In vivo relaxation time measurements on a murine tumor model—Prolongation of T1 after photodynamic therapy

RIF tumors implanted on mice feet were investigated for changes in relaxation times (T₁ and T₂) after photodynamic therapy (PDT). Photodynamic therapy was performed using Photofrin II as the photosensitizer and laser light at 630 nm. A home-built proton solenoid coil in the balanced configuration was used to accommodate the tumors, and the relaxation times were measured before, immediately after, and up to several hours after therapy. Several control experiments were performed using the untreated tumors, tumors treated with Photofrin II alone, or tumors treated with laser light alone. Significant increases in T₁s of water protons were observed after PDT treatment. In all experiments, ³¹P spectra were recorded before and after the therapy to study the tumor status and to confirm the onset of PDT. These studies show significant prolongation of T₁s after the PDT treatment. The spin-spin relaxation measurements, on the other hand, did not show such prolongation in T₂ values after PDT treatment.     

Quantitation of phosphorus metabolites in newborn human brain using internal water as reference standard

A new method for noninvasive, in vivo quantitation of cerebral phosphorus (³¹P) metabolites is described. The technique employs point-resolved spectroscopy (PRESS) to obtain both ³¹P-metabolite and proton (¹H) water spectra: brain water is used as an internal concentration reference. Spin-spin relaxation times (T₂s) of cerebral ³¹P metabolites are much longer than the minimum echo time (TE) usable on a spectrometer equipped with actively shielded gradient coils. With short-TE (≈10 ms) ³¹P PRESS, T₂ relaxation is minimal and phase modulation of the nucleotide triphosphate (NTP) multiplets can be accounted for. ¹H water spectra were acquired using several TEs so that extra- and intracellular water signals could be separated from that due to cerebrospinal fluid. Prior calibration of the ³¹P and ¹H spectrometer channels and an assumed brain-water concentration enabled estimations of metabolite concentrations. Using this method, mean ³¹P metabolite concentrations in the brains of eight normal infants of gestational plus postnatal age 34 to 39 wk were: phosphomonoester (PME) 5.6 (SD 0.9); inorganic phosphate 1.4 (0.4); mobile phosphodiester 2.3 (0.6); phosphocreatine 2.9 (0.3); nucleotide triphosphate 2.8 (0.6); and total mobile phosphate 21.4 (2.8) mmol/kg wet.     

Large improvement of RF transmission efficiency and reception sensitivity for human in vivo 31P MRS imaging using ultrahigh dielectric constant materials at 7 T

In vivo ³¹P MRS provides a unique and important imaging tool for studying high-energy phosphate metabolism and bioenergetics noninvasively. However, compared to ¹H MRS, ³¹P MRS with a relatively low gyromagnetic ratio (γ) has a lower and limited sensitivity even at ultrahigh field. The proof of concept has been recently demonstrated that the use of high dielectric constant (HDC) materials between RF coil and object sample could increase MRI signal and reduce required RF transmission power for reaching the same RF pulse flip angle in the region of interest. For low-γ MRS applications operated at relatively lower frequency, however, it demands the dielectric materials with a much higher permittivity for achieving optimal performance. We conducted a ³¹P MRS imaging study using ultra-HDC (uHDC; with a relative permittivity of ~ 1200) material blocks incorporated with an RF volume coil at ultrahigh field of 7.0 T. The experimental results from phantom and human calf muscle demonstrate that the uHDC technique significantly enhanced RF magnetic transmit field (B₁⁺) and reception field (B₁⁻) and the gain could reach up to two folds in the tissue near the uHDC blocks. The overall results indicate that the incorporation of the uHDC materials having an appropriate permittivity value with a RF coil can significantly increase detection sensitivity and reduces RF transmission power for X-nuclei MRS applications at ultrahigh field. The uHDC technology could provide an efficient, cost-effective engineering solution for achieving high detection sensitivity and concurrently minimizing tissue heating concern for human MRS and MRI applications.     

QuantitativeH MRI and MRS Microscopy of Individual V79 Lung Tumor Spheroids

In this Communication¹H MRI and MRS microscopy experiments of individual V79 lung tumor spheroids with diameters between 550 and 650 μm are reported. The results have been used to determine theT₁,T₂, andDvalues as well as the concentrations of water, total choline, creatine/phosphocreatine, and mobile lipids in the viable rims and in the necrotic centers.     

