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Dan Leotta

Senior Engineer

Email

dfleotta@apl.washington.edu

Phone

206-616-3475

Publications

2000-present and while at APL-UW

An upgraded camera-based imaging system for mapping venous blood oxygenation in human skin tissue

Li, J., X. Zhang, L. Qiu, and D.F. Leotta, "An upgraded camera-based imaging system for mapping venous blood oxygenation in human skin tissue," Opt. Commun., 370, 276-282, doi:10.1016/j.optcom.2016.03.030, 2016.

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1 Jul 2016

Highlights

A camera-based mapping of venous oxygenation saturation SvO2 was further developed.

Monte Carlo method was used for modeling the imaging system.

Curvature and motion correction algorithms were included in the image process.

The spatial resolution for SvO2 map achieved was 1.25 mm×1.25 mm.

The measured SvO2 was validated by a NIRS system and in line with published data.

Development of a duplex ultrasound simulator and preliminary validation of velocity measurements in carotid artery models

Zierler, R.E., D.F. Leotta, K. Sansom, A. Aliseda, M.D. Anderson, and F.H. Sheehan, "Development of a duplex ultrasound simulator and preliminary validation of velocity measurements in carotid artery models," Vasc. Endovascular Surg., 50, 309-316, doi:10.1177/1538574416647502, 2016.

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1 Jul 2016

Duplex ultrasound scanning with B-mode imaging and both color Doppler and Doppler spectral waveforms is relied upon for diagnosis of vascular pathology and selection of patients for further evaluation and treatment. In most duplex ultrasound applications, classification of disease severity is based primarily on alterations in blood flow velocities, particularly the peak systolic velocity (PSV) obtained from Doppler spectral waveforms. We developed a duplex ultrasound simulator for training and assessment of scanning skills.

Custom fenestration templates for endovascular repair of juxtarenal aortic aneurysms

Leotta, D.F., and B.W. Starnes, "Custom fenestration templates for endovascular repair of juxtarenal aortic aneurysms," J. Vasc. Surg., 61, 1637-1641, doi:10.1016/j.jvs.2015.02.016, 2015.

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1 Jun 2015

Physician-modified endovascular grafts, with fenestrations added to accommodate major branch vessels, provide a means for endovascular treatment of abdominal aortic aneurysms that are adjacent to the renal arteries. Manual measurements of vessel origin locations from computed tomography images, however, take time and can lead to errors in the positions of the fenestrations. To make the fenestration process faster and more accurate, we have developed a procedure to create custom templates that serve as patient-specific guides for graft fenestration. We use a three-dimensional printer to create a clear rigid sleeve that replicates the patient's aorta and includes holes placed precisely at the locations of the branch vessels. The sleeve is slipped over the graft, the locations of the openings are marked with a pen, and the fenestrations are created after the sleeve is removed. Custom fenestration templates can potentially save procedural costs and make minimally invasive aortic aneurysm repair available to more patients.

More Publications

Effects of wall distensibility in hemodynamic simulations of an arteriovenous fistula

McGah, P.M., D.F. Leotta, K.W. Beach, and A. Aliseda, "Effects of wall distensibility in hemodynamic simulations of an arteriovenous fistula, " Biomech. Model. Mechanobiol., 13, 679-695, doi:10.1007/s10237-013-0527-7, 2013.

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1 Jun 2014

Arteriovenous fistulae are created surgically to provide adequate access for dialysis patients suffering from end-stage renal disease. It has long been hypothesized that the rapid blood vessel remodeling occurring after fistula creation is in part a process to restore the mechanical stresses to some preferred level, i.e., mechanical homeostasis. The current study presents fluid%u2013structure interaction (FSI) simulations of a patient-specific model of a mature arteriovenous fistula reconstructed from 3D ultrasound scans. The FSI results are compared with previously published data of the same model but with rigid walls. Ultrasound-derived wall motion measurements are also used to validate the FSI simulations of the wall motion. Very large time-averaged shear stresses, 10%u201315 Pa, are calculated at the fistula anastomosis in the FSI simulations, values which are much larger than what is typically thought to be the normal homeostatic shear stress in the peripheral vasculature. Although this result is systematically lower by as much as 50 % compared to the analogous rigid-walled simulations, the inclusion of distensible vessel walls in hemodynamic simulations does not reduce the high anastomotic shear stresses to %u201Cnormal%u201D values. Therefore, rigid-walled analyses may be acceptable for identifying high shear regions of arteriovenous fistulae.

