Quantitative T2 Imaging of Plant Tissues By Means Of Multi-Echo MRI Microscopy

A method for quantitative T₂ imaging is presented which covers the large range of T₂ values in plants (5 to 2000 ms) simultaneously. The transverse relaxation is characterized by phase-sensitive measurement of many echo images in a multi-echo magnetic resonance imaging sequence. Up to 1000 signal-containing echo images can be measured with an inter-echo time of 2.5 ms at 0.47 T. Separate images of water density and of T₂ are obtained. Results on test samples, on the cherry tomato and on the stem of giant hogweed are presented. The effects of field strength, spatial resolution and echo time on the observed T₂ values is discussed. The combination of a relatively low magnetic field strength, short echo time and medium pixel resolution results in excellent T₂ contrast and in images hardly affected by susceptibility artifacts. The characterization of transverse relaxation by multi-echo image acquisition opens a new route for studies of water balance in plants.     

An optimized MP2RAGE sequence for studying both brain and cervical spinal cord in a single acquisition at 3T

Magnetization Prepared 2 Rapid Acquisition Gradient Echo (MP2RAGE) is a T₁ mapping technique that has been used broadly on brain and recently on cervical spinal cord (cSC).The growing interest for combined investigation of brain and SC in numerous pathologies of the central nervous system such as multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS) and traumatic injuries, now brings about the need for optimization with regards to this specific investigation. This implies large spatial coverage with high spatial resolution and short acquisition time, high CNR and low B₁⁺ sensitivity, as well as high reproducibility and robust post-processing tools for T₁ quantification in different regions of brain and SC.In this work, a dedicated protocol (referred to as Pr-BSC) has been optimized for simultaneous brain and cSC T₁ MP2RAGE acquisition at 3T. After computer simulation optimization, the protocol was applied for in vivo validation experiments and compared to previously published state of the art protocols focusing on either the brain (Pr-B) or the cSC (Pr-SC). Reproducibility and in-ROI standard deviations were assessed on healthy volunteers in the perspective of future clinical use.The mean T₁ values, obtained by the Pr-BSC, in brain white, gray and deep gray matters were: (mean ± in-ROI SD) 792 ± 27 ms, 1339 ± 139 ms and 1136 ± 88 ms, respectively. In cSC, T₁ values for white matter corticospinal, posterior sensory, lateral sensory and rubro/reticulospinal tracts were 902 ± 41 ms, 920 ± 35 ms, 903 ± 46 ms, 891 ± 41 ms, respectively, and 954 ± 32 ms for anterior and intermediate gray matter. The Pr-BSC protocol showed excellent agreement with previously proposed Pr-B on brain and Pr-SC on cSC, with very high inter-scan reproducibility (coefficients of variation of 0.52 ± 0.36% and 1.12 ± 0.62% on brain and cSC, respectively).This optimized protocol covering both brain and cSC with a sub-millimetric isotropic spatial resolution in one acquisition of less than 8 min, opens up great perspectives for clinical applications focusing on degenerative tissue such as encountered in MS and ALS.     

Magnetic resonance T21 measurements of the normal human lung in vivo with ultra-short echo times

The objective of this study was to measure T₂1 values of the normal human lung in vivo during breathhold using a rapid gradient-echo sequence with ultra-short echo times (TE). A sagittal slice of the right lung was imaged in six volunteers with various TE ranging from 0.5 ms to 5 ms using a clinical 1.5 Tesla MR scanner. T₂1 values were calculated in a region of interest in the dependent and non-dependent lung. In the dependent lung, T₂1 values of 1.1 ms ± 0.15 ms were measured, and in the non-dependent lung, 0.86 ms ± 0.11 (p < 0.01). T₂1 measurements of the normal human lung during breathhold are feasible with a clinical MR unit. The short T₂1 values require the use of very short TE times (<2.5 ms) in gradient-echo sequences to obtain adequate signal intensity from lung tissue.     

