Matthias Seiwerts

Bedside Estimation of Nonaerated Lung Tissue Using Blood Gas Analysis

Objectives:Studies correlating the arterial partial pressure of oxygen to the fraction of nonaerated lung assessed by CT shunt yielded inconsistent results. We systematically analyzed this relationship and scrutinized key methodological factors that may compromise it. We hypothesized that both physiological shunt and the ratio between PaO2 and the fraction of inspired oxygen enable estimation of CT shunt at the bedside. Design:Prospective observational clinical and laboratory animal investigations. Setting:ICUs (University Hospital Leipzig, Germany) and Experimental Pulmonology Laboratory (University of São Paulo, Brazil). Patients, Subjects and Interventions:Whole-lung CT and arterial blood gases were acquired simultaneously in 77 patients mechanically ventilated with pure oxygen. A subgroup of 28 patients was submitted to different Fio2. We also studied 19 patients who underwent repeat CT. Furthermore we studied ten pigs with acute lung injury at multiple airway pressures, as well as a theoretical model relating PaO2 and physiological shunt. We logarithmically transformed the PaO2/Fio2 to change this nonlinear relationship into a linear regression problem. Measurements and Main Results:We observed strong linear correlations between Riley’s approximation of physiological shunt and CT shunt (R2 = 0.84) and between logarithmically transformed PaO2/Fio2 and CT shunt (R2 = 0.86), allowing us to construct a look-up table with prediction intervals. Strong linear correlations were also demonstrated within-patients (R2 = 0.95). Correlations were significantly improved by the following methodological issues: measurement of PaO2/Fio2 during pure oxygen ventilation, use of logarithmically transformed PaO2/Fio2 instead of the “raw” PaO2/Fio2, quantification of nonaerated lung as percentage of total lung mass and definition of nonaerated lung by the [–200 to +100] Hounsfield Units interval, which includes shunting units within less opacified lung regions. Conclusion:During pure oxygen ventilation, logarithmically transformed PaO2/Fio2 allows estimation of CT shunt and its changes in patients during systemic inflammation. Relevant intrapulmonary shunting seems to occur in lung regions with CT numbers between [–200 and +100] Hounsfield Units.

Value of endorectal magnetic resonance imaging at 3T for the local staging of prostate cancer.

PURPOSE To assess the accuracy of endorectal 3 T magnetic resonance imaging (MRI) in detecting extracapsular extension (ECE) and seminal vesicle invasion (SVI) of prostate cancer (PCa). MATERIALS AND METHODS 38 consecutive patients with biopsy-proven PCa underwent multiparametric endorectal MRI at 3 T prior to prostatectomy. Two readers (A with nine years of experience and B with four) used established criteria for ECE and SVI to diagnose the extent of local disease in six regions (apical, dorsolateral, basal; left and right each) with the highest chance of ECE. The standard of reference was provided by intraoperative frozen section analysis and prostatectomy specimens. RESULTS Histopathology revealed ECE in 15 of the 222 regions (10 of 37 patients) and SVI in 8 of 74 potential regions (5 of 37 patients). The sensitivity, specificity, and accuracy in detecting ECE for reader A/B were 93%/67%, 92%/95% and 92%/93% per region and 90%/80%, 74%/82% and 78%/81% per patient, respectively. The corresponding values for the detection of SVI were 80%/100%, 96%/99% and 95%/97%, respectively. CONCLUSION Endorectal 3 T MRI is a highly reliable noninvasive technique for the local staging of PCa. KEY POINTS ► Endorectal 3 T MRI provided high accuracy for the local staging of prostate cancer. ► The sensitivity in detecting extracapsular tumor growth per patient was 80% or higher. ► The specificity in detecting extracapsular extension (pT3 stage) was good.

