Magnetic Resonance Pulse Sequences Research Articles

Intrinsic Brain Pulsatile Motion Analysis Using Velocity Mapping with Echo-Planar Cine Imaging - Implications for Intracranial Radiosurgery

Brain pulsatile motion during the cardiac cycle was measured with echo-planar magnetic resonance (MR) imaging. The major cerebral lobes, diencephalon, brain stem, cerebellum, cerebellar tonsils, and spinal cord were studied. The authors measured the intrinsic pulsatile motion of normal brain parenchyma in 10 healthy volunteers using Phase-sensitive, electrocardiography-gated, two-dimensional cine images acquired throughout the cardiac cycle by using a spin-echo, blipped echo-planar MR pulse sequence acquired in Transverse and coronal planes. Corrections were made for gross head motion. Brain motion consisted of a rapid displacement in systole, with a slow diastolic recovery. The overall pattern of brain motion showed caudal motion of the central structures (diencephalon, brain stem, and cerebellar tonsils) shortly after carotid systole, with concurrent cephalic motion of the major cerebral lobes and posterior cerebellar hemisphere. Peak brain displacement was in the range of 0.1-0.5 mm for all the structures except the cerebellar tonsils, which had greater displacement (0.4 mm +/- 0.16 [mean +/- SE]). The motion occurred chiefly in the cephalocaudal and lateral directions; the anteroposterior motions were relatively small. Cephalocaudal velocities increase with proximity to the foramen magnum. Brain parenchymal velocities were as high as 2 mm/sec caudally in the brain stem and 1.5 mm/sec medially in the thalami. The lateral motion is mainly a compressive motion of the thalami. Velocity mapping with Cine echo-planar imaging offers a rapid and flexible method of assessing the pulsation velocities of the human brain.The subtle brain motion captured through cine imaging quantified the physiologic oscillatory motion, albeit minor, would have particular relevance in the intracranial Radiosurgery.

View-collaborative fuzzy soft subspace clustering for automatic medical image segmentation

With the rapid development of medical imaging methodologies, such as magnetic resonance (MR) and positron emission tomography (PET)/MR, various types of MR images, which are acquired using inconsistent MR pulse sequences on the same patient, have been applied in medical-image-based diagnoses. A feature map extracted from an MR image describes the patient’s condition from one perspective. By effectively using all feature maps from various MR images, it is possible to completely describe the intrinsic characteristics of the patient’s condition to facilitate a diagnosis. Facing such a scenario, classic machine learning algorithms typically stack these feature maps for unified processing and do not explore the importance of each feature within a single feature map or the relationships among feature maps. To address these challenges, both multiview and subspace learning scenarios are considered in this study, and the multiview collaboration-based fuzzy soft subspace clustering (MVC-FSSC) algorithm is proposed. The MVC-FSSC algorithm not only strives to exploit the agreement of decisions across all views via collaborative learning but also strives to utilize the soft subspace-based weighting mechanism to automatically evaluate the contribution of each dimensional feature to each estimated cluster within a single view. Our experimental results indicate that the proposed MVC-FSSC algorithm can effectively explore the collaborative relations among all views and the importance of features in their respective views. Additionally, our MVC-FSSC method has substantial advantages over traditional clustering algorithms in MR image segmentation. Applying the MVC-FSSC algorithm to five patients’ MR images, the average mean absolute prediction deviation (MAPD) is 98.62 ± 8.34, which is significantly better than the score of 131.90 ± 16.03 that was obtained using the collaborative fuzzy k-means (CO-FKM) algorithm and the score of 128.87 ± 11.32 that was obtained using the quadratic weights and Gini-Simpson diversity-based fuzzy clustering (QWGSD-FC) algorithm.

Coherence transfer delay optimisation in PSYCOSY experiments.

PSYCOSY is an f1 broadband homonuclear decoupled version of the COSY nuclear magnetic resonance pulse sequence. Here, we investigate by a combination of experimental measurements, spatially distributed spin dynamics simulations, and analytical predictions the coherence evolution delay necessary in PSYCOSY experiments to ensure intensity discrimination in favour of the correlations typically arising from short range (n J, n ≤ 3) 1 H-1 H couplings and show that, in general, a coherence evolution delay of around 35 ms is optimum.

