Leadership & Physicians

Driving our mission to return patients to lives of productivity and meaning are our leadership team, physicians, and clinicians. The entire Nexus Health Systems family is committed to mending minds and helping our patients and their families during the recovery process.

Erin Cassidy, MSN, MBA


Erin Cassidy joined Nexus Health Systems in 2008 and is currently the President. Prior to assuming her current role, she held various roles at Nexus Specialty Hospital including CEO and Administrator, Operations Specialist, and Assistant Administrator. She began her career at Nexus as a Marketing Liaison. Prior to joining Nexus, Ms. Cassidy held several leadership positions in medical doctor practice management in Sydney, Australia.

Ms. Cassidy holds a Bachelor of Arts in Sociology and Anthropology from Smith College and a Certificate in Culture Health Sciences from the Five College Consortium. In addition, she holds a Masters in Nursing from the University of Sydney, and a MBA with a concentration in Health Care Management from Rice University.

John Cassidy, MD

Founder, Chief Executive Officer, Chief Medical Officer

Dr. John W. Cassidy is certified by the American Board of Psychiatry and Neurology and has over 30 years of experience in clinical neuroscience and neurobehavioral rehabilitation programs. Currently operating as CEO and Chief Medical Officer of Nexus Health Systems – which he founded in 1992 – Dr. Cassidy was previously the Psychiatrist in Charge and Co-Founder of the Neuropsychiatry Program at McLean Hospital; Chief Medical Officer and Founder of the Neurobehavioral Institute of Houston; Director and Founder of the Neuropsychiatry Subspecialty Services of Del Oro Rehabilitation Hospital; and Medical Director of Neurobehavioral Programs at Cypress Creek Hospital.

Devoting his career to improving the understanding and treatment of individuals with acquired and traumatic brain injuries, Dr. Cassidy continues to help patients return to productive and meaningful lives through a neurospecialty continuum of care. His comprehensive rehabilitative approach delivers more than traditional therapies, addressing a person’s interpersonal, behavioral, cognitive, physical, and emotional challenges to ensure a more successful rehabilitation journey and clinical outcome.

Dr. Cassidy received his Bachelor of the Arts from Hiram College and Doctor of Medicine from the University of Cincinnati College of Medicine. In addition, he received his post-graduate training at Harvard Medical School. Dr. Cassidy has spoken nationally and internationally about the sequela and management of severe traumatic brain injury and authored three books and a number of papers, book chapters, and editorials.

Joel Talley

Chief Operations Officer

Propelling Nexus’ vision, Joel Talley works directly with facility administration to create and communicate facility strategy. He oversees new program development and ensures alignment with corporate goals. Mr. Talley joined the Nexus team in 2012 as a member of the Finance Department. Prior to this latest promotion, he was VP of Business Development. Before his tenure at Nexus, Mr. Talley accumulated nearly ten years in the finance and healthcare industries. Between his sales and finance experience, Mr. Talley looks forward to driving growth and ensuring all facilities run efficiently.

Kim Fields, MBA, CPA

Chief Financial Officer

As the head of the finance department, Kim Fields oversees the accounting and purchasing divisions, manages internal and external financial reporting and cost containment, and develops performance measures that support Nexus’ strategic direction. Mrs. Fields has been with Nexus for nearly ten years, and has worked exclusively for Nexus’ finance department for the last five. Prior to her time with Nexus, she was a Senior Auditor at Deloitte and was a Financial Analyst for an Austin-based healthcare system. Mrs. Field’s extensive background in finance, coupled with her existing knowledge of Nexus Health Systems, proves to be invaluable.

Ann De la Rosa, RN, BSN, CRRN

VP of Complex Care

Ann De la Rosa graduated from UT Health Science Center in Houston, Texas in 1990 with a Bachelor’s of Science in Nursing, and has been a practicing nurse for 26 years. In 2011, she received certification as a Rehabilitation Nurse. Her tenure includes time as a SICU/PACU staff nurse responsible for patient care and clinical liaison responsible for community outreach and education for case managers and physicians.

Mrs. De la Rosa has been with Nexus Health Systems for over 20 years, and has been in a marketing and clinical liaison role for most of that time. She is currently based out of the Nexus Health Systems corporate office as the VP of Complex Care and assists all facilities and clinical teams. She is responsible for national outreach, education, and patient evaluations. Mrs. De La Rosa also collaborates with insurance companies, worker’s compensation, and the military to provide solutions for complex cases.

Kevin McAndrews, MHR

VP of Human Resources

Kevin McAndrews brings a depth of HR management expertise with over 20 years of experience in the bio-instrumentation and healthcare industry. The past 15 years, Mr. McAndrews held executive leadership roles within the private, private equity, and publicly traded organizations. He joined Nexus Health Systems in June 2015 as the Vice President of Human Resources. In his previous roles Mr. McAndrews oversaw all national and international human resources offices, with offices and HR Staff in over 10 countries. Additionally, under Mr. McAndrews leadership, his past companies have been recognized and received the Wall Street Journal Best Places to Work, The International Spirit at Work Award, Red Cross Platinum Award, and Inc. 5000 Fastest Growing Companies.

