Visualization of alveolar recruitment in a porcine model of unilateral lung lavage using 3He-MRI.

BACKGROUND: In the acute respiratory distress syndrome potentially recruitable lung volume is currently discussed. (3)He-magnetic resonance imaging ((3)He-MRI) offers the possibility to visualize alveolar recruitment directly. METHODS: With the approval of the state animal care committee, unilateral lung damage was induced in seven anesthetized pigs by saline lavage of the right lungs. The left lung served as an intraindividual control (healthy lung). Unilateral lung damage was confirmed by conventional proton MRI and spiral-CT scanning. The total aerated lung volume was determined both at a positive end-expiratory pressure (PEEP) of 0 and 10 mbar from three-dimensionally reconstructed (3)He images, both for healthy and damaged lungs. The fractional increase of aerated volume in damaged and healthy lungs, followed by a PEEP increase from 0 to 10 mbar, was compared. RESULTS: Aerated gas space was visualized with a high spatial resolution in the three-dimensionally reconstructed (3)He-MR images, and aeration defects in the lavaged lung matched the regional distribution of atelectasis in proton MRI. After recruitment and PEEP increase, the aerated volume increased significantly both in healthy lungs from 415 ml [270-445] (median [min-max]) to 481 ml [347-523] and in lavaged lungs from 264 ml [71-424] to 424 ml [129-520]. The fractional increase in lavaged lungs was significantly larger than that in healthy lungs (healthy: 17% [11-38] vs. lavage: 42% [14-90] (P=0.031). CONCLUSION: The (3)He-MRI signal might offer an experimental approach to discriminate atelectatic vs. poor aerated lung areas in a lung damage animal model. Our results confirm the presence of potential recruitable lung volume by either alveolar collapse or alveolar flooding, in accordance with previous reports by computed tomography.

[Functional imaging of the lung using a gaseous contrast agent: (3)helium-magnetic resonance imaging]. / Funktionelle Bildgebung der Lunge mit gasförmigem Kontrastmittel: (3)Helium-Magnetresonanztomographie.

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.

[Systematic analysis of the geometry of a defined contrast medium bolus--implications for contrast enhanced 3D MR-angiography of thoracic vessels]. / Systematische Analyse der Geometrie eines definierten Kontrastmittelbolus -- Implikationen für die kontrastmittelverstärkte 3D-MR-Angiographie thorakaler Gefässe.

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.

[Self-organizing neural networks for automatic detection and classification of contrast (media) enhancement of lesions in dynamic MR-mammography]. / Selbstorganisierende neuronale Netze zur automatischen Detektion und Klassifikation von Kontrast(mittel)-verstärkten Läsionen in der dynamischen MR-Mammographie.

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.

Cerebral blood flow and cerebrovascular reserve capacity: estimation by dynamic magnetic resonance imaging.

We have developed a new method for estimation of regional CBF (rCBF) and cerebrovascular reserve capacity on a pixel-by-pixel basis by means of dynamic magnetic resonance imaging (MRI). Thirteen healthy volunteers, 8 patients with occlusion and/or high grade stenosis of the internal carotid artery (ICA), and 2 patients with acute stroke underwent dynamic susceptibility-weighted contrast enhanced MRI. Using principles of indicator dilution theory and deconvolution analysis, maps of rCBF, regional cerebral blood volume, and of the mean transit time (MTT) were calculated. In patients with ICA occlusion/stenosis, cerebrovascular reserve capacity was assessed by the rCBF increase after acetazolamide stimulation. Mean gray and white matter rCBF values in normals were 67.1 and 23.7 mL x 100 g(-1) x min(-1), respectively. Before acetazolamide stimulation, six of eight patients with ICA occlusions showed decreased rCBF values; and in seven patients increased MTT values were observed in tissue ipsilateral to the occlusion. After acetazolamide stimulation, decreased cerebrovascular reserve capacity was observed in five of eight patients with ICA occlusion. In acute stroke, rCBF in the central core of ischemia was less than 8 mL x 100 g(-1) x min(-1). In peri-infarct tissue, rCBF and MTT were higher than in unaffected tissue but rCBF was normal. Dynamic MRI provides important clinical information on the hemodynamic state of brain tissue in patients with occlusive cerebrovascular disease or acute stroke.