Ex vivo study of carotid endarterectomy specimens: quantitative relaxation times within atherosclerotic plaque tissues

Purpose

Previous studies reporting relaxation times within atherosclerotic plaque have typically used dedicated small-bore high-field systems and small sample sizes. This study reports quantitative T₁, T₂ and T₂^? relaxation times within plaque tissue at 1.5 T using spatially co-matched histology to determine tissue constituents.

Methods

Ten carotid endarterectomy specimens were removed from patients with advanced atherosclerosis. Imaging was performed on a 1.5-T whole-body scanner using a custom built 10-mm diameter receive-only solenoid coil. A protocol was defined to allow subsequent computation of T₁, T₂ and T₂^? relaxation times using multi-flip angle spoiled gradient echo, multi-echo fast spin echo and multi-echo gradient echo sequences, respectively. The specimens were subsequently processed for histology and individually sectioned into 2-mm blocks to allow subsequent co-registration. Each imaging sequence was imported into in-house software and displayed alongside the digitized histology sections. Regions of interest were defined to demarcate fibrous cap, connective tissue and lipid/necrotic core at matched slice-locations. Relaxation times were calculated using Levenberg-Marquardt's least squares curve fitting algorithm. A linear-mixed effect model was applied to account for multiple measurements from the same patient and establish if there was a statistically significant difference between the plaque tissue constituents.

Results

T₂ and T₂^? relaxation times were statistically different between all plaque tissues (P=.026 and P=.002 respectively) [T₂: lipid/necrotic core was lower 47±13.7 ms than connective tissue (67±22.5 ms) and fibrous cap (60±13.2 ms); T₂^?: fibrous cap was higher (48±15.5ms) than connective tissue (19±10.6 ms) and lipid/necrotic core (24±8.2 ms)]. T₁ relaxation times were not significantly different (P=.287) [T₁: Fibrous cap: 933±271.9 ms; connective tissue (1002±272.9 ms) and lipid/necrotic core (1044±304.0 ms)]. We were unable to demarcate hemorrhage and calcium following histology processing.

Conclusions

This study demonstrates that there is a significant difference between qT₂ and qT₂^? in plaque tissues types. Derivation of quantitative relaxation times shows promise for determining plaque tissue constituents.     

NMR studies of hydrogen diffusion in hydrogen uranyl phosphate tetrahydrate (HUP)

¹H NMR spin-lattice relaxation times, T₁ (Zeeman) and T_1ϱ (rotating frame) and spin-spin relaxation times, T₂, and ³¹P NMR solid-echoes are reported for phase I and II of hydrogen uranyl phosphate tetrahydrate (HUP) at temperatures in the range 200–323 K. The spectral density functions extracted from the measured relaxation times for phases I and II are consistent with a 2D diffusion mechanism for hydrogen motion. ³¹P second moments determined from the solid-echoes show that all the hydrogens diffuse rapidly in phase I, and that the hydrogen-bond site nearest to the phosphate oxygen is not occupied in phase II. The mechanism for diffusion in phase II is discussed.     

Diffusion tensor magnetic resonance imaging of the normal breast

Purpose

The objective of this study was to evaluate diffusion anisotropy of the breast parenchyma and assess the range and repeatability of diffusion tensor imaging (DTI) parameters in normal breast tissue.

Materials and Methods

The study was approved by our institutional review board and included 12 healthy females (median age, 36 years). Diffusion tensor imaging was performed at 1.5 T using a diffusion-weighted echo planar imaging sequence. Diffusion tensor imaging parameters including tensor eigenvalues (λ₁, λ₂, λ₃), fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were measured for anterior, central and posterior breast regions.

