Diagnostic Imaging Final Flashcards
List 10 indicators for when to order diagnostic imaging
- trauma
- unexplained weight loss
- night pain
- inflammatory arthritis
- neuromotor deficit
- hx of malignancy
- fever of unknown origin
- abnormal blood finding
- medicolegal implications
- failure to respond to therapy
What is conventional tomography? How often is it used? Advantage/disadvantage?
It requires a specific area to be visualized, b/c its difficult to see on plain films and is clinically necessary to see. It creates a small focal point to be clear and other portions in the picture to be blurry. It is not used often.
Advantage: cost effective, minimal radiation, and bony anatomy visualized
Disadvantage: visualize only small areas
What is the difference in appearance between a plain x-ray and conventional tomography?
Plain x-ray does not allow you to see slight bone destruction (need about 30-50%), or axial images, and usually a broad area of focus.
Conventional tomography has radiographic “slices” taken with moving camera and film, where thin “slices” of bony anatomy are visualized but can only visualize a small area (soft tissues are also seen).
Which imaging plane is commonly used in computed tomography (CT)?
Axial (transverse)
Can more than one imaging plane be demonstrated with CT?
Yes, but the resolution is decreased (reconstructed images in sagittal or coronal or direct - small body parts.)??
What is the difference between CT soft tissue and bone window?
Soft tissue window: better visualization of soft tissues, and can be differentiated between different planes of tissues.
Bone window: better visualization of the fine details of the osseous structures. Cortical bone can be differentiated from cancellous (medullary) bone.
What is the appearance of bone in a soft tissue window?
Bone appears as uniformly white without distinction between cortical and medullary bone.
What is the appearance of bone in a bone window?
Cortex and medullary bone are distinctly different in contrast. The cortex is whiter and the medullary bone is more lucent (different contrast).
Does CT utilize the theory of attenuation (absorption of x-rays)?
Yes. [Plain (plane?) is controlled by kVp,] CT is a result of electric manipulation of the digital image, namely window width and leveling setting.
Which is more sensitive in the differentiation of tissue densities, CT or plain x-ray?
CT: more sensitive to structural density and superior for soft tissue contrast. CT uses electronic manipulation of the digital image whereas x-rays are manipulated by how much radiation is emitted.
What is the appearance of fat on a CT vs. an MRI?
CT: black, second to air
MRI: TI = white (T2 = black)
By what routes can CT contrast material be administered?
Oral: barium, to see tumors
IV: liver and kidney will take up contrast - without contrast liver and kidney look like muscle
myelographic: spinal cord pathologies
intra-articular: joint space?
How does MRI acquire images?
NO RADIATION. Nuclei of atoms have spin randomly (usually the dipole moment). That dipole moment of the spin aligns with the magnetic field. Then the field stops and the amount of energy released from going back to equilibrium gives us the picture of densities.
What does a T1 weighted MRI image look like?
T1 (short TE and short TR) = fat image
- fat is bright
- precise anatomy
- low signal cortical bone
- spinal cord
- CSF intermediate
- medullary bone
lightest to darkest: fat, marrow, brain and spinal cord, muscle and CSF, fluid filled cavities, and compact bone
*CORD IS BRIGHTER THAN CSF
What does a T2 weighted image look like?
T2 (long TE and long TR) = water image
- less precise detail
- normal discs bright
- CSF is bright
lightest to darkest: CSF (water base), edema and normal disc, marrow and spinal cord, muscle, ligaments, and compact bone.
*CSF IS BRIGHTER THAN CORD
(tests are based on H atoms, if you have a high concentration of H atoms - like water - they appear white)
What structures are high signal (white) vs. low signal (dark) on each weighting?
T1 = fat will appear bright/white
T2 = water will appear bright (ie. CSF)
T1 and T2 = ligaments and tendons produce little or no signal, and cortical bone will appear as a signal void
Which modality would best demonstrate an intervertebral disc herniation?
MRI
What is the contrast called that is sometimes used with MRI and why is it used?
GADOLINIUM. Used to help physicians get a clear and detailed picture of the patient’s internal organs, tissues, bones and vessels. Highlights tumors and infections.
Where is the contrast material placed in myelography
Subarachnoid space, by injection
What modality besides plain film radiography is myelography often used with?
Usually followed by a CT to better define the anatomy and any abnormalities. Often performed pre-surgically.
When is myelography utilized?
When CT and MRI aren’t available, or when MRI can’t find source of pain. Used to visualize indirectly a lesion within the spinal canal (ie. disc herniation, tumor, hematoma, osteophyte, inflammation, developmental anomaly)
What is a “hot spot” in a bone scan? What is a “cold” spot?
- Small areas of destruction or accumulation of bone (increased cell activity due to fracture or tumor)
- Areas of rapid bone growth or repair absorb increased amounts of tracer, and show up as bright or “hot spots” (ie. arthritis, presence of tumor, fracture, or infection). Only 3-5% of bone destruction needed to see “hot areas” on scan, but don’t specify process.
- “Cold”/dark spots absorb little to no amount of tracer and indicate a lack of blood supply or certain types of cancer.
When might SPECT scan be useful
- Better localization of a lesion
2. Confirming a fatigue fracture in the pars interarticularis
When might PET scan be useful?
- Tumor localization
- Ascertaining treatment success
- Has better resolution than SPECT or scintigraphy
- Dx a health condition/find out, monitor how it’s developing
- Used alongside X-rays or MRI to get more data
When might discography be useful?
- Provocative test for low back pain (may demonstrate desiccated discs and herniated discs
- Documents specific disc as source of pain and examine disc integrity
When might diagnostic ultrasound be useful?
evaluate a fetus guide a needle biopsy check thyroid gland study the heart reveal abnormalities in scrotum/prostate dx gallbaldder dz evaluate flow in blood vessels guide biopsy and treatment of a tumor dx some forms of infxn/cancer
Which modality would be most appropriate to evaluate a stress fracture?
MRI or bone scan
Which modality would be most appropriate to evaluate an intervertebral disc protrusion?
MRI or bone scan
Which modality would be most appropriate to evaluate avascular necrosis?
MRI
Which modality would be most appropriate to evaluate most chest and abdomen pathologies?
Why?
CT, because it’s fast
What are the relative radiation doses for each imaging modality discussed?
CT (many x-rays) > MRI (no ionization) x-ray CT MRI (no radiation) PET ultrasound discography SPECT