Analysis of intrapulmonary O(2) concentration by MR imaging of inhaled hyperpolarized helium-3.

Inhalation of hyperpolarized (3)He allows magnetic resonance imaging (MRI) of ventilated airspaces. (3)He hyperpolarization decays more rapidly when interacting with paramagnetic O(2). We describe a method for in vivo determination of intrapulmonary O(2) concentrations ([O(2)]) based on MRI analysis of the fate of measured amounts of inhaled hyperpolarized (3)He in imaged regions of the lung. Anesthetized pigs underwent controlled normoventilation in a 1.5-T MRI unit. The inspired O(2) fraction was varied to achieve different end-tidal [O(2)] fractions (FET(O(2))). With the use of a specifically designed applicator, (3)He (100 ml, 35-45% polarized) was administered at a predefined time within single tidal volumes. During subsequent inspiratory apnea, serial two-dimensional images of airways and lungs were acquired. At least once in each animal studied, the radio-frequency excitation used for imaging was doubled at constant FET(O(2)). Signal intensity measurements in regions of interest of the animals' lungs (volume range, 54-294 cm(3)), taken at two different radio-frequency excitations, permitted calculation of [O(2)] in these regions of interest. The [O(2)] fractions in the regions of interest correlated closely with FET(O(2)) (R = 0.879; P < 0.0001). O(2)-sensitive (3)He-MRI may allow noninvasive study of regional distribution of ventilation and alveolar PO(2) in the lung.

Quantitative MR temperature monitoring of high-intensity focused ultrasound therapy.

A new quantitative method has been developed for real-time mapping of temperature changes induced by high intensity focused ultrasound (HIFU). It is based on the temperature dependence of the T1 relaxation time and the equilibrium magnetization. To calibrate the temperature measurement, the functional relationship between T1 and temperature was examined in different samples of porcine muscle and fatty tissue. The method was validated by a comparison of calculated temperature maps with fiber-optic measurements in heated muscle tissue. The experiment showed that the accuracy of the MR method for temperature measurements is better than 1 degree C. Since the acquisition time of the employed MR sequence takes only 3 s per slice and the calculation of the temperature map can be performed within seconds, the imaging technique works nearly in real-time. The temperature measurement could be realized during HIFU showing no disturbances by ultrasound sonication. In comparison to other MR approaches, the advantages of the introduced method lie in a sufficient accuracy and time resolution combined with a reasonable robustness against motion as well as the feasibility for temperature monitoring in fatty tissues.

Hyperpolarised gases in magnetic resonance: a new tool for functional imaging of the lung.

In magnetic resonance imaging (MRI), nuclear spins are the source of the image signal. In the lung, low-proton spin density in alveolar gas and abundant gas-tissue interfaces substantially impair conventional native 1H-MRI. Spin polarisation can be increased in two non-radioactive noble gas isotopes, 3He and 129Xe, by exposure to polarised laser light. When inhaled, such "magnetized" gases provide high-intensity MR images of the pulmonary airspaces. Thus, hyperpolarised gas (HPG) MRI opens up new routes to a) morphologic imaging of airways and alveolar spaces, and b) analysis of the intrapulmonary distribution of inhaled aliquots of these tracer gases; c) diffusion-sensitive MRI-techniques allow mapping of the "apparent diffusion coefficient" (ADC) of 3He within lung airspaces, where ADC is physically related to local bronchoalveolar dimensions; d) also, 3He magnetisation decays in an oxygen-containing atmosphere at a rate proportional to ambient PO2. This property allows image-based determination of regional broncho-alveolar PO2 and its decrease during a breathhold. Currently, these modalities of functional lung imaging are being assessed by several European and American research groups in animal models, human volunteers and patients. First results show good imaging quality with excellent spatial and unprecedented temporal resolution, and attest to the reproducibility, feasibility and safety of the technique. Regionally impaired ventilation of both structural and functional origin is detected with high sensitivity, e.g. in smokers, asthmatics, patients with COPD or after lung transplantation. Studies into regional ADC and PO2 measurement demonstrate good agreement with reference methods and physiological predictions. The present limitations of HPG-MRI include the HPG production rate and the US and EU health authorities' still pending final approval for clinical use.

