Thomas Frauenfelder

Endoleaks after endovascular abdominal aortic aneurysm repair: detection with dual-energy dual-source CT.

PURPOSE To assess the diagnostic performance of dual-energy dual-source computed tomography (CT) in the detection of endoleaks after endovascular abdominal aortic aneurysm (AAA) repair. MATERIALS AND METHODS This study was local ethics board approved, and written informed consent was obtained from all patients. One hundred eighteen patients (21 women, 97 men; mean age, 74 years +/- 8 [standard deviation]) underwent follow-up dual-energy dual-source CT during the nonenhanced, arterial, and delayed phases after AAA repair. Delayed phase CT images were acquired in the dual-energy mode for reconstruction of virtual nonenhanced images. Two blinded and independent readers evaluated the data for the presence or absence of endoleaks during three reading sessions: Standard nonenhanced, arterial phase, and delayed phase images were read during session A; virtual nonenhanced, arterial phase, and delayed phase images, during session B; and virtual nonenhanced and delayed phase images, during session C. Sensitivity, specificity, negative predictive value (NPV), and positive predictive value (PPV) were calculated, with the session A image data set as the reference standard. Radiation dose parameters were estimated. RESULTS Reading session A revealed that 52 (44%) of 118 patients had endoleaks. Overall sensitivity, specificity, NPV, and PPV for CT endoleak detection during sessions B and C were identical: 100%, 97%, 100%, and 96%, respectively. The accuracy of the session B and session C readings was not significantly different from that of the session A reading (P = .50). The effective radiation dose in the image acquisition protocol involving one dual-energy scan was significantly (P < .001) lower than the effective doses in the protocols involving standard triple-phase scanning (mean difference, 61%) and standard nonenhanced and delayed phase scanning (mean difference, 41%). CONCLUSION Compared with standard protocols, one dual-energy dual-source CT scan performed during the delayed phase with reconstruction of virtual nonenhanced images enables detection of endoleaks after endovascular AAA repair with high accuracy and a considerably lower radiation dose.

Automated attenuation-based tube potential selection for thoracoabdominal computed tomography angiography: improved dose effectiveness.

Purpose:To introduce a novel algorithm of automated attenuation-based tube potential selection and to assess its impact on image quality and radiation dose of body computed tomography angiography (CTA). Materials and Methods:In all, 40 patients (mean age 71 ± 11.8 years, body mass index (BMI) 25.7 ± 3.8 kg/m2, range 18.8–33.8 kg/m2) underwent 64-slice thoracoabdominal CTA (contrast material: 80 mL, 5 mL/s) using an automated tube potential selection algorithm (CAREkV), which optimizes tube-potential (70–140 kV) and tube-current (138.8 ± 18.6 effective mAs, range 106–177 mAs) based on the attenuation profile of the topogram and on the diagnostic task. Image quality was semiquantitatively assessed by 2 blinded and independent readers (scores 1: excellent to 5: nondiagnostic). Attenuation and noise were measured by another 2 blinded and independent readers. Contrast-to-noise ratio was calculated. The CT dose index (CTDIvol) was recorded and compared with the estimated CTDIvol of a standard 120 kV protocol without using the algorithm in each patient. Selected tube potentials were correlated with BMI and attenuation of the topogram. Results:Diagnostic image quality was obtained in all patients (excellent: 14; good: 21; moderate: 5; interreader agreement: &kgr; = 0.78). Mean attenuation, noise, and contrast-to-noise ratio were 260.8 ± 63.5 Hounsfield units, 15.5 ± 3.3 Hounsfield units, and 14 ± 4.2, respectively, with good to excellent agreement between readers (r = 0.50–0.99, P < 0.01 each). Automated attenuation-based tube potential selection resulted in a kV-reduction from 120 to 100 kV in 23 patients and to 80 kV in 1 patient, whereas tube potential increased to 140 kV in 1 patient. Automatically selected tube potential showed a significant correlation with both BMI (r = 0.427, P < 0.05) and attenuation of the topogram (r = 0.831, P < 0.001). CTDIvol (7.95 ± 2.6 mGy) was significantly lower when using the algorithm compared with the standard 120 kV protocol (10.59 ± 1.8 mGy, P < 0.001), corresponding to an overall dose reduction of 25.1%. Conclusion:Automated attenuation-based tube potential selection based on the attenuation profile of the topogram is feasible, provides a diagnostic image quality of body CTA, and reduces overall radiation dose by 25% as compared with a standard protocol with 120 kV.

