Multi-echo Spin Research Articles

T2and T2* quantification using optimal B1image reconstruction for multicoil arrays

To investigate the accuracy of low signal-to-noise ratio (SNR) T(2) and T(2)* measurements using array coils and optimal B(1) image reconstruction (OBR) compared to the standard root sum of squares (RSS) reconstruction. Calibrated gels were used for the in vitro study of T(2). T(2) and T(2)* measurements were obtained from a volunteer's knee and liver, respectively. T(2) and T(2)* measurements were performed using multiecho spin echo and multiecho gradient echo sequences, respectively. SNR was deliberately kept low. The same raw data were used for both reconstructions. For the in vivo studies the effect of signal averaging was also investigated. The optimal reconstructions demonstrated a lower mean background noise level than RSS. In vitro, the T(2) measurements made with OBR images agreed better with a reference high SNR measurement than measurements made from RSS images; the RSS image results overestimated the T(2.) In vivo, increasing the signal averages decreased the difference between the measurements obtained using the OBR and RSS methods, with RSS resulting in longer relaxation times. This work demonstrates improvements to the accuracy of T(2) and T(2)* measurements obtained when OBR is used compared to RSS, particularly in the case of low SNR.

A comparative study at 3 T of sequence dependence of T2 quantitation in the knee

T2 mapping has been used widely in detecting cartilage degeneration in osteoarthritis. Several scanning sequences have been developed in the determination of T2 relaxation times of tissues. However, the derivation of these times may vary from sequence to sequence. This study seeks to evaluate the sequence-dependent differences in T2 quantitation of cartilage, muscle, fat and bone marrow in the knee joint at 3 T. Three commercial phantoms and 10 healthy volunteers were studied using 3 T MR. T2 relaxation times of the phantoms, cartilage, muscle, subcutaneous fat and marrow were derived using spin echo (SE), multiecho SE (MESE), fast SE (FSE) with varying echo train length (ETL), spiral and spoiler gradient (SPGR) sequences. The differences between these times were then evaluated using Student's t test. In addition, the signal-to-noise ratio (SNR) efficiency and coefficient of variation of T2 from each sequence were calculated. The average T2 relaxation time was 36.38+/-5.76 ms in cartilage and 34.08+/-6.55 ms in muscle, ranging from 27 to 45 ms in both tissues. The times for subcutaneous fat and marrow were longer and more varying, ranging from 41 to 143 ms and from 42 to 160 ms, respectively. In FSE acquisition, relaxation time significantly increases as ETL increases (P<.05). In cartilage, the SE acquisition yields the lowest T2 values (27.52+/-3.10 ms), which is significantly lower than those obtained from other sequences (P<.002). T2 values obtained from spiral acquisition (38.27+/-6.45 ms) were higher than those obtained from MESE (34.35+/-5.62 ms) and SPGR acquisition (31.64+/-4.53 ms). These differences, however, were not significant (P>.05). T2 quantification can be a valuable tool for the diagnosis of degenerative disease. Several different sequences exist to quantify the relaxation times of tissues. Sequences range in scan time, SNR efficiency, reproducibility and two- or three-dimensional mapping. However, when choosing a sequence for quantitation, it is important to realize that several factors affect the measured T2 relaxation time.

T 2 -mapping of osteoarticular and muscular tissues using turbo spin echo sequence

