Final I Flashcards
List 10 indicators for when to order diagnostic imaging. PROBABLE causes
Trauma – recent, old Unexplained weight loss Night pain Neuromotor deficit Inflammatory arthritis History of malignancy Fever of unknown origin (>100 F) Abnormal blood finding Deformity (Scoliosis, etc.) Failure to respond to therapy Medicolegal implications
- What is conventional tomography? Is it used much?
Conventional tomography is an x-ray slice that focuses on a small area of the body. Because of the movement of the x-ray source, everything around the area of interest is blurred.
Tomography has been rendered obsolete by computed tomography (CT)
- What is the difference in appearance between a plain x-ray and conventional tomography?
Plain x-ray is 2-D with everything superimposed.
Conventional tomography blurs everything not in the plane of focus, thus removing some of the difficulties in reading images.
- Which imaging plane is commonly used in computed tomography (CT)? Can more than one imaging plane be demonstrated with CT?
CT commonly takes axial slices of the body. From these axial slices, other image planes can be constructed, but at lower resolution.
- What is the difference between CT soft tissue and bone window?
CT Soft tissue window has the contrast adjusted to make soft tissue more visible. Bone window makes the details of bony structures more visible so that cortex and medullary bone can be easily distinguished.
- What is the appearance of bone in a soft tissue window?
It all looks very white.
- What is the appearance of bone in a bone window?
Much less white with details easily visualized.
- Does CT utilize the theory of attenuation (absorption of x-rays)?
Yes. Each pixel of the final image gets its color based on how much radiation hit it, and consequently represents the amount of attenuation.
- Which is more sensitive in the differentiation of tissue densities, CT or plain
x-ray?
CT provides much better soft tissue contrast
- What is the appearance of fat on CT vs. MRI?
On a CT, fat will be rather dark, whereas on a T1 weighted MRI, it will be white
- By what routes can CT contrast material be administered?
Oral and intravenous
- How does MRI acquire images?
MRI uses a super huge magnet which aligns hydrogen protons. When the magnet moves, the hydrogen goes back to a relaxed state. The energy released is measured by a computer and turned into a meaningful image.
- What does a T1 weighted MRI image look like compared to a T2 weighted image? What structures are high signal (white) vs. low signal (dark) on each weighting
T1 = Fat is white, compact bone is dark T2 = Water is white, compact bone is dark
- Which modality would best demonstrate dehydration (dessication) of the nucleus pulposis, CT or MRI?
MRI because the nucleus pulposis will show up as a darker color due to the lesser water content
- Which modality would best demonstrate an intervertebral disc herniation, CT or MRI?
MRI would show it better since it shows all soft tissue better
What is the contrast called that is sometimes used with MRI and why is it used?
Gadolinium is an intravenous contrast agent that is sometimes used with MRI
It goes to areas of increased vascularity. Performed with T1 weighted images only
- Where is the contrast material placed in myelography?
Into the subarachnoid space
- What modality besides plain film radiography is myelography often used with?
CT
- When is myelography utilized?
When MRI or CT would be contraindicated, or with a CT pre-surgery
- What is a “hot spot” in bone scan?
A hot spot is an area where a large amount of radionuclide migrates to because of increases cellular activity. They appear black
- When might SPECT scan be useful?
To localize a lesion better, particularly good for a fatigue fracture of the pars interarticularis
• When might PET scan be useful?
Excellent for tumor localization, grading and ascertaining treatment success. look for lymph node mets, look at brain activity, lesions
• When might discography be useful?
May demonstrate dessicated discs and herniated discs. Document specific disc as source of pain, Examine disc integrity
When might diagnostic ultrasound be useful?
Evaluate a fetus, Diagnose gallbladder disease, stones, Evaluate flow in blood vessels, Guide a needle biopsy, Guide the biopsy and treatment of a tumor, Check thyroid gland, Study the heart, Diagnose some forms of infection, Diagnose some forms of cancer, Reveal abnormalities in the scrotum and prostate, could help you find an occult fracture
- Which modality would be most appropriate to evaluate an intervertebral disc protrusion?
MRI
- Which modality would be most appropriate to evaluate a stress fracture?
Plain film X-ray ?
- Which modality would be most appropriate to confirm or rule out an occult fracture or questionable fracture initially discovered on plain x-ray?
Diagnostic ultrasound
- Which modality would be most appropriate to evaluate avascular necrosis?
MRI
- Which modality would be most appropriate to evaluate most chest and abdomen pathologies?
CT because you don’t have to worry about movement and you get a good image of soft tissue
- What are the relative radiation doses for each imaging modality discussed?
MRI = No radiation -> X-ray -> CT -> Bone scan = most radiation
