Nicole Wake

Medical 3D Printing for the Radiologist

While use of advanced visualization in radiology is instrumental in diagnosis and communication with referring clinicians, there is an unmet need to render Digital Imaging and Communications in Medicine (DICOM) images as three-dimensional (3D) printed models capable of providing both tactile feedback and tangible depth information about anatomic and pathologic states. Three-dimensional printed models, already entrenched in the nonmedical sciences, are rapidly being embraced in medicine as well as in the lay community. Incorporating 3D printing from images generated and interpreted by radiologists presents particular challenges, including training, materials and equipment, and guidelines. The overall costs of a 3D printing laboratory must be balanced by the clinical benefits. It is expected that the number of 3D-printed models generated from DICOM images for planning interventions and fabricating implants will grow exponentially. Radiologists should at a minimum be familiar with 3D printing as it relates to their field, including types of 3D printing technologies and materials used to create 3D-printed anatomic models, published applications of models to date, and clinical benefits in radiology. Online supplemental material is available for this article.

Mechanisms of Premature Vascular Aging in Children With Hutchinson-Gilford Progeria Syndrome

Hutchinson-Gilford progeria syndrome is a rare, segmental premature aging syndrome of accelerated atherosclerosis and early death from myocardial infarction or stroke. This study sought to establish comprehensive characterization of the fatal vasculopathy in Hutchinson-Gilford progeria syndrome and its relevance to normal aging. We performed cardiovascular assessments at a single clinical site on the largest prospectively studied cohort to date. Carotid-femoral pulse wave velocity was dramatically elevated (mean: 13.00±3.83 m/s). Carotid duplex ultrasound echobrightness, assessed in predefined tissue sites as a measure of arterial wall density, was significantly greater than age- and sex-matched controls in the intima-media (P<0.02), near adventitia (P<0.003), and deep adventitia (P<0.01), as was internal carotid artery mean flow velocity (P<0.0001). Ankle-brachial indices were abnormal in 78% of patients. Effective disease treatments may be heralded by normalizing trends of these noninvasive cardiovascular measures. The data demonstrate that, along with peripheral vascular occlusive disease, accelerated vascular stiffening is an early and pervasive mechanism of vascular disease in Hutchinson-Gilford progeria syndrome. There is considerable overlap with cardiovascular changes of normal aging, which reinforces the view that defining mechanisms of cardiovascular disease in Hutchinson-Gilford progeria syndrome provides a unique opportunity to isolate a subset of factors influencing cardiovascular disease in the general aging population.

Early remodeling of lower extremity vein grafts: Inflammation influences biomechanical adaptation

BACKGROUND The remodeling of vein bypass grafts after arterialization is incompletely understood. We have previously shown that significant outward lumen remodeling occurs during the first month of implantation, but the magnitude of this response is highly variable. We sought to examine the hypothesis that systemic inflammation influences this early remodeling response. METHODS A prospective observational study was done of 75 patients undergoing lower extremity bypass using autogenous vein. Graft remodeling was assessed using a combination of ultrasound imaging and two-dimensional high-resolution magnetic resonance imaging. RESULTS The vein graft lumen diameter change from 0 to 1 month (22.7% median increase) was positively correlated with initial shear stress (P = .016), but this shear-dependent response was disrupted in subjects with an elevated baseline high-sensitivity C-reactive protein (hsCRP) level of >5 mg/L. Despite similar vein diameter and shear stress at implantation, grafts in the elevated hsCRP group demonstrated less positive remodeling from 0 to 1 month (13.5% vs 40.9%, P = .0072). By regression analysis, the natural logarithm of hsCRP was inversely correlated with 0- to 1-month lumen diameter change (P = .018). Statin therapy (beta = 23.1, P = .037), hsCRP (beta = -29.7, P = .006), and initial shear stress (beta = .85, P = .003) were independently correlated with early vein graft remodeling. In contrast, wall thickness at 1 month was not different between hsCRP risk groups. Grafts in the high hsCRP group tended to be stiffer at 1 month, as reflected by a higher calculated elastic modulus (E = 50.4 vs 25.1 Mdynes/cm2, P = .07). CONCLUSIONS Early positive remodeling of vein grafts is a shear-dependent response that is modulated by systemic inflammation. These data suggest that baseline inflammation influences vein graft healing, and therefore, inflammation may be a relevant therapeutic target to improve early vein graft adaptation.

