Daniel Leotta - Academia.edu (original) (raw)

Papers by Daniel Leotta

Bulletin of the American Physical Society, Nov 18, 2012

Ultrasonic Imaging, 2000

A three-dimensional (3D) ultrasound imaging system has been used to study spatial compounding of ... more A three-dimensional (3D) ultrasound imaging system has been used to study spatial compounding of images acquired with different scanhead positions and orientations. A compounding algorithm has been developed that assigns regional weights depending on the local incidence angle of the ultrasound beam. Compound scans were performed of bones in vitro and the shoulder rotator cuff in volunteer subjects. Border measurements (peak value and width) were compiled as a function of ultrasound beam incidence angle and compared for single views and for maximum, mean and weighted mean compounding techniques. The weighted mean produces less variability than that ofthe maximum and mean for both intensity and border width. The weighted method also demonstrates less blurring of borders than the maximum and mean methods. Surfaces derived from the weighted reconstructions exhibited fewer gaps and fewer spurious connections between surfaces. which could be of particular importance for automated image analysis.

Gastroenterology, Jul 1, 1997

Three-dimensional (3D) ultrasound imaging of the total stomach volume has not yet been achieved. ... more Three-dimensional (3D) ultrasound imaging of the total stomach volume has not yet been achieved. The aim of this study was to investigate whether a magnetic position sensor system for acquisition of 3D ultrasonograms could be used to determine gastric emptying rates and intragastric distribution. A system for position and orientation measurement was interfaced to an ultrasound scanner. In vitro accuracy was evaluated by scanning a porcine stomach. Fourteen volunteers, with a median age of 35 years, were scanned fasting and postcibally by two-dimensional (2D) and 3D ultrasound after ingesting a 500-mL soup meal. This 3D system yielded a strong correlation (r = 0.997) between true and estimated volumes in vitro. The limits of agreement were -9.1:70.1 mL in the volume range 1200-1900 mL. The intersubject variability of the total gastric volumes ranged from 12.5% to 46.0%, less than for antral area variability. The average half-emptying time was 22.1 +/- 3.8 minutes. Intragastric distribution of the meal, expressed as proximal distal volume, varied on average from 3.6 +/- 2.1 (5 minutes postpradially) to 2.7 +/- 1.9 (30 minutes postprandially). This 3D ultrasound system using magnetic scanhead tracking showed excellent in vitro accuracy, calculated gastric emptying rates more precisely than by 2D ultrasound, and enabled estimation of intragastric distribution of a soup meal.

Volume 1A: Abdominal Aortic Aneurysms; Active and Reactive Soft Matter; Atherosclerosis; BioFluid Mechanics; Education; Biotransport Phenomena; Bone, Joint and Spine Mechanics; Brain Injury; Cardiac Mechanics; Cardiovascular Devices, Fluids and Imaging; Cartilage and Disc Mechanics; Cell and Tiss..., Jun 26, 2013

Arteriovenous fistulae are created surgically to provide an adequate access for dialysis in patie... more Arteriovenous fistulae are created surgically to provide an adequate access for dialysis in patients with End-Stage Renal Disease (ESRD). Producing an autogenous shunt linking an artery and a vein in the peripheral circulation bypasses the high resistance capillary bed in order to provide the necessary flow rates at sites easily accessible for dialysis. It has long been recognized that hemodynamics constitute the primary external influence on the remodeling process of anastomosed vascular tissue [1, 2]. The high flow rate, together with the exposure of the venous tissue to the high arterial pressure, leads to a rapid process of wall remodeling that may lead to a mature access or end in failure. Recent hemodynamic simulations [3, 4] have computed very high viscous wall shear stresses within dialysis access fistulae; Stresses >15 Pa have been reported. These are much higher than what is typically considered normal or homeostatic (i.e. ≈ 1–1.5 Pa). The abnormal stresses in the fistulae have been hypothesized to cause pathological venous remodeling (i.e. intimal hyperplasia) which causes stenoses and threatens fistula patency. Given the high failure rate of dialysis access sites (up to 50% require surgical revision within one year), understanding the dynamics of blood flow within the fistula is a necessary step in understanding remodeling, and ultimately, in improving clinical outcomes.

