Maximilian F Reiser

Ludwig-Maximilian-University of Munich, München, Bavaria, Germany

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Publications (775)1802.45 Total impact

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    ABSTRACT: Objective: To investigate annexin-based optical fluorescence imaging (OI) for monitoring regorafenib-induced early cell death in experimental colon carcinomas in rats, validated by perfusion MRI and multiparametric immunohistochemistry. Materials and methods: Subcutaneous human colon carcinomas (HT-29) in athymic rats (n = 16) were imaged before and after a one-week therapy with regorafenib (n = 8) or placebo (n = 8) using annexin-based OI and perfusion MRI at 3 Tesla. Optical signal-to-noise ratio (SNR) and MRI tumor perfusion parameters (plasma flow PF, mL/100mL/min; plasma volume PV, %) were assessed. On day 7, tumors underwent immunohistochemical analysis for tumor cell apoptosis (TUNEL), proliferation (Ki-67), and microvascular density (CD31). Results: Apoptosis-targeted OI demonstrated a tumor-specific probe accumulation with a significant increase of tumor SNR under therapy (mean Δ +7.78±2.95, control: -0.80±2.48, p = 0.021). MRI detected a significant reduction of tumor perfusion in the therapy group (mean ΔPF -8.17±2.32 mL/100 mL/min, control -0.11±3.36 mL/100 mL/min, p = 0.036). Immunohistochemistry showed significantly more apoptosis (TUNEL; 11392±1486 vs. 2921±334, p = 0.001), significantly less proliferation (Ki-67; 1754±184 vs. 2883±323, p = 0.012), and significantly lower microvascular density (CD31; 107±10 vs. 182±22, p = 0.006) in the therapy group. Conclusions: Annexin-based OI allowed for the non-invasive monitoring of regorafenib-induced early cell death in experimental colon carcinomas, validated by perfusion MRI and multiparametric immunohistochemistry.
    PLoS ONE 09/2015; 10(9):e0138452. DOI:10.1371/journal.pone.0138452 · 3.23 Impact Factor
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    ABSTRACT: Purpose: To evaluate the use of dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) during free breathing for the detection of acute pulmonary embolism (PE). Materials and Methods: Eighteen subjects underwent free-breathing DCE MRI at 1.5T, eight of whom were patients with acute PE, as confirmed by routine computed tomography pulmonary angiography (CTPA). The remaining 10 subjects were healthy volunteers with no history or signs of pulmonary disease. From all DCE MRI data, maps of relative signal enhancement were calculated and assessed for the presence or absence of perfusion defects in each lung by two readers. Interreader variability, sensitivity, and specificity of free-breathing DCE MRI for the detection of PE were calculated using CTPA as the gold standard. Results: Of the 16 patient's lungs, 15 were affected by acute PE according to CTPA. In patients and volunteers, DCE MRI sensitivity was 93% and 87% for readers 1 and 2, with specificities of 95% and 90%, respectively. Interreader agreement was substantial, with κ = 0.77 (95% confidence interval: 0.44–1.0). Conclusion: Free-breathing DCE MRI may have potential use for the assessment of PE, and does not require patient cooperation in breath-holding.
