Herbert Langenberger

On the origin of respiratory artifacts in BOLD-EPI of the human brain

BOLD-based functional MRI (fMRI) can be used to explicitly measure hemodynamic aspects and functions of human neuro-physiology. As fMRI measures changes in regional cerebral blood flow and volume as well as blood oxygenation, rather than neuronal brain activity directly, other processes that may change the above parameters have to be examined closely to assess sensitivity and specificity of fMRI results. Physiological processes that can cause artifacts include cardiac action, breathing and vasomotion. Although there has been substantial research on physiological artifacts and appropriate compensation methods, controversy still remains on the mechanisms that cause the fMRI signal fluctuations. Respiratory-correlated fluctuations may either be induced by changes of the magnetic field homogeneity due to moving organs, intra-thoracic pressure differences, respiration-dependent vasodilation or oxygenation differences. The aim of this study was to characterize the impact of different breathing patterns by varying respiration frequency and/or tidal volume on EPI time courses of the resting human brain. The amount of respiration-related oscillations during three respiration patterns was quantified, and statistically significant differences were obtained in white matter only: p < 0.03 between 6 vs. 12 ml/kg body weight end tidal volume at a respiration frequency of 15/min, p < 0.03 between 12 vs. 6 ml/kg body weight and 15 vs. 10 respiration cycles/min. There was no significant difference between 15 vs. 10 respiration cycles/min at an end tidal volume of 6 ml/kg body weight (p = 0.917). In addition, the respiration-affected brain regions were very similar with EPI readout in the a-p and l-r direction. Based on our results and published literature we hypothesize that venous oxygenation oscillations due to changing intra-thoracic pressure represent a major factor for respiration-related signal fluctuations and increase significantly with increasing end tidal volume in white matter only.

Endovascular Management of Lost or Misplaced Intravascular Objects: Experiences of 12 Years

This paper reports our experience with endovascular techniques for the retrieval of lost or misplaced intravascular objects. Over 12 years, 78 patients were referred for interventional retrieval of intravascular foreign objects. In this retrospective study, radiological procedure records and patients’ medical records were reviewed to determine the exact removal procedure in every case, to report success rates, and to identify significant procedure-related complications. Written, informed consent was obtained from all patients prior to the intervention; this retrospective analysis was performed according to the guidelines of the Institutional Review Board. Thirty-six of seventy-eight foreign objects (46%) were located in the venous system, 27 of 78 (35%) in the right heart, and 15 of 78 (19%) in the pulmonary arteries. For foreign object removal, in 71 of 78 (91%) cases a snare loop was used, in 6 of 78 (8%) cases a sidewinder catheter combined with a snare loop was used, and in 1 case (1%) a sidewinder catheter alone was used for foreign object removal. In 68 of 78 (87%) cases, primary success was achieved. In 3 of 78 cases (4%), foreign objects were successfully mobilized to the femoral vessels and surgically removed. In 7 of 78 cases (9%), complete removal of the foreign object was not possible. In 5 of 78 cases (6%), minor complications occurred during the removal procedure. In conclusion, endovascular retrieval of lost or misplaced intravascular objects is highly effective, with relatively few minor complications. On the basis of our findings, these techniques should be considered as the therapy of choice.

Antibiotic Abscess Penetration: Fosfomycin Levels Measured in Pus and Simulated Concentration-Time Profiles

