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| REVIEW ARTICLE |
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| Year : 2018 | Volume
: 16
| Issue : 4 | Page : 121-130 |
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Overview of nuclear medicine
Julie Hephzibah
Department of Nuclear Medicine, Christian Medical College, Vellore, Tamil Nadu, India
| Date of Web Publication | 16-Apr-2019 |
Correspondence Address:
Julie Hephzibah
Department of Nuclear Medicine, Christian Medical College, Vellore - 632 004, Tamil Nadu,
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/cmi.cmi_50_18
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. Keywords: Diagnostics, gamma cameras, positron emission tomography, radioactive isotopes
How to cite this article:
Hephzibah J. Overview of nuclear medicine. Curr Med Issues 2018;16:121-30 |
| 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 table
- Nuclides: 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 particles
- Radioactivity: Spontaneous emission of radiation by radionuclides
- Isotopes: Nuclides of the same element with different mass numbers – they have the same number of protons but differ in the number of neutrons
- Radiopharmaceuticals: 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.
| 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.
| 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 justified
- Any decision that alters the radiation exposure situation should do more good than harm
- Should 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 dose
- Effective half-life should be only a few minutes or a few hours
- Radionuclides should not be contaminated by either stable radionuclides or other radionuclides of the same element
- Specific activity should be high, i.e., radioactivity per unit weight (mCi/mg)
- Free of any toxicity or physiological effects
- No disassociationin vitro orin vivo and be readily available
- Rapidly and specifically localize for the proposed study
- Good 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:
 | Figure 2: Schematic diagram showing particle path in a cyclotron with applied magnetic and electric field (image from web).
Click here to view |
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].
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].
The most common diagnostic applications of the Gamma camera and PET scanner are given in [Table 5] and [Table 6], respectively.[4] | Figure 5: Bone scintigraphy. (a) Normal study (left): Symmetric uptake of the tracer. Areas due to proximity to the camera, more intense such as iliac wings and SI region. Presence of renal activity as technetium-99 m methylene diphosphonate is cleared through the renal system (Image courtesy: Nuclear Medicine, CMC Vellore). (b) Osseous metastases (right): 78 M – Metastatic prostate carcinoma, serum alkaline phosphatase – 1698, PSA – 396. Asymmetric irregular intense tracer uptake scattered involving the axial and appendicular skeleton (Image courtesy: Nuclear Medicine, CMC Vellore).
Click here to view |
 | Figure 6: Thyroid whole-body scintigraphy. Papillary thyroid carcinoma, Post total thyroidectomy, Thyroid whole-body scintigraphy with I-131 showing residual thyroid (Image courtesy: Nuclear Medicine, CMC Vellore).
Click here to view |
 | Figure 7: Biliary atresia – Technetium-99 m – mebrofenin scintigraphy: 2m/M – abdominal distension, jaundice since 45 days of life. Images show no tracer clearance from the liver both in the initial and delayed images at 24 h. No biliary channels or gall bladder is visualized (Image courtesy: Nuclear Medicine, CMC Vellore).
Click here to view |
 | Figure 8: Technetium-99 m – mebrofenin scintigraphy showing patent biliary drainage (Image Courtesy: Nuclear Medicine, CMC Vellore).
Click here to view |
 | Figure 9: Normal renal scintigraphy: Evaluation of the images should consist of attention to renal anatomy and position, symmetry and adequacy of function, and patency of the collecting system. Renogram shows symmetric activity between the right and left kidneys, rapid dropoff after the peak, extending to the right (Image courtesy: Nuclear Medicine, CMC Vellore).
Click here to view |
 | Figure 10: F18-fluorodeoxyglucose positron emission tomography-computed tomography: Multiple fluorodeoxyglucose-avid lesions involving the lymph nodes and bone from small-cell lung carcinoma in the right lobe in a 42-year-old male. Stage 4 disease (Image courtesy: Nuclear Medicine, CMC Vellore).
Click here to view |
 | Figure 11: Ga-68 DOTATATE positron emission tomography-computed tomography: 26 F, DOTATATE-avid lesion in the right main bronchus. Biopsy: Small-cell neuroendocrine neoplasm. MIBI index 10%–25%, synaptophysin, chromogranin +ve. Physiological uptake of the pituitary, liver, spleen, kidneys, and bladder is noted (Image Courtesy: Nuclear Medicine, CMC Vellore).
Click here to view |
 | Figure 12: Fluorodeoxyglucose positron emission tomography – cardiac viability study:The figure shows two rows of images – the top row has the MIBI study while the bottom row shows the fluorodeoxyglucose(FDG) uptake. The corresponding images show an increased FDG uptake signifying the viability of the myocardium even in areas of decreased perfusion (as seen on the MIBI images) (Image Courtesy: Nuclear Medicine, CMC Vellore).
Click here to view |
 | Figure 13: Fluorodeoxyglucose positron emission tomography brain: Image showing hypometabolism in the frontal and temporal regions suggestive of frontotemporal dementia (Image courtesy: Nuclear Medicine, CMC Vellore).
Click here to view |
| Common Therapeutic Indications | | |
For benign condition
- 131-iodine ablation thyrotoxicosis
- 90-yttrium synovectomy.
For malignant conditions
- 131-Iodine ablation for differentiated thyroid cancers
- 131-I-MIBG therapy for neuroendocrine tumors
- 177-Lutetium DOTATATE therapy for neuroendocrine tumors
- 153-Samarium and 32-P therapy for painful bone secondaries
- 177-Lutetium PSMA therapy for prostate cancers.
| Conclusion | | |
- Nuclear medicine plays an important role in the evaluation of several diseases
- It is a functional imaging modality
- Offers the advantage of:
- Whole-body imaging
- High degree of sensitivity
- Easy to perform.
- No sedation or specific patient preparation
- Single-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 images
- Therapeutic 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 | | |
| 1. | O'Malley JP, Ziessman HA, Thrall JH. Nuclear medicine the requisites in radiology. 3 rd ed. Elsevier - Health Sciences Division; St Louis, United States; 2006.  |
| 2. | Fahey F, Stabin M. Dose optimization in nuclear medicine. Semin Nucl Med 2014;44:193-201. |
| 3. | The 2007 recommendations of the international commission on radiological protection. ICRP publication 103. Ann ICRP 2007;37:1-332. |
| 4. | Mettler FA, Guiberteau MJ. Essentials of Nuclear medicine imaging. 6 th ed. Saunders, an imprint of Elsevier Inc. Philadelphia, USA; 2012. |
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]
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