Search

Purpose: A segmented inversion-recovery module combined with the 2D ultrashort echo time radial technique is proposed that allows accurate pixel level T-1 mapping of mouse lung in vivo. Methods: Numerical simulations were performed to estimate T-1 measurement accuracy and precision versus flip angle and signal-to-noise ratio. Phantom measurements were used for protocol validation, where the segmented inversion-recovery ultrashort echo-time sequence was compared with the reference technique (inversion-recovery rapid acquisition with refocused echoes). The in vivo experiments were carried out on free-breathing C57 mice (n = 10), breathing first air and then oxygen. Results: The simulations demonstrated the high potential of the technique for accurate and precise T-1 assessment. Phantom experiments showed good agreement for T-1 values measured with segmented inversion-recovery ultrashort echo-time and the reference technique. The in vivo experiment demonstrated the utility of the technique in oxygen-enhanced assessment, where small T-1 changes were detected with high precision. Conclusion: Segmented inversion-recovery ultrashort echo-time provides accurate, high resolution T-1 mapping of the lung parenchyma. Magn Reson Med 71:2180-2185, 2014. (c) 2013 Wiley Periodicals, Inc.

To evaluate whether careful exercise training improves pulmonary perfusion and blood flow in patients with pulmonary hypertension (PH), as assessed by magnetic resonance imaging (MR).Twenty patients with pulmonary arterial hypertension or inoperable chronic thromboembolic PH on stable medication were randomly assigned to control (n = 10) or training groups (n = 10). Training group patients received in-hospital exercise training; patients of the sedentary control group received conventional rehabilitation. Medication remained unchanged during the study period. Changes of 6-min walking distance (6MWD), MR pulmonary flow (peak velocity) and MR perfusion (pulmonary blood volume) were assessed from baseline to week 3.After 3 weeks of training, increases in mean 6MWD (P = 0.004) and mean MR flow peak velocity (P = 0.012) were significantly greater in the training group. Training group patients had significantly improved 6MWD (P = 0.008), MR flow (peak velocity -9.7 ± 8.6 cm/s, P = 0.007) and MR perfusion (pulmonary blood volume +2.2 ± 2.7 mL/100 mL, P = 0.017), whereas the control group showed no significant changes.The study indicates that respiratory and physical exercise may improve pulmonary perfusion in patients with PH. Measurement of MR parameters of pulmonary perfusion might be an interesting new method to assess therapy effects in PH. The results of this initial study should be confirmed in a larger study group.

Tissue microcirculation can be quantified by a deconvolution analysis of concentration–time curves measured by dynamic contrast-enhanced magnetic resonance imaging. However, deconvolution is an ill-posed problem, which requires regularization of the solutions. In this work, four algebraic deconvolution/regularization methods were evaluated: truncated singular value decomposition and generalized Tikhonov regularization (GTR) in combination with the L-curve criterion, a modified LCC (GTR-MLCC), and a response function model that takes a-priori knowledge into account. To this end, dynamic contrast-enhanced magnetic resonance imaging data sets were simulated by an established physiologically reference model for different signal-to-noise ratios and measured on a 1.5-T system in the lung of 10 healthy volunteers and 20 patients. Analysis of both the simulated and measured dynamic contrast-enhanced magnetic resonance imaging datasets revealed that GTR in combination with the L-curve criterion does not yield reliable and clinically useful results. The three other deconvolution/regularization algorithms resulted in almost identical microcirculatory parameter estimates for signal-to-noise ratios > 10. At low signal-to-noise ratios levels (

We proposed to assess the feasibility of low mechanical index (MI) contrast enhanced ultrasound (CEUS) in the characterisation of thoracic lesions. Fifty patients were prospectively examined by CEUS and images acquired on a low MI (0.17-0.24) setting following injection of SonoVue. From region-of-interest (ROI) generated signal intensity (SI) time curves, the maximum SI, bolus arrival time (BAT), time to peak intensity (TTP), wash-in slope and mean transit time (MTT) were calculated. Using the Wilcoxon rank test; parameters and threshold values for positive differentiation were determined. In addition, for the parameters that allowed positive differentiation between malignant and benign lesions receiver operator curves (ROC) were obtained. The wash-in slope, TTP and MTT (p = 0.0003,0.0001, 0.02) allowed positive differentiation. The sensitivity and specificity was 93% and 78%, with 6.87 s(-1) threshold value for the wash-in slope, 78% and 89% with 11.84 s threshold for the TTP and 48% and 89% with 78.6 s threshold for the MTT. CEUS is a useful tool for differentiating malignant and benign thoracic lesions.

PURPOSE Magnetic resonance imaging (MRI) allows for quantitative evaluation of pulmonary perfusion and has shown high clinical usefulness for the evaluation and differentiation of different lung pathologies. The reproducibility of quantitative analysis of whole-lung perfusion has not been investigated previously. Our aim was to assess the intraobserver and interobserver repeatability and reproducibility of perfusion MRI to prove the concept that perfusion is suitable for therapy monitoring. MATERIALS AND METHODS The study was approved by the International Review Board. Fourteen healthy volunteers were examined using a time-resolved FLASH 3-dimensional perfusion sequence (1.5-T MRI, TREAT, GRAPPA 2, coronal orientation, voxel size 3.9×3.9×6.3 mm(3)). Perfusion was assessed initially and after 24 hours during an inspiratory and an expiratory breath hold. For each examination, 0.05 mmol/kg BW of Gd-DTPA was injected. Perfusion parameters such as pulmonary blood flow (PBF), pulmonary blood volume, and mean transit time were calculated. The evaluation was performed independently by 2 blinded observers. Intraobserver and interobserver differences were determined. RESULTS The intraobserver differences between the initial and follow-up examinations for pulmonary blood volume, mean transit time, and time to peak were not significantly different for observers 1 and 2. PBF showed a significant difference for both observers only on inspiration (P