Optics Communications, Jul 1, 2016

A camera-based imaging system was previously developed for mapping venous blood oxygenation in hu... more A camera-based imaging system was previously developed for mapping venous blood oxygenation in human skin. However, several limitations were realized in later applications, which could lead to either significant bias in the estimated oxygen saturation value or poor spatial resolution in the map of the oxygen saturation. To overcome these issues, an upgraded system was developed using improved modeling and image processing algorithms. In the modeling, Monte Carlo (MC) simulation was used to verify the effectiveness of the ratio-to-ratio method for semi-infinite and two-layer skin models, and then the relationship between the venous oxygen saturation and the ratio-to-ratio was determined. The improved image processing algorithms included surface curvature correction and motion compensation. The curvature correction is necessary when the imaged skin surface is uneven. The motion compensation is critical for the imaging system because surface motion is inevitable when the venous volume alteration is induced by cuff inflation. In addition to the modeling and image processing algorithms in the upgraded system, a ring light guide was used to achieve perpendicular and uniform incidence of light. Crosspolarization detection was also adopted to suppress surface specular reflection. The upgraded system was applied to mapping of venous oxygen saturation in the palm, opisthenar and forearm of human subjects. The spatial resolution of the oxygenation map achieved is much better than that of the original system. In addition, the mean values of the venous oxygen saturation for the three locations were verified with a commercial near-infrared spectroscopy system and were consistent with previously published data.

Abscesses are walled-off collections of infected fluids most often treated with percutaneous drai... more Abscesses are walled-off collections of infected fluids most often treated with percutaneous drains placed under CT guidance. Complications such as clogged drains or secondary infections require rehospitalization and wound management. Histotripsy treatment has the potential to eliminate the need for long term catheterization and antibiotics. The progression of abscess development has yet to be fully described. The objective of this study was to use the latest advances in non-contrast ultrasound technologies to characterize abscess development in a porcine animal model. Intramuscular or subcutaneous injections of bacteria plus dextran particles as an irritant led to identifiable abscesses over a 2- to 3-week period. Ultrasound imaging was performed at least weekly, in some cases with a 3D tracking device that provided quantifiable size and shape measurements. Abscess progression was also measured with a plane-wave Doppler mode providing increased sensitivity to low-velocity flows, while abscess stiffness was quantified using shear wave elastography. Most of the mature abscesses were characterized by a rounded core of varying echogenicity surrounded by a hypoechoic capsule that was highly vascularized on Doppler imaging. A treatable abscess was defined by its hypervascular rim and avascular core. Stiffness varied within the abscess but generally decreased over time. Abscess echogenicity, shape, stiffness and vascularity potentially provide features to identify lesions suitable for treatment.

Abscesses are walled-off collections of infected fluids containing pus and bacteria. They are oft... more Abscesses are walled-off collections of infected fluids containing pus and bacteria. They are often treated with percutaneous drainage in which a drainage catheter may be sutured in place for up to several weeks. Complications such as clogged drains or secondary infections require rehospitalization and wound management. Bacteria are susceptible to mechanical damage, and thus we hypothesize that histotripsy may be a potential new paradigm for treating abscesses noninvasively, without the need for long term catheterization and antibiotics. We developed a porcine animal model that recapitulates some of the features of human abscesses (including size and loculations). Boiling and cavitation histotripsy treatments were applied to subcutaneous and intramuscular abscesses in this porcine model. Ultrasound imaging was used to evaluate abscess maturity, for treatment monitoring and assessment of post-treatment outcomes. Disinfection was quantified by counting bacteria colonies from samples aspirated before and after treatment. Histopathological evaluation of the abscesses was performed to identify changes resulting from histotripsy treatment and potential collateral damage. The results of this pilot study suggest focused ultrasound may lead to a technology for in situ treatment of acoustically accessible abscesses.

Journal of the Acoustical Society of America, May 1, 2022

Phase aberration induced by soft tissue inhomogeneities often complicates high-intensity focused ... more Phase aberration induced by soft tissue inhomogeneities often complicates high-intensity focused ultrasound (HIFU) therapies by distorting the field and, previously, we designed and fabricated a bilayer gel phantom to reproducibly mimic that effect. A surface pattern containing size scales relevant to inhomogeneities of a porcine body wall was introduced between gel materials with fat- and muscle-like acoustic properties—ballistic and polyvinyl alcohol gels. Here, the phantom design was refined to achieve relevant values of ultrasound absorption and scattering and make it more robust, facilitating frequent handling and use in various experimental arrangements. The fidelity of the interfacial surface of the fabricated phantom to the design was confirmed by three-dimensional ultrasound imaging. The HIFU field distortions—displacement of the focus, enlargement of the focal region, and reduction of focal pressure—produced by the phantom were characterized using hydrophone measurements with a 1.5 MHz 256-element HIFU array and found to be similar to those induced by an ex vivo porcine body wall. A phase correction approach was used to mitigate the aberration effect on nonlinear focal waveforms and enable boiling histotripsy treatments through the phantom or body wall. The refined phantom represents a practical tool to explore HIFU therapy systems capabilities.