Switching Circuit Optimization for Matrix Gradient Coils.

Matrix gradient coils with up to 84 coil elements were recently introduced for magnetic resonance imaging. Ideally, each element is driven by a dedicated amplifier, which may be technically and financially infeasible. Instead, several elements can be connected in series (called a “cluster”) and driven by a single amplifier. In previous works, a set of clusters, called a “configuration,” was sought to approximate a target field shape. Because a magnetic resonance pulse sequence requires several distinct field shapes, a mechanism to switch between configurations is needed. This can be achieved by a hypothetical switching circuit connecting all terminals of all elements with each other and with the amplifiers. For a predefined set of configurations, a switching circuit can be designed to require only a limited amount of switches. Here we introduce an algorithm to minimize the number of switches without affecting the ability of the configurations to accurately create the desired fields. The problem is modeled using graph theory and split into 2 sequential combinatorial optimization problems that are solved using simulated annealing. For the investigated cases, the results show that compared to unoptimized switching circuits, the reduction of switches in optimized circuits ranges from 8% to up to 44% (average of 31%). This substantial reduction is achieved without impeding circuit functionality. This study shows how technical effort associated with implementation and operation of a matrix gradient coil is related to different hardware setups and how to reduce this effort.

Comparison of PET image quality using simultaneous PET/MR by attenuation correction with various MR pulse sequences

Abstract Positron emission tomography (PET)/magnetic resonance (MR) scanning has the advantage of less additional exposure to radiation than does PET/computed tomography (CT). In particular, MR based attenuation correction (MR AC) can greatly affect the image quality of PET and is frequently obtained using various MR sequences. Thus, the purpose of the current study was to quantitatively compare the image quality between MR non-AC (MR NAC) and MR AC in PET images with three MR sequences. Percent image uniformity (PIU), percent contrast recovery (PCR), and percent background variability (PBV) were estimated to evaluate the quality of PET images with MR AC. Based on the results of PIU, 15.2% increase in the average quality was observed for PET images with MR AC than for PET images with MR NAC. In addition, 28.6% and 71.1% improvement in the average results of PCR and PBV respectively, was observed for PET images with MR AC compared with that with MR NAC. Moreover, no significant difference was observed among the average values using three MR sequences. In conclusion, the current study demonstrated that PET with MR AC improved the image quality and can be help diagnosis in all MR sequence cases.

Volume Isotropic Turbo Spin Echo Acquisition Magnetic Resonance Imaging Pulse Sequence in Assessment of Temporomandibular Disorders

Background: Magnetic resonance imaging is the chief imaging modality used in assessment of temporomandibular disorders.Aim of the study: This study aimed to investigate the validity of Volume ISotropic Turbo spin echo Acquisition (VISTA) pulse sequence in the assessment of temporomandibular disorders.Subjects and Methods: Fifteen patients with temporomandibular joint related complaints performed MRI bilaterally using VISTA proton density and two-dimensional proton density turbo spin echo pulse sequences. Four-point scale was used to assess the clarity of articular disc position, disc morphology, cortical bone delineation, and overall image quality of both tested techniques. Besides, the final diagnosis of each case was obtained.Results: The main and standard deviation of traditionally used 2D proton density images in determination of disc position, disc morphology, delineation of cortical bone and overall image quality were (2.57± 0.49), (2.37± 0.60), (2.8± 0.4), (2.57± 0.49), respectively. While those for VISTA images were (1.8± 0.4), (1.53± 0.72), (2.1± 0.60), (1.7± 0.64) with the same order. The final diagnosis was similar in both techniques in 25 cases out of 30.Conclusion: Volume ISotropic Turbo Spin Echo Acquisition (VISTA) magnetic resonance pulse sequence could reveal the temporomandibular joint related structures, but with less image quality than that of traditionally used two-dimensional proton density images.

Excitation of singlet-triplet coherences in pairs of nearly-equivalent spins.

