[Radiologic Physics] Ep 7 – Magnetism

[Radiologic Physics] Ep 9 – Transformers

This episode examines transformers — electromagnetic devices that modify voltage and current in AC circuits without converting electrical energy to another form. Prof. Arya covers the principle of mutual induction, the three structural types — closed core, autotransformer, and shell type — and how each design affects efficiency and application in clinical equipment. The turns ratio is developed through worked calculations using the transformer voltage and current laws, showing how step-up transformers drive kilovoltage x-ray production while step-down transformers supply the low voltage needed to heat the filament circuit. The episode closes with transformer efficiency — examining copper loss, eddy currents, and hysteresis, and the engineering solutions that minimize each. This episode aligns with the Safety content category — Radiation Physics and Radiobiology subcategory — of the ARRT Radiography Examination Content Specifications. Audio content is adapted from original instructional material developed by Professor Sanjay Arya, M.S., R.T.(R)(MR) for radiologic technology education. Part of the Radiologic Physics series — Quantum Imaging Lab. © 2026 Quantum Imaging Lab. All rights reserved.

[Radiation Biology] Ep 5 – Molecular and Cellular Radiobiology

Radiobiology is the study of how ionizing radiation interacts with and injures living systems, and understanding the factors that govern that injury is central to both radiation protection and therapeutic application. This episode opens with the physical factors that influence radiosensitivity — Linear Energy Transfer (LET), Relative Biological Effectiveness (RBE), protraction, and fractionation. LET is examined as the rate of energy deposition per micrometer of soft tissue, with low-LET radiation such as X-rays causing indirect, often repairable DNA damage through free radical formation, while high-LET radiation such as alpha particles causes dense, direct, and frequently irreparable damage. RBE is introduced as the comparative measure of how effectively a given radiation type produces a specific biologic response relative to 250 kVp X-rays as the standard reference. The direct proportionality between LET and RBE is discussed alongside the clinical rationale for protracted and fractionated dose delivery, which allows intracellular repair and reduces biologic effect. The biological factors modifying radiosensitivity are then addressed — including the Oxygen Enhancement Ratio (OER), age, recovery, chemical agents, and hormesis. The OER describes the amplifying role of oxygen in radiation damage, with low-LET radiation showing the highest OER values due to free radical interaction with oxygen producing irreparable organic peroxides, while high-LET radiation produces direct damage regardless of oxygen presence. The episode closes with a thorough treatment of radiation dose-response relationships, covering the four curve types — Linear Non-Threshold (LNT), Linear Threshold (LT), Non-Linear Non-Threshold (NLNT), and Non-Linear Threshold (NLT, or sigmoid) — alongside the Linear Quadratic model, and concludes by distinguishing deterministic from stochastic radiation effects. Content is structured to support radiologic technology programs preparing for imaging coursework and ARRT certification review. This episode aligns with the Safety content category — Radiation Physics and Radiobiology subcategory — of the ARRT Radiography Examination Content Specifications. Audio content is adapted from original instructional material developed by Professor Sanjay Arya, M.S., R.T.(R)(MR) for radiologic technology education. Part of the Radiation Biology series — Quantum Imaging Lab. © 2026 Quantum Imaging Lab. All rights reserved.

[Radiologic Physics] Ep 8 – Electromagnetism

This episode explores electromagnetism — the branch of physics studying how moving electric charges create magnetic fields — and traces its historical development from Alessandro Volta's invention of the Voltaic pile in 1800 to Hans Oersted's 1820 discovery that electric current deflects a compass needle. The Right Hand Thumb Rule is introduced to determine the direction of magnetic field lines around a current-carrying conductor, followed by a progression from straight wire to wire loop to solenoid to electromagnet, showing how field strength increases with coil turns and applied current. Faraday's Law (1831) is then presented — a changing magnetic field induces a voltage in a nearby conductor — along with the four factors that determine the magnitude of induced current: field strength, velocity, angle, and number of coil turns. The second half covers Lenz's Law, establishing that induced current always opposes the change that produced it, followed by the distinction between self-induction and mutual induction, with transformers identified as a key application of mutual induction. Electric generators and motors are compared as inverse electromechanical devices — one converting mechanical energy to electrical, the other electrical to mechanical. The induction motor is examined in detail, including its rotor-stator structure, operating speeds of 3,000–12,000 rpm, and its critical role in rotating the x-ray tube anode. The episode closes with the capacitor and its application in portable x-ray systems. This episode aligns with the Safety content category — Radiation Physics and Radiobiology subcategory — of the ARRT Radiography Examination Content Specifications. Audio content is adapted from original instructional material developed by Professor Sanjay Arya, M.S., R.T.(R)(MR) for radiologic technology education. Part of the Radiologic Physics series — Quantum Imaging Lab. © 2026 Quantum Imaging Lab. All rights reserved.