Simultaneous measurements of diffusion and transverse relaxation in exercising skeletal muscle

The aim of this study was to compare proton T₂ and apparent diffusion coefficient (ADC) variations induced by exercise in skeletal muscle, to provide some more information on the source of their variations. T₂ and ADC were measured in the forearm flexor digitorum muscles in 12 healthy volunteers at rest and after an exercise, using a sequence allowing simultaneous measurements of both parameters. At rest, T₂ was 30.6 ± 1.8 ms (mean ± 1 SD) and ADC was 1.82 ± 0.11 × 10⁻⁹ m²/s. With exercise, T₂ varied by +28 ± 12% (p < .001 vs. rest) and ADC varied by +12 ± 3% (p < .001). The recovery of T₂ after exercise was faster than that of ADC, with half-times of 7 ± 2 min and of 15 ± 8 min (p < .01), respectively. It is concluded that both T₂ and ADC increase with exercise. However, the mechanisms of variation of T₂ and ADC with exercise are probably different, T₂ mostly reflecting changes in water content and ADC reflecting temperature variations.     

Large angle spin-echo imaging

A study was undertaken to assess the use of excitation flip angles greater than 90° for T₁ weighted spin-echo (SE) imaging with a single 180° refocusing pulse and short TR values. Theoretical predictions of signal intensity for SE images with excitation pulse angles of 90–180° were calculated based on the Bloch equations and then measured experimentally from MR images of MnCl₂ phantoms of various concentrations. Liver signal-to-noise ratios (SNR) and liver-spleen contrast-to-noise ratios (CNR) were measured from breathhold MR images of the upper abdomen in 16 patients using 90 and 110° excitation flip angles. The theoretical predictions showed significant improvements in SNR with excitation flip angles >90°, which were more pronounced at small TR values. The phantom studies showed reasonably good agreement with the theoretical predictions in correlating the excitation pulse angle with signal intensity. In the human imaging studies, the 110° excitation pulse angle resulted in a 7.4% (p < .01) increase in liver SNR and an 8.2% (p = .2) increase in liver-spleen CNR compared to the 90° pulse angle at TR = 275 ms. Increased signal intensity resulting from the use of large flip angle excitation pulses with a single echo SE pulse sequence was predicted and confirmed experimentally in phantoms and humans.     

Charged hadron production ine + e − annihilation in the Υ and Υ′ region

Charged hadron production ine ⁺ e ^? annihilation is studied in the 7 to 10 GeV CM energy region and at the Υ (9.46) and Υ′ (10.01) resonances with the LENA detector at DORIS. The statistical moments of the charged multiplicities are studied. The data show KNO scaling behaviour and suggest the presence of long range correlations. An average charged multiplicityrise of Δn(Υ)=0.55±0.19 and Δn(Υ′)=1.26±0.29 over the continuum is observed for the Υ and Υ′ direct decays. The jet structure of the Υ and Υ′ direct decays is investigated using the charged particles. The polar angular distributions of the jet axis behave like 1+α(T) cos²θ with 〈α(T)〉_Υ=0.7±0.3 and 〈α(T)〉_Υ′=0.6±0.4. The 〈α(T)〉_Υ value is in agreement with the QCD vector gluon assignment and excludes scalar gluons by more than four standard deviations.     

