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Oxygen-sensitive 3He-MRI was studied for the detection of differences in intrapulmonary oxygen partial pressure (pO2) between patients with normal lung transplants and those with bronchiolitis obliterans syndrome (BOS). Using software developed in-house, oxygen-sensitive 3He-MRI datasets from patients with normal lung grafts (n = 8) and with BOS (n = 6) were evaluated quantitatively. Datasets were acqiured on a 1.5-T system using a spoiled gradient echo pulse sequence. Underlying diseases were pulmonary emphysema (n = 10 datasets) and fibrosis (n = 4). BOS status was verified by pulmonary function tests. Additionally, 3He-MRI was assessed blindedly for ventilation defects. Median intrapulmonary pO2 in patients with normal lung grafts was 146 mbar compared with 108 mbar in patients with BOS. Homogeneity of pO2 distribution was greater in normal grafts (standard deviation pO2 34 versus 43 mbar). Median oxygen decrease rate during breath hold was higher in unaffected patients (-1.75 mbar/s versus -0.38 mbar/s). Normal grafts showed fewer ventilation defects (5% versus 28%, medians). Oxygen-sensitive 3He-MRI appears capable of demonstrating differences of intrapulmonary pO2 between normal lung grafts and grafts affected by BOS. Oxygen-sensitive 3He-MRI may add helpful regional information to other diagnostic techniques for the assessment and follow-up of lung transplant recipients. [ABSTRACT FROM AUTHOR]

Magnetic resonance imaging of inhaled fluorinated inert gases ((19)F-MRI) such as sulfur hexafluoride (SF(6)) allows for analysis of ventilated air spaces. In this study, the possibility of using this technique to image lung function was assessed. For this, (19)F-MRI of inhaled SF(6) was compared with respiratory gas analysis, which is a global but reliable measure of alveolar gas fraction. Five anesthetized pigs underwent multiple-breath wash-in procedures with a gas mixture of 70% SF(6) and 30% oxygen. Two-dimensional (19)F-MRI and end-expiratory gas fraction analysis were performed after 4 to 24 inhaled breaths. Signal intensity of (19)F-MRI and end-expiratory SF(6) fraction were evaluated with respect to linear correlation and reproducibility. Time constants were estimated by both MRI and respiratory gas analysis data and compared for agreement. A good linear correlation between signal intensity and end-expiratory gas fraction was found (correlation coefficient 0.99+/-0.01). The data were reproducible (standard error of signal intensity 8% vs. that of gas fraction 5%) and the comparison of time constants yielded a sufficient agreement. According to the good linear correlation and the acceptable reproducibility, we suggest the (19)F-MRI to be a valuable tool for quantification of intrapulmonary SF(6) and hence lung function.

Purpose: To compare three different autocalibrated parallel acquisition techniques (PAT) for quantitative and semiquantitative myocardial perfusion imaging., Materials and Methods: Seven healthy volunteers underwent myocardial first-pass perfusion imaging at rest using an SR-TrueFISP pulse sequence without PAT and while using GRAPPA, mSENSE, and TSENSE. signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), normalized upslopes (NUS), and myocardial blood flow (MBF) were calculated. Artifacts, image noise, and overall image quality were qualitatively assessed. Furthermore, the relation between signal intensity (SI) and contrast medium (CM) concentration was determined in phantoms., Results: Using PAT the linear range of the SR-TrueFISP sequence was increased about 40%. All three PAT methods introduced significant loss in SNR and CNR. GRAPPA yielded slightly better values then mSENSE and TSENSE. Both SENSE techniques introduced significantly residual aliasing artifacts. Image noise was increased with all three PAT methods. However, overall image quality was reduced only with mSENSE. Even though GRAPPA yielded smaller NUS values than non-PAT, mSENSE, and TSENSE, no differences were found in MBF between all applied techniques., Conclusion: Quantitative and semiquantitative myocardial perfusion imaging can benefit from PAT due to shorter acquisition times and increased linearity of the pulse sequence. GRAPPA and TSENSE turned out to be well suited for quantitative myocardial perfusion imaging., ((c) 2008 Wiley-Liss, Inc.)

