The field of Nuclear Medicine is a rapidly evolving specialty which is based on evaluation of function of living tissue. The Department of Nuclear Medicine in Hinduja Hospital is dedicated in providing advanced diagnostic and treatment solutions to many diseases, as well as many fundamental insights into the complex workings of the human body. The scans can help detect physiological changes that often occur prior to morphological changes leading to early diagnosis of disease.
What is Nuclear Medicine and how it works
Nuclear Medicine works by examining the regional chemistry of any living tissue using radioactive agents and is used to diagnose and treat patients. Very small amounts of unsealed (open) radioactive sources are used internally through a vein or mouth or inhalation. It is separate from Radiation therapy where large amounts of radiation from sealed radioactive sources are used externally. Nuclear Medicine imaging identifies the functional changes caused by diseases.
Nuclear Medicine, Radiology and Medical Imaging
Essentially, it falls under the broad umbrella of Medical Imaging in most modern health care institutions. Morphologic or structural modalities of diagnostic imaging (the branch of Radiology) such as X-ray, Magnetic Resonance Imaging (MRI), Transmission Computed tomography (CT scan) or Ultrasonography are complemented by Nuclear medicine procedures like SPECT (Single Photon Emission Computed Tomography) or PET (Positron Emission Tomography). Anatomical abnormalities are best diagnosed by morphologic modality’s high-resolution examinations whereas Nuclear Medicine studies are optimally utilized when the information sought is primarily physiological and biochemical in nature. As a result, most of the current equipments are hybrid, capable of looking at both the structure and function through one examination (SPECT-CT or PET-CT). The diagnostic accuracy and the confidence of the reporting physician are enhanced by hybrid imaging.
The strength of Nuclear Medicine: tissue characterization
Nuclear Medicine evaluates several biological processes like metabolism, receptor expression, apoptosis and other molecular changes happening at a cellular level. Indeed, Nuclear Medicine is more often referred to as “molecular imaging” in recent times. Biological molecules which are specific to certain cells or tumors can be radiolabelled and injected to the patient to monitor specific cell functions or tumor behavior. This makes “tissue characterization” possible, which is a big step towards fulfilling the concept of “personalized medicine”, where no two patients with the same disease are treated in an identical way. For example, the current method of assessing tumor response to therapy, by measuring tumor volume or glucose metabolism, is useful but clearly inadequate and in the near future we will not only be looking at these parameters but also be able to measure other indices of tumor behaviour like cell proliferation, receptor expression or internal hypoxia and may therefore treat patients in an individually tailored and a truly personalized manner.
Over-regulation of the specialty
Yet, the specialty continues to remain over regulated, which is the biggest threat to its expansion. Mass radiation hysteria following the atomic holocaust during the second world war was craftily utilized by a group of professionals (health physicists) in the United States in the 1950’s who scared the senators to a great extent to pass a vast body of legislations that were too harsh and disproportionate to the risk involved in most diagnostic nuclear medicine procedures. The dose of radiation involved in atomic bomb survivors were extrapolated to the miniscule amount of radiation involved in diagnostic procedures to predict detriment (adverse effect), a method which is not unquestionable. Indeed, there is accumulating data that a small dose of radiation has no effect on human body and probably has some beneficial effect (radiation hormesis), stimulating the activation of repair mechanisms that protect against disease that are not activated in absence of ionizing radiation.
Is radiation harmful and how to measure it
Radiation exposure is an intangible concept, not measurable by commonly perceived yardsticks. An average nuclear medicine procedure (4-5 mSv) gives a third of the amount of exposure to individuals of what an inhabitant of the coast of Kerala is exposed to in one calendar year (14 mSv) through natural radiation from the Monazite sands and we are not aware of any increased incidence of cancer in them. This piece of information can probably put radiation exposure in some sort of a comprehensible perspective. When one out of every three individuals is likely to have cancer in their lifetime, a small increase (if at all) in the risk (incidence of 1 in 2000 or 1 in 5000) does not really make a difference.
Other legislative constraints
There has been a significant impediment to radiopharmaceutical (the radioactive chemical injected to trace a biological process) development because of heavy legislations. The process of registration of new radiopharmaceuticals, which are administered once or twice, in quantities less than a milligram with extremely rare side effects, is the same as for drugs that are given daily in doses of several hundreds of milligrams. It is not a fair bargain for the specialty!
Both diagnosis and therapy
Although most of the current nuclear medicine practice is diagnostic, there are many therapeutic uses of unsealed radioactivity. Therapy is performed with a different group of radioisotopes which can potentially cause cellular kill and damage. Because of their potential to cause damage, radionuclide therapy has got to be targeted at the organ of interest with a greater precision. The following sections will outline the uses of SPECT/Gamma imaging, PET and radionuclide therapy.