C Andres

Dynamic CT Angiography after Abdominal Aortic Endovascular Aneurysm Repair: Influence of Enhancement Patterns and Optimal Bolus Timing on Endoleak Detection

PURPOSE To determine the time course of enhancement patterns in the aorta and endoleaks at dynamic computed tomographic (CT) angiography as well as their effect on the endoleak detection rate in patients who have undergone abdominal aortic endovascular aneurysm repair (EVAR). MATERIALS AND METHODS This retrospective study was approved by the local ethics committee and compliant with the Declaration of Helsinki. All patients gave written informed consent for the scientific analysis of their data. Seventy-one patients (mean age, 72 years ± 8 [standard deviation]) were retrospectively included after EVAR of the abdominal aorta. All patients underwent dynamic CT angiography with 10 unidirectional scan phases, followed by a venous phase. Endoleaks were detected visually in all scan phases; the magnitude of enhancement was assessed by using region-of-interest measurements in the aorta and the detectable endoleaks. Statistical analysis was performed with the χ(2) test, the paired t test, and analysis of variance with repeated measurements. RESULTS The highest mean aortic enhancement was achieved 12 seconds after the bolus-tracking threshold, and the highest mean endoleak enhancement was achieved 22 seconds after the bolus-tracking threshold. In total, 44 endoleaks were detected. The detection rates differed significantly in between the dynamic CT angiography phases (minimum, seven endoleaks at 2 seconds after the bolus-tracking threshold; maximum, 44 endoleaks at 27 seconds after the bolus-tracking threshold; P = .001). The highest detection rate was achieved when the contrast between aortic and endoleak enhancement reached its maximum. CONCLUSION Dynamic CT angiography revealed that the peak enhancement of endoleaks is significantly different than that of the aorta and that endoleaks may not be adequately evaluated with conventional biphasic CT protocols. The use of dynamic CT angiography is associated with a significantly increased detection rate of endoleaks compared with the detection rates at the time points of conventional biphasic CT.

Role of Preprocedural Computed Tomography in Transcatheter Aortic Valve Implantation

UNLABELLED Transcatheter aortic valve implantation (TAVI) is currently considered an acceptable alternative for the treatment of patients with severe aortic stenosis and a high perioperative risk or a contraindication for open surgery. The benefit of TAVI significantly outweighs the risk of the procedure in patients requiring treatment that are not suitable for open surgery, and leads to a lower mortality in the one-year follow-up. The absence of a direct view of the aortic root and valve remains a challenge for the transcatheter approach. While direct inspection of the aortic valve during open surgery allows an adequate prosthesis choice, it is crucial for TAVI to know the individual anatomical details prior to the procedure in order to assure adequate planning of the procedure and proper prosthesis choice and patient selection. Among the imaging modalities available for the evaluation of patients prior to TAVI, computed tomography (CT) plays a central role in patient selection. CT reliably visualizes the dimensions of the aortic root and allows a proper choice of the prosthesis size. The morphology of the access path and relevant comorbidities can be assessed. The present review summarizes the current state of knowledge regarding the value of CT in the evaluation of patients prior to TAVI. KEY POINTS CT plays a central role in patient selection and planning prior to TAVI. ▶ CT reliably detects the dimensions of the aortic root including the size of the aortic annulus, the degree of valve calcification and the morphology of the access routes. ▶ CT provides a more accurate measurement of the aortic annulus than 2D TEE and CT is the only imaging modality that allows a risk assessment for paravalvular leakages based on the calcification of the aortic valve.

Phylogenetic analysis of the Lacerta agilis subspecies complex

The Sand lizard Lacerta agilis inhabits a huge area across Eurasia with several subspecies. Nine subspecies are generally approved, L. a. agilis, L. a. argus, L. a. bosnica; L. a. chersonensis, L. a. exigua, L. a. grusinica, L. a. iorinensis, L. a. brevicaudata and L. a. boemica, but several more have been described. The emergence of this large number of subspecies is connected with the phylogeographic history of this species, defined by geographic and climatic processes. A study revealing phylogenetic relationships of this species was already conducted with a broad taxon sampling and coverage. However, the latter study was based solely on the cytochrome b gene and, furthermore, the Balkan Peninsula inhabited by the subspecies L. a. bosnica was underrepresented. This peninsula is a centre of European herpetofaunal endemism with high levels of phenotypic and genotypic variation. Therefore, the inclusion of the subspecies L. a. bosnica is important to clarify the overall view of the phylogenetic relations within the Lacerta agilis subspecies complex and to investigate the level of population differentiation within this highly diverse area. Thus, the aim of the present study was a more thorough analysis of the Balkan Peninsula with a broader taxon sampling. Furthermore, we extended the available datasets by adding the mitochondrial d-loop region and by further samples of different areas of the distribution range apart from the Balkan Peninsula. Our study reveals that the Balkan Peninsula is apparently inhabited by several differentiated lineages, whereby the Central Greek lineage might deserve subspecies status. Furthermore, the distribution area of the two subspecies L. a. agilis and L. a. argus should be revised, as the results of our study raise doubt about the commonly assumed distribution of both subspecies. As the most important outcome our results support that L. a. boemica deserves species status.

