Fundamentals of Medical Imaging (E1)

Why are more dense objects white on x-ray films?

More X-rays reaching film --> more dark

More dense --> less x-rays reaching film--> more white

Order from least dense to most dense (gas, fat, water, bone)

(least) gas → fat → water → bone (most)

What 4 factors affect image quality?

⚬Thickness of the body part

⚬Motion

⚬Magnification

⚬Distortion

What are distortion and magnification?

•Magnification: As an object moves toward the source of the x-ray beam, its shadow becomes larger

•Distortion occurs when the object is not perpendicular to the x-ray beam

What is the most common diagnostic x-ray format? What are two variations?

plain films

Fluorosopy and tomography

When is fluoroscopy used?

•Uses an X-ray tube and a fluorescent screen

•Used for watching real-time motion

•Used for viewing motion of the heart, diaphragm, esophagus or abdomen

⚬Can also be used for guided placement of GI tubes

When should you use contrast?

•Contrast agents are often used with plain films to highlight adjacent structures of similar densities

•Indications – Plain films - evaluation of GI tract, urinary system or blood vessels.

What is tomography? what is it used for?

•X-ray tube and film move synchronously around a focal point

•Objects in the focal point remain in focus, but other aspects are blurred

•Images are slices of the area scanned

•Most useful in evaluating the lungs, kidneys, and bony structures

What is computerized tomography? What are indications

•X-ray beam and detector system move in a 360 degree arc around the organ

•A very fine x-ray beam is directed through the patient to the detector system

•The detector system measures the amount of radiation passing through the patient

The data is analyzed and varying shades of gray are assigned to different radiation level

•Indications - evaluation of internal organs, infections, injuries, masses, and suspected tumors

What is the radioisotope used for nuclear imaging radionuclide scans? What are nuclear imaging scans used for?

Technetium-99. Evaluate physiology of organs such as bone, heart, lungs, thyroid and kidneys

What are PET scans used for?

•PET scan measures important body functions, such as blood flow, oxygen use, and glucose metabolism

•PET can be used to evaluate tumors and cancers, myocardial functioning and brain functioning.

What is a tagged RBC used for? How is the test performed?

•Indication

⚬Occult bleed --> slow bleed from unknown location, allows you to track where it's coming from

•How

⚬Tag RBCs with Tc99m-pertechnetate

￭Once inside the cell, Tc99-pertechnetate is reduced and can not diffuse back out.

Contradindications for thyroid scan

⚬No CT scan or contrast media within the last 8 weeks.

How does a renal scan work?

⚬Kidneys absorbs the material and it is cleared by glomerular filtration

What is a thallium stress test used for?

⚬Assess regional blood flow of the coronary arteries-blood supply to heart muscle

What is ventilation/perfusion scan used for?

How much RBC is being taken up at the capillaries and how much O2 is being taken up. (tagged RBCs also used)

When is gastric emptying study used?

Indication: suspect delayed gastric emptying

- tag food, have pt eat and see how long food remains in stomach.