Objective To determine the feasibility of tissue T_2 measurement with turbo spin echo (TSE)sequence as an alternative method for a standard multi-echo spin echo sequence(MSE),and to evaluate the feasibility of single-slice and multi-slice acquisition for quantitative assessment of T_2 relaxation time.Methods(1)The phantom consisted of 8 small plastic bottles of phosphate buffer saline doped with known amounts of Gd-DTPA(Magnevist)to prepare solutions with different T_2 times.T_2 values measured using a TSE sequence were experimentally assessed against a gold-standard MSE protocol to evaluate the feasibility of single-slice and multi-slice acquisition for quantitative assessment of T_2 relaxation time.(2) The consistency of T_2 values obtained by MSE and TSE sequence in six cases of in vivo knee joint measurement was compared.Results(1)Apart from phosphate buffer saline(T_2 value was around 2000 ms),the discrepancy in T_2 values was less than 10% from phantom experiments between TSE (89.9±3.0)—(1228.0±128.0)ms and the conventional MSE technique(89.6±1.0)—(1221.0± 18.0)ms.The standard deviation in measured T_2 was increased for TSE sequence than for MSE sequenoe, (2)For tissues with T_2 value less than 1000 ms,the discrepancy in T_2 values was less than 10% from phantom experiments between single-slice(89.9±3.0)—(930.0±71.0)ms and multi-slice acquisition (85.8±5.0)—(902.7±354)ms for quantitative assessment of T_2 relaxation time.For tissues with T_2 value more than 1000 ms and around 600 ms,the discrepancy in measured T_2 was increased(10%). (3)In vivo knee joint measurement,T_2 values of the other tissues apart from yellow bone marrow obtained by the MSE,single-slice and multi-slice TSE sequence(51.5±15.4)—(476.5±69.7)ms yielded a delicate consistency(ICC0.75).Conclusions The method of single-slice and multi-slice TSE sequence in T_2 measurement is feasible.For bone marrow and extremely long T_2 tissue(for instance,cerebrospinal fluid),however,there may be considerable discrepancy on T_2 values obtained by TSE sequence.

Magnetic resonance microneurography of rabbit sciatic nerve on a 1.5‐T clinical MR system correlated with gross anatomy

This study was performed to investigate the feasibility and accuracy of magnetic resonance (MR) microneurography of the rabbit sciatic nerve on a 1.5-T clinical MR system by correlation with the gross anatomy. The 3D T2-weighted imaging (3D-T2WI), 3D T2-weighted imaging plus spectral presaturation with inversion recovery (SPIR), and T1-weighted imaging (T1WI) of the sciatic nerve in ten rabbits were performed on a 1.5-T MR system. The radiological anatomy of the sciatic nerve was observed and correlated with the gross anatomy. The anterior-posterior diameter of the sciatic nerve trunk was measured on 3D T2WI and on gross anatomy. The T1 and T2 relaxation times were also measured with multiecho spin echo and mixed sequence, respectively. The tibial nerve and peroneal nerve in the sciatic nerve trunk in all ten rabbits could be clearly displayed on T2WI and T2WI. The fine branches of the gastrocnemius nerve, posterior femoral cutaneous nerve, and the posterior gluteal nerve could be clearly depicted on T2WI. The T1 and T2 relaxation times of the sciatic nerves were 915 and 40 ms, respectively. The anterior-posterior diameter of sciatic nerve trunk was measured grossly, and on T2WI was 3.17 +/- 0.21 mm and 3.15 +/- 0.19 mm, respectively. There was no statistically significant difference (t = 0.768, P = 0.462). With the 1.5-T clinical MR system, the microneurography of the sciatic nerve could be revisualized, and the finer structure of the sciatic nerve trunk could be clearly and accurately delineated.

Effect of multislice acquisition on T1 and T2 measurements of articular cartilage at 3T

The aim of this study was to investigate the effect of magnetization transfer on multislice T1 and T2 measurements of articular cartilage. A set of phantoms with different concentrations of collagen and contrast agent (Gd-DTPA2-) were used for the in vitro study. A total of 20 healthy knees were used for the in vivo study. T1 and T2 measurements were performed using fast-spin-echo inversion-recovery (FSE-IR) sequence and multi-spin-echo (MSE) sequence, respectively, in both in vitro and in vivo studies. We investigated the difference in T1 and T2 values between that measured by single-slice acquisition and that measured by multislice acquisition. Regarding T1 measurement, a large drop of T1 in all slices and also a large interslice variation in T1 were observed when multislice acquisition was used. Regarding T2 measurement, a substantial drop of T2 in all slices was observed; however, there was no apparent interslice variation when multislice acquisition was used. This study demonstrated that the adaptation of multislice acquisition technique for T1 measurement using FSE-IR methodology is difficult and its use for clinical evaluation is problematic. In contrast, multislice acquisition for T2 measurement using MSE was clinically applicable if inaccuracies caused by multislice acquisition were taken into account.

