Differentiation of symptomatic and asymptomatic carotid intraplaque hemorrhage using 3D high-resolution diffusion-weighted stack of stars imaging.

Ischemic events related to carotid disease are far more strongly associated with plaque instability than stenosis. 3D high-resolution diffusion-weighted (DW) imaging can provide quantitative diffusion measurements on carotid atherosclerosis and may improve detection of vulnerable intraplaque hemorrhage (IPH). The 3D DW-stack of stars (SOS) sequence was implemented with 3D SOS acquisition combined with DW preparation. After simulation of signals created from 3D DW-SOS, phantom studies were performed. Three healthy subjects and 20 patients with carotid disease were recruited. Apparent diffusion coefficient (ADC) values were statistically analyzed on three subgroups by using a two-group comparison Wilcoxon-Mann-Whitney U test with p values less than 0.05: symptomatic versus asymptomatic; IPH-positive versus IPH-negative; and IPH-positive symptomatic versus asymptomatic plaques to determine the relationship with plaque vulnerability. ADC values calculated by 3D DW-SOS provided values similar to those calculated from other techniques. Mean ADC of symptomatic plaque was significantly lower than asymptomatic plaque (0.68 ± 0.18 vs. 0.98 ± 0.16 x 10-3  mm2 /s, p < 0.001). ADC was also significantly lower in IPH-positive versus IPH-negative plaque (0.68 ± 0.13 vs. 1.04 ± 0.11 x 10-3  mm2 /s, p < 0.001). Additionally, ADC was significantly lower in symptomatic versus asymptomatic IPH-positive plaque (0.57 ± 0.09 vs. 0.75 ± 0.11 x 10-3  mm2 /s, p < 0.001). Our results provide strong evidence that ADC measurements from 3D DW-SOS correlate with the symptomatic status of extracranial internal carotid artery plaque. Further, ADC improved discrimination of symptomatic plaque in IPH. These data suggest that diffusion characteristics may improve detection of destabilized plaque leading to elevated stroke risk.

Critical curves of a piecewise linear map.

We study the parameter space of a family of planar maps, which are linear on each of the right and left half-planes. We consider the set of parameters for which every orbit recurs to the boundary between half-planes. These parameters consist of algebraic curves, determined by the symbolic dynamics of the itinerary that connects boundary points. We study the algebraic and geometrical properties of these curves, in relation to such a symbolic dynamics.

Complementary and Alternative Medicine Use in Psoriatic Arthritis Patients: a Review.

PURPOSE OF REVIEW: While complementary and alternative medicine (CAM) use is prevalent in the general population and is known to be used in systemic rheumatic disease such as rheumatoid arthritis and systemic lupus erythematosus, its use in psoriatic arthritis (PsA) is less well-studied. The purpose of this review was to identify published data describing the use of CAM in patients with PsA. RECENT FINDINGS: PsA patients report frequent use of CAM. Diet is believed to affect disease activity, and dietary approaches are used by patients to mitigate symptoms. Dietary supplements have been studied, especially fatty acids, with some positive results. Herbal remedies show promise, but more and better studies are needed, including evaluating medical cannabis. Studies of some the most commonly used CAM, such as acupuncture and massage, are conspicuously absent. CAM use is common among patients with PsA. There is, however, a significant knowledge gap, and there is a critical need for rigorous research to ensure safe and effective use of CAM for these patients.

Motion-insensitive carotid intraplaque hemorrhage imaging using 3D inversion recovery preparation stack of stars (IR-prep SOS) technique.