    Journal of Magnetic Resonance Imaging 09/2015; DOI:10.1002/jmri.25050 · 3.21 Impact Factor
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    ABSTRACT: The purpose of this study was to evaluate differences of plaque composition and morphology within the same patient in different vascular beds using non-invasive MR-plaque imaging. 28 patients (67.8 ± 7.4 years, 8 females) with high Framingham general cardiovascular disease 10-year risk score and mild-to-moderate atherosclerosis were consecutively included in the study. All subjects underwent a dedicated MRI-plaque imaging protocol using TOF and T1w and T2w black-blood-sequences with fat suppression at 1.5 T. The scan was centered on the carotid bulb of the carotid arteries and on the most stenotic lesion of the ipsilateral femoral artery, respectively. Plaques were classified according to the American Heart Association (AHA) lesion type classification and area measurements of lumen, wall and the major plaque components, such as calcification, necrotic core and hemorrhage were determined in consensus by two blinded reviewers using dedicated software (Cascade, Seattle, USA). Plaque components were recorded as maximum percentages of the wall area. Carotid arteries had larger maximum wall and smaller minimum lumen areas (p < 0.001) than femoral arteries, whereas no significant difference was find with respect to the max. NWI (p = 0.87). Prevalence of lipid-rich AHA lesion type IV/V and complicated AHA lesion type VI with hemorrhage/thrombus/fibrous cap rupture was significantly higher in the carotid arteries compared to the femoral arteries. Plaque composition as percentage of the vessel wall differed significantly between carotid and femoral arteries: Max. %necrotic core and max. %hemorrhage were significantly higher in the carotid arteries compared to the femoral arteries (p = 0.001 and p = 0.02, respectively). Max. %calcification did not differ significantly. Average stenotic degree of carotid arteries at duplex was 49.7 ± 12.5 (%). Non-invasive MR plaque-imaging is able to visualize differences in plaque composition across the vascular tree. We observed significant differences in quantitative and qualitative plaque features between carotid and femoral arteries within the same patient, which in the future could help to improve risk stratification in patients with atherosclerosis.
    The international journal of cardiovascular imaging 08/2015; 31(8). DOI:10.1007/s10554-015-0737-4 · 1.81 Impact Factor
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    ABSTRACT: Clinical cases of stent-fractures show that corrosion behavior might play a role in these fractures. Implanted in vivo, especially in combination with other implanted foreign materials, these metallic products are exposed to special conditions, which can cause a process of corrosion. Here, we aimed to test the corrosion potential of stents made of different materials in an in vitro setting. A total of 28 peripheral stents of different materials (nitinol, cobalt-chromium-nickel, tantalum, V4A) and surface treatments (electropolish, mechanical polish, no polish) were tested in vitro. Corrosion was accelerated by applying a constant voltage of 3.5 V and amperage of 1.16 mA in 0.9% NaCl. Nitinol stents showed the lowest susceptibility to corrosion and the longest period without damage. The Memotherm II® (BARD Angiomed®) was the only stent that showed neither macroscopic nor microscopic damages. The worst performing material was cobalt-chromium-nickel, which showed corrosion damages about ten times earlier compared to nitinol. Considering the reasons for termination of the test, nitinol stents primarily showed length deficits, while V4A and tantalum stents showed fractures. Cobalt-chromium-nickel stents had multiple fractures or a complete lysis in equal proportions. When placed in direct contact, nitinol stents showed best corrosion resistance, regardless of what material they were combined with. In terms of polishing treatments, electropolished stents performed the best, mechanical-polished stents and those without polishing treatment followed. The analysis of corrosion behavior may be useful to select the right stent fulfilling the individual needs of the patient within a large number of different stents.
    Diagnostic and interventional radiology (Ankara, Turkey) 08/2015; 21(5). DOI:10.5152/dir.2015.15062 · 1.43 Impact Factor
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    ABSTRACT: The investigation of dedicated contrast agents for x-ray dark-field imaging, which exploits small-angle scattering at microstructures for contrast generation, is of strong interest in analogy to the common clinical use of high-atomic number contrast media in conventional attenuation-based imaging, since dark-field imaging has proven to provide complementary information. Therefore, agents consisting of gas bubbles, as used in ultrasound imaging for example, are of particular interest. In this work, we investigate an experimental contrast agent based on microbubbles consisting of a polyvinyl-alcohol shell with an iron oxide coating, which was originally developed for multimodal imaging and drug delivery. Its performance as a possible contrast medium for small-animal angiography was examined using a mouse carcass to realistically consider attenuating and scattering background signal. Subtraction images of dark field, phase contrast and attenuation were acquired for a concentration series of 100%, 10% and 1.3% to mimic different stages of dilution in the contrast agent in the blood vessel system. The images were compared to the gold-standard iodine-based contrast agent Solutrast, showing a good contrast improvement by microbubbles in dark-field imaging. This study proves the feasibility of microbubble-based dark-field contrast-enhancement in presence of scattering and attenuating mouse body structures like bone and fur. Therefore, it suggests a strong potential of the use of polymer-based microbubbles for small-animal dark-field angiography.
