Heather Greaves, CNMT, RT(CT)
Heather is a native of Redding, CA, and was certified as a nuclear medicine technologist (CNMT) in 2013 followed by certification in computed tomography (R.T. (CT)) in 2014. After working at Munroe Regional Medical Center in Ocala, FL for a year, Heather joined the NMA team in August of 2014. Heather pays her education forward through her work with Gurnick Academy and Nuclear Medicine Associates as a clinical affiliate supervising technologist.
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Ashlyn Nieves CNMT, NMTCB(CT)
Ashlyn spent 10 years in the United States Air Force prior to joining the NMA team in 2019. She spent her time in the service learning and performing multiple different radiology modalities, from X-ray to computed tomography (CT) and finally nuclear medicine. She holds a national certification in both nuclear medicine and CT through the Nuclear Medicine Technology Certification Board.
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Riki Graham
Riki has been with Nuclear Medicine Associates since Jan 2015. She has a great personality and greets patients with a friendly smile as they check-in. In addition to working at NMA, Riki is currently attending school to become a nuclear medicine technologist. She is looking forward to starting a new chapter with NMA as a nuc med tech in 2026.
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Mariah Thurber
After joining the Nuclear Medicine Associates team in 2020, Mariah quickly became an integral part of the team. Her winning smile and congenial voice greet patients in person and on the phone daily as she assists in reception as well as with other nuclear medicine procedures.
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About Our Professional Staff
Peter S. Robbins, MD
Peter S. Robbins, MD received his MD and Nuclear Medicine training at Temple University, becoming Board Certified in Nuclear Medicine in 1983 where he stayed on as Assistant Professor until relocating to Hawaii. He was the Clinical Associate Professor in Medicine and Pediatrics and directed Nuclear Medicine at Kapiolanii Medical Center for Women and Children, and served as President of the Hawaii Chapter of the Society of Nuclear Medicine. He joined NMA in 1999, and directed NMA from 2003 until he retired from full-time practice in 2022. He continues to provide radionuclide therapy at NMA and remains our Radiation Safety Officer.
Mickaila Johnston, MD
Mickaila is from Bend, Oregon and graduated from Oregon State University with an HBS in Radiation Health Physics, from the College of Engineering and the University Honors College. Afterward, he attended USUHS in Bethesda, Maryland, where he earned his MD in 2003.
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Francis Isidoro, MD
Francis Isidoro, MD is a Diplomate of the American Board of Nuclear Medicine. His background includes a degree in Nuclear Engineering and Bioengineering from the College of Engineering at the University of Illinois Urbana-Champaign, followed by an MD from the University of the East Medical Center. He completed an internship in Internal Medicine with Northeastern Ohio University College of Medicine followed by a residency in Nuclear Medicine and a fellowship in PET/CT at the University of Tennessee Medical Center – Knoxville. He received the Roentgen Resident/ Fellow Research Award for two consecutive years and has multiple publications and presentations. Francis is a staff physician and is also actively involved with cancer treatment research. Also a software developer, he has created scientific and educational applications for iOS and iPadOS, completed projects at the National Institutes of Health, and contributed to the open-source community. He enjoys skiing.
Twyla Bartel, MD
Dr. Twyla Bartel is board-certified in Nuclear Medicine and Diagnostic Radiology. She is Co-Owner of Global Advanced Imaging, PLLC (GAI). Her specific expertise is in PET/CT imaging. She is very involved in her field serving on multiple profession-related boards and committees of the SNMMI, ACNM, and ACR. She is the Past President of The American College of Nuclear Medicine. She is currently an SNMMI board member and the President of the ACNM Academic Council. She is a Fellow of the SNMMI and ACNM. She mentors many, is involved in research and publications, and is a Director on the American Board of Nuclear Medicine. She grew up in Japan for 17 years, speaks Japanese, and is a musician (vocal and instrumental).