PURPOSE: Carotid artery imaging is important in the clinical management of patients at risk for stroke. Carotid intraplaque hemorrhage (IPH) presents an important diagnostic challenge. 3D magnetization prepared rapid acquisition gradient echo (MPRAGE) has been shown to accurately image carotid IPH; however, this sequence can be limited due to motion- and flow-related artifact. The purpose of this work was to develop and evaluate an improved 3D carotid MPRAGE sequence for IPH detection. We hypothesized that a radial-based k-space trajectory sequence such as "Stack of Stars" (SOS) incorporated with inversion recovery preparation would offer reduced motion sensitivity and more robust flow suppression by oversampling of central k-space. MATERIALS AND METHODS: A total of 31 patients with carotid disease (62 carotid arteries) were imaged at 3T magnetic resonance imaging (MRI) with 3D IR-prep Cartesian and SOS sequences. Image quality was determined between SOS and Cartesian MPRAGE in 62 carotid arteries using t-tests and multivariable linear regression. Kappa analysis was used to determine interrater reliability. RESULTS: In all, 25 among 62 carotid plaques had carotid IPH by consensus from the reviewers on SOS compared to 24 on Cartesian sequence. Image quality was significantly higher with SOS compared to Cartesian (mean 3.74 vs. 3.11, P < 0.001). SOS acquisition yielded sharper image features with less motion (19.4% vs. 45.2%, P < 0.002) and flow artifact (27.4% vs. 41.9%, P < 0.089). There was also excellent interrater reliability with SOS (kappa = 0.89), higher than that of Cartesian (kappa = 0.84). CONCLUSION: By minimizing flow and motion artifacts and retaining high interrater reliability, the SOS MPRAGE has important advantages over Cartesian MPRAGE in carotid IPH detection. LEVEL OF EVIDENCE: 1 J. Magn. Reson. Imaging 2017;45:410-417.

Amino acid modified Ni catalyst exhibits reversible H2 oxidation/production over a broad pH range at elevated temperatures.

Hydrogenases interconvert H2 and protons at high rates and with high energy efficiencies, providing inspiration for the development of molecular catalysts. Studies designed to determine how the protein scaffold can influence a catalytically active site have led to the synthesis of amino acid derivatives of [Ni(P2(R)N2(R'))2](2+) complexes, [Ni(P2(Cy)N2(Amino acid))2](2+) (CyAA). It is shown that these CyAA derivatives can catalyze fully reversible H2 production/oxidation at rates approaching those of hydrogenase enzymes. The reversibility is achieved in acidic aqueous solutions (pH = 0-6), 1 atm 25% H2/Ar, and elevated temperatures (tested from 298 to 348 K) for the glycine (CyGly), arginine (CyArg), and arginine methyl ester (CyArgOMe) derivatives. As expected for a reversible process, the catalytic activity is dependent upon H2 and proton concentrations. CyArg is significantly faster in both directions (∼300 s(-1) H2 production and 20 s(-1) H2 oxidation; pH = 1, 348 K, 1 atm 25% H2/Ar) than the other two derivatives. The slower turnover frequencies for CyArgOMe (35 s(-1) production and 7 s(-1) oxidation under the same conditions) compared with CyArg suggests an important role for the COOH group during catalysis. That CyArg is faster than CyGly (3 s(-1) production and 4 s(-1) oxidation) suggests that the additional structural features imparted by the guanidinium groups facilitate fast and reversible H2 addition/release. These observations demonstrate that outer coordination sphere amino acids work in synergy with the active site and can play an important role for synthetic molecular electrocatalysts, as has been observed for the protein scaffold of redox active enzymes.

Standard Reduction Potentials for Oxygen and Carbon Dioxide Couples in Acetonitrile and N,N-Dimethylformamide.

A variety of next-generation energy processes utilize the electrochemical interconversions of dioxygen and water as the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Reported here are the first estimates of the standard reduction potential of the O2 + 4e(-) + 4H(+) ⇋ 2H2O couple in organic solvents. The values are +1.21 V in acetonitrile (MeCN) and +0.60 V in N,N-dimethylformamide (DMF), each versus the ferrocenium/ferrocene couple (Fc(+/0)) in the respective solvent (as are all of the potentials reported here). The potentials have been determined using a thermochemical cycle that combines the free energy for transferring water from aqueous solution to organic solvent, -0.43 kcal mol(-1) for MeCN and -1.47 kcal mol(-1) for DMF, and the potential of the H(+)/H2 couple, - 0.028 V in MeCN and -0.662 V in DMF. The H(+)/H2 couple in DMF has been directly measured electrochemically using the previously reported procedure for the MeCN value. The thermochemical approach used for the O2/H2O couple has been extended to the CO2/CO and CO2/CH4 couples to give values of -0.12 and +0.15 V in MeCN and -0.73 and -0.48 V in DMF, respectively. Extensions to other reduction potentials are discussed. Additionally, the free energy for transfer of protons from water to organic solvent is estimated as +14 kcal mol(-1) for acetonitrile and +0.6 kcal mol(-1) for DMF.

Acidic ionic liquid/water solution as both medium and proton source for electrocatalytic H2 evolution by [Ni(P2N2)2]2+ complexes.