Three-dimensional black-blood T2 mapping with compressed sensing and data-driven parallel imaging in the carotid artery

PurposeTo develop a 3D black-blood T₂ mapping sequence with a combination of compressed sensing (CS) and parallel imaging (PI) for carotid wall imaging.Materials and methodsA 3D black-blood fast-spin-echo (FSE) sequence for T₂ mapping with CS and PI was developed and validated. Phantom experiments were performed to assess T₂ accuracy using a Eurospin Test Object, with different combination of CS and PI acceleration factors. A 2D multi-echo FSE sequence was used as a reference to evaluate the accuracy. The concordance correlation coefficient and Bland-Altman statistics were calculated. Twelve volunteers were scanned twice to determine the repeatability of the sequence and the intraclass correlation coefficient (ICC) was reported. Wall-lumen sharpness was calculated for different CS and PI combinations. Six patients with carotid stenosis > 50% were scanned with optimised sequence. The T₂ maps were compared with multi-contrast images.ResultsPhantom scans showed good correlation in T₂ measurement between current and reference sequence (r = 0.991). No significant difference was found between different combination of CS and PI accelerations (p = 0.999). Volunteer scans showed good repeatability of T₂ measurement (ICC: 0.93, 95% CI 0.84–0.97). The mean T₂ of the healthy wall was 48.0 ± 9.5 ms. Overall plaque T₂ values from patients were 54.9 ± 12.2 ms. Recent intraplaque haemorrhage and fibrous tissue have higher T₂ values than the mean plaque T₂ values (88.1 ± 6.8 ms and 62.7 ± 9.3 ms, respectively).ConclusionThis study demonstrates the feasibility of combining CS and PI for accelerating 3D T₂ mapping in the carotid artery, with accurate T₂ measurements and good repeatability.     

Bi-Exponential T2 Decay in Dairy Cream Phantoms

MRI phantoms are an important part of any experiment because they provide a reference of known parameters. There are many choices of mono-exponential T₂ phantoms, but few choices for bi-exponential T₂ phantoms. We have found that dairy cream provides an excellent bi-exponential T₂ model with similar relaxation times to those found in white matter. Five cream phantoms of different milk fat percentages (2, 6, 10, 18 and 35%) were imaged with an optimized Carr–Purcell–Meiboom–Gill sequence. The decay curves for each of the phantoms were fit using Non-Negative Least Squares. We found that the short T₂ component fraction relative to the total energy in the distribution correlated linearly (r = 0.9973) with the milk fat percentage. The short T₂ time was 38 ± 4 ms and the long T₂ time was 135 ± 4 ms.     

Characterization of parotid gland tissue: A description of an MRI protocol set-up and results of in-vivo applications

A reliable protocol for proton T₂ mapping of the parotid region was set up for future characterization of parotid gland disease. A Carr-Purcell-Meiboom-Gill sequence, phase compensated, available on our 1.5 T imager, was selected and acquisition parameters were chosen on the basis of tests performed on phantoms (agarose-doped gels with T₂ in the physiological range). Some experiments were carried out to evaluate the accuracy of T₂ calculations for selective and nonselective refocussing pulses, for image uniformity corrections, and for different situations of slice shift and repetition times. The chosen protocol was then applied to in vivo evaluations to check the long-term precision by means of repeated measurements performed on the same subject over a 2-month period. Two or more reference gels were positioned both in the phantom and volunteer at the edge of the field-of-view (FOV). Image postprocessing consisted of an automatic procedure, written by the authors in Fortran 77, that selected the best fit for each pixel between mono- and biexponential decay models, and prepared four parametric images (T₂ and Rho slow and fast contribution, Rho being a function of proton density and of T₁) that may be used for future elaborations. The phantom experiment results showed an accuracy of 2.5% if a linear correction was performed using the reference gels at the edge of the FOV. No significant differences in accuracy were found between selective and nonselective refocussing pulse, and a homogeneity correction was not demonstrated necessary. The measurements performed on four volunteers showed that the best decaying model for healthy parotid tissue was monoexponential. Evaluated T₂ resulted 80.18 ± 6.11 ms (72.96 ± 4.97 ms for uncorrected results). Long-term reproducibility of the group of measurements from one volunteer, summarizing all the measurement errors, ranged from 0.9 to 8.5%. The two-way ANOVA that was carried out considering the two classes of volunteers and of parotid positions (right or left) showed that differences found between the two parotids were not significant, while T₂ differences among individuals are significant if a probability level higher than 1.1% is accepted. As in this cases, the main source of error can be attributed to the biological variations among individuals. Future statistics collected on patients for the T₂ evaluations of the pathologic tissue will clarify whether the T₂ relaxation is a sufficient parameter for T₂ discrimination of healthy and pathologic tissue.     