A reflectance model for non-contact mapping of venous oxygen saturation using a CCD camera

Li, J., B. Dunmire, K.W. Beach, and D.F. Leotta, "A reflectance model for non-contact mapping of venous oxygen saturation using a CCD camera," Opt. Commun., 308, 78-84, doi:10.1016/j.optcom.2013.06.041, 2013.

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1 Nov 2013

A method of non-contact mapping of venous oxygen saturation (SvO2) is presented. A CCD camera is used to image skin tissue illuminated alternately by a red (660 nm) and an infrared (800 nm) LED light source. Low cuff pressures of 30–40 mmHg are applied to induce a venous blood volume change with negligible change in the arterial blood volume. A hybrid model combining the Beer–Lambert law and the light diffusion model is developed and used to convert the change in the light intensity to the change in skin tissue absorption coefficient. A simulation study incorporating the full light diffusion model is used to verify the hybrid model and to correct a calculation bias. SvO2 in the fingers, palm, and forearm for five volunteers are presented and compared with results in the published literature. Two-dimensional maps of venous oxygen saturation are given for the three anatomical regions.

Three-dimensional ultrasonography measurements after endovascular aneurysm repair

Causey, M.W., A. Jayaraj, D.F. Leotta, M. Paun, K.W. Beach, T.R. Kohler, E.R. Zierler, and B.W. Starnes, "Three-dimensional ultrasonography measurements after endovascular aneurysm repair," Ann. Vascular Surg., 27, 146-153, doi:10.1016/j.avsg.2012.01.018, 2013.

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1 Feb 2013

Background
Ultrasonographic (US) assessment of abdominal aortic aneurysms is typically performed by measuring maximal aneurysm diameter from two-dimensional images. These measurements are prone to inaccuracies owing to image planes and interobserver variability. The purpose of this study was to compare the variability in diameter, cross-sectional area (CSA), and volume measurements of abdominal aortic aneurysms obtained using a three-dimensional (3D) US imaging system with those obtained using computed tomographic (CT) angiography, and to determine the reliability of these measures.

Methods
Seven patients in whom endovascular aneurysm repairs were performed underwent CT angiography in addition to a 3D US scan. Measurements computed using 3D surface reconstructions of CT and 3D US scans included maximum diameter, CSA, and aneurysm volume. The seven matched CT and 3D US scans were compared at baseline and 6 to 8 weeks later.

Results
The average aneurysm measured 57.2 mm on CT and 56.2 mm on US (P = 0.14). Correlation coefficients for diameter, CSA, and volume were 0.88, 0.90, and 0.93, respectively (all P values < 0.001). A Bland–Altman analysis demonstrated a strong agreement between 92% of the diameter, 96.4% of the CSA, and 100% of the volume measurements. The interrater reliability was remarkably high comparing the modalities (CT vs. US), and ranged from 0.934 to 0.997 for single measurements and 0.965 to 0.998 for all measurements together; moreover, there was a strong reliability when the tests were reviewed 6 to 8 weeks later, with a reliability of 0.962 to 0.998 for single measurements and 0.992 to 0.999 for all tests (all P values < 0.001).

Conclusions
The 3D US is an accurate and noninvasive method of determining aneurysm size and geometry that is reproducible. Volumetric measurements may represent a significant advancement in long-term follow-up after endovascular aneurysm repair.