ABSTRACT The present study was performed to evaluate the ability of fosfomycin, a broad-spectrum antibiotic, to penetrate into abscess fluid. Twelve patients scheduled for surgical or computer tomography-guided abscess drainage received a single intravenous dose of 8 g of fosfomycin. The fosfomycin concentrations in plasma over time and in pus upon drainage were determined. A pharmacokinetic model was developed to estimate the concentration-time profile of fosfomycin in pus. Individual fosfomycin concentrations in abscess fluid at drainage varied substantially, ranging from below the limit of detection up to 168 mg/liter. The fosfomycin concentrations in pus of the study population correlated neither with plasma levels nor with the individual ratios of abscess surface area to volume. This finding was attributed to highly variable abscess permeability. The average concentration in pus was calculated to be 182 ± 64 mg/liter at steady state, exceeding the MIC50/90s of several bacterial species which are commonly involved in abscess formation, such as streptococci, staphylococci, and Escherichia coli. Hereby, the exceptionally long mean half-life of fosfomycin of 32 ± 39 h in abscess fluid may favor its antimicrobial effect because fosfomycin exerts time-dependent killing. After an initial loading dose of 10 to 12 g, fosfomycin should be administered at doses of 8 g three times per day to reach sufficient concentrations in abscess fluid and plasma. Applying this dosing regimen, fosfomycin levels in abscess fluid are expected to be effective after multiple doses in most patients.

Transcapillary insulin transfer in human skeletal muscle

Background Transcapillary insulin transfer is considered a rate‐limiting step in insulin action at supraphysiological insulin concentrations. However, it remains unclear whether this concept also applies for physiological conditions.

Autocorrelation analysis of bone structure

We propose a method called spatial autocorrelation analysis (SACA) to determine the spatial anisotropy of the trabecular bone in order to investigate osteoporosis. For demonstrating the potential of SACA we first evaluate the method on rectangular, simulated test patterns as a simple model for the anisotropic pore structure of the bone. As a next step towards biomedical application, photographic reference images of human vertebral bone were investigated by SACA. Osteoporotic bone structure could be clearly differentiated from non‐osteoporotic sample images. Moreover, for demonstration of the applicability and potential of the method for in vivo characterization of osteoporosis, the microstructure of the human calcaneus was investigated by MR‐microimaging on a young healthy male subject and an osteoporotic female. The measurements were performed using a high‐field (3T) whole‐body MR tomograph equipped with a special, strong head gradient system. The signal was acquired with a surface coil mounted on an in‐house‐built device for convenient immobilization of the subjects foot. Using a 3D gradient echo sequence a resolution of 0.254 × 0.254 × 2.188 mm3 was achieved in vivo. Selected images were inverted, gradient corrected for the inhomogeneous but sensitive detection by the surface coil, and subsequently analyzed by SACA. The anisotropy of bone structure detected by SACA is a possible candidate for noninvasive determination of the osteoporotic status, potentially complementing standard bone mineral density measurements. J. Magn. Reson. Imaging 2001;14:87–93.

Extracorporeal shockwave treatment is effective in calcific tendonitis of the shoulder. A randomized controlled trial.

SummaryBackgroundCalcific tendonitis of the shoulder is often associated with chronic pain and impairment of function. Extracorporeal Shockwave therapy (ESWT) is considered to be a treatment option. We compared the effects of two different ESWT regimens.Methods43 patients (57 shoulders) with symptomatic calcific tendonitis of the shoulder for more than six months were included in a double-blinded study. Thirty-one shoulders were treated at the area of maximum pain with application of 2×2000 impulses of 0.28mJ/mm2 at an interval of two weeks (treatment group) and 26 shoulders with 2×2000 impulses of <0.07mJ/mm2 at an interval of two weeks (control group), without pretreatment analgesia. Shoulder function (Constant score) and pain (visual analogue scale, VAS) were assessed before treatment and at one week, three months and seven months after treatment. Shoulder X-rays were performed at the 3- and 7-month follow-up visits.ResultsImprovement in Constant score was significantly higher in the treatment group at all follow-up visits (p<0.05). Seven months post-treatment, calcifications dissolved completely in 19% of the treatment group and 8% of the control group, and a >50% reduction was observed in 19% and 8% respectively. With regard to reduction of pain, there was significant improvement in the treatment group compared with the control group at the 1-week follow-up (p<0.05). However, at the 3-month and 7-month visits, no significant between-group difference in pain could be detected.ConclusionAs applied, ESWT with an energy flux density of 0.28mJ/mm2 led to a significantly greater improvement in shoulder function and a slightly higher, nonsignificant, rate of > 50% disintegration of calcific deposits compared with the control group. However, this did not result in reduction of pain.