T2mapping of hip articular cartilage in healthy volunteers at 3T: A study of topographic variation

To perform baseline T2 mapping of the hips of healthy volunteers, focusing on topographic variation, because no detailed study has involved hips. T2 mapping is a quantitative magnetic resonance imaging (MRI) technique that evaluates cartilage matrix components. Hips of 12 healthy adults (six men and six women; mean age = 29.5 +/- 4.9 years) were studied with a 3.0-Tesla MRI system. T2 measurement in the oblique-coronal plane used a multi-spin-echo (MSE) sequence. Femoral cartilage was divided into 12 radial sections; acetabular cartilage was divided into six radial sections, and each section was divided into two layers representing the superficial and deep halves of the cartilage. T2 of these sections and layers were measured. Femoral cartilage T2 was the shortest (-20 degrees to 20 degrees and -10 degrees to 10 degrees, superficial and deep layers), with an increase near the magic angle (54.7 degrees ). Acetabular cartilage T2 in both layers was shorter in the periphery than the other parts, especially at 20 degrees to 30 degrees. There were no significant differences in T2 between right and left hips or between men and women. Topographic variation exists in hip cartilage T2 in young, healthy adults. These findings should be taken into account when T2 mapping is applied to patients with degenerative cartilage.

Water mobility in the endosperm of high beta-glucan barley mutants as studied by nuclear magnetic resonance imaging

(1)H NMR imaging (MRI) was used as a noninvasive technique to study water distribution and mobility in hydrated barley (Hordeum vulgare L.) seeds of accessions with varying content of beta glucan (BG), a highly hygroscopic cell wall component. High contents of BG in barley are unfavorable in malting where it leads to clotting of filters and hazing of beer as well as in animal feed where it hinders the rapid uptake of energy. However, a high content of BG has a positive nutritional effect, as it lowers the cholesterol and the glycaemic index. It was studied whether water distribution and mobility were related to content and location of BG. Water mobility was investigated by following the rate and mode of desiccation in hydrated single seeds. In order to determine the different water components, a multispin echo experiment was set up to reveal the T(2) transverse relaxation rates of water within the seeds. A principal component analysis (PCA) discriminated control seeds from the high-BG mutant seeds. MRI proved efficient in tracing the differences in water-holding capacity of contrasting barley seeds. All accessions showed nonuniform distribution of water at full hydration as well as during desiccation. The embryo retained water even after 36 h of drying, whereas the endosperm showed low and heterogeneous mobility of the water after drying. The relaxation time constants indicated that the BG mutants had regions of much higher water mobility around the ventral crease compared to the control. It is concluded that MRI can be applied to investigate temporal and spatial differences in the location of specific chemical compounds in single seeds.

The application of polymer gel dosimeters to dosimetry for targeted radionuclide therapy

There is a lack of standardized methodology to perform dose calculations for targeted radionuclide therapy and at present no method exists to objectively evaluate the various approaches employed. The aim of the work described here was to investigate the practicality and accuracy of calibrating polymer gel dosimeters such that dose measurements resulting from complex activity distributions can be verified. Twelve vials of the polymer gel dosimeter, ‘MAGIC’, were uniformly mixed with varying concentrations of P-32 such that absorbed doses ranged from 0 to 30 Gy after a period of 360 h before being imaged on a magnetic resonance scanner. In addition, nine vials were prepared and irradiated using an external 6 MV x-ray beam. Magnetic resonance transverse relaxation time, T2, maps were obtained using a multi-echo spin echo sequence and converted to R2 maps (where T2 = 1/R2). Absorbed doses for P-32 irradiated gel were calculated according to the medical internal radiation dose schema using EGSnrc Monte Carlo simulations. Here the energy deposited in cylinders representing the irradiated vials was scored. A relationship between dose and R2 was determined. Effects from oxygen contamination were present in the internally irradiated vials. An increase in O2 sensitivity over those gels irradiated externally was thought to be a result of the longer irradiation period. However, below the region of contamination dose response appeared homogenous. Due do a drop-off of dose at the periphery of the internally irradiated vials, magnetic resonance ringing artefacts were observed. The ringing did not greatly affect the accuracy of calibration, which was comparable for both methods. The largest errors in calculated dose originated from the initial activity measurements, and were approximately 10%. Measured R2 values ranged from 5–35 s−1 with an average standard deviation of 1%. A clear relationship between R2 and dose was observed, with up to 40% increased sensitivity for internally irradiated gels. Curve fits to the calibration data followed a single exponential function. The correlation coefficients for internally and externally irradiated gels were 0.991 and 0.985, respectively. With the ability to accurately calibrate internally dosed polymer gels, this technology shows promise as a means to evaluate dosimetry methods, particularly in cases of non-uniform uptake of a radionuclide.