Background: In vitro studies have shown that the 3-Tesla (T) magnetic resonance (MR) characteristics of high- and standard-molar gadolinium-based contrast agents differ. Such differences may indicate that high-molar (1.0 M) agents offer advantages for perfusion-weighted imaging (PWI) at 3T, as has been previously reported at 1.5T. Purpose: To investigate possible intraindividual differences of high- versus low-molar contrast agents on PWI at 3T in patients with intracranial space-occupying lesions. Material and Methods: Six patients with intraaxial and five patients with extraaxial tumors underwent two MR examinations at 3T, separated by at least 48 hours. On each occasion, an exogenous contrast-based, T2*-weighted, gradient-recalled echo-planar imaging (EPI) technique was used to determine the intracranial perfusion characteristics using one of two intravenous contrast agents: either 5 ml of 1.0 M gadobutrol or 10 ml of 0.5 M gadopentetate dimeglumine. The primary PWI outcome measure was region-of-interest maximal signal change (Cmax). Results: The difference in Cmax for gray and white matter (ΔCmax) was significantly higher for gadobutrol compared to gadopentetate dimeglumine ( Pmax between gray and white matter (rCmax = CmaxGray/CmaxWhite) was also significantly higher (median 24.6%, range 13.7–36.5%) for gadobutrol ( Pmax between the whole tumor and whole normal side hemisphere was higher in five out of the six intraaxial tumor cases. A significantly higher ratio (ΔCmax/Cmax) in the difference between Cmax of gray and white matter (from hemisphere without brain lesion) compared to Cmax for the hemisphere containing the neoplasm (hemisphere with brain lesion) was demonstrated for gadobutrol in intraaxial tumors ( P Conclusion: Higher-concentration 1.0 M gadobutrol can offer advantages over standard 0.5 M gadopentetate dimeglumine, particularly with respect to delineation between gray and white matter and for the demarcation of highly vascularized tumor tissue on brain PWI performed at 3T.

The purpose of the study was to evaluate the feasibility of suppressing the pulmonary vasculature in lung perfusion MRI using cross-correlation analysis (CCA). Perfusion magnetic resonance imaging (MRI) (3D FLASH, TR/TE/flip angle: 0.8 ms/2.1 ms/40 degrees ) of the lungs was performed in seven healthy volunteers at 1.5 Tesla after injection of Gd-DTPA. CCA was performed pixel-wise in lung segmentations using the signal time-course of the main pulmonary artery and left atrium as references. Pixels with high correlation coefficients were considered as arterial or venous and excluded from further analysis. Quantitative perfusion parameters [pulmonary blood flow (PBF) and volume (PBV)] were calculated for manual lung segmentations separately, with the entire left and right lung with all intrapulmonary vessels (IPV) included, excluded manually or excluded using CCA. The application of CCA allowed reliable suppression of hilar and large IPVs. Using vascular suppression by CCA, perfusion parameters were significantly reduced (p/= 0.001). The reduction was 8% for PBF and 13% for PBV compared with manual exclusion and 15% for PBF and 25% for PBV when all vessel structures were included. The application of CCA improves the visualisation and quantification of lung perfusion in MRI. Overestimation of perfusion parameters caused by pulmonary vessels is significantly reduced.

Recently it has been shown that regional lung perfusion can be assessed using time-resolved contrast-enhanced magnetic resonance (MR) imaging. Quantification of the perfusion images has been attempted, based on definition of small regions of interest (ROIs). Use of complete lung segmentations instead of ROIs could possibly increase quantification accuracy. Due to the low signal-to-noise ratio, automatic segmentation algorithms cannot be applied. On the other hand, manual segmentation of the lung tissue is very time consuming and can become inaccurate, as the borders of the lung to adjacent tissues are not always clearly visible. We propose a new workflow for semi-automatic segmentation of the lung from additionally acquired morphological HASTE MR images. First the lung is delineated semi-automatically in the HASTE image. Next the HASTE image is automatically registered with the perfusion images. Finally, the transformation resulting from the registration is used to align the lung segmentation from the morphological dataset with the perfusion images. We evaluated rigid, affine and locally elastic transformations, suitable optimizers and different implementations of mutual information (MI) metrics to determine the best possible registration algorithm. We located the shortcomings of the registration procedure and under which conditions automatic registration will succeed or fail. Segmentation results were evaluated using overlap and distance measures. Integration of the new workflow reduces the time needed for post-processing of the data, simplifies the perfusion quantification and reduces interobserver variability in the segmentation process. In addition, the matched morphological data set can be used to identify morphologic changes as the source for the perfusion abnormalities.