Dynamic CT Angiography after Abdominal Aortic Endovascular Aneurysm Repair: Differences in Contrast Agent Dynamics in the Aorta and Endoleaks—Preliminary Results

PURPOSE To assess differences in aortic and endoleak enhancement in patients after endovascular aneurysm repair (EVAR) with dynamic computed tomography (CT) angiography. MATERIALS AND METHODS Twenty-one consecutive patients (mean age, 74.5 y ± 6; range, 61-88 y) with endoleaks after EVAR of the abdominal aorta were examined on a second-generation dual-source CT unit with 10 unidirectional scan phases (temporal resolution, 5 s; 80 kV; 120 reference-mAs; z-axis field of view, 283 mm), followed by a venous scan phase. Enhancement was assessed in aorta and endoleaks for all phases by density measurements. The diagnostic reliability of endoleak detection was assessed on a five-point confidence scale. RESULTS In total, 26 endoleaks (type I, n = 1; type II, n = 25) were detected. The highest detection rate was found in phase 5 (22 s after threshold; P < .01 vs other dynamic phases). Mean peak aortic enhancement (560 HU ± 96) was present in an early arterial phase (phase 3, 12 s after threshold), whereas the mean peak endoleak enhancement (398 HU ± 174) for type II endoleaks was present later, in phase 4 (17 s after threshold). Despite perceived high diagnostic confidence in phases 1 and 2 (ie, typical arterial phase of biphasic CT protocol), only 23% and 62% of endoleaks were detected, respectively, whereas peak diagnostic confidence (phases 4 and 5) corresponded well with the maximum endoleak detection rate but decreased significantly in later phases (ie, 6-10). CONCLUSIONS Preliminary dynamic CT angiography results in post-EVAR follow-up revealed notably different peaks of endoleak and aortic enhancement, which are not covered sufficiently by conventional biphasic CT protocols. Phase 5 demonstrated the highest type II endoleak detection rate, with high diagnostic confidence.

Are species genetically more sensitive to habitat fragmentation on the periphery of their range compared to the core? A case study on the sand lizard (Lacerta agilis)

ContextSpecies show different sensitivity to habitat loss and fragmentation depending on their specialization. Populations of a species at the range margin are generally assumed to be more stenoecious than populations at the core of the distribution and should therefore be more sensitive to habitat fragmentation.ObjectivesWe evaluated the hypothesis that fragmentation effects species more strongly at the range periphery of their range compared to the core, resulting in lower genetic variability in comparable patch sizes and lower gene flow among populations.MethodsWe compared the genetic diversity and structure of five sand lizard (Lacerta agilis) populations at the margin of its range in Bulgaria and of 11 populations at the core of its distribution in Germany. We based the analysis on microsatellites, comprising 15 loci in Bulgaria and 12 in Germany.ResultsAll diversity indices declined with patch size. For medium-sized patches all diversity indices were lower at the range periphery compared to the core, with two of them being significant. AICc based model selection showed strong support for core/periphery and patch size effects for observed and expected heterozygosity but only a patch size effect for allelic richness. There was no isolation-by-distance and each sampled population was allocated to a separate cluster with high probability for both countries, indicating that all populations are (almost) completely isolated.ConclusionOur study indicates an increased sensitivity of a species to fragmentation at the periphery compared to the core of its distribution. This differential sensitivity should be accounted for when prioritizing species based on their fragmentation sensitivity in landscape management.

