Introduction

Nuclear medicine techniques are integral to modern urological practice and can be used to investigate almost any organ in the body. Urological usage is primarily confined to—

• Assessment of renal imaging, function, and drainage

• Management of metastatic prostate cancer

Isotopes of an element share the same atomic number (and therefore the same biochemical characteristics) but differ in their mass number (as well as their energy states). An example is the isotopes of iodine (123I, 131I, 125I). When an isotope has radioactive properties, it is called a radioisotope or radionuclide. Radionu-clides undergo spontaneous disintegration, while emitting high— penetrating, electromagnetic gamma rays (measured in electron volts [eV]). Radionuclides are used to label a compound, with a specific interaction with the target organ (e.g., kidney, bone) and the resulting ionizing radiation is detected and quantified by a gamma camera. A nuclear medicine image, therefore, is a map of where the tracer has accumulated, and is dependent on blood flow to the target organ as well as tracer metabolism by the organ (an indicator of function).

The characteristics of the three main radionuclides used in uro-logical practice are summarized in Table 4.1.

The half-life of a radiopharmaceutical (radionuclide + labeled compound) is determined by its natural rate of nuclide decay and metabolism/handling by the body. Decay is measured in Becquer-als (Bq) and 1 Bq equals 1 disintegration per second. Typically, diagnostic procedures result in a dose delivery of 106 Bq (1 MBq) and therapeutic interventions in 109 Bq (1 GBq). The ideal radiopharmaceutical should have the following characteristics:

Table 4.1. Radionuclides

Radionuclide

Isotopes

Half-Life

Energy of Gamma Rays (keV)

Labeled Compounds

Technetium-99m

99mTc

6.02 h

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