    PLoS ONE 07/2015; 10(7-7):e0129512. DOI:10.1371/journal.pone.0129512 · 3.23 Impact Factor
  • Olaf Dietrich · Tobias Geith · Maximilian F Reiser · Andrea Baur-Melnyk ·
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    ABSTRACT: Diffusion-weighted MRI (DWI) of the vertebral bone marrow is a clinically important tool for the characterization of bone-marrow pathologies and, in particular, for the differentiation of benign (osteoporotic) and malignant vertebral compression fractures. DWI of the vertebral bone marrow is, however, complicated by some unique MR and tissue properties of vertebral bone marrow. Due to both the spongy microstructure of the trabecular bone and the proximity of the lungs, soft tissue, or large vessels, substantial magnetic susceptibility variations occur, which severely reduce the magnetic field homogeneity as well as the transverse relaxation time T(*) 2 , and thus complicate MRI in particular with echoplanar imaging (EPI) techniques. Therefore, alternative diffusion-weighting pulse sequence types such as single-shot fast-spin-echo sequences or segmented EPI techniques became important alternatives for quantitative DWI of the vertebral bone marrow. This review first describes pulse sequence types that are particularly important for DWI of the vertebral bone marrow. Then, data from 24 studies that made diffusion measurements of normal vertebral bone marrow are reviewed; summarizing all results, the apparent diffusion coefficient (ADC) of normal vertebral bone marrow is typically found to be between 0.2 and 0.6 × 10(-3) mm(2) /s. Finally, DWI of vertebral compression fractures is discussed. Numerous studies demonstrate significantly greater ADCs in osteoporotic fractures (typically between 1.2 and 2.0 × 10(-3) mm(2) /s) than in malignant fractures or lesions (typically 0.7-1.3 × 10(-3) mm(2) /s). Alternatively, several studies used the (qualitative) image contrast of diffusion-weighted acquisitions for differentiation of lesion etiology: a very good lesion differentiation can be achieved, particularly with diffusion-weighted steady-state free precession sequences, which depict malignant lesions as hyperintense relative to normal-appearing vertebral bone marrow, in contrast to hypointense or isointense osteoporotic lesions. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.
    NMR in Biomedicine 06/2015; DOI:10.1002/nbm.3333 · 3.04 Impact Factor

  • 06/2015; 2(2). DOI:10.14440/bladder.2015.46
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    ABSTRACT: Acceleration of the image acquisition is an ever important technique in dynamic contrast-enhanced (DCE) MRI. Conventional parallel imaging is limited by the SNR loss at higher acceleration factors and by potential reconstruction artefacts. A recently introduced method, CAIPIRINHA, promises a more robust image reconstruction by modifying the k-space sampling schema. In the present study, we perform phantom measurements to identify the optimal CAIPIRINHA sampling pattern for a 3D DCE MRI perfusion measurement with coverage of the entire neurocranium at high temporal resolution, and we demonstrate the application of CAIPIRINHA acceleration for cerebral DCE MRI in patient measurements.
    23rd Scientific Meeting International Society for Magnetic Resonance in Medicine (ISMRM), At Toronto, Canada, Volume: Proc. Intl. Soc. Mag. Reson. Med. 23: 2346 (2015), Toronto; 06/2015
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    ABSTRACT: The purpose of this study was to analyze the influence of the regularization parameters on the results of quantitative susceptibility mapping using the superfast dipole inversion (SDI) technique. SDI is performed in the Fourier domain by multiplication with an SDI kernel, which depends on two regularization parameters for the regularization (1) of the Laplace operator inversion and (2) of the unit dipole inversion (in the Fourier domain). Both parameters were varied and the susceptibility of the substantia nigra and the red nucleus were assessed. The results showed a substantial variation of the susceptibility depending on the regularization.
