Ulrike Wedegärtner

Comparative Effectiveness of 18f-fdg Pet/ct Versus Whole-body Mri for Detection of Malignant Peripheral Nerve Sheath Tumors in Neurofibromatosis Type 1

Purpose The aim of this study was to compare the diagnostic performance of 18F-fluorodeoxyglucose (FDG) PET/CT and whole-body MRI for the detection of malignant peripheral nerve sheath tumors (MPNSTs) in patients with neurofibromatosis type 1, and to evaluate a panel of imaging-based criteria serving that purpose. Patients and Methods Thirty-one patients were examined by whole-body MRI and 18F-FDG PET/CT. A panel of imaging-based criteria including tumor region, size, shape, margin definition, contrast enhancement, heterogeneity before and after contrast, intratumoral lobulation, target sign, and mean and maximum standardized uptake values (SUVs) were evaluated. A SUVmax cut-off value of 3.5 was used for lesion analysis. Histopathologic evaluation and/or clinical follow-up served as the reference standard. Results 18F-FDG PET/CT had a sensitivity of 100%, whereas MRI had a sensitivity of 66.7%. On PET/CT, tumor size (P < 0.005), SUVmax (P < 0.0001), SUVmean (P < 0.0001), and tracer uptake heterogeneity (P = 0.002) were significantly associated with MPNSTs. On MRI, intratumoral lobulation (P < 0.02), ill-defined margins (P = 0.007), and irregular enhancement on T1-weighted imaging (P < 0.001) were significantly associated with MPNSTs. Conclusions Both PET/CT and whole-body MRI may distinguish benign and malignant PNSTs, but PET/CT has higher sensitivity for that purpose. Imaging-based criteria for identification of MPNSTs on both modalities were identified. False-positive results, requiring biopsy or clinical follow-up, may be reduced by using a combination of MRI and PET derived markers, but only at the price of reduced sensitivity.

Cardiac MRI of the fetal heart using a novel triggering method: Initial results in an animal model

To investigate MRI of the fetal heart by way of a novel triggering method with the use of an MR‐compatible cardiotocography (CTG) in an animal model.

DWI of the brain: Postmortal DWI of the brain in comparison with in vivo data

PURPOSE Changes in water diffusion can be quantified by diffusion-weighted MR imaging. However, there are only few reports about changes in post mortem brain. The aim of this study was to investigate the temporal pattern of the apparent diffusion coefficient (ADC) in the brain after death, to compare the values to in vivo brain and to assess the value of ex vivo DWI as a forensic tool. MATERIAL AND METHODS The study was approved by the local Ethics Committee, and informed consent was obtained from all relatives and the control subjects. Twenty-one corpses, died of natural cause, were examined (13 males, 8 females; age: 70.5±8.7 y, weight 74±18 kg). Diffusion-Weighted Imaging (DWI) was performed with b-values of 0 and 1000 s/mm(2) at 1.5 T. Scans were repeated in intervals of 1 h. ADC-maps were calculated in thalamus, cerebrum and cerebellum. The obtained values were statistically compared to healthy volunteers (n=3) and to literature data. RESULTS The ADC in the three regions decreased characteristically during the examination time. In the cerebrum there was a significant difference between ex vivo and in vivo ADC (p<0.001) as well as in the other regions (thalamus: p<0.001, cerebellum: p=0.045). CONCLUSION DWI of the postmortal brain can be added to the MRI methods for a post mortem imaging.

In vivo MRI measurement of fetal blood oxygen saturation in cardiac ventricles of fetal sheep: A feasibility study

The purpose of this study was to assess the feasibility to determine fetal blood oxygen saturation (sO2) with T2‐weighted MR sequences using a fetal sheep model. T2 measurements were performed on a 1.5‐T scanner using a T2 preparation pulse in combination with a three‐dimensional balanced steady‐state free precession sequence repeated at different echo times. Eight sheep fetuses were examined during a control, hypoxic, and recovery phase to perform T2‐weighted scans of the fetal blood in the heart. Signal intensities in the left and right ventricle were measured to calculate the MR blood sO2. During each phase, fetal carotid artery sO2 was directly measured and correlated with MR sO2. A Bland‐Altman plot was performed. Fetal carotid artery sO2 was 69% sO2 during control, 16% sO2 during hypoxemia, and 67% sO2 during recovery. Mean values of the MR sO2 were 49% sO2 and 40% sO2 for control, 6% sO2 and 3% sO2 for hypoxemia, and 51% sO2 and 43% sO2 for recovery in left ventricle and right ventricle, respectively. Mean values of fetal carotid artery sO2 and MR sO2 were highly correlated (left ventricle: r = 0.87, right ventricle: r = 0.89). According to the Bland‐Altman plot, MR sO2 was lower compared to fetal carotid artery sO2 (left ventricle: 15%, right ventricle: 20%). Based on our preliminary results, it seems to be possible to assess fetal sO2 with MR oximetry. Magn Reson Med, 2010.