The electrocatalytic reduction of protons to H(2) by [Ni((P(Ph)(2)N(C6H4-hex))(2)(2)]((BF(4))(2) (where P(Ph)(2)N(C6H4-hex)(2) = 1,5-di(4-n-hexylphenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane) in the highly acidic ionic liquid dibutylformamidium bis(trifluoromethanesulfonyl)amide shows a strong dependence on added water. A turnover frequency of 43,000-53,000 s(-1) has been measured for hydrogen production at 25 °C when the mole fraction of water (χ(H(2)O)) is 0.72. The same catalyst in acetonitrile with added dimethylformamidium trifluoromethanesulfonate and water has a turnover frequency of 720 s(-1). Thus, the use of an ionic liquid/aqueous solution enhances the observed catalytic rate by more than a factor of 50, compared to a similar acid in a traditional organic solvent. Complexes [Ni((P(Ph)(2)N(C6H4X))(2)(2)]((BF(4))(2) (X = H, OMe,CH(2)P(O)(OEt)(2), Br) are also catalysts in the ionic liquid/water mixture, and the observed catalytic rates correlate with the hydrophobicity of X.

Enzyme design from the bottom up: an active nickel electrocatalyst with a structured peptide outer coordination sphere.

Catalytic, peptide-containing metal complexes with a well-defined peptide structure have the potential to enhance molecular catalysts through an enzyme-like outer coordination sphere. Here, we report the synthesis and characterization of an active, peptide-based metal complex built upon the well-characterized hydrogen production catalyst [Ni(P(Ph)2N(Ph))2](2+) (P(Ph)2N(Ph)=1,3,6-triphenyl-1-aza-3,6-diphosphacycloheptane). The incorporated peptide maintains its ß-hairpin structure when appended to the metal core, and the electrocatalytic activity of the peptide-based metal complex (≈100,000 s(-1)) is enhanced compared to the parent complex ([Ni(P(Ph)2N(APPA))2](2+); ≈50,500 s(-1)). The combination of an active molecular catalyst with a structured peptide provides a scaffold that permits the incorporation of features of an enzyme-like outer-coordination sphere necessary to create molecular electrocatalysts with enhanced functionality.

A hydrogen-evolving Ni(P2N2)2 electrocatalyst covalently attached to a glassy carbon electrode: preparation, characterization, and catalysis. comparisons with the homogeneous analogue.

A hydrogen-evolving homogeneous Ni(P2N2)2 electrocatalyst with peripheral ester groups has been covalently attached to a 1,2,3-triazolyllithium-terminated planar glassy carbon electrode surface. Coupling proceeds with both the Ni(0) and the Ni(II) complexes. X-ray photoemission spectra show excellent agreement between the Ni(0) coupling product and its parent complex, and voltammetry of the surface-confined system shows that a single species predominates with a surface density of 1.3 × 10(-10) mol cm(-2), approaching the value estimated for a densely packed monolayer. With the Ni(II) system, both photoemission and voltammetric data show speciation to unidentified products on coupling, and the surface density is 6.7 × 10(-11) mol cm(-2). The surface-confined Ni(0) complex is an electroctalyst for hydrogen evolution, showing the onset of catalytic current at the same potential as the soluble parent complex. Decomposition of the surface-confined species is observed in acidic acetonitrile. This is interpreted to reflect the lability of the Ni(II)-phosphine interaction and the basicity of the free phosphine and bears on concurrent efforts to implement surface-confined Ni(P2N2)2 complexes in electrochemical or photoelectrochemical devices.

Arginine-containing ligands enhance H2 oxidation catalyst performance.

Hydrogenase enzymes use Ni and Fe to oxidize H2 at high turnover frequencies (TOF) (up to 10,000 s(-1)) and low overpotentials (<100 mV). In comparison, the fastest reported synthetic electrocatalyst, [Ni(II)(P(Cy)2N(tBu)2)2](2+), oxidizes H2 at 60 s(-1) in MeCN under 1 atm H2 with an unoptimized overpotential of ca. 500 mV using triethylamine as a base. Here we show that a structured outer coordination sphere in a Ni electrocatalyst enhances H2 oxidation activity: [Ni(II)(P(Cy)2N(Arg)2)2](8+) (Arg=arginine) has a TOF of 210 s(-1) in water with high energy efficiency (180 mV overpotential) under 1 atm H2 , and 144,000 s(-1) (460 mV overpotential) under 133 atm H2. The complex is active from pH 0-14 and is faster at low pH, the most relevant condition for fuel cells. The arginine substituents increase TOF and may engage in an intramolecular guanidinium interaction that assists in H2 activation, while the COOH groups facilitate rapid proton movement. These results emphasize the critical role of features beyond the active site in achieving fast, efficient catalysis.