    23rd Scientific Meeting International Society for Magnetic Resonance in Medicine (ISMRM), Toronto, Canada; 05/2015
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    ABSTRACT: This study evaluated the cost-effectiveness of different noninvasive imaging strategies in patients with possible basilar artery occlusion. A Markov decision analytic model was used to evaluate long-term outcomes resulting from strategies using computed tomographic angiography (CTA), magnetic resonance imaging, nonenhanced CT, or duplex ultrasound with intravenous (IV) thrombolysis being administered after positive findings. The analysis was performed from the societal perspective based on US recommendations. Input parameters were derived from the literature. Costs were obtained from United States costing sources and published literature. Outcomes were lifetime costs, quality-adjusted life-years (QALYs), incremental cost-effectiveness ratios, and net monetary benefits, with a willingness-to-pay threshold of $80 000 per QALY. The strategy with the highest net monetary benefit was considered the most cost-effective. Extensive deterministic and probabilistic sensitivity analyses were performed to explore the effect of varying parameter values. In the reference case analysis, CTA dominated all other imaging strategies. CTA yielded 0.02 QALYs more than magnetic resonance imaging and 0.04 QALYs more than duplex ultrasound followed by CTA. At a willingness-to-pay threshold of $80 000 per QALY, CTA yielded the highest net monetary benefits. The probability that CTA is cost-effective was 96% at a willingness-to-pay threshold of $80 000/QALY. Sensitivity analyses showed that duplex ultrasound was cost-effective only for a prior probability of ≤0.02 and that these results were only minimally influenced by duplex ultrasound sensitivity and specificity. Nonenhanced CT and magnetic resonance imaging never became the most cost-effective strategy. Our results suggest that CTA in patients with possible basilar artery occlusion is cost-effective. © 2015 The Authors.
    Stroke 05/2015; 46(7). DOI:10.1161/STROKEAHA.115.008841 · 5.72 Impact Factor
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    Bernhard Bischoff · Lucas L. Geyer · Maximilian F. Reiser · Ullrich G. Mueller Lisse ·

    05/2015; 3(2). DOI:10.5812/acvi.28932v2
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    ABSTRACT: The objective of this study was to assess the potential of grating-based phase-contrast computed tomography (gb-PCCT) for the detection and characterization of human coronary artery disease in an experimental ex vivo validation study. The study was approved by the institutional review board, and informed consent was obtained from all patients. Specimens were examined using a conventional low-coherence x-ray tube (40 kV) and a Talbot-Lau grating interferometer. Histopathologic assessment was used as the standard of reference. Signal characteristics of calcified, fibrous (FIB), and lipid-rich (LIP) tissue were visually and quantitatively assessed by phase-contrast Hounsfield units (HU). Conventional absorption-based HU values were also measured. Conservative measurements of diagnostic accuracy for the detection and differentiation of plaque components as well as quantitative measurements of vessel dimensions were obtained, and receiver operating characteristic curve analysis for plaque differentiation was performed. A total of 15 coronary arteries from 5 subjects were available for analysis (386 sections). Calcified, FIB, and LIP displayed distinct gb-PCCT signal criteria. The diagnostic accuracy of gb-PCCT was high with sensitivity, specificity, and negative and positive predictive values of 0.89 or greater for all plaque components with good interrater agreement (к ≥ 0.88). In addition, quantitative measurements of vessel dimensions in gb-PCCT were strongly correlated with measurements obtained from histopathology (Pearson R ≥ 0.86). Finally, phase-contrast Hounsfield units were superior to conventional HU in differentiating FIB and LIP (receiver operating characteristic analysis, 0.86 vs. 0.77, respectively; P < 0.05). In an ex vivo setting, gb-PCCT provides improved differentiation and quantification of coronary atherosclerotic plaque and may thus serve as a tool for nondestructive histopathology.