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.     

Oxygen-induced MR signal changes in murine tumors

Breathing of 100% oxygen was used to challenge vascular autoregulation in 14 mice with either osteosarcomas (n = 6) or mammary carcinomas (n = 8). Reproducible and statistically significant signal intensity changes of –29 ± 6% to +35 ± 3% were observed on heavily T₂1-weighted images in the tumors during the oxygen challenge. No significant changes were observed in muscle. For the mammary carcinomas a higher percentage of tumor voxels showed significant signal-intensity decrease (31 ± 8%) compared to the percentage of voxels showing a signal-intensity increase (22 ± 3%). In contrast, for the osteosarcomas, a higher percentage of tumor voxels showed signal-intensity increase (52 ± 9%) compared to the percentage of voxels showing signal-intensity decrease (27 ± 9%). The regional distribution of these signal intensity changes did not correlate with the signal pattern on T₁-, T₂-,and T₂1-weighted and Gd-DTPA enhanced images acquired without breathing 100% oxygen. Most likely, the signal intensity changes represented the inability of the tumor’s neovascularization for autoregulation during the oxygen challenge, particularly in hypoxic regions. Although further investigation is needed, the findings that malignant tumor tissue showed signal intensity changes, whereas normal muscle tissue did not, suggests that this technique may prove useful in distinguishing benign from malignant tissue.     

Assessment of acute myocardial infarction in man with magnetic resonance imaging and the use of a new paramagnetic contrast agent gadolinium-bopta

To assess the feasibility of and characterize the new paramagnetic contrast agent gadolinium-BOPTA/dimeglumine (Gd-BOPTA) to detect acute myocardial infarctions with MR imaging, 24 patients (53.3 ± 8.3 yr) were examined 9.3 ± 3.6 days after a first myocardial infarction. Short-axis T₁-weighted and T₂-weighted MR imaging was performed at three slice levels. T₁-weighted images were obtained before, immediately after, 15, 30, and 45 min after injection. Patients received either 0.05 or 0.1 mmol/kg body weight Gd-BOPTA. Images were qualitatively and quantitatively analyzed. Two patients showed no signs of infarction on T₂-weighted images as opposed to contrast-enhanced T₁-weighted images. Contrast-to-noise ratio was not affected by the dosage level. Signal intensity (SI) of normal to infarcted myocardium was significantly improved by both dosages (p < .0005) but a dosage of 0.05 mmol/kg produced significantly higher SI inf/norm (1.42 ± 0.07 vs. 1.34 ± 0.06, respectively, p = .015). SI of normal and infarcted myocardium enhanced immediately after administration of 0.05 mmol/kg (29.3 ± 5.1% and 53.8 ± 9.6% respectively), which decreased thereafter to 5.3 ± 4.8% and 40.2 ± 8.5% respectively, at 45 min (p < .002 for normal myocardium). SI enhancement immediately after 0.1 mmol/kg Gd-BOPTA showed no decrease within the first 45 min. Gd-BOPTA enables the detection of myocardial infarction. Optimal infarct delineation is achieved from 15 to 45 min after administration of 0.05 mmol/kg body weight Gd-BOPTA. Gd-BOPTA at 0.05 mmol/kg does improve image quality as measured by contrast-to-noise ratio and SI enhancement as compared to 0.10 mmol/kg.     

