Biomedical subjects

Matthias Günther

Publications and source records attributed to Matthias Günther.

11 recordsLinked to original sources

PubMed2006

Immunization with an adjuvant hepatitis B vaccine in liver transplant recipients: antibody decline and booster vaccination with conventional vaccine.

Patients after orthotopic liver transplantation (OLT) due to hepatitis B virus (HBV)-related disease are at risk of endogenous hepatitis B reinfection and may receive life long prophylaxis with hepatitis B hyperimmunoglobulin (HBIG). In a previous study 16 of 20 OLT patients were immunized successfully with an adjuvant hepatitis B vaccine. To maintain protective antibody levels under immunosuppressive therapy, 11 of these patients were revaccinated with a double dosed conventional hepatitis B vaccine. Median interval between last vaccination and booster was 24 months (range 22-31 months). Antibody titres against hepatitis B surface antigen (anti-HBs) were monitored at the day of booster vaccination (day 0), at day 7 and day 28. At day 0, all vaccinees but one had anti-HBs titres greater than 500 IU/L (median 1,925 IU/L, range 196-7,612 IU/L). Maximum antibody titres after previous vaccination declined by a median of 82% (range 47-96%). After booster vaccination the anti-HBs titre increased significantly by a median factor of 2.42 (P<0.05). In conclusion, the majority of liver transplant recipients who previously had responded to adjuvant hepatitis B vaccine exhibited sufficient immunocompetence to produce a substantial antibody response after booster immunization with a conventional vaccine.

Adjuvants, Immunologic↗

PubMed2006

Efficient visualization of vascular territories in the human brain by cycled arterial spin labeling MRI.

Intracranial vascular territories are usually visualized with the use of angiographic techniques. However, because it is difficult to visualize the distal vascular bed with any angiographic technique, it is also difficult to infer the parenchymal borders of vascular territories. Arterial spin labeling (ASL) MRI provides information on cerebral perfusion, and a regional ASL (regASL) approach offers the potential to visualize perfusion of the anterior and posterior circulation separately. Current techniques perform the labeling in each feeding artery as a separate experiment, which is very time-consuming. In this work a very time-efficient regASL technique is presented that acquires all vascular territories within the same experiment. Images with different combinations of labeled arteries are combined to delineate the vascular territory of interest. Five subjects were examined with a clinical 1.5T MR scanner. A sharp delineation of the middle cerebral artery (MCA) and posterior cerebral artery (PCA) territories with whole-brain coverage was achieved in all subjects. The resulting signal-to-noise ratios (SNRs) for conventional regASL and the proposed cycled regASL were 9.3+/-2.4 and 15.3+/-5.1, respectively. An optimized setup was achieved by combining the regional labeling scheme with an efficient readout technique, which yielded a total measurement time of 2 min for three vascular territories.

Algorithms↗

PubMed2005

Single-shot 3D imaging techniques improve arterial spin labeling perfusion measurements.

Arterial spin labeling (ASL) can be used to measure perfusion without the use of contrast agents. Due to the small volume fraction of blood vessels compared to tissue in the human brain (typ. 3-5%) ASL techniques have an intrinsically low signal-to-noise ratio (SNR). In this publication, evidence is presented that the SNR can be improved by using arterial spin labeling in combination with single-shot 3D readout techniques. Specifically, a single-shot 3D-GRASE sequence is presented, which yields a 2.8-fold increase in SNR compared to 2D EPI at the same nominal resolution. Up to 18 slices can be acquired in 2 min with an SNR of 10 or more for gray matter perfusion. A method is proposed to increase the reliability of perfusion quantification using QUIPSS II derivates by acquiring low-resolution maps of the bolus arrival time, which allows differentiation between lack of perfusion and delayed arrival of the labeled blood. For arterial spin labeling, single-shot 3D imaging techniques are optimal in terms of efficiency and might prove beneficial to improve reliability of perfusion quantitation in a clinical setup.

Adult↗

PubMed2005

Simultaneous spin-echo refocusing.

A new approach to spin-echo imaging is presented in which the 180 degrees RF pulse refocuses two or more spin-echoes at different positions in the readout period. When simultaneous echo refocusing (SER) is implemented using multiple 180 degrees pulses, an undesirable mixing of stimulated echoes and primary echoes from different slices can occur. A novel periodic gradient spoiler scheme eliminates this potential source of artifacts without spoiling the correctly timed stimulated echoes, which, similar to RARE (TSE) sequences, add coherently to the primary echoes. Comparisons show equivalent artifact elimination using phase cycling, periodic spoiling, and a previously developed spoiling scheme for non-Carr-Purcell-Meiboom-Gill sequences. A comparison of head images at 1.5 T acquired with SER-TSE and conventional TSE T1-weighted sequences show no degradation in image quality nor SNR. T2-weighted imaging is not achievable with the current implementation, but possible solutions are proposed. The proposed technique might prove especially beneficial at higher field strengths, where the reduced number of refocusing pulses for multislice SER-TSE decreases RF power deposition. SER spin-echo imaging offers an approach that is very different from low flip angle imaging to mitigate RF heating limitations in high-field clinical imaging.