    Investigative radiology 05/2015; 50(10). DOI:10.1097/RLI.0000000000000169 · 4.44 Impact Factor
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    ABSTRACT: Purpose To detail the rationale, design, and future perspective of implementing whole-body magnetic resonance (MR) imaging in the German National Cohort, a large multicentric population-based study. Materials and Methods All institutional review boards approved the study, and informed consent is obtained before study enrollment. Participants are enrolled from a random sample of the general population at five dedicated imaging sites among 18 recruitment centers. MR imaging facilities are equipped with identical 3.0-T imager technology and use uniform MR protocols. Imager-specific hardware and software settings remained constant over the study period. On-site and centralized measures of image quality enable monitoring of completeness of the acquisitions and quality of each of the MR sequences. Certified radiologists read all MR imaging studies for presence of incidental findings according to predefined algorithms. Results Over a 4-year period, six participants per day are examined at each center, totaling a final imaging cohort of approximately 30 000 participants. The MR imaging protocol is identical for each site and comprises a set of 12 native series to cover neurologic, cardiovascular, thoracoabdominal, and musculoskeletal imaging phenotypes totaling approximately 1 hour of imaging time. A dedicated analysis platform as part of a central imaging core incorporates a thin client-based integrative and modular data handling platform to enable multicentric off-site image reading for incidental findings. Scientific analysis will be pursued on a per-project hypothesis-driven basis. Conclusion Population-based whole-body MR imaging as part of the German National Cohort will serve to compile a comprehensive image repository, will provide insight into physiologic variants and subclinical disease burden, and has the potential to enable identification of novel imaging biomarkers of risk. (©) RSNA, 2015 Online supplemental material is available for this article.
    Radiology 05/2015; 277(1):142242. DOI:10.1148/radiol.2015142272 · 6.87 Impact Factor
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    ABSTRACT: (1) To examine how many patients have clinically and/or radiologically active chronic recurrent multifocal osteomyelitis (CRMO) ≥ 10 years after first onset of symptoms, and (2) to compare clinical and whole-body magnetic resonance imaging (WB-MRI) findings. Seventeen patients (82% women) who were diagnosed with childhood-onset CRMO at least 10 years (average 12) before reexamination were reevaluated. Patients completed a standardized questionnaire, and underwent clinical and laboratory investigation and WB-MRI. Clinical features were compared with imaging findings. Five patients were found to be in clinical and radiological remission. One of these patients demonstrated 1 radiologically inactive lesion on WB-MRI. Four patients showed radiologically active lesions despite full clinical remission, 2 of them in 3 vertebral bodies. Spinal involvement in 6 patients (35%) caused vertebral compression fractures, vertebra plana, or vertebral hemifusion. Eight patients presented with ongoing clinical disease activity. When applying a CRMO activity score based on clinical and imaging findings, 2 patients were identified as having pain amplification. Overall, 22/55 known CRMO lesions were identified; 11 of them were radiologically active lesions. Additionally, 14 so far unknown clinically silent lesions were detected: 8 radiologically active lesions and 6 radiologically inactive lesions. CRMO activity on longterm followup might have been underestimated. Our study demonstrates that clinical remission does not necessarily mean radiological remission. We therefore propose that all patients with CRMO, including patients in clinical remission, require longterm clinical followup and should undergo evaluation with WB-MRI on a regular basis until radiological remission or a steady state of disease is achieved.