Dual-energy contrast-enhanced computed tomography for the detection of urinary stone disease

Objectives:To assess the value of dual-energy contrast-enhanced computed tomography (CT) imaging for the detection of urinary stone disease using dual-source CT. Materials and Methods:Forty consecutive patients (mean age 46.6 ± 16.2 years, range 27–85 years) suspected of having urinary stone disease underwent dual-source CT of the urinary tract. A 3-phasic CT scan protocol consisting of a standard unenhanced scan, a nephrographic, and an excretory phase of contrast enhancement was performed. The nephrographic phase scan was acquired in the dual-energy mode (80 kV/400 mA and 140 kV/95 mA) allowing reconstruction of virtual unenhanced images. Two blinded readers independently compared standard and virtual unenhanced CT for the number, size, and location of urinary stones. Measurements of anteroposterior abdominal diameters were performed to determine abdominal obesity. Results:Standard unenhanced CT revealed 35 uroliths in 18 of the 40 patients (18 of 40; 45%), virtual unenhanced CT demonstrated 26 uroliths in 15 of the 40 patients (15 of 40; 38%) ([kappa] value 0.89). Three false-negative and no false-positive ratings occurred using virtual unenhanced CT, and false-negative ratings solely occurred in obese patients. Sensitivity, specificity, positive predictive, and negative predictive values for virtual unenhanced CT for the diagnosis of urinary stone disease were 83%, 100%, 100%, and 88%, respectively. Conclusions:Virtual unenhanced CT images reconstructed from contrast-enhanced dual-energy CT allow detection of urinary stones with good sensitivity and excellent specificity, but sensitivity is decreased in abdominal obese patients.

Ultralow-dose chest computed tomography for pulmonary nodule detection: first performance evaluation of single energy scanning with spectral shaping.

PurposeThe purpose of this study was to evaluate the image quality and sensitivity of ultralow radiation dose single-energy computed tomography (CT) with tin filtration for spectral shaping and iterative reconstructions for the detection of pulmonary nodules in a phantom setting. MethodsSingle-energy CT was performed using third-generation dual-source CT (SOMATOM Force; 2 × 192 slices) at 70 kVp, 100 kVp with tin filtration (100Sn kVp), and 150Sn kV with tube current-time product adjustments resulting in standard dose (CT volume dose index, 3.1 mGy/effective dose, 1.3 mSv at a scan length of 30 cm), 1/10th dose level (0.3 mGy/0.13 mSv), and 1/20th dose level (0.15 mGy/0.06 mSv). An anthropomorphic chest phantom simulating an intermediate-sized adult with randomly distributed solid pulmonary nodules of various sizes (2–10 mm; attenuation, 75 HU at 120 kVp) was used. Images were reconstructed with advanced model-based iterative reconstruction (ADMIRE; strength levels 3 and 5) and were compared with those acquired with second-generation dual-source CT at 120 kVp (reconstructed with filtered back projection) and sinogram-affirmed iterative reconstruction (strength level 3) at the lowest possible dose at 120 kVp (CT volume dose index, 0.28 mGy). One blinded reader measured image noise, and 2 blinded, independent readers determined overall image quality on a 5-grade scale (1 = nondiagnostic to 5 = excellent) and marked nodule localization with confidence rates on a 5-grade scale (1 = unsure to 5 = high confidence). The constructional drawing of the phantom served as reference standard for calculation of sensitivity. Two patients were included, for proof of concept, who were scanned with the 100Sn kVp protocol at the 1/10th and 1/20th dose level. ResultsImage noise was highest in the images acquired with second-generation dual-source CT and reconstructed with filtered back projection. At both the 1/10th and 1/20th dose levels, image noise at a tube voltage of 100Sn kVp was significantly lower than in the 70 kVp and 150Sn kV data sets (ADMIRE 3, P < 0.01; ADMIRE 5, P < 0.05). Sensitivity of nodule detection was lowest in images acquired with second-generation dual-source CT at 120 kVp and the lowest possible dose. Protocols at 100Sn kVp and ADMIRE 5 showed highest sensitivity at the 1/10th and 1/20th dose levels. Highest numbers of false-positives occurred in second-generation dual-source CT images (range, 12–15), whereas lowest numbers occurred in the 1/10th and 1/20th dose data sets acquired with third-generation dual-source CT at 100Sn kVp and reconstructed with ADMIRE strength levels 3 and 5 (total of 1 and 0 false-positives, respectively). Diagnostic confidence at 100Sn kVp was significantly higher than at 70 kVp or 150Sn kV (ADMIRE 3, P < 0.05; ADMIRE 5, P < 0.01) at both the 1/10th and 1/20th dose levels. Images of the 2 patients scanned with 100Sn kVp at the 1/10th and 1/20th dose levels were of diagnostic quality. ConclusionsOur study suggests that chest CT for the detection of pulmonary nodules can be performed with third-generation dual-source CT producing high image quality, sensitivity, and diagnostic confidence at a very low effective radiation dose of 0.06 mSv when using a single-energy protocol at 100 kVp with spectral shaping and when using advanced iterative reconstruction techniques.

