Current Pharmaceutical Design, 2009, 15, 1123-1130 1123 1381-6128/09 $55.00+.00 © 2009 Bentham Science Publishers Ltd. The Biological Effects of Diagnostic Cardiac Imaging L. Landini 1, * , A. Ripoli 2 , M.F. Santarelli 3 , L. Landini Jr. 4 and V. Positano 2 1 Department of Information Engineering, University of Pisa, Pisa, Italy; 2 Gabriele Monasterio Foundation, Pisa, Italy; 3 CNR Institute of Clinical Physiology, Pisa, Italy and 4 Dept of Internal Medicine, University of Pisa, Pisa, Italy Abstract: In this paper the authors deal with the main imaging techniques available to clinical cardiologists, with a brief overview of biophysical and biological aspects which are of relevance for the assessment of health effects related to the exposure of patients to both ionizing and non ionizing radiation. A main contribute is the reviewing published evidence on biological effects of radiation, trying to compose a balanced issue in order to increase awareness and knowledge about radiation exposure from cardiac imaging and implications for health risk. Key Words: Cardiac imaging, biological effects, ionizing radiation, non-ionizing radiation. INTRODUCTION During diagnostic imaging procedures, clinician uses all available imaging modalities for optimal management of patients with cardiovascular disease [1]. These include dif- ferent forms of radiation broadly divided in two groups: non- ionizing radiation, i.e., echocardiography and magnetic reso- nance imaging, and ionizing radiation, i.e., multi-slice chest computed tomography (CT), cardiac catheterization angiogra- phy, radio-opaque contrast angiography and nuclear imaging. Much has been written, also recently, about biological effects issue and discussions about potential health hazards associated with diagnostic cardiac imaging systems and pro- cedures. Moreover, technological advances in diagnostic imaging continue to raise new concerns about occupational and patient exposure to radiation as well. On the other hand, the sequence of events bringing to radiation harmful is very complex and deals with the concept of dose and with a series of biological transformations evolving on different time scales. This article summarizes biophysical and biological as- pects which are of relevance for the assessment of health effects related to the exposure of patients to both ionizing and non ionizing radiation. It also reviews published evi- dence on biological effects of radiation employed in cardiac imaging procedures. Based on these contributions, the pre- sent paper will try to compose a balanced issue in order to increase awareness and knowledge about radiation exposure from cardiac imaging and implications for health risk. DOSIMETRIC DEFINITIONS Medical imaging techniques can be broadly grouped into those which use ionizing radiation versus those that do not [2]. The term ‘radiation’ covers a wide spectrum of different forms of energy, broadly classified in electromagnetic radia- *Address correspondence to this author at the Professor of Biomedical Engineering, University of Pisa, Via Diotisalvi, 2, 56126 Pisa, Italy; Tel :++39 050 3152615; E-mail: luigi.landini@iet.unipi.it tion travelling at the speed of light, that includes X rays and gamma rays, and mass radiation that travels at speed lower than the speed of light, including electrons, protons and neu- trons. The mass radiation technique is not used in medical imaging procedures. The ionizing form of radiation consists of highly- energetic particles or waves that can ionize (remove) at least one electron from an atom or molecule, producing ions and making them chemically reactive and potentially capable of cell damage. Ionizing ability depends on the energy of the impinging individual particles or waves, and not on their number. A large flux of particles or waves generally will not cause ionization if these particles or waves do not carry enough energy to be ionizing. The ionizing radiation imaging techniques consist of those images created by the use of x-rays or gamma rays. Gamma rays arise from the nuclear decays of radioactive tracers introduced into the body, while x-rays arise from an x-ray tube where high speed electrons bombard a small spot on a tungsten anode target. In calculating the radiation concentration (dose) to the tissue a person receives during a ionizing diagnostic exami- nation and in determining the biological effects, a number of factors must be accounted, including exposure dose, absorbed dose, integral dose, equivalent dose, effective dose, and collective dose. Tables 1 and 2 are a brief summary of the units used in radiation measurements and conversion factors. Ionizing Radiation Indices Exposure Dose We recall that the exposure dose, commonly expressed in units of roentgens (R), is a quantity that reflects the extent of ionization events taking place when air is irradiated by ioniz- ing photons (gamma radiation, x rays). In the international system of units, exposure is measured in coulombs per kg (C/kg), and 1 R = 2.58 x 10 -4 C/kg. The exposure rate expresses the rate of charge production per unit mass of air and is commonly expressed in roentgens