Quantitative Measurement Of Susceptibility Research Articles

Iron-sensitive magnetic resonance imaging in Parkinson's disease: a systematic review and meta-analysis.

To evaluate the diagnostic performance of iron-sensitive sequences targeting the substantia nigra for distinguishing patients with Parkinson's disease from control participants and to identify factors causing heterogeneity. A systematic literature search in the Ovid-MEDLINE and EMBASE databases was performed for studies reporting the relevant topic before March 6, 2020. The pooled sensitivity and specificity values with their 95% confidence intervals were calculated using bivariate random-effects modeling. Subgroup and meta-regression analyses were also performed to determine factors influencing heterogeneity affecting the diagnostic performance among the clinical, MRI, and analytic characteristics. A total of 22 articles including 1126 patients with Parkinson's disease and 933 control participants were enrolled in this systematic review and meta-analysis. Of those, 12 studies used objective analyses of quantitative susceptibility measurements, and 10 visually assessed the nigrosome-1 in subjective analyses. Iron-sensitive nigral magnetic resonance imaging showed a pooled sensitivity of 92% (95% confidence interval 88-95%) and a pooled specificity of 90% (95% confidence interval 81-95%). According to subgroup and meta-regression analyses, a longer mean disease duration in patients with Parkinson's disease (≥ 5years), subjective analysis, a smaller size of pixel (< 0.6 mm2), a larger flip angle (> 15°), a smaller slice thickness (≤ 1mm), and specific targeting of the substantia nigra pars compacta improved the diagnostic performance. Iron-sensitive nigral magnetic resonance imaging had a favorable diagnostic performance in discriminating patients with Parkinson's disease from control participants. Subjective analytic methods remain superior to objective approaches. Further improvements of the spatial resolution and contrast-to-noise ratio to specifically target the nigrosome-1 with objective analytic methods will be needed.

Low thalamostriate venous quantitative susceptibility measurements correlate with higher presenting NIH stroke scale score in emergent large vessel occlusion stroke.

ObjectiveHyperacute stroke affects various patient subgroups who may benefit from different management strategies. Magnetic resonance imaging (MRI) quantitative susceptibility mapping (QSM) is a recent MRI technique for measuring deoxyhemoglobin levels. The results of QSM thus have the potential to act as a quantitative biomarker for predicting the success of endovascular interventions.MethodsTwenty-five patients with M1 occlusions were evaluated retrospectively. QSM measurements were obtained based on susceptibility-weighted imaging sequences from the most prominent veins in each of the four standard regions of interest: the cortical and thalamostriate veins ipsilateral and contralateral to the side of the stroke. The results were analyzed using Wilcoxon’s signed rank test and compared with presenting National Institutes of Health stroke scale (NIHSS) score.ResultsCortical veins ipsilateral to the stroke showed the greatest elevation in susceptibility compared with all other vein groups. Both ipsilateral and contralateral thalamostriate vein susceptibilities showed strong inverse correlation with presenting NIHSS score.ConclusionThalamostriate vein susceptibility shows a strong inverse correlation with presenting NIHSS in adult patients with hyperacute stroke who are selected for endovascular intervention by advanced imaging.

The choice of embedding media affects image quality, tissue R2*, and susceptibility behaviors in post‐mortem brain MR microscopy at 7.0T

The quality and precision of post-mortem MRI microscopy may vary depending on the embedding medium used. To investigate this, our study evaluated the impact of 5 widely used media on: (1) image quality, (2) contrast of high spatial resolution gradient-echo (T1 and T2 * -weighted) MR images, (3) effective transverse relaxation rate (R2 * ), and (4) quantitative susceptibility measurements (QSM) of post-mortem brain specimens. Five formaldehyde-fixed brain slices were scanned using 7.0T MRI in: (1) formaldehyde solution (formalin), (2) phosphate-buffered saline (PBS), (3) deuterium oxide (D2 O), (4) perfluoropolyether (Galden), and (5) agarose gel. SNR and contrast-to-noise ratii (SNR/CNR) were calculated for cortex/white matter (WM) and basal ganglia/WM regions. In addition, median R2 * and QSM values were extracted from caudate nucleus, putamen, globus pallidus, WM, and cortical regions. PBS, Galden, and agarose returned higher SNR/CNR compared to formalin and D2 O. Formalin fixation, and its use as embedding medium for scanning, increased tissue R2 * . Imaging with agarose, D2 O, and Galden returned lower R2 * values than PBS (and formalin). No major QSM offsets were observed, although spatial variance was increased (with respect to R2 * behaviors) for formalin and agarose. Embedding media affect gradient-echo image quality, R2 * , and QSM in differing ways. In this study, PBS embedding was identified as the most stable experimental setup, although by a small margin. Agarose and Galden were preferred to formalin or D2 O embedding. Formalin significantly increased R2 * causing noisier data and increased QSM variance.