We present approaches for an efficient excitation of singlet-triplet coherences in pairs of nearly-equivalent spins. Standard Nuclear Magnetic Resonance (NMR) pulse sequences do not excite these coherences at all or with very low efficiency. The single quantum singlet-triplet coherences, here termed the outer singlet-triplet coherences, correspond to lines of low intensity in the NMR spectrum of a strongly-coupled spin pair (they are sometimes referred to as "forbidden transitions"), whereas the zero-quantum coherences, here termed the inner singlet-triplet coherences, do not have a direct spectral manifestation. In the present study, we investigated singlet-triplet coherences in a pair of nearly-equivalent carbon spins of the 13C-isotopomer of a specially designed naphthalene derivative with optimized relaxation properties. We propose and compare several techniques to drive the singlet-triplet coherence in strongly coupled spin pairs. First, we study different methods for efficient excitation of the outer singlet-triplet coherences. The achieved conversion efficiency of magnetization to the coherences of interest is close to the theoretically allowed maximum. Second, we propose methods to convert the outer coherences into the inner singlet-triplet coherence. The inner singlet-triplet coherence is insensitive to field inhomogeneity and can be long-lived. By probing this coherence, we perform a very precise measurement of the spin-spin J-couplings. A remarkable property of this coherence is that it can be preserved even in absence of a spin-locking radiofrequency field. Consequently, it is possible to shuttle the sample between different magnetic fields preserving the coherence. This allows one to study the field dependence of the relaxation time, TIST, of the inner singlet-triplet coherence by performing field-cycling experiments. We observed dramatic changes of the ratio TIST/T1 from about 1 (in strong fields) up to 2.4 (in weak fields), which is the evidence of a significant influence of the chemical shift anisotropy on relaxation. We have detected a remarkably long lifetime of the inner singlet-triplet coherence of about 200 s at the magnetic field of 5 mT.

Capillary-tube package devices for the quantitative performance evaluation of nuclear magnetic resonance spectrometers and pulse sequences.

With the increased sensitivity of modern nuclear magnetic resonance (NMR) spectrometers, the minimum amount needed for chemical-shift referencing of NMR spectra has decreased to a point where a few microliters can be sufficient to observe a reference signal. The reduction in the amount of required reference material is the basis for the NMR Capillary-tube Package (CapPack) platform that utilizes capillary tubes with inner diameters smaller than 150 µm as NMR-tube inserts for external reference standards. It is shown how commercially available electrophoresis capillary tubes with outer diameters of 360 µm are filled with reference liquids or solutions and then permanently sealed by the arc discharge plasma of a commercially available fusion splicer normally employed for joining optical fibers. The permanently sealed capillaries can be used as external references for chemical-shift, signal-to-noise, resolution, and concentration calibration. Combining a number of permanently sealed capillaries to form CapPack devices leads to additional applications such as performance evaluation of NMR spectrometers and NMR pulse sequences. A 10-capillary-tube side-by-side Gradient CapPack device is used in combination with one or two constant gradients, produced by room-temperature shim coils, to monitor the excitation profiles of shaped pulses. One example illustrates the performance of hyperbolic secant (sech) pulses in the EXponentially Converging Eradication Pulse Train (EXCEPT) solvent suppression sequence. The excitation profile of the pulse sequence is obtained in a single gradient NMR experiment. A clustered T 1 CapPack device is introduced consisting of a coaxial NMR-tube insert that holds seven capillary tubes filled with aqueous solutions of different concentrations of the paramagnetic relaxation agent copper(ii) sulfate (CuSO4). The different CuSO4 concentrations lead to spin-lattice relaxation times in the seven capillary tubes that cover a range which extends to more than an order of magnitude. Clustered T 1 CapPack devices are best suited to quantify the effects that relaxation has on magnetizations and coherences during the execution of NMR experiments, which is demonstrated for the order-of-magnitude T 1 insensitivity of signal suppression with EXCEPT.

Preoperative MR staging of cervical carcinoma: are oblique and contrast-enhanced sequences necessary?