Objective: Dynamic ventilation (3)He-MRI is a new method to assess pulmonary gas inflow. As differing airway diameters throughout the ventilatory cycle can influence gas inflow this study intends to investigate the influence of volume and timing of a He gas bolus with respect to the beginning of the tidal volume on inspiratory gas distribution., Materials and Methods: An ultrafast 2-dimensional spoiled gradient echo sequence (temporal resolution 100 milliseconds) was used for dynamic ventilation (3)He-MRI of 11 anesthetized and mechanically ventilated pigs. The applied (3)He gas bolus was varied in volume between 100 and 200 mL. A 150-mL bolus was varied in its application time after the beginning of the tidal volume between 0 and 1200 milliseconds. Signal kinetics were evaluated using an in-house developed software after definition of parameters for the quantitative description of (3)He gas inflow., Results: The signal rise time (time interval between signal in the parenchyma reaches 10% and 90% of its maximum) was prolonged with increasing bolus volume. The parameter was shortened with increasing delay of (3)He application after the beginning of the tidal volume. Timing variation as well as volume variation showed no clear interrelation to the signal delay time 10 (time interval between signal in the trachea reaches 50% of its maximum and signal in the parenchyma reaches 10% of its maximum)., Conclusions: Dynamic ventilation (3)He-MRI is able to detect differences in bolus geometry performed by volume variation. Pulmonary gas inflow as investigated by dynamic ventilation (3)He-MRI tends to be accelerated by an increasing application delay of a (3)He gas bolus after the beginning of the tidal volume.

Purpose: To investigate the parallel acquisition technique sensitivity encoding incorporating temporal filtering (TSENSE) with three saturation-recovery (SR) prepared pulse sequences (SR turbo fast low-angle shot [SR-TurboFLASH], SR true fast imaging with steady precession [SR-TrueFISP], and SR-prepared segmented echo-planar-imaging [SR-segEPI]) for semiquantitative first-pass myocardial perfusion imaging., Materials and Methods: In blood- and tissue-equivalent phantoms the relationship between signal intensity (SI) and contrast-medium concentration was evaluated for the three pulse sequences. In volunteers, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and normalized upslopes (NUS) were calculated from signal-time curves (STC). Moreover, artifacts, image noise, and overall image quality were qualitatively evaluated., Results: Phantom data showed a 40% increased linear range of the relation between SI and contrast-medium concentration with TSENSE. In volunteers, TSENSE introduced significantly residual artifacts and loss in SNR and CNR. No differences were found for NUS values with TSENSE. SR-TrueFISP yielded highest SNR, CNR, and quality scores. However, in SR-True-FISP images, dark-banding artifacts were most pronounced. NUS values obtained with SR-TrueFISP were significantly higher and with SR-segEPI significantly lower than with SR-TurboFLASH., Conclusion: Semiquantitative myocardial perfusion imaging can significantly benefit from TSENSE due to shorter acquisition times and increased linearity of the pulse sequences. Among the three pulse sequences tested, SR-TrueFISP yielded best image quality. SR-segEPI proved to be an interesting alternative due to shorter acquisition times, higher linearity and fewer dark-banding artifacts., ((c) 2007 Wiley-Liss, Inc.)

This paper describes a study performed to evaluate the feasibility of using a 1.5-T whole-body magnetic resonance imaging (MRI) equipment, in combination with pharmacokinetic modeling, to obtain in vivo information about the morphology and perfusion of tarantulas (Eurypelma californicum). MRI was performed on three tarantulas using spin-echo sequences for morphological imaging and a rapid spoiled gradient-echo sequence for dynamic imaging during and after contrast medium (CM; Gd-DTPA) injection. Signal enhancement in dynamic measurements was evaluated with a pharmacokinetic two-compartment model. Spin-echo images showed morphological structures well. Dynamic images were of sufficient quality and allowed a model analysis of CM kinetics, which provides information about regional perfusion. In conclusion, morphological and dynamic contrast-enhanced MRI of tarantulas is feasible with a conventional clinical scanner. Studies of this kind are therefore possible without a dedicated high-field animal scanner.