Pathological changes of the peripheral pulmonary arteries induce pulmonary arterial hypertension (PAH). Aim of this study was to quantitatively assess the effect of PAH on pulmonary perfusion by 3D-MR-perfusion techniques and to compare findings to healthy controls. Furthermore, quantitative perfusion data were correlated with invasive pressure measurements.Five volunteers and 20 PAH patients (WHO class II or III) were examined using a 1.5T MR scanner. Measurement of pulmonary perfusion was done in an inspiratory breathhold (FLASH3D; 3.5 mm x 1.9 mm x 4mm; TA per 3D dataset 1.5s). Injection of contrast media (0.1 mmol Gd-DTPA/kg BW) and image acquisition were started simultaneously. Evaluation of 3D perfusion was done using singular value decomposition. Lung borders were outlined manually. Each lung volume was divided into three regions (anterior, middle, posterior), and the following parameters were assessed: Time-to-Peak (TTP), blood flow (PBF), blood volume (PBV), and mean transit time (MTT). In 10 patients invasive pulmonary artery pressure measurements were available and correlated to the perfusion measurements.In both, controls and patients, an anterior-to-posterior gradient with higher PBF and PBV posterior was observed. In the posterior lung region, a significant difference (p0.05) was found for TTP (12s versus 16s) and MTT (4s versus 6s) between volunteers and patients. PBF and PBV were lower in patients than in volunteers (i.e. dorsal regions: 124 versus 180 ml/100 ml/min and 10 versus 12 ml/100 ml), but the difference failed to be significant. The ratio of PBF and PBV between the posterior and the middle or ventral regions showed no difference between both groups. A moderate linear correlation between mean pulmonary arterial pressure (mPAP) and PBV (r=0.51) and MTT (r=0.56) was found.The only measurable effect of PAH on pulmonary perfusion is a prolonging of the MTT. There is only a moderate linear correlation of invasive mPAP with PBV and MTT.

Objectives: We sought to assess the agreement between lung perfusion ratios calculated from pulmonary perfusion magnetic resonance imaging (MRI) and those calculated from radionuclide (RN) perfusion scintigraphy. Materials and Methods: A retrospective analysis of MR and RN perfusion scans was conducted in 23 patients (mean age, 60 ± 14 years) with different lung diseases (lung cancer = 15, chronic obstructive pulmonary disease = 4, cystic fibrosis = 2, and mesothelioma = 2). Pulmonary perfusion was assessed by a time-resolved contrast-enhanced 3D gradient-echo pulse sequence using parallel imaging and view sharing (TR = 1.9 milliseconds; TE = 0.8 milliseconds; parallel imaging acceleration factor = 2; partition thickness = 4 mm; matrix = 256 X 96; in-plane spatial resolution = 1.87 X 3.75 mm; scan time for each 3D dataset = 1.5 seconds), using gadolinium-based contrast agents (injection flow rate = 5 mL/s, dose = 0.1 mmol/kg of body weight). The peak concentration (PC) of the contrast agent bolus, the pulmonary blood flow (PBF), and blood volume (PBV) were computed from the signal-time curves of the lung. Left-to-right ratios of pulmonary perfusion were calculated from the MR parameters and RN counts. The agreement between these ratios was assessed for side prevalence (sign test) and quantitatively (Deming-regression). Results: MR and RN ratios agreed on side prevalence in 21 patients (91%) with PC, in 20 (87%) with PBF, and in 17 (74%) with PBV. The MR estimations of left-to-right perfusion ratios correlated significantly with those of RN perfusion scans (P < 0.01). The correlation was higher using PC (r = 0.67) and PBF (r = 0.66) than using PBV (r = 0.50). The MR ratios computed from PBF showed the highest accuracy, followed by those from PC and PBV. Independently from the MR parameter used, in some patients the quantitative difference between the MR and RN ratios was not negligible. Conclusions: Pulmonary perfusion MRI can be used to assess the differential blood flow of the lung. Further studies in a larger group of patients are required to fully confirm the clinical suitability of this imaging method.

Radiofrequency ablation (RFA) is an attractive minimally invasive treatment option for small renal masses. The purpose of this study was to investigate the morphologic imaging appearance of RF lesions immediately after the ablation of kidney tissue using standard clinical MR sequences, as well as to investigate the correlation between MR and gross lesion size.Ablations were performed 17 times in a standardized model of ex-vivo perfused porcine kidneys using a resistance-controlled RF device (250 W, 470 kHz) and a nonexpandable bipolar applicator inserted into the center of healthy renal parenchyma. The RF current was applied for 9 minutes at 20 W. Imaging was performed after ablation using standard clinical MR sequences: morphologic T(1)/T(2)- weighted images and an isotropic post-contrast T(1) high-resolution measurement (VIBE). Maximum lesion diameters were measured in three directions and were compared with the measurements of the gross lesions. Histologic (hematoxylin + eosin and nicotinamide adenine dinucleotide staining) and statistical analyses were performed.The gross pathologic examination showed a firm, white-yellow ablation zone sharply demarcated from the untreated tissue. The histologic examination confirmed cellular viability outside but not in the treatment zone. The RF lesions were hyperintense on T(1)-weighted images and hypointense on T(2)-weighted images. The lesion size measured in the VIBE images correlated best with the macroscopic lesion size (N = 16).Morphologic MR T(1) and T(2) sequences of RF lesions immediately after ablation produce reliable and consistent imaging characteristics. The post-contrast, high-resolution sequence (VIBE) enables the extent of the lesion to be determined accurately. The potential uses of this imaging strategy in clinical practise warrant further investigation on human renal-cell carcinoma.

Lung perfusion is a crucial prerequisite for effective gas exchange. Quantification of pulmonary perfusion is important for diagnostic considerations and treatment planning in various diseases of the lungs. Besides disorders of pulmonary vessels such as acute pulmonary embolism and pulmonary hypertension, these also include diseases of the respiratory tract and lung tissue as well as pulmonary tumors. This contribution presents the possibilities and technical requirements of MRI for diagnostic work-up of pulmonary perfusion.