Magnetic Susceptibility Changes in the Basal Ganglia and Brain Stem of Patients with Wilson's Disease: Evaluation with Quantitative Susceptibility Mapping.

Objectives:Wilson’s disease (WD) is characterized with the accumulation of copper in the liver and brain. The objective of this study is to quantitatively measure the susceptibility changes of basal ganglia and brain stem of pediatric patients with neurological WD using quantitative susceptibility mapping (QSM) in comparison to healthy controls.Methods:Eleven patients with neurological WD (mean age 15 ± 3.3 years, range 10–22 years) and 14 age-matched controls were prospectively recruited. Both groups were scanned on a 1.5 Tesla clinical scanner. In addition to T1- and T2-weighted MR images, a 3D multi-echo spoiled gradient echo (GRE) sequence was acquired and QSM images were derived offline. The quantitative measurement of susceptibility of corpus striatum, thalamus of each hemisphere, midbrain, and pons were assessed with the region of interest analysis on the QSM images. The susceptibility values for the patient and control groups were compared using two-sample t-test.Results:One patient with WD had T1 shortening in the bilateral globus pallidus. Another one had hyperintensity in the bilateral putamen, caudate nuclei, and substantia nigra on T2-weighted images. The rest of the patients with WD and all subjects of the control group had no signal abnormalities on conventional MR images. The susceptibility measures of right side of globus pallidus, putamen, thalamus, midbrain, and entire pons were significantly different in patients compared to controls (P < 0.05).Conclusion:QSM method exhibits increased susceptibility differences of basal ganglia and brain stem in patients with WD that have neurologic impairment even if no signal alteration is detected on T1- and T2-weighted MR images.

MR imaging differentiation of Fe2+ and Fe3+ based on relaxation and magnetic susceptibility properties.

The aim of this study is to evaluate the MR imaging behavior of ferrous (Fe2+) and ferric (Fe3+) iron ions in order to develop a noninvasive technique to quantitatively differentiate between both forms of iron. MRI was performed at 3T in a phantom consisting of 21 samples with different concentrations of ferrous and ferric chloride solutions (between 0 and 10mmol/L). A multi-echo spoiled gradient-echo pulse sequence with eight echoes was used for both T 2* and quantitative susceptibility measurements. The transverse relaxation rate, R 2*=1/T 2*, was determined by nonlinear exponential fitting based on the mean signals in each sample. The susceptibilities, χ, of the samples were calculated after phase unwrapping and background field removal by fitting the spatial convolution of a unit dipole response to the measured internal field map. Relaxation rate changes, ΔR 2*(c Fe), and susceptibility changes, Δχ(c Fe), their linear slopes, as well as the ratios ΔR 2*(c Fe)/Δχ(c Fe) were determined for all concentrations. The linear slopes of the relaxation rate were (12.5±0.4)s-1/(mmol/L) for Fe3+ and (0.77±0.09)s-1/(mmol/L) for Fe2+ (significantly different, z test P<0.0001). The linear slopes of the susceptibility were (0.088±0.003)ppm/(mmol/L) for Fe3+ and (0.079±0.006)ppm/(mmol/L) for Fe2+. The individual ratios ΔR 2*/Δχ were greater than 40s-1/ppm for all samples with ferric solution and lower than 20s-1/ppm for all but one of the samples with ferrous solution. Ferrous and ferric iron ions show significantly different relaxation behaviors in MRI but similar susceptibility patterns. These properties can be used to differentiate ferrous and ferric samples.

Abstract W P248: Cerebral Tissue Iron Quantification on MRI Following Intracerebral Hemorrhage