T1 mapping for Head and Neck Cancer Patients undergoing Chemoradiotherapy: Feasibility of 3D Stack of Star Imaging.

BACKGROUND: Measuring tissue oxygen concentration is crucial in understanding the pathophysiological process of hypoxia in head and neck cancer (HNC) and its significant role in cancer biology. This study aimed to determine the feasibility of T1 mapping using a variable flip angle (VFA) technique with stack of stars (SOS) trajectory sampling in HNC patients undergoing chemoradiotherapy (CRT). METHODS: To evaluate the ability of SOS acquisition to detect T1, a phantom study was conducted and compared to conventional Cartesian acquisition (CART). Additionally, four newly diagnosed patients were recruited and underwent two scans each at baseline and inter-treatment. The repeatability of SOS and CART acquisitions was assessed by comparing the T1 measurements of CSF from the baseline and intra-treatment MRI studies. The changes in ∆T1 of the tumors during air and oxygen inhalation between baseline and inter-treatment scans were also evaluated. RESULTS: Our study found that the 3D VFA SOS sequence was effective in reducing motion artifacts compared to the conventional VFA sequence with CART sampling and the same scan time, as demonstrated by the results from the phantom and patient studies. In terms of repeatability, no significant correlation was observed between the variability in ΔT1 measurements of CSF obtained from SOS T1 maps. The SOS ΔT1 measurements showed higher consistency, as evidenced by the ICC values ranging from 0.52 to 0.92. The ∆T1 measurements on the primary tumors increased after the first CRT (p<0.05) for all patients who showed a positive treatment response, except for one patient (0.05

Minimal proton channel enables H2 oxidation and production with a water-soluble nickel-based catalyst.

Hydrogenase enzymes use first-row transition metals to interconvert H2 with protons and electrons, reactions that are important for the storage and recovery of energy from intermittent sources such as solar, hydroelectric, and wind. Here we present Ni(P(Cy)2N(Gly)2)2, a water-soluble molecular electrocatalyst with the amino acid glycine built into the diphosphine ligand framework. Proton transfer between the outer coordination sphere carboxylates and the second coordination sphere pendant amines is rapid, as observed by cyclic voltammetry and FTIR spectroscopy, indicating that the carboxylate groups may participate in proton transfer during catalysis. This complex oxidizes H2 (1-33 s(-1)) at low overpotentials (150-365 mV) over a range of pH values (0.1-9.0) and produces H2 under identical solution conditions (>2400 s(-1) at pH 0.5). Enzymes employ proton channels for the controlled movement of protons over long distances-the results presented here demonstrate the effects of a simple two-component proton channel in a synthetic molecular electrocatalyst.

The role of a dipeptide outer-coordination sphere on H2-production catalysts: influence on catalytic rates and electron transfer.

The outer-coordination sphere of enzymes acts to fine-tune the active site reactivity and control catalytic rates, suggesting that incorporation of analogous structural elements into molecular catalysts may be necessary to achieve rates comparable to those observed in enzyme systems at low overpotentials. In this work, we evaluate the effect of an amino acid and dipeptide outer-coordination sphere on [Ni(P(Ph)(2)N(Ph-R)(2))(2)](2+) hydrogen production catalysts. A series of 12 new complexes containing non-natural amino acids or dipeptides was prepared to test the effects of positioning, size, polarity and aromaticity on catalytic activity. The non-natural amino acid was either 3-(meta- or para-aminophenyl)propionic acid terminated as an acid, an ester or an amide. Dipeptides consisted of one of the non-natural amino acids coupled to one of four amino acid esters: alanine, serine, phenylalanine or tyrosine. All of the catalysts are active for hydrogen production, with rates averaging ∼1000 s(-1), 40 % faster than the unmodified catalyst. Structure and polarity of the aliphatic or aromatic side chains of the C-terminal peptide do not strongly influence rates. However, the presence of an amide bond increases rates, suggesting a role for the amide in assisting catalysis. Overpotentials were lower with substituents at the N-phenyl meta position. This is consistent with slower electron transfer in the less compact, para-substituted complexes, as shown in digital simulations of catalyst cyclic voltammograms and computational modeling of the complexes. Combining the current results with insights from previous results, we propose a mechanism for the role of the amino acid and dipeptide based outer-coordination sphere in molecular hydrogen production catalysts.