Incomplete restoration of homeostatic shear stress within arteriovenous fistulae

McGah, P.M., D.F. Leotta, K.W. Beach, R. Eugene Zierler, and A. Aliseda, "Incomplete restoration of homeostatic shear stress within arteriovenous fistulae," J. Biomech. Eng., 135, 011005, doi:10.1115/1.4023133, 2013.

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1 Jan 2013

Arteriovenous fistulae are surgically created to provide adequate access for dialysis patients suffering from end-stage renal disease. It has long been hypothesized that the rapid blood vessel remodeling occurring after fistula creation is, in part, a process to restore the mechanical stresses to some preferred level, i.e., mechanical homeostasis. We present computational hemodynamic simulations in four patient-specific models of mature arteriovenous fistulae reconstructed from 3D ultrasound scans. Our results suggest that these mature fistulae have remodeled to return to "normal" shear stresses away from the anastomoses: about 1.0 Pa in the outflow veins and about 2.5 Pa in the inflow arteries. Large parts of the anastomoses were found to be under very high shear stresses >15 Pa, over most of the cardiac cycle. These results suggest that the remodeling process works toward restoring mechanical homeostasis in the fistulae, but that the process is limited or incomplete, even in mature fistulae, as evidenced by the elevated shear at or near the anastomoses. Based on the long term clinical viability of these dialysis accesses, we hypothesize that the elevated nonhomeostatic shear stresses in some portions of the vessels were not detrimental to fistula patency.

Carotid Doppler velocity measurements and anatomic stenosis: Correlation is futile

Beach, K.W., D.F. Leotta, and R.E. Zierler, "Carotid Doppler velocity measurements and anatomic stenosis: Correlation is futile," Vascular Endovascular Surg., 46, 466-474, doi:10.1177/1538574412452159, 2012.

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21 Aug 2012

Background: Duplex ultrasound with Doppler velocimetry is widely used to evaluate the presence and severity of internal carotid artery stenosis; however, a variety of velocity criteria are currently being applied to classify stenosis severity. The purpose of this study is to compare published Doppler velocity measurements to the severity of internal carotid artery stenosis as assessed by x-ray angiography in order to clarify the relationship between these 2 widely used approaches to assess carotid artery disease. Methods: Scatter diagrams or "scattergrams" of correlations between Doppler velocity measurements and stenosis severity as assessed by x-ray contrast angiography were obtained from published articles for native and stented internal carotid arteries. The scattergrams were graphically digitized, combined, and segmented into categories bounded by 50% and 70% diameter reduction. These data were combined and divided into 3 sets representing different velocity parameters: (1) peak systolic velocity, (2) end-diastolic velocity, and (3) the internal carotid artery to common carotid artery peak systolic velocity ratio. The horizontal axis of each scattergram was transformed to form a cumulative distribution function, and thresholds were established for the stenosis categories to assess data variability. Results: Nineteen publications with 22 data sets were identified and included in this analysis. Wide variability was apparent between all 3 velocity parameters and angiographic percent stenosis. The optimal peak systolic velocity thresholds for stenosis in stented carotid arteries were higher than those for native carotid arteries. Within each category of stenosis, the variability of all 3 velocity parameters was significantly lower in stented arteries than in native arteries. Conclusion: Although Doppler velocity criteria have been successfully used to classify the severity of stenosis in both native and stented carotid arteries, the relationship to angiographic stenosis contains significant variability. This analysis of published studies suggests that further refinements in Doppler velocity criteria will not lead to improved correlation with carotid stenosis as demonstrated by angiography.

A longitudinal study of remodeling in a revised peripheral artery bypass graft using 3D ultrasound imaging and computational hemodynamics.

McGah, P.M., D.F. Leotta, K.W. Beach, J.J. Riley, and A. Aliseda, "A longitudinal study of remodeling in a revised peripheral artery bypass graft using 3D ultrasound imaging and computational hemodynamics." J. Biomed. Eng., 133, 041008, doi: 10.1115/1.4003622, 2011.