Adrenal venous sampling using Dyna-CT--a practical guide.

Primary hyperaldosteronism due to aldosterone secreting adrenal adenomas is an important and potentially curable cause for hypertension. The differentiation between unilateral or bilateral adrenal adenomas is crucial, as unilateral adenomas can easily be cured by surgery whereas bilateral adenomas have to be treated conservatively. Exact diagnosis can be made when unilateral or bilateral hormone production is proven with adrenal vein sampling. We present an effective step-by-step technique how to perform an adrenal vein sampling with a special emphasis on how to reliably catheterize the right adrenal vein using Dyna CT.

Impaired vascular nitric oxide bioactivity in women with previous gestational diabetes

ZusammenfassungHINTERGRUND: Eine Dysfunktion des Gefäß-Endothels, die vaskulären Erkrankungen und Typ 2 Diabetes vorausgehen kann, zeigt sich bei Patientinnen nach Gestationsdiabetes. Es ist allerdings nicht geklärt ob Adipositas, asymetrisches Dimethylarginin (ADMA), ein endogener Stickstoffmonoxid (NO) Synthese Inhibitor oder Insulin-Resistenz die beobachteten Gefäß-Veränderungen bei diesen Patientinnen zusätzlich verstärken. Ziel dieser Studie war es daher, Faktoren zu finden, die die Gefäß-Dysfunktion zusätzlich zum Gestationsdiabetes beeinträchtigen. METHODEN: 7 übergewichtige und 5 normalgewichtigen Patientinnen nach Gestationsdiabetes wurden in diese Studie eingeschlossen. Die Gefäß-Funktion wurde durch Änderungen des Unterarm-Blutflusses auf den Endothel-abhängigen Vasodilatator Acetylcholin (ACh), den Endothel-unabhängigen Vasodilatator Nitroglycerin (GTN), den Vasokonstriktor Norepinephrin (NE) und den NO-Synthase Inhibitor N(G)-monomethyl-L-arginine (L-NMMA) gemessen. ADMA wurde aus venösen Blutproben bestimmt und die Insulin-Resistenz wurde mittels eines modifizierten intravenösen Glukose-Toleranz Tests abgeschätzt. 20 gesunde, männliche Probanden dienten als historische Kontroll-Gruppe. RESULTATE: Verglichen mit Normalgewichtigen war die Reaktion des Unterarm-Blutflusses auf ACh bei übergewichtigen Frauen gestört (p < 0.05); ebenso war die Antwort auf den Vasokonstriktor NE tendenziell bei dieser Gruppe verringert. Weiters gab es signifikante Korrelationen zwischen der vaskulären Antwort auf ACh beziehungsweise L-NMMA und Body Mass Index, Serum ADMA Konzentrationen und stimulierten Glukose Werten (alle p < 0.05). Normalgewichtigen Patientinnen hatten mit der gesunden Kontrollgruppe vergleichbares Ansprechen auf ACh und ADMA Konzentrationen. SCHLUSSFOLGERUNG: Faktoren wie Übergewicht, erhöhte ADMA Werte und Insulin-Resistenz dürften starken Einfluss auf die Endotheliale Dysfunktion bei Patientinnen nach Gestationsdiabetes haben.SummaryBACKGROUND: Dysfunction of the vascular endothelium, preceding vascular morbidity and type 2 diabetes, is present in women with previous gestational diabetes (GDM). However, it is unknown whether excess weight, insulin resistance, and asymmetric dimethylarginine (ADMA) – an endogenous nitric oxide (NO) synthase inhibitor – also contribute to the vascular changes observed in these patients. The aim of this study was therefore to identify factors other than GDM that impair vascular function. METHODS: Seven overweight and five non-overweight women with previous GDM were included in this study. Vascular function was assessed from forearm blood-flow responses to the endothelium-dependent vasodilator acetylcholine (ACh), the endothelium-independent vasodilator glyceryltrinitrate, the vasoconstrictor norepinephrine and the NO synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA). ADMA was measured in venous blood, and insulin resistance was estimated from a modified intravenous glucose tolerance test. Twenty healthy male volunteers served as a historical control group. RESULTS: Vasodilation of forearm resistance vessels in response to ACh was impaired in overweight women when compared with non-overweight women (P < 0.05); similarly, vasoconstrictor reactivity tended to be smaller in the overweight group. In addition, there was a significant relationship between vascular responsiveness to ACh and L-NMMA, body-mass index, serum ADMA concentrations and stimulated glucose levels (all P < 0.05). ACh responses and ADMA levels in non-overweight women were similar to those of healthy controls. CONCLUSION: Factors such as obesity, increased ADMA levels and insulin resistance appear to be strong contributors to endothelial dysfunction observed in women with GDM.

