How do they work?

Okay, how do these types of medical imaging work?

* Ultrasound

How it works: Bombardment of sound waves above 20,000 hertz (20khZ), 20khz being the upper limit of human hearing

What is actually measured: Ultrasound actually measures the echoes received by the ultrasound machine after they bounce back from hitting body parts.

An electrical pulse transducer in the machine causes it to vibrate at a certain frequency. Likewise, the echoes cause the transducer to vibrate in various ways, converted into electrical pulses which are then converted into a digital image

Advantages: Light if any side effects, very good at imaging soft tissue (vary frequency for different kinds of soft tissue), can produce a "live video" feed during the procedure

* fMRI (Functional Magnetic Resonance Imaging)

How it works: Images the brain and brain activity, though the method would technically work on other areas of the body
What is actually measured: It does this by detecting the increased blood flow typically associated with neural activity

How does it act as a proxy: Neural activity kicks up blood flow, with the areas of increased blood flow being measured

* SPECT

How it works: Radioisotopes fed into body, and the gamma rays are detected by the SPECT equipment
What is actually measured: The rays received by the machine are measured as 2-D images, but are measured form different angles, enabling a 3D image to be produced

How does it act as a proxy?: See info about 3-D reconstruction method above. Also, the radio decay particles behave differently when passing through different body structures, hence the ability for this to measure anything at all

* electromicroscopy


How it works: Magnifies samples to a much higher degree of resolution than is possible with a light microscope.

What is actually measured: Very small/thin sample bombarded with an electron beam. As electrons go through the object (in tunneling electron microscopy, or TEM), they are recorded as how they were 'behaving' as they come out

How does it act as a proxy?: Impediments inside the sample modify the outgoing electron beam.