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Michael Bock

Publications and source records attributed to Michael Bock.

51 records · Page 3Linked to original sources
PubMed2003

Partially parallel three-dimensional magnetic resonance imaging for the assessment of lung perfusion--initial results.

RATIONALE: Contrast-enhanced magnetic resonance imaging (MRI) of lung perfusion requires a high spatial and temporal resolution. Partially parallel MRI offers an improved spatial and temporal resolution. OBJECTIVE: To assess the feasibility of partially parallel MRI for the assessment of lung perfusion. METHODS: Two healthy volunteers and 14 patients were examined with a contrast-enhanced 3D gradient-echo pulse sequence with partially parallel image acquisitions (TE/TR/alpha: 0.8/1.9 milliseconds/40 degrees; voxel size 3.6 x 2.0 x 5.0 mm3, TA: 1.5 seconds). The image analysis included an analysis of the signal-to-noise ratio in the lungs in areas with normal and impaired perfusion. 3D MR perfusion image data were analyzed for perfusion defects and compared with radionuclide perfusion scans, which were available for 10 of 14 patients. RESULTS: The analysis of the 3D perfusion-weighted data allowed a clear differentiation of perfusion abnormalities: MRI showed normal lung perfusion in 9 of 16 cases, whereas perfusion abnormalities were observed in 7 cases. When compared with the radionuclide perfusion scans, a good intermodality agreement was shown (kappa = 0.74). When compared with normally perfused lung a significantly lower signal to noise ratio was observed in hypoperfused lung (7 versus 17; P = 0.02). CONCLUSION: Partially parallel MRI might be used for the assessment of lung perfusion. Future studies are required to further evaluate the diagnostic impact of this technique.

Adult↗
PubMed2003

Feline foamy virus genome and replication strategy.

Crucial aspects of the foamy virus (FV) replication strategy have so far only been investigated for the prototypic FV (PFV) isolate, which is supposed to be derived from nonhuman primates. To study whether the unusual features of this replication pathway also apply to more-distantly related FVs, we constructed feline FV (FFV) infectious molecular clones and vectors. It is shown by quantitative RNA and DNA PCR analysis that FFV virions contain more RNA than DNA. Full-length linear DNA was found in extracellular FFV by Southern blot analysis. Similar to PFV, azidothymidine inhibition experiments and the transfection of nucleic acids extracted from extracellular FFV indicated that DNA is the functional relevant FFV genome. Unlike PFV, no evidence was found indicating that FFV recycles its DNA into the nucleus.

Animals↗
PubMed2003

An MRI-compatible surgical robot for precise radiological interventions.

OBJECTIVE: A variety of medical robots have been developed in recent years. MRI, including MR angiography and morphological imaging, with its excellent soft-tissue contrast is attractive for the development of interventional MRI-guided therapies and operations. This paper presents a telerobotic device for use in CT- and/or MR-guided radiological interventions. A robotic device for precise needle insertion during MR-guided therapy of spinal diseases will be briefly described. MATERIALS AND METHODS: Actuation of robots in an MRI environment is difficult due to the presence of strong magnetic fields. Therefore, the robot was constructed of nonmagnetic materials. The system frame was built from polyether ether ketone (PEEK) and fiber-reinforced epoxy, and actuated using ultrasonic and pneumatic motors. Completely MR-compatible sensors were developed for positioning control. RESULTS: Accuracy evaluation procedures and phantom tests were performed, with the required accuracy of approximately 1 mm being achieved and no significant artifacts being caused by the robotic device during MR image acquisition.

Animals↗
PubMed2002

Determination of regional blood volume and intra-extracapillary water exchange in human myocardium using Feruglose: First clinical results in patients with coronary artery disease.

The aim of this pilot study in humans was to investigate the effect of an intravascular contrast agent (CA) on relaxation rate in myocardium (R(1,myo)) in the steady state. The dependence of R(1,myo) on R(1,blood) was characterized and compared with a theoretical model which allowed determination of the intra- extracapillary water proton exchange frequency (f = 0.48 s(-1)) and the intracapillary blood volume (RBV = 12.9 %). A linear response range of DeltaR(1,myo) on DeltaR(1,blood) was estimated which in future studies will allow the determination of RBV with intravascular CA.

Aged↗
PubMed2002

Three-dimensional spiral MR imaging: Application to renal multiphase contrast-enhanced angiography.