Left Ventricular Function Declines with Increasing Myocardial Ferritin Iron in Thalassemia Major.

Using a new magnetic resonance method that separately estimates the two principal forms of storage iron, ferritin and hemosiderin, in the heart, we examined the relationship between myocardial storage iron fractions and left ventricular function in thalassemia major. In patients with iron overload, the amount of iron in functional and transport pools changes only slightly. Virtually all of the excess is sequestered in storage forms of iron, as ferritin, a diffuse, soluble fraction, and as hemosiderin, an aggregate, insoluble fraction. The two storage forms of iron strongly affect signal intensity in both T2 and T2* weighted images but influence MRI signal decay through different means because of their differences in solubility and in intracellular distribution (Magn Reson Med 2002; 47:1131–8). Separate estimates of the iron concentrations of the two forms of storage iron may be obtained by measuring two distinct relaxation parameters, the “ferritin iron index” (“reduced” transverse relaxation rate) RR2, and the “hemosiderin iron index”, A. We studied 14 patients with thalassemia major, all being treated with subcutaneous deferoxamine. Study participants were examined with a Philips 1.5 T Intera scanner using three Carr-Purcell-Meiboom-Gill (CPMG)-like multi-echo spin echo sequences with varied inter-echo times, using electrocardiographic triggering and respiratory navigator gating to estimate RR2 and A. The left ventricular shortening fraction was measured using standard echocardiographic methods. The Figure shows the relationship (R=0.91, p<0.0001) between the ferritin index, RR2, and the left ventricular shortening fraction. [Display omitted] Overall, variation in the ferritin index explained more than 80% of the variation in ventricular function. For comparison, variation in the hemosiderin index, A, accounted for only about 33% of the variation in shortening fraction. Using an empirical calibration to estimate iron concentrations, variation in total (ferritin + hemosiderin) iron accounted for only about 40% of the variation in ventricular function. In patients with thalassemia major, the concentration of ferritin iron may provide a better indicator of the magnitude of the toxic iron pool than the total storage iron concentration. Magnetic resonance determinations of the partition of storage iron between ferritin and hemosiderin may be clinically valuable in evaluating tissue iron toxicity in patients with transfusional iron overload.

Methods for Noninvasive Measurement of Tissue Iron in Cooley's Anemia

To examine the relationship between myocardial storage iron and body iron burden, as assessed by hepatic storage iron measurements, we studied 22 patients with transfusion-dependent thalassemia syndromes, all being treated with subcutaneous deferoxamine, and 6 healthy subjects. Study participants were examined with a Philips 1.5-T Intera scanner using three multiecho spin echo sequences with electrocardiographic triggering and respiratory navigator gating. Myocardial and hepatic storage iron concentrations were determined using a new magnetic resonance method that estimates total tissue iron stores by separately measuring the two principal forms of storage iron, ferritin and hemosiderin. In a subset of 10 patients with beta-thalassemia major, the hepatic storage iron concentration had been monitored repeatedly for 12-14 years by chemical analysis of tissue obtained by liver biopsy and by magnetic susceptometry. In this subset, we examine the relationship between hepatic iron concentration over time and our current magnetic resonance estimates of myocardial iron stores. No significant relationship was found between simultaneous estimates of myocardial and hepatic storage iron concentrations. By contrast, in the subset of 10 patients with beta-thalassemia major, the correlation between the 5-year average of hepatic iron concentration and the current myocardial storage iron was significant (R = .67, P = .03). In these patients, myocardial storage iron concentrations seem to reflect the control of body iron over a period of years. Magnetic resonance methods promise to provide more effective monitoring of iron deposition in vulnerable tissues, including the liver, heart, and endocrine organs, and could contribute to the development of iron-chelating regimens that more effectively prevent iron toxicity.