Diffusion- and T2-weighted MRI of closed-head injury in rats: A time course study and correlation with histology

Diffusion- and T₂-weighted MRI were used to evaluate changes in brain water characteristics following closed-head injury in rats. Images were collected within the first 2 h and at 24 h and 7 days following the traumatic event and then compared with histology. The ratios between the apparent diffusion coefficients (ADCs) of the traumatized tissues and normal brain tissues were significantly different from unity and were found to be 0.79 ± 0.25 (p < 0.01), 0.49 ± 0.33 (p < 0.0002), and 3.47 ± 1.36 (p < 10⁻⁶) at 1–2 h, 24 h, and 1 week after the trauma, respectively. In severe trauma, areas of hyperintensity which were not apparent on the T₂-weighted images could be detected on the diffusion-weighted images within 1–2 h after the trauma. At 24 h following the traumatic event, large areas of hyperintensity are observed in both types of images. One week following the trauma, the ADCs of the traumatized tissues (1.84 ± 0.69 × 10⁻⁵ cm²/s) are much larger than those of normal brain (0.57 ± 0.19 × 10⁻⁵ cm²/s) and approach the value of free water. At 7 days, the areas of hyperintensity in the T₂-weighted images seem to underestimate the injured areas found by histology. At this time point a good correlation is obtained between the areas of hypointensity observed on the diffusion-weighted images and the infarct areas obtained by histology (r = 0.88).     

Alpha decay properties of199Rn and199mRn

Theα-decays of¹⁹⁹Rn (E _α = (6.989±0.010) MeV,T _1/2>300ms) and of^199m Rn (E _α = (7.060±0.015) MeVT _1/2=(61 _?2 ⁺³² ) ms) were identified by anα-α-correlation method. They proceed via separated decay paths to¹⁹⁵Po and^195m Po, respectively. The spins of the involved states are discussed by aid of the shell model, and a tentative spin assignment is given.     

Synthetic T2-weighted images of the lumbar spine derived from an accelerated T2 mapping sequence: Comparison to conventional T2w turbo spin echo

ObjectivesTo evaluate the diagnostic usefulness of synthetic T₂-weighted images of the lumbar spine derived from ten-fold undersampled k-space data using GRAPPATINI, a combination of a model-based approach for rapid T₂ and M₀ quantification (MARTINI) extended by generalized autocalibrating partial parallel acquistion (GRAPPA).Materials and methodsOverall, 58 individuals (26 female, mean age 23.3 ± 8.1 years) were examined at 3 Tesla with sagittal and axial T₂w turbo spin echo (TSE) sequences compared to synthetic T₂₋weighted contrasts derived at identical effective echo times and spatial resolutions. Two blinded readers graded disk degeneration and evaluated the lumbar intervertebral disks for present herniation or annular tear. One reader reassessed all studies after four weeks. Weighted kappa statistics were calculated to assess inter-rater and intra-rater agreement. Also, all studies were segmented manually by one reader to compute contrast ratios (CR) and contrast-to-noise ratios (CNR) of the nucleus pulposus and the annulus fibrosus.ResultsOverall, the CR_T2w was 4.45 ± 1.80 and CR_T2synth was 4.71 ± 2.14. Both correlated (rsp = 0.768;p < 0.001) and differed (0.26 ± 1.38;p = 0.002) significantly. The CNR_T2w was 1.73 ± 0.52 and CNR_T2synth was 1.63 ± 0.50. Both correlated (rsp = 0.875;p < 0.001) and differed (−0.10 ± 0.25;p < 0.001) significantly. The inter-rater agreement was substantial to almost perfect (κ = 0.808–0.925) with the intra-rater agreement also substantial to almost perfect (κ = 0.862–0.963). The area under the curve of the receiver operating characteristics assessing disk herniation or annular tear ranged from 0.787 to 0.892.ConclusionsThis study concludes that synthetic images derived by GRAPPATINI can be used for clinical routine assessment with inter-rater and intra-rater agreements comparable to conventional T₂w TSE.     