Direct determination of equilibrium potentials for hydrogen oxidation/production by open circuit potential measurements in acetonitrile.

Open circuit potentials were measured for acetonitrile solutions of a variety of acids and their conjugate bases under 1 atm H2. Acids examined were triethylammonium, dimethylformamidium, 2,6-dichloroanilinium, 4-cyanoanilinium, 4-bromoanilinium, and 4-anisidinium salts. These potentials, along with the pKa values of the acids, establish the value of the standard hydrogen electrode (SHE) potential in acetonitrile as -0.028(4) V vs the ferrocenium/ferrocene couple. Dimethylformamidium forms homoconjugates and other aggregates with dimethylformamide; open circuit potentials (OCPs) were used to quantify the extent of these reactions. Overpotentials for electrocatalytic hydrogen production and oxidation were determined from open circuit potentials and voltammograms of acidic or basic catalyst solutions under H2. For these solutions, agreement between OCP values and potentials calculated using the Nernst equation is within 12 mV. Use of the measured equilibrium potential allows direct comparison of catalytic systems in different media; it requires neither pKa values, homoconjugation constants, nor the SHE potential.

The electrode as organolithium reagent: catalyst-free covalent attachment of electrochemically active species to an azide-terminated glassy carbon electrode surface.

The reaction of a lithium acetylide-ethylenediamine complex with azide-terminated glassy carbon surfaces affords 1,2,3-triazolyllithium surface groups that are active toward covalent C-C coupling reactions, including salt metathesis with an aliphatic halide and nucleophilic addition at an aldehyde. Surface ferrocenyl groups were introduced by reaction with (6-iodohexyl)ferrocene; the voltammetry of electrode samples shows narrow, symmetric peaks indicating uniform attachment. X-ray photoelectron and reflectance infrared spectroscopic data provide further support for the surface-attached products. Formation of the 1,2,3-triazolyllithium linkage requires neither a catalyst nor a strained alkyne. Coverages obtained by this route are similar to those obtained by the more common Cu(I)-catalyzed alkyne-azide coupling (CuAAC) of ethynylferrocene with surface azides. Preconditioning of the glassy carbon disk electrodes at ambient temperature under nitrogen affords coverages comparable to those reported with preconditioning at 1000 °C under hydrogen/nitrogen.

Synthesis and electrochemical studies of cobalt(III) monohydride complexes containing pendant amines.

Two new tetraphosphine ligands, P(nC-PPh2)2N(Ph)2 (1,5-diphenyl-3,7-bis((diphenylphosphino)alkyl)-1,5-diaza-3,7-diphosphacyclooctane; alkyl = (CH2)2, n = 2 (L2); (CH2)3, n = 3 (L3)), have been synthesized. Coordination of these ligands to cobalt affords the complexes [Co(II)(L2)(CH3CN)](2+) and [Co(II)(L3)(CH3CN)](2+), which are reduced by KC8 to afford [Co(I)(L2)(CH3CN)](+) and [Co(I)(L3)(CH3CN)](+). Protonation of the Co(I) complexes affords [HCo(III)(L2)(CH3CN)](2+) and [HCo(III)(L3)(CH3CN)](2+). The cyclic voltammetry of [HCo(III)(L2)(CH3CN)](2+), analyzed using digital simulation, is consistent with an ErCrEr reduction mechanism involving reversible acetonitrile dissociation from [HCo(II)(L2)(CH3CN)](+) and resulting in formation of HCo(I)(L2). Reduction of HCo(III) also results in cleavage of the H-Co bond from HCo(II) or HCo(I), leading to formation of the Co(I) complex [Co(I)(L2)(CH3CN)](+). Under voltammetric conditions, the reduced cobalt hydride reacts with a protic solvent impurity to generate H2 in a monometallic process involving two electrons per cobalt. In contrast, under bulk electrolysis conditions, H2 formation requires only one reducing equivalent per [HCo(III)(L2)(CH3CN)](2+), indicating a bimetallic route wherein two cobalt hydride complexes react to form 2 equiv of [Co(I)(L2)(CH3CN)](+) and 1 equiv of H2. These results indicate that both HCo(II) and HCo(I) can be formed under electrocatalytic conditions and should be considered as potential catalytic intermediates.

MRI Assessment of Sacroiliitis With High-Resolution Protocol.