Results

Mean normal breast DTI measures were λ₁=2.51×10⁻³ mm²/s, λ₂=1.89×10⁻³ mm²/s, λ₃=1.39×10⁻³ mm²/s, ADC=1.95±0.24×10⁻³ mm²/s and FA=0.29±0.05 for b=600 s/mm². Significant regional differences were observed for both FA and ADC (P<.05), with higher ADC in the central breast and higher FA in the posterior breast. Comparison of DTI values calculated using b=0, 600 s/mm² vs. b=0, 1000 s/mm², showed significant differences in ADC (P<.001), but not FA. Repeatability assessment produced within-subject coefficient of variations of 4.5% for ADC and 11.4% for FA measures.

Conclusion

This study demonstrates anisotropy of water diffusion in normal breast tissue and establishes a normative range of breast FA values. Attention to the influence of breast region and b value on breast DTI measurements may be important for clinical interpretation and standardization of techniques.     

Shock-tube study of HCN self-broadening and broadening by argon for the P(10) line of the ν1 band at 3 μm

A tunable infrared diode laser was used to measure the fully resolved absorption line shape of the P(10) line in the ν₁ band (10°0–00°0) of HCN for shock-heated mixtures of HCN-Ar at temperatures of 1000, 1500 and 2000 K. The temperature dependence of the collision-broadening coefficients 2γ (cm^-1 atm^-1, FWHM) were inferred for both self-broadening and broadening by argon. For the assumed form 2γ = 2γ₀(T₀/T)ⁿ the exponent n was determined to be 0.63 ± 0.06 with 2γ₀ = 0.11 cm^-1atm^-1 and T₀ = 300 K for argon-broadening in the range 300 < T < 2000 K, and 1.2 ± 0.6 with 2γ₀ = 0.68 cm^-1atm^-1 and T₀ = 1000 K for self-broadening in the range 1000 < T < 2000 K.     

Spin-lattice relaxation of 25Al and 28P in Pt

The spin-lattice relaxation times T ₁ for short-lived β emitters ²⁵Al(I?=?5/2, T _1/2?= 7.2 s) and ²⁸P(I?=?3, T _1/2?= 270 ms) in Pt were measured by means of the β-NMR technique. As a result, T ₁[²⁵Al in Pt] = (1.1 $^{+\ 0.7}_{-\ 0.3})$ s and T ₁[²⁸P in Pt] >0.5 s were obtained at temperatures of 17 and 20 K, respectively. The Knight shifts were estimated from the Korringa relation, which were evaluated by comparing to the first principle calculations.     

Diffusion-weighted magnetic resonance imaging to evaluate microvascular density after transarterial embolization ablation in a rabbit VX2 liver tumor model

Objective

To evaluate the correlation between findings from diffusion weighted imaging (DWI) and microvascular density (MVD) measurements in VX2 liver tumors after transarterial embolization ablation (TEA).

Materials and Methods

Eighteen New Zealand white rabbits were used in this study. VX2 tumor cells were implanted in livers by percutaneous puncture under computed tomography (CT) guidance. Two weeks later, all rabbits underwent conventional magnetic resonance imaging (MRI) (T1 and T2 imaging), DWI, (b = 100, 600, and 1000 s/mm²) and TEA. MRI was performed again1 week after TEA. Liver tissue was then harvested and processed for hematoxylin and eosin (H&E) staining and immunohistochemical staining for CD31to determine MVD.

Results

VX2 liver tumors were successfully established in all 18 rabbits. Optimal contrast was achieved with a b value of 600 s/mm².The maximum pre-operative apparent diffusion coefficient (ADC)_difference value was 0.28 × 10^− 3 ± 0.10 × 10^− 3 mm²/s, and was significantly different (P < 0.001) from the maximum postoperative ADC_difference value of 0.47 × 10^− 3 ± 0.10 × 10^− 3 mm²/s. However, the mean ADC value for the entire tumor was not significantly correlated with MVD (r = 0.221, P = 0.379), nor was the ADC value for the regions of viable tumor (r = − 0.044, P = 0.862). However, the maximum postoperative ADC_difference value was positively correlated with MVD(r = 0.606, F = 12.247, P = 0.003).

Conclusion

DWI is effective to evaluate the therapeutic efficacy of TEA. The maximum ADC_difference offers a promising new method to noninvasively assess tumor angiogenesis.     

