Current Medical Issues

REVIEW ARTICLE
Year
: 2018  |  Volume : 16  |  Issue : 4  |  Page : 121--130

Overview of nuclear medicine


Julie Hephzibah 
 Department of Nuclear Medicine, Christian Medical College, Vellore, Tamil Nadu, India

Correspondence Address:
Julie Hephzibah
Department of Nuclear Medicine, Christian Medical College, Vellore - 632 004, Tamil Nadu,
India

Abstract

Nuclear medicine is a medical speciality that uses radioactive materials for diagnostic and therapeutic purposes. The various techniques have made inroads into several other medical and surgical specialities. This article aims to provide an overview of the various diagnostic and therapeutic techniques available in the nuclear medicine armamentarium.



How to cite this article:
Hephzibah J. Overview of nuclear medicine.Curr Med Issues 2018;16:121-130


How to cite this URL:
Hephzibah J. Overview of nuclear medicine. Curr Med Issues [serial online] 2018 [cited 2019 Jul 16 ];16:121-130
Available from: http://www.cmijournal.org/text.asp?2018/16/4/121/256318


Full Text

 Introduction



Nuclear medicine specializes in diagnostic tests and treatments using radioactive materials which emit radiations, i.e., γ-rays, α-particles, β-particles, and positron. Nuclear medicine imaging is unique. It offers an integration of structural and functional details of organs. In addition, it is convenient and noninvasive.

Nuclear medicine work mainly involves imaging using radioactive isotopes. The major fraction of isotopes used in clinical nuclear medicine in India is produced at Bhabha Atomic Research Center, Trombay, and the remaining is imported.

Chemicals labeled with very small amounts of radioactive material (isotope), called radiopharmaceuticals, are used for diagnosis and treatment. Different radiopharmaceuticals are used for different tests. If the kidneys are to be evaluated, radiopharmaceuticals specific to the kidneys are used. The radiopharmaceuticals are then injected to the patients, or taken as a capsule, and after few minutes/hours or days, the patients are scanned with a special camera that acquires images of radiopharmaceutical accumulation in the body. The special types of cameras used are the gamma camera and positron emission tomography-computed tomography (PET-CT) scanners with computer assistance to provide detailed images about the region of the body imaged.

In therapy for various ailments, both malignant and benign, the radiopharmaceuticals go directly to the organ treated. Hence, this is also termed targeted molecular therapy.

Both diagnostic and therapeutic options from nuclear medicine are well established in many specialties including endocrinology, oncology, urology, cardiology, neurology, gastroenterology, orthopedics, and pediatrics. This article is aimed at providing a simplified overview of the principles and applications of nuclear medicine.

 Basic Terminology



Elements: Defined as a specific type of atom characterized by its atomic number (Z). Atomic number denotes the number of protons in the nucleus and also determines the position of the element in the periodic tableNuclides: Different types of nuclei are termed nuclides. Each nuclide is characterized by its atomic number (Z) and mass number (A)Radionuclides: Unstable nuclides which try to become stable during radioactive decay by emission of electromagnetic radiation or charged particlesRadioactivity: Spontaneous emission of radiation by radionuclidesIsotopes: Nuclides of the same element with different mass numbers – they have the same number of protons but differ in the number of neutronsRadiopharmaceuticals: They consist of a radioactive nuclide combined with a biologically active molecule. The radionuclide permits external detection, and the biologically active molecule acts as a carrier and determines localization and bio-distribution [Table 1].[1] In some radiotracers (e.g., radioiodine, gallium, and thallium), the radioactive atoms by itself have the desired localization characteristics.{Table 1}

 Administration of Radiopharmaceuticals



The radiotracer is injected, swallowed, or inhaled to assess the functional information of the system being studied [Table 2] and [Table 3]. Except for intravenous injections, the procedures are rarely associated with any discomfort or adverse effects.{Table 2}{Table 3}

 Radiation Risks



Nuclear medicine procedures lead to a potential risk of radiation exposure for patients and caregivers. The exact balance between risks and benefits is to be maintained. Radiation safety methods need to be ensured for every procedure, and the principle of as-low-as-reasonably-achievable (ALARA) radiation exposure should be followed at all times. Performing the right test with the right dose on the right patient at the right time is the key to dose optimization.[2]

 Radiation Protection Principles



The International Commission on Radiological Protection (ICRP) on its 2007 publication states that practices involving the use of ionizing radiation are regulated by three fundamental principles of radiological protection, namely justification, optimization, and limitation of doses.[3]

The first principle:

Any medical practice involving patient exposures must be justifiedAny decision that alters the radiation exposure situation should do more good than harmShould be in the right balance between risks and benefits by taking into account the social, economic, and technical factors

The second principle:

Once the exposure to ionizing radiation is justified, each examination must be performed so that individual doses should all be kept ALARA.