Purpose: Intracerebral hemorrhage (ICH) is a fatal subtype of Hemorrhagic stroke. Tissue iron at the periphery of ICH has been demonstrated to be neurotoxic in animal models. No robust method to quantify tissue iron following ICH currently exists. Our aim is to determine a robust algorithm based on MRI to quantify tissue iron in the wake of ICH. Methods: Following Institutional review board approval we constructed an MRI phantom. Eight 4 cc vials with 50 % decreasing dilutions of Ferraheme (iron for IV therapy) were prepared starting from 0.6 mg/ml ending at 0.005 mg/ml. The vials were stuck to the undersurface of the lid of a water bath container and scanned in a 3T MRI with T2* sequences. The T2* signal magnitudes were calculated for each concentration. Subsequently a human control brain and two patients with left basal ganglia ICH were scanned with identical parameters. The T2* signal magnitude was calculated at 3 ROIs at the periphery of the ICH. Results: The R2* maps demonstrated a near linear correlation with the iron concentration in the phantom. The control T2* signal magnitude corresponded to 0.01 mg/ml iron concentration. The two patients on ICH day 7 had measurements of iron concentration of 0.04 mg/ml (4 x baseline) at the periphery of the hematoma. This corresponds favorably to a threefold increase in measured tissue iron levels in animal ICH model studies. Conclusion: Our experiment demonstrates that quantitative susceptibility measurements on MRI may be a robust technique to assess iron level in brain tissue following ICH. Encouraged by the results we have applied to the NIH (#GRANT11426089) for funding to be able to evaluate the validity of the algorithm. Tissue iron quantification by MRI may assist in judging severity of ICH and act as a surrogate marker for assessing treatment with iron chelator.

Antimicrobial susceptibility testing: general principles and contemporary practices.

One of the most important tasks in the clinical microbiology laboratory is the performance of antimicrobial susceptibility tests on significant bacterial isolates. The goal of susceptibility testing is to predict the likely outcome of treating a patient's infection with a particular antimicrobial agent. Empirical therapy continues to be effective for some bacterial pathogens because resistance mechanisms have not yet been acquired or are still rare; examples include penicillin therapy for group A streptococcal infections, erythromycin for legionellosis, and penicillin for N. meningitidis infections in the United States. Susceptibility testing is useful and important for the common bacterial species that are not predictably susceptible to drugs of choice because of acquired resistance mechanisms (e.g., members of the Enterobacteriaceae, Pseudomonas species, Staphylococcus species, Enterococcus species, Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria gonorrhoeae). The two important and related functions of susceptibility testing are the detection of frank resistance and the quantitative measurement of susceptibility to antimicrobial agents with some species that may have direct therapeutic relevance, e.g., the magnitude of the penicillin and cephalosporin MICs for Streptococcus pneumoniae [1-3].

A comparison of serial plate agar dilution, bauer-kirby disk diffusion, and the vitek automicrobic system for the determination of susceptibilities of Klebsiella spp., Enterobacter spp., and Pseudomonas aeruginosa to ten antimicrobial agents

The use of rapid, automated technologies for assessment of antimicrobial susceptibility and determination of minimum inhibitory concentrations has been evolving for over a decade. We compared the Vitek AutoMicrobic system and Bauer-Kirby disk diffusion with the National Committee for Clinical Laboratory Standards methods of serial plate agar dilution for qualitative and quantitative susceptibilities of 301 hospital isolates of Klebsiella spp., Enterobacter spp., and Pseudomonas aeruginosa. Antibiotics tested were aztreonam, cefoperazone, ceftazidime, ceftriaxone, ciprofloxacin, gentamicin, imipenem, piperacillin, ticarcillin-clavulanic acid, and tobramycin. Agar dilution and Bauer-Kirby results were more strongly correlated for all three genera than were the results for agar dilution and Vitek. If agar dilution is presumed to be the “gold standard,” Bauer-Kirby disk diffusion had only half the number of false susceptibles as did the Vitek. Thus, the Vitek AutoMicrobic system seems to be somewhat less reliable for both qualitative and quantitative measurement of susceptibility and resistance than is Bauer-Kirby disk diffusion.

Use of Infernal Damping Measurements in the Study of Environmental Cracking

Abstract The problem of environmental cracking of metals and their alloys has become very important and warrants a concentrated study with new ideas for its solution. The major objectives of such a study are, (1) detection of susceptibility, (2) quantitative measurement of susceptibility, and (3) understanding the mechanism of susceptibility. An approach utilizing measurements of the internal damping characteristics of materials prone to environmental cracking is presented to show the feasibility of detecting significant changes occurring in the materials long before any macroscopic evidence of such changes becomes noticeable. Tests on 2024-T4 aluminum, 2024-T3 aluminum, Ti-6Al-4V and Ti-8Al-1Mo-1 V are reported wherein considerable changes in the internal damping of these materials were observed following their exposure in a stressed state to environments in which they are known to be susceptible to cracking. (Corroborative tests on 1020 mild steel and electrolytic copper stressed and exposed to a corroding environment of air saturated synthetic sea water produced no changes in internal damping. These materials are normally immune to stress corrosion cracking under the above conditions of exposure.) Theoretical ideas with supporting experimental evidence are presented in an attempt to arrive at a basic understanding of the phenomenon of environmental cracking by correlating the laws of diffusional mechanics of materials to those pertaining to changes in their internal damping.