Purpose: To study the influence of admixing inert buffer gases to laser-polarized (3)He in terms of resulting diffusion coefficients and the consequences for image contrast and resolution., Materials and Methods: The diffusion coefficient of (3)He was altered by admixing buffer gases of various molecular weights ((4)He, N(2), and SF(6)). The influence of the pulse sequence and the diffusion coefficient on the appearance of MRI of (laser-polarized) gases was analyzed by comparison of basic theoretical concepts with demonstrative experiments., Results: Excellent agreement between theoretical description and observed signal in simple gradient echoes was observed. A maximum signal gain can be predicted and was experimentally validated. Images acquired under such conditions revealed improved resolution. The nature and concentration of the admixed gas defines a structural threshold for the observed apparent diffusion coefficient (ADC) as demonstrated with diffusion-weighted MRI on a pig's lung flooded with suitable gas mixtures., Conclusion: A novel procedure is proposed to control the diffusion coefficient of gases in MRI by admixture of inert buffer gases. Their molecular mass and concentration enter as additional parameters into the equations that describe structural contrast. This allows for setting a structural threshold up to which structures contribute to the image. For MRI of the lung this enables images of very small structural elements (alveoli) only, or in the other extreme, all airways can be displayed with minimal signal loss due to diffusion., ((c) 2006 Wiley-Liss, Inc.)

Minimal scan times in rapid fluorine-19 MRI using sulfur hexafluoride (SF6) have been on the order of 10 s. Because of the very short T1 relaxation time of SF6 (T1 = 1.65 ms), high receiver bandwidths are necessary to allow for a high number of excitations. Since high bandwidths cause high levels of electronic noise, SNR per acquisition has been too low to further reduce scan time. The purpose of this study was to investigate whether scan times could be reduced using hexafluoroethane (C2F6), a gas with a longer T1 (T1 = 7.9 ms) at a relatively low bandwidth of 488 Hz/pixel. Gradient-echo images were acquired during and after completion of the wash-in of a 70% C2F6- 30% O2 mixture. Peak SNR values of 16 and 7.9 were observed for coronal projection images acquired within 2 s and 260 ms, respectively. These results demonstrate that subsecond imaging is feasible using C2F6., ((c) 2006 Wiley-Liss, Inc.)

Imaging methods to study the lung are traditionally based on x-ray or on radioactive contrast agents. Conventional magnetic resonance imaging (MRI) has only limited applications for lung imaging because of the low tissue density of protons concentration of hydrogen atoms, which are usually the basis for the imaging. The introduction of hyperpolarized noble gases as a contrast agent in MRI has opened new possibilities for lung diagnosis. The present paper describes this new technique. Diffusion-weighted MRI for assessment of the lung microstructure is presented here as an example of the new possibilities of functional imaging. Studies to determine the sensitivity of the diffusion measurement and regarding the correlation with traditionally established methods are also presented, along with results of the measurement of the reproducibility determined in a clinical pilot study on healthy volunteers and patients. Furthermore, a pilot measurement of the 3He diffusion tensor in the lung is presented.

The aim of this study was to validate oxygen-sensitive 3He-MRI in noninvasive determination of the regional, two- and three-dimensional distribution of oxygen partial pressure. In a gas-filled elastic silicon ventilation bag used as a lung phantom, oxygen sensitive two- and three-dimensional 3He-MRI measurements were performed at different oxygen concentrations which had been equilibrated in a range of normal and pathologic values. The oxygen partial pressure distribution was determined from 3He-MRI using newly developed software allowing for mapping of oxygen partial pressure. The reference bulk oxygen partial pressure inside the phantom was measured by conventional respiratory gas analysis. In two-dimensional measurements, image-based and gas-analysis results correlated with r=0.98; in three-dimensional measurements the between-methods correlation coefficient was r=0.89. The signal-to-noise ratio of three-dimensional measurements was about half of that of two-dimensional measurements and became critical (below 3) in some data sets. Oxygen-sensitive 3He-MRI allows for noninvasive determination of the two- and three-dimensional distribution of oxygen partial pressure in gas-filled airspaces.

Magnetic resonance imaging of the apparent diffusion coefficient (ADC) of hyperpolarized Helium-3 is a new technique for probing pulmonary microstructure in vivo. The aim of this study was the assessment of potential sources of systematic errors of the ADC measurement. The influence of macroscopic motion was determined by measurements at two different delays after initiating the breath-hold, and before and after cardiac arrest. An intercentre comparison was performed in two age- and lung function-matched groups of lung-healthy volunteers at two research sites. Moreover, measurements of diffusion anisotropy were performed. We found no dependency of the ADC as a function of the delay after stop of inspiration. The influence of cardiac motion was less than 10%. In the intercentre comparison study, an excellent agreement between the two sites was found. First measurements of the diffusion tensor of intrapulmonary Helium-3 are shown.