BackgroundAs the choice of treatment in patients with cervical carcinoma depends on cancer stage at diagnosis, accurate staging is essential.PurposeTo compare three different combinations of magnetic resonance (MR) sequences for preoperative staging.Material and MethodsFifty-seven consecutive patients with biopsy proven cervical carcinoma underwent MR imaging (MRI) staging followed by primary surgical treatment. Thirty-two of 57 patients had had a cone biopsy prior to MRI. Three MR pulse sequence combinations were retrospectively reviewed by two experienced radiologists. The first imaging protocol consisted of pre-contrast sagittal and transverse images (protocol A), the second protocol included additionally oblique high-resolution T2-weighted (T2W) MR images of the cervix (protocol A+B), and the third included also contrast-enhanced sequences (protocol A+B+C). The imaging findings in the three steps (A, A+B, A+B+C) were recorded. The TNM stage was used for comparison between preoperative imaging and histopathology. Histopathology, together with surgical findings, served as gold standard.ResultsIn 4/57 (7%) patients, the MR assessment of tumor stage (mrT) was altered when oblique sequences were added to the standard two plane imaging protocol (A+B). The mrT stage was altered in 1/57 (2%) patient when contrast-enhanced sequences were added to standard and oblique sequences (protocol A+B+C). The correlation between visible tumor on MRI and presence of tumor in the resected specimen did not change by adding oblique or contrast-enhanced images.ConclusionIt is not necessary to perform oblique and contrast-enhanced sequences in small cervical carcinomas, i.e. without parametrial invasion. To avoid erroneous interpretation, information on previous cone biopsy is essential.

LEFT ATRIAL FIBROSIS IN PATIENTS WITH ATRIAL FIBRILLATION ACCORDING TO MAGNETIC RESONANCE IMAGING WITH LATE GADOLINIUM ENHANCEMENT

Актуальность. Фибрилляция предсердий (ФП) – самая распространенная сердечная аритмия. Изучение структуры миокарда предсердий при ФП может послужить основой для создания новых методов лечения аритмии.

A heteronuclear intermolecular single-quantum coherence scheme for high-resolution 2D J-resolved 1H NMR spectra in inhomogeneous magnetic fields

ABSTRACTBased on heteronuclear intermolecular single-quantum coherences between proton (1H) and quadrupolar nuclei (i.e. deuterium 2H), a three-dimensional nuclear magnetic resonance (NMR) pulse sequence is proposed for recovering high-resolution two-dimensional J-resolved NMR spectra from samples mixed with a deuterated solvent in the presence of large magnetic field inhomogeneities. Benefitting from excitation of spins via two different radio frequency (RF) transmit channels, this sequence is suitable for applications in randomly large inhomogeneous fields and the solvent suppression generally required in homonuclear intermolecular multiple-quantum coherence approaches is no longer necessary. Systematic theoretical analyses are given based on the distant dipolar field treatment. Experiment on a sample of corn oil in deuterated acetone and ethyl 3-bromopropionate and acetone dissolved in DMSO-d6 in a deshimmed field with severe inhomogeneous broadening is performed to show the feasibility and applicability of this sequence.

A medical device-grade T1 and ECV phantom for global T1 mapping quality assurance-the T1 Mapping and ECV Standardization in cardiovascular magnetic resonance (T1MES) program.