The third principle:

Dose limits are established to make sure no individual is exposed to radiation risk level which exceeds limits recommended by the ICRP.

Understanding the mechanism of radiopharmaceutical localization and rationale is important for the normal and pathological findings depicted in a nuclear medicine scan or scintigraphy.

Properties of an ideal radiopharmaceutical

Radionuclide decay should result in gamma emissions of suitable energy (100–200 keV is ideal for gamma cameras and 511 keV for PET)No particulate radiation (e.g., beta emissions), as this increases the radiation doseEffective half-life should be only a few minutes or a few hoursRadionuclides should not be contaminated by either stable radionuclides or other radionuclides of the same elementSpecific activity should be high, i.e., radioactivity per unit weight (mCi/mg)Free of any toxicity or physiological effectsNo disassociationin vitro orin vivo and be readily availableRapidly and specifically localize for the proposed studyGood target-to-background ratios by having good clearance.

Technetium-99 m (Tc99 m) is ideal as it has the desired features for gamma camera and fluorine-18 (F-18) for PET.

 Production of Radionuclides



Clinically used radionuclides are artificially produced by nuclear fission/through the bombardment of stable materials by neutrons or charged particles.

They can be produced from:

Nuclear reactorCyclotron [Figure 1] and [Figure 2]Generator.{Figure 1}{Figure 2}

The most important radionuclide generator system is the molybdenum–technetium generator (Mo-99/Tc-99 m). Tc99 m is rightly called the workhorse of a nuclear medicine setup.

 Imaging Equipment



Gamma camera

Radionuclide decay resulting in gamma emissions of energy between 100 and 200 KeV is ideal for gamma camera imaging. Tc99 m is a pure gamma emitter, which has an energy of 140 KeV with a physical half-life of 6 h [Figure 3].{Figure 3}

Positron emission tomography scanner

PET has higher spatial resolution. The superiority of tomographic images is compared with planar images for discriminating bone from soft tissue [Figure 4]. The half lives of various radio-isotopes used in PET imaging are given in [Table 4].{Figure 4}{Table 4}

The most common diagnostic applications of the Gamma camera and PET scanner are given in [Table 5] and [Table 6], respectively.[4]{Table 5}{Table 6}{Figure 5}{Figure 6}{Figure 7}{Figure 8}{Figure 9}{Figure 10}{Figure 11}{Figure 12}{Figure 13}

 Common Therapeutic Indications



For benign condition

131-iodine ablation thyrotoxicosis90-yttrium synovectomy.

For malignant conditions

131-Iodine ablation for differentiated thyroid cancers131-I-MIBG therapy for neuroendocrine tumors177-Lutetium DOTATATE therapy for neuroendocrine tumors153-Samarium and 32-P therapy for painful bone secondaries177-Lutetium PSMA therapy for prostate cancers.

 Conclusion



Nuclear medicine plays an important role in the evaluation of several diseasesIt is a functional imaging modality

Offers the advantage of:

Whole-body imagingHigh degree of sensitivityEasy to perform.No sedation or specific patient preparationSingle-photon emission CT/CT and PET-CT are useful for three-dimensional functional imaging and anatomical delineation

Knowledge of pathophysiology and recognition of limitation and technical pitfalls is essential for interpretation of imagesTherapeutic options are also an integral part in the practice of nuclear medicine.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

References

1O'Malley JP, Ziessman HA, Thrall JH. Nuclear medicine the requisites in radiology. 3rd ed. Elsevier - Health Sciences Division; St Louis, United States; 2006.
2Fahey F, Stabin M. Dose optimization in nuclear medicine. Semin Nucl Med 2014;44:193-201.
3The 2007 recommendations of the international commission on radiological protection. ICRP publication 103. Ann ICRP 2007;37:1-332.
4Mettler FA, Guiberteau MJ. Essentials of Nuclear medicine imaging. 6th ed. Saunders, an imprint of Elsevier Inc. Philadelphia, USA; 2012.