Epidemiology and main clinical applications

In recent years, the main causes of mortality and morbidity across the world have changed. Heart disease, stroke, cancer, diabetes and other non-communicable diseases (NCDs) used to be considered public health issues only in high income countries. However, changes in lifestyle, increasing life expectancies and ageing populations are bringing the developing world closer to the developed world with regard to the nature of health problems [16].

Chronic diseases and NCDs, especially cardiovascular diseases and cancer, are now leading causes of mortality, followed by infectious diseases; and 70% of cancer deaths now occur in LMICs. Although the incidence of cardiovascular diseases has declined in developed countries following appropriate therapeutic approaches and prevention measures, it has become a major public health concern in LMICs. According to the Global Action Plan for the Prevention and Control of Noncommunicable Diseases 2013–2020 [17] of the World Health Organization (WHO), NCDs are the world’s biggest killers.

Individuals can reduce the chances of developing NCDs through preventive measures that address identified risk factors associated with chronic disease, such as an unhealthy diet, physical inactivity, tobacco use and harmful alcohol consumption. However, this does not prevent the development of NCDs, and it often takes time to have a clinical impact. Indeed, other factors, such as hereditary predisposition, may influence the development of disease. While prevention is important, key factors to enhance the survival rate of NCDs, especially cancer and cardiovascular diseases, are early detection, diagnosis and treatment.

Given these demographic changes and the rising impact of NCDs and infectious diseases, the role of nuclear medicine in both communicable and non-communicable disease management is becoming more salient, and its potential impact should no longer be limited to any particular region of the world [16].

Nuclear medicine can effectively monitor changes in tissue, diagnose and characterize disease, treat disease and evaluate the patient’s response to treatment.

Despite converging needs for nuclear medicine across the developed and developing worlds, there remain key differences between these areas because of socioeconomic disparities [16]. Making nuclear medicine centres more accessible and efficient in LMICs will lead to earlier diagnosis and better treatment.

2.2.1. Nuclear medicine resource distribution

The introduction of nuclear medicine into routine use in LMICs continues to encounter significant delays and impediments, where limited often infrastructure hampers the rising demand for nuclear medicine services — especially in the management of cancer, cardiovascular diseases and other NCDs. Although the average equipment age is over six years for all types of camera in all regions of the developing world, prolonged use of instrumentation often goes beyond the obsolescence period [16].

Medical imaging modalities have been adopted and developed under various scenarios in different countries and have also proliferated through different routes and in various settings. Moreover, both socioeconomic disparities and academic heterogeneity have resulted in unbalanced development in scientific trials. If nuclear medicine is to play a key role in the current imaging revolution in new diagnostics, it will remain a complex discipline.

2.2.2. Nuclear medicine needs

The differences in the practice of nuclear medicine across the world is because of heterogeneity in factors such as instrumentation, radiopharmaceuticals and educated human resources [16]. Nuclear medicine is a highly technical field and requires a particular infrastructure. It should be established in a hospital with

specialties such as radiology and clinical pathology, where at least some of the clinical specialties are flourishing. Not only is it advisable to have a centralized nuclear medicine facility in a hospital, it is equally desirable to have a consortium of interested clinicians associated with the unit because of the diverse range of medical disciplines that nuclear medicine serves.

The main interests and activities of the facility should first be assessed, in order to set up the needed facilities. Orders can then be placed for the instruments which would be most useful for the intended work. The total available space of the unit can be planned in an effective way. An integrated service is essential to the efficient conduct of nuclear medicine procedures. Nonetheless, the interrelations of radionuclide imaging and other imaging modalities, among them angiography, ultrasonography, CT and magnetic resonance imaging (MRI) should be appreciated, and the competing claims of the latter given due recognition. For these reasons, it may be convenient to locate radionuclide imaging facilities adjacent to other imaging facilities in the institution to share some of the necessary infrastructure, for example the patient reception area.

2.2.3. Clinical applications

In nuclear medicine imaging, gamma cameras and positron emission scanners detect and form images from the radiation emitted by the radiopharmaceuticals.

There are several techniques of diagnostic nuclear medicine:

(a) Gamma camera performs both scintigraphy, as a 2-D image.

(b) Single photon emission computed tomography (SPECT) as a 3-D tomographic technique that uses data from many projections and can be reconstructed in different planes.

(c) PET uses coincidence detectors to image annihilation photons derived by positron emitting radiopharmaceuticals.

(d) Multimodality imaging exploit SPECT and PET images superimposed to CT or MRI for a detailed anatomical localization. This practice is often referred to as hybrid imaging.

In nuclear medicine therapy, radiopharmaceuticals with a very specific uptake in pathological tissue and emitting ionizing radiation with a high local energy deposition are used to maximize the damage to the disease area while minimizing side effects to healthy tissues or nearby structures.

2.2.3.1. Fields of application

The main fields of applications include the following (see Section 9 for more information):

— Neoplastic processes;

— Cardiovascular diseases;

— Central nervous disorders;

— Bone and joints diseases;

— Respiratory diseases;

— Gastrointestinal diseases;

— Urinary and genital diseases;

— Endocrine diseases;

— Haematopoetic and lymphatic diseases;

— Inflammatory and degenerative processes.

2.2.3.2. World distribution

With the aim of collecting information, the IAEA launched a nuclear medicine database (NumDAB).¹ Periodic assessments indicated that about two thirds of the practice was used to perform bone, thyroid and renal scans [16].

Bone scans accounted for 25–28% of all procedures performed over a three year period and remained the most widely used application of nuclear medicine.

Thyroid scans ranked in second place. Remarkably, renal scans ranked in third place, and they remain widely applied in the developing world. Cardiovascular applications, widely applied in developed countries, ranked in fourth place. In general, data collected from voluntary contributors show a positive trend on nuclear medicine practice worldwide (see Fig. 1).