Research Square (Research Square), Sep 30, 2022

Background: Upper urinary tract stones are increasingly prevalent in pet cats and are di cult to ... more Background: Upper urinary tract stones are increasingly prevalent in pet cats and are di cult to manage. Surgical procedures to address obstructing ureteroliths have short-and long-term complications, and medical therapies (e.g. uid diuresis and smooth muscle relaxants) are infrequently effective. Burst wave lithotripsy is a non-invasive, ultrasound-guided, handheld focused ultrasound technology to disintegrate urinary stones, which is now undergoing human clinical trials in awake unanesthetized subjects. Results: In this study, we designed and performed in vitro testing of a modi ed burst wave lithotripsy system to noninvasively fragment stones in cats. The design accounted for differences in anatomic scale, acoustic window, skin-to-stone depth, and stone size. Prototypes were fabricated and tested in a benchtop model using 35 natural calcium oxalate monohydrate stones from cats. In an initial experiment, burst wave lithotripsy was performed using peak ultrasound pressures of 7.3 (n = 10), 8.0 (n = 5), or 8.9 MPa (n =10) for up to 30 minutes. Fourteen of 25 stones fragmented to <1 mm within the 30 minutes. In a second experiment, burst wave lithotripsy was performed using a second transducer and peak ultrasound pressure of 8.0 MPa (n = 10) for up to 50 minutes. In the second experiment, 9 of 10 stones fragmented to <1 mm within the 50 minutes. Across both experiments, an average of 73-97% of stone mass could be reduced to fragments < 1 mm. A third experiment found negligible injury with in vivo exposure of kidneys and ureters in a porcine animal model. Conclusions: These data support further evaluation of burst wave lithotripsy as a noninvasive intervention for obstructing ureteroliths in cats.

Journal of the Acoustical Society of America, Oct 1, 2019

Abscesses are infected walled-off liquid collections of pus and bacteria. They can affect any par... more Abscesses are infected walled-off liquid collections of pus and bacteria. They can affect any part of the body. Current treatment is typically limited to antibiotics, catheter drainage and hospitalization. Although bacteria can develop drug resistance, they are susceptible to mechanical damage from cavitation, as demonstrated in our prior in vitro work [Brayman et al., UMB 43, 1476–1485 (2017); Brayman et al., UMB 44, 1996–2008 (2018)]. Histotripsy is a pulsed focused ultrasound regime that generates localized cavitation and represents a potential new noninvasive treatment modality. Here, we present preliminary reports of inactivation of bacteria in a newly developed porcine abscess model. In this model, multiple large (2–4 cm) multiloculated bimicrobial abscesses can be formed at distinct sites in the same animal. The abscesses satisfy the true definition of an abscess and are formed within a relatively short period (2–4 weeks). The model was developed toward testing new abscess treatment technologies. We will describe the animal model, and preliminary results of histotripsy treatments in which liquefaction of the viscous pus contents and up to 5-fold reduction in bacteria viability were achieved. Funded in part by NIH NIBIB #R01EB019365 and R01GM122859.

Ultrasound in Medicine and Biology, Jul 1, 2021

Abscesses are walled-off collections of infected fluids that often develop as complications in th... more Abscesses are walled-off collections of infected fluids that often develop as complications in the setting of surgery and trauma. Treatment is usually limited to percutaneous catheterization with a course of antibiotics. As an alternative to current treatment strategies, a histotripsy approach was developed and tested in a novel porcine animal model. The goal of the current work is to use advanced ultrasound imaging modes to extract sonographic features associated with the progression of abscess development in a porcine model. Intramuscular or subcutaneous injections of a bimicrobial bacteria mixture plus dextran particles as an irritant led to identifiable abscesses over a 2- to 3-week period. Selected abscesses were imaged at least weekly with B-mode, 3D B-mode, shear-wave elastography (SWE) and plane-wave Doppler imaging. Mature abscesses were characterized by a well-defined core of varying echogenicity surrounded by a hypoechoic capsule that was highly vascularized on Doppler imaging. 3D imaging demonstrates the natural history of abscess morphology, with the abscess becoming less complex in shape and increasing in volume. Furthermore, SWE demonstrated variations in stiffness as phlegmon becomes abscess and then liquifies, over time. These ultrasound features potentially provide biomarkers to aid selection of treatment strategies for abscesses.

