100 Basic Principles of Medical Imaging

background info see book notes for differences and why one would be used over the other

Radiologist’s Elements

(5) air, fat, water, soft tissue, and bone

parts of X-ray machine and what they do

2D scan; air, bone & water and soft tissue

1. X-ray Tube: Produces radiation inside tube housing

2. Tube Housing: shield enviro from X-ray, X-ray exits here

3. Collimator: Controls X-ray beam size with lead “iris”

4. Detector: Captures X-ray that penetrates pt

radio opaque (white structure on x-ray)

Metal and bones

Attenuate (reduce effect; does not go through) of x-ray; high density

gray structures on x-ray

soft-tissues

Only some X-rays penetrate

radio lucent (black structures on x-ray)

air

most x-rays penetrate

CT

computed tomography; stack 2D x-ray to make 3D matrix

air, bone, & hard to distinguish difference between fat, water and soft tissue

same grey scale as x-ray

cone beam used: 3D area wide beam, area detector, and single exposure but pt is sitting which is more difficult (vs fan beam)

common challenges

technology, interpretation, dose, radiosensitive organs, digital panorex, and cone beam

rectangular collimation

limits the x-ray beam to the shape of the image receptor, reducing unnecessary radiation exposure and scatter

ALARA

as low as reasonably possible

artifacts

limitations ie metal attenuates

bone scan

musculoskeletal system

normal bone has low uptake

see kidney and bladder due to renal clearance

pathology is decreased or increased uptake (fracture, tumor, infection)

PET/CT

PET gamma rays , similar to nm camera

CT anatomic correlation and attenuation correction

nuclear medicine

anatomy function

lower spatial resolution

gamma rays

decreased or increased uptake of lesion

*air

MR

can distinguish fat, water, soft tissue

direct multi-planar imaging with no ionizing radiation

excited H+ in water and fat and image is created

decay constants T1 low water signal and T2 high water signal

ferromagnetic

cause artifacts that limit imaging

MRI limitation

teeth poorly seen on MRI due to limited free water ~ cortical bone = black hole

utlrasound

no ionizing radiation

transducer: transmits high freq sound pulses, receives echos fro conversion to an image

cannot penetrate air or bone

determine origin of palpable finding