Simulated low-dose computed tomography in oncological patients: a feasibility study.

Objective: Image quality of chest and abdominal computed tomographic (CT) scans was evaluated at different doses to assess the lowest value of x-ray dose at which the image quality was not being affected. Materials and Methods: Using multislice CT (MSCT), 29 patients who submitted to follow-up examinations were examined using a combined MSCT protocol of the chest and the abdomen on 4-raw MSCT (Siemens, Erlangen, Germany). For each examination, approximately 120 mL of contrast agent (Bracco-Altana, Konstanz, Germany) was applied intravenously. The raw data were transferred to an external personal computer equipped with an image reconstruction software (CardioRecon 6; Siemens, Forchheim, Germany) to simulate 5 different dose levels. To simulate them correctly, a milliampere second-dependent noise was added to every image, so that the changes in a current-time product could be imitated. The images were compared in consensus by 2 radiologists who were not informed about the technical scanning parameters, that is, dose parameters, and were graded in 4 different subcategories on a 1-to-5-point scale. For statistical analysis, the Friedman test was used. Additional evaluations for lesions smaller than 1.0 cm were performed and analyzed separately. Results: For image noise, there was a significant change between 40 and 60 mA s. For lesion detection, there was no significant change. The contour of the small objects did not differ between 90, 60, and 40 mA s. However, a dose reduction to 30 mA s had a significant effect. The contrast did not differ between 90, 60, 40, and even down to 30 mA s. Only a maximal dose reduction to 20 mA s had a significant effect on the contrast. The level of noise was most sensitive to the current. Whereas a dose reduction to 60 mA s did not yet have a significant effect, there was a significant increase of noise at 40 mA s. Conclusions: The MSCT can be applied with a lower dose than that usually selected in examinations at present to follow-up and stage the oncological patients adequately.

Magnetic resonance angiography of fetal vessels: feasibility study in the sheep fetus.

PurposeThe aim of this study was to perform fetal magnetic resonance angiography (MRA) in utero in a sheep model.Material and methodsImages of the great vessels, the heart, and the tracheal tree were performed on four pregnant ewes with a 1.5-T scanner (Philips Medical Systems, Best, The Netherlands). MRA was achieved in utero using a nontriggered free-breathing three-dimensional balanced fast field echo (FFE) technique. All obtained MRA images were evaluated in consensus on a three-point scale by two radiologists with 9 and 4 years of experience in fetal MRI, respectively.ResultsThe fetal heart frequencies were between 130 and 160 bpm. The aorta from the aortic bulb to the bifurcation as well as some of the main aortic branches could be depicted. The pulmonary trunk and arteries, the superior and inferior caval veins, and the subsegmental branches of the trachea could also be visualized.ConclusionThe nontriggered MRA of the fetal great vessels with images of the tracheal tree allowed an excellent evaluation of anatomical structures.

ΔR2* in Fetal Sheep Brains during Hypoxia: MR Imaging at 3.0 T versus That at 1.5 T

