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64 Cards in this Set
- Front
- Back
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CT Scan Risk
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Radiation
Possible allergic rxn Kidney failure Incidentalomas |
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Risk of radiation exposure in what studies
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plain films (CXR, KUB, etc)
mammography CT scans Fluoroscopy |
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Clinical trials showing cancer risk from diagnostic radiology
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Chest fluoroscopy for TB in 20-50s
- for therapeutic pneumothorax - 1.3 increase in br ca mortality than controls (under 40 at exposure) Spinal films for scoliosis 30-60s -teens, mean 44 films -1.8 incidence of breast ca than controls |
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Average radiation dose / yr
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2.4 mSv
14% from medical radiation |
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Radiation equivalents in terms of chest xray
Bone scan Chest CT Ab/pelvic CT |
Bone - 189
Chest - 400 Ab/pelv - 750 |
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PA CXR in mrems?
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2
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Occupational dose limits>
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Person - 5000 mrem/year
Fetus 500 mrem |
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50 fatal
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400,000 mrads
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Risk of fatal cancer induction by 1 Sv?
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8%
16% in children 4% with fractionation |
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Radiation in pregnancy
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0-2 weeks -- all or nothing
2-10 - teratogenic below 50 mSV probably no effect (5 is limit) 8-25 - neurotoxic no threshold 0.2-0. IQ pts per 10 mSV |
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Imaging and breast feeding
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only nuclear medicine is a problem
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MRI risks
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Metabolic foreign bodies can move
ruptured orbit Devices - pacemakers, etc malfunction No radiation |
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Nephrogenic systemic fibrosis NSF
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rare, untreatable, sometimes fatal sclerosing disorder -- skin and internal organs
4% incidence in pts w/ chronic renal failure receiving gadolinium high dose |
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Ultrasound risks
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No proven risk
Theoretical risk of prolonged high risk US causing heating Avoid length high power doppler to embryos |
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IV contrast risks
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Allergy -- iodinated >>> gadolinium
ionic was 5x worse Renal failure Cardiac failure Extravasation Thyrotoxicosis |
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Contrast allergy
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Not true allergy
Unknown mechanisms not related to dose 1-2% have ild to mod rxn Fatal in 1:75,000 doses Risk factors -- asthma, previous contrast rxn, severe alleries |
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Renal toxicity w/ contrast
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Increased creatinine by more than 25% or >0.5mg
2-7% Risks -- increased creatinine, dehydration, age >70, CHF, nephrotoxic drugs (NSAIDS_ |
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Metformin and contrast
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risk of lactic acidosis (if renal insufficiency
withhold 48hr post contrast |
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Myeloma and contrast
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Increased risk of renal failure if BJ proteinuria
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Pheochromocytomas and contrast
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Increases risk of hypertensive crisis
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Barium safety
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Dangerous in peritoneum or mediastium -- fibrosis
No allergies Not great in lungs |
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Gastrograffin safety
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Dangerous in lungs
Okay in peritoneal cavity |
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Incidental finding of pulmonary nodule on chest CT
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10-25% of chest CTs have pulmonary nodules
99%< 4 mm are benign 94% 4-8 mm are benign 50% > 8mm are benign |
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Incidental finding of adrenal mas on CT
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4% of chest/abdo CTs find one
75% are benign 50% are non-functioning adenomas |
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Cost:
CXR Chest CT Ab/pelv CT PET/CT |
CXR - 338
Chest CT - 1947 Ab/pelvic - 3223 Pet/CT - 5873 |
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Attenuated on x-ray
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X-ray absorbed, less arrives at detector
Appears white/light on film Bone, calcium, metal |
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Lucent on xray
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Most of beam makes it to detector
Appears dark gray/black Air, fat |
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3 Factors influences appearance of object on xray
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Density
Thickness Shape |
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Lag time for cancer risk from xray exposure
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5-20 years
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Common sites of xray
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chest
abdomen spine long bones joints |
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CT better than x-ray at?
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Differentiating tissues of more similar density
Viewing internal organs less summation |
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Housfield unit
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Density value
Assigned to eat pixel in an image |
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Window on CT determines
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Level of contrast
narrow - more contrast |
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Best study for spatial resolution
Best study for soft tissue contrast |
Resolution - CT
Contrast - MRI |
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Signal intensity on MRI
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High - white or bright
Low - dark |
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Enhancement on MRI
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Tissues that take up IV gadolinium
Appear brighter on T1 images |
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Sequence on MRI
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Techniques used to create a particular set of images
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TE on MRI
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time when scanner listens for signal
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TR
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time to repeat the radiofrequency pulse
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T1 weighted MRI
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Best for anatomy
Use when contrast given Short TR and TE |
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T2 weight MRI
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Good for fluid filled structures
Used for detecting swelling Long TR/TE |
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MR angiography (MRA)
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T1 weighted, IV contrast
Background tissue signal suppressed |
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MR cholangiopancreatography (MRCP
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heavily T2 weighted (making fluid filled structures bright)
Used to look for stenosis, occlusions, abnormal dilitation of biliary and pancreatic ducts |
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Mammography singular objective
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Screening and dx of breast ca
Begin at 40, 35 w/ high risk Sam center if possible |
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Mammography views
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CC- craniocaudal
MLO - mediolateral oblique view up to pec major to see into axilla for nodes or deep breast cancers |
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Mammographic findings
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Mass
Assymetric density Microcalfications certain patterns assoc w/ breast ca |
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Ultrasound mechanism
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Imaging based on sound
Transducer emits sound waves and specificy high freq Bouncnes of tissue and returns to transducer as echos |
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HIFU
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High intensity focused US
lower frequency but hgh energy generates heat - used to treat tumors |
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Brighest signals on US?
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Interfaces between tissues of great difference in acoustic impedence
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Brightness on US
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Echo strength
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Hyperechoic/echogenic on US
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White
Solid organs echogenic -- tissues w/ multiple acoustic interfaces |
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Hypoechoic
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Gray
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Anechoic
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Black
Fluid filled tissues -- 2/2 lack of interal acoustic interfaces |
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Isoechoic
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same
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Not well visualized on US?
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Air and bone
Impedence mismatch is too great, nearly all sound energy reflected back Fat can also be a problem |
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Depth of structure on US?
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Determined by how long it takes for signal to return to transducer
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US uses
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Fluid filled structures (gallbladder, blatter, fetus in amnio fluid)
Superficial structures (scrotum, testes, thyroid, breast) Solid abdominal organs (liver, kidneys, spleen Uterus, ovaries, prostate via endoluminal |
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Doppler US
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Depicts flow in blood vessels
Color can indicate direction of flow Can measure velocity Relies on doppler effect |
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Procedular US
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Used for guidance - real time imaging
Metal is echogenic |
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Nuclear medicine
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Functional, phsyiologic, metabolic imaging
Using radioisotope tagged to specific compound that localizes Detecting radiation emitted from pt Very low anatomic resolution study Used as specific, problem solving image |
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Radioisotopes used in nuc med
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Radioactive iodine - thyroid
Radioactive diphonate - tecnetium-99m - bone Radiolabeled RBCs - bleeding Radiolabeled WBC - infection |
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Flouroscopy
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Continuous x-rays, live xray image
Can view dynamic processes High radiation dose to pt |
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Flouroscopy indicaitons
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Imaging blood flow
Guiding procedures Evaluation peristalsis of GI tract |
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Guidance to choose appriopriate radiologic study?
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American College of Radiologists (ACR) Appropriateness criteria
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