Structure-mediated transition in the behavior of elastic and inelastic properties of beach tree bio-carbon

Microstructural characteristics and amplitude dependences of the Young modulus E and of internal friction (logarithmic decrement δ) of bio-carbon matrices prepared from beech tree wood at different carbonization temperatures T _carb ranging from 600 to 1600°C have been studied. The dependences E(T _carb) and δ(T _carb) thus obtained revealed two linear regions of increase of the Young modulus and of decrease of the decrement with increasing carbonization temperature, namely, ΔE ～ AΔT _carb and Δδ ～ BΔT _carb, with A ≈ 13.4 MPa/K and B ≈ ?2.2 × 10^?6 K^?1 for T _carb < 1000°C and A ≈ 2.5 MPa/K and B ≈ ?3.0 × 10^?7 K^?1 for T _carb > 1000°C. The transition observed in the behavior of E(T _carb) and δ(T _carb) at T _carb = 900–1000°C can be assigned to a change of sample microstructure, more specifically, a change in the ratio of the fractions of the amorphous matrix and of the nanocrystalline phase. For T _carb < 1000°C, the elastic properties are governed primarily by the amorphous matrix, whereas for T _carb > 1000°C the nanocrystalline phase plays the dominant part. The structurally induced transition in the behavior of the elastic and microplastic characteristics at a temperature close to 1000°C correlates with the variation of the physical properties, such as electrical conductivity, thermal conductivity, and thermopower, reported in the literature.     

Anomalous pulse-angle and phase dependence of Hahn’s electron spin echo and multiple-quantum echoes of the spin correlated radical pair P700+A 1 − in photosystem I

In a spin-correlated radical pair system, anomalous pulse-angle and phase dependence of electron spin echo and multiple-quantum echoes were theoretically calculated by Tanget al. (J. Chem. Phys.106, 7471 (1997)). The maximum intensity of the out of phase signal at 45 degree of spin rotation angle was experimentally verified in two-pulse echoes of the light-induced P700⁺A ₁ ^? radical pair in Photosystem I. The values,D = 1.64 G andJ = 0.00 G, fit well with the experimental ESEEM spectra. Single and double quantum echoes were observed at the value oft = τ andT = 2τ with the laser flash-t-P1_70,ζ1-τ-P2_{140, ζ2}-T pulse sequence, which led to determination of the relaxation time T₂₃ between the singlet and triplet ¦T₀〉 states. The relaxation times of the zero and single quantum transitions were determinedT ₂₃ ≈ 100 ns andT ₂ = 1000 ns, respectively. The field sweep ESE signal shape can be fitted with the hyperfine inhomogeneities of 7 G for P700⁺ and of 10 G for A ₁ ^? .     

Rapid high-resolution volumetric T1 mapping using a highly accelerated stack-of-stars Look Locker technique

PurposeTo develop a fast volumetric T₁ mapping technique.Materials and methodsA stack-of-stars (SOS) Look Locker technique based on the acquisition of undersampled radial data (>30× relative to Nyquist) and an efficient multi-slab excitation scheme is presented. A principal-component based reconstruction is used to reconstruct T₁ maps. Computer simulations were performed to determine the best choice of partitions per slab and degree of undersampling. The technique was validated in phantoms against reference T₁ values measured with a 2D Cartesian inversion-recovery spin-echo technique. The SOS Look Locker technique was tested in brain (n = 4) and prostate (n = 5). Brain T₁ mapping was carried out with and without k_z acceleration and results between the two approaches were compared. Prostate T₁ mapping was compared to standard techniques. A reproducibility study was conducted in brain and prostate. Statistical analyses were performed using linear regression and Bland Altman analysis.ResultsPhantom T₁ values showed excellent correlations between SOS Look Locker and the inversion-recovery spin-echo reference (r² = 0.9965; p < 0.0001) and between SOS Look Locker with slab-selective and non-slab selective inversion pulses (r² = 0.9999; p < 0.0001). In vivo results showed that full brain T₁ mapping (1 mm³) with k_z acceleration is achieved in 4 min 21 s. Full prostate T₁ mapping (0.9 × 0.9 × 4 mm³) is achieved in 2 min 43 s. T₁ values for brain and prostate were in agreement with literature values. A reproducibility study showed coefficients of variation in the range of 0.18–0.2% (brain) and 0.15–0.18% (prostate).ConclusionA rapid volumetric T₁ mapping technique was developed. The technique enables high-resolution T₁ mapping with adequate anatomical coverage in a clinically acceptable time.     