Bone homogeneity factor: an advanced tool for the assessment of osteoporotic bone structure in high-resolution magnetic resonance images.

Rationale and ObjectivesOsteoporosis is characterized by low bone mass and inferior structural competence. In this study we introduce the bone homogeneity factor (BHF) as a quantitative measurement of bone structure, which could be equally important as bone mineral density. MethodsBHF represents an advanced texture analysis tool based on the spatial autocorrelation function calculated in 9 different directions. These calculations were performed on high-resolution magnetic resonance images of the calcaneus at 3.0 T and compared with dual-energy x-ray absorptiometry measurements of the femoral neck. ResultsThe quality and resolution of the high-resolution magnetic resonance images is sufficient for reliably calculating BHF. The mean BHF of the control group (n = 5, mean BHF = 525,0) with normal bone is significantly (P = 0.009, Mann-Whitney U test) higher than in the osteoporotic group (n = 7, mean BHF = 137,8). The BHF correlates with the DXA measurements of the femoral neck (correlation coefficient = 0.75). ConclusionsBy calculating the BHF, it was possible to distinguish between osteoporotic and nonosteoporotic bone structure. Hence, BHF could be a possible candidate for noninvasive assessment of osteoporotic bone structure giving additional information to routinely used bone mineral densitometry.

Endovascular Repair of the Descending Aorta and the Aortic Arch With the Relay Stent Graft

PURPOSE The aim of this study was to evaluate the efficacy and safety of thoracic endovascular aortic repair with a newly designed Relay thoracic stent graft (Bolton Medical, Sunrise, FL). DESCRIPTION Between 2005 and 2007, 22 patients (71.8 +/- 8.5) received 24 stent grafts. Indications were aneurysms (n = 13), penetrating atherosclerotic ulcers (n = 7), and dissections (n = 2). Due to the proximity of the lesions to the aortic arch, rerouting procedures (ie, subclavian transposition [n = 1], double transposition [n = 12], and total arch rerouting [n = 6] were performed pre-interventionally; three patients did not undergo rerouting). All patients were followed-up with a computed tomographic scan of the entire aorta at discharge, 3 months, 6 months, and annually thereafter (mean follow-up, 13 months). EVALUATION Primary technical success was obtained in 20 of 22 patients, with one persisting type I endoleak and one asymptomatic type II endoleak. One patient died due to malignant arrhythmia 3 days after stent-graft placement. During follow-up, 1 nonaortic related death was observed. No additional endoleaks were observed. Finally, all supra-aortic rerouting procedures remained patent. CONCLUSIONS In the treatment of degenerative disease of the descending aorta and the aortic arch, the Bolton Relay stent graft offers acceptable efficacy and safety in short-term follow-up.