Mr. McAndrews holds a Bachelor’s Degree in Sociology & Psychology from Loyola Marymount University in Los Angeles and holds a Master of Science in Human Resources from Golden Gate University in San Francisco. He is a native of Los Angeles and a full-time resident of Houston since 2015.

Eric Cantrell

Eric Cantrell

VP of Business Development

Eric Cantrell

Eric Cantrell currently serves as the Vice President of Development here at Nexus Health Systems. In his role he is charged with finding and developing new facilities and revenue streams for Nexus. Mr. Cantrell looks for markets that need our services, builds relationships in the markets to understand volume, cost, and possible locations, and formulates detailed proformas. He also manages build out and operational startup of facilities throughout opening.  Mr. Cantrell comes to Nexus with over 25 years of experience in healthcare administration where he has held several roles including Vice President and Chief Executive Officer. During his free time Mr. Cantrell enjoys spending time with his family, and a variety of recreational activities that include hunting, fishing, and sports.

His educational background includes B.S. in Healthcare Administration, with a minor in Finance from Southwestern Oklahoma State University.

Mary Harbeson, BSN, MS

VP of Pediatric Services

Mary Harbeson joined Nexus Health Systems in 2018 with over 30 years of experience in the healthcare industry. As VP of Pediatric Services in Houston, she oversees all aspects of operations, patient care and satisfaction, clinical staff, and medical decisions.

As an RN, Ms. Harbeson has held positions in various leadership roles including VP Clinical Operations, Chief Clinical Officer, and CEO. She is a focused and resourceful executive with a solid background in advancing quality patient care through strategic planning, program development, and physician recruitment. She has advanced expertise in designing and leading hospital construction from the ground up, as well as expanding market share and controlling costs. Ms. Harbeson also has a notable history of recognition for quality and safety, in addition to improving customer perception of care.

Ms. Harbeson holds a Bachelor of Science in Nursing from UTMB Galveston and a Master of Science – Nursing and Healthcare Administration from Texas Women’s University.

Yobi Kasper

VP of IT

Yobi Kasper serves as the Vice President of Information Technology.  He has 20+ years of healthcare accomplishments in aligning technology with excellence in patient care.  Mr. Kasper’s role is to provide Nexus Health Systems with a technology vision that supports business continuity and the corporate mission, utilizing proven industry standards and best practices in healthcare technologies.  He is charged with developing, implementing, optimizing, and supporting all traditional IT platforms and healthcare systems across the enterprise. Before joining Nexus, Mr. Kasper held several leadership positions with various multi-site healthcare systems.  During his free time, he enjoys traveling with his wife and various recreational activities like hunting, mountain bike riding, PC gaming, and downhill skiing.

Vanessa Blaze, MBA

Corporate Director of Human Resources

Vanessa Blaze joined Nexus Health Systems in 2014 as part of the Support Services Human Resources team, supporting frontline heroes through oversight of all things HR. Vanessa holds a Master of Business Administration with a minor in Human Resource Management. She has 20 years of experience in the human resources field, working in a variety of HR roles in oil & gas, pharmaceutical, and retail industries. She enjoys cooking for her family, watching documentaries, and reading in free time.

Bijoy Varghese, MBA

Director of Network Management

Bijoy Varghese comes to Nexus with over 10 years in the healthcare field. With extensive experience in practice management, provider consulting, and practice start-ups, he has been able to develop stable structures for the in-house provider group. With current oversight of patient specific contracts and payor contracts, Bijoy aims to bring clinical understanding and alignment for the special population at Nexus Health System.

With a focus on positive leadership, and a deep desire to raise people’s internal capacity, Bijoy focuses on challenging Nexus leadership to think outside the box while maintaining healthy relationships with all payor partners.

He holds a BS in Healthcare Administration from University of Illinois and a MBA from Texas A&M University.

Anita Marban

Corporate Director of Clinical Operations

Anita has a wealth of experience as a Clinical Leader, including past positions as Director/Chief Nursing Officer at Houston Methodist, HealthSouth, and Memorial Hermann Health Systems. She also held Director positions at the National Institutes of Health in Bethesda, Maryland. Anita obtained her Bachelor of Science in Nursing from the University of Florida and her Master of Health Administration from the University of Maryland. She advances clinic care and improves outcomes by working with all facility leadership as a resource for best practices, clinical operations, accreditations, quality, and risk management. Her role is crucial in helping Nexus meet and exceed our clinical goals and outcomes.

