Joseph R. Leach

• Doctor of Medicine
• University of California, San Francisco

Background Ascending thoracic aortic aneurysms (aTAA) can lead to life-threatening dissection and rupture. Recent studies highlighted aTAA mechanical properties as relevant factors associated with progression. The aim of this study was to quantify in vivo aortic wall stretch in healthy participants and aTAA patients using displacement encoding with...

OBJECTIVES Diameter-based risk stratification for elective repair of ascending aortic aneurysm fails to prevent type A dissection in many patients. Aneurysm wall stresses may contribute to risk prediction; however, rates of wall stress change over time are poorly understood. Our objective was to examine aneurysm wall stress changes over three to fi...

This report presents the case of a 66-year-old man with acute torrential aortic insufficiency after a Ross procedure 20 years earlier, a biologic aortic valve replacement 16 years earlier, and a transcatheter valve-in-valve 4 years earlier. He underwent third-time sternotomy, revealing that the pulmonary autograft was heavily calcified and frozen t...

Objectives Current diameter-based guidelines for ascending thoracic aortic aneurysms (aTAA) do not consistently predict risk of dissection/rupture. ATAA wall stresses may enhance risk stratification independent of diameter. The relation of wall stresses and diameter indexed to height and body surface area (BSA) is unknown. Our objective was to comp...

Introduction: Current guidelines recommend ascending aortic surveillance at 6-24 month intervals regardless of sex. However, emerging evidence suggests that ascending aortic growth is faster in women than men. It is unknown whether this difference is affected by presenting aortic size. Objective: To characterize aortic growth by sex and presenting...

Background Management of asymptomatic abdominal aortic aneurysm (AAA) based on maximum aneurysm diameter and growth rate fails to preempt many ruptures. Assessment of aortic wall biomechanical properties may improve assessment of progression and rupture risk. This study aimed to assess the accuracy of AAA wall strain measured by cine magnetic reson...

Objectives: Rapid diameter growth is a criterion for ascending thoracic aortic aneurysm repair; however, there is sparse data on aneurysm elongation rate. The purpose of this study was to assess aortic elongation rates in nonsyndromic, nonsurgical aneurysms to understand length dynamics and correlate with aortic diameter over time. Methods: Pati...

Background: In ascending thoracic aortic aneurysm risk stratification, aortic area/height ratio is a reasonable alternative to maximum diameter. Biomechanically, aortic dissection may be initiated by wall stress exceeding wall strength. Our objective was to evaluate the association between aortic area/height and peak aneurysm wall stresses in rela...

Objectives: To determine if three-dimensional (3D) radiomic features of contrast-enhanced CT (CECT) images improve prediction of rapid abdominal aortic aneurysm (AAA) growth. Methods: This longitudinal cohort study retrospectively analyzed 195 consecutive patients (mean age, 72.4 years ± 9.1) with a baseline CECT and a subsequent CT or MR at lea...

Background: Abdominal aortic aneurysms (AAAs) may rupture before reaching maximum diameter (Dmax ) thresholds for repair. Aortic wall microvasculature has been associated with elastin content and rupture sites in specimens, but its relation to progression is unknown. Purpose: To investigate whether dynamic contrast-enhanced (DCE) MRI of AAA is a...

Introduction: Current diameter-based guidelines for ascending thoracic aortic aneurysms do not consistently predict risk of dissection/rupture. Aneurysm wall stresses may better predict risk but correlate weakly with diameter. Our objective was to correlate aneurysm wall stresses with indexed diameters in relation to 3-year all-cause mortality. Met...

Risk of aortic dissection in ascending thoracic aortic aneurysms is not sufficiently captured by size-based metrics. From a biomechanical perspective, dissection may be initiated when wall stress exceeds wall strength. Our objective was to assess the association between aneurysm peak wall stresses and 3-year all-cause mortality. Finite element anal...

Background Abdominal aortic aneurysm (AAA) screening programs have been active in the United States since 2005, but are not the only way AAAs are detected. AAA management and outcomes have not been investigated broadly in the context of “implicit AAA screening,” whereby radiologic examinations not intended for focused screening can identify AAAs....

Introduction: Natural history studies of ascending thoracic aortic aneurysm (aTAA) identified maximum diameter as a predictor of aortic dissection, informing guidelines for prophylactic surgery. Studies have since challenged the biomechanical basis of diameter-based risk assessment. Indices of diameter with measures of body size were proposed to ac...

Objective: Historic studies of nonsyndromic ascending thoracic aortic aneurysms (aTAAs) suggested that aTAA growth rate was approximately 0.6mm/year, but data were limited, with relatively few studies using computed tomography (CT) imaging. Our objective was to reevaluate the annual growth rate of nonsyndromic ATAAs that do not meet criteria for su...

Accurate and reproducible measurement of abdominal aortic aneurysm (AAA) size is an essential component of patient management, and most reliably performed at CT using a multiplanar reformat (MPR) strategy. This approach is not universal, however. This study aims to characterize the measurement error present in routine clinical assessment of AAAs an...