Extrapolation in the analysis of lung aeration by computed tomography: a validation study

IntroductionComputed tomography (CT) is considered the gold standard for quantification of global or regional lung aeration and lung mass. Quantitative CT, however, involves the exposure to ionizing radiation and requires manual image processing. We recently evaluated an extrapolation method which calculates quantitative CT parameters characterizing the entire lung from only 10 reference CT-slices thereby reducing radiation exposure and analysis time. We hypothesized that this extrapolation method could be further validated using CT-data from pigs and sheep, which have a different thoracic anatomy.MethodsWe quantified volume and mass of the total lung and differently aerated lung compartments in 168 ovine and 55 porcine whole-lung CTs covering lung conditions from normal to gross deaeration. Extrapolated volume and mass parameters were compared to the respective values obtained by whole-lung analysis. We also tested the accuracy of extrapolation for all possible numbers of CT slices between 15 and 5. Bias and limits of agreement (LOA) were analyzed by the Bland-Altman method.ResultsFor extrapolation from 10 reference slices, bias (LOA) for the total lung volume and mass of sheep were 18.4 (-57.2 to 94.0) ml and 4.2 (-21.8 to 30.2) grams, respectively. The corresponding bias (LOA) values for pigs were 5.1 (-55.2 to 65.3) ml and 1.6 (-32.9 to 36.2) grams, respectively. All bias values for differently aerated lung compartments were below 1% of the total lung volume or mass and the LOA never exceeded ± 2.5%. Bias values diverged from zero and the LOA became considerably wider when less than 10 reference slices were used.ConclusionsThe extrapolation method appears robust against variations in thoracic anatomy, which further supports its accuracy and potential usefulness for clinical and experimental application of quantitative CT.

A patient with a large recurrent pheochromocytoma demonstrating the pitfalls of diagnosis

Background. A 59-year-old man presented for a follow-up, 6 years after surgery for a large pheochromocytoma. He had suffered from diabetes mellitus, hypertension and abdominal pain in the right flank region. Previous postoperative follow-up did not reveal tumor recurrence.Investigation. Measurement of plasma free metanephrine and normetanephrine by high-performance liquid chromatography and radioimmunoassay; 123I-metaiodobenzylguanidine (MIBG) scintigraphy; hybrid 123I-MIBG single-photon emission CT (SPECT)–CT; MRI; testing for plasma norepinephrine and epinephrine; intraoperative ultrasonography; histological staining for chromogranin A and synaptophysin; and postoperative 18F-dihydroxyphenylalanine (DOPA) PET scan.Diagnosis. Recurrent pheochromocytoma.Management. Laparotomy with tumor resection. Reduction of antihypertensive medications. Further follow-up by MRI, hybrid 123I-MIBG SPECT–CT and testing for plasma catecholamines and free metanephrines.

Computed tomographic assessment of lung weights in trauma patients with early posttraumatic lung dysfunction

IntroductionQuantitative computed tomography (qCT)-based assessment of total lung weight (Mlung) has the potential to differentiate atelectasis from consolidation and could thus provide valuable information for managing trauma patients fulfilling commonly used criteria for acute lung injury (ALI). We hypothesized that qCT would identify atelectasis as a frequent mimic of early posttraumatic ALI.MethodsIn this prospective observational study, Mlung was calculated by qCT in 78 mechanically ventilated trauma patients fulfilling the ALI criteria at admission. A reference interval for Mlung was derived from 74 trauma patients with morphologically and functionally normal lungs (reference). Results are given as medians with interquartile ranges.ResultsThe ratio of arterial partial pressure of oxygen to the fraction of inspired oxygen was 560 (506 to 616) mmHg in reference patients and 169 (95 to 240) mmHg in ALI patients. The median reference Mlung value was 885 (771 to 973) g, and the reference interval for Mlung was 584 to 1164 g, which matched that of previous reports. Despite the significantly greater median Mlung value (1088 (862 to 1,342) g) in the ALI group, 46 (59%) ALI patients had Mlung values within the reference interval and thus most likely had atelectasis. In only 17 patients (22%), Mlung was increased to the range previously reported for ALI patients and compatible with lung consolidation. Statistically significant differences between atelectasis and consolidation patients were found for age, Lung Injury Score, Glasgow Coma Scale score, total lung volume, mass of the nonaerated lung compartment, ventilator-free days and intensive care unit-free days.ConclusionsAtelectasis is a frequent cause of early posttraumatic lung dysfunction. Differentiation between atelectasis and consolidation from other causes of lung damage by using qCT may help to identify patients who could benefit from management strategies such as damage control surgery and lung-protective mechanical ventilation that focus on the prevention of pulmonary complications.