Endothelial function predicts positive arterial-venous fistula remodeling in subjects with stage IV and V chronic kidney disease

Purpose The maturation of an arteriovenous fistula (AVF) requires remodeling of the arterial inflow and the venous outflow limbs to sustain flows sufficient to support hemodialysis. However, factors influencing remodeling of AVF are poorly understood. We hypothesized that AVF remodeling was an endothelium-dependent process. Methods This is a prospective cohort study of patients (n=25) undergoing autologous AVF formation. Brachial artery vasoreactivity studies were performed pre-operatively to assess endothelium-dependent, flow-mediated vasodilation (FMD). High-resolution ultrasound was used to assess venous and arterial diameters intraoperatively, and at 3 months. Results The mean age was 64.5 ± 13.6 yrs. Twelve patients (48%) had diabetes. The mean FMD for the entire cohort was (mean ± SEM) 5.82 ± 0.9%, (range) 0–17.3%. The vein increased in size 3.19 ± .28 to 6.11 ± .41 mm, 108.4 ± 17.9%, p=.0001, while the artery increased from 3.29 ± .14 to 4.48 ± .30 mm, 20.47 ± 10.8%, p=.013. There was a significant positive correlation between the degree of arterial and venous remodeling, r=.52, p=.023. Brachial artery FMD most strongly correlated with the magnitude of arterial remodeling, r=.47, p=.038. Patients with diabetes failed to undergo venous remodeling to the same extent as did those without diabetes, 59.2 ± 24.4% vs. 141.5 ± 25.4%, p=.04. Conclusion Impairment of endothelial function is associated with decreased arterial remodeling and final venous lumen diameter attained at 3 months. Further investigation is needed to determine whether modulation of endothelial function in this cohort can improve AVF maturation.

In vivo human lower extremity saphenous vein bypass grafts manifest flow mediated vasodilation

OBJECTIVE As in arteries, venous endothelium modulates vessel homeostasis and tone. The effect of an arterialized environment on venous endothelial function remains poorly understood. In particular, regulation of saphenous vein graft (SVG) blood flow and lumen caliber remains undefined. We hypothesized that mature SVGs would exhibit endothelium-dependent, flow-mediated vasodilation (FMD). We further hypothesized that endothelium-derived nitric oxide (NO) was an important mediator. METHODS Patients with femoral to popliteal artery SVGs that had maintained primary patency and were at least 1 year from surgery were enrolled. High-resolution, B-mode ultrasound scans were used to measure vein graft diameter before and 1 minute after reactive hyperemia (RH) to determine FMD. RH was created through application of 220 mm Hg to the calf for 5 minutes with a sphygmomanometric cuff. After a 10-minute recovery period, nitroglycerin-mediated, endothelium-independent vasodilation was measured 3 minutes after administration of nitroglycerin 0.4 mg sublingually. Brachial artery FMD was determined by validated techniques. L-N(G)monomethyl arginine (L-NMMA; 1 mg/kg infusion over 10 minutes) was used in a subset of patients (n = 6) to competitively inhibit endothelial NO synthase. RESULTS Nineteen subjects were enrolled. The median age of the SVGs was 34.6 (21.0-49.7) months. SVG flow-mediated, endothelium-dependent vasodilation was measured at 5.28% +/- 3.1% mean change in lumen diameter (range, 1.99%-9.36%; P < .0001 for diameter change). Nitroglycerin-mediated vasodilation was 3.7% +/- 1.0%, (range, 16%-10.04%; P < .005). Intravenous administration of L-NMMA abolished SVG FMD (5.7 +/- 1.4% before L-NMMA vs 0.01 +/- 0.01% during L-NMMA infusion; P = .0088) and attenuated brachial artery FMD (7.54% +/- 1.0% vs 5.7 +/- 1.4; P = .05). CONCLUSION SVGs manifest flow-mediated, endothelium-dependent, and nitroglycerin-mediated endothelium-independent vasodilation. Vein graft endothelium-dependent FMD is likely mediated by NO. Further investigation will be required to determine the role of endothelial function in vein graft patency.

Computed tomography and echocardiography in patients with acute pulmonary embolism: part 2: prognostic value.

Purpose: The aim of the study was to compare the prognostic value of right ventricular (RV) dysfunction detected on computed tomography pulmonary angiography (CTPA) and transthoracic echocardiography (TTE) in patients with acute pulmonary embolism (PE). Materials and Methods: From all consecutive CTPAs performed between August 2003 and May 2010 that were positive for acute PE (n=1744), those with TTE performed within 48 hours of CTPA (n=785) were selected as the study cohort. Multivariate logistic regression analysis was performed to assess the association of CTPA RV/left ventricular (LV) diameter ratio and TTE RV strain with PE-related 30-day mortality, including other associated factors as covariates. The predictive ability (area under the curve) was compared between the model including the CT RV/LV diameter ratio and that including TTE RV strain. Test characteristics of the 2 modalities were calculated. Results: Both CT RV/LV diameter ratio and TTE RV strain were independently associated with PE-related 30-day mortality (adjusted odds ratio=1.14, P=0.023 for 0.1 increment of the CT RV/LV diameter ratio; and odds ratio=2.13, P=0.041 for TTE RV strain). History of congestive heart failure and malignancy were independent predictors of PE-related mortality, while there was significantly lower mortality associated with anticoagulation use. The model including TTE RV strain and that including CT RV/LV had similar predictive ability (area under the curve=0.80 vs. 0.81, P=0.50). The sensitivity, specificity, and positive and negative predictive values of TTE RV strain and CT RV/LV diameter ratio at a cutoff of ≥1.0 were similar for PE-related 30-day mortality. Conclusions: Both RV strain on TTE and an increased CT RV/LV diameter ratio are predictors of PE-related 30-day mortality with similar prognostic significance.

