Since the establishment of the American Board of Nuclear Medicine (ABNM) in 1971 and the first subspecialty certification from the ABR titled Special Competence in Nuclear Radiology in 1973, the practice of nuclear medicine (NM) has changed dramatically, with the addition of new diagnostic radiopharmaceuticals, advanced instrumentation and parenteral therapies [1,2]. Training pathways for NM underwent significant expansion in 2007 with ACGME requiring three years of training for residents and offering accelerated curricula for graduates of internal medicine (two years) or radiology (one year, akin to a fellowship) residencies [1,3]. NM has also increasingly overlapped with nuclear radiology (NR), a subspecialty fellowship program also accredited by the ACGME.
There are three traditional training pathways to NM/NR practice, and recent additions of fourth and fifth pathways offer flexibility to bring physicians into NM/NR from a variety of training backgrounds [4–7]. The first traditional training pathway is three years of ACGME-accredited NM-specific training following one year of postgraduate medical education. The second pathway involves two years of ACGME-accredited NM-specific training following two or more years of postgraduate medical education. These two pathways currently lead to eligibility only for certification through the ABNM. Maintenance of certification (MOC) for ABNM has traditionally been performed as a 10-year recertification exam, but a recent longitudinal assessment pilot, CertLink, has been developed for American Board of Medical Specialties (ABMS) member boards [4,5].
The third pathway includes completing an ACGME-accredited diagnostic radiology (DR) residency and a one-year ACGME-accredited fellowship in NR leading to certifications in DR and NR through the ABNM or ABR . Under these three pathways, there has been a decrease in the number of ACGME-accredited NM/NR programs and the number of residents/fellows from 79 programs and 173 trainees in 2007 to 58 programs and 82 trainees in 2018 (52.6% decrease) .
Two newer pathways have been added, partly to help integrate DR and NM/NR. The first new pathway was introduced by the ABR in 2010 and redesigned in 2017 and involved a new 16-month pathway to certifications in DR and NR. From 2010 to 2016, only ACGME-accredited DR programs with companion ACGME-accredited NM/NR programs were qualified to participate, restricting adoption and limiting enrollment . Starting in 2017, the DR program was no longer required to be paired with a NM/NR program. Four months are still dedicated to DR core NM/NR training, but only eight of the additional 12 months need to be solely in NM/NR, given that up to four months can be dedicated to NM/NR/molecular imaging-related training (recognizing the correlative aspects in practice). In contrast to the original pathway, this redesign allowed any sequence of the 16 months during the 48-month DR residency. The newer design allows any ACGME-accredited DR or IR program to accommodate the ABR 16-month pathway, but it has more stringent requirements than the original pathway. Positron emission tomography/computed tomography (PET/CT) and single-photon emission/computed tomography (SPECT/CT) are now mandated. Also, an increased number of therapies are required. As of December 2019, there are 47 DR or IR residency programs with 85 trainees .
The second new nontraditional pathway is a comprehensive, integrated five-year DR/NM/NR program from medical school through the National Resident Matching Program (NRMP). The curriculum includes 36 months of DR and 24 months of NR/NM. This program is currently only available at three universities . At present, these two new nontraditional pathways are recognized by the ABR, but not by the ABNM, although graduates might meet the criteria to sit for the ABNM examination. MOC for the ABR is through the OLA, which covers both DR and special competency in NR. There is no separate MOC test for NR .
It will be critical in the future to have enough trained physicians in this field to meet the demands imposed from new diagnostic and therapeutic radiopharmaceuticals. All five pathways to NM/NR practice will be necessary. NM/NR has struggled to maintain its attraction for trainees, partly as a result of some decisions that affect training pathways, including those noted previously. Although a prior attempt of having one unification certification board for NM/NR was unsuccessful, greater collaboration of the ABNM and ABR will be vital for the future of this field. Approximately half of ABNM diplomates from 2001 to 2016 were also certified in DR by the ABR . Steps to rectify this divide have included the ABNM’s recent encouragement of dual certification in NM and DR  to improve trainees’ employment options and greater collaboration between NM and radiology professional societies, notably the Society of Nuclear Medicine and Molecular Imaging (SNMMI) and the ACR .