Artifacts↗

PubMed2004

Ultrasound-guided MRI: preliminary results using a motion phantom.

In principal, both ultrasound (US) imaging and MRI can be performed simultaneously within the magnetic field of the scanner due to their different physical natures (i.e., sound waves vs. electromagnetic radiation). One potential application is to use US information for dynamic spatial organ localization to improve MR imaging, similar to MR navigator echoes. In this work, preliminary results are presented for US-guided MRI using position and orientation information extracted from US data to update the image slice position of an SSFP sequence in real time. Effective prospective motion compensation is shown for a phantom whose sinusoidal displacement can be fully corrected. Possible applications of simultaneous US-MRI acquisitions include real-time US-guided cardiac MRI or interventional procedures.

Algorithms↗

PubMed2004

Assessment of irradiated brain metastases by means of arterial spin-labeling and dynamic susceptibility-weighted contrast-enhanced perfusion MRI: initial results.

RATIONALE AND OBJECTIVES: To assess if preradiation and early follow-up measurements of relative regional cerebral blood flow (rrCBF) can predict treatment outcome in patients with cerebral metastases and to evaluate rrCBF changes in tumor and normal tissue after stereotactic radiosurgery using arterial spin-labeling (ASL) and first-pass dynamic susceptibility-weighted contrast-enhanced (DSC) perfusion MRI. METHODS: In 25 patients with a total of 28 brain metastases, DSC MRI and ASL perfusion MRI using the Q2TIPS sequence were performed with a 1.5-T unit. Measurements were performed prior to and at 6 weeks, 12 weeks, and 24 weeks after stereotactic radiosurgery. Follow-up examinations were completely available in 25 patients for Q2TIPS and 17 patients with 18 metastases for DSC MRI. The rrCBF of the metastases and the normal brain tissue was determined by a region-of-interest analysis. rrCBF values were correlated with the treatment outcome that was classified according to tumor volume changes at 6 months. RESULTS: The alteration of the rrCBF at the 6-week follow-up was highly predictive for treatment outcome. A decrease of the rrCBF value predicted tumor response correctly in all metastases for Q2TIPS and in 13 of 16 metastases for DSC MRI. The pretherapeutic rrCBF was not able to predict treatment outcome. The rrCBF values in normal brain tissue affected by radiation doses less than 0.5 Gy remained unchanged after therapy. CONCLUSION: These preliminary results suggest that ASL and DSC MRI techniques determining rrCBF changes in brain metastases after stereotactic radiosurgery allow the prediction of treatment outcome.

Adult↗

PubMed2003

Immunization with an adjuvant hepatitis B vaccine after liver transplantation for hepatitis B-related disease.

Patients who undergo transplantation for hepatitis B virus (HBV)-related diseases are treated indefinitely with hepatitis B hyperimmunoglobulin (HBIG) to prevent endogenous HBV reinfection of the graft. Active immunization with standard hepatitis B vaccines in these patients has recently been reported with conflicting results. Two groups of 10 liver transplant recipients on continuous HBIG substitution who were hepatitis B surface antigen (HBsAg) positive and HBV DNA negative before transplantation were immunized in a phase I study with different concentrations of hepatitis B s antigen formulated with the new adjuvants 3-deacylated monophosphoryl lipid A (MPL) and Quillaja saponaria (QS21) (group I/vaccine A: 20 microg HBsAg, 50 microg MPL, 50 microg QS21; group II/vaccine B: 100 microg HBsAg, 100 microg MPL, 100 microg QS21). Participants remained on HBIG prophylaxis and were vaccinated at weeks 0, 2, 4, 16, and 18. They received 3 additional doses of vaccine B at bimonthly intervals if they did not reach an antibody titer against hepatitis B surface antigen (anti-HBs) greater than 500 IU/L. Sixteen (8 in each group) of 20 patients (80%) responded (group I: median, 7,293 IU/L; range, 721-45,811 IU/L anti-HBs; group II: median, 44,549 IU/L; range, 900-83,121 IU/L anti-HBs) and discontinued HBIG. They were followed up for a median of 13.5 months (range, 6-22 months). The vaccine was well tolerated. In conclusion, most patients immunized with the new vaccine can stop HBIG immunoprophylaxis for a substantial, yet to be determined period of time.

