Medical Imaging

X-rays: very good for imaging bone, but not soft tissue
Still useful on kidneys - would see kidney stones

Before Roentgen's X-ray discovery, no way to look at body besides cutting it open

Some medical imaging methods (like X-ray) provide a picture, some (like ultrasound) provide a real-time picture

Where in the electromagnetic spectrum do we look?

Two parameters: resolution and attenuation (attenuation: how the radiation changes as goes through the body during the imaging process). Often, it is a tradeoff between the two.
Both of these parameters are a function of wavelength

We can't medical-image with visible light, since the human body is opaque to it

-How X-rays work-
Tungsten cathode: bombards tungsten target with electrons, the target is hooked up to a copper anode
X-rays produced by the electron/target collision

X-rays are 2D representation of a 3D object; thus aren't good for analyzing abnormal structures where you aren't sure what structure to expect

-Computer tomography-
Uses X-rays
Takes 2D images of a 3D volume (like the human body) - "slices" - target needs to be aligned straight with the beam generator
Several of these images, aggregated into one picture

Backprojection: Looking at the same slice of the body from different angles

-Positron emission tomography (PET)-

Proton --> Neutron + Neutrino + Positron
[Part of radioactive decay: inject radioactive agent during PET to cause this to happen]

Positron + Electron: antimatter annihilation that produces a gamma-ray signature. The latter is detected

Areas of higher metabolism (like cancer tumors) give off a stronger signature

-MRI-
This has been covered before
Hydrogen protons on particular become excited in a strong magnetic field, then turn the field off, which thus changes the signal behavior.
You image based on this.

-Ultrasound-
Useful on pregnant women because it's safe/not radioactive
Has other uses as well

We know the speed of sound in the body because know the speed of sound in water, and the body is mostly water

You image based on the ultrasound's echoes

Doppler ultrasound can image blood flow

Visible Human Project: part of NIH
Gathers data about human body parts that can be use din designing and tweaking these imaging processes

modality: a term for a different medical-imaging process

Often get complementary images from using different processes on the same object
Could look at these images side-by-side or no top of each other

Images often pseudocolored to help humans read + analyze them

Simulated/"phantom" images are often useful for gathering general information