    The Journal of Rheumatology 05/2015; 42(8). DOI:10.3899/jrheum.141026 · 3.19 Impact Factor
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    ABSTRACT: To evaluate the in vivo response by detecting the anti-angiogenic and invasion-inhibiting effects of a triple-combination-therapy in an experimental-small-animal-squamous-cell-carcinoma-model using the "flash-replenishment" (FR) method to assess tissue hemodynamics via contrast-enhanced-ultrasound (CEUS). Human hypopharynx-carcinoma-cells were subcutaneously injected into the left flank of 22-female-athymic-nude-rats. After seven days of subcutaneous tumor growth, FR-measurements were performed on each rat. Treatment-group and control-group were treated every day for a period of one week, with the treatment-group receiving solvents containing a triple therapy of Upamostat®, Celecoxib® and Ilomastat® and the control-group solvents only. On day seven, follow-up measurements were performed using the same measurement protocol to assess the effects of the triple therapy. VueBox® was used to quantify the kinetic parameters and additional immunohistochemistry analyses were performed for comparison with and validation of the CEUS results against established methods (Proliferation/Ki-67, vascularization/CD31, apoptosis/caspase3). Compared to the control-group, the treatment-group that received the triple-therapy resulted in a reduction of tumor growth by 48.6% in size. Likewise, the immunohistochemistry results showed significant decreases in tumor proliferation and vascularization in the treatment-group in comparison to the control-group of 26%(p≤0.05) and 32.2%(p≤0.05) respectively. Correspondingly, between the baseline and follow-up measurements, the therapy-group was associated with a significant(p ≤ 0.01) decrease in the relative-Blood-Volume(rBV) in both the whole tumor(wt) and hypervascular tumor(ht) areas (p≤0.01), while the control-group was associated with a significant (p≤0.01) increase of the rBV in the wt area and a non-significant increase (p≤0.16) in the ht area. The mean-transit-time (mTT) of the wt and the ht areas showed a significant increase (p≤0.01) in the follow-up measurements in the therapy group. The triple-therapy is feasible and effective in reducing both tumor growth and vascularization. In particular, compared with the placebo-group, the triple-therapy-group resulted in a reduction in tumor growth of 48.6% in size when assessed by CEUS and a significant reduction in the number of vessels in the tumor of 32% as assessed by immunohistochemistry. As the immunohistochemistry supports the CEUS findings, CEUS using the "flash replenishment"(FR) method appears to provide a useful assessment of the anti-angiogenic and invasion-inhibiting effects of a triple combination therapy.
    BMC Cancer 05/2015; 15(1):373. DOI:10.1186/s12885-015-1333-7 · 3.36 Impact Factor
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    ABSTRACT: The aim of this study was to assess the impact of cardiovascular risk factors and plaque inflammation on the progression of atherosclerosis as assessed by positron emission tomography/computed tomography (PET/CT) imaging with 18F-radiolabled fluorodeoxyglucose (18F-FDG). This study was designed as a retrospective cohort study. Patients who received a 18F-FDG PET/CT scan and follow-up scan 9–24 months later without systemic inflammation or steroid medication were eligible for the study. 18F-FDG PET/CT included a full diagnostic contrast enhanced CT scan. Cardiovascular risk factors and medication were documented. Calcified plaque volume, lumen area and 18F-FDG uptake, quantified by the target-to-background ratio (TBR), were measured in the carotid arteries, aorta and iliac arteries. Influence of cardiovascular risk factors and vessel wall inflammation on atherosclerotic disease progression was analyzed. Ninety-four patients underwent baseline and follow-up whole body 18F-FDG PET/CT (mean follow-up time 14.5 ± 3.5 months). Annualized calcified plaque volume increased by 15.4 % (p
    The international journal of cardiovascular imaging 04/2015; DOI:10.1007/s10554-015-0660-8 · 1.81 Impact Factor