[Combination of low and high resolution T1-weighted sequences for improved evaluation of morphologic criteria in dynamic contrast enhanced MRI of the breast]. / Eine Kombination niedrig und hochauflösender dynamischer T1-gewichteter Sequenzen zur besseren Beurteilung der Morphologie Kontrastmittel aufnehmender Läsionen in der MRT der weiblichen Brust.

PURPOSE: Presentation of a new protocol for simultaneous acquisition of both low and high resolution T 1 -weighted images of breast lesions for dynamic contrast-enhanced MR mammography. Demonstration of possible diagnostic improvement with representative measurements in patients with suspected breast cancer by adding morphologic parameters from high resolution sequences to the analysis of the signal-time curve. MATERIALS AND METHODS: Dynamic MR imaging was performed with a 1.5 T system (Magnetom SONATA, Siemens Medical Systems, Germany) and the manufacturer's double-breast coil. Coronal T 1 -weighted 3D FLASH sequences (spatial resolution 1.25 x 1.25 mm 2; slice thickness 1.7 mm) were acquired once before and five times after administration of contrast medium (Gd-DTPA, 0.15 mmol/kg) injection. In addition, a high resolution T 1 -weighted 3D-FLASH sequence (spatial resolution, 0.63 x 0.63 mm 2) was obtained before administration of contrast medium and after the third post-contrast low-resolution sequence. Except for the acquisition matrix, all imaging parameters were identical for both 3D pulse sequences. To assure comparison of the measured signal intensities for both T 1 -weighted sequences, calibrating phantom measurements were performed using a dilution series of Gd-DTPA. RESULTS: Phantom measurements demonstrated similar signal intensities and enhancement pattern for both sequences. A combined protocol consisting of both pulse sequences can be employed and does not interfere with the signal-time curve analysis. By measuring one high resolution sequence 3:18 minutes after administration of contrast medium, morphologic features can be evaluated without interference from barely enhancing surrounding tissue. The overall study time is not increased. The improved spatial resolution slightly increases the severity of motion artifacts. CONCLUSION: The new protocol is a clever way to improve the measurement of morphologic features without relevant loss of dynamic information. It is superior to converting the entire investigation to high resolution sequences and does not add any costs by not extending or duplicating the investigation. How much the new protocol can improve the specificity or sensitivity of MR-mammography is currently investigated on a larger patient group.

[Preliminary results of coronary artery examination using a 3D-navigator sequence on a high performance MR system]. / Erfahrungen mit einer 3D-Navigatorsequenz zur Koronargefässdarstellung an einem Hochleistungs-MR-System.

PURPOSE: To evaluate MR coronary angiography using a three-dimensional navigator echo sequence on a MR scanner with a high performance gradient system. MATERIAL AND METHODS: Five healthy volunteers were examined with a 1.5 Tesla MR system, using a high performance prototype gradient system (peak amplitude 50 mT/m, rising time 600 mus). For imaging, a navigated gradient-echo pulse sequence with an in-plane resolution between 0.63 x 0.63 and 0.78 x 0.78 mm2 was used. Per patient two overlapping slabs were acquired. The number of visualized coronary artery segments was estimated (AHA classification). In addition, signal-to-noise measurements were performed in the ascending aorta at the level of the proximal right and left coronary arteries. RESULTS: In all volunteers the left main, the right coronary artery up to segment 3, the LAD up to segment 8 and the RCX with segment 11 and 13 were clearly visualized. The average signal-to-noise value at the level of the right coronary artery was 11.4 +/- 5.0, at the level of the left coronary artery 12.3 +/- 4.5. One volunteer was measured with an in-place resolution of 0.63 x 0.63 mm2. This resulted in a too low signal-to-noise ratio so that an adequate assessment of coronary arteries was no longer possible. CONCLUSION: 3D-MR coronary angiography using the navigator technique is limited by the signal-to-noise ratio.