BackgroundT1 mapping and extracellular volume (ECV) have the potential to guide patient care and serve as surrogate end-points in clinical trials, but measurements differ between cardiovascular magnetic resonance (CMR) scanners and pulse sequences. To help deliver T1 mapping to global clinical care, we developed a phantom-based quality assurance (QA) system for verification of measurement stability over time at individual sites, with further aims of generalization of results across sites, vendor systems, software versions and imaging sequences. We thus created T1MES: The T1 Mapping and ECV Standardization Program.MethodsA design collaboration consisting of a specialist MRI small-medium enterprise, clinicians, physicists and national metrology institutes was formed. A phantom was designed covering clinically relevant ranges of T1 and T2 in blood and myocardium, pre and post-contrast, for 1.5 T and 3 T. Reproducible mass manufacture was established. The device received regulatory clearance by the Food and Drug Administration (FDA) and Conformité Européene (CE) marking.ResultsThe T1MES phantom is an agarose gel-based phantom using nickel chloride as the paramagnetic relaxation modifier. It was reproducibly specified and mass-produced with a rigorously repeatable process. Each phantom contains nine differently-doped agarose gel tubes embedded in a gel/beads matrix. Phantoms were free of air bubbles and susceptibility artifacts at both field strengths and T1 maps were free from off-resonance artifacts. The incorporation of high-density polyethylene beads in the main gel fill was effective at flattening the B1 field. T1 and T2 values measured in T1MES showed coefficients of variation of 1 % or less between repeat scans indicating good short-term reproducibility. Temperature dependency experiments confirmed that over the range 15–30 °C the short-T1 tubes were more stable with temperature than the long-T1 tubes. A batch of 69 phantoms was mass-produced with random sampling of ten of these showing coefficients of variations for T1 of 0.64 ± 0.45 % and 0.49 ± 0.34 % at 1.5 T and 3 T respectively.ConclusionThe T1MES program has developed a T1 mapping phantom to CE/FDA manufacturing standards. An initial 69 phantoms with a multi-vendor user manual are now being scanned fortnightly in centers worldwide. Future results will explore T1 mapping sequences, platform performance, stability and the potential for standardization.Electronic supplementary materialThe online version of this article (doi:10.1186/s12968-016-0280-z) contains supplementary material, which is available to authorized users.

An equation-free introduction to post-mortem MR image contrast and pulse sequence optimization

Abstract Due to the excellent sensitivity of Magnetic Resonance (MR) imaging to subtle differences in soft tissues, MR enables non-invasive anatomical imaging with superior soft tissue contrast relative to X-ray Computed Tomography (CT). However, relative to the X-ray modalities, the utility of MR in the post-mortem setting is currently less well-defined. MR is significantly different from the X-ray modalities, in terms of the underlying principles of image formation, the equipment and expertise necessary to acquire the images, and the appearance of the images themselves. Because MR is sensitive to subtle differences in soft tissues, factors unique to the post-mortem setting, particularly variations in body temperature, tend to have a greater effect on MR imaging relative to the X-ray modalities. Fortunately, MR is inherently flexible and adaptable; there are many types of MR protocols, each with user-controlled parameters that can be adjusted to achieve the best imaging of a specific pathology or anatomic structure, at a given temperature or post-mortem interval (PMI). Optimizing, validating, and standardizing post-mortem MR (PMMR) protocols represents a challenging yet achievable long-term goal. For those interested in developing a better understanding of how to optimize PMMR image quality, this review is intended to provide some guidance, from a technical (but non-mathematical) perspective. A practical explanation of basic pulse sequences and MR relaxation times, and their relationship to tissue contrast, is provided. Strategies for optimizing PMMR for forensic imaging applications, suitable for users with varying levels of expertise, are discussed in the context of current progress in this area.

New pulse sequence for robust filtering of hyperpolarized multiplet spin order

A new Nuclear Magnetic Resonance (NMR) pulse sequence is proposed for manipulating ParaHydrogen Induced Polarization (PHIP) at high magnetic fields. The technique enables conversion of the multiplet spin order into net polarization, which is much easier to exploit in many practical applications of PHIP. The pulse sequence is easy to implement; moreover, it filters out all residual signals from thermally polarized spins. Such “background free” detection is promising for sensitivity enhancement in NMR spectroscopy and improved contrast in NMR imaging.

Multiqubit gates protected by adiabaticity and dynamical decoupling applicable to donor qubits in silicon

We present a strategy for producing multi-qubit gates that promise high fidelity with minimal tuning requirements. Our strategy combines gap protection from the adiabatic theorem with dynamical decoupling in a complementary manner. To avoid degenerate states and maximize the benefit of the gap protection, the scheme is best suited when there are two different kinds of qubits (not mutually resonant). Furthermore, we require a robust operating point in control space where the qubits interact with little sensitivity to noise. This allows us to circumvent a No-Go theorem that prevents block-box dynamically corrected gates [Phys. Rev. A 80, 032314 (2009)]. We show how to apply our strategy to an architecture in Si with P donors where we assume we can shuttle electrons between different donors. Electron spins act as mobile ancillary qubits and P nuclear spins act as long-lived data qubits. This system can have a very robust operating point where the electron spin is bound to a donor in the quadratic Stark shift regime. High fidelity single qubit gates may be performed using well-established global magnetic resonance pulse sequences. Single electron spin preparation and measurement has also been demonstrated. Putting this all together, we present a robust universal gate set for quantum computation.