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    ABSTRACT: The objective of this study was to evaluate the feasibility of a novel 3-dimensional turbo spin-echo technique with isotropic resolution for the diagnosis of deep vein thrombosis (DVT) in comparison with contrast-enhanced magnetic resonance imaging (CE-MRI) and sonography. Thirteen patients (8 males, 17-93 years) with proven DVT in duplex ultrasound (n = 11) or with pulmonary embolism and suspected to have DVT (n = 2) were consecutively imaged at 3.0 T with 1.2-mm isotropic-resolution volumetric isotropic turbo spin-echo acquisition (VISTA). Sensitivity (SE), specificity (SP), positive and negative predictive values (PPV and NPV, respectively), Cohen κ, as well as accuracy of VISTA-MRI were calculated and compared with CE-MRI and sonography as a standard of reference. Image quality and diagnostic confidence were assessed on a 4-point scale. Image quality and diagnostic confidence level of VISTA-MRI and CE-MRI were comparable (3.54 vs 3.55 and 3.80 vs 3.77; both P values are nonsignificant). Using CE-MRI as the criterion standard, there was a high agreement between the CE-MRI and the 3-dimensional VISTA examinations for the detection of DVT, with κ of 0.89 for reader 1 and κ of 0.88 for reader 2 (both P < 0.001). The SE, SP, PPV, NPV, as well as accuracy of VISTA-MRI were 92.5%, 97.9%, 89.3%, 98.6%, and 97.1% for reader 1 as well as 90.7%, 97.9%, 89.1%, 98.3%, and 96.8% for reader 2. For both readers, combined comparison of VISTA-MRI and sonography resulted in an SE, SP, PPV, and NPV of 77.8%, 94.8%, 85.4%, and 91.6%, respectively. Volumetric isotropic turbo spin-echo acquisition magnetic resonance imaging can be used to diagnose DVT with good to excellent agreement compared with CE-MRI and sonography. It might be useful when contrast media is prohibited and in patients with suspected thrombosis of the iliac veins, which can be hard to detect with sonography.
    Investigative radiology 03/2015; 50(6). DOI:10.1097/RLI.0000000000000142 · 4.44 Impact Factor
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    ABSTRACT: To analyze the flip angle dependence and to optimize the statistical precision of a fast three-dimensional (3D) T1 mapping technique based on the variable flip angle (VFA) method. The proposed single flip angle (1FA) approach acquires only a single 3D spoiled gradient echo data set for each time point of the dynamical series in combination with a longer baseline measurement. The optimal flip angle for the dynamic series can be calculated as αdyn,opt = arccos[(2E1 - 1)/(2 - E1 )] (with E1 = exp(-TR /T1 )) by minimizing the statistical error of T1 . T1 maps of a liquid phantom with step-wise increasing concentrations of contrast agent were measured using a saturation recovery (SR) and a VFA/1FA technique with 11 flip angles. The standard deviation of the parameter maps was defined as statistical error of the 1FA measurement. The measured statistical error of the 1FA technique as a function of αdyn agrees with the derived theoretical curve. The optimal flip angle increases from about 5° for T1 = 2629 ms to 30° for T1 = 137 ms. The relative deviation between 1FA and SR measurements varies between -2.9 % and +10.3 %. Measurements in vivo confirm the expression for the optimal flip angle. The proposed flip angle-optimized 1FA technique optimizes the precision of T1 values in dynamic phantom measurements. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.
    Magnetic Resonance in Medicine 03/2015; 73(3):1158-1163. DOI:10.1002/mrm.25199 · 3.57 Impact Factor
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    ABSTRACT: To determine the feasibility of free-breathing, GRAPPA-based, real-time (RT) cine 3T cardiac magnetic resonance imaging (MRI) with high acceleration factors for the assessment of left-ventricular function in a cohort of patients as compared to conventional segmented cine imaging. In this prospective cohort study, subjects with various cardiac conditions underwent MRI involving two RT cine sequences (high resolution and low resolution) and standard segmented cine imaging. Standard qualitative and quantitative parameters of left-ventricular function were quantified. Among 25 subjects, 24 were included in the analysis (mean age: 50.5±21 years, 67% male, 25% with cardiomyopathy). RT cine derived quantitative parameters of volumes and left ventricular mass were strongly correlated with segmented cine imaging (intraclass correlation coefficient [ICC]: >0.72 for both RT cines) but correlation for peak ejection and filling rates were moderate to poor for both RT cines (ICC<0.40). Similarly, RT cines significantly underestimated peak ejection and filling rates (>103.2±178ml/s). Among patient-related factors, heart rate was strongly predictive for deviation of measurements (p<0.05). RT cine MRI at 3T is feasible for qualitative and quantitative assessment of left ventricular function for low and high-resolution sequences but results in significant underestimation of systolic function, peak ejection and filling rates. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.