85 Initial Experiences of Magnetic Resonance Imaging and Spectroscopy of the Newborn Brain At 4.7 Tesla

Background. The potential benefits of high-field magnetic resonance (MR) include increased signal, contrast, and spectral/spatial resolution, however there are specific safety and cost implications. Aims. (i) to explore the feasibility of MR imaging (MRI) and proton (1H) MR spectroscopy (MRS) at 4.7T of the newborn brain; (ii) to assess specific advantages and disadvantages of 4.7T versus low-field MR. Methods. Informed parental consent and ethical approval were obtained. Nine ventilated infants were studied at a median corrected gestational age 41+4 weeks using a whole-body 4.7T MR system with continuous monitoring (skin temperature, pulse oximetry, ECG). Acoustic noise was attenuated with incubator-lining, ear-plugs and mini-muffs. MRI included: T1- and T2-weighted single and multi-echo spin-echo, and 3D gradient-echo. Quantitative T1 and T2 maps were calculated where possible. A modified PRESS sequence was used for 1H-MRS localised to an 8mm3 thalamic voxel (echo times 144 and 288ms). Sequences were programmed to keep RF heating at less than half the recommended adult maximum levels. Results. Physiological indices were stable and no adverse events occurred. As expected, brain water T1 was higher and T2 lower at 4.7T versus lower fields. The T1-weighted images displayed poor contrast, however high spatial resolution T2-weighted imaging with a 4.7T-optimised fast spin-echo technique delivered remarkable contrast and structure differentiation (figure). 1H-MRS detected brain metabolites including lactate. Conclusions. Safety considerations at high-field limit sequence flexibility and rapidity of data acquisition. Nevertheless our initial experience demonstrates the feasibility of scanning sick newborn infants at 4.7T: The quality of T2-weighted images was significantly improved, whilst T1-weighted images and 1H-MRS were not superior at high vs low-field. Further research on the application of high-field MR to the developing brain is imperative as exploitation of specific features and use of dedicated coils may improve the diagnostic and prognostic accuracy of MR techniques.

Fundamental Physics of MR Imaging

Learning the basic concepts required to understand magnetic resonance (MR) imaging is a straightforward process. Although the individual concepts are simple, there are many concepts to learn and retain simultaneously; this situation may give the illusion that learning the physics of MR imaging is complicated. It is important for the radiologist who interprets MR images to understand the methods used to create the images because image contrast specifically depends on how the image data were acquired. Initial concepts include formation of magnetic fields from electric currents in loops of wire, the resonance phenomenon, the hydrogen proton and its frequency of precession, and absorption of radiofrequency energy. These concepts can then be applied to learn about T1 and T2 relaxation and contrast and how the acquisition parameters of echo time and repetition time can be used to achieve these image contrasts. Basic pulse sequences include the spin-echo, multiecho spin-echo, turbo spin-echo, inversion-recovery, and gradient-recalled-echo sequences.

MRI evaluation of the basal ganglia size and iron content in patients with Parkinson's disease

To evaluate by MRI the area size and the degree of iron accumulation in basal ganglia nuclei that are implicated in the pathogenesis of Parkinson's disease (PD). 40 patients with idiopathic PD and 40 controls were examined on a 1. 5 Tesla MR imager, using a multiecho SE sequence 2000/20, 40, 60, 80, 100, 120, 140, 160 (TR/TE). The T2 relaxation time (T2) and the area of substantia nigra zona compacta (SNc), substantia nigra zona reticulata (SNr), putamen (Pu), globus pallidus external (GPe), globus pallidus internal (GPi), caudate nucleus (CN), locus coeruleus (LC) and subthalamic nucleus (STN) were assessed. The T2 of SNc (76. 8 +/- 6. 0) was lower and of Pu (79.5 +/- 6.0) and GPe (69.5 +/- 7.0) was higher in patients than in controls (78.6 +/- 3.8, 77.4 +/- 3.9 and 67.3 +/- 5.7, respectively), p < 0.05. The area of CN (125.9 +/- 20.2) and Pu (201.5 +/- 48.7) was higher in patients than in controls (110.7 +/- 21.5 and 180.1 +/- 41.1, respectively), p < 0.05. A more pronounced decrease in the T2 of SNc (73.6 +/- 8.9) was observed when the more affected side of patients was evaluated separately. In patients with disease duration > 5 years the T2 of STN (71.5 +/- 6.3) was lower and the area of Pu was higher (215.3 +/- 54.9) compared with those with disease duration < or = 5 years (75.8 +/- 10.9 and 190.9 +/- 41.0 respectively), p < 0.05. These findings suggest that dysfunction of the basal ganglia circuitry in PD may affect iron content not only in SNc but in STN, Pu and GPe as well. Compensatory sprouting of the remaining dopaminergic fibers could account for the increased area of the CN and Pu.

