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Our Leaders

Our executive leadership strives to continually achieve our aim of providing better health care - and a better health care system - to every patient we serve.

Hal Teitelbaum
Hal Teitelbaum MD, JD, MBA

Managing Partner & CEO

Dr. Hal Teitelbaum is the Founder, Managing Partner and Chief Executive Officer of Crystal Run Healthcare—a premier multi-specialty group medical practice. Dr. Teitelbaum completed his training in Internal Medicine at New York Hospital-Cornell Medical Center, and in Medical Oncology and Hematology at Memorial Sloan-Kettering Cancer Center. After beginning his career in full-time academic practice, Dr. Teitelbaum established a solo practice in Orange County, New York, in 1982. He established Crystal Run Healthcare in 1996. Dr. Teitelbaum is a 1998 Honors graduate of Columbia Business School, where he earned his MBA. He earned his Juris Doctor degree from Columbia Law School, Class of 2012, where he was a Harlan Fiske Stone Scholar.

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Gregory A. Spencer MD, FACP

Chief Medical Officer & Chief Medical Information Officer

Dr. Gregory A. Spencer is the Chief Medical Officer and Chief Medical Information Officer at Crystal Run Healthcare. Dr. Spencer graduated from the Medical College of Wisconsin (Marquette University) Medical School and completed his residency in Internal Medicine while in the US Air Force at Wilford Hall USAF Medical Center in San Antonio, TX. Dr. Spencer joined Crystal Run as an internist in 1996 and was appointed as Chief Medical Officer and Chief Clinical Information Officer in 2008. Dr. Spencer is board certified in Internal Medicine and is a Fellow of the American College of Physicians.

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Mary DeFreitas BBA, MPS

Chief Human Resources Officer

Mary DeFreitas is the Chief Human Resources Officer at Crystal Run Healthcare. Ms. DeFreitas is a graduate of Pace University in Pleasantville, NY, where she earned her Bachelor of Business Administration in Marketing. Ms. DeFreitas holds her Masters of Professional Studies in Humanistic Education from SUNY New Paltz. Ms. DeFreitas is also a graduate of Leadership Orange, class of 2002.

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Gaynor Rosenstein MS, CMPE

Chief Clinical Operations Officer

Gaynor Rosenstein is the Chief Clinical Operations Officer at Crystal Run Healthcare, a position she has held since 2008. Ms. Rosenstein holds a Bachelor of Arts from Crewe and Alsager College in Crewe, UK, and her General Nursing (RN) degree from Blackburn School of Nursing, Blackburn, UK. Ms. Rosenstein earned her Master of Science in Healthcare Administration from New School University in New York, NY and is a Licensed Nursing Home Administrator by the State of New York. In addition, Ms. Rosenstein is a Certified Six Sigma Black Belt and Certified Medical Practice Executive as well as a graduate of Leadership Orange, class of 2011.

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Douglas Sansted JD

Chief Strategy Officer, Chief Legal Officer

Douglas Sansted is the Chief Strategy Officer and Chief Legal Officer at Crystal Run Healthcare. Mr. Sansted holds a Bachelor of Science degree in Nursing from the City University of New York Hunter College where he was a summa cum laude graduate and class valedictorian. Mr. Sansted earned his Juris Doctor degree from New York University School of Law in New York, NY. Mr. Sansted is a member of the New York State Bar Association and is a member of the American Health Lawyers Association.

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Francis H. Cheung

Chief Information Officer

Francis H. Cheung is the Chief Information Officer at Crystal Run Healthcare. Mr. Cheung is a graduate of University of Wisconsin, Madison in Madison, Wisconsin where he earned his Bachelor and Master of Science in Industrial Engineering. Mr. Cheung is Lean Production Certified and his professional affiliations include membership to the College of Healthcare Information Management Executives (CHIME) and the Healthcare Information and Management Systems Society (HIMSS).

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Scott Hines MD

Chief Quality Officer, Medical Director

Scott Hines, MD, is Crystal Run Healthcare’s Chief Quality Officer, Medical Director, and physician leader for Crystal Run Healthcare’s medical specialties division. Dr. Hines is board certified in Internal Medicine, Endocrinology, Diabetes and Metabolism. Dr. Hines earned his Medical Degree from the Wake Forest University in Winston-Salem, NC, and completed his residency in Internal Medicine at the Dartmouth-Hitchcock Medical Center in Lebanon, NH. Dr. Hines completed his Endocrinology Fellowship at the University of Maryland Medical Center in Baltimore, MD. In 2006, Dr. Hines joined Crystal Run Healthcare. 

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Jonathan Nasser MD


Jonathan Nasser, MD is the President of Crystal Run Healthcare. Dr. Nasser is board certified in Pediatrics and Internal Medicine. Dr. Nasser earned his Medical Degree from the University of Virginia in Charlottesville, VA, and completed his residency at the University of Rochester Medical Center in Rochester, NY. In 2002, Dr. Nasser joined Crystal Run Healthcare. As President, Dr. Nasser oversees the executive team and works directly with Crystal Run’s Managing Partner and CEO to ensure the successful implementation of the Practice’s strategic goals.

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Steve Zeng MBA

Chief Financial Officer

Steve Zeng is the Chief Financial Officer at Crystal Run Healthcare. Mr. Zeng is a graduate of LeMoyne College in Syracuse, NY where he earned his Bachelor of Science in Accounting. Zeng also holds a Master of Business Administration in Management from the Stern School of Business at New York University.

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