Detection rate, location, and size of pulmonary nodules in trimodality PET/CT-MR: comparison of low-dose CT and Dixon-based MR imaging.

ObjectiveThe objective of this study was to prospectively compare the detection rate, the location, and the size of pulmonary nodules in low-dose computed tomography (CT) and in magnetic resonance (MR) imaging with a 3-dimensional (3D) dual-echo gradient-echo (GRE) pulse sequence using a trimodality positron emission tomography (PET)/CT-MR setup. MethodsForty consecutive patients (25 men and 15 women; mean [SD] age 64 [12] years) referred for staging of malignancy were prospectively included in this single-center, Institutional Review Board-approved study. Imaging using trimodality PET/CT-MR setup (full ring, time-of-flight PET/CT and 3-T whole-body MR imager) comprised PET, low-dose CT for anatomic referencing/attenuation correction of PET, and MR imaging with 3D dual-echo GRE pulse sequence, allowing the reconstruction of water-only (WO) and in-phase (IP) images. Two blinded and independent readers assessed all images randomly for the presence, the location, and the size of pulmonary nodules. Detection rates, defined as the proportion of screened participants with at least 1 pulmonary nodule, were compared between low-dose CT and MR imaging including both WO and IP images. ResultsInter-reader agreements were high regarding the location (k = 0.93–0.98) and the size of pulmonary nodules (intraclass correlation analysis = 0.94–0.98) in CT and in MR imaging. Computed tomographic scans revealed 66 pulmonary nodules in 34 of the 40 patients (85%), whereas WO and IP images showed 56 and 58 pulmonary nodules in 33 of the 40 patients (83%), respectively. The detection rates of CT and MR imaging were similar (P’s >; 0.05) regarding all nodules, 18F-Fluordesoxyglucose-positive pulmonary nodules, and 18F-Fluordesoxyglucose-negative pulmonary nodules. The size of pulmonary nodules was significantly smaller on WO (P <; 0.05; mean difference, 3 mm; 95% confidence interval, − 13 to 18 mm) and IP images (P <; 0.001; mean difference, 4 mm; 95% confidence interval, −5 to 12 mm) compared with in CT. ConclusionsOur study indicates that a 3D Dixon-based, dual-echo GRE pulse sequence might be suitable for lung imaging in clinical whole-body PET/MR examinations. Although the detection rates were lower, there was no statistically significant difference on a patient-based evaluation concerning detection rates of pulmonary nodules compared with low-dose CT. Assessment of nodule location can be performed equally well with MR imaging.