Lung imaging is traditionally done using X-ray-based methods, since MRI is limited by low proton density as well as inherent magnetic field inhomogeneities of the lung tissue. After introduction of MRI using hyperpolarized noble gases, a totally new field of MRI of the chest has rapidly evolved. These techniques reveal new functional information of the lungs, which could not be obtained before. The first part of this review describes the underlying MR technology explaining distribution of static ventilation, dynamic distribution of ventilation, lung microstructure (apparent diffusion coefficient [ADC]), measurement of oxygen partial pressure (pO(2)), and safety. The clinical potential is afterwards demonstrated in the second part. Therefore, the effort in normal lungs and the mainly focused diseases chronic obstructive pulmonary disease (COPD), smoker's lung, cystic fibrosis, asthma, lung transplantation, and pulmonary embolism are reported.

Purpose: To determine the reproducibility of several parameters of the ADC measurement by calculating the scan-to-scan intrasubject variability., Materials and Methods: Measurements were performed using a gradient-echo sequence with a bipolar gradient for diffusion weighting (b=3.89 sec/cm2). Five patients with pulmonary emphysema, and six healthy-lung volunteers were included in the study. Images were acquired after inspiration of 3He during a single inspiratory breath-hold. To assess the reproducibility, the measurement was performed twice (time between measurements=20 minutes) without repositioning the subjects. Analysis was performed on the basis of region-of-interest (ROI) analysis and global lung ADC histograms., Results: The mean ADC of a ROI varied by 5.1% between two measurements for volunteers and by 6.1% for patients. In the global evaluation, the 75th percentile demonstrated the best reproducibility (2%), while other parameters showed variations up to 12%. Only the variation of the standard deviation (SD) and the measure of homogeneity of the ADC map showed a significant difference between patients and volunteers., Conclusion: Diffusion-weighted imaging (DWI) is a well-reproducible method for assessing the lung microstructure., (Copyright (c) 2005 Wiley-Liss, Inc.)

Purpose: Investigation and statistical evaluation of "Self-Organizing Maps," a special type of neural networks in the field of artificial intelligence, classifying contrast enhancing lesions in dynamic MR-mammography., Material and Methods: 176 investigations with proven histology after core biopsy or operation were randomly divided into two groups. Several Self-Organizing Maps were trained by investigations of the first group to detect and classify contrast enhancing lesions in dynamic MR-mammography. Each single pixel's signal/time curve of all patients within the second group was analyzed by the Self-Organizing Maps. The likelihood of malignancy was visualized by color overlays on the MR-images. At last assessment of contrast-enhancing lesions by each different network was rated visually and evaluated statistically., Results: A well balanced neural network achieved a sensitivity of 90.5 % and a specificity of 72.2 % in predicting malignancy of 88 enhancing lesions. Detailed analysis of false-positive results revealed that every second fibroadenoma showed a "typical malignant" signal/time curve without any chance to differentiate between fibroadenomas and malignant tissue regarding contrast enhancement alone; but this special group of lesions was represented by a well-defined area of the Self-Organizing Map., Discussion: Self-Organizing Maps are capable of classifying a dynamic signal/time curve as "typical benign" or "typical malignant." Therefore, they can be used as second opinion. In view of the now known localization of fibroadenomas enhancing like malignant tumors at the Self-Organizing Map, these lesions could be passed to further analysis by additional post-processing elements (e.g., based on T2-weighted series or morphology analysis) in the future.

Current imaging methods of the lung concentrate on morphology as well as on the depiction of the pulmonary parenchyma. The need of an advanced and more subtle imaging technology compared to conventional radiography is met by computed topography as the method of choice. Nevertheless, computed tomography yields very limited functional information. This is to be derived from arterial blood gas analysis, spirometry and body plethysmography. These methods, however, lack the scope for regional allocation of any pathology. Magnetic resonance imaging of the lung has been advanced by the use of hyperpolarised (3)Helium as an inhaled gaseous contrast agent. The inhalation of the gas provides functional data by distribution, diffusion and relaxation of its hyperpolarised state. Because anatomical landmarks of the lung can be visualised as well, functional information can be linked with regional information. Furthermore, the method provides high spatial and temporal resolution and lacks the potential side-effects of ionising radiation. Four different modalities have been established: 1. Spin density imaging studies the distribution of gas, normally after a single inhalation of contrast gas in inspiratory breath hold. 2. Dynamic cine imaging studies the distribution of gas with respect to regional time constants of pulmonary gas inflow. 3. Diffusion weighted imaging can exhibit the presence and severity of pulmonary airspace enlargement, as in pulmonary emphysema. 4. Oxygen sensitive imaging displays intrapulmonary oxygen partial pressure and its distribution. Currently, the method is limited by comparably high costs and limited availability. As there have been recent developments which might bring this modality closer to clinical use, this review article will comprise the methodology as well as the current state of the art and standard of knowledge of magnetic resonance imaging of the lung using hyperpolarised (3)Helium.