Access Path Angle in Transapical Aortic Valve Replacement: Risk Factor for Paravalvular Leakage

BACKGROUND The aim of this study was to analyze the angle between the left ventricular (LV) long axis and the LV outflow tract (αLV-LVOT) on cardiac computed tomography and to describe its effect on the occurrence of paravalvular leakage (PL), fluoroscopy time, and postoperative creatine kinase-MB levels in transapical transcatheter aortic valve replacement (TA-TAVR). METHODS High-risk patients with severe aortic stenosis scheduled for TA-TAVR using an Edwards SAPIEN (Edwards Lifesciences, Irvine, CA) prosthesis were retrospectively included. The αLV-LVOT was measured during systole and diastole as far as retrospectively gated data sets were available. The αLV-LVOT was correlated with the occurrence of PL, total fluoroscopy time, and postoperative creatine kinase-MB levels. Interobserver variability was assessed in all cases. RESULTS The study included 81 patients (57 women [70.4%], 24 men [29.6%]) with an average age of 81.9±5.8 years. The mean αLV-LVOTs were 61.8±9.9 degrees during systole and 61.1±10.0 degrees during diastole. There was a minimal, nonsignificant change in the αLV-LVOT between systole and diastole of 0.2±4.1 degrees (p=0.7). PL was found in 39 patients: grade 0 in 42 (51.9%), grade I in 30 (37.0%), and grade II in 9 (11.1%). Patients with a clinically significant PL (grade≥II) showed a significantly greater mean αLV-LVOT than patients with grade I or without PL (mean difference, 13.8±3.2 degrees; p<0.001). No significant correlation was found between the αLV-LVOT and total fluoroscopy time (r=-0.17, p=0.16) and postoperative creatine kinase-MB levels (r=-0.1, p=0.44). CONCLUSIONS During TA-TAVR, greater αLV-LVOTs were associated with significantly higher grades of PL. Thus, the αLV-LVOT might influence the selection of the transapical implantation path and could have a significant effect on designs for future stents or novel delivery devices.

Impact of heart rate and rhythm on radiation exposure in prospectively ECG triggered computed tomography

PURPOSE To evaluate the influence of different heart rates and arrhythmias on scanner performance, image acquisition and applied radiation exposure in prospectively ECG triggered computed tomography (pCT). MATERIALS AND METHODS An ECG simulator (EKG Phantom 320, Müller & Sebastiani Elektronik GmbH, Munich, Germany) was used to generate different heart rhythms and arrhythmias: sinus rhythm (SR) at 45, 60, 75, 90 and 120/min, supraventricular arrhythmias (e.g. sinus arrhythmia, atrial fibrillation) and ventricular arrhythmias (e.g. ventricular extrasystoles), pacemaker-ECGs, ST-changes and technical artifacts. The analysis of the image acquisition process was performed on a 64-row multidetector CT (Brilliance, Philips Medical Systems, Cleveland, USA). A prospectively triggered scan protocol as used for routine was applied (120 kV; 150 mAs; 0.4s rotation and exposure time per scan; image acquisition predominantly in end-diastole at 75% R-R-interval, in arrythmias with a mean heart rate above 80/min in systole at 45% of the R-R-interval; FOV 25 cm). The mean dose length product (DLP) and its percentage increase from baseline (SR at 60/min) were determined. RESULT Radiation exposure can increase significantly when the heart rhythm deviates from sinus rhythm. ECG-changes leading to a significant DLP increase (p<0.05) were bifocal pacemaker (61%), pacemaker dysfunction (22%), SVES (20%), ventricular salvo (20%), and atrial fibrillation (14%). Significantly (p<0.05) prolonged scan time (>8 s) could be observed in bifocal pacemaker (12.8 s), pacemaker dysfunction (10.7 s), atrial fibrillation (10.3 s) and sinus arrhythmia (9.3 s). CONCLUSION In prospectively ECG triggered CT, heart rate and rhythm can provoke different types of scanner performance, which can significantly alter radiation exposure and scan time. These results might have an important implication for indication, informed consent and contrast agent injection protocols.

Post-Processing in Cardiovascular Computed Tomography: Performance of a Client Server Solution versus a Stand-Alone Solution