PURPOSE Evaluation of lung perfusion by contrast-enhanced 3D MRI using partial parallel imaging techniques. MATERIALS AND METHODS Eight healthy volunteers were examined using a contrast-enhanced dynamic FLASH 3D sequence with partial parallel imaging technique at 1.5 T MRI with a TA of 1.5 sec. The whole lung was covered by 36 coronal slices. A ventral, middle and dorsal slice of each lung was manually segmented and signal-to-time curves were computed. For absolute quantification of blood flow through the right and left pulmonary artery, phase-contrast flow measurements were performed. RESULTS No significant difference was found between the signal intensity in the right (8.9 +/- 2.6) and left (8.0 +/- 3.5) lung, corresponding to a left-to-right signal intensity ratio of 0.9. A significantly higher signal intensity was found in the dorsal regions of the lungs (p = 0.01) compared to the ventral regions. The time to peak of the signal intensity was significantly shorter in the dorsal (15.3 sec) and middle (15.7 sec) regions of the lungs (p = 0.03 and p = 0.04, respectively) than in the ventral regions (16.3 sec). The ratio between blood flow through the left (2.2 L/min) and right (2.7 L/min) lung was 0.84. CONCLUSION Partial parallel image acquisition can assess the perfusion of the lungs at high temporal resolution. The perfusion is slightly higher on the right than on the left. The signal increases faster and has a higher peak in the dorsal lung regions.

Purpose To assess the use of time-resolved parallel 3D MRI for a quantitative analysis of pulmonary perfusion in patients with cardiopulmonary disease. Materials and methods Eight patients with pulmonary embolism or pulmonary hypertension were examined with a time-resolved 3D gradient echo pulse sequence with parallel imaging techniques (FLASH 3D, TE/TR: 0.8/1.9 ms; flip angle: 40 degrees; GRAPPA). A quantitative perfusion analysis based on indicator dilution theory was performed using a dedicated software. Results Patients with pulmonary embolism or chronic thromboembolic pulmonary hypertension revealed characteristic wedge-shaped perfusion defects at perfusion MRI. They were characterized by a decreased pulmonary blood flow (PBF) and pulmonary blood volume (PBV) and increased mean transit time (MTT). Patients with primary pulmonary hypertension or Eisenmenger syndrome showed a more homogeneous perfusion pattern. The mean MTT of all patients was 3.3 - 4.7 s. The mean PBF and PBV showed a broader interindividual variation (PBF: 104 - 322 ml/100 ml/min; PBV: 8 - 21 ml/100 ml). Conclusion Time-resolved parallel 3D MRI allows at least a semi-quantitative assessment of lung perfusion. Future studies will have to assess the clinical value of this quantitative information for the diagnosis and management of cardiopulmonary disease.

A segmented inversion-recovery module combined with the 2D ultrashort echo time radial technique is proposed that allows accurate pixel level T(1) mapping of mouse lung in vivo.Numerical simulations were performed to estimate T(1) measurement accuracy and precision versus flip angle and signal-to-noise ratio. Phantom measurements were used for protocol validation, where the segmented inversion-recovery ultrashort echo-time sequence was compared with the reference technique (inversion-recovery rapid acquisition with refocused echoes). The in vivo experiments were carried out on free-breathing C57 mice (n = 10), breathing first air and then oxygen.The simulations demonstrated the high potential of the technique for accurate and precise T(1) assessment. Phantom experiments showed good agreement for T(1) values measured with segmented inversion-recovery ultrashort echo-time and the reference technique. The in vivo experiment demonstrated the utility of the technique in oxygen-enhanced assessment, where small T(1) changes were detected with high precision.Segmented inversion-recovery ultrashort echo-time provides accurate, high resolution T(1) mapping of the lung parenchyma.

Tissue microcirculation can be quantified by a deconvolution analysis of concentration-time curves measured by dynamic contrast-enhanced magnetic resonance imaging. However, deconvolution is an ill-posed problem, which requires regularization of the solutions. In this work, four algebraic deconvolution/regularization methods were evaluated: truncated singular value decomposition and generalized Tikhonov regularization (GTR) in combination with the L-curve criterion, a modified LCC (GTR-MLCC), and a response function model that takes a-priori knowledge into account. To this end, dynamic contrast-enhanced magnetic resonance imaging data sets were simulated by an established physiologically reference model for different signal-to-noise ratios and measured on a 1.5-T system in the lung of 10 healthy volunteers and 20 patients. Analysis of both the simulated and measured dynamic contrast-enhanced magnetic resonance imaging datasets revealed that GTR in combination with the L-curve criterion does not yield reliable and clinically useful results. The three other deconvolution/regularization algorithms resulted in almost identical microcirculatory parameter estimates for signal-to-noise ratios10. At low signal-to-noise ratios levels (10) typically occurring in pathological lung regions, GTR in combination with a modified L-curve criterion approximates the true response function much more accurately than truncated singular value decomposition and GTR in combination with response function model with a difference in accuracy of up to 76%. In conclusion, GTR in combination with a modified L-curve criterion is recommended for the deconvolution of dynamic contrast-enhanced magnetic resonance imaging curves measured in the lung parenchyma of patients with highly heterogeneous signal-to-noise ratios.

The ratios of prompt to delayed fission yields for the isotopes U-233, U-234, U-235, U-236, U-238, Np-237, Pu-242, and Pu-244 and the fission probabilities relative to each other have been investigated experimentally. Using the value of the total fission probability for Np-237 the absolute probabilities for prompt and delayed fission have been determined. The fission probabilities per muon capture P(fc) have been derived for all the isotopes and compared with an evaluation based on excitation functions from theory.

