The Process of Annihilation When a positron is emitted from a tracer in the body, it travels less than a millimetre before it collides with an electron The positron and the electron will?annihilate...
Radioactive Tracers A?radioactive tracer?is defined as: A radioactive substance that can be absorbed by tissue in order to study the structure and function of organs in the body Radioactive?isotope...
Computed Tomography Scanning A simple X-ray image can provide useful, but limited, information about internal structures in a 2D image When a more comprehensive image is needed, a?computerised axia...
Attenuation of X-rays in Matter Bones?absorb?X-ray radiation This is why they appear white on the X-ray photograph When the collimated beam of X-rays passes through the patient’s body, they are?abs...
Production of X-rays X-rays are short wavelength, high-frequency part of the electromagnetic spectrum They have wavelengths in the range 10?8?to 10?13?m X-rays are produced when fast-moving electro...
Attenuation of Ultrasound in Matter Attenuation of ultrasound is defined as: The reduction of energy due to the absorption of ultrasound as it travels through a material The attenuation coefficient...
Intensity Reflection Coefficient The intensity reflection coefficient α is defined as: The ratio of the intensity of the reflected wave relative to the incident (transmitted) wave This can be calcu...
Specific Acoustic Impedance The?acoustic impedance, Z, of a medium is defined as: The product of the speed of the ultrasound in the medium and the density of the medium This quantity describes how ...
Generating Ultrasound An ultrasound is defined as: A high frequency sound above the range of human hearing This is above 20 kHz, although in medical applications the frequencies can be up to the MH...
The Piezoelectric Transducer The piezoelectric effect is defined as: The ability of particular materials to generate a potential difference (p.d.) by transferring mechanical energy to electrical en...
Half-Life Definition Half life is defined as: The time taken for the initial number of nuclei to reduce by half This means when a time equal to the half-life has passed, the activity of the sample ...
Activity & The Decay Constant Since radioactive decay is spontaneous and random, it is useful to consider the average number of nuclei which are expected to decay per unit time This is known as...