PURPOSE To compare the performance of server-based (CSS) versus stand-alone post-processing software (ES) for the evaluation of cardiovascular CT examinations (cvCT) and to determine the crucial steps. MATERIALS AND METHODS Data of 40 patients (20 patients for coronary artery evaluation and 20 patients prior to transcatheter aortic valve implantation [TAVI]) were evaluated by 5 radiologists with CSS and ES. Data acquisition was performed using a dual-source 128-row CT unit (SOMATOM Definition Flash, Siemens, Erlangen, Germany) and a 64-row CT unit (Brilliance 64, Philips, Hamburg, Germany). The following workflow was evaluated: Data loading, aorta and coronary segmentation, curved multiplanar reconstruction (cMPR) and 3 D volume rendering technique (3D-VRT), measuring of coronary artery stenosis and planimetry of the aortic annulus. The time requirement and subjective quality for the workflow were evaluated. RESULTS The coronary arteries as well as the TAVI data could be evaluated significantly faster with CSS (5.5  ±  2.9  min and 8.2  ±  4.0  min, respectively) than with ES (13.9  ±  5.2  min and 15.2  ±  10.9  min, respectively, p ≤  0.01). Segmentation of the aorta (CSS: 1.9 ±  2.0  min, ES: 3.7  ±  3.3  min), generating cMPR of coronaries (CSS: 0.5  ±  0.2  min, ES: 5.1  ±  2.6  min), aorta and iliac vessels (CSS: 0.5  ±  0.4  min and 0.4  ±  0.4  min, respectively, ES: 1.6  ±  0.7  min and 2.8  ±  3  min, respectively) could be performed significantly faster with CSS than with ES with higher quality of cMPR, measuring of coronary stenosis and 3D-VRT (p < 0.05). CONCLUSION Evaluation of cvCT can be accomplished significantly faster and better with CSS than with ES.  The segmentation remains the most time-consuming workflow step, so optimization of segmentation algorithms could improve performance even further.

Assessment of sub-clinical acute cellular rejection after heart transplantation: Comparison of cardiac magnetic resonance imaging and endomyocardial biopsy

Objective Comparing the diagnostic value of multi-sequential cardiac magnetic resonance imaging (CMR) with endomyocardial biopsy (EMB) for sub-clinical cardiac allograft rejection.

Abweichungen zwischen unterschiedlich basierten aortalen Expansionsraten in der CT

Fragestellung: Die bestehenden Abweichungen zwischen den jahrlichen Expansionsraten von Aortensegmenten in der CT, die aus dem Gefassegmentvolumen, dem maximalen orthogonalen Durchmesser, der maximalen orthogonalen Querschnittsflache und der Gefassegmentausenoberflache berechnet wurden, sollen bestimmt werden. Material und Methoden: Es wurden 73 Patienten (66±8,0 Jahre) retrospektiv in die Studie eingeschlossen, die zur Beurteilung des Gefasdiameters zwei CT-Angiografien der thorakalen und/oder abdominellen Aorta im mittleren Verlaufsintervall von 1,8±0,8 Jahren erhielten. Die Aorta wurde in 9 Segmente unterteilt (sinotubularer Ubergang bis Iliakalbifurkation). 346 Segmente konnten hinsichtlich Gefassegmentvolumen, maximalen orthogonalen Durchmesser, maximaler orthogonaler Querschnittsflache und Gefassegmentausenoberflache ausgewertet, die jahrlichen Expansionsraten berechnet und jeweils mit der des Gefassegmentvolumens als Standard verglichen werden. Ergebnisse: Die mittleren Differenzen zwischen Ausgangs- und Folgeuntersuchung betrugen fur das Volumen 5,7%±13,1 (4,8cm3±12,2), fur den Durchmesser 2,1%±4,9 (0,7mm±1,6), fur die Querschnittsflache 4,6%±13,6 (0,5cm2±1,1) und fur Ausenoberflache 4,8%±7,9 (3,7cm2±6,1). Im Vergleich mit der prozentualen Expansionsrate des Volumens war die prozentuale Expansionsrate des Durchmessers 2,7-fach, die der Querschnittsflache und der Ausenoberflache 1,2-fach niedriger. Zwischen den prozentualen Expansionsraten bestanden signifikante (p<0,01) Korrelationen. Die starkste Korrelation mit der prozentualen volumetrischen Expansionsrate wurde mit der der Ausenoberflache (r=0,53) beobachtet, gefolgt von der des Durchmessers (r=0,39) und der der Querschnittsflache (r=0,33). Anhand akzeptierter Diametergrenzwerte wurden 72% der Segmente als aneurysmatisch und 28% als nicht aneurysmatisch definiert. Das wirkte sich auf die Verhaltnisse der Expansionsraten zueinander allerdings nicht wesentlich aus. Schlussfolgerung: Die Kalkulation der Expansionsraten von Aortenabschnitten ergibt, in Abhangigkeit der zugrunde liegenden Messgrose, deutlich differierende Ergebnisse. Besonders anhand durchmesser- und querschnittsflachenbasierter Raten wird die Grosenveranderung unterschatzt.