The probability for delayed muon induced fission of209Bi has been determined from a (μ−,f1f2) measurement. The measured fission probability Pf=(4.2±0.7)×10−5 is compared with theoretical predictions. The high fission threshold reaction seems well suited for studying the influence of two-body meson-exchange currents in nuclear muon capture.

A study of muonic238U has been performed in a combined (μ−,γ f) and (μ−,γγ) coincidence experiment to investigate the role of non-radiative transitions and their fission probabilities. An augmentation of the outer fission barrier ofΔEb=(0.6±0.1) MeV due to the presence of the muon is deduced. A significant contribution to the prompt fission yield not only results from the (2p→1s) and (3d→1s) non-radiative transitions, but also from other radiationless transitions. Specifically, the measured fission probabilities of the transitions (2p→1s), (3d→1s), and (3p→1s) are (1.5±0.4)%, (5.7±1.7)%, and (5.3±1.9)%, respectively.

Chromium (Cr) is of known biological importance, necessary for the maintenance of normal glucose metabolism. There is a lower level of blood Cr concentrations in cases of diabetes. Diabetes carries a risk of cataract development, so the potential effects of Cr on the eye may need to be studied in more depth. The presence of this trace element in both normal and cataractous human lenses has to our knowledge not been investigated so far. The concentration of total Cr in 61 human lenses and 38 blood samples was determined by electrothermal atomic absorption spectrometry with Zeeman effect (EAASZ). Analysis of the levels of Cr in human lenses shows a significant difference between normal and diabetic populations, and an absence of difference between senile and diabetic populations.

Purpose Assessment of lung cancer perfusion is impaired by respiratory motion. Imaging times for contrast agent wash-out studies often exceed breath hold capabilities, and respiration triggering reduces temporal resolution. Temporally resolved volume acquisition of entire tumors is required to assess heterogeneity. Therefore, we developed and evaluated an MR measurement technique that exceeds a single breath hold, and provides a variable temporal resolution during acquisition while suspending breath-dependent motion. Materials and methods 20 patients with suspected lung cancer were subjected to perfusion studies using a spoiled 3D gradient echo sequence after bolus injection of 0.07 mmol/kg body weight of Gd-DTPA. 10 acquisitions in expiratory breath hold were followed by 50 navigator-triggered acquisitions under free breathing. Post-processing allowed for co-registration of the 3D data sets. An ROI-based visualization of the signal-time curves was performed. Results In all cases motion-suspended, time-resolved volume data sets (40 x 33 x 10 cm(3), voxel size: 2.1 x 2.1 x 5.0 mm(3)) were generated with a variable, initially high temporal resolution (2.25 sec) that was synchronized with the breath pattern and covered up to 8 1/2 min. In 7 / 20 cases a remaining offset could be reduced by rigid co-registration. The tumors showed fast wash-in, followed by rapid signal decay (8 / 20) or a plateau. Conclusion The feasibility of a perfusion study with hybrid breath hold and navigator-triggered time-resolved 3D MRI which combines high initial temporal resolution during breath hold with a long wash-out period under free breathing was demonstrated.

Introduction The investigation of pulmonary perfusion by three-dimensional (3D) dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was proposed recently. Subtraction images are generated for clinical evaluation, but temporal information is lost and perfusion defects might therefore be masked in this process. The aim of this study is to demonstrate a simple analysis strategy and classification for 3D-DCE-MRI perfusion datasets in the lung without omitting the temporal information. Materials and methods Pulmonary perfusion measurements were performed in patients with different lung diseases using a 1.5 T MR-scanner with a time-resolved 3D-GRE pulse sequence. 25 3D-volumes were acquired after iv-injection of 0.1 mmol/kg KG Gadolinium-DTPA. Three parameters were determined for each pixel: (1) peak enhancement S n ,max normalized to the arterial input function to detect regions of reduced perfusion; (2) time between arterial peak enhancement in the large pulmonary artery and tissue peak enhancement τ to visualize regions with delayed bolus onset; and (3) ratio R = S n ,max / τ was calculated to visualize impaired perfusion, irrespectively of whether related to reduced or delayed perfusion. Results A manual selection of peak perfusion images is not required. Five different types of perfusion can be found: (1) normal perfusion; (2) delayed non-reduced perfusion; (3) reduced non-delayed perfusion; (4) reduced and delayed perfusion; and (5) no perfusion. Types II and IV could not be seen in subtraction images since the temporal information is necessary for this purpose. Conclusions The analysis strategy in this study allows for a simple and observer-independent visualization and classification of impaired perfusion in dynamic contrast-enhanced pulmonary perfusion MRI by using the temporal information of the datasets.

Fission fragments from the reaction237Np(μ−,γ,f) have been measured in coincidence with muonic X-rays. The efficiency of the fission fragment detector is determined from (μ−,γ,f)-data of the same experiment. The total fission probability perμ-stopPt has been measured as well as the fission probabilities Pf of the non-radiative muonic (3d→1s)- and (2p→1s)-transitions; the latter has been divided into two parts leading to different mean excitation energiesE:P t =(54±17)%,P f (3d→1s)=(41±21)%,P f (2p→1s,E=6.218 MeV)=(61±19)%, andP f (2p→1s,E=6.525 MeV)=(57±18)%. The influence of the muon on the fission barrier is discussed. The fission probability after muon capture is compared with a calculated value using a distribution of nuclear excitation energies following muon capture and the fission probability as measured in a238U(3He,αf)-reaction.