In vivo glenohumeral analysis using 3D MRI models and a flexible software tool: Feasibility and precision†

To implement a PC‐based morphometric analysis platform and to evaluate the feasibility and precision of MRI measurements of glenohumeral translation.

Einfluss der CT-Bildrekonstruktion auf die quantitative Messung der alveolären Belüftung: Intraindividueller Vergleich bei Tieren mit normaler und experimentell geschädigter Lunge

Ziele: Bestimmung des Einflusses von CT-Parametern auf die CT-basierte Messung der alveolaren Uberblahung fur normale und geschadigte Lungenzustande. Methode: Sieben anasthesierte und paralysierte Tiere wurden unter kontinuierlich positivem Atemwegsdruck von 25cm H2O mit normalen und experimentell geschadigten Lungen (NaCl-Lavage) an einem 16-Zeilen CT (Philips MX 8000 IDT) untersucht. Die CT-Rohdaten wurden mit zwei CT-Untersuchungsprotokollen (Multislice MS und Low-Dose LD), drei Rekonstruktionsfiltern (FT=weich, mittel und hart) und drei Schichtdicken (SL=7,5, 5,0 und 3,3mm) rekonstruiert. Das uberblahte Volumen V_hyper wurde auf segmentierten CT-Schichten der gesamten Lunge uber die Summe der Voxel mit CT-Werten unterhalb -900 HU bestimmt. Zur Untersuchung von Unterschieden zwischen beiden Lungenzustanden (LC) wurde ein Wilcoxon-Test durchgefuhrt; fur die LD-Daten erfolgte eine ANOVA mit Messwertwiederholung mit zwei Innergruppen- (FT und SL) und einem Zwischengruppen-Faktor (LC). Die Protokolle wurden an 5-mm-Daten nach Rekonstruktion mit einem Standardfilter verglichen. Ergebnis: Median- (Extrem-Werte) fur V_hyper waren 8,4 (4,1–81,6)ml (MS) bzw. 15,5 (4,3–82,8)ml (LD) fur normale und 2,3 (0,1–5,2)ml (MS) bzw. 4,4 (0,2–24,8)ml (LD) fur geschadigte Lungen. Bei beiden Protokollen war V_hyper fur normale Lungen signifikant groser (p<0,05) als fur geschadigte. Signifikante Innergruppeneffekte wurden fur die Faktoren FT (p<0,001) und SL (p<0,001) als auch fur die Wechselwirkungsterme FT x LC (p<0,05) und SL x LC (p<0,01) beobachtet. Schlussfolgerung: Bei Untersuchungen an den gleichen Tieren hatten Schichtdicke und Rekonstruktionsfilter sowohl fur normale als auch fur geschadigte Lungenzustande einen signifikanten Einfluss auf V_hyper. Daher halten wir eine genaue Angabe der verwendeten CT-Aufnahme- und Bildrekonstruktionsparameter bei der Erfassung uberblahter Lungenareale fur unabdingbar. Dies gilt insbesondere bei der Beurteilung spezieller Beatmungsstrategien fur Patienten mit geschadigter Lunge. Korrespondierender Autor: Busse H Universitatsklinikum Leipzig, Diagnostische und Interventionelle Radiologie, Liebigstr. 20, 04103 Leipzig E-Mail: harald.busse@medizin.uni-leipzig.de

Intraoperative Bildverarbeitung zur Verbesserung MRT-gestützter Interventionen Erweiterung auf nicht-neurochirurgische Anwendungen

Neben der pra- und postoperativen Diagnostik wird die MRT auch zunehmend zur Navigation therapeutischer Masnahmen eingesetzt. In einem vertikal offenen MRT-System konnen Intervention und Bildgebung ohne zwischenzeitliche Umlagerung des Patienten durchgefuhrt werden. Die fortlaufende Bildgebung genugt jedoch nicht immer den Anforderungen an eine zielgenaue und schnelle Navigation. Daher wurde in eine vorhandene iMRT-Umgebung ein in dieser Hinsicht verbessertes Navigationssystem auf PC-Basis implementiert und klinisch eingesetzt. Im Gegensatz zur herkommlichen Navigation auf der Basis praoperativer Daten erlaubt das erweiterte System eine intraoperative Aktualisierung der Referenzdaten und somit auch einen Einsatz in verschieblichen Organen.