Background Non-contrast 3D black blood MRI is a promising tool for abdominal aortic aneurysm (AAA) surveillance, permitting accurate aneurysm diameter measurements needed for patient management. Purpose To evaluate whether automated AAA volume and diameter measurements obtained from computer-aided segmentation of non-contrast 3D black blood MRI ar...

Background: Historic studies of nonsyndromic ascending thoracic aortic aneurysms (aTAAs) reported that the typical aTAA growth rate was approximately 0.6 mm/year, but data were limited due to relatively few studies using computed tomography (CT) imaging. Our purpose was to reevaluate the annual growth rate of nonsyndromic aTAAs that do not meet cr...

We present the case of a 60-year-old man with a complex medical history, presenting to the hospital with generalized weakness and found to be markedly hyperglycemic. Early in the patient’s hospital course, he developed abdominal pain and was found to have a small bowel obstruction secondary to intraluminal migrated surgical mesh entrapped in the te...

Introduction: Guidelines for ascending thoracic aortic aneurysm (ATAA) repair use ATAA diameter, with repair recommended at ≥5.5cm, but ATAA biomechanics may better predict acute type A dissection (ATAD) risk. However, little is known regarding changes in wall stresses among clinically followed patients with <5.5cm ATAA over time. This information...

Purpose Idiopathic Intracranial Hypertension (IIH) is a pathologic elevation of the intracranial pressure (ICP) with normal CSF composition which mostly affects younger women who are obese. IIH is most commonly presented along with focal stenosis of venous transverse sinus (TS). Venous sinus stenting (VSS) is an effective procedure that can resolve...

Background: The factors influencing common iliac artery aneurysm (CIA) growth are not fully known. Intraluminal thrombus (ILT) has been studied as a marker of growth in abdominal aortic aneurysms (AAA), but its role in CIAs is unknown. This study aims to examine the factors associated with growth of CIAs coexistent with AAA using serial cross-sect...

Background Intraluminal thrombus (ILT) within abdominal aortic aneurysms (AAAs) may be a potential marker for subsequent aneurysm growth. Purpose To investigate the role of ILT in AAA progression as assessed with CT and MRI. Materials and Methods This was a retrospective study, with patient data included from January 2004 to December 2018 at a Vete...

Hypothesis: We hypothesize patient-specific flow models to be an adequate in vitro surrogate to allow for characterization of pulsatile tinnitus (PT) that affects three to five million Americans. Background: PT, rhythmic sounds without an extracorporeal source that patients appreciate, can be caused by aberrant blood flow in large cerebral veins...

Introduction Pulsatile tinnitus (PT) can be caused by aberrant blood flow in large cerebral veins near the cochlea. In our previous works we evaluated flow patterns in patient’s cerebral venous sinuses to try and identify patterns of flow unique to symptomatic PT patients. However, the exact mechanism of sound production remains unclear. In order t...

Intraluminal thrombus (ILT) is present in the majority of abdominal aortic aneurysms (AAA) of a size warranting consideration for surgical or endovascular intervention. The rupture risk of AAAs is thought to be related to the balance of vessel wall strength and the mechanical stress caused by systemic blood pressure. Previous finite element analyse...

Background and purpose: Idiopathic intracranial hypertension is commonly associated with transverse sinus stenosis, a venous cause of pulsatile tinnitus. In patients with idiopathic intracranial hypertension, CSF drainage via lumbar puncture decreases intracranial pressure, which relieves the stenosis, and may provide at least temporary cessation...

Biomechanical analyses can be used to better understand the rupture risk of abdominal aortic aneurysms (AAAs) on a patient-specific basis using vascular geometries obtained from medical imaging. Methodologies of varying complexity are used to estimate the unloaded state of the imaged vessel to provide a reference configuration for finite element si...

Background and purpose: Case reports demonstrate that coiling of a sigmoid sinus diverticulum can treat pulsatile tinnitus. We hypothesized that MR imaging 4D flow and computational fluid dynamics would reveal distinct blood flow patterns in the venous outflow tract in these patients. Materials and methods: Patients with pulsatile tinnitus of su...

Objectives Management of abdominal aortic aneurysms (AAAs) is based on diameter. CT angiography (CTA) is commonly used, but requires radiation and iodinated contrast. Non-contrast MRI is an appealing alternative that may allow better characterization of intraluminal thrombus (ILT). This study aims to 1) validate non-contrast MRI for measuring AAA d...

We present the case of a 67-year-old man with concomitant stroke and pulmonary embolism 1 day after radiofrequency catheter ablation for refractory atrial tachycardia. A chest computed tomographic angiogram revealed "thrombus-in-transit" across a patent foramen ovale, confirming the diagnosis of paradoxical embolism. Paradoxical embolism is a rare...

Ischemic mitral regurgitation is associated with substantial risk of death. We sought to: (1) detail significant recent improvements to the Dassault Systèmes human cardiac function simulator (HCFS); (2) use the HCFS to simulate normal cardiac function as well as pathologic function in the setting of posterior left ventricular (LV) papillary muscle...