Predicting final infarct size using acute and subacute multiparametric MRI measurements in patients with ischemic stroke

To identify early MRI characteristics of ischemic stroke that predict final infarct size three months poststroke. Multiparametric MRI (multispin echo T2-weighted [T2W] imaging, T1-weighted [T1W] imaging, and diffusion-weighted imaging [DWI]) was performed acutely (<24 hours), subacutely (three to five days), and at three months. MRI was processed using maps of apparent diffusion coefficient (ADC), T2, and a self-organizing data analysis (ISODATA) technique. Analyses began with testing for individual MRI parameter effects, followed by multivariable modeling with assessment of predictive ability (R(2)) on final infarct size. A total of 45 patients were studied, 15 of whom were treated with tissue plasminogen activator (tPA) before acute MRI. The acute DWI and DWI-ISODATA mismatch lesion size, and the interactions of ADC, T2, and T2W imaging lesion with tPA remained in the final multivariable model (R(2) = 70%). A large acute DWI lesion or DWI < ISODATA lesion independently predicted increase in the final infract size, with predictive ability 68%. Predictive ability increased (R(2) = 83%) when subacute MRI parameters were included along with acute DWI, DWI-ISODATA mismatch, and acute T2W image lesion size by tPA treatment interaction. Subacute DWI > acute DWI lesion size predicted an increased final infarct size (P < 0.01). Acute-phase DWI and DWI-ISODATA mismatch strongly predict the final infarct size. An acute-to-subacute DWI lesion size change further increases the predictive ability of the model.

Water distribution patterns inside bovine articular cartilage as visualized by1H magnetic resonance imaging

Objective To develop a magnetic resonance imaging (MRI) technique to non-invasively map water volume fraction (WVF) in articular cartilage. Special emphasis was placed on spatial resolution and temporal considerations, aimed at creating a procedure feasible for eventual human studies.DesignAbsolute proton density MR images of intact, ex vivo bovine patellae were calculated from fullyT1 relaxed, short echo time images. This was accomplished through compensation for T2decay with calculated T2maps. Calibration of the signal intensity in the image was accomplished with the use of H2O:D2O phantoms, where the WVF was varied from 0.95 to 0.75. Application of the calibration curve to the entire image yielded images that represent WVF on a pixel by pixel basis. Calculations of water content by weight were performed by considering the density of the solid content.Results Using four echo time points, experiments comparing MR images from single-echo and multi-echo spin echo sequences yielded similar results. T2decreased with depth through the cartilage, with a maximum at the articular surface of approx 100ms, and a ∼50ms minimum at the bone/cartilage interface. The WVF through the depth of the cartilage showed a similar trend, decreasing from 0.9 at the surface, to 0.7 at the bone/cartilage interface. Translation to a weight percent yielded ∼86% weight at the surface, trending down to ∼63% at the bone/cartilage interface, with an average of 74.5% for five patellae. These MRI derived values were compared to the measured weight of water in excised cartilage plugs from the same patellae and showed remarkably close agreement.Conclusion We have demonstrated that MRI can non-invasively map WVF in cartilage in a pixel by pixel manner. This was accomplished in a time span that was clinically feasible, allowing the routine use of this method in a clinical setting. Moreover, this procedure employed standard MRI equipment and pulse sequences, avoiding the need for hardware modifications and using simple post processing methods. However, baseline studies need to be performed prior to incorporation into a standard radiological evaluation. Implications in the diagnosis of osteoarthritis (OA) are discussed.

Diffusional anisotropy of T2 components in bovine optic nerve.