Qualitative and semiquantitative contrast-enhanced (CE) dynamic perfusion MRI techniques are established as noninvasive diagnostic means of assessing coronary artery disease. However, to date quantification of myocardial blood flow (MBF) has not reached the same acceptance as MBF quantification with nuclear techniques. To validate quantification of MBF at rest using the extracellular contrast agent (CA) Gd-DTPA, we performed an animal study in a pig model of acute myocardial ischemia. We quantified MBF from MRI data with a mathematical model (MMID4) of the underlying vasculature. These MBF results were subsequently compared with the results from fluorescent microspheres. The study showed a correlation of r = 0.66 between MBF estimates obtained with MRI and those obtained with fluorescent microspheres. The correlation for ischemic and nonischemic myocardium was r = 0.86 and r = 0.47, respectively. In conclusion, quantification of resting MBF using MMID4 is a valid method under conditions of acute myocardial ischemia., (Copyright 2005 Wiley-Liss, Inc.)

Purpose: Little is known about the dispersion of a defined contrast bolus during its passage through the heart and pulmonary vasculature. The purpose of this study was to analyze factors influencing a defined contrast bolus for ce-MRA of thoracic vessels., Materials and Methods: For analysis of bolus geometry, an ECG-gated saturation-recovery Turbo-Flash sequence with a TI of 20 msec was used. It was acquired axially at the level of the pulmonary trunc, so that with one data acquisition a curve analysis was possible in the ascending and descending aorta, and in the pulmonary trunc. Twenty-nine patients received 3 ml of Gd-DTPA diluted with saline to a total of 20 ml. Contrast injection was done using a MR compatible power injector with injection rates varying between 1, 2 and 4 ml/sec. Each injection was followed by a saline flush of 20 ml with the same injection rate and mode. Cardiac function was assessed by cine imaging, and phase contrast measurements. After normalization to baseline signal intensity (SI), bolus curves were fitted using a gamma-variate fit and peak signal intensity (peak SI), time-to-peak (TP), upslope, mean transit time (MTT) and dispersion of the contrast bolus were calculated. Furthermore, T (1) and [Gd] in the experimental setting were calculated as follows: T (1) = T (1 o)/ ln [SI/SI (0)], and [Gd] (exp) = [1/T (1) - 1/T (1 o)]/ R (1.) They were then extrapolated [Gd] to clinical conditions by [Gd] (clin) = [Gd] (exp) . 10/1.5, and minimal blood T (1) by T (1)(clin) = 1 / [1/T (1 o) + R (1) [Gd] (clin)]., Results: With increasing injection rate, there was a significant decrease (p < 0.001) of MTT in all target vessels. However, this decrease was not linear: a 4-fold increase in injection rate lead to a 2-fold decrease in MTT e. g. in the ascending aorta. MTT was significantly shorter in the pulmonary trunc compared with that in the ascending and descending aorta (p < 0.001), regardless of injection rate (p < 0.001). Vice versa, dispersion of the contrast bolus was significantly lower in the pulmonary trunc, and increased with higher injection rates. There was no clinically relevant difference in minimal blood T (1) between the different target vessels, for clinical conditions extrapolated values ranged between 20 und 79 msec. Heart function parameters only had a minor influence of bolus curve parameters., Conclusion: Analysis of bolus geometry enables determination of transit times of a defined contrast bolus through a defined target vessel in the thoracic cavity. Bolus geometry is mainly determined by injection parameters, cardiac function is of minor importance. Dispersion of contrast bolus and MTT increase from the pulmonary trunc to the ascending aorta. The knowledge of these facts may help optimizing of injection parameters and the total amount of contrast agent for contrast-enhanced MRA of thoracic vessels.