    European journal of radiology 02/2015; 84(5). DOI:10.1016/j.ejrad.2015.02.016 · 2.37 Impact Factor
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    ABSTRACT: To investigate a multimodal, multiparametric perfusion MRI / 18F-fluoro-deoxyglucose-(18F-FDG)-PET imaging protocol for monitoring regorafenib therapy effects on experimental colorectal adenocarcinomas in rats with immunohistochemical validation. Human colorectal adenocarcinoma xenografts (HT-29) were implanted subcutaneously in n = 17 (n = 10 therapy group; n = 7 control group) female athymic nude rats (Hsd:RH-Foxn1rnu). Animals were imaged at baseline and after a one-week daily treatment protocol with regorafenib (10 mg/kg bodyweight) using a multimodal, multiparametric perfusion MRI/18F-FDG-PET imaging protocol. In perfusion MRI, quantitative parameters of plasma flow (PF, mL/100 mL/min), plasma volume (PV, %) and endothelial permeability-surface area product (PS, mL/100 mL/min) were calculated. In 18F-FDG-PET, tumor-to-background-ratio (TTB) was calculated. Perfusion MRI parameters were correlated with TTB and immunohistochemical assessments of tumor microvascular density (CD-31) and cell proliferation (Ki-67). Regorafenib significantly (p<0.01) suppressed PF (81.1±7.5 to 50.6±16.0 mL/100mL/min), PV (12.1±3.6 to 7.5±1.6%) and PS (13.6±3.2 to 7.9±2.3 mL/100mL/min) as well as TTB (3.4±0.6 to 1.9±1.1) between baseline and day 7. Immunohistochemistry revealed significantly (p<0.03) lower tumor microvascular density (CD-31, 7.0±2.4 vs. 16.1±5.9) and tumor cell proliferation (Ki-67, 434.0 ± 62.9 vs. 663.0 ± 98.3) in the therapy group. Perfusion MRI parameters ΔPF, ΔPV and ΔPS showed strong and significant (r = 0.67-0.78; p<0.01) correlations to the PET parameter ΔTTB and significant correlations (r = 0.57-0.67; p<0.03) to immunohistochemical Ki-67 as well as to CD-31-stainings (r = 0.49-0.55; p<0.05). A multimodal, multiparametric perfusion MRI/PET imaging protocol allowed for non-invasive monitoring of regorafenib therapy effects on experimental colorectal adenocarcinomas in vivo with significant correlations between perfusion MRI parameters and 18F-FDG-PET validated by immunohistochemistry.
    PLoS ONE 02/2015; 10(2):e0115543. DOI:10.1371/journal.pone.0115543 · 3.23 Impact Factor

Publication Stats

17k Citations
1,802.45 Total Impact Points


  • 1997-2015
    • Ludwig-Maximilian-University of Munich
      • Department of Clinical Radiology
      München, Bavaria, Germany
  • 2008-2014
    • Technische Universität München
      München, Bavaria, Germany
  • 2003-2013
    • University Hospital München
      München, Bavaria, Germany
  • 2011
    • Harvard University
      Cambridge, Massachusetts, United States
  • 2010
    • Trinity College Dublin
      • School of Medicine
      Dublin, L, Ireland
  • 2009
    • Scott & White
      Temple, Texas, United States
    • Universität Heidelberg
      • Faculty of Medicine Mannheim and Clinic Mannheim
      Heidelberg, Baden-Wuerttemberg, Germany
  • 2007
    • University of Wisconsin, Madison
      • Department of Radiology
      Mississippi, United States
  • 2004
    • Brown University
      Providence, Rhode Island, United States
  • 2002
    • Huazhong University of Science and Technology
      Wu-han-shih, Hubei, China
  • 2001
    • Tongji Medical University
  • 1992-1993
    • University of Bonn
      • Radiologische Klinik
      Bonn, North Rhine-Westphalia, Germany