Sub-millimeter resolution electrical conductivity images of brain tissues using magnetic resonance-based electrical impedance tomography

Recent magnetic resonance (MR)-based electrical impedance tomography (MREIT) of in vivo animal and human subjects enabled the imaging of electromagnetic properties, such as conductivity and permittivity, on tissue structure and function with a few millimeter pixel size. At those resolutions, the conductivity contrast might be sufficient to distinguish different tissue type for certain applications. Since the precise measurement of electrical conductivity under the tissue levels can provide alternative information in a wide range of biomedical applications, it is necessary to develop high-resolution MREIT technique to enhance its availability. In this study, we provide the experimental evaluation of sub-millimeter resolution conductivity imaging method using a 3T MR scanner combined with a multi-echo MR pulse sequence, multi-channel RF coil, and phase optimization method. From the phantom and animal imaging results, sub-millimeter resolution exhibited similar signal-to-noise ratio of MR magnitude and noise levels in magnetic flux density comparing to the existing millimeter resolution. The reconstructed conductivity images at sub-millimeter resolution can distinguish different brain tissues with a pixel size as small as 350 μm.

Magnetic Resonance-Visible Polypropylene Mesh for Pelvic Organ Prolapse Repair

Aim: To develop a magnetic resonance (MR)-visible mesh using iron oxides and prove visibility. Methods: In a phantom study, a suitable iron oxide, Fe₃O₄ [iron(II,III) oxide] and FeOOH [iron(III) oxide-hydroxide], concentration was determined using relaxometric MR measurements of the transverse relaxation rates R2 and R2*. Next, a nonabsorbable mesh was designed from the MR-visible threads woven into a polypropylene mesh. The mesh was implanted into a fresh female cadaver via the transobturator route, and MR visibility was assessed with various MR pulse sequences in a clinical 3-tesla system. Results: Optimal contrast was achieved with Fe₃O₄ at 0.2 weight-% in all imaging sequences, and the optimal contrast was achieved in a 3D spoiled gradient-echo (fast low-angle shot) acquisition. In this concentration range the apparent transverse relaxation rate R2* is below 10 ms. The mesh was visible in the cadaver on T1-weighted 3D spoiled gradient-echo images and T1-weighted fast spin-echo images. Conclusion: Mesh materials can be manufactured to be visible on MR with a negative contrast. Fe₃O₄ meshes could simplify follow-up examinations and help diagnose origins of postsurgical lesions after urogynecological procedures with mesh material.

Multinuclear MR and Multilevel Data Processing: An Insight into Morphologic Assessment of In Vivo Knee Articular Cartilage

Quantitative assessment of knee articular cartilage (AC) morphology using magnetic resonance (MR) imaging requires an accurate segmentation and 3D reconstruction. However, automatic AC segmentation and 3D reconstruction from hydrogen-based MR images alone is challenging because of inhomogeneous intensities, shape irregularity, and low contrast existing in the cartilage region. Thus, the objective of this research was to provide an insight into morphologic assessment of AC using multilevel data processing of multinuclear ((23)Na and (1)H) MR knee images. A dual-tuned ((23)Na and (1)H) radio-frequency coil with 1.5-TMR scanner is used to scan four human subjects using two separate MR pulse sequences for the respective sodium and proton imaging of the knee. Postprocessing is performed using customized routines written in MATLAB. MR data were fused to improve contrast of the cartilage region that is further used for automatic segmentation. Marching cubes algorithm is applied on the segmented AC slices for 3D volume rendering and volume is then calculated using the divergence theorem. Fusion of multinuclear MR images results in an improved contrast (factor >3) in the cartilage region. Sensitivity (80.21%) and specificity (99.64%) analysis performed by comparing manually segmented AC shows a good performance of the automated AC segmentation. The average cartilage volume (23.19±1.38 cm(3); coefficient of variation [COV] -0.059) measured from 3D AC models of four data sets shows a marked improvement over average cartilage volume (23.24cm(3); COV -0.19) reported earlier. This study confirms the use of multinuclear MR data for cartilage morphology (volume) assessment that can be used in clinical settings.

