Bioimaging

What has biomedical imaging allowed us to do?

Visualize biological structure and function at macroscopic and microscopic levels

Questions to ask about imaging

• How to generate the image

• How to process the image

• Issues that may be faced

• What more do you need to know

What was the first imaging technology used?

X-rays which were invented by William Roentgenin 1895 to visualize internal structures.

Properties of X-rays

• Wavelengths of about 0.1 nm

• A form of ionizing radiation

• Useful for imaging

• Can penetrate or be absorbed based on tissue density

What might an x-ray show?

• fractures/breaks in bones

• cavities in teeth

• fluid in lungs

• cancer in breasts

What are some cons of x-ray imaging?

Not good at visualizing soft tissue due to lack of variety in density

What is x-ray computed tomography? (CT scan)

X-ray images taken as previously described but from multiple projections; constructed into a 3-D image w/ numbers assigned to pixel values to represent different materials (bone, water, air)

Cons of x-ray computed tomography

Contrast is limited in soft tissues

Pros of x-ray computed tomography

• speed

• microCT allows small structures

• versatile for head, abdomen, pelvis, and extremities

• no superimposition of images outside area of interest

• higher contrast

What are contrast agents?

Used to enhance contrast in certain features

• Iodinated agents for intravascular imaging

• Barium-based agents for gastro-intestinal imaging

What is an ultrasound?

An image created by sound waves instead of light to create images

What is the frequency range used for an ultrasound?

2 MHz — 18 MHz; speed is c = 1540 m/s

How are ultrasound sound waves produced?

They are produced by a transducer made of piezoelectric material whihc resonates when stimulated by a wave, generating a voltage

Formula for depth of interface in an ultrasound:

c = (2d)/t or d = (ct)/2 where c = 1540 m/s

What is Doppler imaging?

Ultrasound used to measure the velocity of a tissue (e.g. rate of blood flow)