Medical Imaging - BPK 326

radiological orientation

left / right reversed

- you are looking at the patient

radiograph

produced by passing x-rays through a patient to produce an image (amount of x-rays that reach the detector produce an image)

- based on body density of different tissues (different shades produced)

- X-ray generator - object - x-ray detector

principle of x-ray imaging

variations in tissue density (5 levels of densities)

- density determines whether an x-rray passes through

DENSER = BRIGHTER

1. brightest - metal / contrast agents

2. bone

3. soft tissue

4. fat

5. darkest - air

opaque / HYPERDENSE

opacity - the tendency for a structure to block (scatter/absorb) x-rays from reaching the detector

- appears brighter on image

Lucent / HYPODENSE

tendency for a structure to allow x-rays to pass through and reach the scanner

- appears darker on image

isodense

about the same brightness

X-ray

CT

MRI

x-ray - fast, inexpensive, limited soft tissue resolution (very shadowy)

CT - better for imaging soft tissue than x-ray, faster and less expensive than MRI

- can be preformed on people with metal implants

- less anatomical resolution

- bones are brighter and whiter

MRI - best anatomical resolution, optimized for specific applications

- relatively slow, expensive and dangerous for people with metal

contrast agents - x-ray

improve soft tissue resolution over conventional radiography

- blocks x-rays in organ, enhances the ability to see

ex. barium enema

computed tomography (CT)

uses x-rays but captures many measurements of density across a single digital slice of the patient (rather than a single view)

brain acronym for density

hypodense

anagram -air

for - fat

when - water

CT - CSF

was - white matter

generated - grey matter

concerning - congealed blood

brain - bone

hyper dense

CT angiogram

contrast agent that makes the structure filled hyper dense

- common clinical test in which radio-opaque contrast is introduced into the vasculature

- can be delivered orally and rectally

MRI

tissue contrast based on proton behaviour

- water and fat content

brighter = hyperintense

darker = hypo intense

contrast images MRI

uses gadolinium which is paramagnetic

- changes proton behaviour in tissue where absorbed

- highlights (bright) pathological structures like tumours