Pablo Bächler

Assessment of normal flow patterns in the pulmonary circulation by using 4D magnetic resonance velocity mapping.

OBJECTIVE The purpose of this study was to analyze flow patterns in the pulmonary circulation of healthy volunteers by using 4D flow magnetic resonance imaging. MATERIALS AND METHODS The study was approved by the local ethics committee and all subjects gave written informed consent. Eighteen volunteers underwent a 4D flow scan of the whole-heart. Two patients with congenital heart disease were also included to detect possible patterns of flow abnormalities (Patient 1: corrected transposition of great arteries (TGA); Patient 2: partial anomalous pulmonary venous return and atrial septal defect). To analyze flow patterns, 2D planes were placed on the main pulmonary artery (PA), left and right PA. Flow patterns were assessed manually by two independent viewers using vector fields, streamlines and particle traces, and semi-automatically by vorticity quantification. RESULTS Two counter-rotating helices were found in the main PA of volunteers. Right-handed helical flow was detected in the right PA of 15 volunteers. Analysis of the helical flow by particles traces revealed that both helices contributed mainly to the flow in the right PA. In the patient with corrected TGA helical flow was not detected. Abnormal vortical flow was visualized in the main PA of patient 2, suggesting elevated mean PA pressure. CONCLUSIONS Helical flow is normally present in the main PA and right PA. 4D flow is an excellent tool to evaluate noninvasively complex blood flow patterns in the pulmonary circulation. Knowledge of normal and abnormal flow patterns might help to evaluate patients with congenital heart disease adding functional information undetectable with other imaging modalities.

Caval blood flow distribution in patients with Fontan circulation: quantification by using particle traces from 4D flow MR imaging.

PURPOSE To validate the use of particle traces derived from four-dimensional (4D) flow magnetic resonance (MR) imaging to quantify in vivo the caval flow contribution to the pulmonary arteries (PAs) in patients who had been treated with the Fontan procedure. MATERIALS AND METHODS The institutional review boards approved this study, and informed consent was obtained. Twelve healthy volunteers and 10 patients with Fontan circulation were evaluated. The particle trace method consists of creating a region of interest (ROI) on a blood vessel, which is used to emit particles with a temporal resolution of approximately 40 msec. The flow distribution, as a percentage, is then estimated by counting the particles arriving to different ROIs. To validate this method, two independent observers used particle traces to calculate the flow contribution of the PA to its branches in volunteers and compared it with the contribution estimated by measuring net forward flow volume (reference method). After the method was validated, caval flow contributions were quantified in patients. Statistical analysis was performed with nonparametric tests and Bland-Altman plots. P < .05 was considered to indicate a significant difference. RESULTS Estimation of flow contributions by using particle traces was equivalent to estimation by using the reference method. Mean flow contribution of the PA to the right PA in volunteers was 54% ± 3 (standard deviation) with the reference method versus 54% ± 3 with the particle trace method for observer 1 (P = .4) and 54% ± 4 versus 54% ± 4 for observer 2 (P = .6). In patients with Fontan circulation, 87% ± 13 of the superior vena cava blood flowed to the right PA (range, 63%-100%), whereas 55% ± 19 of the inferior vena cava blood flowed to the left PA (range, 22%-82%). CONCLUSION Particle traces derived from 4D flow MR imaging enable in vivo quantification of the caval flow distribution to the PAs in patients with Fontan circulation. This method might allow the identification of patients at risk of developing complications secondary to uneven flow distribution. SUPPLEMENTAL MATERIAL http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12120778/-/DC1.

Hemodynamic assessment in patients with one-and-a-half ventricle repair revealed by four-dimensional flow magnetic resonance imaging.

We report hemodynamic findings in two patients with pulmonary atresia and intact ventricular septum (PAIVS) after “one-and-a-half ventricle repair” and placement of a bidirectional Glenn shunt using four-dimensional (4D) flow magnetic resonance imaging. Quantification of flow and analysis of flow patterns revealed the hemodynamic “battle” between the right ventricle (RV) and the Glenn shunt. Moreover, with a novel approach we calculated during Glenn anastomosis the flow distribution from the superior vena cava (SVC) to the pulmonary arteries. Our results showed a highly asymmetric flow distribution, with most of the flow from the SVC toward the RV and not to the lungs. The evidence provided by 4D flow demonstrates poor efficiency of this system and suggests that both patients might benefit from adding an artificial pulmonary valve to avoid right heart failure.