Computational Fluid Dynamics: Hemodynamic Changes in Abdominal Aortic Aneurysm After Stent-Graft Implantation

The aim of this study was to demonstrate quantitatively and qualitatively the hemodynamic changes in abdominal aortic aneurysms (AAA) after stent-graft placement based on multidetector CT angiography (MDCT-A) datasets using the possibilities of computational fluid dynamics (CFD). Eleven patients with AAA and one patient with left-side common iliac aneurysm undergoing MDCT-A before and after stent-graft implantation were included. Based on the CT datasets, three-dimensional grid-based models of AAA were built. The minimal size of tetrahedrons was determined for grid-independence simulation. The CFD program was validated by comparing the calculated flow with an experimentally generated flow in an identical, anatomically correct silicon model of an AAA. Based on the results, pulsatile flow was simulated. A laminar, incompressible flow-based inlet condition, zero traction-force outlet boundary, and a no-slip wall boundary condition was applied. The measured flow volume and visualized flow pattern, wall pressure, and wall shear stress before and after stent-graft implantation were compared. The experimentally and numerically generated streamlines are highly congruent. After stenting, the simulation shows a reduction of wall pressure and wall shear stress and a more equal flow through both external iliac arteries after stenting. The postimplantation flow pattern is characterized by a reduction of turbulences. New areas of high pressure and shear stress appear at the stent bifurcation and docking area. CFD is a versatile and noninvasive tool to demonstrate changes of flow rate and flow pattern caused by stent-graft implantation. The desired effect and possible complications of a stent-graft implantation can be visualized. CFD is a highly promising technique and improves our understanding of the local structural and fluid dynamic conditions for abdominal aortic stent placement.

Is There a Role for Tamsulosin in the Treatment of Distal Ureteral Stones of 7 mm or Less? Results of a Randomised, Double-Blind, Placebo-Controlled Trial

BACKGROUND Numerous randomised trials have confirmed the efficacy of medical expulsive therapy with tamsulosin in patients with distal ureteral stones; however, to date, no randomised, double-blind, placebo-controlled trials have been performed. OBJECTIVE The objective of this trial was to evaluate the efficacy of medical expulsive therapy with tamsulosin in a randomised, double-blind, placebo-controlled setting. DESIGN, SETTING, AND PARTICIPANTS Patients presenting with single distal ureteral stones < or = 7 mm were included in this trial. INTERVENTION Patients were randomised in a double-blind fashion to receive either tamsulosin or placebo for 21 d. The medication was discontinued after either stone expulsion or intervention. Abdominal computed tomography was performed to assess the initial and final stone status. MEASUREMENTS AND LIMITATIONS: The primary end point was the stone expulsion rate. Secondary end points were time to stone passage, the amount of analgesic required, the maximum daily pain score, safety of the therapy, and the intervention rate. RESULTS Ten of 100 randomised patients were excluded from the analysis. No statistically significant differences in patient characteristics and stone size (median: 4.1 mm [tamsulosin arm] vs 3.8 mm [placebo arm], p=0.3) were found between the two treatment arms. The stone expulsion rate was not significantly different between the tamsulosin arm (86.7%) and the placebo arm (88.9%; p=1.0). Median time to stone passage was 7 d in the tamsulosin arm and 10 d in the placebo arm (log-rank test, p=0.36). Patients in the tamsulosin arm required significantly fewer analgesics than patients in the placebo arm (median: 3 vs 7, p=0.011). A caveat is that the exact time of stone passage was missing for 29 patients. CONCLUSIONS Tamsulosin treatment does not improve the stone expulsion rate in patients with distal ureteral stones < or = 7 mm. Nevertheless, patients may benefit from a supportive analgesic effect. CLINICALTRIALS.GOV: NCT00831701.

Multiple periscope and chimney grafts to treat ruptured thoracoabdominal and pararenal aortic aneurysms.