Adult↗

PubMed2003

Comparison of arterial spin-labeling techniques and dynamic susceptibility-weighted contrast-enhanced MRI in perfusion imaging of normal brain tissue.

OBJECTIVES: To evaluate relative cerebral blood flow (rCBF) in normal brain tissue using arterial spin-labeling (ASL) methods and first-pass dynamic susceptibility-weighted contrast-enhanced (DSC) magnetic resonance imaging (MRI). METHODS: Sixty-two patients with brain metastases were examined on a 1.5 T-system up to 6 times during routine follow-up after stereotactic radiosurgery. Perfusion values in normal gray and white matter were measured using the ASL techniques ITS-FAIR in 38 patients, Q2TIPS in 62 patients, and the first-pass DSC echo-planar (EPI) MRI after bolus administration of gadopentetate dimeglumine in 42 patients. Precision of the ASL sequences was tested in follow-up examinations in 10 healthy volunteers. RESULTS: Perfusion values in normal brain tissue obtained by all sequences correlated well by calculating Pearson's correlation coefficients (P < 0.0001) and remained unchanged after stereotactic radiosurgery as shown by analysis of variance (P > 0.05). CONCLUSION: Both ASL and DSC EPI MRI yield highly comparable perfusion values in normal brain tissue.

Adult↗

PubMed2002

Immunisations in solid-organ transplant recipients.

Solid-organ transplant recipients are at increased risk of various infectious diseases, some of which are vaccine preventable mmunisations are among the most efficient interventions available. Solid-organ tranplant recipients would greatly benefit from effective immunisations, provided the recommendations are based on a careful risk-benefit analysis in which the effectiveness of the vaccine is weighed against possible adverse reactions, including graft rejection. In this review, we summarise the data from studies on relevant immunisations in solid-organ transplant recipients. The major issues are the immunogenicity and safety of immunisations, the factors associated with poor immune response, and recommendations for immunisation schemes.

Adult↗

PubMed2002

Successful hepatitis B vaccination in patients who underwent transplantation for hepatitis B virus-related cirrhosis: preliminary results.

Long-term hepatitis B immunoglobulin (HBIg) prophylaxis prevents endogenous hepatitis B virus (HBV) reinfection in the majority of liver transplant recipients. Active hepatitis B vaccination after orthotopic liver transplantation (OLT) in these patients has produced conflicting results to date. On this study, patients who remained hepatitis B surface antigen (HBsAg) negative with passive immunization after OLT for HBV cirrhosis were actively immunized using recombinant HBV antigen (Engerix), together with a novel adjuvant system (monophosphoryl lipid A and a natural saponine molecule). This led to a sustained antibody response to HBsAg (>500 IU/L) in 5 of 10 patients. This antibody response prevented reinfection and allowed termination of prophylactic HBIg substitution for more than 12 months in these patients.

Adjuvants, Immunologic↗

PubMedDate not supplied

Risk and spectrum of diseases in travelers to popular tourist destinations.

BACKGROUND: Traveling to tropical regions is related to increased health risks. Travelers' diarrhea is the most frequent health problem, but the range of travel-related diseases also includes potential life-threatening diseases such as malaria. The actual risk of European travelers acquiring specific infectious diseases and other hazards in the tropics is to a large extent unknown and is therefore often adopted from that of the indigenous population. The objective of this study was to elucidate the risk for travel-related diseases, symptoms, and accidents in a population of Europeans who travel to popular tourist destinations. METHODS: From July 2003 to June 2004, 794 travelers consulting the travel clinic of the Berlin Institute of Tropical Medicine were recruited for a questionnaire-based observational study before traveling to Kenya, Tanzania, Senegal, the Gambia, India, Nepal, Thailand, or Brazil. RESULTS: Overall, illness was reported by 42.9% of travelers, with 10.2% reporting more than one adverse health event. Most frequently gastrointestinal symptoms were noted (34.6%), followed by respiratory symptoms (13.7%). More than 5% experienced an accident. Travel to the Indian subcontinent nearly doubled the risk of becoming ill; travel to Thailand significantly decreased the risk. Additional risk factors were a long duration of staying abroad, young age, and traveling under basic conditions. Of all travelers, 80% did not follow the traditionally recommended dietary restrictions. Among travelers visiting malaria-endemic areas, 20% did not carry any antimalarial drugs with them, not continuous chemoprophylaxis or standby medication. CONCLUSIONS: Because of the rising travel activity, especially to tropical countries, the importance of qualified pretravel advice consultation is increasing. To improve the travelers' health, attention needs to be paid to individual risk factors, the prevention and therapy of travelers' diarrhea, malaria prophylaxis, management of respiratory illness, and personal safety.

Accidents↗