[Radiologic Physics] Ep 7 – Magnetism

This episode introduces the fundamental principles of magnetism and its relevance to radiologic imaging. The episode opens with the definition of a magnet as a vector quantity and the concept of magnetic dipoles, followed by an explanation of magnetic domains — how atomic dipoles align to produce magnetism in materials. The three types of magnets are then examined: natural magnets such as lodestones and Earth itself, artificial permanent magnets including compass needles and hardened steel, and electromagnets created by current flowing through a coiled wire. Magnetic fields are defined in terms of flux lines and flux density, and the role of electron spin and proton spin in generating magnetic moments is explained — including how hydrogen proton spin forms the physical foundation of MRI. The second half covers material magnetic properties across four categories in increasing strength: diamagnetism, paramagnetism, superparamagnetism, and ferromagnetism — with clinical examples including MRI contrast agents and projectile hazards. Hysteresis is explained as the tendency of ferromagnetic materials to retain magnetization, with safety implications for MRI environments. The four laws of magnetism are then presented — dipoles, attraction and repulsion, magnetic induction, and magnetic force — followed by a comparison of magnetic field units (gauss and tesla) across common sources from Earth to clinical MRI scanners. This episode aligns with the Safety content category — Radiation Physics and Radiobiology subcategory — of the ARRT Radiography Examination Content Specifications. Audio content is adapted from original instructional material developed by Professor Sanjay Arya, M.S., R.T.(R)(MR) for radiologic technology education. Part of the Radiologic Physics series — Quantum Imaging Lab. © 2026 Quantum Imaging Lab. All rights reserved.

[Radiation Biology] Ep 4 – Fundamental Principles of Radiobiology

Radiobiology is the study of how ionizing radiation interacts with and injures living systems, and understanding the factors that govern that injury is central to both radiation protection and therapeutic application. This episode opens with the physical factors that influence radiosensitivity — Linear Energy Transfer (LET), Relative Biological Effectiveness (RBE), protraction, and fractionation. LET is examined as the rate of energy deposition per micrometer of soft tissue, with low-LET radiation such as X-rays causing indirect, often repairable DNA damage through free radical formation, while high-LET radiation such as alpha particles causes dense, direct, and frequently irreparable damage. RBE is introduced as the comparative measure of how effectively a given radiation type produces a specific biologic response relative to 250 kVp X-rays as the standard reference. The direct proportionality between LET and RBE is discussed alongside the clinical rationale for protracted and fractionated dose delivery, which allows intracellular repair and reduces biologic effect. The biological factors modifying radiosensitivity are then addressed — including the Oxygen Enhancement Ratio (OER), age, recovery, chemical agents, and hormesis. The OER describes the amplifying role of oxygen in radiation damage, with low-LET radiation showing the highest OER values due to free radical interaction with oxygen producing irreparable organic peroxides, while high-LET radiation produces direct damage regardless of oxygen presence. The episode closes with a thorough treatment of radiation dose-response relationships, covering the four curve types — Linear Non-Threshold (LNT), Linear Threshold (LT), Non-Linear Non-Threshold (NLNT), and Non-Linear Threshold (NLT, or sigmoid) — alongside the Linear Quadratic model, and concludes by distinguishing deterministic from stochastic radiation effects. Content is structured to support radiologic technology programs preparing for imaging coursework and ARRT certification review. This episode aligns with the Safety content category — Radiation Physics and Radiobiology subcategory — of the ARRT Radiography Examination Content Specifications. Audio content is adapted from original instructional material developed by Professor Sanjay Arya, M.S., R.T.(R)(MR) for radiologic technology education. Part of the Radiation Biology series — Quantum Imaging Lab. © 2026 Quantum Imaging Lab. All rights reserved.