PURPOSE To investigate the feasibility of fetal blood oxygen level-dependent magnetic resonance (MR) imaging at 1.5 T and to compare DeltaR2* in the brains of fetal sheep during hypoxia at 3.0 T with that at 1.5 T. MATERIALS AND METHODS All experimental protocols were reviewed and approved by the local authorities on animal protection. Between January 2006 and May 2006, fetal brain measurements were performed in eight pregnant ewes with 1.5-T and 3.0-T MR imaging units after fetal paralysis was achieved by administering pancuronium bromide. With both imaging units, a T2*-weighted single-shot gradient-echo echo-planar imaging sequence (echo time, 30 msec at 3.0 T and 50 msec at 1.5 T) was used to measure T2* signal changes (DeltaR2*) in the fetal brain in control conditions and during hypoxia (maternal oxygenation, 50%-70%). A carotid catheter was placed and maintained in the fetuses to enable measurement of the fetal arterial oxygen saturation (SaO(2)). DeltaR2* was correlated with fetal SaO(2), and linear regression analysis was performed. A paired t test was used to evaluate differences, with a significance level of P < .05. RESULTS At both field strengths, a signal intensity decrease on T2*-weighted images during hypoxia was detected. At 1.5 T, mean fetal SaO(2) was reduced from 65.4% +/- 9.2 (standard deviation) during control conditions to 17.7% +/- 6.2 during hypoxia. DeltaR2* and fetal SaO(2) correlated significantly (r = 0.98, P = .018). At 3.0 T, fetal SaO(2) was reduced from 62.4% +/- 7.5 during control conditions to 18% +/- 7.5 during hypoxia. DeltaR2* and fetal SaO(2) also correlated significantly (r = 0.95, P = .012). A linear fit resulted in a slope value of 0.084 +/- 0.003 for 1.5 T and 0.166 +/- 0.016 for 3.0 T. This means a doubled sensitivity of DeltaR2* for oxygen saturation variations at 3.0 T compared with 1.5 T. CONCLUSION MR imaging at 3.0 T is more sensitive than that at 1.5 T in the detection of DeltaR2* in the fetal brain during hypoxia. However, there was a signal decrease in the fetal brain in all 1.5-T experiments during hypoxia. Thus it is possible to measure fetal DeltaR2* at 1.5 T, which may be of more practical relevance for the evaluation of pregnant women.

Cardiac MR: Imaging of the Foetal Heart Dynamics using Doppler Ultrasound Triggering

Magnetic Resonance Imaging (MRI) could be of high importance for imaging the foetal heart, especially to diagnose anomalies of the heart and the great vessels. While in the imaging of adult hearts MR triggering can be done through Electro-Cardiogram (ECG) or finger pulse oximetry (POX), these methods cannot apply because the foetus lies within the uterus. The aim of this project was to demonstrate the feasibility of non-invasive triggering of the MR by the foetal heart beat using Doppler Ultrasound. An artefact-free Doppler transducer was used to pick up the heart motion signals. An algorithm was developed which allowed triggering of the MR system. In an animal study, successful imaging of the foetal sheep heart was performed on 9 pregnant ewes at a 1.5T scanner. With dedicated software, MR cine sequences of the foetal heart beat and standard twoand four chamber images of the structures of the hearts of 124 days old foetuses could be recorded with a good resolution.

High-Resolution In Utero 3D MR Imaging of Inner Ear Microstructures in Fetal Sheep

BACKGROUND AND PURPOSE: Developmental inner ear abnormalities can occur due to embryopathies as well as in the context of syndromal diseases like the CHARGE association. In severe cases, an early and definite in utero diagnosis is important for decision-making; here, fetal MR imaging can be a helpful tool. We present results of performing high-resolution MR imaging of the inner ear structures of fetal sheep in vivo. METHODS AND MATERIALS: Six ewes carrying singleton fetuses (mean gestational age, 120 days) were examined under general anesthesia at 1.5T. A 3D true FISP sequence with isotropic voxel size (0.7 mm) was applied; acquisition time was 2:35 minutes. For a standard of reference, 1 stillborn lamb of equivalent gestation age was examined. Image analysis was performed in consensus by 2 radiologists regarding the depiction of anatomic landmarks on a 5-point scale. Motion artifacts were quantified on a 3-point scale. RESULTS: The turns and modiolus of the cochlea as well as the origins of all 3 semicircular canals of the vestibular system of both sides could be reliably identified in every animal. Motion artifacts due to maternal breathing excursions or movements of the fetus were minimal. In case of breech presentation, the ventilation of the ewe had to be paused during the image acquisition to achieve acceptable results. CONCLUSIONS: High-resolution intrauterine MR imaging of the inner ear microstructures in an animal model is feasible. However, the acquisition time of the sequence applied is still too long to perform such measurement in a clinical setting.

Evaluation of an Mr Compatible Doppler-Ultrasound Device as a New Trigger Method in Cardiac Mri: A Quantitative Comparison to ECG.

The aim was to investigate the feasibility to perform cardiac magnetic resonance imaging (MRI) using a MR compatible Doppler-ultrasound (US) device as a new method to trigger the human heart cycle. MRI images were compared between ECG and Dopplerultrasound triggered examination in terms of image quality by an objective measure of acutance and functional assessment.