Background: Sacroiliac (SI) joint subchondral resorption on high-resolution magnetic resonance imaging (MRI) may be an early sign of the development of sacroiliitis. At our institution, high-resolution intermediate-weighted (proton density) MRI sequences are used in the workup of suspected spondyloarthritis (SpA). Questions/Purpose: We sought to test the hypothesis that SI joint subchondral resorption might be a useful MRI feature in the diagnosis of sacroiliitis. Methods: We retrospectively reviewed the records of patients with suspected SpA from a single rheumatologist's practice from January 1, 2010, to December 31, 2017. Patients had an MRI of the SI joints, using our institution's specialized protocol, and underwent standard physical examination and laboratory evaluation. The sensitivity and specificity of SI joint subchondral resorption in the identification of sacroiliitis were estimated using the clinical diagnosis as the reference standard and from a Bayesian latent class model with conditional dependence. Results: SI joint subchondral resorption on SI joint MRI was highly correlated with a positive diagnosis in patients worked up for axial SpA. It demonstrated superior sensitivity when compared with other MRI features used in the MRI diagnosis of sacroiliitis, such as bone marrow edema pattern, erosion, and ankylosis. Interobserver reliability was high for subchondral resorption. Conclusion: This retrospective study found that subchondral resorption on MRI evaluation of the SI joints appeared to be a sensitive indicator of SpA, potentially of early disease. This imaging feature warrants evaluation in other cohorts of patients suspected of having axial SpA to validate diagnostic performance in diverse populations.

Ultrahigh-Quality Infrared Polaritonic Resonators Based on Bottom-Up-Synthesized van der Waals Nanoribbons.

van der Waals nanomaterials supporting phonon polariton quasiparticles possess extraordinary light confinement capabilities, making them ideal systems for molecular sensing, thermal emission, and subwavelength imaging applications, but they require defect-free crystallinity and nanostructured form factors to fully showcase these capabilities. We introduce bottom-up-synthesized α-MoO3 structures as nanoscale phonon polaritonic systems that feature tailorable morphologies and crystal qualities consistent with bulk single crystals. α-MoO3 nanoribbons serve as low-loss hyperbolic Fabry-Pérot nanoresonators, and we experimentally map hyperbolic resonances over four Reststrahlen bands spanning the far- and mid-infrared spectral range, including resonance modes beyond the 10th order. The measured quality factors are the highest from phonon polaritonic van der Waals structures to date. We anticipate that bottom-up-synthesized polaritonic van der Waals nanostructures will serve as an enabling high-performance and low-loss platform for infrared optical and optoelectronic applications.

Validation of an arterial tortuosity measure with application to hypertension collection of clinical hypertensive patients.

BACKGROUND: Hypertension may increase tortuosity or twistedness of arteries. We applied a centerline extraction algorithm and tortuosity metric to magnetic resonance angiography (MRA) brain images to quantitatively measure the tortuosity of arterial vessel centerlines. The most commonly used arterial tortuosity measure is the distance factor metric (DFM). This study tested a DFM based measurement's ability to detect increases in arterial tortuosity of hypertensives using existing images. Existing images presented challenges such as different resolutions which may affect the tortuosity measurement, different depths of the area imaged, and different artifacts of imaging that require filtering. METHODS: The stability and accuracy of alternative centerline algorithms was validated in numerically generated models and test brain MRA data. Existing images were gathered from previous studies and clinical medical systems by manually reading electronic medical records to identify hypertensives and negatives. Images of different resolutions were interpolated to similar resolutions. Arterial tortuosity in MRA images was measured from a DFM curve and tested on numerically generated models as well as MRA images from two hypertensive and three negative control populations. Comparisons were made between different resolutions, different filters, hypertensives versus negatives, and different negative controls. RESULTS: In tests using numerical models of a simple helix, the measured tortuosity increased as expected with more tightly coiled helices. Interpolation reduced resolution-dependent differences in measured tortuosity. The Korean hypertensive population had significantly higher arterial tortuosity than its corresponding negative control population across multiple arteries. In addition one negative control population of different ethnicity had significantly less arterial tortuosity than the other two. CONCLUSIONS: Tortuosity can be compared between images of different resolutions by interpolating from lower to higher resolutions. Use of a universal negative control was not possible in this study. The method described here detected elevated arterial tortuosity in a hypertensive population compared to the negative control population and can be used to study this relation in other populations.