Incidental venous thromboembolism detected by PET-CT in patients with cancer: Prevalence and impact on survival rate

INTRODUCTION People with cancer are at increased risk of incidental venous thromboembolism (VTE) and PET-CT imaging is commonly used in this population. However, the prevalence of incidental VTE detected by PET-CT in patients with cancer and its impact on survival are unknown. MATERIALS AND METHODS This retrospective study was approved by the local Institutional Review Board. 1331 consecutive adult patients with cancer who underwent PET-CT examination between 2009 and 2012 were included in the study (mean age: 57 ± 15 years). PET-CT reports were reviewed to identify patients with incidental VTE at the time of examination. Survival rates were assessed with Kaplan-Meier curves. The Cox proportional hazards model was used to determine the association between incidental VTE and overall survival, after controlling for clinical variables. RESULTS Incidental VTE was detected in 19 patients (1.4%). Patients with genitourinary malignancies, colorectal cancer and lung cancer had the highest rates of incidental VTE at PET-CT. At multivariate analysis, incidental VTE detected by PET-CT was associated with worse overall survival independently of patient age, hospitalization status at time of PET-CT examination, and the presence of metastatic disease (Hazard ratio=2.03; 95% confidence interval=1.08-3.81, p=0.028). CONCLUSION Incidental VTE was detected in 1.4% of adult patients with cancer undergoing PET-CT imaging. Diagnosis of incidental VTE at PET-CT imaging was associated with worse overall survival in this population.

Multimodality Imaging of Liver Infections: Differential Diagnosis and Potential Pitfalls

Imaging plays an important role in the diagnosis, characterization, and management of infectious liver disease. In clinical practice, the main contributions of imaging are in detecting early disease, excluding other entities with a similar presentation, establishing a definitive diagnosis when classic findings are present, and guiding appropriate antimicrobial, interventional, or surgical treatment. The most common imaging features of bacterial, viral, parasitic, and fungal hepatic infections are described, and key imaging and clinical manifestations are reviewed that may be useful to narrow the differential diagnosis and avoid pitfalls in image interpretation. Ultrasonography (US), computed tomography (CT), and magnetic resonance imaging allow accurate detection of most hepatic infections and, in some circumstances, may provide specific signs to identify the underlying pathogen and exclude other entities with similar imaging features. In bacterial and parasitic infections, specific imaging features may be enough to exclude a neoplasm and, occasionally, to identify the underlying infectious agent. US and CT are important means to guide percutaneous aspiration or drainage when needed. In viral infections, imaging is critical to exclude entities that may manifest with similar clinical and laboratory findings. Disseminated fungal infections require early detection at imaging because they can be fatal if not promptly treated. Familiarity with the epidemiology, pathogenesis, clinical manifestations, imaging features, and treatment of hepatic infections can aid in radiologic diagnosis and guide appropriate patient care. (©)RSNA, 2016.

Normal values of wall shear stress in the pulmonary artery from 4D flow data

m 2 ; RPA = 0.36±0.1N/m 2 ; LPA = 0.28±0.14N/m 2 . Figure 1 shows the average WSS-M calculated along the cardiac cycle for each segment. Figure 2 depicts Bland Altman plots of the mean WSS measured by the two observers, showing a small bias and standard deviations (mean difference of 0.016N/m 2 , 0.008N/m 2 and 0.005N/ m 2 for the WSS-M in the PA, RPA and LPA respectively). Conclusions In this work we proposed a novel and reproducible method to calculate WSS derived from 4D flow data in the main PA, RPA and LPA. In volunteers, we found a greater WSS in the RPA compared with the LPA, which is probably associated with more complex flow patterns (helices) in the RPA (2). Values of WSS obtained in patients showed increasing values of WSS, probably owe to complex and retrograde flow patterns in the pulmonary circulation.

Quantification of pulmonary regurgitation in patients with repaired Tetralogy of Fallot by 2D phase-contrast MRI: Differences between the standard method of velocity averaging and a pixel-wise analysis:

Objectives To compare the values of pulmonary regurgitation in patients with repaired Tetralogy of Fallot quantified from two-dimensional phase-contrast data, by using a new pixel-wise analysis and the standard velocity-averaging method. Design Quantitative in silico and in vivo analysis. Setting Hospital Sótero del Río. The magnetic resonance images were acquired using a Philips Achieva 1.5T scanner. Participants Twenty-five patients with repaired Tetralogy of Fallot who underwent cardiovascular magnetic resonance imaging requested by their referring physicians were included in this study. Main outcome measures Using a computational fluid dynamics simulation, we validated our pixel-wise method, quantifying the error of our method in comparison with the standard method. The patients underwent a standard two-dimensional phase-contrast magnetic resonance imaging acquisition for quantifying pulmonary artery flow. Pulmonary regurgitation fraction was estimated by using our pixel-wise and the standard method. The two-dimensional flow profiles were inspected looking for simultaneous antegrade and retrograde flows in the same cardiac phase. Statistical analysis was performed with t-test for related samples, Bland–Altman plots, and Pearson correlation coefficient. Results Estimation of pulmonary regurgitation fraction using the pixel-wise analysis revealed higher values compared with the standard method (39 ± 16% vs. 30 ± 22%, p-value <0.01). Eight patients (32%) had a difference of more than 10% between methods. Analysis of two-dimensional flow profiles in these patients revealed simultaneous antegrade and retrograde flows through the pulmonary artery during systole–early diastole. Conclusion Quantification of pulmonary regurgitation fraction in patients with repaired Tetralogy of Fallot through a pixel-wise analysis yields higher values of pulmonary regurgitation compared with the standard velocity-averaging method.

Pseudo-hemothorax at computed tomography due to residual contrast media.

Pleural effusion is a clinical problem that has many causes, with hemothorax being one of them. Computed tomography readily characterizes pleural fluid with determination of the attenuation value, helping to distinguish hemothorax from other types of effusion. Herein, we report the case of a 67-year-old man with end-stage renal disease in which a high-density pleural effusion due to residual contrast media was misinterpreted as hemothorax. Radiologists should consider the possibility of contrast media retention when interpreting a high-density pleural effusion in patients with end-stage renal disease. Recognition of this entity is crucial to avoid misdiagnosis, which might lead to unnecessary testing or procedures.

Utilidad de la biopsia percutánea core guiada por tomografía computada (TC) en lesiones pulmonares: experiencia de 7 años

Background: CT guided percutaneous biopsy of pulmonary lesions is a widely used technique. Aim: To evaluate the yield and complication rate of CT-guided percutaneous core biopsy of pulmonary lesions. Material and Methods: A retrospective study of 153 consecutive lung biopsies performed in a 7-yearperiod was undertaken. Patients and lesions characteristics were reviewed. The yield for the diagnosis of malignant and benign lesions and the complication rate were calculated. Lesion size and depth from the pleural surface were analyzed as potential predictive variables for occurrence of a false-negative diagnosis of malignancy. The final diagnosis was established by surgical biopsy of the lesion or clinical and imaging follow up. Results: The mean age of patients was 66 ± 14 years and 55% were mole. The final diagnosis of the lesion was malignant in 139 and benign in 14 cases (prevalence of malignancy 90.8%). For the diagnosis of malignancy, the overall yield ofthe biopsy was 91.5%o with a sensitivity of 90.6%>. A specific diagnosis of benign lesions was obtained in 5 out ofl4 biopsies (35%). We did not identify an association between the lesion size or depth and the rate of false-negative diagnosis of malignancy. The pneumothorax rate was 13.7%o (n = 21) and eight (38%) required drainage. The average lesion depth of patients that had a pneumothorax was significant greater than the cases without the complication. No major bleeding complications occurred. Conclusions: Percutaneous CT-guided cutting needle biopsies of pulmonary lesions have an excellent diagnostic accuracy for malignant pulmonary lesions, at a low complication rate.

Quantification of Caval contribution to flow in the Right and Left Pulmonary Artery of Fontan patients with 4D Flow MRI

Background Knowledge of caval contribution to flow in the Right and Left Pulmonary Artery (RPA and LPA) of Fontan patients is of great interest, because uneven flow distribution to the lungs is associated with pulmonary arteriovenous malformations. However, in Fontan circulation more than 1 source of flow to the RPA and LPA is present, which makes difficult to quantify the flow distribution with standard methods. Although a novel MRI application was developed to quantify caval contribution years ago, it has limitations and it is not applicable to patients with turbulent flow in the Pulmonary Arteries (PA)[1]. We propose a new method to easily quantify the flow distribution in Fontan patients. Methods A 4D Flow sequence was acquired in 12 healthy volunteers and 9 Fontan patients on a 1.5T Philips scan. Flow distribution was quantified with particles traces using the software “GTFlow”. The new method consists of emitting particles from a Region Of Interest (ROI) with a temporal resolution of ~40 ms. Then, we quantified the flow distribution by counting the particles arriving to a different ROI. To validate this method, 2 independent observers compared the flow contribution of the main PA to the RPA and LPA in healthy volunteers. This was done calculating net forward flow, which was used to validate the distribution of flow obtained with our new method. Thereafter, we quantified the flow distribution of the Superior and Inferior Vena Cava (SVC and IVC) to the RPA and LPA in Fontan patients.