The variability in prognostic values of right ventricular-to-left ventricular diameter ratios derived from different measurement methods on computed tomography pulmonary angiography: a patient outcome study.

Purpose: To evaluate variability in right ventricular-to-left ventricular (RV/LV) diameter ratios introduced by differences in measurement methods and the subsequent influence on the accuracy of predicting outcomes for patients with acute pulmonary embolism (PE). Materials and Methods: For 200 consecutive computed tomography pulmonary angiograms positive for acute PE, RV/LV diameter ratios were retrospectively measured using 3 different 4-chamber reformations and from axial images alone. The first 4-chamber reformation method (4ch-1) was a single oblique technique using LV morphology landmarks; the other 2 methods (4ch-2 and 4ch-3) were double oblique techniques that created an intermediate short-axis image to identify the maximum RV diameter but with different approaches to reach short-axis images. Interobserver variability was measured using 30 cases. Receiver-operating characteristic analysis compared the accuracy of predicting outcomes among the 4 measurements for PE-related death, and for death or the need for intensive therapies (composite outcome). Results: The difference in median RV/LV diameter ratios was insignificant among 4ch-2 (1.01), 4ch-3 (1.02), and axial (1.03) datasets, whereas that from 4ch-1 (0.93) was significantly lower (P<0.001). Correlation between observers was excellent for all 4 datasets (r=0.881 to 0.925). Compared with 4ch-1, the other 3 datasets equally achieved higher accuracy in predicting PE-related 30-day mortality (area under curve: 0.55 vs. 0.69 to 0.73, P=0.007 to 0.019) and a composite outcome (area under curve: 0.65 vs. 0.77 to 0.78, P=0.003 to 0.010). Conclusions: Double oblique 4-chamber reformation methods that use intermediate short-axis images to optimize RV size predict outcomes better in patients with acute PE than do single oblique methods using only LV landmarks; however, their accuracy is not superior to that from measurements based on axial images.

3D printed ventricular septal defect patch: a primer for the 2015 Radiological Society of North America (RSNA) hands-on course in 3D printing

Hand-held three dimensional models of the human anatomy and pathology, tailored-made protheses, and custom-designed implants can be derived from imaging modalities, most commonly Computed Tomography (CT). However, standard DICOM format images cannot be 3D printed; instead, additional image post-processing is required to transform the anatomy of interest into Standard Tessellation Language (STL) format is needed. This conversion, and the subsequent 3D printing of the STL file, requires a series of steps. Initial post-processing involves the segmentation-demarcation of the desired for 3D printing parts and creating of an initial STL file. Then, Computer Aided Design (CAD) software is used, particularly for wrapping, smoothing and trimming. Devices and implants that can also be 3D printed, can be designed using this software environment. The purpose of this article is to provide a tutorial on 3D Printing with the test case of complex congenital heart disease (CHD). While the infant was born with double outlet right ventricle (DORV), this hands-on guide to be featured at the 2015 annual meeting of the Radiological Society of North America Hands-on Course in 3D Printing focused on the additional finding of a ventricular septal defect (VSD). The process of segmenting the heart chambers and the great vessels will be followed by optimization of the model using CAD software. A virtual patch that accurately matches the patient’s VSD will be designed and both models will be prepared for 3D printing.

CT Angiography for Surgical Planning in Face Transplantation Candidates

SUMMARY: Facial allotransplantation replaces missing facial structures with anatomically identical tissues, providing desired functional, esthetic, and psychosocial benefits far superior to those of conventional methods. On the basis of very encouraging initial results, it is likely that more procedures will be performed in the near future. Typical candidates have extremely complex vascular anatomy due to severe injury and/or multiple prior reconstructive attempts; thus, each procedure is uniquely determined by the defects and vascular anatomy of the candidate. We detail CT angiography vascular mapping, noting the clinical relevance of the imaging, the angiosome concept and noninvasive delineation of the key vessels, and current controversies related to the vascular anastomoses.

Volumetric Quantification of Type II Endoleaks: An Indicator for Aneurysm Sac Growth Following Endovascular Abdominal Aortic Aneurysm Repair

Delayed enhanced phase CT images can be used to perform volumetric quantification of type II endoleak cavities, a parameter that can be used to indicate which aneurysm sac will enlarge and which will be stable or shrink at follow-up CT.