[Prospective feasibility study of chest X-ray vs. thoracic MRI in breath-hold technique at an open low-field scanner]. / Prospektive Machbarkeitsstudie zum Vergleich von Röntgenübersichtsaufnahme und Thorax-MRT in Atemanhaltetechnik am offenen Niederfeldgerät.

PURPOSE: MR investigations using a breath-hold sequence at an open low-field MR had to be compared to chest X-rays in patients with a wide spectrum of cardio-thoracic pathologies. MATERIAL AND METHODS: 114 patients and three volunteers who actually received a chest X-ray due to different indications underwent triplanar breath-hold (17 - 20 s) True-FISP sequence using a 0.2 T low-field MR (Siemens Magnetom Open, TR/TE/alpha: 7.3/3.5/80 degrees, SD: 10 mm, Pixel: 2.81 x 1.41 mm) a mean of 5.1 (+/- 8.2) days later. RESULTS: Signal-to-noise ratio as basics for pattern recognition was 3.2 in nodule, 5.0 in infiltration, and 12.0 in effusion, and therefore True-FISP is usable for the detection of these findings. MRI demonstrated nodules (89 % vs. 57 %), infiltration (81 % vs. 71 %), pleural effusions (86 % vs. 75 %), pericardial effusions (100 % vs. 21 %) and pulmonary congestion (90 % vs. 80 %) clearly more frequently compared to chest X-ray. DISCUSSION: MRI of the lung has been implemented successfully at an open low-field MR system. Diagnostic safety and accuracy are at least comparable to those of chest X-ray. The lack of superimposition led to a major improvement in the detection of pericardial effusions and nodules, and an increase in identification of infiltration, pleural effusion, and pulmonary congestion.

[A software program for quantitative analysis of alveolar oxygen partial pressure (p(A)O(2)) with oxygen-sensitive (3)He-MRI]. / Ein Auswerteprogramm zur quantitativen Analyse von Messungen des alveolären Sauerstoffpartialdrucks (p(A)O(2)) mit der sauerstoffsensitiven (3)He-MR-Tomographie.

PURPOSE: To develop a software tool for quantitative analysis of alveolar oxygen partial pressure (p(A)O(2)) as well as its time course during apnea. MATERIAL AND METHODS: T (1)-relaxation times of hyperpolarized (3)He are reduced by paramagnetic oxygen rendering (3)He-MRI sensitive to oxygen and thus allowing the assessment of the local oxygen partial pressure in the pulmonary airspaces. Oxygen-related relaxation and loss of polarization by RF-excitation can be discriminated by acquiring two image series with varying interscan delay and/or flip angles. Software was developed to calculate the p(A)O(2) and the decay rate in user-defined regions of interest (ROIs) automatically. Moreover, parameter maps can be calculated. In addition to the analysis of 2-dimensional data sets, the software allows the evaluation of 3-dimensional measurements for the first time. Artifacts due to lung motion were reduced by implementing a motion correction algorithm. RESULTS: The software was successfully applied to data sets from healthy volunteers and from patients with various lung diseases. The parameter maps demonstrated a more homogeneous distribution of p(A)O(2) for the volunteers than for the patients. A regional increase in p(A)O(2) was found in a few patients. CONCLUSION: The described software allows the absolute quantification of p(A)O(2) as well as its variation over time. In the future, therefore, the software may gain importance for detecting mismatches between ventilation and perfusion, e. g., in patients with pulmonary embolism or chronic obstructive lung diseases.

[A software tool for analysis and quantification of regional pulmonary ventilation using dynamic hyperpolarised-(3)He-MRI]. / Ein Auswerteprogramm zur quantitativen Untersuchung der Lungenventilation mittels dynamischer MRT von hochpolarisiertem.