The probabilities of muon attachment to fission fragments in the prompt fission of237Np have been determined as a function of fragment mass and total kinetic energy release in a (μ −,f 1 f 2 e −)-coincidence measurement. A strong dependence of the attachment probability on the fragment mass is observed. The experimental results are compared with theoretical predictions.

Pulmonary perfusion is the blood flow of an organ at the capillary level. It is closely related to the blood supply of the lung and moreover to lung function. It is altered in various diseases of the lung such as pulmonary hypertension or cystic fibrosis, etc. Therefore, perfusion is an important functional parameter in the diagnosis of pulmonary diseases and quantitative values are urgently required to study physiology and pathophysiology of various lung diseases as well as monitor treatment response and identify differences under therapy. Pulmonary perfusion MRI is based on three-dimensional time-resolved contrast-enhanced T1-weighted sequences. The rapid acquisition of perfusion images facilitates the tracking of the first pass of a contrast agent through the lung parenchyma. Based on this information, it is possible to quantify perfusion in the entire lung using the indicator dilution theory. Quantification is challenging due to potential extravasation of the contrast agent during the first pass as well as the non-linear relationship between the concentration of the contrast agent and signal intensity. Some of these challenges can be addressed by a dual bolus technique.

New results were obtained on pionic 1s levels in 24Mg, 27Al and 28Si, on 2p states in 93Nb and natRu, as well as on 3d states in 93Nb, natRu, natAg and natCd. For the first time the predicted repulsive shifts for the pionic 2p level have been observed. The following values were obtained for the strong-interaction shifts and widths (all values in keV); 24Mg: e1s0 = −80.5 ± 0.6 and Γ1s0 = 24.3 ± 1.6; 27Al: e1s0 = −115.5 ± 1.4 and Γ1s0 = 28.8 ± 1.2, 28Si: e1s0 = −131.6 ± 2.0 and Γ1s0 = 41 ± 4;93Nb: e2p0 = −11 ± 3, Γ2p0 = 64 ± 8, e3d0 = 0.74 ± 0.02 and Γ3d0 = 0.402 ± 0.016; natRu: e2p0 = −48 ± 7, Γ2p0 = 77 ± 24, e3d0 = 1.39 ± 0.08 and Γ3d0 = 0.75 ± 0.08; natAg: e3d0 = 1.94 ± 0.07 and Γ3d0 = 1.44 ± 0.05 and natCd: e3d0 = 2.14 ± 0.09 and Γ3d0 = 1.65 ± 0.07. The results are in reasonable agreement with the predictions of the standard optical potentials.

The time spectra for muon induced fission of233U,234U,235U,236U,238U, and237Np were measured simultaneously, detecting both fragments in coincidence in a fast multi parallel plate avalanche detector. The observed mean lifetimes τ are 68.9 ± 0.3 ns, 70.6 ± 0.2 ns, 72.2 ±0.2 ns, 74.3 ± 0.3 ns, 77.0 ±0.4 ns, and 69.8 ±0.2 ns for the above isotopes, respectively. No second time component, tentatively ascribed to a possible fission isomer, was observed. The deduced total capture rates are compared with theoretical predictions.

Purpose To evaluate an optimized method for oxygen-enhanced MRI of the lung, using simultaneous electrocardiograph (ECG) and navigator triggering. To correlate oxygen-enhanced MRI with lung function tests assessing alveolar-capillary gas exchange. Materials and Methods A total of 12 healthy volunteers (aged 20–32 years) and 10 patients (aged 37–87 years) with interstitial lung diseases (ILD) underwent oxygen-enhanced MRI and pulmonary functional tests (PFTs) assessing alveolar-capillary gas exchange. The paradigm room-air–oxygen–room-air was acquired with a nonselective inversion-recovery half-Fourier single-shot turbo spin-echo sequence (inversion time = 1200 msec; acquisition time = 134.5 msec; slice thickness = 20 mm; matrix size = 128 × 128), using simultaneous double triggering (navigator plus ECG trigger). Cross-correlation was performed in regions of interest (ROIs) encompassing both lungs. The number of oxygen-activated pixels over the total number of pixels in the ROIs (OAP%) of volunteers and patients was compared. OAP%s were correlated with PFTs. Results The mean OAP% of patients was significantly lower than that of volunteers (36.7 vs. 81.7, P = 0.001). OAP% correlated with the transfer lung factor for carbon monoxide (Tlco) (r = 0.64; P = 0.002), the transfer coefficient (Kco) (r = 0.75; P = 0.001), the arterial partial pressure (r = 0.77; P < 0.001), and the saturation (r = 0.70; P < 0.001) of oxygen. Conclusion Navigator-triggered oxygen-enhanced MRI of the lung may have a potential role in the quantitative assessment of lung function in ILD. J. Magn. Reson. Imaging 2007. © 2007 Wiley-Liss, Inc.