Purpose To report midterm outcomes after urgent endovascular repair of ruptured pararenal or thoracoabdominal aortic aneurysms using multiple periscope and chimney grafts to preserve renovisceral branch perfusion and facilitate aneurysm exclusion. Methods Nine consecutive men (mean age 72±14 years, range 40–88) presenting with ruptured thoracoabdominal (n=6), pararenal (n=2), or infrarenal (n=1) aortic aneurysm underwent urgent endovascular repair with at least 1 periscope graft delivered via a transfemoral access; chimney grafts were installed from an axillary access. In all, 17 periscope and 7 chimney grafts were used to reperfuse 11 renal and 13 visceral arteries in the 9 patients. The aortic aneurysms were excluded using thoracic devices (n=7), an aortic extension cuff (n=1), and bifurcated stent-grafts (n=2). Results All procedures were completed without technical complications except for a dislocated stent-graft from the right renal artery; the artery could not be re-accessed, and the right kidney was sacrificed. One patient died of multiple organ failure (11% 30-day mortality). At a mean follow-up of 10 months (range 3–24), 5 of the 9 patients had recovered completely; 3 patients died of unrelated causes. Imaging showed no aneurysm growth in any patient, with a mean 20% shrinkage in aneurysm size. All periscope and chimney grafts remained patent, and no aortic stent-graft migration was observed. Renal function and the glomerular filtration rate remained stable in all patients. Conclusion The periscope and chimney graft technique provides a simpler, less invasive way to maintain blood flow to the renovisceral arteries during urgent endovascular aortic repairs. The very low 30-day mortality rate and the stability of the repairs in the midterm are encouraging. This technique has the potential to profoundly influence the treatment of acute aortic pathologies.

Complete endovascular renal and visceral artery revascularization and exclusion of a ruptured type IV thoracoabdominal aortic aneurysm.

Purpose: To present a technique for renal and visceral revascularization allowing complete endovascular treatment of a ruptured type IV thoracoabdominal aneurysm using devices already stocked in most centers performing endovascular aneurysm repair. Technique: Open arterial access is obtained to both common femoral arteries and the left subclavian artery (LSA). Access to the visceral and renal arteries is obtained through separate 8-F sheaths for each visceral and renal branch. Both visceral arteries (celiac trunk and superior mesenteric artery) are accessed through 2 separate sheaths placed into the LSA, and both renal arteries are accessed through 2 separate sheaths placed into the left common femoral artery. Corresponding covered stents are introduced and positioned in the celiac trunk, superior mesenteric artery, and both renal arteries but not deployed. The aortic stent-graft is then introduced and deployed through the right common femoral artery. Once the aneurysm exclusion is completed, the stent-grafts to the branches are deployed so that they are positioned between the aortic wall and the aortic stent-graft. Finally, the branch stent-grafts as well as the aortic stent-graft are fully expanded with balloon catheters inflated simultaneously as in the kissing balloon technique. Conclusion: To our knowledge, no one has reported using this technique to successfully treat a ruptured thoracoabdominal aneurysm and revascularize all 4 major renovisceral arteries. A main advantage of this technique over use of branched stent-grafts is that it can be performed even in the emergency setting with devices that are in stock in most institutions performing endovascular aneurysm exclusion.

Prenatally engineered autologous amniotic fluid stem cell-based heart valves in the fetal circulation

Prenatal heart valve interventions aiming at the early and systematic correction of congenital cardiac malformations represent a promising treatment option in maternal-fetal care. However, definite fetal valve replacements require growing implants adaptive to fetal and postnatal development. The presented study investigates the fetal implantation of prenatally engineered living autologous cell-based heart valves. Autologous amniotic fluid cells (AFCs) were isolated from pregnant sheep between 122 and 128 days of gestation via transuterine sonographic sampling. Stented trileaflet heart valves were fabricated from biodegradable PGA-P4HB composite matrices (n = 9) and seeded with AFCs in vitro. Within the same intervention, tissue engineered heart valves (TEHVs) and unseeded controls were implanted orthotopically into the pulmonary position using an in-utero closed-heart hybrid approach. The transapical valve deployments were successful in all animals with acute survival of 77.8% of fetuses. TEHV in-vivo functionality was assessed using echocardiography as well as angiography. Fetuses were harvested up to 1 week after implantation representing a birth-relevant gestational age. TEHVs showed in vivo functionality with intact valvular integrity and absence of thrombus formation. The presented approach may serve as an experimental basis for future human prenatal cardiac interventions using fully biodegradable autologous cell-based living materials.