PURPOSE: (3)He-MRI is able to visualize the regional distribution of lung ventilation with a temporal and spatial resolution so far unmatched by any other technique. The aim of the study was the development of a new software tool for quantification of dynamic ventilation parameters in absolute physical units. MATERIALS AND METHODS: During continuous breathing, a bolus of hyperpolarized (3)He (300 ml) was applied at inspiration and a series of 168 coronal projection images simultaneously acquired using a 2D FLASH-sequence. Postprocessing software was developed to analyze the (3)He distribution in the lung. After correction for lung motion, several ventilation parameters (rise time, delay time, (3)He amount and (3)He peak flow) were calculated. Due to normalization of signal intensities, these parameters are presented in absolute physical units. The data sets were analyzed on a ROI basis as well as on a pixel-by-pixel basis. RESULTS: Using the developed software, the measurements were analyzed in 6 lung-healthy volunteers, in one patient after lung transplantation, and in one patient with lung emphysema. The volunteers' parameter maps of the pixel-based analysis showed an almost homogeneous distribution of the ventilation parameters within the lung. In the parameter maps of both patients, regions with poor ventilation were observed. CONCLUSION: The developed software permits an objective and quantitative analysis of regional lung ventilation in absolute physical units. The clinical significance of the parameters, however, has to be determined in larger clinical studies. The software may become valuable in grading and following pulmonary function as well as in monitoring any therapy.

[Cryotherapy of malignant tumors: studies with MRI in an animal experiment and comparison with morphological changes]. / Kryotherapie maligner Tumoren: Untersuchungen mittels MRT im Tierexperiment und Vergleich mit morphologischen Veränderungen.

PURPOSE: Aim of our study was to investigate the efficacy of 7 F cryoprobes for percutaneous use morpho- and histologically, to examine the role of apoptosis after cryotherapy, and to compare contrast-enhanced MRI with histopathological findings at different time intervals in a tumor-mouse model. METHODS: Percutaneous cryotherapy was performed in 15 immunocompromised nude mice with subcutaneously implanted tumors using the non-small-cell lung cancer cell line Lu 1. In group a) 7 mice were sacrificed after definite time intervals and histological examinations were done for evaluation of necrosis and apoptosis (HE; TUNEL assay); 2 mice are in long-term follow-up. In group b) in 6 mice tumor destruction and perfusion before and after freezing were investigated with native and contrast-enhanced MR imaging (T1- and T2-weighted spin-echo) and compared with histopathological findings. Histological control were done in 2 untreated mice. RESULTS: We observed fast tumor-reduction within two weeks (ca. 50%). On long-term follow-up (> 6 months) no recurrence has been noticed so far. Tumors were well vascularized prior to treatment and did not-show contrast enhancement an any time after cryotherapy. A narrow contrast-enhanced zone was seen on the tumor border subcutaneously as a sign of peripheral hyperemia and central vascular stasis after cryotherapy. On histology there was evidence of both apoptosis and necrosis. CONCLUSION: We have established a tumor-mouse model for further investigations. Two minutes freezing of a 2-cm tumor in the mouse model is sufficient for tumor ablation with scarred healing. Apoptosis may play a role in cryotherapy of experimental tumors. Contrast-enhanced MRI is suitable for the estimation of the cryolasion.

[Reformation as proposed solution for the problem of sectioning different levels with 3He-MRT and HR-CT of the chest]. / Reformatierungen als Lösungsansatz für die Problematik der unterschiedlichen Schichtführung beim Vergleich von 3He-MRT und HR-CT der Lunge.

PURPOSE: 3He-MRI of the lung has been shown to be a sensitive method for functional imaging of the lung. A previous study compared 3He-MRI (coronal planes) with CT (transverse planes) by looking for ventilation defects and their pathomorphologic correlation. Anatomic structures, such as lobar fissures and hilar vessels, were used for orientation, but the reliable assignment of ventilation defects to lung segments is problematic. The present work compares multiplanar reformations of 3He-MRI and HR-CT, which were generated from planes determined by the respective method, and investigates their suitability as a solution of this problem. MATERIALS AND METHODS: A total of 16 data sets taken from 15 patients with unilateral lung transplantation and one patient with lung emphysema were retrospectively evaluated. Transverse planes of 3He-MRI and coronal planes of HR-CT were reformatted on an external workstation and images evaluated by two readers in consensus. The evaluation searched for ventilation defects on 3He-MRI and their corresponding defects on HR-CT. The defects were related to anatomic structures, with hilar vessels and tracheobronchial tree selected for 3He-MRI reformations and lobar fissures for HR-CT reformations. RESULTS: All cases were successfully reformatted and all ventilation defects were correctly assigned to anatomic structures. On HR-CT reformations, the lobar fissures were partially visible in 12 of 16 cases and completely visible in the remaining 4 cases. Since reformation compromises the spatial resolution, the reformatted images should be evaluated together with the source images. CONCLUSION: Looking at HR-CT and 3He-MRI images and their reformations enables the detection of ventilation defects and their assignment to lung segments, facilitating the correlation of ventilation defects with a pathomorphologic pattern on HR-CT.