A fast MR pulse sequence with spiral in-plane readout and conventional 3D partition encoding was developed for multiphase contrast-enhanced magnetic resonance angiography (CE-MRA) of the renal vasculature. Compared to a standard multiphase 3D CE-MRA with FLASH readout, an isotropic in-plane spatial resolution of 1.4 x 1.4 mm(2) over 2.0 x 1.4 mm(2) could be achieved with a temporal resolution of 6 sec. The theoretical gain of spatial resolution by using the spiral pulse sequence and the performance in the presence of turbulent flow was evaluated in phantom measurements. Multiphase 3D CE-MRA of the renal arteries was performed in five healthy volunteers using both techniques. A deblurring technique was used to correct the spiral raw data. Thereby, the off-resonance frequencies were determined by minimizing the imaginary part of the data in image space. The chosen correction algorithm was able to reduce image blurring substantially in all MRA phases. The image quality of the spiral CE-MRA pulse sequence was comparable to that of the FLASH CE-MRA with increased spatial resolution and a 25% reduced contrast-to-noise ratio. Additionally, artifacts specific to spiral MRI could be observed which had no impact on the assessment of the renal arteries.

Adult↗
PubMed2002

[Proton spinlocking and T1 rho-weighted MR imaging at 1.5 T].

During spinlocking, the magnetization is aligned along an oscillating field (RF) and relaxes with time constant T1 rho, the spin-lattice relaxation time in the rotating frame. Using a clinical whole-body MR scanner, methods of spinlocking preparation and signal acquisition were combined to evaluate the potential of T1 rho-weighted MR imaging (T1 rho w-MRI) at B0 = 1.5 T. Examinations of the brain of healthy volunteers yielded images with pronounced contrast and T1 rho-variation of the tissue. However, the contrast resembled that of T2-weighted MRI, which is explained by the restricted spinlocking-field strength (BSL < or = 6 microT) on the tomograph. The result (mono-exponential fit) of serial T1 rho w-MRI data from examinations of 8 volunteers was on average 105 +/- 4 ms in the gray matter and 86 +/- 4 ms in the white matter (for BSL = 3 microT). The values are comparable to T2 of both tissues. MRT with spinlocking is less susceptible to local magnetic field inhomogeneities than conventional MRI.

Humans↗
PubMed2002

Interstitial magnetic resonance lymphography with gadobutrol in rats: evaluation of contrast kinetics.

RATIONALE AND OBJECTIVE: To evaluate the contrast kinetics of gadobutrol for interstitial MR lymphography. MATERIALS AND METHODS: In 11 rats, 0.5 mL undiluted gadobutrol was injected subcutaneously into the hind paw. Contrast kinetics were measured in lymph nodes, kidney, liver, muscle, and blood of six animals using a time-resolved 2D GRE sequence. Additionally, high-resolution 3D T1-weighted data sets were obtained in five animals. RESULTS: Immediately after injection, a pronounced signal intensity loss was observed in popliteal, inguinal and aorto-iliac lymph nodes, followed by a continuous signal intensity increase. From the data peak concentrations of up to 78 mmol/L were estimated for selected lymph nodes. A contrast enhancement was also observed in kidneys, liver, muscle, and blood. Regional lymphatic vessels, the thoracic duct, as well as popliteal, inguinal, aorto-iliac, and axillary lymph node groups could be visualized with the high-resolution 3D MRI. CONCLUSION: Gadobutrol is suitable for interstitial MR lymphography, as it rapidly appears in the lymphatic system. Based on estimates of local tissue concentrations future studies have to assess the optimal contrast agent dosage. Furthermore, the investigation of metastatic lymph nodes is required to evaluate the further potential of gadobutrol for interstitial MR lymphography.

Animals↗
PubMed2002

High-throughput genetic screening using matrix-assisted laser desorption/ionization mass spectrometry.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has become a powerful and widespread analytical tool in all fields of life science. Compared with other techniques, its high accuracy and sensitivity makes it a superior method, especially for the analysis of nucleic acids. Recent problems in the analysis of nucleic acids by MALDI-TOF MS can be solved using an automated MALDI-compatible sample-preparation system. Together with the reliable minisequencing assay, high-throughput genotyping of single nucleotide polymorphisms by MALDI-TOF MS is able to become a routine method in research, clinical genetics and diagnostics.