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1 Apr 2011

We report a study of the role of hemodynamic shear stress in the remodeling and failure of a peripheral artery bypass graft. Three separate scans of a femoral to popliteal above-knee bypass graft were taken over the course of a 16 month period following a revision of the graft. The morphology of the lumen is reconstructed from data obtained by a custom 3D ultrasound system. Numerical simulations are performed with the patient-specific geometries and physiologically realistic flow rates. The ultrasound reconstructions reveal two significant areas of remodeling: a stenosis with over 85% reduction in area, which ultimately caused graft failure, and a poststenotic dilatation or widening of the lumen. Likewise, the simulations reveal a complicated hemodynamic environment within the graft. Preliminary comparisons with in vivo velocimetry also showed qualitative agreement with the flow dynamics observed in the simulations. Two distinct flow features are discerned and are hypothesized to directly initiate the observed in vivo remodeling. First, a flow separation occurs at the stenosis. A low shear recirculation region subsequently develops distal to the stenosis. The low shear region is thought to be conducive to smooth muscle cell proliferation and intimal growth. A poststenotic jet issues from the stenosis and subsequently impinges onto the lumen wall. The lumen dilation is thought to be a direct result of the high shear stress and high frequency pressure fluctuations associated with the jet impingement.

Inventions

Supplemental Know How for Pushing, Imaging, and Breaking Kidney Stones

Record of Invention Number: 47878

Mike Bailey, Larry Crum, Bryan Cunitz, Barbrina Dunmire, Vera Khokhlova, Wayne Kreider, John Kucewicz, Dan Leotta

Disclosure

9 Nov 2016

Automated Monitoring of Vascular Flow and Morphology by 3D Ultrasound

Record of Invention Number: 47678

Shahram Aarabi, Dan Leotta, Nathan White

Disclosure

13 Apr 2016

Fenestration template for endovascular repair of aortic aneurysms

Patent Number: 9,305,123

Dan Leotta, Benjamin Starnes

More Info

Patent

5 Apr 2016

To provide simple yet accurate stent graft fenestration, a patient-specific fenestration template is used as a guide for graft fenestration. To generate the fenestration template, a patient's medical imaging data such as CT scan data may be used to generate a 3-D digital model of an aorta lumen of the patient. The aorta lumen may encompass one or more branch vessels, which may be indicated on the 3-D digital model. Based on the 3-D digital model or a segment thereof, the fenestration template may be generated, for example, using 3-D printing technology. The fenestration template may include one or more holes or openings that correspond to the one or more branch vessels. To fenestrate a stent graft, the fenestration template is coupled to the stent graft so that the holes or openings on the fenestration template indicate the fenestration locations.

More Inventions

Software to Create Custom Fenestration Templates for Endovascular Grafts

Record of Invention Number: 47107

Dan Leotta

Disclosure

21 Oct 2014

Ultrasound-Guided Automatic Vascular Access Device

Record of Invention Number: 46421

Benjamin Starnes, Dan Leotta

Disclosure

28 Feb 2013

Non-Contact Reflectance Imaging of Oxygen Saturation in Venous Blood

Record of Invention Number: 46171

Jun Li, Barbrina Dunmire, Dan Leotta

Disclosure

1 Aug 2012

A Vascular Duplex Ultrasound Simulator for Training and Competency Testing

Record of Invention Number: 45659

Dan Leotta, Florence Sheehan, Alberto Aliseda, Kirk Beach, R. Eugene Zierler

Disclosure

14 Jun 2011

A Fenestration Template for Endovascular Repair of Juxtarenal Aortic Aneurysms

Record of Invention Number: 45651

Ray Illian, Dan Leotta, Benjamin Starnes

Disclosure

7 Jun 2011

Computational Flow Modeling for Dialysis Access Surgical Planning

Record of Invention Number: 8701D

Barbrina Dunmire, Dan Leotta, Alberto Aliseda, James J. Riley, Kirk W. Beach, Edward Stutzman, R. Eugene Zierler

Disclosure

20 May 2010

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center
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