Electronic and vibrational absorption spectra in falcondoite

Optical absorption spectrum of Ni²⁺ ion in Falcondoite, a new mineral has been studied at 300 K. From the nature and positions of the observed bands a succesful interpretation of all the bands could be made assuming octahedral symmetry for the Ni²⁺ ion in the crystal. The bands at 9255, 15 380 and 27 390cm⁻¹ are assigned to ³T_2g(F), ³T_1g and ³T_1g(P) and the other band at 24385 cm⁻¹ assigned to ¹T_2g(D). The crystal field and the Racah parameters are evaluated to be Dq = 925 cm⁻¹, B = 1000 cm⁻¹ and C = 4095 cm⁻¹. NIR and IR spectra of the sample are also studied. The fundamental vibrational modes of H₂O are identified in the IR spectrum. The bands observed in the NIR spectrum are due to overtones and combination tones of water molecule.     

Retrospective correction for T1-weighting bias in T2 values obtained with various spectroscopic spin-echo acquisition schemes

Localized tissue transverse relaxation time (T₂) is obtained by fitting a decaying exponential to the signals from several spin-echo experiments at different echo times (TE). Unfortunately, time constraints in magnetic resonance spectroscopy (MRS) often mandate in vivo acquisition schemes at short repetition times (TR), that is, comparable with the longitudinal relaxation constant (T₁). This leads to different T₁-weighting of the signals at each TE. Unaccounted for, this varying weighting causes systematic underestimation of the T₂'s, sometimes by as mush as 30%. In this article, we (i) analyze the phenomenon for common MRS spin-echo T₂ acquisition schemes; (ii) propose a general post hoc T₁-bias correction for any (TR, TE) combination; (iii) show that approximate knowledge of T₁ is sufficient, since a 20% uncertainty in T₁ leads to under 3% bias in T₂; and consequently, (iv) efficient, precision-optimized short TR spin-echo T₂ measurement protocols can be designed and used without risk of accuracy loss. Tables of correction for single-refocusing (conventional) spin-echo and double refocusing, such as, PRESS acquisitions, are provided.     

Magic-angle-spinning NMR on solid biological systems. Analysis Of the origin of the spectral linewidths

Magic-angle-spinning (MAS) high-power ¹H-decoupled ¹³C and ³¹P NMR has been applied to solid biological materials to obtain information about the mechanisms that determine the spectral linewidths. The line broadening in MAS ³¹P NMR spectra of solid tobacco mosaic virus (TMV) has been investigated by selective saturation and T₂ measurements. About 90 Hz stems from homogeneous effects, whereas the inhomogeneous contribution is approximately 100 Hz. The inhomogeneous line broadening is assigned to macroscopic inhomogeneities in the sample and not to variations in the nucleotide bases along the RNA strand in TMV. It is concluded that sample preparation is of vital importance for obtaining well-resolved spectra. Under optimal preparation techniques the isotropic values of the chemical shift of the different ³¹P sites have been determined to obtain information about the secondary structure of the viral RNA. The chemical shift anisotropy has been determined from the relative intensities of the spinning side bands in the spectra. The chemical shift information is used to make a tentative assignment of the resonance in terms of the three structurally distinguishable phosphate groups in TMV. The origin of the linewidths in MAS NMR has been examined further by ¹³C NMR of approximately 10% ¹³C-enriched coat protein of cowpea chlorotic mottle virus, using selective excitation and saturation techniques, as well as measurements of the relaxation times T_1γ and T₂. The CO resonance in the spectrum is composed of an inhomogeneous and homogeneous part with a total linewidth of 700 Hz. The homogeneous linewidth, contributing with 200 Hz, is found to arise from slow molecular motions in the solid on a millisecond timescale.     