Ultrasound in Medicine & Biology, 2020

Infected abscesses are walled-off collections of pus and bacteria. They are a common sequela of c... more Infected abscesses are walled-off collections of pus and bacteria. They are a common sequela of complications in the setting of surgery, trauma, systemic infections, and other disease states. Current treatment is typically limited to antibiotics with long-term catheter drainage, or surgical wash-out when inaccessible to percutaneous drainage or unresponsive to initial care efforts. Antibiotic resistance is also a growing concern. Although bacteria can develop drug resistance, they remain susceptible to thermal and mechanical damage. In particular, short pulses of focused ultrasound (i.e., histotripsy) generate mechanical damage through localized cavitation, representing a potential new paradigm for treating abscesses non-invasively, without the need for long-term catheterization and antibiotics. In this pilot study, boiling and cavitation histotripsy treatments were applied to subcutaneous and intramuscular abscesses developed in a novel porcine model. Ultrasound imaging was used to evaluate abscess maturity, for treatment monitoring and assessment of post-treatment outcomes. Disinfection was quantified by counting bacteria colonies from samples aspirated before and after treatment. Histopathological evaluation of the abscesses was performed to identify changes resulting from histotripsy treatment and potential collateral damage. Cavitation histotripsy was more successful in reducing the bacterial load while having a smaller treatment volume compared with boiling histotripsy. The results of this pilot study suggest focused ultrasound may lead to a technology for in situ treatment of acoustically accessible abscesses.

Endovascular Aortic Repair, 2017

Physician-modified endovascular grafts (PMEGs), with fenestrations added to accommodate major bra... more Physician-modified endovascular grafts (PMEGs), with fenestrations added to accommodate major branch vessels, provide a means for endovascular treatment of juxta-renal abdominal aortic aneurysms. 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 placed over the graft, the locations of the openings are marked with a sterile 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 many more patients. This chapter summarizes the 3D printing applications to create models for preoperative planning of PMEGs.

Vascular and Endovascular Surgery, Jun 23, 2019

Objective: We developed a duplex ultrasound simulator and used it to assess accuracy of volume fl... more Objective: We developed a duplex ultrasound simulator and used it to assess accuracy of volume flow measurements in dialysis access fistula (DAF) models. Methods: The simulator consists of a mannequin, computer, and mock transducer. Each case is built from a patient's B-mode images that are used to create a 3-dimensional surface model of the DAF. Computational fluid dynamics is used to determine blood flow velocities based on model vessel geometry. The simulator displays real-time B-mode and color-flow images, and Doppler spectral waveforms are generated according to user-defined settings. Accuracy was assessed by scanning each case and measuring volume flow in the inflow artery and outflow vein for comparison with true volume flow values. Results: Four examiners made 96 volume flow measurements on four DAF models. Measured volume flow deviated from the true value by 35 + 36%. Mean absolute deviation from true volume flow was lower for arteries than veins (22 + 19%, N ¼ 48 vs. 58 + 33%, N ¼ 48, p < 0.0001). This finding is attributed to eccentricity of outflow veins which resulted in underestimating true cross-sectional area. Regression analysis indicated that error in measuring cross-sectional area was a predictor of error in volume flow measurement (b ¼ 0.948, p < 0.001). Volume flow error was reduced from 35 + 36% to 9 + 8% (p < 0.000001) by calculating vessel area as an ellipse. Conclusions: Duplex volume flow measurements are based on a circular vessel shape. DAF inflow arteries are circular, but outflow veins can be elliptical. Simulation-based analysis showed that error in measuring volume flow is mainly due to assumption of a circular vessel.

Journal of biomechanical engineering, Sep 29, 2022

The Journal of the Acoustical Society of America

Abscesses are infected walled-off collections of pus and bacteria. They can affect any part of th... more Abscesses are infected walled-off collections of pus and bacteria. They can affect any part of the body. Current treatment is typically limited to antibiotics, catheter drainage and hospitalization, or surgical wash-out. Although bacteria can develop drug resistance, they remain susceptible to thermal and mechanical damage. Histotripsy generates localized cavitation without heating and represents a potential new noninvasive treatment modality. Successful histotripsy treatments were demonstrated with gram-negative E-coli in both in vitro and in vivo studies [Brayman et al., UMB 44, 1996–2008 (2018); Matula et al., UMB 47, 603–619 (2020)]. Interestingly, preliminary data showed that boiling histotripsy was less effective than cavitation histotripsy in killing bacteria. In this talk, we will describe more in-depth studies that compare cavitation histotripsy (low number of cycles, high-pulse repetition rate) with boiling histotripsy (high number of cycles, low-pulse repetition rate) on ...

1995 IEEE Ultrasonics Symposium. Proceedings. An International Symposium

An object spinning scan method was applied to acquire high resolution in vitro ultrasound images ... more An object spinning scan method was applied to acquire high resolution in vitro ultrasound images for the purpose of studying volume interpolation and rendering. Three dimensional (3D) reconstructions were accomplished for nineteen excised porcine and canine hearts. The resulting 3D images clearly revealed the 3D features with a user developed weighted opacity based interactive volume rendering approach. The 3D calculated