[Possible mutagenic effects of magnetic fields]. / Untersuchung eines möglichen mutagenen Potenzials von Magnetfeldern.

AIM: To assess the potential mutagenic effect of static magnetic fields of 1.5 T and 7 T, gradient fields and high frequency magnetic fields. METHOD: We used the Salmonella mutagenicity test (Ames test), which detects mutations in a gene of a histidine-requiring (his-) strain to produce a histidine-independent (his+) strain, Exposure to a static magnetic field of 1.5 T and 7.2 T, in a bipolar magnetic gradient and additionally in a high frequency field took place with and without known genotoxic chemicals. RESULTS: No differences in the number of revertants between the bacterial strains of exposed and control cells could be detected and the exposure with known genotoxic chemicals showed no significant difference in mutagenicity. CONCLUSION: In conclusion our data do not provide evidence that exposure to a static magnetic field exerts effects on the mutagenicity in our standard tester strains and whether the exposure took place in a diagnostic 1.5 T MR scanner which is used in the clinical routine or at 7.2 T which is a much stronger field made no difference. Also an exposure in a gradient field or in a high frequency field did not show any alteration in the number of revertants.

[Perfusion MR imaging of the heart with TrueFISP]. / MR-Perfusionsbildgebung des Herzens mit TrueFISP.

OBJECTIVE: Development and test of a saturation-recovery TrueFISP (SR-Trufi) pulse sequence for myocardial perfusion MR imaging (MRI) using improved gradient hardware. MATERIAL AND METHODS: Measurements were performed on a 1.5 T scanner with prototype gradients (50 mT/m, minimum rise time 300 microseconds). T1-weighted first-pass MRI of Gd-DTPA (0.025 mumol/kg) kinetics in the myocardium was performed using an SR-Trufi pulse sequence (TR/TE/alpha = 2.6 ms/1.4 ms/55 degrees) with a saturation preparation of TD = 30 ms before the TrueFISP readout. Measurements were performed in volunteers (n = 4) and in a pig model of chronic ischemia (n = 1). RESULTS: In phantoms, the signal intensity was linear with contrast concentration up to 0.9 mmol/kg Gd-DTPA. MR images obtained with SR-Trufi had a good image quality and high spatial resolution of 2.1 mm x 2.1 mm. Differences of the contrast agent's kinetics between a subendocardial perfusion deficit and neighboring myocardium were well visible on both MR images and signal-time curves derived from the region-of-interest analysis. CONCLUSION: SR-Trufi appears to be an interesting new technique for the assessment of myocardial microcirculation using dedicated cardiovascular MR systems.

[19F-MRT of pulmonary ventilation in the breath-hold technic using SF6 gas]. / 19F-MRT der Lungenventilation in Atemanhaltetechnik mittels SF6-Gas.

