titanium and glass fibre-reinforced composite (FRC) orbital floor implants using cone beam CT (CBCT). FRC implants are nonmetallic and these implants have not been analysed in CBCT images before. The purpose of this study is to compare the artefact formation of the titanium and the FRC orbital floor implants in CBCT images. One commercially pure titanium and one S-glass FRC with bioactive glass particles implant were imaged with CBCT using the same imaging values (80 kV, 1 mA, FOV 60 × 60 mm). CBCT images were analysed in axial slices from three areas to determine the magnitude of the artefacts in the vicinity of the implants. Quantified results based on the gray values of images were analysed using analysis-of-variance. Compared to the reference the gray values of the titanium implant are more negative in every region of interest in all slices (p < 0.05) whereas the gray values of the FRC implant differ statistically significantly in less than half of the examined areas. The titanium implant caused artefacts in all of the analysed CBCT slices. Compared to the reference the gray values of the FRC implant changed only slightly and this feature enables to use wider imaging options postoperatively.

F04. Quantification of rapid eye movement sleep muscle tone in epilepsy

Rapid eye movement (REM) sleep typically inhibits seizures and epileptiform activity in persons with epilepsy. In animal models, REM sleep without atonia has been shown to facilitate seizures and epileptiform activity. We sought to rigorously examine muscle tone in the REM sleep of persons with epilepsy for the first time using a novel quantitative electroencephalographic (QEEG) technique. QEEG software (Persyst, USA) analyzed continuously recorded EEG in the University of Manitoba Epilepsy Monitoring Unit (EMU) over a 12-month period to quantify muscle artifact intensity during REM sleep. Additional electrooculogram and muscle electrodes were included for REM sleep identification. QEEG represented muscle artifact as green bars of varying intensity. The maximal degree of greenness (M) was calculated as RGB values in order to represent the overall muscle tone of a REM sleep epoch. 790 REM sleep epochs were identified from 94 patients (mean age 37.6 years, 66% female). 58 patients were on medications capable of affecting muscle tone. Of patients not on these medications, 30 were epileptic (n = 272 epochs) and 6 were nonepileptic controls (n = 56 epochs). While half of epileptic patients were male, all nonepileptic patients were female. Age and gender were not significantly correlated with M. M was significantly lower in epileptic patients (M = 5.05 vs. 8.68, p < 0.001). As additional controls, M was also calculated for patients outside the 12-month period: a nonepileptic patient with REM sleep behavior disorder (M = 13.95), and another epileptic patient during a generalized tonic-clonic seizure (M = 128). This study shows for the first time that QEEG can be used to detect and quantify muscle tone in persons with epilepsy. We found that REM sleep muscle tone was significantly lower in epileptic patients than nonepileptic controls. Given the association of REM sleep without muscle atonia and seizure facilitation in animal models, this phenomenon may be a homeostatic protective mechanism against seizures in persons with epilepsy.

Clinical value of [18F]FDG-PET/CT and 3D-black-blood 3T-MRI for the diagnosis of large vessel vasculitis and single-organ vasculitis of the aorta.

We aimed to investigate the clinical value of a 3D-T1w turbo-spin-echo (TSE) sequence and [18F]fluorodeoxyglucose positron emission tomography/computed tomography ([18F]FDG-PET/CT) for the diagnosis of active large vessel vasculitis (LVV) and single-organ vasculitis (SOV) of the aorta. Twenty-four patients with suspected vasculitis who underwent MRI and PET/CT were retrospectively evaluated. MRI was analyzed for concentric contrast enhancement and wall thickening, and flow artifact intensity (4-point-scales). PET/CT analysis comprised qualitative, quantitative and semiquantitative methods. Imaging findings were correlated with final diagnosis derived from the clinical follow-up data. Fifteen of 24 patients had a clinically confirmed active vasculitis, two had inactive vasculitis and 7 no vasculitis. [18F]FDG-PET/CT and 3D-T1w TSE-MRI revealed both a high diagnostic accuracy of 88% and 83%, respectively. In patients in whom both PET/CT and MRI showed concordant findings (19 patients), the accuracy increased to 95% with a high positive predictive value (92%) and negative predictive value (100%); thus, a correct diagnosis was obtained in 18 of 19 patients. Among the five patients with discordant findings PET/CT correctly identified the two patients without active vasculitis while rated false positive on MRI. Of the three remaining patients with active vasculitis, two were correctly identified by MRI and one by PET/CT. 3D-T1w TSE-MRI and [18F]FDG-PET/CT are both useful in the diagnosis of active vasculitis with high diagnostic accuracies. The diagnostic accuracy was even optimized by combining the two analysis methods. Therefore, there might be substantial potential for the application of whole-body hybrid PET/MRI in the evaluation of vasculitis in future studies.