Automation↗
PubMed2002

Lack of evidence for pulmonary venous thrombosis in cryptogenic stroke: a magnetic resonance angiography study.

BACKGROUND: Even after extensive evaluation, the etiology of ischemic stroke remains undefined in a considerable proportion of cases, suggesting that causes of stroke may exist that have not yet been established. We tested the hypothesis that pulmonary venous thrombosis (PVT) is a potential source of brain embolism in patients with cryptogenic stroke. SUMMARY OF REPORT: Within 7 days after mild to moderately severe ischemic stroke or transient ischemic attack, 18 patients (9 women, 9 men; mean age, 48 years) were studied in whom the etiology remained undefined despite complete workup. All patients received high-resolution pulmonary venography with the use of multiple-bolus, multiphase, 3-dimensional, gadolinium-enhanced MR angiography (MRA). Overall quality of the MRA was good in 14 and insufficient in 4 patients, mainly as a result of breathing artifacts. Visualization of the main and segmental veins and evaluability of their patency were good for most right pulmonary veins but often inadequate for left pulmonary veins, particularly for those in the left lower lobe. There was no evidence for PVT in any of the sufficiently visualized pulmonary veins. CONCLUSIONS: The results do not support the hypothesis of PVT as a contributor to the etiology of ischemic stroke. However, the study was limited regarding scan volume, spatial discrimination, patient selection, and delay between ischemia and MRA. Therefore, further investigations, including postmortem studies, are needed to resolve the question of whether PVT may contribute to ischemic stroke.

Adult↗
PubMed2000

Correlation of hemodynamic impact and morphologic degree of renal artery stenosis in a canine model.

In a noninvasive comprehensive magnetic resonance (MR) examination, the morphologic degree of renal artery stenosis was correlated to corresponding changes in renal artery flow dynamics. Different degrees of stenosis were created with the use of a chronically implanted inflatable arterial cuff in seven dogs. For each degree of stenosis, an ultrafast three-dimensional gadolinium MR angiography with high spatial resolution was performed, followed by cardiac-gated MR flow measurements with high temporal resolution for determination of pulsatile flow profiles and mean flow. Flow was also measured by a chronically implanted flow probe. In three of the dogs, trans-stenotic pressure gradients (DeltaP) also were measured via implanted catheters. Five different degrees of stenosis could be differentiated in the MR angiograms (0%, 30%, 50%, 80%, >90%). The MR flow data agreed with the flow probe within +/-20%. Stenoses between 30 and 80% gradually reduced the early systolic peak (Max(1)) of the flow profile but only minimally affected the midsystolic peak (Max(2)) or mean flow. Stenoses of more than 90% significantly depressed mean flow by more than 50%. The ratio between Max(1) and Max(2) (Rmax(1/2)) gradually fell with the degree of stenosis. The onset of significant mean flow reduction and DeltaP was indicated by a drop of Rmax(1/2) below 1 to 1.2. Thus, the analysis of high-resolution flow profiles allows detection of early hemodynamic changes even at degrees of stenoses not associated with a reduction of mean flow. Rmax(1/2) allows differentiation of the grade of hemodynamic compromise for a given morphologic stenosis independent of mean flow in a single comprehensive MR examination.

Angiotensin II↗
PubMedDate not supplied

Synthesis and characterization of HE-24.8: a polymeric contrast agent for magnetic resonance angiography.

The physical and biological properties of a water-soluble polymeric contrast agent based on a complex of N-(2-hydroxypropyl)methacrylamide copolymer with gadolinium (HE-24.8) were investigated, and its potential for experimental magnetic resonance (MR) angiography was assessed. Relaxivities of Gd-DTPA-BMA, Gd-DTPA-HSA (human serum albumin), and HE-24.8 were determined at 1.5 T. Thermic stability and biocompatibility of HE-24.8 were assessed in vitro and by analyzing kinetics and organ distribution in rats for up to 2 weeks. For comparison, HE-24.8- and Gd-DTPA-HSA-enhanced micro-MR angiographies of brain, chest, and subcutaneous tumors in rats were performed. T1 relaxivity of HE-24.8 (21.3 +/- 1.1 mM(-1) s(-1)) was 5-fold higher than that of Gd-DTPA-BMA (4.1 +/- 0.1 mM(-1) s(-1)) and twice as high as that of Gd-DTPA-HSA (12.4 +/- 0.2 mM(-1) s(-1)). Varying the molecular weight of the polymer (15-46 kDa) did not significantly change the T1 relaxivity. In rats, 20 and 10% of the injected dose of HE-24.8 was detected at 24 and 168 h postinjection, respectively. Upon a relatively rapid initial renal clearance, no specific retention in any organ was noted, with some exception for the reticulo-endothelial system. No measurable release of gadolinium from the polymer-Gd complex or cell toxicity was observed during its incubation in aqueous environment. Excellent display of rat and tumor vascularization was achieved with Gd-DTPA-HSA and HE-24.8; however, contrast of vessels was higher in HE-24.8-enhanced scans. HE-24.8 is considered a macromolecular contrast agent highly suited for experimental MR studies.

