Johns Hopkins All Children's Hospital

Meet Our Radiology and Neuroradiology Team

Douglas Yim, MD Radiology

Dr. Yim is an Interventional Radiologist and the Chief of Pediatric Radiology at Johns Hopkins All Children’s. He joined the hospital staff in 2021. Most recently, he served on faculty at the University of South Dakota Sanford School of Medicine, focused on clinical education and integration of Interventional Radiology in rural medicine.
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Michael Collard, MD Radiology

Dr. Collard specializes in pediatric interventional radiology at Johns Hopkins All Children’s Hospital. He joined the medical staff in 2021. Dr. Collard earned his medical degree from the University of Missouri Kansas City School of Medicine in Kansas City, Missouri. He completed an internship in internal medicine at the University of Missouri Kansas City School of Medicine and a residency in diagnostic radiology at the University of Texas Southwestern Medical Center in Dallas. He then completed a fellowship in vascular and interventional radiology at Massachusetts General Hospital/Harvard Medical School in Boston, followed by a fellowship in pediatric radiology with an emphasis in interventional radiology at Boston Children’s Hospital/Harvard Medical School.
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Jane Cook, DO Radiology

Dr. Cook specializes in pediatric radiology with a focus on PET/CT and musculoskeletal imaging at Johns Hopkins All Children’s Hospital. She joined the hospital staff in 2019.
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Kimberly Fagen, MD Radiology

Dr. Fagen specializes in pediatric radiology at Johns Hopkins All Children’s. She joined the hospital staff in 2019. Dr. Fagen earned her medical degree from the Uniformed Services University of the Health Sciences in Bethesda, Maryland. She completed her internship at National Capital Consortium and residency in diagnostic radiology at Naval Medical Center San Diego. She completed a fellowship in pediatric radiology at Children’s National Medical Center.
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Christopher Francis, MD Radiology

Dr. Francis specializes in adult and pediatric interventional radiology. He joined the Johns Hopkins All Children’s medical staff in 2018. His clinical expertise includes performing a wide range of image guided minimally invasive procedures such as treatment of congenital vascular malformations, tumor ablation, venous thrombolysis for deep vein thrombosis (DVT), management of dialysis graft dysfunction, biopsy/drainage procedures, urinary and GI tract access procedures, nerve and facet blocks, and pediatric trauma patients. He is a member of the Society of Interventional Radiology and Society of Pediatric Interventional Radiology.
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Christopher Keup, MD Radiology

Dr. Keup specializes in pediatric radiology at Johns Hopkins All Children’s Hospital. He joined the hospital staff in 2019. Dr. Keup also serves in the U.S. Army Reserve.  He is currently attached to the Army Medical Department Personnel Management Command in Forest Park, Georgia, and is a Lieutenant Colonel in the Medical Corps. Dr. Keup earned his medical degree from the University of Missouri in Columbia, Missouri. He completed an internship in internal medicine from the University of Missouri-Kansas City in Kansas City, Missouri, followed by a residency in diagnostic radiology from the University of Missouri-Kansas City and a fellowship in pediatric radiology from Children’s Mercy Hospital in Kansas City, Missouri.
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Jennifer Kucera, MD Radiology

Dr. Kucera is a pediatric radiologist at Johns Hopkins All Children’s Hospital, specializing in ultrasound, fetal MRI and musculoskeletal radiology. She joined hospital staff in 2014. She also is an assistant professor in the Johns Hopkins University School of Medicine and the University of South Florida College of Medicine. She serves as the residency site director for the USF radiology residency program.
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Sally Mitchell, MD Radiology

Dr. Mitchell is an interventional radiologist at Johns Hopkins All Children’s. She joined the hospital staff in 2021. She was most recently director of pediatric interventional radiology and director of vascular anomalies interventional radiology at Johns Hopkins University School of Medicine in Baltimore.
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Javier Quintana, MD Radiology

Dr. Quintana is a radiologist at Johns Hopkins All Children’s Hospital. He joined hospital staff in 2010. Dr. Quintana earned his medical degree at the University of South Florida. He trained in general pediatrics at Jackson Memorial Hospital/University of Miami and completed a diagnostic radiology residency at Geisinger Medical Center in Danville, Pennsylvania. Dr. Quintana completed a pediatric radiology fellowship at Children’s Hospital of Philadelphia. He is fluent in Spanish.
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William Schaaf, MD Radiology

Dr. Schaaf is a graduate of the Drexel University College of Medicine (formerly Medical College of Pennsylvania Hahnemann School of Medicine). He completed his residency in diagnostic radiology at Eastern Virginia Medical School, Norfolk, VA, where he served as chief resident. He also completed his pediatric radiology fellowship at Cincinnati Children’s Hospital Medical Center. Dr. Schaaf is board-certified in radiology and board-admissible in pediatric radiology.
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Susan Buffington MSN, APRN, CPNP

Susan Buffington MSN, APRN, CPNP



Paul Herlan MPAS, PA-C

Paul Herlan MPAS, PA-C



Natalie Mercado MPAS, PA-C

Natalie Mercado MPAS, PA-C



Michelle Walker MSN, APRN, CPNP

Michelle Walker MSN, APRN, CPNP