Usefulness of diffusion derived vessel density computed from a simplified IVIM imaging protocol: An experimental study with rat biliary duct blockage induced liver fibrosis

ObjectivesLiver vessel density can be evaluated by DDVD (diffusion derived vessel density): DDVD_(b0b1) = Sb0/ROIarea0 – Sb1/ROIarea1, where Sb0 and Sb1 refer to the liver signal when b is 0 or 1 s/mm². Sb1 and ROIarea1 may be replaced by other b-values. With a rat biliary duct ligation (BDL) model, this study assesses the usefulness of liver DDVD computed from a simplified IVIM imaging protocol using b = 25 and b = 50 to replace b = 1 s/mm², alone and in combination with other IVIM parameters.MethodsMale Sprague-Dawley rats were used. The rat number was 5, 5, 5, and 3 respectively, for the timepoints of 7, 14, 21, 28 days post-BDL surgery. 12 rats had partial biliary duct recanalization performed after the rats had BDL for 7 days and then again followed-up for a mean of 14 days. Liver diffusion MRIs were acquired at 3.0 T with a b-value distribution of 0, 25, 50, 75, 100, 150, 300, 700, 1000 s/mm². DDVD_mean (control rats n = 6) was the mean of DDVD_(b0b25) and DDVD_(b0b50). IVIM fitting started from b = 0 s/mm² with segmented fitting and a threshold b of 50 s/mm² (n = 5 for control rats). Three 3-D spaces were constructed using a combination of the four diffusion parameters.ResultsThe control rats and BDL rats (n = 18) had a liver DDVD_mean of 84.0 ± 26.2 and 44.7 ± 14.4 au/pixel (p < 0.001). All 3-D spaces totally separated healthy livers and all fibrotic livers (n = 30, BDL rats and recanalization rats). The mean relative distance between healthy liver cluster and fibrotic liver cluster was 0.331 for PF, D_slow, and D_fast; 0.381 for PF, D_fast, and DDVD_mean; and 0.384 for PF, D_slow, and DDVD_mean.ConclusionA combination of PF, D_slow, and D_fast allows total separation of healthy livers and fibrotic livers and the integration of DDVD improved the separation.     

The structure of 32S I. Spectroscopy of highly-excited states

Assignments of I, π, T are made to 30 levels in ³²S between 7.35 and 11.76 MeV excitation energy, making the spectroscopy of the T= 0 states rather complete up to 10 MeV and that of the T = 1 states up to 12 MeV. A reassessment of existing data in the light of the new results clarifies the spectrum of I ^π = 1⁺, T = 1 states up to 15 MeV excitation energy. High-spin states (I = 52 - 7) below 10 MeV excitation energy have been investigated by n t γ angular-correlation measurements with the ²⁹Si(α, nγ) reaction at E _α 14.4 MeV. Five g-wave resonances of the ³¹P(p, γ) reaction, leading to the formation of I _π + 4⁺, 5⁺ states in ³²S, have been identified between 10 and 12 MeV excitation energy. The spectrum of T = 1 states between 10.7 and 12 MeV, has been investigated by measurements of γ-ray angular distributions on resonances of the ³¹P(p, γ) reaction and by measurements of resonance strengths. Several ³²S levels between 7.35 and 8.75 MeV excitation energy were studied as final states in resonance decays. Finally a search was performed for I ^π = 0⁺ resonances of the ²⁸Si(α, γ) reaction.     

MR imaging of teeth using a silent single point imaging technique

Magnetic resonance imaging (MRI) of teeth is an emerging application area which is still in development. Previous investigations did not fully focus on potential in vivo applications. Using ¹H and ³¹P MRI, we obtained ex vivo microimages of teeth with a silent single point imaging (SPI) technique. ¹H Images with an in-plane resolution of 310×310 μm² were obtained. Utilizing sine-shaped gradient ramps significantly reduced the sound pressure level of the experiment to that of background noise. ¹H magnetic resonance spectroscopy (MRS) was used to characterize the major components in the observed resonance. The spin–spin (T₂) relaxation times of water in enamel and dentin differed by at least one order of magnitude. Three-dimensional surface reconstruction of the data allowed for complete visualization of the tooth’s surface while volume reconstruction displayed the internal geometry. PACS 82.56.Na; 83.85.Fg; 87.61.-c; 87.19.-j; 43.50.Cb