The charge radii of198Pt-183Pt

The reactions⁵⁸Ni+¹⁰²Pd→¹⁶⁰W and⁵⁸Ni+¹⁰⁶Cd→¹⁶⁴Os were investigated to search for new decay data of neutron deficient nuclei. Excitation energies of the compound nuclei covered a range from 47 to 89 MeV. Velocity separation of the evaporation residues and position time correlations with the a decays of the implanted nuclei were used. The following new decay data were measured:¹⁶²Os (E_α=(6611 ±30) keV, T_1/2=(1.9±0.7) ms);¹⁵⁸W (T_1/2=(0.9±0.3) ms);¹⁵⁸m_W (E=1.88 MeV, E_α=(8280±30) keV, T_1/2=(0.01-1) ms);^155mLu (E_α=(5575±10) keV); β decay of¹⁵⁶Ta (T_1/2 > 10 ms) to the 8⁺ yrast isomer in¹⁵⁶Hf. A cross section of 5μb was measured for the new isotope¹⁵⁶Ta produced in a p3n evaporation channel from¹⁶⁰W at 64 MeV excitation energy.     

NMR study of tomato pericarp tissue by spin-spin relaxation and water self-diffusion

Pericarp tissues of tomato varieties Quest and Cameron were studied by low-field nuclear magnetic resonance (NMR) at a controlled temperature of 20°C. The spin-spin relaxation times and the water diffusion coefficients were measured with Carr-Parcell-Meiboom-Gill and pulsed field gradient multi-spin-echo (PFGMSE) NMR sequences. Four relaxing components were extracted from the spin-spin relaxation. The components withT ₂=11 ms,T ₂=65 ms,T ₂=430 ms andT ₂=1500 ms were related to the nonexchangeable protons and water proton in each cell compartment (i.e., cell wall-extracellular space, cytoplasm and vacuole, respectively). In contrast to the relative intensities, theT ₂ values appeared insensitive to variety and harvest period. The difference in relative intensity was related to the size of the pericarp cell. The water self-diffusion coefficients for each cell compartment were determined simultaneously with the PFGMSE sequence. The water self-diffusion coefficients for the vacuole and cytoplasm were not affected by the harvest date or variety. However, the water self-diffusion in the cell wall-extracellular space was significantly different between the two varieties.     

In vivo NMR imaging and T1 measurements of water protons in the human brain

Nuclear magnetic resonance (NMR) proton density images of the human brain have been made by the FONAR method. Spin-lattice relaxation times, T₁, of water hydrogen protons have been determined at random positions within frontal and temporal regions of the human brain. The primary purpose of this ongoing research is to accumulate a large data base of normal T₁ values for water protons in normal human brain tissue. Our experience to data includes 31 measurements on 18 volunteer subjects, and the mean value ± standard deviation is 215 ± 42 msec. In addition, two metastatic lesions of the brain were studied and found to have T₁ values longer than those for normal brain tissue.     

High field NMR microscopic imaging of cultivated strawberry fruit

The experimental conditions required for discrimination of various types of tissue in fruits of cultivated strawberry (Fragaria × Ananassa) at high fields (ca. 7 T) have been investigated. In marked contrast to soft fruits of other species, from which informative images have been derived at high fields using a variety of pulse sequences and acquisition parameters, appreciable image intensities from parenchymal and vascular tissues in healthy strawberry fruits were obtained only with a spin-echo imaging sequence using large sweep widths (ca. 100,000 Hz), and consequently small values for TE (<5 ms), indicating predominantly short T₂ values for these tissues. Damage caused by infection by the fungal pathogen Botrytis cinerea is readily seen as a result of a large increase in T₂ in the infected tissue, whereas ripening processes appear to be characterized primarily by small variations in the T₂-weighted contrast and in the relative magnitudes of T₁ between vascular and parenchymal tissue. In addition, it was possible selectively to enhance the contributions to images from the achenes (“seeds”) by using very short relaxation delays, thereby enhancing T₁-dominated contrast mechanisms.