A linear relationship between MR signal and contrast-agent concentration (CAC) of the arterial-input function (AIF) is crucial for MR lung-perfusion quantification. The aim was to determine the in-vivo real maximum CAC of the AIF, using cine CT measurements in a porcine model. A dilution series (Gd-DTPA, 0-20 mM) was examined by clinical time-resolved 3D-GRE MRI and by MDCT in cine CT mode. Using the CT setup, data were acquired in five pigs immediately after the injection of 0.05 mmol and 0.07 mmol/kg BW Gd-DTPA. For phantom measurements, mean signal values were determined using a region-of-interest (ROI) analysis and for animal measurements, a ROI was placed in the pulmonary trunk of the cine CT perfusion data sets. The CT phantom measurements were used to calculate the in-vivo maximum CAC corresponding to the HU values obtained in the pulmonary trunk by the cine CT study. Linearity of the AIF of the CT perfusion measurements was verified using the MR phantom measurement results. MR phantom measurements demonstrated linearity for concentrations of 0-4 mM. CT phantom measurements showed linear relation for the entire CAC range. Comparing in-vivo and in-vitro measurements, three of five CA injections at 0.05 mmol/kg and all 0.07 mmol/kg injections exceeded the range of linearity in MRI. The CA dose for quantification of lung perfusion with time-resolved MR studies must be chosen carefully since even with low doses (0.05 mmol/kg) the CAC may exceed the range of linearity in the AIF.

Oxygen-enhanced magnetic resonance (MR)-ventilation imaging of the lung is based on the inhalation of a high concentration of oxygen (hyperoxia). However, the effect of hyperoxia on the pulmonary circulation is not yet fully understood. In this study the impact of hyperoxia on the pulmonary circulation was evaluated.Ten healthy volunteers were examined in a 1.5 T MRI system with contrast-enhanced perfusion MRI (saturation recovery 2D turboFLASH) of the lung and phase-contrast flow measurements in the pulmonary trunk. Both measurements were performed breathing room air (RA) and, subsequently, 100% oxygen (15 L/min) (O(2)).The perfusion measurements showed a significant difference between RA and O(2) for the pulmonary blood flow (181 vs. 257 mL/min/100 mL, P = 0.04) and blood volume (14 vs. 21 mL/100 mL, P = 0.008). The mean transit time of the contrast bolus was not changed (P = 0.4) in the dorsal part of the lung, whereas it was significantly prolonged (P = 0.006) in the central part. The mean heart rate during flow measurements breathing RA (67 +/- 11 beats/min) and O(2) (61 +/- 12 beats/min) were not significantly different (P = 0.055). The average cardiac output (pulmonary trunk) was not significantly lower while breathing O(2) (RA: 5.9 vs. O(2): 5.5 L/min, P = 0.054).Hyperoxia causes a significant increase and redistribution of the pulmonary perfusion, whereas it leads to a not significant decrease in cardiac output. Thus, for MR-perfusion and MR-flow measurements oxygen inhalation should be avoided, if possible. In the context of oxygen-enhanced MR-ventilation imaging of the lung the contribution of this effect needs to be further evaluated.

Three-dimensional (3D) dynamic contrast-enhanced magnetic resonance imaging (3D DCE-MRI) has been proposed for the assessment of regional perfusion. The aim of this work was the implementation of an algorithm for a 3D parametric visualization of lung perfusion using different cutting planes and volume rendering. Our implementation was based on 3D DCE-MRI data of the lungs of five patients and five healthy volunteers. Using the indicator dilution theory, the regional perfusion parameters, tissue blood flow, blood volume and mean transit time were calculated. Due to the required temporal resolution, the volume elements of dynamic MR data sets show a reduced spatial resolution in the z-direction. Therefore, perfusion parameter volumes were interpolated. Linear interpolation and a combination of linear and nearest-neighbor interpolation were evaluated. Additionally, ray tracing was applied for 3D visualization. The linear interpolation algorithm caused interpolation errors at the lung borders. Using the combined interpolation, visualization of perfusion information in arbitrary cutting planes and in 3D using volume rendering was possible. This facilitated the localization of perfusion deficits compared with the coronal orientated source data. The 3D visualization of perfusion parameters using a combined interpolation algorithm is feasible. Further studies are required to evaluate the additional benefit from the 3D visualization.

PURPOSE To evaluate a dual-bolus approach to pulmonary perfusion MRI. MATERIALS AND METHODS The dual-bolus approach uses a separate low-dose measurement for the arterial input function (AIF) to ensure linearity. The measured AIF is constructed according to a subsequent higher dose used for the tissue concentration curves in the lung. In this study a prebolus of 0.01 mmol/kg followed by doses of 0.04 mmol/kg and 0.08 mmol/kg was used. Measurements were performed using time-resolved two-dimensional fast low-angle shot (2D FLASH) MRI (TE/TR = 0.73 msec/1.73 msec; flip angle = 40 degrees ; generalized autocalibrating partially parallel acquisitions (GRAPPA) factor = 3; temporal resolution = 400 msec) in end-inspiratory breath-hold. RESULTS The combination of prebolus/0.04 mmol/kg resulted in a pulmonary blood flow (PBF) of 211 +/- 77 mL/min/100 mL, and a pulmonary blood volume (PBV) of 20 +/- 3 mL/100 mL. The combination of prebolus/0.08 mmol/kg resulted in approximately 50% lower perfusion values, most likely due to saturation effects in the lung tissue. CONCLUSION A dual-bolus approach to pulmonary perfusion MRI is feasible and may reduce the problem of lacking linear relationship between the contrast-agent concentration and signal intensity.