OBJECTIVE: Development of a method to analyze lung ventilation by 19F-magnetic resonance imaging (MRI) of inspired SF6 gas during breath hold. MATERIAL AND METHODS: Measurements were performed with a Siemens Magnetom Vision 1.5 T scanner using the conventional gradient overdrive. Coronal images of the lung were acquired using ultrafast gradient-echo pulse sequences with TR/TE/alpha = 1.4 ms/0.48 ms/40 degrees without slice selection. With NEX = 200 averages and MA = 32 x 64 raw data matrix, the acquisition time was 9 s/image. Higher spatial resolution of 4.7 x 6.3 x 15 mm3 was obtained with a three-dimensional pulse sequence (TR/TE/alpha = 1.6 ms/0.48 ms/65 degrees, NEX = 20) running for 49 s. Measurements wer performed in three anesthetized and ventilated pigs (18 kg). RESULTS: A nearly linear relation between SF6 concentration and 19F signal intensity was observed. The signal-to-noise ratio in images obtained without slice selection was 30.9, with slice selection it was 14.9. No differences between SF6 distribution to both lungs were observed in the animals. CONCLUSION: Breath-hold MRI of SF6 gas distribution in the lung was demonstrated for the first time. The low spin-density was compensated for by highly repetitive signal averaging. Breath-hold 19F-MR imaging of ventilated airspaces to assess SF6 distribution in the human lung appears to be an interesting new method, which can be implemented with little technical efforts, and does not rely on radioactive isotopes.

[Evaluation of myocardial perfusion reserve in patients with CAD using contrast-enhanced MRI: a comparison between semiquantitative and quantitative methods]. / Bestimmung der myokardialen Perfusionsreserve bei KHK-Patienten mit der kontrastmittelverstärkten MRT: Ein Vergleich zwischen semiquantitativer und quantitativer Auswertung.

OBJECTIVE: Comparison between two semiquantitative methods and a quantitative evaluation of myocardial blood flow (MBF) for assessment of myocardial perfusion reserve (MPR) in patients with CAD. MATERIAL AND METHODS: 9 patients with coronary stenoses > 50 % were examined with an ECG-gated Saturation Recovery Turbo FLASH sequence by using Gd-DTPA as contrast agent (CA). The entive measurements were performed both during rest and hyperemia induced by adenosine. The up-slopes of the signal-time S(t) curves in the myocardium and left ventricular (LV) cavity were evaluated by a linear fit. MPR was calculated from the original up-slopes of the myocardial S(t) curves and from the up-slopes, which were normalized to the up-slopes of the LV S(t) curves, respectively. For quantification of MBF values, the mathematical model MMID 4 was used and MPR was evaluated from the MBF values. RESULTS: With all tested methods, MPR was reduced in myocardial regions subtended by arteries with stenoses >/= 70 % compared with remote regions. With MMID 4 and the normalized up-slope method, differences between severe ischemic and remote regions were statistically significant. CONCLUSION: The up-slope method with normalization and quantification with MMID 4 are more sensitive methods to differentiate between remote and ischemic myocardium than the up-slope method without normalization.

[Ultrafast MRI of lung ventilation using hyperpolarized helium-3]. / Ultraschnelle MRT der Lungenventilation mittels hochpolarisiertem Helium-3.

OBJECTIVE: Assessment of the temporal and spatial dynamics of hyperpolarized Helium-3 (3He) distribution in the lung with ultrafast gradient-echo magnetic-resonance imaging. MATERIAL AND METHODS: Coronal images of the lung were acquired using ultrafast gradient-echo pulse sequences with TR/TE = 3.3 ms/1.3 ms (slice thickness, 40 mm) and TR/TE = 2.0 ms/0.7 ms (without slice selection). A series of 80 or 160 projection images was obtained with 210 ms or 130 ms temporal resolution, respectively. Imaging was performed during several respiratory cycles after application of a single bolus of 300 mL hyperpolarized 3He. Measurements were performed in six healthy volunteers (spontaneous breathing). RESULTS: Different phases of in- and expiration could be visualized. During the course of consecutive respiratory cycles the 3He signal decreased due to dilution of 3He in residual alveolar gas and by inspired air, relaxation due to oxygen and the RF pulses, and due to Helium-3 washout. The signal of a single bolus of 3He was detected in the lung for up to four respiratory cycles. Anatomical structures were better visualized on slice selective images than on images without slice selection. CONCLUSION: Distribution of inspired 3He within the tracheobronchial tree and alveolar space and its washout can be visualized by ultrafast imaging of a single bolus of hyperpolarized 3He gas. This method may allow for regional analysis of lung function with temporal and spatial resolution superior to conventional methods.