21/07/2022
I'm off clinics this summer studying for the ACVR Preliminary Board Exam, the first of two exams required to become board certified. The prelim exam covers physics of radiology, anatomy & physiology.
X-rays were discovered by accident in 1895 by Wilhelm Roentgen, a German physicist/engineer. He produced the first medical x-ray image of his wife's hand in 1896, & within just a few years, x-rays were used in medical applications.
Thomas Edison developed the fluoroscope in 1898, but abandoned his x-ray research after his assistant and long-time friend, Clarence Dally, experienced a severe x-ray burn that led to amputation of both arms & subsequent death in 1904, counted as the first x-ray fatality in the US.
X-rays production is complicated. In a nutshell:
- Electric current heats a tungsten filament in the cathode; electrons are "boiled off" the filament & form an electron "cloud"
- When a voltage differential is applied across the x-ray tube, these electrons are hurled towards the anode at a high velocity
- Projectile electrons collide with a tungsten target in the anode & interact with tungsten atoms in various ways
- "Characteristic" x-rays: produced when a projectile electron collides with an inner shell electron of the tungsten atom & deposits its energy. Inner shell electron is ejected, leaving a vacancy. An outer shell electron fills the vacancy, & the energy deposited by the projectile electron is released as a "characteristic" x-ray
- Bremsstrahlung ("braking") x-rays: produced when a projectile electron passes close to a tungsten target nucleus but does not hit or eject a tungsten electron. The projectile electron slows down ("brakes") as it bends around the nucleus. As it slows down, the electron releases energy as a Bremsstrahlung x-ray
Crazy that people can figure this smaller-than-microscopic stuff out through experimentation & deduction. Or maybe it's just Mrs. Frizzle reporting back from her shrunken Magic School Bus. "Take chances, make mistakes, get messy!" Hopefully not too many mistakes on the exam...