Intro To Medical Imaging Flashcards
Why do we order imaging tests?
. Help rule in or rule out a suspected diagnosis (diagnostic)
. Detect disease early at asymptomatic stage (screening)
Main imaging modalities
. x-ray . Computerized tomography (CT/ CAT) . Ultrasound . Magnetic resonance imaging (MRI) . nuclear medicine. (Scans, bone scans)
Who made a cathode ray tube and when?
Wilhelm Roentgen in 1895
How did the cathode ray tube work?
Invisible rays from tube made fluorescent screen glow in darkened lab (x-rays)
How do x-rays work?
An x-rays generator emits x-rays that go through an object and reach an x-ray detector creating a radiograph image
How many tissue densities are demonstrated in x-rays?
5 (range from black to white)
What does density determine in x-rays?
How many x-rays are detected by the x-ray film
What is black on x-ray?
Air, not dense, doesn’t absorb many x-rays
What does calcium look like in x-rays?
White, dense, absorbs lots of x-rays
What does fat look like in x-rays?
Blackish gray, more dense than air, absorbs some x-rays
What does soft tissue/fluid look like in x-rays?
Whitish gray, less dense than bone, absorbs some x-rays
What does metal look like in x-rays?
Really white, really dense, absorbs the most x-rays
Antero-posterior (AP) x-rays
. Taken from the front side of body
. Heart is enlarged
Posterio-anterior (PA) x-rays
Taken from back side
. Heart looks normal
Science behind CT
. Rotating x-ray beams and detectors
. Lots of computer processing
. Images made w/ thousands of pixels
. Each pixel is small piece of tissue with particular density
. Density assigned HU nu,bear
. Oral or IV (used for venous obstruction or bleed) used to enhance image
CT numbers
. Hounsfield Units (HU)
. Range between -1000 and +1000
air HU number
-1000 HU
Bone HU number
400-600 HU
Fat HU number
-100 to -40 HU
Water HU number
0 HU
Soft tissue HU number
20-100 HU
What color are dense structures on CT and why?
White: absorb lots of x-rays, high CT number, inc. attenuation
What color are less dense structure on CT and why?
Black: absorbs fewer x-rays, low CT nu,her, dec. attenuation
Ultrasonography
. Sound waves used to evaluate tissue
. No radiation
. Safe for all patients
. Used to produce still images or videos
How does ultrasonography work?
Pattern of sound waves bounce back/deflected by tissue or transmission through tissue creates image
What kind of tissue appears white on ultrasound?
Tissue that reflected sound waves (echogenic)
What kind of tissues are black in ultrasound?
Tissue that reflects few/no sound waves (sonolucent)
Magnetic resonance imaging (MRI)
. Tissue imaged analyzing potential energy in body’s H atoms
. Radiation not used
. Safety issues from presence of strong magnetic field
How does MRI work?
. H atoms manipulated by magnetic field with pulsed radio frequency waves
. Computer analyzes atom response to produce image
Nuclear medicine
. Uses radioactive isotope which decay to non-radioactive state in short amt of time
How does nuclear medicine work?
. Isotopes have affinity for certain tissues
. Isotope injected in patient via IV
. Amt/patient of isotope uptake measured via gamma camera and produces image
When/why should you order an x-ray?
. Imaging chest, abdomen, bone
. Quick, easy, inexpensive
Disadvantages to x-ray
. Uses radiation
. Limited detail about area being analyzed
Diagnoses and symptoms that would call for chest x-ray
. Pneumonia, bronchitis, lung tumor, pneumothorax, pleural effusion, heart/aorta abnormalities
. Symptoms include cough, shortness of breath, chest pain
When do you order abdominal x-ray?
Symptoms: abdominal pain, constipation, vomiting
. Diagnoses: small bowel obstruction, large bowel obstruction, fecal impact ion, perf. Bowel
When do you order limb x-ray?
. Symptoms: pain in extremity/joint
. Diagnoses: fracture, arthritis, tumor
. Good at imaging bone, fair for cartilage and soft tissue
When do you order CT of abdomen?
. Symptoms: abdominal pain, pain w/ urination, blood in urine or stool, fever, fatigue
. Diagnoses: diverticulitis, appendicitis, kidney stone, pyelonephritis
. When you need more info than x-ray can give you
When to order ultrasound?
. Symptoms: abdominal pain, breast lump in woman under 40, abnormal uterine bleeding, swelling of 1 leg
. Diagnoses: gall stone, breast cyst, uterine cancer, blood clots
. Screening: abdominal aorta screening in men over 65 that smoked
How can you tell if there is an aneurysm in aorta?
A pseudo wall is present in ultrasound inside of aorta
when to order MRI of lumbar spine?
. Symptoms: low back pain, pain travels down 1 leg to foot, numbness/tingling of foot, low back pains w/ issues controlling bowel or bladder
. Diagnoses: degenerative disc disease, herniated disc w/ radiculopathy, cauda equina syndrome
When to order nuclear medicine study
. Symptoms: chest pain (cardiac), hyperactive metabolism (thyroid), pain in spine/other bones
. Diagnoses: MI, thyroid gland dysfunction/.cancer, cancer in bones