Animals↗
PubMedDate not supplied

Diagnostic accuracy of staging renal cell carcinomas using multidetector-row computed tomography and magnetic resonance imaging: a prospective study with histopathologic correlation.

OBJECTIVE: The aim of this prospective study is to compare the diagnostic accuracy of multidetector-row computed tomography (CT) and magnetic resonance imaging (MRI) in tumor staging of renal cell carcinomas. METHODS: In a prospective study, 82 renal cell carcinomas were assessed for tumor staging before surgery using multidetector-row CT and MRI, the results of which were then correlated to histopathologic staging. Triphasic CT (noncontrast, arterial phase, and parenchymal phase) imaging was performed using multidetector-row CT with a reconstructed slice thickness of 2 mm. In MRI, a transverse T1-weighted gradient echo sequence with and without administration of Gd-DTPA, a transverse T2-weighted respiratory-gated turbo spin echo (TSE) sequence, and a coronal T1-weighted gradient echo sequence with Gd-DTPA were used. In addition, multiphasic 3-dimensional angiography after Gd-DTPA injection and a transverse T1-weighted fat-suppression sequence were performed. RESULTS: With MRI, readers 1 and 2 correctly staged 71 and 64 tumors (overall accuracy of 0.87 and 0.78, respectively) and achieved Mantel-Haenszel chi(2) values of 66 and 63 (P < 0.0001). Computed tomography allowed correct staging of 68 and 66 tumors (readers 1 and 2, overall accuracy of 0.83 and 0.80, respectively) with Mantel-Haenszel chi(2) values of 54 and 54 for CT staging (P < 0.0001). No statistically significant difference between overall accuracy was found in the chi(2) test (P > 0.15). CONCLUSION: Magnetic resonance imaging and multidetector-row CT with its multiplanar reconstruction capabilities achieve similar accuracy in tumor staging of renal cell carcinomas.

Adult↗
PubMedDate not supplied

Preoperative staging of renal cell carcinoma with inferior vena cava thrombus using multidetector CT and MRI: prospective study with histopathological correlation.

OBJECTIVE: To evaluate the accuracy of multidetector computed tomography (CT) and magnetic resonance imaging (MRI) in staging and estimating renal carcinomas with caval thrombus. METHODS: Initially, 23 patients with suspected caval thrombi were admitted into this prospective study. Triphasic CT imaging was performed using a multidetector CT with a reconstructed slice thickness of 2 mm. 3D CT reconstructions were used to improve surgical planning. MRI protocol included: a transversal T1-weighted GE sequence with and without Gd-DTPA, a transversal T2-weighted respiratory-gated TSE, and a coronal T1-weighted GE sequence with Gd-DTPA and fat saturation. In addition, a multiphase 3D angiography was performed after Gd-DTPA injection. Patients were divided into 3 groups: caval thrombus below the insertion of the hepatic veins, within the intrahepatic vena cava, and intra-atrial extension. The results the tumor thrombus extension and staging results of 2 independent readers were correlated with surgical and histopathological staging. RESULTS: Of the 23 patients admitted, CT and MR scans of 14/13 patients respectively were correlated with histopathological workup. CT thrombus detection sensitivity and specificity for both readers was 0.93 and 0.8 respectively. MRI sensitivity and specificity for both readers was 1.0/0.85 and 0.75. Readers I and II evaluated the uppermost extension of the cranial tumor thrombus by both CT and MRI. CT and MR accuracy was 78% and 72%, 88% and 76% respectively. CONCLUSION: In cases of a suspected tumor thrombus, MRI and multidetector CT imaging showed similar staging results. Consequently, these staging modalities can be used to assess the extension of the tumor thrombus.

Adult↗