How accurate is multiparametric MR imaging in evaluation of prostate cancer volume?

To assess the factors influencing multiparametric (MP) magnetic resonance (MR) imaging accuracy in estimating prostate cancer histologic volume (Vh). A prospective database of 202 patients who underwent MP MR imaging before radical prostatectomy was retrospectively used. Institutional review board approval and informed consent were obtained. Two independent radiologists delineated areas suspicious for cancer on images (T2-weighted, diffusion-weighted, dynamic contrast material-enhanced [DCE] pulse sequences) and scored their degree of suspicion of malignancy by using a five-level Likert score. One pathologist delineated cancers on whole-mount prostatectomy sections and calculated their volume by using digitized planimetry. Volumes of MR true-positive lesions were measured on T2-weighted images (VT2), on ADC maps (VADC), and on DCE images [VDCE]). VT2, VADC, VDCE and the greatest volume determined on images from any of the individual MR pulse sequences (Vmax) were compared with Vh (Bland-Altman analysis). Factors influencing MP MR imaging accuracy, or A, calculated as A = Vmax/Vh, were evaluated using generalized linear mixed models. For both readers, Vh was significantly underestimated with VT2 (P < .0001, both), VADC (P < .0001, both), and VDCE (P = .02 and P = .003, readers 1 and 2, respectively), but not with Vmax (P = .13 and P = .21, readers 1 and 2, respectively). Mean, 25th percentile, and 75th percentile, respectively, for Vmax accuracy were 0.92, 0.54, and 1.85 for reader 1 and 0.95, 0.57, and 1.77 for reader 2. At generalized linear mixed (multivariate) analysis, tumor Likert score (P < .0001), Gleason score (P = .009), and Vh (P < .0001) significantly influenced Vmax accuracy (both readers). This accuracy was good in tumors with a Gleason score of 7 or higher or a Likert score of 5, with a tendency toward underestimation of Vh; accuracy was poor in small (<0.5 cc) or low-grade (Gleason score ≤6) tumors, with a tendency toward overestimation of Vh. Vh can be estimated by using Vmax in aggressive tumors or in tumors with high Likert scores.

Kinetic Studies of the [NpO2(CO3)3]4– Ion at Alkaline Conditions Using 13C NMR

Carbonate ligand-exchange rates on the [NpO2(CO3)3]4– ion were determined using a saturation-transfer 13C nuclear magnetic resonance (NMR) pulse sequence in the pH range of 8.1 ≤ pH ≤ 10.5. Over the pH range 9.3 ≤ pH ≤ 10.5, which compares most directly with previous work of Stout et al.,1 we find an average rate, activation energy, enthalpy, and entropy of kex298 = 40.6(±4.3) s–1, Ea =45.1(±3.8) kJ mol–1, ΔH‡ = 42.6(±3.8) kJ mol–1, and ΔS‡ = −72(±13) J mol–1 K–1, respectively. These activation parameters are similar to the Stout et al. results at pH 9.4. However, their room-temperature rate at pH 9.4, kex298 = 143(±1.0) s–1, is 3 times faster than what we experimentally determined at pH 9.3: kex298 = 45.4(±5.3) s–1. Our rates for [NpO2(CO3)3]4– are also faster by a factor of 3 relative to the isoelectronic [UO2(CO3)3]4– as reported by Brucher et al.2 of kex298 = 13(±3) s–1. Consistent with results for the [UO2(CO3)3]4– ion, we find evidence for a proton-enhanced pathway for carbonate exchange for the [NpO2(CO3)3]4– ion at pH < 9.0.