Tiffani Todd BA, MSN, RN, CMRN

Corporate Director of Compliance and Quality

Tiffani began her nursing career in Neonatal ICU and has spent the past 18 years excelling in Quality, Risk Management, and Compliance roles. Her experience ranges from VP Quality at one of Houston’s largest Federally Qualified Health Centers, to Director of Compliance at one of Houston’s Level I trauma centers.  She received her Bachelor of Arts with a Pre-law emphasis from University of Central Oklahoma.  She went on to complete a Bachelor of Science in Nursing and Master of Science in Nursing from University of Texas Health Science Center Houston School of Nursing.  She received the JP McGovern Award of Excellence from the University of Texas for her research poster project.  She has also received recognition for her QI projects and Risk Management experience, including being an approved provider of nursing education entitled Legal Aspects of Nursing Documentation through the Louisiana State Nurses Association.   Tiffani originally joined Nexus in 2011 as Director of Quality for Nexus Children’s Hospital.  She rejoins Nexus executive team as the Corporate Director of Compliance & Quality.  In her spare time, Tiffani enjoys gardening, Crossfit with her husband, and time with her Australian Shepherds.

Justin Sanderson

Chief Executive Officer, Nexus Neurorecovery Center – San Antonio

Justin Sanderson is a passionate leader, native Texan, a former high school football coach, and Licensed Professional Counselor specializing in trauma treatment. He is trained in Eye Movement Desensitization and Reprocessing, Applied Suicide Intervention Skills. He successfully led the daily staff and clinical operations of recovery and treatment centers in Texas and Colorado before joining Nexus Neurorecovery Center.

Mr. Sanderson earned a dual undergraduate degree in English and Psychology from the University of Missouri. He went on to earn his Master’s in Counseling from Webster University, becoming the School Support and Education Coordinator for a non-profit where he oversaw the development of more than 30 grief support groups in the Greater St. Louis Area. His supervisory and leadership roles grew as the Assistant Clinical Director with Fire Mountain Treatment Center in Estes Park, Colorado. In 2018, Mr. Sanderson returned to his home state of Texas. He became Managing Director of Innova Recovery Center, where he led the establishment and successful Accreditation from the Joint Commission at Innova Recovery Center, a residential treatment center in San Antonio, Texas.

With a strong commitment to helping individuals recover from trauma and combined love for coaching and teamwork, he brings energy and dedication to his role with Nexus.

Bill Elsesser

Chief Executive Officer, Nexus Children's Hospital - Dallas

Bill Elsesser comes to Nexus Health Systems with over 25 years of experience in the health care industry. After 18 years in progressively responsible sales and marketing roles, Mr. Elsesser developed a passion for hospital operations and administration. In recent time Bill has spent the last seven years leading Long Term Acute Care Hospital, most recently serving as the Administrator for Noland LTAC in Montgomery, Alabama. Bill currently serves as the Chief Executive Officer of our new Nexus facility, Nexus Children’s Hospital – Dallas; his primary focus is on patient outcomes along with physician and employee engagement. He enjoys spending time with his family, cooking, and a variety of outdoor recreational activities.

Bill Elsesser received a Bachelor of Business Administration from Mississippi State University.

Roger Caron

Chief Executive Officer, Nexus Children's Hospital - Houston & Nexus Children's Hospital - The Woodlands

Roger Caron began his career in health care while serving in the Navy. During his 28 years of service, he participated in multiple deployments and held various health service support roles. Most recently Mr. Caron served as the CEO of Long-Term Acute Care hospital in Pennsylvania.  Roger joined Nexus as the CEO of Nexus Children’s Hospital – Houston in August of 2022.  He is committed to building a team that provides the best possible care for our patients. Mr. Caron enjoys hiking through the Appalachian Mountain range with his wife and family.

Mr. Caron received a bachelor’s from Southern Illinois University and Master of Healthcare Administration from Baylor University.

Mike Warren

Administrator, Nexus Children’s Hospital - The Woodlands

Michael W. Warren, Sr. is the Administrator and Director of Nursing (DON).

He is a healthcare professional with 37 years of Nursing experience, which includes 12 years of executive nurse experience.
Michael joined NEXUS Children’s Hospital Woodlands in March of 2022. He is successfully leading the nursing staff in obtaining the organization’s vision, utilizing transformational leadership principles for improving the delivery of care systems to increase positive patient outcomes. He is a change agent and is dedicated to improving delivery of care systems to meet the Affordable Care Act demands for safe and quality care. He promotes and supports change through the use of teams and collaboration, evidence-based practice quality improvement, innovation, health informatics, and advanced technology. In addition, he is committed to creating an environment that supports professional growth, changing the professional nurse’s image, and creating a culture of safety for patients and nurses.

Michael is a native of Wells, Texas and received his Bachelor of Science degree in nursing from Colorado Tech University.

Journey Toward Independence

Nexus' NeuroContinuum sequence provides a range of care for those recovering from acquired or traumatic brain injuries and other complicated illnesses or diseases.
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