A diffusion-CPMG hybrid experiment was used to analyze the diffusion characteristics of different T2 relaxation components in bovine optic nerve. Data were collected using a pulsed field gradient (PFG) multi spin echo (MSE) CPMG sequence for parallel and perpendicular axon orientation and four diffusion times. The apparent diffusion coefficient (ADC) was evaluated for two observed T2 components as a function of axonal orientation and diffusion time delta. The short T2 component exhibited minor diffusional anisotropy and larger ADC, whereas the long T2 component showed significant anisotropy effects. This is consistent with the hypothesis that the short T2 component is associated with water within the myelin sheath, which is less restricted than axonal water that is limited by cell membrane permeability.

Water dynamics in human blood via combined measurements of T2 relaxation and diffusion in the presence of gadolinium.

An analytical model of tissue relaxation and restricted diffusion in human blood is presented. The blood tissue model is composed of three different compartments: red blood cells, plasma, and macromolecular protons. The relaxation rate constants and free diffusion coefficients of intracellular and extracellular water may differ. Analytical formulas for signal loss due to relaxation and diffusion in the Carr-Purcell Meiboom-Gill and pulsed-field-gradient multispin echo experiments for this tissue model are derived. The model is fitted to the experimental data for human blood with various concentrations of Gadolinium contrast agent. The obtained model parameters are realistic. The validity and sensitivity of the model are also discussed.

Quantitative 1H-NMR imaging of water in white button mushrooms ( Agaricus bisporus)

MRI represents a valuable tool for studying the amount and physical status of water in plants and agricultural products, for example, mushrooms ( Agaricus bisporus). Contrast in NMR images originates from the mixed influence of the fundamental NMR parameters, amongst others, spin-density, T 2- and T 1 relaxation processes. Maps of these parameters contain valuable anatomical and physiological information. They can, however, be severely distorted, depending on the combination of parameter settings and anatomy of the object under study. The influence of the tissue structure of mushrooms, for example, tissue density (susceptibility inhomogeneity) and cell shape on the amplitude, T 2, and T 1 images is analyzed. This is achieved by vacuum infiltration of the cavities in the mushroom's spongy structure with Gd-DTPA solutions and acquiring Saturation Recovery-Multispin Echo images. It is demonstrated that the intrinsic long T 2 values in the cap and outer stipe tissue strongly relate to the size and geometry of the highly vacuolated cells in these spongy tissues. All observed T 2 values are strongly affected by susceptibility effects. The T 2 of gill tissue is shorter than T 2 of the cap and outer stipe, probably because these cells are less vacuolized and smaller in size. The calculated amplitude images are not directly influenced by susceptibility inhomogeneities as long as the observed relaxation times remained sufficient long. They reflect the water distribution in mushrooms best if short echo times are applied in a multispin echo imaging sequence at low magnetic field strength.

Comparison of conventional single echo and multi‐echo sequences with a fast spin‐echo sequence for quantitative T2 mapping: Application to the prostate

The accuracy of water T2 maps generated from a fast spin-echo (FSE) sequence was compared with data obtained by conventional single and multi-echo spin-echo pulse sequences using a commercial gel phantom. Spatially localized stimulated echo acquisition mode (STEAM) proton spectroscopy was also used to confirm the reported water T2 values of the gels contained in the phantom. The FSE sequence was shown to be superior in accuracy to both the single and multi-echo spin echo sequences and comparable to STEAM, producing results that were within 10% of known values. The effectiveness of the FSE sequence was further demonstrated by generating T2 maps of the normal and diseased prostate in clinically acceptable imaging times, resulting in comparable T2 values to those obtained using STEAM. Accurate quantitative T2 maps can be produced with the FSE sequence.

Radial turbo spin echo imaging.

Fast MR imaging methods should provide a familiar contrast behavior at a reduced scan time. The multi-spin echo approach (TSE) is one of the most promising techniques satisfying this condition. Although the data acquisition time is significantly reduced, image quality may still suffer from artifacts due to patient motion and flow. The radial turbo spin echo (rTSE) approach combines TSE methods and projection reconstruction (PR) techniques. In PR images, artifacts induced by patient motion or flow are known to have a different appearance with lower level of intensity. The contrast and artifact behavior of the rTSE approach has been investigated. The new technique has been applied to abdominal imaging with acquisition times shorter than 30 s and to heart imaging in combination with cardiac triggering.