In cases where surgeons consider different interventional options for flow alterations in the setting of pathological basilar artery hemodynamics, a virtual model demonstrating the flow fields resulting from each of these options can assist in making clinical decisions. In this study, image-based computational fluid dynamics (CFD) models were used...

Giant intracranial aneurysms present a grave danger of hemorrhage, cerebral compression, and thromboembolism. Fusiform aneurysms present a particular challenge for interventional treatment since these lesions cannot be completely removed from the circulation by clipping or coiling without sacrificing flow to the distal vasculature. In some cases, t...

In hematologic diseases, such as sickle cell disease (SCD) and hemolytic uremic syndrome (HUS), pathological biophysical interactions among blood cells, endothelial cells, and soluble factors lead to microvascular occlusion and thrombosis. Here, we report an in vitro "endothelialized" microfluidic microvasculature model that recapitulates and integ...

We investigate the quantum fluctuations of a single atom in a weakly driven cavity where the center-of-mass motion of the atom is quantized in one dimension. We present analytic results for the second-order intensity correlation function g(2)(τ) and the intensity-field correlation function hθ(τ) for both transmitted and fluorescent light for weak d...

Thrombus formation in intracranial aneurysms, while sometimes stabilizing lesion growth, can present additional risk of thrombo-embolism. The role of hemodynamics in the progression of aneurysmal disease can be elucidated by patient-specific computational modeling. In our previous work, patient-specific computational fluid dynamics (CFD) models wer...

Atherosclerosis at the carotid bifurcation is a major risk factor for stroke. As mechanical forces may impact lesion stability, finite element studies have been conducted on models of diseased vessels to elucidate the effects of lesion characteristics on the stresses within plaque materials. It is hoped that patient-specific biomechanical analyses...

Many of the world’s leading causes of death involve pathology of the vasculature, both arterial and venous. In addition to the biochemical and genetic factors governing vascular health and disease, mechanics strongly modulates the form and function of the vessel wall. Biomechanical analysis is being increasingly used to not only elucidate key disea...

We investigate the quantum fluctuations of a single atom in a weakly driven cavity, where the center of mass motion of the atom is quantized in one dimension. We present analytic results for the second order intensity correlation function $g^{(2)}(\tau)$ and the intensity-field correlation function $h_{\theta}(\tau)$, for both transmitted and fluor...

Patient-specific biomechanical modeling of atherosclerotic arteries has the potential to aid clinicians in characterizing lesions and determining optimal treatment plans. To attain high levels of accuracy, recent models use medical imaging data to determine plaque component boundaries in three dimensions, and fluid-structure interaction is used to...

Atherosclerosis in the carotid bifurcation is a highly variable disease that, in its stable form, can cause a dangerous reduction of blood flow to the brain. If the plaque ruptures or ulcerates, the patient is likely to experience a thrombotic or embolic stroke. Stroke is the 3rd leading cause of death in the western world, and approximately 10–15%...

Estimation of the stability of fusiform aneurysms of the basilar artery requires precise monitoring of the luminal and outer wall volumes. In this report we describe the use of MR imaging and 3D postprocessing methods to study the evolution of those aneurysms. Nine patients with fusiform basilar artery aneurysms underwent MR imaging studies coverin...

We consider intensity-field correlation functions for a two-level atom in a degenerate optical parametric oscillator (OPO), which would result from a conditioned homodyne measurement. Analytic results are obtained in the limit of weak driving fields using quantum trajectory methods for both the transmitted and fluorescent fields. This system is uni...

We investigate the quantum fluctuations of a single atom in a weakly driven cavity, where the center of mass motion of the atom is quantized in one dimension. We present analytic results for the second order intensity correlation function g((2))(tau) and the intensity-field correlation function h(theta)(tau), for transmitted light in the weak drivi...

We investigate intensity cross-correlation functions for two cavity QED systems. These are a driven optical cavity containing a single two-level atom interacting with a single mode of the cavity field with quantized centre of mass motion, and a two-level atom in an optical parametric oscillator. We find analytic results in the weak driving field li...

We investigate the quantum fluctuations of a single atom in a weakly driven cavity, where the center of mass motion of the atom is quantized in one dimension

We consider two-level atoms inside a small driven optical cavity, a typical cavity QED setup. In this case however, we include an external potential due to an optical lattice. The use of atomic beams leads to doppler broadening, atoms experiencing a time dependent coupling to the cavity field, and atom number fluctuations. The inclusion of the latt...

We consider two systems in the weak driving field limit. The first is an optical parametric oscillator, the transmitted field of which is highly bunched. We discuss a conditioned measurement of the second order intensity correlation function that yields antibunching. The second system we consider is a single two level atom inside a weakly driven ca...

Title from first page of PDF document. Document formatted into pages; contains iv, 198 p. Thesis (M.S.)--Miami University, Dept. of Physics, 2003. Includes bibliographical references (p. 188-189). Mode of access: World Wide Web. System requirements: Adobe Acrobat Reader.