The advantages of a spine coil over a torso coil in magnetic resonance imaging examination of the sternoclavicular joints.

PurposeThere are two standard methods for an magnetic resonance imaging (MRI) examination of the sternoclavicular joints: with loop coils and the patient in the prone position, or with torso coils with the patient in a supine position. In some centres these joints are examined with the spine coil in a patient laying prone. There are no reports on the advantages of this method. Our hypothesis is that despite different MRI systems, application of a spine coil will improve examination quality.Material and methodsTwenty-one healthy volunteers (10 female, 11 male, mean age 25 years) were randomised into three groups and scanned using three different MRI scanners (1.5T: Siemens Avanto, Philips Ingenia, 3.0T: Philips Achieva). Each volunteer was examined twice: using a standard protocol with a torso coil and with a spine coil, in prone position. The two groups were compared with regard to the intensity of motion artefacts using the χ2 test, and to the signal-to-noise ratio with the Wilcoxon signed-rank test.ResultsApplication of a spine coil resulted in a significant decrease in the number of motion artefacts in all three planes (axial: p = 0.0004; sagittal: p < 0.0001; coronal: p = 0.0054). Moreover, the signal-to-noise ratio was significantly increased with the application of a spine coil (28.6 ± 8.6 vs. 18.5 ± 7.3, respectively; p = 0.0002).ConclusionsApplication of a spine coil with the patient in a prone position is suitable for MRI evaluation of the sternoclavicular joints. It allows a higher signal-to-noise ratio and a lower intensity of motion artefacts to be obtained compared to a torso coil.

Improvements, extensions, and practical aspects of rapid ASAP-HSQC and ALSOFAST-HSQC pulse sequences for studying small molecules at natural abundance

Previously we introduced two novel NMR experiments for small molecules, the so-called ASAP-HSQC and ALSOFAST-HSQC (Schulze-Sünninghausen et al., 2014), which allow the detection of heteronuclear one-bond correlations in less than 30s at natural abundance. We propose an improved symmetrized pulse scheme of the basic experiment to minimize artifact intensities and the combination with non-uniform sampling to enable the acquisition of conventional HSQC spectra in as short as a couple of seconds and extremely 13C-resolved spectra in less than ten minutes. Based on steady state investigations, a first estimate to relative achievable signal intensities with respect to conventional, ASAP-, and ALSOFAST-HSQC experiments is given. In addition, we describe several extensions to the basic pulse schemes, like a multiplicity-edited version, a revised symmetrized CLIP-ASAP-HSQC, an ASAP-/ALSOFAST-HSQC sequence with broadband BIRD-based 1H,1H decoupling, and a symmetrized sequence optimized for water suppression. Finally, RF-power considerations with respect to the high duty cycle of the experiments are given.

TH‐CD‐207B‐03: How to Quantify Temporal Resolution in X‐Ray MDCT Imaging?

Purpose:In modern CT scanners, a quantitative metric to assess temporal response, namely, to quantify the temporal resolution (TR), remains elusive. Rough surrogate metrics, such as half of the gantry rotation time for single source CT, a quarter of the gantry rotation time for dual source CT, or measurements of motion artifact's size, shape, or intensity have previously been used. In this work, a rigorous framework which quantifies TR and a practical measurement method are developed.Methods:A motion phantom was simulated which consisted of a single rod that is in motion except during a static period at the temporal center of the scan, termed the TR window. If the image of the motion scan has negligible motion artifacts compared to an image from a totally static scan, then the system has a TR no worse than the TR window used. By repeating this comparison with varying TR windows, the TR of the system can be accurately determined. Motion artifacts were also visually assessed and the TR was measured across varying rod motion speeds, directions, and locations. Noiseless fan beam acquisitions were simulated and images were reconstructed with a short‐scan image reconstruction algorithm.Results:The size, shape, and intensity of motion artifacts varied when the rod speed, direction, or location changed. TR measured using the proposed method, however, was consistent across rod speeds, directions, and locations.Conclusion:Since motion artifacts vary depending upon the motion speed, direction, and location, they are not suitable for measuring TR. In this work, a CT system with a specified TR is defined as having the ability to produce a static image with negligible motion artifacts, no matter what motion occurs outside of a static window of width TR. This framework allows for practical measurement of temporal resolution in clinical CT imaging systems.Funding support: GE Healthcare; Conflict of Interest: Employee, GE Healthcare.