Inhomogeneous hypoxic pulmonary vasoconstriction causing regional overperfusion and high capillary pressure is postulated for explaining how high pulmonary artery pressure leads to high-altitude pulmonary edema in susceptible (HAPE-S) individuals.Because different species of animals also show inhomogeneous hypoxic pulmonary vasoconstriction, we hypothesized that inhomogeneity of lung perfusion in general increases in hypoxia, but is more pronounced in HAPE-S. For best temporal and spatial resolution, regional pulmonary perfusion was assessed by dynamic contrast-enhanced magnetic resonance imaging.Dynamic contrast-enhanced magnetic resonance imaging and echocardiography were performed during normoxia and after 2 h of hypoxia (Fi(O2) = 0.12) in 11 HAPE-S individuals and 10 control subjects. As a measure for perfusion inhomogeneity, the coefficient of variation for two perfusion parameters (peak signal intensity, time-to-peak) was determined for the whole lung and isogravitational slices.There were no differences in perfusion inhomogeneity between the groups in normoxia. In hypoxia, analysis of coefficients of variation indicated a greater inhomogeneity in all subjects, which was more pronounced in HAPE-S compared with control subjects. Discrimination between HAPE-S and control subjects was best in gravity-dependent lung areas. Pulmonary artery pressure during hypoxia increased from 22 +/- 3 to 53 +/- 9 mm Hg in HAPE-S and 24 +/- 4 to 33 +/- 6 mm Hg in control subjects (mean +/- SD; p0.001), respectively.This study shows that hypoxic pulmonary vasoconstriction is inhomogeneous in hypoxia in humans, particularly in HAPE-S individuals where it is accompanied by a greater increase in pulmonary artery pressure compared with control subjects. These findings support the hypothesis of exaggerated and uneven hypoxic pulmonary vasoconstriction in HAPE-S individuals.

Lung perfusion is a crucial prerequisite for effective gas exchange. Quantification of pulmonary perfusion is important for diagnostic considerations and treatment planning in various diseases of the lungs. Besides disorders of pulmonary vessels such as acute pulmonary embolism and pulmonary hypertension, these also include diseases of the respiratory tract and lung tissue as well as pulmonary tumors. This contribution presents the possibilities and technical requirements of MRI for diagnostic work-up of pulmonary perfusion.

High intensity focused ultrasound (HIFU) under magnetic resonance imaging (MRI) guidance is an attractive instrument to ablate tissue non‐invasively. The aim of this work was to investigate the coagulation volume and the perfusion changes after HIFU‐ablation in an isolated kidney model using MRI. Ablation was performed at least at two regions of the renal cortex. Morphological T1‐/T2‐weighted, temperature sensitive images and contrast‐enhanced perfusion measurements were performed. The detection of single HIFU induced coagulation necroses and HIFU induced tissue cavities was feasible. Perfusion changes could only be detected in few experiments because of relatively inhomogeneous kidney perfusion patterns. MR‐imaging is a sensitive method to detect and to quantify the HIFU‐focus. Moreover, MRI is a valuable approach for the detection of HIFU induced coagulation necroses. The investigation of perfusion changes, particularly important in tumor treatment, was sometimes hampered due to limitations in the used organ model. However, in patients MR perfusion imaging as well as volumetric and morphological imaging can be used to control the outcome of HIFU‐therapy.

Ausgelost werden konnen das HUS/TTP durch bakterielle oder virale Infektionen (z. T. Toxin-vermittelt), hormonelle Veranderungen (Schwangerschaft, Antikonzeption), Autoimmunerkrankungen, Malignome, einen hereditaren Defekt des Prostazyklinstoffwechsels und verschiedene Medikamente. Eines dieser Medikamente ist Mitomycin C. Der genaue Pathomechanismus ist bis heute nicht bekannt. Zimmermann et al. [20] vermuteten, das Immunkomplexe, welche beim Untergang von Tumorzellen durch Mitomycin entstehen, eine vaskulare Schadigung mit anschliesender Thrombozytenaggregation verursachen. Price et al. [13] konnten aber solche Immunkomplexe nicht nachweisen. Auch wird diskutiert, das Mitomycin C durch Hemmung der Prostazyclinsynthese in endothelialen Zellen [3] oder durch Reduktion von Plasminogenaktivatoren im Gewebe in Folge einer Endothelschadigung ein HUS/TTP bedingt [11]. Der Mitomycin C-induzierte Endothelschaden selbst kann auch eine thrombotische Mikroangiopathie hervorrufen [11].

Purpose To compare the signal characteristics and bolus dynamics of 1.0 M gadobutrol and 0.5 M Gd-DTPA for time-resolved, three-dimensional, contrast-enhanced (CE) MRA of the upper torso. Materials and Methods Ten healthy volunteers were examined with time-resolved three-dimensional CE-MRA (scan time per three-dimensional data set: 0.86 second; voxel size: 3.6 × 2 × 6.3 mm3). Each volunteer underwent eight individual examinations after intravenous injection of 0.05 and 0.1 mmol/kg body weight (b.w.) of 1.0 M gadobutrol and 0.5 M Gd-DTPA using two injection rates (2.5 and 5 mL/second). The data analysis included quantitative measurements of the peak signal-to-noise ratio (SNR) and bolus dispersion (full width at half maximum (FWHM)) in the pulmonary artery, left atrium, and thoracic and abdominal aortas. Results No significant differences in the peak SNR and bolus dispersion were observed between gadobutrol and Gd-DTPA for all dose levels and injection rates in any of the vascular segments. For both contrast agents a dose of 0.1 mmol/kg b.w. injected with 5 mL/second achieved the highest SNR in all vascular segments. Conclusion For the imaging parameters used in this study, higher-concentrated gadolinium chelates offer no relevant advantages for time-resolved three-dimensional CE-MRA of the upper torso. J. Magn. Reson. Imaging 2005;22:286–290. © 2005 Wiley-Liss, Inc.